NEW YORK (Reuters Health) - Myocardial infarction (MI) patients who are transferred to another hospital for care are less likely to be followed up and more likely to be readmitted to the hospital, new findings show.

"This group of patients may represent a vulnerable population and we really need to come up with specific strategies to make their post-discharge transition back to their local community as seamless as possible," corresponding author Dr. Amit Vora, of Duke University in Durham, North Carolina, told Reuters Health.

Many patients admitted to their local hospital for acute MI must be transferred to another hospital for care, for example, to receive revascularization, Dr. Vora and his team note in their report, to be published online in Circulation: Cardiovascular Quality and outcomes. Logistical factors may lead to poor communication and coordination when it's time for the patient to be transferred back to their community, they add, which could be particularly problematic for older patients who may have more comorbidity and require closer follow-up after discharge.

To investigate, the researchers looked at outcomes for 39,136 acute MI patients 65 and older who were treated between 2007 and 2010 at 451 hospitals participating in Acute Coronary Treatment and Intervention Outcomes Network Registry-Get With the Guidelines.

Thirty-six percent of patients were transferred to another hospital for acute MI care, traveling a median of 43 miles.Within 30 days of discharge, 69.9% of the transferred patients had received outpatient follow-up, versus 78.2% of direct-arrival patients.

The adjusted risk of readmission for any cause was 14.5% for transferred patients versus 14% for direct-admit patients, while the risk of readmission for cardiovascular causes was 9.5% for

transferred patients and 9.1% for the direct-admit patients.However, the risk adjusted 30-day mortality was 1.6% for each group.

"Post-discharge care for acute MI patients is a performance measure, and we do track how often these patients are admitted

to the hospital following their discharge," Dr. Vora said. "A big focus of quality improvement is identifying strategies to reduce rehospitalization."

The next step in the research will be to identify the specific barriers to receiving follow-up care for transferred patients, he added, and then "define clear pathways and clear plans following discharge to ensure that these patients receive the care and the follow-up that they need."

The Agency for Healthcare Research and Quality funded this research. Three coauthors reported relevant relationships.

NEW YORK (Reuters Health) - Myocardial infarction (MI) patients who are transferred to another hospital for care are less likely to be followed up and more likely to be readmitted to the hospital, new findings show.

"This group of patients may represent a vulnerable population and we really need to come up with specific strategies to make their post-discharge transition back to their local community as seamless as possible," corresponding author Dr. Amit Vora, of Duke University in Durham, North Carolina, told Reuters Health.

Many patients admitted to their local hospital for acute MI must be transferred to another hospital for care, for example, to receive revascularization, Dr. Vora and his team note in their report, to be published online in Circulation: Cardiovascular Quality and outcomes. Logistical factors may lead to poor communication and coordination when it's time for the patient to be transferred back to their community, they add, which could be particularly problematic for older patients who may have more comorbidity and require closer follow-up after discharge.

To investigate, the researchers looked at outcomes for 39,136 acute MI patients 65 and older who were treated between 2007 and 2010 at 451 hospitals participating in Acute Coronary Treatment and Intervention Outcomes Network Registry-Get With the Guidelines.

Thirty-six percent of patients were transferred to another hospital for acute MI care, traveling a median of 43 miles.Within 30 days of discharge, 69.9% of the transferred patients had received outpatient follow-up, versus 78.2% of direct-arrival patients.

The adjusted risk of readmission for any cause was 14.5% for transferred patients versus 14% for direct-admit patients, while the risk of readmission for cardiovascular causes was 9.5% for

transferred patients and 9.1% for the direct-admit patients.However, the risk adjusted 30-day mortality was 1.6% for each group.

"Post-discharge care for acute MI patients is a performance measure, and we do track how often these patients are admitted

to the hospital following their discharge," Dr. Vora said. "A big focus of quality improvement is identifying strategies to reduce rehospitalization."

The next step in the research will be to identify the specific barriers to receiving follow-up care for transferred patients, he added, and then "define clear pathways and clear plans following discharge to ensure that these patients receive the care and the follow-up that they need."

The Agency for Healthcare Research and Quality funded this research. Three coauthors reported relevant relationships.

NEW YORK (Reuters Health) - Myocardial infarction (MI) patients who are transferred to another hospital for care are less likely to be followed up and more likely to be readmitted to the hospital, new findings show.

"This group of patients may represent a vulnerable population and we really need to come up with specific strategies to make their post-discharge transition back to their local community as seamless as possible," corresponding author Dr. Amit Vora, of Duke University in Durham, North Carolina, told Reuters Health.

Many patients admitted to their local hospital for acute MI must be transferred to another hospital for care, for example, to receive revascularization, Dr. Vora and his team note in their report, to be published online in Circulation: Cardiovascular Quality and outcomes. Logistical factors may lead to poor communication and coordination when it's time for the patient to be transferred back to their community, they add, which could be particularly problematic for older patients who may have more comorbidity and require closer follow-up after discharge.

To investigate, the researchers looked at outcomes for 39,136 acute MI patients 65 and older who were treated between 2007 and 2010 at 451 hospitals participating in Acute Coronary Treatment and Intervention Outcomes Network Registry-Get With the Guidelines.

Thirty-six percent of patients were transferred to another hospital for acute MI care, traveling a median of 43 miles.Within 30 days of discharge, 69.9% of the transferred patients had received outpatient follow-up, versus 78.2% of direct-arrival patients.

The adjusted risk of readmission for any cause was 14.5% for transferred patients versus 14% for direct-admit patients, while the risk of readmission for cardiovascular causes was 9.5% for

transferred patients and 9.1% for the direct-admit patients.However, the risk adjusted 30-day mortality was 1.6% for each group.

"Post-discharge care for acute MI patients is a performance measure, and we do track how often these patients are admitted

to the hospital following their discharge," Dr. Vora said. "A big focus of quality improvement is identifying strategies to reduce rehospitalization."

The next step in the research will be to identify the specific barriers to receiving follow-up care for transferred patients, he added, and then "define clear pathways and clear plans following discharge to ensure that these patients receive the care and the follow-up that they need."

The Agency for Healthcare Research and Quality funded this research. Three coauthors reported relevant relationships.

Injuries around the hip and groin occurring in professional baseball players can present as muscle strains, avulsions, contusions, hip subluxations or dislocations, femoroacetabular impingement (FAI) causing labral tears or chondral defects, and athletic pubalgia.^1-9 Several recent articles have reported on the epidemiology of musculoskeletal injuries in Major League Baseball (MLB) players^4,8,10 but with little attention to injuries to the hip and groin, likely because prior studies show only a 6.3% overall incidence for these injuries, much less than the more commonly discussed shoulder or elbow injuries.⁸ Despite the lower proportion of hip and groin injuries overall, these injuries lead to a relatively long period of disability for the players and often have a high rate of recurrence.^4,8,9

The important contribution of hip mechanics and the surrounding muscular function in the kinetic chain during overhead athletic activities, such as a tennis serve or throwing, has recently been discussed.^11,12 In sports requiring overhead activities, trunk rotation is a key component to generating force, and hip internal and external rotation is necessary for this trunk rotation to occur.^12,13 Alterations in hip morphology causing constrained motion, as seen in FAI, may predispose an overhead throwing athlete to intra-articular injury such as labral tears or chondral injuries, or to a compensatory movement pattern causing an extra-articular soft tissue injury about the hip.¹² Decreased hip range of motion may also lead to increased forces across the upper extremity during the throwing motion, which puts the shoulder and elbow at increased risk of injury.¹²

Increased awareness of hip and groin injuries, advances in diagnostic imaging, and an understanding of the relationship between the throwing motion in baseball and hip mechanics have improved our ability to appropriately identify and treat athletes with injuries of the hip and groin. Several studies on hip and groin injuries in elite athletes treated both operatively and nonoperatively have reported a high rate of return to sport.^3,7,14-19 A systematic review on return to sport following hip arthroscopy for intra-articular pathology associated with FAI showed a 95% return to sport rate and a 92% rate of return to pre-injury level of play in a subgroup of professional athletes in 9 studies.²⁰

Despite the large body of literature on upper extremity injuries, there is no study specifically focusing on the epidemiology of hip and groin injuries in MLB or Minor League Baseball (MiLB) players. The incidence of all injuries in professional baseball players has steadily increased over the last 2 decades,⁸ and the reported incidence of hip and groin injuries will likely increase as well. The current incidence of this injury, the positions most at risk, the mechanism of injury, and the time to return to sport are important to understand given the large number of players who participate in baseball not only at a professional level, but also at an amateur level, where this information may also be applicable. This information could improve our efforts at prevention and rehabilitation of these injuries, and can guide efforts to counsel and train players at high risk of a hip or groin injury. To address this gap in the literature, the purpose of this study was to describe the epidemiology of hip and groin injuries in MLB and MiLB players from 2011 to 2014.

Materials and Methods

Population and Sample

US MLB is comprised of the major and minor leagues. The major leagues are divided into 30 clubs, with 25 active players, for a total of 750 active players. Each club has a 40-man roster consisting of 25 active players and up to 15 additional players who are either not active or optioned to the minor leagues. The minor leagues are comprised of a network of over 200 clubs that are each affiliated with a major league club, and organized by geography and level of play. The minor leagues consist of roughly 7500 players, of whom about 6500 are actively playing at any given time. The entire population of players in the MLB who sustained a hip or groin injury over the study period was eligible for this study.

Data

The MLB’s Health and Injury Tracking System (HITS) is a centralized database that contains the de-identified medical data from the electronic medical record (EMR) system. Data on all injuries are entered into the EMR by each team’s certified athletic trainer. An injury is defined as any physical complaint sustained by a player that affects or limits participation in any aspect of baseball-related activity (eg, game, practice, warm-up, conditioning, weight training). The data extracted from HITS only relates to injuries that resulted in lost game time for a player and that occurred during spring training, regular season, or postseason play; off-season injuries were not included. Injury events that were classified as “season-ending” were not included in the analysis of assessing days missed because many of these players may not have been cleared to play until the beginning of the following season. For each injury, data were collected on the diagnosis, body part, activity, location, and date of injury.

Materials and Methods

Hip and groin injuries were defined as cases having a body region variable classified as “hip/groin” or a Sports Medicine Diagnostic Coding System (SMDCS) that included any “adductor” or “hernia” or “hip pointer” labels. Cases categorized as inguinal and femoral hernia (n = 26) and testicular contusions (n = 87) were excluded. Characteristics about each hip and groin injury were also extracted from HITS. These variables included level of play, player position (activity at the time of injury), field location, injury mechanism, chronicity of the injury, and days missed. Chronicity of the injury was documented as acute, overuse, or undetermined. For level of play, the injury event was categorized as the league in which the game was played when the injury occurred. Players were excluded if they had an unknown level of play or were in the amateur league. The injuries of the hip and groin were further classified as intra-articular and extra-articular. Treatment for each injury was characterized as surgical or nonsurgical, and correlated with days missed for each type of injury.

Statistical Analysis

Data for the 2011-2014 seasons were combined, and results presented for all players and separately for MiLB and MLB. Frequencies and comparative analyses for hip and groin injuries were performed across the aforementioned injury characteristics. The distribution of days missed for the variables considered was often skewed to the right, even after excluding the season-ending injuries; hence, the mean days missed was often larger than the median days missed. Reporting the median would allow for a robust estimate of the expected number of days missed, but would down weight those instances when hip and groin injuries result in much longer missed days, as reflected by the mean. Because of the importance of the days missed measure for professional baseball, both the mean and median are presented. Chi-square tests were used to test the hypothesis of equal proportions between the various categories of hip and groin characteristics, with statistical significance determined at the P = .05 level.

In order to estimate exposure, the average number of players per team per game was calculated based on analysis of regular season game participation via box scores that are publicly available. This average number over a season, multiplied by the number of team games at each professional level of baseball, was used as an estimate of athlete exposures in order to provide rates comparable to those of other injury surveillance systems. Injury rates were reported as injuries per 1000 athlete-exposures (AE) for those hip and groin injuries that occurred during the regular season. It should be noted that the number of regular season hip and groin injuries and the subsequent AE rates are based on injuries that were deemed work-related during the regular season. This does not necessarily only include injuries occurring during the course of a game, but injuries in game preparation as well. Due to the variations in spring training games and fluctuating rosters, an exposure rate could not be calculated for spring training hip and groin injuries.

Data analysis was performed in the R statistical computing Environment (R Core Team 2014). Study procedures were approved by the Johns Hopkins Bloomberg School of Public Health Institutional Review Board.

Results

Overall Summary

A total of 1823 hip and groin injuries occurred from 2011-2014, with 83% occurring in MiLB and 17% occurring in MLB (Table 1). There were 1146 acute injuries, 252 overuse injuries, and 425 injuries of undetermined chronicity. The average age of players experiencing a hip and groin injury in MiLB was 22.9 years compared to 29.7 years in MLB. Of the 1514 hip and groin injuries in MiLB, 76 (5.0%) required surgery and of the 309 hip and groin injuries in MLB, 24 (7.8%) required surgery. Compared to league-wide injury events, hip and groin injuries ranked 6th highest in prevalence in MiLB and 8th highest in prevalence in MLB, accounting for 5.4% and 5.6%, respectively, of the 28,116 MiLB and 5507 MLB injury events that occurred between 2011-2014.

For regular season games, it was estimated that there were 1,197,738 MiLB and 276,608 MLB AE from 2011-2014. The overall hip and groin rate across both MLB and MiLB was 1.2 per 1000 AE, based on the 238 and 1152 regular season hip and groin injuries in MLB and MiLB, respectively. The rate of hip and groin injury was 1.5 times more likely in MiLB than in MLB (P < .0001) (rate of 1.26 per 1000 AE in MiLB and 0.86 per 1000 AE in MLB).

Characteristics of Injuries

Injury activity was based on the position being played at the time of injury, with categories of infield and outfield corresponding to fielding activities (defense), with batting and base runner categories corresponding to activities while on offense (Table 2). The occurrence of hip and groin injuries while players are fielding on defense (MiLB 33.0%, MLB 37.2%, all players 33.8%) was significantly greater compared to injuries while batting and base running on offense (MiLB 24.9%, MLB 21.7%, all players 24.3%) (all P values < .001). There was a high percentage of missing data for the event position variable, which resulted from this field not being available in HITS for 2011. Time lost due to hip and groin injuries was similar across leagues with respect to injury activity, ranging on average between 8 and 18 days.

There were statistically significant differences for MiLB and MLB separately, and combined, in the number of hip and groin injuries by field location (all P values < .0001) (Table 2). For MiLB, MLB, and across both leagues, by injury location, the majority of hip and groin injuries occurred in the infield (MiLB 34.1%, MLB 35.3%, all players 34.3%). As a single location, the pitcher’s mound accounted for a large proportion of hip and groin injuries (MiLB 19.2%, MLB 23.3%, all players 19.9%). Time lost due to hip and groin injuries was similar across leagues with respect to field location, ranging on average between about 10 and 22 days. Among all players, injuries on the pitcher’s mound resulted in the largest mean days missed after injury.

There were statistically significant differences across the mechanisms of injury for MiLB and MLB, as well as both leagues combined (all P values < .0001) (Table 2). The majority of hip and groin injuries were noncontact-related (MiLB 73.7%, MLB 75.7%, all players 74.1%) compared to those resulting from some form of contact (MiLB 11.4%, MLB 12.6%, all players 11.7%) or other mechanisms. Time lost across these mechanisms varied, ranging on average between 4 and 15 days with noncontact-related hip and groin injuries resulting in the largest time lost.

Surgery

The 1823 hip and groin injuries across both leagues were further classified using the SMDCS descriptions as intra-articular (N = 84) or extra-articular (N = 1739) (Table 3). A much larger percentage of hip and groin injuries were extra-articular (MiLB 95.6%, MLB 94.4%, all players 95.4%) compared to those classified as intra-articular (Table 3). The most common extra-articular injuries were strains or contusions of the adductor, iliopsoas, or gluteal muscles, making up 79.1% of this group of injuries. The most common intra-articular injuries were FAI and a labral tear, accounting for 80.9% of these injuries. Only a small percentage of the extra-articular cases required surgery (MiLB 3.4%, MLB 5.8%, all players 3.8%) (Table 4). This finding was in contrast to the larger percentage of intra-articular cases requiring surgery (MiLB 40.3%, MLB 41.2%, all players 40.5%). Time lost varied greatly by surgery status, as well as extra-articular or intra-articular, as would be expected even after excluding season-ending injuries. For both types of injuries, the average time lost was consistently greater for injuries that required surgery versus the ones that did not result in surgery.

Discussion

The incidence of overall injuries in MLB players is increasing.⁸ Injuries to the hip and groin for professional baseball players continue to be of concern both in the number of injuries and the potential for these injuries to be debilitating or to recur. The correct diagnosis of hip injuries can be challenging in these athletes due to the complex anatomy of the region. However, our understanding of the pathoanatomy of hip and groin injuries, combined with the utilization of improved magnetic resonance imaging (MRI,) has aided in making the correct diagnosis more reliable. Although upper extremity injuries have traditionally been the focus of MLB injury reporting, hip injuries have been shown to cause an average of 23 days missed per player.⁴ This was similar to the more commonly highlighted elbow and knee injuries in the same study (23 and 27 days, respectively). The purpose of this study was to explore the epidemiology of hip and groin injuries in MLB. The lack of existing data on this issue is important for sports injury research. Exploring these injuries increases the understanding of which players are at risk, and how we can tailor training programs for prevention or rehabilitation programs for those players who suffer these injuries.

In addition to the increased awareness of hip injuries, there has been a recent focus on the contribution of hip range of motion, leg drive, and pelvic rotation to the overall mechanics of overhead activities such as throwing, a tennis serve, or pitching.¹² Pelvic rotation and leg drive have been correlated to throwing velocity,²¹ and therefore if hip range of motion is inhibited by pain or a structural issue such as FAI, there will likely be altered upper extremity mechanics leading to less power and possibly injury.¹² Additionally, it has been shown that limited hip range of motion due to FAI is correlated with compensatory lower extremity muscular injuries such as hamstring and adductor strains as well as overload of the lumbar spine and sacroiliac joint.²²

In the current study, extra-articular injuries about the hip were the most common, making up 95.4% of the total injuries. Many (79.1%) of these were strains or contusions of the adductor, iliopsoas, or gluteal muscles. This is consistent with other articles reporting hip injuries in athletes.^3,9 A study on hip injuries in the National Football League found that strains and contusions comprised 92% of all hip injuries.³ Another report on European professional football found that 72% of hip injuries over a 7-season period were adductor or iliopsoas injuries.⁹ This prior study also reported that 15% of the hip and groin strains were re-injuries. Intra-articular injuries comprised only 4.6% of the hip injuries in our study. FAI and labral tears were the most common intra-articular diagnosis at 80.9%.

Almost all (96.2%) of the extra-articular hip injuries in this series were able to be treated nonoperatively and caused a mean of 12.4 days missed. Those which required operative treatment caused a mean of 54.6 days missed. For intra-articular injuries, 40.5% were treated surgically and these players missed a mean 122.5 days. Those treated nonsurgically missed an average of 22.2 days. Whether treated surgically or nonsurgically, the mean days missed following an intra-articular injury was approximately twice that of extra-articular injuries. Our findings regarding time or games missed are similar to other reports studying hip injuries in professional athletes.^2,3,9 Intra-articular injuries such as FAI, chondral injuries, or labral tears caused between 46 and 64 days missed compared to 3 to 27 days missed for extra-articular injuries in professional soccer players.⁹ Feeley and colleagues³ found a mean of 5.07 to 33.6 days missed for extra-articular injuries such as strains or contusions, and 63.5 to 126.2 days missed for intra-articular injuries including arthritis, labral tears, subluxations, dislocations, and fractures. A report on National Hockey League players found that intra-articular injuries made up 10.6% of all hip and groin injuries and caused significantly more games missed than extra-articular injuries.²

In both minor and major league players, for all reported positions at the time of hip or groin injury, infield players collectively were more commonly injured than outfielders, batters, or base runners, and fielding was the most common activity being performed at the time of injury. The pitcher’s mound was the most common single location for injuries and these players had the longest time missed following injury. The correlation between hip and groin pathology and upper extremity injuries in overhead athletes has been discussed in previous studies.^12,21 Interestingly, we found that the specific location on the field with the highest incidence of hip and groin injuries was the pitcher’s mound. As we follow these players over time, a future correlation between the incidence of hip and groin injuries and the incidence of shoulder and elbow injuries may be noted. A noncontact injury was the most frequent mechanism of injury. This corroborates the finding that muscle strains and contusions made up the majority of injuries in this series. Other series on hip injuries have also found that noncontact mechanisms are common.³

Although this was one of the first studies exploring the epidemiology of hip and groin injury, there are some limitations of this study. The retrospective nature of this study relied upon the reporting of injuries in the MLB database. As such, there may be underreporting of injuries into the official database by players or medical staff for a variety of reasons. Differences in technique for diagnosis and treatment among the medical staff for different teams were not controlled for. Due to the wide range of hip and groin pathology, and the often difficult diagnosis, a specific injury was not always provided. Therefore, the category of “other” hip injury was entered in to the database when symptoms were nonspecific or not all details were provided. Fortunately, this category made up a small percentage of the reported injuries, but does remain a confounding factor in describing the etiology of hip injuries in these players. Our data were taken from professional baseball players only, and so we cannot recommend extrapolation to other sports or nonprofessional baseball athletes.

Despite the inherent limitations of reporting registry data, this study serves as the initial report of the occurrence of hip and groin injuries in professional baseball players, and improves our knowledge of the positions and situations that put players at most risk for these injuries. An understanding of the overall epidemiology of these injuries serves as a platform for more focused research in this area in the future. We can now focus research on specific positions, such as pitchers, that have a high incidence of injury to determine the physiologic and environmental factors which put them at higher risk for injury in general and for more significant injuries with more days missed. This information can help to guide position-specific training programs for injury prevention as well as improve rehabilitation protocols for more efficient recovery and return to sports.

Injuries around the hip and groin occurring in professional baseball players can present as muscle strains, avulsions, contusions, hip subluxations or dislocations, femoroacetabular impingement (FAI) causing labral tears or chondral defects, and athletic pubalgia.^1-9 Several recent articles have reported on the epidemiology of musculoskeletal injuries in Major League Baseball (MLB) players^4,8,10 but with little attention to injuries to the hip and groin, likely because prior studies show only a 6.3% overall incidence for these injuries, much less than the more commonly discussed shoulder or elbow injuries.⁸ Despite the lower proportion of hip and groin injuries overall, these injuries lead to a relatively long period of disability for the players and often have a high rate of recurrence.^4,8,9

The important contribution of hip mechanics and the surrounding muscular function in the kinetic chain during overhead athletic activities, such as a tennis serve or throwing, has recently been discussed.^11,12 In sports requiring overhead activities, trunk rotation is a key component to generating force, and hip internal and external rotation is necessary for this trunk rotation to occur.^12,13 Alterations in hip morphology causing constrained motion, as seen in FAI, may predispose an overhead throwing athlete to intra-articular injury such as labral tears or chondral injuries, or to a compensatory movement pattern causing an extra-articular soft tissue injury about the hip.¹² Decreased hip range of motion may also lead to increased forces across the upper extremity during the throwing motion, which puts the shoulder and elbow at increased risk of injury.¹²

Increased awareness of hip and groin injuries, advances in diagnostic imaging, and an understanding of the relationship between the throwing motion in baseball and hip mechanics have improved our ability to appropriately identify and treat athletes with injuries of the hip and groin. Several studies on hip and groin injuries in elite athletes treated both operatively and nonoperatively have reported a high rate of return to sport.^3,7,14-19 A systematic review on return to sport following hip arthroscopy for intra-articular pathology associated with FAI showed a 95% return to sport rate and a 92% rate of return to pre-injury level of play in a subgroup of professional athletes in 9 studies.²⁰

Despite the large body of literature on upper extremity injuries, there is no study specifically focusing on the epidemiology of hip and groin injuries in MLB or Minor League Baseball (MiLB) players. The incidence of all injuries in professional baseball players has steadily increased over the last 2 decades,⁸ and the reported incidence of hip and groin injuries will likely increase as well. The current incidence of this injury, the positions most at risk, the mechanism of injury, and the time to return to sport are important to understand given the large number of players who participate in baseball not only at a professional level, but also at an amateur level, where this information may also be applicable. This information could improve our efforts at prevention and rehabilitation of these injuries, and can guide efforts to counsel and train players at high risk of a hip or groin injury. To address this gap in the literature, the purpose of this study was to describe the epidemiology of hip and groin injuries in MLB and MiLB players from 2011 to 2014.

Materials and Methods

Population and Sample

US MLB is comprised of the major and minor leagues. The major leagues are divided into 30 clubs, with 25 active players, for a total of 750 active players. Each club has a 40-man roster consisting of 25 active players and up to 15 additional players who are either not active or optioned to the minor leagues. The minor leagues are comprised of a network of over 200 clubs that are each affiliated with a major league club, and organized by geography and level of play. The minor leagues consist of roughly 7500 players, of whom about 6500 are actively playing at any given time. The entire population of players in the MLB who sustained a hip or groin injury over the study period was eligible for this study.

Data

The MLB’s Health and Injury Tracking System (HITS) is a centralized database that contains the de-identified medical data from the electronic medical record (EMR) system. Data on all injuries are entered into the EMR by each team’s certified athletic trainer. An injury is defined as any physical complaint sustained by a player that affects or limits participation in any aspect of baseball-related activity (eg, game, practice, warm-up, conditioning, weight training). The data extracted from HITS only relates to injuries that resulted in lost game time for a player and that occurred during spring training, regular season, or postseason play; off-season injuries were not included. Injury events that were classified as “season-ending” were not included in the analysis of assessing days missed because many of these players may not have been cleared to play until the beginning of the following season. For each injury, data were collected on the diagnosis, body part, activity, location, and date of injury.

Materials and Methods

Hip and groin injuries were defined as cases having a body region variable classified as “hip/groin” or a Sports Medicine Diagnostic Coding System (SMDCS) that included any “adductor” or “hernia” or “hip pointer” labels. Cases categorized as inguinal and femoral hernia (n = 26) and testicular contusions (n = 87) were excluded. Characteristics about each hip and groin injury were also extracted from HITS. These variables included level of play, player position (activity at the time of injury), field location, injury mechanism, chronicity of the injury, and days missed. Chronicity of the injury was documented as acute, overuse, or undetermined. For level of play, the injury event was categorized as the league in which the game was played when the injury occurred. Players were excluded if they had an unknown level of play or were in the amateur league. The injuries of the hip and groin were further classified as intra-articular and extra-articular. Treatment for each injury was characterized as surgical or nonsurgical, and correlated with days missed for each type of injury.

Statistical Analysis

Data for the 2011-2014 seasons were combined, and results presented for all players and separately for MiLB and MLB. Frequencies and comparative analyses for hip and groin injuries were performed across the aforementioned injury characteristics. The distribution of days missed for the variables considered was often skewed to the right, even after excluding the season-ending injuries; hence, the mean days missed was often larger than the median days missed. Reporting the median would allow for a robust estimate of the expected number of days missed, but would down weight those instances when hip and groin injuries result in much longer missed days, as reflected by the mean. Because of the importance of the days missed measure for professional baseball, both the mean and median are presented. Chi-square tests were used to test the hypothesis of equal proportions between the various categories of hip and groin characteristics, with statistical significance determined at the P = .05 level.

In order to estimate exposure, the average number of players per team per game was calculated based on analysis of regular season game participation via box scores that are publicly available. This average number over a season, multiplied by the number of team games at each professional level of baseball, was used as an estimate of athlete exposures in order to provide rates comparable to those of other injury surveillance systems. Injury rates were reported as injuries per 1000 athlete-exposures (AE) for those hip and groin injuries that occurred during the regular season. It should be noted that the number of regular season hip and groin injuries and the subsequent AE rates are based on injuries that were deemed work-related during the regular season. This does not necessarily only include injuries occurring during the course of a game, but injuries in game preparation as well. Due to the variations in spring training games and fluctuating rosters, an exposure rate could not be calculated for spring training hip and groin injuries.

Data analysis was performed in the R statistical computing Environment (R Core Team 2014). Study procedures were approved by the Johns Hopkins Bloomberg School of Public Health Institutional Review Board.

Results

Overall Summary

A total of 1823 hip and groin injuries occurred from 2011-2014, with 83% occurring in MiLB and 17% occurring in MLB (Table 1). There were 1146 acute injuries, 252 overuse injuries, and 425 injuries of undetermined chronicity. The average age of players experiencing a hip and groin injury in MiLB was 22.9 years compared to 29.7 years in MLB. Of the 1514 hip and groin injuries in MiLB, 76 (5.0%) required surgery and of the 309 hip and groin injuries in MLB, 24 (7.8%) required surgery. Compared to league-wide injury events, hip and groin injuries ranked 6th highest in prevalence in MiLB and 8th highest in prevalence in MLB, accounting for 5.4% and 5.6%, respectively, of the 28,116 MiLB and 5507 MLB injury events that occurred between 2011-2014.

For regular season games, it was estimated that there were 1,197,738 MiLB and 276,608 MLB AE from 2011-2014. The overall hip and groin rate across both MLB and MiLB was 1.2 per 1000 AE, based on the 238 and 1152 regular season hip and groin injuries in MLB and MiLB, respectively. The rate of hip and groin injury was 1.5 times more likely in MiLB than in MLB (P < .0001) (rate of 1.26 per 1000 AE in MiLB and 0.86 per 1000 AE in MLB).

Characteristics of Injuries

Injury activity was based on the position being played at the time of injury, with categories of infield and outfield corresponding to fielding activities (defense), with batting and base runner categories corresponding to activities while on offense (Table 2). The occurrence of hip and groin injuries while players are fielding on defense (MiLB 33.0%, MLB 37.2%, all players 33.8%) was significantly greater compared to injuries while batting and base running on offense (MiLB 24.9%, MLB 21.7%, all players 24.3%) (all P values < .001). There was a high percentage of missing data for the event position variable, which resulted from this field not being available in HITS for 2011. Time lost due to hip and groin injuries was similar across leagues with respect to injury activity, ranging on average between 8 and 18 days.

There were statistically significant differences for MiLB and MLB separately, and combined, in the number of hip and groin injuries by field location (all P values < .0001) (Table 2). For MiLB, MLB, and across both leagues, by injury location, the majority of hip and groin injuries occurred in the infield (MiLB 34.1%, MLB 35.3%, all players 34.3%). As a single location, the pitcher’s mound accounted for a large proportion of hip and groin injuries (MiLB 19.2%, MLB 23.3%, all players 19.9%). Time lost due to hip and groin injuries was similar across leagues with respect to field location, ranging on average between about 10 and 22 days. Among all players, injuries on the pitcher’s mound resulted in the largest mean days missed after injury.

There were statistically significant differences across the mechanisms of injury for MiLB and MLB, as well as both leagues combined (all P values < .0001) (Table 2). The majority of hip and groin injuries were noncontact-related (MiLB 73.7%, MLB 75.7%, all players 74.1%) compared to those resulting from some form of contact (MiLB 11.4%, MLB 12.6%, all players 11.7%) or other mechanisms. Time lost across these mechanisms varied, ranging on average between 4 and 15 days with noncontact-related hip and groin injuries resulting in the largest time lost.

Surgery

The 1823 hip and groin injuries across both leagues were further classified using the SMDCS descriptions as intra-articular (N = 84) or extra-articular (N = 1739) (Table 3). A much larger percentage of hip and groin injuries were extra-articular (MiLB 95.6%, MLB 94.4%, all players 95.4%) compared to those classified as intra-articular (Table 3). The most common extra-articular injuries were strains or contusions of the adductor, iliopsoas, or gluteal muscles, making up 79.1% of this group of injuries. The most common intra-articular injuries were FAI and a labral tear, accounting for 80.9% of these injuries. Only a small percentage of the extra-articular cases required surgery (MiLB 3.4%, MLB 5.8%, all players 3.8%) (Table 4). This finding was in contrast to the larger percentage of intra-articular cases requiring surgery (MiLB 40.3%, MLB 41.2%, all players 40.5%). Time lost varied greatly by surgery status, as well as extra-articular or intra-articular, as would be expected even after excluding season-ending injuries. For both types of injuries, the average time lost was consistently greater for injuries that required surgery versus the ones that did not result in surgery.

Discussion

The incidence of overall injuries in MLB players is increasing.⁸ Injuries to the hip and groin for professional baseball players continue to be of concern both in the number of injuries and the potential for these injuries to be debilitating or to recur. The correct diagnosis of hip injuries can be challenging in these athletes due to the complex anatomy of the region. However, our understanding of the pathoanatomy of hip and groin injuries, combined with the utilization of improved magnetic resonance imaging (MRI,) has aided in making the correct diagnosis more reliable. Although upper extremity injuries have traditionally been the focus of MLB injury reporting, hip injuries have been shown to cause an average of 23 days missed per player.⁴ This was similar to the more commonly highlighted elbow and knee injuries in the same study (23 and 27 days, respectively). The purpose of this study was to explore the epidemiology of hip and groin injuries in MLB. The lack of existing data on this issue is important for sports injury research. Exploring these injuries increases the understanding of which players are at risk, and how we can tailor training programs for prevention or rehabilitation programs for those players who suffer these injuries.

In addition to the increased awareness of hip injuries, there has been a recent focus on the contribution of hip range of motion, leg drive, and pelvic rotation to the overall mechanics of overhead activities such as throwing, a tennis serve, or pitching.¹² Pelvic rotation and leg drive have been correlated to throwing velocity,²¹ and therefore if hip range of motion is inhibited by pain or a structural issue such as FAI, there will likely be altered upper extremity mechanics leading to less power and possibly injury.¹² Additionally, it has been shown that limited hip range of motion due to FAI is correlated with compensatory lower extremity muscular injuries such as hamstring and adductor strains as well as overload of the lumbar spine and sacroiliac joint.²²

In the current study, extra-articular injuries about the hip were the most common, making up 95.4% of the total injuries. Many (79.1%) of these were strains or contusions of the adductor, iliopsoas, or gluteal muscles. This is consistent with other articles reporting hip injuries in athletes.^3,9 A study on hip injuries in the National Football League found that strains and contusions comprised 92% of all hip injuries.³ Another report on European professional football found that 72% of hip injuries over a 7-season period were adductor or iliopsoas injuries.⁹ This prior study also reported that 15% of the hip and groin strains were re-injuries. Intra-articular injuries comprised only 4.6% of the hip injuries in our study. FAI and labral tears were the most common intra-articular diagnosis at 80.9%.

Almost all (96.2%) of the extra-articular hip injuries in this series were able to be treated nonoperatively and caused a mean of 12.4 days missed. Those which required operative treatment caused a mean of 54.6 days missed. For intra-articular injuries, 40.5% were treated surgically and these players missed a mean 122.5 days. Those treated nonsurgically missed an average of 22.2 days. Whether treated surgically or nonsurgically, the mean days missed following an intra-articular injury was approximately twice that of extra-articular injuries. Our findings regarding time or games missed are similar to other reports studying hip injuries in professional athletes.^2,3,9 Intra-articular injuries such as FAI, chondral injuries, or labral tears caused between 46 and 64 days missed compared to 3 to 27 days missed for extra-articular injuries in professional soccer players.⁹ Feeley and colleagues³ found a mean of 5.07 to 33.6 days missed for extra-articular injuries such as strains or contusions, and 63.5 to 126.2 days missed for intra-articular injuries including arthritis, labral tears, subluxations, dislocations, and fractures. A report on National Hockey League players found that intra-articular injuries made up 10.6% of all hip and groin injuries and caused significantly more games missed than extra-articular injuries.²

In both minor and major league players, for all reported positions at the time of hip or groin injury, infield players collectively were more commonly injured than outfielders, batters, or base runners, and fielding was the most common activity being performed at the time of injury. The pitcher’s mound was the most common single location for injuries and these players had the longest time missed following injury. The correlation between hip and groin pathology and upper extremity injuries in overhead athletes has been discussed in previous studies.^12,21 Interestingly, we found that the specific location on the field with the highest incidence of hip and groin injuries was the pitcher’s mound. As we follow these players over time, a future correlation between the incidence of hip and groin injuries and the incidence of shoulder and elbow injuries may be noted. A noncontact injury was the most frequent mechanism of injury. This corroborates the finding that muscle strains and contusions made up the majority of injuries in this series. Other series on hip injuries have also found that noncontact mechanisms are common.³

Although this was one of the first studies exploring the epidemiology of hip and groin injury, there are some limitations of this study. The retrospective nature of this study relied upon the reporting of injuries in the MLB database. As such, there may be underreporting of injuries into the official database by players or medical staff for a variety of reasons. Differences in technique for diagnosis and treatment among the medical staff for different teams were not controlled for. Due to the wide range of hip and groin pathology, and the often difficult diagnosis, a specific injury was not always provided. Therefore, the category of “other” hip injury was entered in to the database when symptoms were nonspecific or not all details were provided. Fortunately, this category made up a small percentage of the reported injuries, but does remain a confounding factor in describing the etiology of hip injuries in these players. Our data were taken from professional baseball players only, and so we cannot recommend extrapolation to other sports or nonprofessional baseball athletes.

Despite the inherent limitations of reporting registry data, this study serves as the initial report of the occurrence of hip and groin injuries in professional baseball players, and improves our knowledge of the positions and situations that put players at most risk for these injuries. An understanding of the overall epidemiology of these injuries serves as a platform for more focused research in this area in the future. We can now focus research on specific positions, such as pitchers, that have a high incidence of injury to determine the physiologic and environmental factors which put them at higher risk for injury in general and for more significant injuries with more days missed. This information can help to guide position-specific training programs for injury prevention as well as improve rehabilitation protocols for more efficient recovery and return to sports.

Injuries around the hip and groin occurring in professional baseball players can present as muscle strains, avulsions, contusions, hip subluxations or dislocations, femoroacetabular impingement (FAI) causing labral tears or chondral defects, and athletic pubalgia.^1-9 Several recent articles have reported on the epidemiology of musculoskeletal injuries in Major League Baseball (MLB) players^4,8,10 but with little attention to injuries to the hip and groin, likely because prior studies show only a 6.3% overall incidence for these injuries, much less than the more commonly discussed shoulder or elbow injuries.⁸ Despite the lower proportion of hip and groin injuries overall, these injuries lead to a relatively long period of disability for the players and often have a high rate of recurrence.^4,8,9

The important contribution of hip mechanics and the surrounding muscular function in the kinetic chain during overhead athletic activities, such as a tennis serve or throwing, has recently been discussed.^11,12 In sports requiring overhead activities, trunk rotation is a key component to generating force, and hip internal and external rotation is necessary for this trunk rotation to occur.^12,13 Alterations in hip morphology causing constrained motion, as seen in FAI, may predispose an overhead throwing athlete to intra-articular injury such as labral tears or chondral injuries, or to a compensatory movement pattern causing an extra-articular soft tissue injury about the hip.¹² Decreased hip range of motion may also lead to increased forces across the upper extremity during the throwing motion, which puts the shoulder and elbow at increased risk of injury.¹²

Increased awareness of hip and groin injuries, advances in diagnostic imaging, and an understanding of the relationship between the throwing motion in baseball and hip mechanics have improved our ability to appropriately identify and treat athletes with injuries of the hip and groin. Several studies on hip and groin injuries in elite athletes treated both operatively and nonoperatively have reported a high rate of return to sport.^3,7,14-19 A systematic review on return to sport following hip arthroscopy for intra-articular pathology associated with FAI showed a 95% return to sport rate and a 92% rate of return to pre-injury level of play in a subgroup of professional athletes in 9 studies.²⁰

Despite the large body of literature on upper extremity injuries, there is no study specifically focusing on the epidemiology of hip and groin injuries in MLB or Minor League Baseball (MiLB) players. The incidence of all injuries in professional baseball players has steadily increased over the last 2 decades,⁸ and the reported incidence of hip and groin injuries will likely increase as well. The current incidence of this injury, the positions most at risk, the mechanism of injury, and the time to return to sport are important to understand given the large number of players who participate in baseball not only at a professional level, but also at an amateur level, where this information may also be applicable. This information could improve our efforts at prevention and rehabilitation of these injuries, and can guide efforts to counsel and train players at high risk of a hip or groin injury. To address this gap in the literature, the purpose of this study was to describe the epidemiology of hip and groin injuries in MLB and MiLB players from 2011 to 2014.

Materials and Methods

Population and Sample

US MLB is comprised of the major and minor leagues. The major leagues are divided into 30 clubs, with 25 active players, for a total of 750 active players. Each club has a 40-man roster consisting of 25 active players and up to 15 additional players who are either not active or optioned to the minor leagues. The minor leagues are comprised of a network of over 200 clubs that are each affiliated with a major league club, and organized by geography and level of play. The minor leagues consist of roughly 7500 players, of whom about 6500 are actively playing at any given time. The entire population of players in the MLB who sustained a hip or groin injury over the study period was eligible for this study.

Data

The MLB’s Health and Injury Tracking System (HITS) is a centralized database that contains the de-identified medical data from the electronic medical record (EMR) system. Data on all injuries are entered into the EMR by each team’s certified athletic trainer. An injury is defined as any physical complaint sustained by a player that affects or limits participation in any aspect of baseball-related activity (eg, game, practice, warm-up, conditioning, weight training). The data extracted from HITS only relates to injuries that resulted in lost game time for a player and that occurred during spring training, regular season, or postseason play; off-season injuries were not included. Injury events that were classified as “season-ending” were not included in the analysis of assessing days missed because many of these players may not have been cleared to play until the beginning of the following season. For each injury, data were collected on the diagnosis, body part, activity, location, and date of injury.

Materials and Methods

Hip and groin injuries were defined as cases having a body region variable classified as “hip/groin” or a Sports Medicine Diagnostic Coding System (SMDCS) that included any “adductor” or “hernia” or “hip pointer” labels. Cases categorized as inguinal and femoral hernia (n = 26) and testicular contusions (n = 87) were excluded. Characteristics about each hip and groin injury were also extracted from HITS. These variables included level of play, player position (activity at the time of injury), field location, injury mechanism, chronicity of the injury, and days missed. Chronicity of the injury was documented as acute, overuse, or undetermined. For level of play, the injury event was categorized as the league in which the game was played when the injury occurred. Players were excluded if they had an unknown level of play or were in the amateur league. The injuries of the hip and groin were further classified as intra-articular and extra-articular. Treatment for each injury was characterized as surgical or nonsurgical, and correlated with days missed for each type of injury.

Statistical Analysis

Data for the 2011-2014 seasons were combined, and results presented for all players and separately for MiLB and MLB. Frequencies and comparative analyses for hip and groin injuries were performed across the aforementioned injury characteristics. The distribution of days missed for the variables considered was often skewed to the right, even after excluding the season-ending injuries; hence, the mean days missed was often larger than the median days missed. Reporting the median would allow for a robust estimate of the expected number of days missed, but would down weight those instances when hip and groin injuries result in much longer missed days, as reflected by the mean. Because of the importance of the days missed measure for professional baseball, both the mean and median are presented. Chi-square tests were used to test the hypothesis of equal proportions between the various categories of hip and groin characteristics, with statistical significance determined at the P = .05 level.

In order to estimate exposure, the average number of players per team per game was calculated based on analysis of regular season game participation via box scores that are publicly available. This average number over a season, multiplied by the number of team games at each professional level of baseball, was used as an estimate of athlete exposures in order to provide rates comparable to those of other injury surveillance systems. Injury rates were reported as injuries per 1000 athlete-exposures (AE) for those hip and groin injuries that occurred during the regular season. It should be noted that the number of regular season hip and groin injuries and the subsequent AE rates are based on injuries that were deemed work-related during the regular season. This does not necessarily only include injuries occurring during the course of a game, but injuries in game preparation as well. Due to the variations in spring training games and fluctuating rosters, an exposure rate could not be calculated for spring training hip and groin injuries.

Data analysis was performed in the R statistical computing Environment (R Core Team 2014). Study procedures were approved by the Johns Hopkins Bloomberg School of Public Health Institutional Review Board.

Results

Overall Summary

A total of 1823 hip and groin injuries occurred from 2011-2014, with 83% occurring in MiLB and 17% occurring in MLB (Table 1). There were 1146 acute injuries, 252 overuse injuries, and 425 injuries of undetermined chronicity. The average age of players experiencing a hip and groin injury in MiLB was 22.9 years compared to 29.7 years in MLB. Of the 1514 hip and groin injuries in MiLB, 76 (5.0%) required surgery and of the 309 hip and groin injuries in MLB, 24 (7.8%) required surgery. Compared to league-wide injury events, hip and groin injuries ranked 6th highest in prevalence in MiLB and 8th highest in prevalence in MLB, accounting for 5.4% and 5.6%, respectively, of the 28,116 MiLB and 5507 MLB injury events that occurred between 2011-2014.

For regular season games, it was estimated that there were 1,197,738 MiLB and 276,608 MLB AE from 2011-2014. The overall hip and groin rate across both MLB and MiLB was 1.2 per 1000 AE, based on the 238 and 1152 regular season hip and groin injuries in MLB and MiLB, respectively. The rate of hip and groin injury was 1.5 times more likely in MiLB than in MLB (P < .0001) (rate of 1.26 per 1000 AE in MiLB and 0.86 per 1000 AE in MLB).

Characteristics of Injuries

Injury activity was based on the position being played at the time of injury, with categories of infield and outfield corresponding to fielding activities (defense), with batting and base runner categories corresponding to activities while on offense (Table 2). The occurrence of hip and groin injuries while players are fielding on defense (MiLB 33.0%, MLB 37.2%, all players 33.8%) was significantly greater compared to injuries while batting and base running on offense (MiLB 24.9%, MLB 21.7%, all players 24.3%) (all P values < .001). There was a high percentage of missing data for the event position variable, which resulted from this field not being available in HITS for 2011. Time lost due to hip and groin injuries was similar across leagues with respect to injury activity, ranging on average between 8 and 18 days.

There were statistically significant differences for MiLB and MLB separately, and combined, in the number of hip and groin injuries by field location (all P values < .0001) (Table 2). For MiLB, MLB, and across both leagues, by injury location, the majority of hip and groin injuries occurred in the infield (MiLB 34.1%, MLB 35.3%, all players 34.3%). As a single location, the pitcher’s mound accounted for a large proportion of hip and groin injuries (MiLB 19.2%, MLB 23.3%, all players 19.9%). Time lost due to hip and groin injuries was similar across leagues with respect to field location, ranging on average between about 10 and 22 days. Among all players, injuries on the pitcher’s mound resulted in the largest mean days missed after injury.

There were statistically significant differences across the mechanisms of injury for MiLB and MLB, as well as both leagues combined (all P values < .0001) (Table 2). The majority of hip and groin injuries were noncontact-related (MiLB 73.7%, MLB 75.7%, all players 74.1%) compared to those resulting from some form of contact (MiLB 11.4%, MLB 12.6%, all players 11.7%) or other mechanisms. Time lost across these mechanisms varied, ranging on average between 4 and 15 days with noncontact-related hip and groin injuries resulting in the largest time lost.

Surgery

The 1823 hip and groin injuries across both leagues were further classified using the SMDCS descriptions as intra-articular (N = 84) or extra-articular (N = 1739) (Table 3). A much larger percentage of hip and groin injuries were extra-articular (MiLB 95.6%, MLB 94.4%, all players 95.4%) compared to those classified as intra-articular (Table 3). The most common extra-articular injuries were strains or contusions of the adductor, iliopsoas, or gluteal muscles, making up 79.1% of this group of injuries. The most common intra-articular injuries were FAI and a labral tear, accounting for 80.9% of these injuries. Only a small percentage of the extra-articular cases required surgery (MiLB 3.4%, MLB 5.8%, all players 3.8%) (Table 4). This finding was in contrast to the larger percentage of intra-articular cases requiring surgery (MiLB 40.3%, MLB 41.2%, all players 40.5%). Time lost varied greatly by surgery status, as well as extra-articular or intra-articular, as would be expected even after excluding season-ending injuries. For both types of injuries, the average time lost was consistently greater for injuries that required surgery versus the ones that did not result in surgery.

Discussion

The incidence of overall injuries in MLB players is increasing.⁸ Injuries to the hip and groin for professional baseball players continue to be of concern both in the number of injuries and the potential for these injuries to be debilitating or to recur. The correct diagnosis of hip injuries can be challenging in these athletes due to the complex anatomy of the region. However, our understanding of the pathoanatomy of hip and groin injuries, combined with the utilization of improved magnetic resonance imaging (MRI,) has aided in making the correct diagnosis more reliable. Although upper extremity injuries have traditionally been the focus of MLB injury reporting, hip injuries have been shown to cause an average of 23 days missed per player.⁴ This was similar to the more commonly highlighted elbow and knee injuries in the same study (23 and 27 days, respectively). The purpose of this study was to explore the epidemiology of hip and groin injuries in MLB. The lack of existing data on this issue is important for sports injury research. Exploring these injuries increases the understanding of which players are at risk, and how we can tailor training programs for prevention or rehabilitation programs for those players who suffer these injuries.

In addition to the increased awareness of hip injuries, there has been a recent focus on the contribution of hip range of motion, leg drive, and pelvic rotation to the overall mechanics of overhead activities such as throwing, a tennis serve, or pitching.¹² Pelvic rotation and leg drive have been correlated to throwing velocity,²¹ and therefore if hip range of motion is inhibited by pain or a structural issue such as FAI, there will likely be altered upper extremity mechanics leading to less power and possibly injury.¹² Additionally, it has been shown that limited hip range of motion due to FAI is correlated with compensatory lower extremity muscular injuries such as hamstring and adductor strains as well as overload of the lumbar spine and sacroiliac joint.²²

In the current study, extra-articular injuries about the hip were the most common, making up 95.4% of the total injuries. Many (79.1%) of these were strains or contusions of the adductor, iliopsoas, or gluteal muscles. This is consistent with other articles reporting hip injuries in athletes.^3,9 A study on hip injuries in the National Football League found that strains and contusions comprised 92% of all hip injuries.³ Another report on European professional football found that 72% of hip injuries over a 7-season period were adductor or iliopsoas injuries.⁹ This prior study also reported that 15% of the hip and groin strains were re-injuries. Intra-articular injuries comprised only 4.6% of the hip injuries in our study. FAI and labral tears were the most common intra-articular diagnosis at 80.9%.

Almost all (96.2%) of the extra-articular hip injuries in this series were able to be treated nonoperatively and caused a mean of 12.4 days missed. Those which required operative treatment caused a mean of 54.6 days missed. For intra-articular injuries, 40.5% were treated surgically and these players missed a mean 122.5 days. Those treated nonsurgically missed an average of 22.2 days. Whether treated surgically or nonsurgically, the mean days missed following an intra-articular injury was approximately twice that of extra-articular injuries. Our findings regarding time or games missed are similar to other reports studying hip injuries in professional athletes.^2,3,9 Intra-articular injuries such as FAI, chondral injuries, or labral tears caused between 46 and 64 days missed compared to 3 to 27 days missed for extra-articular injuries in professional soccer players.⁹ Feeley and colleagues³ found a mean of 5.07 to 33.6 days missed for extra-articular injuries such as strains or contusions, and 63.5 to 126.2 days missed for intra-articular injuries including arthritis, labral tears, subluxations, dislocations, and fractures. A report on National Hockey League players found that intra-articular injuries made up 10.6% of all hip and groin injuries and caused significantly more games missed than extra-articular injuries.²

In both minor and major league players, for all reported positions at the time of hip or groin injury, infield players collectively were more commonly injured than outfielders, batters, or base runners, and fielding was the most common activity being performed at the time of injury. The pitcher’s mound was the most common single location for injuries and these players had the longest time missed following injury. The correlation between hip and groin pathology and upper extremity injuries in overhead athletes has been discussed in previous studies.^12,21 Interestingly, we found that the specific location on the field with the highest incidence of hip and groin injuries was the pitcher’s mound. As we follow these players over time, a future correlation between the incidence of hip and groin injuries and the incidence of shoulder and elbow injuries may be noted. A noncontact injury was the most frequent mechanism of injury. This corroborates the finding that muscle strains and contusions made up the majority of injuries in this series. Other series on hip injuries have also found that noncontact mechanisms are common.³

Although this was one of the first studies exploring the epidemiology of hip and groin injury, there are some limitations of this study. The retrospective nature of this study relied upon the reporting of injuries in the MLB database. As such, there may be underreporting of injuries into the official database by players or medical staff for a variety of reasons. Differences in technique for diagnosis and treatment among the medical staff for different teams were not controlled for. Due to the wide range of hip and groin pathology, and the often difficult diagnosis, a specific injury was not always provided. Therefore, the category of “other” hip injury was entered in to the database when symptoms were nonspecific or not all details were provided. Fortunately, this category made up a small percentage of the reported injuries, but does remain a confounding factor in describing the etiology of hip injuries in these players. Our data were taken from professional baseball players only, and so we cannot recommend extrapolation to other sports or nonprofessional baseball athletes.

Despite the inherent limitations of reporting registry data, this study serves as the initial report of the occurrence of hip and groin injuries in professional baseball players, and improves our knowledge of the positions and situations that put players at most risk for these injuries. An understanding of the overall epidemiology of these injuries serves as a platform for more focused research in this area in the future. We can now focus research on specific positions, such as pitchers, that have a high incidence of injury to determine the physiologic and environmental factors which put them at higher risk for injury in general and for more significant injuries with more days missed. This information can help to guide position-specific training programs for injury prevention as well as improve rehabilitation protocols for more efficient recovery and return to sports.

While the exact origins of the game of baseball are commonly debated, one thing is certain: statistics have been an integral part of the game since its existence.^1-3 This is true at nearly every level of baseball, especially in Major League Baseball (MLB). As our knowledge and technical capabilities advance, new statistical measures of baseball performance are added at a rapid pace.^1,3 One example is the Pitch f/x video tracking system (Sportvision, Inc.), which now analyzes over 60 variables on each of the estimated 660,000 pitches thrown in the MLB annually. In addition to measuring performance and production, these advancements are being leveraged to better understand the epidemiology and impact of injuries in MLB players.^4,5 As with any sport, performance at the most elite level is highly dependent upon player health and functional capacity. Accordingly, player injuries can have a profound impact not only on individual performance but also on the success of the team as a whole.

The first epidemiologic study of injuries in professional baseball was published by Conte and colleagues⁴ in 2001. This work utilized publically available disabled list (DL) data to perform a comprehensive review of injury patterns in MLB from 1989 to 1999. They demonstrated that injuries were on the rise and that pitchers were more commonly injured (48.4% of all DL reports) and had greater time out of play compared to players of other positions.⁴ Shoulder and elbow injuries were responsible for 49.8% of all DL assignments, distantly followed by knee (7.3%), wrist/hand (6.1%), and back (5.0%).⁴ In a later study, Posner and colleagues⁵ analyzed DL data spanning the 2002 to 2008 seasons. Similarly, they found that injuries continued to increase, and over half (51.2%) of DL assignments occurred secondary to upper extremity injuries.⁵ Although the DL is primarily designed as a roster management tool rather than an injury database, it has provided valuable epidemiologic injury information through the years. Out of concern for player health and well-being, MLB and the MLB Players Association (MLBPA) worked together to create and implement an electronic medical record and Health and Injury Tracking System (HITS) for all MLB and Minor League Baseball (MiLB) players. Now active for over 5 seasons, this database has provided valuable, detailed reports regarding specific injuries occurring in professional baseball, such as hamstring strains and concussions.^6,7

With shoulder and elbow injuries in pitchers representing the greatest proportion of DL assignments in recent years, a large body of literature on these injuries, particularly medial ulnar collateral ligament (MUCL) injuries, has been published.^8-13 Since the initial description of MUCL reconstruction, or “Tommy John surgery,” by Dr. Frank Jobe in 1986, much has been done to improve the technique and rehabilitation to maximize player performance following surgery.^10,14-16 Despite this increased attention, large-scale epidemiologic reporting of MUCL injuries in MLB is lacking, but such a report is desirable. The purpose of this work is to: 1) provide a large-scale analysis of injuries occurring in MLB baseball over the course of 18 seasons (1998-2015); 2) highlight the financial implications of these injuries; and 3) detail the evolution of MUCL injuries and reconstructive surgery since it was first performed on a MLB pitcher in 1974. Our study represents the largest longitudinal analysis of MLB injuries since the league expanded to its current level of 30 teams in 1998. It is our hope that this work will serve as a framework for future study of the most common and highest impact injuries occurring in baseball.

Materials And Methods

We performed a retrospective review of the MLB DL from 1998 to 2015. Data analyzed included player demographics such as club, year of placement, age, and position. Injury-specific variables included date of placement on DL, length of time on DL, date of reinstatement, body part injured, diagnosis, and cost of replacement. If a player was put on the DL multiple times during a season, each placement was viewed as a different injury, even if it was to the same body part. If a player was put on the DL for injuries to multiple body parts, the primary injury was analyzed.

Disabled List Data

Although the DL has existed since 1916, this current study covers 18 seasons from 1998 to 2015. The 1998 season was chosen as a starting point because this is the year when MLB expanded to 30 teams. Since then, the number of teams and the active roster limits (25 players) have remained constant, allowing for reliable comparisons across seasons. Initially designed as a roster management tool to allow injured players to temporarily be replaced with healthy players, the DL was not created as an injury database. However, the rules and regulations of the DL have remained fairly constant over the last 18 years, allowing reasonable comparisons of injury data and trends across this timespan. In order for a player to be assigned to the DL, the nature and extent of injury must be certified by a physician. Once designated for the DL, a player cannot return to the major league team for a minimum of 15 days. If the injury is severe, the player can remain on the DL for the remainder of the season or until he is deemed healthy enough to return to play by a physician. One notable exception is the treatment of concussions. Since 2011, a player diagnosed with a concussion may be placed on the DL for a minimum of 7 days rather than 15. The introduction of the HITS database in 2010 should allow for more detailed and reliable study of injuries in baseball moving forward. Although it contains robust data for every injury that has occurred in MLB and MiLB over the last 5 seasons, it does not allow for epidemiologic and longitudinal study of injury patterns and trends in baseball prior to 2010.

Cost of Placing Players on the DL

The dollars lost were calculated by prorating the injured player’s daily salary and multiplying by the number of days missed on the DL. For example, if a player’s annual salary is $1,820,000, his daily salary for the 182 day season is $10,000. If assigned to the DL for 15 days, $150,000 is paid to that player while he is inactive and unable to play. An additional cost is the salary of the replacement player who fills the roster spot. For this work, the replacement player’s prorated, daily salary was assumed to be the league minimum for that specific year. For example, if the league minimum for a given season is $182,000, and the season is 182 days long, a replacement player earns a minimum of $1,000 per day while he is on the 25-man active roster. Thus, the dollars paid to the replacement would be $15,000. In this scenario, that brings the team’s total cost to $165,000 ($150,000 plus $15,000). Because the league minimum salary changes year to year, salaries specific to the year of injury were utilized in this analysis.

MUCL Injury Analysis

In order to better understand the evaluation of MUCL injuries over time, all MLB players undergoing MUCL reconstruction (“Tommy John surgery”) were analyzed separately. Similar to prior studies of UCL injuries, these players were identified using DL data, team websites, and publically available internet databases (primarily www.heatmaps.com).^9,12,17-19 Variables studied include the number of procedures, year of surgery, player position, and mean time until return to play at the MLB level. All MLB players undergoing MUCL reconstruction since 1974 (the year the first procedure was performed) were included.

Statistical Methods

Epidemiologic data are reported using descriptive statistics (mean, range, and percentage) where indicated. To determine the significance of trends over time, a best-fit line was generated to illustrate the change over the years. These lines are reported with corresponding R² values. To assess the trend for significance, the slope was compared to a line with a slope of zero (no change over time) using t tests. For all statistical comparisons, the threshold for alpha was set to P < .05.

Results

Between 1998 and 2015, there were 8357 placements of players on the DL, at an average rate of 464 designations per year (Table 1, Figure 1). This resulted in 460,432 days lost to injury, with a mean of 25,186 days out of play per season (Table 1, Figure 2). The mean length of DL assignment per year was 55.1 days per injury, with a low of 49.1 days in 2011 and a high of 59.2 days in 2001 (Table 1, Figure 3). During the study period, the number of players placed on the DL and the total number of DL days steadily increased (P < .001 and P = .003, respectively), while the average length of DL assignments remained steady (P = .647). When analyzing the data by body region injured, the shoulder (20.6%) and elbow (19.6%) were the 2 leading causes of time out of play (Table 2). This was followed distantly by the chest/back/spine (13.7%), wrist/hand/fingers (10.1%), lower leg/knee (9.8%), and the upper leg/thigh (9.5%). Although the percentage of injuries occurring to the upper extremity remained stable, the rate of shoulder injuries steadily decreased (P = .023) as elbow injuries increased (P = .015) (Table 3, Figure 4). This inverse relationship was also demonstrated for the annual number of DL days for shoulder (P = .033) and elbow (P = 0.005) injuries (Figure 5).

Regarding the financial impact of these injuries, the mean annual cost of replacing players on the DL was $423,267,633.78 (Table 4). This ranged from a low of $136,397,147 in 1998 to a high of $694,835,359 in 2015. There was a steady increase in the cost of replacement during the study period (P < .001) that coincides with the increasing salaries during that time span (Figure 6). In total, $6,732,167,180 was paid to players assigned to the DL and $886,650,228 was spent to fill their positions. This brings the total cost of DL assignments to $7,618,817,407 for the study period.

Looking specifically at MUCL injuries, a total of 400 MUCL reconstructions have been performed on MLB players since the procedure was first developed in 1974. The vast majority of these were performed in pitchers (n = 361, 90.3%) followed by outfielders (n = 16, 4.0%), infielders (n = 14, 3.5%) and catchers (n = 9, 2.3%) (Table 5). The mean time to return to competition at the MLB level was 17.8 months for pitchers, 11.1 months for outfielders, 9.6 months for infielders, and 10.5 months for catchers. The overall mean time to return was 17.1 months. The annual number of MUCL reconstructions continues to rise dramatically (P < .001) (Figure 7). During the first 12 years (1974-1985), a total of 8 (2.0%) MUCL reconstructions were performed on MLB players. In subsequent decades, this number increased to 44 (11.0%) from 1986-1995, 123 (30.8%) from 1996-2005, and 225 (56.3%) from 2006-2015. Of all Tommy John surgeries performed over 42 years, nearly one-third (n = 131, 32.75%) were performed in the last 5 years alone (2011-2015).

Discussion

To date, a number of studies have been published on injuries in professional baseball. These can primarily be categorized as either studies with a detailed focus on a single injury type or body region^6-13,17,19 or broader reviews that are limited by the relatively short time span covered.^4,5 The purpose of this work was to provide a comprehensive review of injury trends in MLB since the league expanded to 30 teams in 1998 while paying special attention to the financial impact of those injuries. Additionally, we sought to provide an up-to-date review of MUCL injuries and surgeries since the procedure was first developed in 1974. Ultimately, this data demonstrates that injuries continue to rise in MLB and this increase is accompanied by increased expense for teams. Thankfully, the rates of DL assignments for shoulder injuries are on the decline; however, this decrease is countered by a reciprocal increase in elbow injuries. Similarly, the rates of MUCL reconstruction have also risen dramatically in recent years.

The fact that injury rates are on the rise is confirmed by other published reports. This trend was demonstrated in prior analyses of DL data from the 1989 to 1998⁴ and 2002 to 2008 seasons.⁵ These 2 studies represent the only comprehensive reviews of MLB injury trends to date, and each provides valuable information. Both are consistent with the current study findings that pitchers are the most commonly injured players and that shoulder and elbow injuries represent about half of all injuries.^4,5 Similar injury rates and characteristics have been reported at the collegiate²⁰ and minor league levels.²¹ Despite this consistency, this analysis of injuries from 1998 to 2015 is the first to report that DL designations for shoulder injuries are on the decline while designations for elbow injuries continue to rise. Although the exact etiology of this decline in shoulder injuries remains unknown, there are a number of possible explanations. In recent years, increased emphasis has been placed on shoulder rehabilitation, reduction of glenohumeral internal rotation deficits, scapular stabilization, and overall kinetic chain balance and coordination. However, this does not explain why elbow injuries continue to rise annually.

With this increase in injuries, the cost of maintaining an active 25-man roster is also climbing. As expected, this growing expense is primarily due to the increased number of DL days each year as well as the increase in league salaries. Fortunately, this increased financial strain has been met with steadily increased annual revenues in professional baseball. In 2014, the prorated salary cost to players designated to the DL and their replacements was $579,568,059. This figure represents an estimated 6.4% of the $9 billion in total revenue for MLB that same year.²² Although this may represent a small percentage of the whole, it still embodies an exceptionally large financial responsibility. This does not include the medical expenses incurred to treat and rehabilitate the players’ injuries.

Every injury that occurs in MLB players has the potential to adversely affect players, teams, and MLB as a whole. With its increasing prevalence, need for surgical treatment, and prolonged return to play, injuries to the MUCL of the elbow may represent the most costly of all injuries. Although a multitude of reports on MUCL injuries, treatments, techniques, rehabilitation, and outcomes have been reported,^{8,9,12,14-19,23-25} to our knowledge, a comprehensive and longitudinal incidence study in MLB players has not yet been published. By including every MUCL reconstruction that has been performed on a MLB player, our study demonstrates the dramatic increase in the annual incidence of MUCL surgeries. Studies performed over shorter time intervals corroborate these findings. A recent review of a privately insured patient database revealed an annual increase in MUCL reconstructions of 4.2% in that cohort.²⁶ When looking specifically at the MLB, a recent survey of all 30 clubs found that 25% (96 of 382) of MLB pitchers and 15% (341 of 2324) of minor league pitchers have undergone MUCL reconstruction.⁸ Because it occurs so frequently and requires a mean of 17 months to return to sport, MUCL injuries represent a very significant cause of time out of play.

While this study represents a unique epidemiologic report on injuries in baseball, it is certainly not without its limitations. As stated previously, it relies on DL data that was initially intended to serve as a roster management tool rather than an injury database. Accordingly, detailed and specific information about every injury is not always available. The limitations of DL data will largely be overcome in future studies thanks to the implementation of the HITS database in 2010. Moving forward, this system will allow for more detailed analysis of injury patterns, characteristics, time out of play, treatments rendered, etc. Its main limitation is that the earliest data dates back to 2010, making it less applicable for longitudinal studies like the present one. Another limitation of this study is the estimations used for the cost of replacing players designated to the DL. For each injury, it was assumed that the replacement player was paid a prorated portion of the league minimum salary while on the major league roster, but in some instances, that may not have been the case. It is possible that some players filling roster spots were already under contract for amounts higher than the league minimum. Since that player would be making that amount regardless of the level of play, the team may not have paid them any additional salary while filling the position of the injured player. The strengths of this study are its comprehensive nature and inclusion of 18 years of data, making it the longest such study of injuries in MLB. It also represents the first report of cost of replacement for players designated to the DL. To our knowledge, this study also represents the first comprehensive report of every MUCL surgery that has been performed on MLB players.

Conclusion

Injury rates continue to rise in MLB, and upper extremity injuries continue to represent approximately half of all injuries resulting in time out of play. Although shoulder injuries have been on the decline in recent years, this decline is offset by a steady increase in elbow injuries. Each year, MLB players are designated to the DL an average of 464 times for a total of 25,579.6 days. This results in a mean annual cost of over $400 million dollars to replace players lost to injury. Looking specifically at MUCL injuries, a total of 400 MUCL reconstructions have been performed in the MLB since 1974, and nearly one-third of these were performed in the last 5 years. Pitchers represent 90.3% of players requiring MUCL surgery, and the average time to return to sport for all players is 17 months. These data may serve as a foundation for identifying appropriate targets for continued study into the etiologies, strategies for prevention, and optimal treatments of injuries commonly affecting professional baseball players.

While the exact origins of the game of baseball are commonly debated, one thing is certain: statistics have been an integral part of the game since its existence.^1-3 This is true at nearly every level of baseball, especially in Major League Baseball (MLB). As our knowledge and technical capabilities advance, new statistical measures of baseball performance are added at a rapid pace.^1,3 One example is the Pitch f/x video tracking system (Sportvision, Inc.), which now analyzes over 60 variables on each of the estimated 660,000 pitches thrown in the MLB annually. In addition to measuring performance and production, these advancements are being leveraged to better understand the epidemiology and impact of injuries in MLB players.^4,5 As with any sport, performance at the most elite level is highly dependent upon player health and functional capacity. Accordingly, player injuries can have a profound impact not only on individual performance but also on the success of the team as a whole.

The first epidemiologic study of injuries in professional baseball was published by Conte and colleagues⁴ in 2001. This work utilized publically available disabled list (DL) data to perform a comprehensive review of injury patterns in MLB from 1989 to 1999. They demonstrated that injuries were on the rise and that pitchers were more commonly injured (48.4% of all DL reports) and had greater time out of play compared to players of other positions.⁴ Shoulder and elbow injuries were responsible for 49.8% of all DL assignments, distantly followed by knee (7.3%), wrist/hand (6.1%), and back (5.0%).⁴ In a later study, Posner and colleagues⁵ analyzed DL data spanning the 2002 to 2008 seasons. Similarly, they found that injuries continued to increase, and over half (51.2%) of DL assignments occurred secondary to upper extremity injuries.⁵ Although the DL is primarily designed as a roster management tool rather than an injury database, it has provided valuable epidemiologic injury information through the years. Out of concern for player health and well-being, MLB and the MLB Players Association (MLBPA) worked together to create and implement an electronic medical record and Health and Injury Tracking System (HITS) for all MLB and Minor League Baseball (MiLB) players. Now active for over 5 seasons, this database has provided valuable, detailed reports regarding specific injuries occurring in professional baseball, such as hamstring strains and concussions.^6,7

With shoulder and elbow injuries in pitchers representing the greatest proportion of DL assignments in recent years, a large body of literature on these injuries, particularly medial ulnar collateral ligament (MUCL) injuries, has been published.^8-13 Since the initial description of MUCL reconstruction, or “Tommy John surgery,” by Dr. Frank Jobe in 1986, much has been done to improve the technique and rehabilitation to maximize player performance following surgery.^10,14-16 Despite this increased attention, large-scale epidemiologic reporting of MUCL injuries in MLB is lacking, but such a report is desirable. The purpose of this work is to: 1) provide a large-scale analysis of injuries occurring in MLB baseball over the course of 18 seasons (1998-2015); 2) highlight the financial implications of these injuries; and 3) detail the evolution of MUCL injuries and reconstructive surgery since it was first performed on a MLB pitcher in 1974. Our study represents the largest longitudinal analysis of MLB injuries since the league expanded to its current level of 30 teams in 1998. It is our hope that this work will serve as a framework for future study of the most common and highest impact injuries occurring in baseball.

Materials And Methods

We performed a retrospective review of the MLB DL from 1998 to 2015. Data analyzed included player demographics such as club, year of placement, age, and position. Injury-specific variables included date of placement on DL, length of time on DL, date of reinstatement, body part injured, diagnosis, and cost of replacement. If a player was put on the DL multiple times during a season, each placement was viewed as a different injury, even if it was to the same body part. If a player was put on the DL for injuries to multiple body parts, the primary injury was analyzed.

Disabled List Data

Although the DL has existed since 1916, this current study covers 18 seasons from 1998 to 2015. The 1998 season was chosen as a starting point because this is the year when MLB expanded to 30 teams. Since then, the number of teams and the active roster limits (25 players) have remained constant, allowing for reliable comparisons across seasons. Initially designed as a roster management tool to allow injured players to temporarily be replaced with healthy players, the DL was not created as an injury database. However, the rules and regulations of the DL have remained fairly constant over the last 18 years, allowing reasonable comparisons of injury data and trends across this timespan. In order for a player to be assigned to the DL, the nature and extent of injury must be certified by a physician. Once designated for the DL, a player cannot return to the major league team for a minimum of 15 days. If the injury is severe, the player can remain on the DL for the remainder of the season or until he is deemed healthy enough to return to play by a physician. One notable exception is the treatment of concussions. Since 2011, a player diagnosed with a concussion may be placed on the DL for a minimum of 7 days rather than 15. The introduction of the HITS database in 2010 should allow for more detailed and reliable study of injuries in baseball moving forward. Although it contains robust data for every injury that has occurred in MLB and MiLB over the last 5 seasons, it does not allow for epidemiologic and longitudinal study of injury patterns and trends in baseball prior to 2010.

Cost of Placing Players on the DL

The dollars lost were calculated by prorating the injured player’s daily salary and multiplying by the number of days missed on the DL. For example, if a player’s annual salary is $1,820,000, his daily salary for the 182 day season is $10,000. If assigned to the DL for 15 days, $150,000 is paid to that player while he is inactive and unable to play. An additional cost is the salary of the replacement player who fills the roster spot. For this work, the replacement player’s prorated, daily salary was assumed to be the league minimum for that specific year. For example, if the league minimum for a given season is $182,000, and the season is 182 days long, a replacement player earns a minimum of $1,000 per day while he is on the 25-man active roster. Thus, the dollars paid to the replacement would be $15,000. In this scenario, that brings the team’s total cost to $165,000 ($150,000 plus $15,000). Because the league minimum salary changes year to year, salaries specific to the year of injury were utilized in this analysis.

MUCL Injury Analysis

In order to better understand the evaluation of MUCL injuries over time, all MLB players undergoing MUCL reconstruction (“Tommy John surgery”) were analyzed separately. Similar to prior studies of UCL injuries, these players were identified using DL data, team websites, and publically available internet databases (primarily www.heatmaps.com).^9,12,17-19 Variables studied include the number of procedures, year of surgery, player position, and mean time until return to play at the MLB level. All MLB players undergoing MUCL reconstruction since 1974 (the year the first procedure was performed) were included.

Statistical Methods

Epidemiologic data are reported using descriptive statistics (mean, range, and percentage) where indicated. To determine the significance of trends over time, a best-fit line was generated to illustrate the change over the years. These lines are reported with corresponding R² values. To assess the trend for significance, the slope was compared to a line with a slope of zero (no change over time) using t tests. For all statistical comparisons, the threshold for alpha was set to P < .05.

Results

Between 1998 and 2015, there were 8357 placements of players on the DL, at an average rate of 464 designations per year (Table 1, Figure 1). This resulted in 460,432 days lost to injury, with a mean of 25,186 days out of play per season (Table 1, Figure 2). The mean length of DL assignment per year was 55.1 days per injury, with a low of 49.1 days in 2011 and a high of 59.2 days in 2001 (Table 1, Figure 3). During the study period, the number of players placed on the DL and the total number of DL days steadily increased (P < .001 and P = .003, respectively), while the average length of DL assignments remained steady (P = .647). When analyzing the data by body region injured, the shoulder (20.6%) and elbow (19.6%) were the 2 leading causes of time out of play (Table 2). This was followed distantly by the chest/back/spine (13.7%), wrist/hand/fingers (10.1%), lower leg/knee (9.8%), and the upper leg/thigh (9.5%). Although the percentage of injuries occurring to the upper extremity remained stable, the rate of shoulder injuries steadily decreased (P = .023) as elbow injuries increased (P = .015) (Table 3, Figure 4). This inverse relationship was also demonstrated for the annual number of DL days for shoulder (P = .033) and elbow (P = 0.005) injuries (Figure 5).

Regarding the financial impact of these injuries, the mean annual cost of replacing players on the DL was $423,267,633.78 (Table 4). This ranged from a low of $136,397,147 in 1998 to a high of $694,835,359 in 2015. There was a steady increase in the cost of replacement during the study period (P < .001) that coincides with the increasing salaries during that time span (Figure 6). In total, $6,732,167,180 was paid to players assigned to the DL and $886,650,228 was spent to fill their positions. This brings the total cost of DL assignments to $7,618,817,407 for the study period.

Looking specifically at MUCL injuries, a total of 400 MUCL reconstructions have been performed on MLB players since the procedure was first developed in 1974. The vast majority of these were performed in pitchers (n = 361, 90.3%) followed by outfielders (n = 16, 4.0%), infielders (n = 14, 3.5%) and catchers (n = 9, 2.3%) (Table 5). The mean time to return to competition at the MLB level was 17.8 months for pitchers, 11.1 months for outfielders, 9.6 months for infielders, and 10.5 months for catchers. The overall mean time to return was 17.1 months. The annual number of MUCL reconstructions continues to rise dramatically (P < .001) (Figure 7). During the first 12 years (1974-1985), a total of 8 (2.0%) MUCL reconstructions were performed on MLB players. In subsequent decades, this number increased to 44 (11.0%) from 1986-1995, 123 (30.8%) from 1996-2005, and 225 (56.3%) from 2006-2015. Of all Tommy John surgeries performed over 42 years, nearly one-third (n = 131, 32.75%) were performed in the last 5 years alone (2011-2015).

Discussion

To date, a number of studies have been published on injuries in professional baseball. These can primarily be categorized as either studies with a detailed focus on a single injury type or body region^6-13,17,19 or broader reviews that are limited by the relatively short time span covered.^4,5 The purpose of this work was to provide a comprehensive review of injury trends in MLB since the league expanded to 30 teams in 1998 while paying special attention to the financial impact of those injuries. Additionally, we sought to provide an up-to-date review of MUCL injuries and surgeries since the procedure was first developed in 1974. Ultimately, this data demonstrates that injuries continue to rise in MLB and this increase is accompanied by increased expense for teams. Thankfully, the rates of DL assignments for shoulder injuries are on the decline; however, this decrease is countered by a reciprocal increase in elbow injuries. Similarly, the rates of MUCL reconstruction have also risen dramatically in recent years.

The fact that injury rates are on the rise is confirmed by other published reports. This trend was demonstrated in prior analyses of DL data from the 1989 to 1998⁴ and 2002 to 2008 seasons.⁵ These 2 studies represent the only comprehensive reviews of MLB injury trends to date, and each provides valuable information. Both are consistent with the current study findings that pitchers are the most commonly injured players and that shoulder and elbow injuries represent about half of all injuries.^4,5 Similar injury rates and characteristics have been reported at the collegiate²⁰ and minor league levels.²¹ Despite this consistency, this analysis of injuries from 1998 to 2015 is the first to report that DL designations for shoulder injuries are on the decline while designations for elbow injuries continue to rise. Although the exact etiology of this decline in shoulder injuries remains unknown, there are a number of possible explanations. In recent years, increased emphasis has been placed on shoulder rehabilitation, reduction of glenohumeral internal rotation deficits, scapular stabilization, and overall kinetic chain balance and coordination. However, this does not explain why elbow injuries continue to rise annually.

With this increase in injuries, the cost of maintaining an active 25-man roster is also climbing. As expected, this growing expense is primarily due to the increased number of DL days each year as well as the increase in league salaries. Fortunately, this increased financial strain has been met with steadily increased annual revenues in professional baseball. In 2014, the prorated salary cost to players designated to the DL and their replacements was $579,568,059. This figure represents an estimated 6.4% of the $9 billion in total revenue for MLB that same year.²² Although this may represent a small percentage of the whole, it still embodies an exceptionally large financial responsibility. This does not include the medical expenses incurred to treat and rehabilitate the players’ injuries.

Every injury that occurs in MLB players has the potential to adversely affect players, teams, and MLB as a whole. With its increasing prevalence, need for surgical treatment, and prolonged return to play, injuries to the MUCL of the elbow may represent the most costly of all injuries. Although a multitude of reports on MUCL injuries, treatments, techniques, rehabilitation, and outcomes have been reported,^{8,9,12,14-19,23-25} to our knowledge, a comprehensive and longitudinal incidence study in MLB players has not yet been published. By including every MUCL reconstruction that has been performed on a MLB player, our study demonstrates the dramatic increase in the annual incidence of MUCL surgeries. Studies performed over shorter time intervals corroborate these findings. A recent review of a privately insured patient database revealed an annual increase in MUCL reconstructions of 4.2% in that cohort.²⁶ When looking specifically at the MLB, a recent survey of all 30 clubs found that 25% (96 of 382) of MLB pitchers and 15% (341 of 2324) of minor league pitchers have undergone MUCL reconstruction.⁸ Because it occurs so frequently and requires a mean of 17 months to return to sport, MUCL injuries represent a very significant cause of time out of play.

While this study represents a unique epidemiologic report on injuries in baseball, it is certainly not without its limitations. As stated previously, it relies on DL data that was initially intended to serve as a roster management tool rather than an injury database. Accordingly, detailed and specific information about every injury is not always available. The limitations of DL data will largely be overcome in future studies thanks to the implementation of the HITS database in 2010. Moving forward, this system will allow for more detailed analysis of injury patterns, characteristics, time out of play, treatments rendered, etc. Its main limitation is that the earliest data dates back to 2010, making it less applicable for longitudinal studies like the present one. Another limitation of this study is the estimations used for the cost of replacing players designated to the DL. For each injury, it was assumed that the replacement player was paid a prorated portion of the league minimum salary while on the major league roster, but in some instances, that may not have been the case. It is possible that some players filling roster spots were already under contract for amounts higher than the league minimum. Since that player would be making that amount regardless of the level of play, the team may not have paid them any additional salary while filling the position of the injured player. The strengths of this study are its comprehensive nature and inclusion of 18 years of data, making it the longest such study of injuries in MLB. It also represents the first report of cost of replacement for players designated to the DL. To our knowledge, this study also represents the first comprehensive report of every MUCL surgery that has been performed on MLB players.

Conclusion

Injury rates continue to rise in MLB, and upper extremity injuries continue to represent approximately half of all injuries resulting in time out of play. Although shoulder injuries have been on the decline in recent years, this decline is offset by a steady increase in elbow injuries. Each year, MLB players are designated to the DL an average of 464 times for a total of 25,579.6 days. This results in a mean annual cost of over $400 million dollars to replace players lost to injury. Looking specifically at MUCL injuries, a total of 400 MUCL reconstructions have been performed in the MLB since 1974, and nearly one-third of these were performed in the last 5 years. Pitchers represent 90.3% of players requiring MUCL surgery, and the average time to return to sport for all players is 17 months. These data may serve as a foundation for identifying appropriate targets for continued study into the etiologies, strategies for prevention, and optimal treatments of injuries commonly affecting professional baseball players.

While the exact origins of the game of baseball are commonly debated, one thing is certain: statistics have been an integral part of the game since its existence.^1-3 This is true at nearly every level of baseball, especially in Major League Baseball (MLB). As our knowledge and technical capabilities advance, new statistical measures of baseball performance are added at a rapid pace.^1,3 One example is the Pitch f/x video tracking system (Sportvision, Inc.), which now analyzes over 60 variables on each of the estimated 660,000 pitches thrown in the MLB annually. In addition to measuring performance and production, these advancements are being leveraged to better understand the epidemiology and impact of injuries in MLB players.^4,5 As with any sport, performance at the most elite level is highly dependent upon player health and functional capacity. Accordingly, player injuries can have a profound impact not only on individual performance but also on the success of the team as a whole.

The first epidemiologic study of injuries in professional baseball was published by Conte and colleagues⁴ in 2001. This work utilized publically available disabled list (DL) data to perform a comprehensive review of injury patterns in MLB from 1989 to 1999. They demonstrated that injuries were on the rise and that pitchers were more commonly injured (48.4% of all DL reports) and had greater time out of play compared to players of other positions.⁴ Shoulder and elbow injuries were responsible for 49.8% of all DL assignments, distantly followed by knee (7.3%), wrist/hand (6.1%), and back (5.0%).⁴ In a later study, Posner and colleagues⁵ analyzed DL data spanning the 2002 to 2008 seasons. Similarly, they found that injuries continued to increase, and over half (51.2%) of DL assignments occurred secondary to upper extremity injuries.⁵ Although the DL is primarily designed as a roster management tool rather than an injury database, it has provided valuable epidemiologic injury information through the years. Out of concern for player health and well-being, MLB and the MLB Players Association (MLBPA) worked together to create and implement an electronic medical record and Health and Injury Tracking System (HITS) for all MLB and Minor League Baseball (MiLB) players. Now active for over 5 seasons, this database has provided valuable, detailed reports regarding specific injuries occurring in professional baseball, such as hamstring strains and concussions.^6,7

With shoulder and elbow injuries in pitchers representing the greatest proportion of DL assignments in recent years, a large body of literature on these injuries, particularly medial ulnar collateral ligament (MUCL) injuries, has been published.^8-13 Since the initial description of MUCL reconstruction, or “Tommy John surgery,” by Dr. Frank Jobe in 1986, much has been done to improve the technique and rehabilitation to maximize player performance following surgery.^10,14-16 Despite this increased attention, large-scale epidemiologic reporting of MUCL injuries in MLB is lacking, but such a report is desirable. The purpose of this work is to: 1) provide a large-scale analysis of injuries occurring in MLB baseball over the course of 18 seasons (1998-2015); 2) highlight the financial implications of these injuries; and 3) detail the evolution of MUCL injuries and reconstructive surgery since it was first performed on a MLB pitcher in 1974. Our study represents the largest longitudinal analysis of MLB injuries since the league expanded to its current level of 30 teams in 1998. It is our hope that this work will serve as a framework for future study of the most common and highest impact injuries occurring in baseball.

Materials And Methods

We performed a retrospective review of the MLB DL from 1998 to 2015. Data analyzed included player demographics such as club, year of placement, age, and position. Injury-specific variables included date of placement on DL, length of time on DL, date of reinstatement, body part injured, diagnosis, and cost of replacement. If a player was put on the DL multiple times during a season, each placement was viewed as a different injury, even if it was to the same body part. If a player was put on the DL for injuries to multiple body parts, the primary injury was analyzed.

Disabled List Data

Although the DL has existed since 1916, this current study covers 18 seasons from 1998 to 2015. The 1998 season was chosen as a starting point because this is the year when MLB expanded to 30 teams. Since then, the number of teams and the active roster limits (25 players) have remained constant, allowing for reliable comparisons across seasons. Initially designed as a roster management tool to allow injured players to temporarily be replaced with healthy players, the DL was not created as an injury database. However, the rules and regulations of the DL have remained fairly constant over the last 18 years, allowing reasonable comparisons of injury data and trends across this timespan. In order for a player to be assigned to the DL, the nature and extent of injury must be certified by a physician. Once designated for the DL, a player cannot return to the major league team for a minimum of 15 days. If the injury is severe, the player can remain on the DL for the remainder of the season or until he is deemed healthy enough to return to play by a physician. One notable exception is the treatment of concussions. Since 2011, a player diagnosed with a concussion may be placed on the DL for a minimum of 7 days rather than 15. The introduction of the HITS database in 2010 should allow for more detailed and reliable study of injuries in baseball moving forward. Although it contains robust data for every injury that has occurred in MLB and MiLB over the last 5 seasons, it does not allow for epidemiologic and longitudinal study of injury patterns and trends in baseball prior to 2010.

Cost of Placing Players on the DL

The dollars lost were calculated by prorating the injured player’s daily salary and multiplying by the number of days missed on the DL. For example, if a player’s annual salary is $1,820,000, his daily salary for the 182 day season is $10,000. If assigned to the DL for 15 days, $150,000 is paid to that player while he is inactive and unable to play. An additional cost is the salary of the replacement player who fills the roster spot. For this work, the replacement player’s prorated, daily salary was assumed to be the league minimum for that specific year. For example, if the league minimum for a given season is $182,000, and the season is 182 days long, a replacement player earns a minimum of $1,000 per day while he is on the 25-man active roster. Thus, the dollars paid to the replacement would be $15,000. In this scenario, that brings the team’s total cost to $165,000 ($150,000 plus $15,000). Because the league minimum salary changes year to year, salaries specific to the year of injury were utilized in this analysis.

MUCL Injury Analysis

In order to better understand the evaluation of MUCL injuries over time, all MLB players undergoing MUCL reconstruction (“Tommy John surgery”) were analyzed separately. Similar to prior studies of UCL injuries, these players were identified using DL data, team websites, and publically available internet databases (primarily www.heatmaps.com).^9,12,17-19 Variables studied include the number of procedures, year of surgery, player position, and mean time until return to play at the MLB level. All MLB players undergoing MUCL reconstruction since 1974 (the year the first procedure was performed) were included.

Statistical Methods

Epidemiologic data are reported using descriptive statistics (mean, range, and percentage) where indicated. To determine the significance of trends over time, a best-fit line was generated to illustrate the change over the years. These lines are reported with corresponding R² values. To assess the trend for significance, the slope was compared to a line with a slope of zero (no change over time) using t tests. For all statistical comparisons, the threshold for alpha was set to P < .05.

Results

Between 1998 and 2015, there were 8357 placements of players on the DL, at an average rate of 464 designations per year (Table 1, Figure 1). This resulted in 460,432 days lost to injury, with a mean of 25,186 days out of play per season (Table 1, Figure 2). The mean length of DL assignment per year was 55.1 days per injury, with a low of 49.1 days in 2011 and a high of 59.2 days in 2001 (Table 1, Figure 3). During the study period, the number of players placed on the DL and the total number of DL days steadily increased (P < .001 and P = .003, respectively), while the average length of DL assignments remained steady (P = .647). When analyzing the data by body region injured, the shoulder (20.6%) and elbow (19.6%) were the 2 leading causes of time out of play (Table 2). This was followed distantly by the chest/back/spine (13.7%), wrist/hand/fingers (10.1%), lower leg/knee (9.8%), and the upper leg/thigh (9.5%). Although the percentage of injuries occurring to the upper extremity remained stable, the rate of shoulder injuries steadily decreased (P = .023) as elbow injuries increased (P = .015) (Table 3, Figure 4). This inverse relationship was also demonstrated for the annual number of DL days for shoulder (P = .033) and elbow (P = 0.005) injuries (Figure 5).

Regarding the financial impact of these injuries, the mean annual cost of replacing players on the DL was $423,267,633.78 (Table 4). This ranged from a low of $136,397,147 in 1998 to a high of $694,835,359 in 2015. There was a steady increase in the cost of replacement during the study period (P < .001) that coincides with the increasing salaries during that time span (Figure 6). In total, $6,732,167,180 was paid to players assigned to the DL and $886,650,228 was spent to fill their positions. This brings the total cost of DL assignments to $7,618,817,407 for the study period.

Looking specifically at MUCL injuries, a total of 400 MUCL reconstructions have been performed on MLB players since the procedure was first developed in 1974. The vast majority of these were performed in pitchers (n = 361, 90.3%) followed by outfielders (n = 16, 4.0%), infielders (n = 14, 3.5%) and catchers (n = 9, 2.3%) (Table 5). The mean time to return to competition at the MLB level was 17.8 months for pitchers, 11.1 months for outfielders, 9.6 months for infielders, and 10.5 months for catchers. The overall mean time to return was 17.1 months. The annual number of MUCL reconstructions continues to rise dramatically (P < .001) (Figure 7). During the first 12 years (1974-1985), a total of 8 (2.0%) MUCL reconstructions were performed on MLB players. In subsequent decades, this number increased to 44 (11.0%) from 1986-1995, 123 (30.8%) from 1996-2005, and 225 (56.3%) from 2006-2015. Of all Tommy John surgeries performed over 42 years, nearly one-third (n = 131, 32.75%) were performed in the last 5 years alone (2011-2015).

Discussion

To date, a number of studies have been published on injuries in professional baseball. These can primarily be categorized as either studies with a detailed focus on a single injury type or body region^6-13,17,19 or broader reviews that are limited by the relatively short time span covered.^4,5 The purpose of this work was to provide a comprehensive review of injury trends in MLB since the league expanded to 30 teams in 1998 while paying special attention to the financial impact of those injuries. Additionally, we sought to provide an up-to-date review of MUCL injuries and surgeries since the procedure was first developed in 1974. Ultimately, this data demonstrates that injuries continue to rise in MLB and this increase is accompanied by increased expense for teams. Thankfully, the rates of DL assignments for shoulder injuries are on the decline; however, this decrease is countered by a reciprocal increase in elbow injuries. Similarly, the rates of MUCL reconstruction have also risen dramatically in recent years.

The fact that injury rates are on the rise is confirmed by other published reports. This trend was demonstrated in prior analyses of DL data from the 1989 to 1998⁴ and 2002 to 2008 seasons.⁵ These 2 studies represent the only comprehensive reviews of MLB injury trends to date, and each provides valuable information. Both are consistent with the current study findings that pitchers are the most commonly injured players and that shoulder and elbow injuries represent about half of all injuries.^4,5 Similar injury rates and characteristics have been reported at the collegiate²⁰ and minor league levels.²¹ Despite this consistency, this analysis of injuries from 1998 to 2015 is the first to report that DL designations for shoulder injuries are on the decline while designations for elbow injuries continue to rise. Although the exact etiology of this decline in shoulder injuries remains unknown, there are a number of possible explanations. In recent years, increased emphasis has been placed on shoulder rehabilitation, reduction of glenohumeral internal rotation deficits, scapular stabilization, and overall kinetic chain balance and coordination. However, this does not explain why elbow injuries continue to rise annually.

With this increase in injuries, the cost of maintaining an active 25-man roster is also climbing. As expected, this growing expense is primarily due to the increased number of DL days each year as well as the increase in league salaries. Fortunately, this increased financial strain has been met with steadily increased annual revenues in professional baseball. In 2014, the prorated salary cost to players designated to the DL and their replacements was $579,568,059. This figure represents an estimated 6.4% of the $9 billion in total revenue for MLB that same year.²² Although this may represent a small percentage of the whole, it still embodies an exceptionally large financial responsibility. This does not include the medical expenses incurred to treat and rehabilitate the players’ injuries.

Every injury that occurs in MLB players has the potential to adversely affect players, teams, and MLB as a whole. With its increasing prevalence, need for surgical treatment, and prolonged return to play, injuries to the MUCL of the elbow may represent the most costly of all injuries. Although a multitude of reports on MUCL injuries, treatments, techniques, rehabilitation, and outcomes have been reported,^{8,9,12,14-19,23-25} to our knowledge, a comprehensive and longitudinal incidence study in MLB players has not yet been published. By including every MUCL reconstruction that has been performed on a MLB player, our study demonstrates the dramatic increase in the annual incidence of MUCL surgeries. Studies performed over shorter time intervals corroborate these findings. A recent review of a privately insured patient database revealed an annual increase in MUCL reconstructions of 4.2% in that cohort.²⁶ When looking specifically at the MLB, a recent survey of all 30 clubs found that 25% (96 of 382) of MLB pitchers and 15% (341 of 2324) of minor league pitchers have undergone MUCL reconstruction.⁸ Because it occurs so frequently and requires a mean of 17 months to return to sport, MUCL injuries represent a very significant cause of time out of play.

While this study represents a unique epidemiologic report on injuries in baseball, it is certainly not without its limitations. As stated previously, it relies on DL data that was initially intended to serve as a roster management tool rather than an injury database. Accordingly, detailed and specific information about every injury is not always available. The limitations of DL data will largely be overcome in future studies thanks to the implementation of the HITS database in 2010. Moving forward, this system will allow for more detailed analysis of injury patterns, characteristics, time out of play, treatments rendered, etc. Its main limitation is that the earliest data dates back to 2010, making it less applicable for longitudinal studies like the present one. Another limitation of this study is the estimations used for the cost of replacing players designated to the DL. For each injury, it was assumed that the replacement player was paid a prorated portion of the league minimum salary while on the major league roster, but in some instances, that may not have been the case. It is possible that some players filling roster spots were already under contract for amounts higher than the league minimum. Since that player would be making that amount regardless of the level of play, the team may not have paid them any additional salary while filling the position of the injured player. The strengths of this study are its comprehensive nature and inclusion of 18 years of data, making it the longest such study of injuries in MLB. It also represents the first report of cost of replacement for players designated to the DL. To our knowledge, this study also represents the first comprehensive report of every MUCL surgery that has been performed on MLB players.

Conclusion

Injury rates continue to rise in MLB, and upper extremity injuries continue to represent approximately half of all injuries resulting in time out of play. Although shoulder injuries have been on the decline in recent years, this decline is offset by a steady increase in elbow injuries. Each year, MLB players are designated to the DL an average of 464 times for a total of 25,579.6 days. This results in a mean annual cost of over $400 million dollars to replace players lost to injury. Looking specifically at MUCL injuries, a total of 400 MUCL reconstructions have been performed in the MLB since 1974, and nearly one-third of these were performed in the last 5 years. Pitchers represent 90.3% of players requiring MUCL surgery, and the average time to return to sport for all players is 17 months. These data may serve as a foundation for identifying appropriate targets for continued study into the etiologies, strategies for prevention, and optimal treatments of injuries commonly affecting professional baseball players.

NEW ORLEANS—Intrathecal levels of T and B cells are comparable in progressive multiple sclerosis (MS), compared with relapsing-remitting MS, according to research described at the ACTRIMS 2016 Forum. The major difference between the two forms of the disease, according to the researchers, is that although the immune cells are mobile in relapsing-remitting MS, they are predominantly embedded in CNS tissue in progressive MS. “This compartmentalization of the immune responses is likely the major reason for the failure of current immunomodulatory treatments in both subtypes of progressive MS,” said Mika Komori, MD, PhD, of the Neuroimmunological Unit at the National Institute of Neurological Disorders and Stroke.

Neurologists have interpreted immunomodulatory therapies’ lack of efficacy in progressive MS as evidence that neurodegeneration, rather than immunopathology, stimulates CNS tissue destruction. Dr. Komori and colleagues sought to develop a methodology that reliably quantifies immune-cell infiltration of CNS tissue by combining CSF immunophenotyping with analysis of immune-cell specific soluble markers.

The researchers collected CSF from 198 subjects, including patients with relapsing-remitting MS, secondary progressive MS, primary progressive MS, noninflammatory neurologic disorders, and other inflammatory neurologic disorders, as well as from healthy donors, and processed the samples in a blinded fashion. They optimized electroluminescent assays to quantify 19 soluble biomarkers in the CSF. Cell-specific secretion was assessed in supernatants from sorted primary immune cells. The investigators quantified absolute numbers of CSF immune cells by flow cytometry in 50-fold concentrated CSF and used them to define three ratios between the concentrations of cell-specific soluble CSF biomarkers and absolute numbers of corresponding CSF cells per milliliter of CSF (ie, sCD14:monocyte, sCD21:B-cell, and CD27:T-cell).

The sCD14:monocyte ratio did not differ among diagnostic groups, but the sCD21:B-cell and especially sCD27:T-cell ratios were significantly higher in progressive MS, compared with all other diagnostic groups. The sCD21:B-cell and sCD27:T-cell ratios differentiated patients with progressive MS from those with relapsing-remitting MS with an area under reviewer operator characteristic curve (AUC) comparable to that of current clinically used tests (AUC, 0.76–0.77). An excess of the soluble biomarkers in comparison with the number of CSF cells that produce it implies presence of the second, nonmobile pool of secreting immune cells embedded in CNS tissue. Dr. Komori and colleagues validated the interpretation that higher biomarker ratios parallel infiltration of CNS tissue by corresponding immune cells in patients with available CNS autopsy or biopsy results with 100% concordance.

NEW ORLEANS—Intrathecal levels of T and B cells are comparable in progressive multiple sclerosis (MS), compared with relapsing-remitting MS, according to research described at the ACTRIMS 2016 Forum. The major difference between the two forms of the disease, according to the researchers, is that although the immune cells are mobile in relapsing-remitting MS, they are predominantly embedded in CNS tissue in progressive MS. “This compartmentalization of the immune responses is likely the major reason for the failure of current immunomodulatory treatments in both subtypes of progressive MS,” said Mika Komori, MD, PhD, of the Neuroimmunological Unit at the National Institute of Neurological Disorders and Stroke.

Neurologists have interpreted immunomodulatory therapies’ lack of efficacy in progressive MS as evidence that neurodegeneration, rather than immunopathology, stimulates CNS tissue destruction. Dr. Komori and colleagues sought to develop a methodology that reliably quantifies immune-cell infiltration of CNS tissue by combining CSF immunophenotyping with analysis of immune-cell specific soluble markers.

The researchers collected CSF from 198 subjects, including patients with relapsing-remitting MS, secondary progressive MS, primary progressive MS, noninflammatory neurologic disorders, and other inflammatory neurologic disorders, as well as from healthy donors, and processed the samples in a blinded fashion. They optimized electroluminescent assays to quantify 19 soluble biomarkers in the CSF. Cell-specific secretion was assessed in supernatants from sorted primary immune cells. The investigators quantified absolute numbers of CSF immune cells by flow cytometry in 50-fold concentrated CSF and used them to define three ratios between the concentrations of cell-specific soluble CSF biomarkers and absolute numbers of corresponding CSF cells per milliliter of CSF (ie, sCD14:monocyte, sCD21:B-cell, and CD27:T-cell).

The sCD14:monocyte ratio did not differ among diagnostic groups, but the sCD21:B-cell and especially sCD27:T-cell ratios were significantly higher in progressive MS, compared with all other diagnostic groups. The sCD21:B-cell and sCD27:T-cell ratios differentiated patients with progressive MS from those with relapsing-remitting MS with an area under reviewer operator characteristic curve (AUC) comparable to that of current clinically used tests (AUC, 0.76–0.77). An excess of the soluble biomarkers in comparison with the number of CSF cells that produce it implies presence of the second, nonmobile pool of secreting immune cells embedded in CNS tissue. Dr. Komori and colleagues validated the interpretation that higher biomarker ratios parallel infiltration of CNS tissue by corresponding immune cells in patients with available CNS autopsy or biopsy results with 100% concordance.

NEW ORLEANS—Intrathecal levels of T and B cells are comparable in progressive multiple sclerosis (MS), compared with relapsing-remitting MS, according to research described at the ACTRIMS 2016 Forum. The major difference between the two forms of the disease, according to the researchers, is that although the immune cells are mobile in relapsing-remitting MS, they are predominantly embedded in CNS tissue in progressive MS. “This compartmentalization of the immune responses is likely the major reason for the failure of current immunomodulatory treatments in both subtypes of progressive MS,” said Mika Komori, MD, PhD, of the Neuroimmunological Unit at the National Institute of Neurological Disorders and Stroke.

Neurologists have interpreted immunomodulatory therapies’ lack of efficacy in progressive MS as evidence that neurodegeneration, rather than immunopathology, stimulates CNS tissue destruction. Dr. Komori and colleagues sought to develop a methodology that reliably quantifies immune-cell infiltration of CNS tissue by combining CSF immunophenotyping with analysis of immune-cell specific soluble markers.

The researchers collected CSF from 198 subjects, including patients with relapsing-remitting MS, secondary progressive MS, primary progressive MS, noninflammatory neurologic disorders, and other inflammatory neurologic disorders, as well as from healthy donors, and processed the samples in a blinded fashion. They optimized electroluminescent assays to quantify 19 soluble biomarkers in the CSF. Cell-specific secretion was assessed in supernatants from sorted primary immune cells. The investigators quantified absolute numbers of CSF immune cells by flow cytometry in 50-fold concentrated CSF and used them to define three ratios between the concentrations of cell-specific soluble CSF biomarkers and absolute numbers of corresponding CSF cells per milliliter of CSF (ie, sCD14:monocyte, sCD21:B-cell, and CD27:T-cell).

The sCD14:monocyte ratio did not differ among diagnostic groups, but the sCD21:B-cell and especially sCD27:T-cell ratios were significantly higher in progressive MS, compared with all other diagnostic groups. The sCD21:B-cell and sCD27:T-cell ratios differentiated patients with progressive MS from those with relapsing-remitting MS with an area under reviewer operator characteristic curve (AUC) comparable to that of current clinically used tests (AUC, 0.76–0.77). An excess of the soluble biomarkers in comparison with the number of CSF cells that produce it implies presence of the second, nonmobile pool of secreting immune cells embedded in CNS tissue. Dr. Komori and colleagues validated the interpretation that higher biomarker ratios parallel infiltration of CNS tissue by corresponding immune cells in patients with available CNS autopsy or biopsy results with 100% concordance.

NEW ORLEANS—Light-, moderate-, and vigorous-intensity treadmill walking may particularly improve inhibitory control in fully ambulatory people with multiple sclerosis (MS), according to research described at the ACTRIMS 2016 Forum. Furthermore, the increase in core body temperature associated with such exercise may not negate its potentially beneficial effects on inhibitory control.

“This [study] represents the next step in delineating the optimal exercise stimuli for improving cognition in fully ambulatory persons with MS and supports the feasibility of chronic treadmill walking exercise training for improving inhibitory control in thermosensitive persons with MS,” said Brian M. Sandroff, PhD, of the Kessler Foundation in West Orange, New Jersey.

Exercise training is a promising approach for managing cognitive impairment in persons with MS. Although preliminary evidence indicates that treadmill walking might have the greatest beneficial effects on inhibitory control, compared with other forms of exercise, in fully ambulatory persons with MS, the effects of varying intensities of treadmill walking exercise on inhibitory control are unknown. In addition, previous research has not indicated whether increases in core body temperature negate the potentially beneficial effects of treadmill walking exercise on inhibitory control in thermosensitive people with MS.

To better determine the optimal form of exercise for improving cognition in MS, Dr. Sandroff and colleagues first compared the acute effects of light-, moderate-, and vigorous-intensity treadmill walking exercise on inhibitory control in 24 participants with MS using a within-subjects, repeated-measures design. In a second study, the researchers examined the acute effects of core body temperature on inhibitory control during vigorous treadmill walking exercise in 14 thermosensitive persons with MS.

Participants in the first study completed four experimental conditions (ie, 20 minutes of light-, moderate-, and vigorous-intensity treadmill walking exercise and quiet rest) in a randomized, counterbalanced order. The investigators measured inhibitory control before and after each condition using a modified flanker task. In the second study, thermosensitive participants with MS completed two experimental conditions (ie, 20 minutes of vigorous treadmill walking exercise and 20 minutes of quiet rest) in a randomized, counterbalanced order. The researchers measured core body temperature throughout both conditions. Inhibitory control was measured before and after each condition using a modified flanker task.

In the first study, the investigators observed large, statistically significant improvements in inhibitory control for all three intensities of treadmill walking exercise, compared with quiet rest. The improvements were of similar magnitude. The second study indicated that, compared with rest, vigorous exercise was followed by improvements in inhibitory control, despite significant elevations in core body temperature (~0.6 °C) in thermosensitive persons with MS.

NEW ORLEANS—Light-, moderate-, and vigorous-intensity treadmill walking may particularly improve inhibitory control in fully ambulatory people with multiple sclerosis (MS), according to research described at the ACTRIMS 2016 Forum. Furthermore, the increase in core body temperature associated with such exercise may not negate its potentially beneficial effects on inhibitory control.

“This [study] represents the next step in delineating the optimal exercise stimuli for improving cognition in fully ambulatory persons with MS and supports the feasibility of chronic treadmill walking exercise training for improving inhibitory control in thermosensitive persons with MS,” said Brian M. Sandroff, PhD, of the Kessler Foundation in West Orange, New Jersey.

Exercise training is a promising approach for managing cognitive impairment in persons with MS. Although preliminary evidence indicates that treadmill walking might have the greatest beneficial effects on inhibitory control, compared with other forms of exercise, in fully ambulatory persons with MS, the effects of varying intensities of treadmill walking exercise on inhibitory control are unknown. In addition, previous research has not indicated whether increases in core body temperature negate the potentially beneficial effects of treadmill walking exercise on inhibitory control in thermosensitive people with MS.

To better determine the optimal form of exercise for improving cognition in MS, Dr. Sandroff and colleagues first compared the acute effects of light-, moderate-, and vigorous-intensity treadmill walking exercise on inhibitory control in 24 participants with MS using a within-subjects, repeated-measures design. In a second study, the researchers examined the acute effects of core body temperature on inhibitory control during vigorous treadmill walking exercise in 14 thermosensitive persons with MS.

Participants in the first study completed four experimental conditions (ie, 20 minutes of light-, moderate-, and vigorous-intensity treadmill walking exercise and quiet rest) in a randomized, counterbalanced order. The investigators measured inhibitory control before and after each condition using a modified flanker task. In the second study, thermosensitive participants with MS completed two experimental conditions (ie, 20 minutes of vigorous treadmill walking exercise and 20 minutes of quiet rest) in a randomized, counterbalanced order. The researchers measured core body temperature throughout both conditions. Inhibitory control was measured before and after each condition using a modified flanker task.

In the first study, the investigators observed large, statistically significant improvements in inhibitory control for all three intensities of treadmill walking exercise, compared with quiet rest. The improvements were of similar magnitude. The second study indicated that, compared with rest, vigorous exercise was followed by improvements in inhibitory control, despite significant elevations in core body temperature (~0.6 °C) in thermosensitive persons with MS.

NEW ORLEANS—Light-, moderate-, and vigorous-intensity treadmill walking may particularly improve inhibitory control in fully ambulatory people with multiple sclerosis (MS), according to research described at the ACTRIMS 2016 Forum. Furthermore, the increase in core body temperature associated with such exercise may not negate its potentially beneficial effects on inhibitory control.

“This [study] represents the next step in delineating the optimal exercise stimuli for improving cognition in fully ambulatory persons with MS and supports the feasibility of chronic treadmill walking exercise training for improving inhibitory control in thermosensitive persons with MS,” said Brian M. Sandroff, PhD, of the Kessler Foundation in West Orange, New Jersey.

Exercise training is a promising approach for managing cognitive impairment in persons with MS. Although preliminary evidence indicates that treadmill walking might have the greatest beneficial effects on inhibitory control, compared with other forms of exercise, in fully ambulatory persons with MS, the effects of varying intensities of treadmill walking exercise on inhibitory control are unknown. In addition, previous research has not indicated whether increases in core body temperature negate the potentially beneficial effects of treadmill walking exercise on inhibitory control in thermosensitive people with MS.

To better determine the optimal form of exercise for improving cognition in MS, Dr. Sandroff and colleagues first compared the acute effects of light-, moderate-, and vigorous-intensity treadmill walking exercise on inhibitory control in 24 participants with MS using a within-subjects, repeated-measures design. In a second study, the researchers examined the acute effects of core body temperature on inhibitory control during vigorous treadmill walking exercise in 14 thermosensitive persons with MS.

Participants in the first study completed four experimental conditions (ie, 20 minutes of light-, moderate-, and vigorous-intensity treadmill walking exercise and quiet rest) in a randomized, counterbalanced order. The investigators measured inhibitory control before and after each condition using a modified flanker task. In the second study, thermosensitive participants with MS completed two experimental conditions (ie, 20 minutes of vigorous treadmill walking exercise and 20 minutes of quiet rest) in a randomized, counterbalanced order. The researchers measured core body temperature throughout both conditions. Inhibitory control was measured before and after each condition using a modified flanker task.

In the first study, the investigators observed large, statistically significant improvements in inhibitory control for all three intensities of treadmill walking exercise, compared with quiet rest. The improvements were of similar magnitude. The second study indicated that, compared with rest, vigorous exercise was followed by improvements in inhibitory control, despite significant elevations in core body temperature (~0.6 °C) in thermosensitive persons with MS.

Upper extremity injuries are very common in pitchers in amateur and professional baseball. The vast majority involving labral or rotator cuff pathology.^1-3 While uncommon, injuries to the latissimus dorsi (LD) (Figure) and teres major (TM) have been reported in Major League Baseball (MLB) pitchers.⁴ Jobe and colleagues⁵ demonstrated the role of the LD during the various phases of pitching. The LD is most active during the acceleration phase and remains active during the deceleration phase and follow-through.⁶ Anatomically, the TM lies posterior to the LD separated by bursal tissue. The tendon fibers converge and unite along their lower borders, leading to a synergistic mechanism of action.

Due to the rarity of LD and TM injuries, literature on the pathology and appropriate treatments for these injuries is limited. The goal of this review is to present the current literature on professional baseball players who have undergone either nonsurgical treatment or surgery for LD and TM strains and/or avulsion injuries. This review will ultimately assist clinicians when deciding on the optimal treatment method for professional baseball players.

Methods

We performed an extensive Medline database search with the following search algorithm: ([latissimus OR latissimus dorsi OR teres major] AND baseball). The search returned 20 citations. Inclusion criteria consisted of clinical studies that focused on professional baseball pitchers with TM and/or LD injuries that underwent either conservative nonsurgical treatment or surgical repair. There was no exclusion based on the type of injury present, such as avulsion vs strain. Any study with amateur athletes or athletes from other sports such as handball or rugby were excluded. Due to the limited amount of data available, the majority of included studies were case reports and case series.

Based on these parameters, 5 articles met criteria for inclusion. Of the 5 included studies, 3 were case reports and 2 were case series. From the eligible articles, the following information was obtained: publication year, sample size, mean age, mean follow-up duration, type of treatment (conservative vs surgical), ability to return to original level of play, time required to return to original form, and complications (Tables 1, 2).

Results

Nonoperative Management

Four of the 5 included studies implemented only conservative therapy for their patients.^4,7-9 The average duration these patients were followed for during treatment and rehabilitation was 26.3 months. Malcolm and colleagues⁷ followed patients for 8 months, the shortest length among the 4 conservative studies in this review. Leland and colleagues8 followed patients for 17 months, and Nagda and colleagues⁹ had the longest length of observation of 36 months (range 12 to 82 months).Schickendantz and colleagues⁴ followed patients for >12 months, but the exact duration was not specified. In order to calculate the average duration of observation, each patient was assigned a duration of 12 months.

Of the 30 patients included in this review, 29 were treated conservatively. All of the included studies consisted of male patients. The mean age was 26.8 years (range 22 to 28.1 years). Of the 29 injuries treated conservatively, there were 2 LD tendon avulsions, 4 TM tendon avulsions, 1 LD and TM tendon avulsion, 7 LD intramuscular strains, 9 TM intramuscular strains, and 6 LD and TM intramuscular strains.

Treatment Protocol

The various treatment and rehabilitation programs used for the conservative patient population all followed a similar pathway. After initial injury, a rest period focused on stretching was implemented. Patients were started on steroid or anti-inflammatory medications, cryotherapy, or other therapeutic modalities. Once pain-free and full range of motion was achieved, patients began the strength and throwing components of the rehabilitation program. Reoccurrence of symptoms would halt the throwing component of the rehabilitation program until symptoms improved. Patients were progressed through a return-to-throw program and once they could throw off the mound and achieve their preinjury velocity, strength, and range of motion, they were cleared to return to competitive pitching.

In the senior author’s (MSS) practice, all throwers are managed with the same nonoperative protocol.⁴ Initial treatment consists of short periods of rest and symptom control via the application of cryotherapy, among other modalities. Restoration of preinjury range of motion is achieved with active-assisted stretching exercises. As range of motion begins approaching pre-injury levels, strength training is initiated with isometric strengthening of the LD and TM progressing to resistance exercises. Exercising the abdominal core, strengthening the lower body, and cardiovascular conditioning are focal points of the rehabilitation period. Once patients regain preinjury shoulder strength and range of motion without pain, they begin a throwing program that consists of 4 weeks of long toss followed by 2 weeks of throwing from the pitching mound. After completion of the throwing program, the patient is allowed to return to competitive pitching. For patients who did not suffer season-ending injury, the average time required to return to play was 99.8 days (range 72.3 to 182.6 days).

Complications and Reinjury

The patients in Leland and colleagues⁸ and Malcolm and colleagues⁷ did not suffer any complications or reinjuries. In Schickendantz and colleagues⁴, all but 3 of the 10 patients were able to return to full speed pitching by 3 months. The other 3 required 4, 6, and 10 months. The patient that required 10 months tore both his LD and TM and the patient that required 6 months tore his TM and was never able to regain his pre-injury throwing velocity. None of the TM tears had a recurrence, while 1 LD tear had a recurrence of injury 6 months after returning to competitive pitching. This patient was successfully treated with 6 weeks of conservative rest and rehabilitation.

In Nagda and colleagues⁹, 2 athletes suffered injury recurrence. One athlete with a LD strain suffered 2 subsequent LD strains, 4 months and 1 year after initial injury. The other athlete with a LD avulsion suffered a subsequent TM avulsion 13 months after initial injury. One pitcher who had an LD and TM strain suffered a superior labrum anterior and posterior (SLAP) tear and was never able to return to his prior level of play.

Surgical Treatment

Only 1 of the 5 included studies utilized surgical repair for their patient.¹⁰ The single patient suffered an avulsion injury of the distal LD tendon and its insertion on the humerus. The LD tendon was retracted approximately 5 cm from the distal humeral insertion. The TM was not involved. Eight days post-injury, the patient underwent surgical repair.¹¹ Postoperatively, the patient started passive range of motion after 2 weeks and active range of motion after 6 weeks. He started throwing at 12 weeks and returned to play at 30 weeks after he had returned to his preinjury form in regards to muscle strength, pitch control, and velocity. The patient was able to resume pitching at a high level in MLB.

Discussion

Overhand throwing athletes, especially professional baseball players, have to constantly deal with a variety of shoulder injuries.^12,13 Currently, there is minimal literature on isolated TM and LD injuries. As a result, there is still debate about the optimal treatment method for these injuries, especially in athletes who compete at the highest level. In order to treat isolated injuries of these muscles, it is important to understand their anatomic relationship, as these 2 muscles are intimately associated. The LD originates from the thoracolumbar spine and inserts on the proximal humerus between the pectoralis<hl name="2"/> major and TM tendons. The TM originates from the scapula and, similar to the LD, inserts on the proximal humerus. In an anatomic study, the TM tendon inserted into the LD tendon before its humeral insertion in the majority of cadavers.^14,15

The LD is responsible for extension, adduction, and internal rotation of the humerus. The TM, while not as extensively studied, is believed to also contribute to extension, adduction, and internal rotation of the humerus.¹⁶ As Jobe and colleagues⁵ demonstrated, the LD is vital during the acceleration phase of pitching. While they were unable to make any conclusions about the role of the TM during the pitching cycle, it is reasonable to hypothesize that these 2 muscles work together. While it is thought that these 2 muscles work as a unit, it is significant to note that a professional pitcher can sustain an isolated injury to the TM without injury to the LD, and vice versa. This questions whether these 2 muscles work more independently than once thought. One hypothesis is that the physical size of the LD provides protection from injuries that the smaller TM cannot overcome. This is a potential area of further research.

The most common findings in patients with TM injuries include swelling, bruising, tenderness of the proximal arm, and limitations of shoulder range of motion in abduction, flexion, and external rotation. There is also weakness when resistance is applied against internal rotation and extension. Similar to the TM, common findings in patients with LD injuries include pain in the posterior shoulder, bruising, and weakness when resistance is applied against internal rotation of the shoulder. Pitchers are often able to pinpoint the occurrence of their acute pain during a specific time in the game. They commonly experience a pulling sensation and sometimes even feel a “pop” in their shoulder followed by an acute onset of pain and stiffness in the posterior aspect of the axilla. These injuries seem to be associated with the pitcher throwing a “breaking ball,” a pitch that requires greater shoulder rotation since it changes trajectory while traveling towards home plate. Despite the clear role of the LD and hypothesized role of the TM in the pitching sequence, there has been limited research on the optimal treatment of isolated injuries of these muscles in MLB pitchers. The majority of studies in this review opted for conservative treatment for both LD and TM injuries. The only study that presented a surgical option was for a LD avulsion injury.

Athletes undergoing either conservative or surgical treatment required a significant period of recovery and rehabilitation before they were able to compete at the professional level. In Leland and colleagues⁸, it took about 10 to 12 weeks of rehabilitation for both pitchers to return to pitching against competition. In Schickendantz and colleagues⁴, barring any complications or injury recurrence, it took patients 12 weeks to return to their preinjury level. In Malcolm and colleagues⁷, magnetic resonance imaging after 8 weeks showed marked recovery, and shortly after the pitcher was able to return to the pitching rotation. In Nagda and colleagues⁹, the time lost to injury ranged from 7 weeks to an entire season. Of the 9 pitchers who were lost for the season, 6 had avulsion injuries. The other 3 consisted of an LD strain, TM strain, and LD plus TM strain.⁹ In this study, it seems that avulsion injuries had a more significant impact on patient recovery. On average, it took 35.6 days after injury for players to begin throwing. In contrast, it took an average of 65.5 days after an avulsion injury for players to begin throwing. Ellman and colleagues¹⁰ included the only surgically repaired injury, and it was for an avulsion of the LD tendon. In the surgical case, it took slightly longer for the pitcher to return to preinjury form. It took him 12 to 16 weeks to begin light throwing and his full return to pitching took about 20 to 30 weeks. Since muscle strains and tendon avulsions are significantly different injuries in regards to the type of soft tissue damage and healing potential, they may require different treatment strategies. An avulsion injury may require more aggressive intervention, whereas a strain may only require conservative rehabilitation. Ultimately, there does not seem to be a significant benefit of one treatment option compared to the other. The majority of conservatively managed pitchers were able to return to previous form in a reasonable time frame. While each rehabilitation protocol was slightly different, multiple studies advocated for rehab programs that centered around the following goals: slowly progressing pitchers to light throwing once their pain resolved, followed by long throwing, then throwing off of the mound, and finally returning to competitive pitching. It is important to discuss with patients that rehabilitation generally takes 12 to 16 weeks before they are able to fully return to pitching against competition and that rest should immediately follow any recurrence of pain or stiffness. Once those symptoms resolve, patients may continue the rehabilitation protocol.

As with any form of treatment, there are risks involved. This holds true for both conservative and nonconservative therapy for LD and TM injuries. One risk of nonoperative treatment of an LD avulsion is the development of strength deficits in the muscle.¹⁷ While this deficit may go unnoticed in a recreational athlete, it may be more pronounced in a professional athlete, especially since the LD of a professional baseball pitcher is more active on electromyography during the acceleration phase of the pitching cycle compared to a recreational athlete.¹⁸ Another risk of conservative treatment of an LD avulsion is jeopardizing the potential for future surgery. As a result, some advocate for early surgical intervention of an acute LD avulsion.^19,20 Others, however, recommend conservative management with subsequent surgical intervention if conservative measures fail. One caveat is that surgical intervention to restore the original anatomy may become difficult after a certain period of time due to the buildup of scar tissue. Surgical intervention also has associated risks, such as nerve injury, infection, vascular damage, persistent pain, and the buildup of large amounts of scar tissue. It is important to discuss these risks with patients when deciding on a treatment option.

LD and TM avulsion and tears typically present after an acute event in throwing athletes. There are a number of case reports published that demonstrate successful outcomes with both nonoperative management²¹ and operative repair of LD injuries in non-throwing athletes such as competitive water skiers,^22,23 steer wrestlers,²⁴ professional wrestlers,²⁵ and recreational rock climbers.²⁶ The 5 studies included in this review were the first ones to present LD and TM injuries in MLB pitchers. They discussed the outcomes of mainly conservative and surgical management of LD and TM avulsion and tears. Unfortunately, there remains a limited number of cases on the treatment of these injuries in highly competitive throwing athletes. Further research is required to elucidate the advantages and disadvantages of operative vs nonoperative treatment. The goal of this review is to provide clinicians with a concise summary of the current literature so that they may offer some evidence to their patients when discussing appropriate treatment plans.

Upper extremity injuries are very common in pitchers in amateur and professional baseball. The vast majority involving labral or rotator cuff pathology.^1-3 While uncommon, injuries to the latissimus dorsi (LD) (Figure) and teres major (TM) have been reported in Major League Baseball (MLB) pitchers.⁴ Jobe and colleagues⁵ demonstrated the role of the LD during the various phases of pitching. The LD is most active during the acceleration phase and remains active during the deceleration phase and follow-through.⁶ Anatomically, the TM lies posterior to the LD separated by bursal tissue. The tendon fibers converge and unite along their lower borders, leading to a synergistic mechanism of action.

Due to the rarity of LD and TM injuries, literature on the pathology and appropriate treatments for these injuries is limited. The goal of this review is to present the current literature on professional baseball players who have undergone either nonsurgical treatment or surgery for LD and TM strains and/or avulsion injuries. This review will ultimately assist clinicians when deciding on the optimal treatment method for professional baseball players.

Methods

We performed an extensive Medline database search with the following search algorithm: ([latissimus OR latissimus dorsi OR teres major] AND baseball). The search returned 20 citations. Inclusion criteria consisted of clinical studies that focused on professional baseball pitchers with TM and/or LD injuries that underwent either conservative nonsurgical treatment or surgical repair. There was no exclusion based on the type of injury present, such as avulsion vs strain. Any study with amateur athletes or athletes from other sports such as handball or rugby were excluded. Due to the limited amount of data available, the majority of included studies were case reports and case series.

Based on these parameters, 5 articles met criteria for inclusion. Of the 5 included studies, 3 were case reports and 2 were case series. From the eligible articles, the following information was obtained: publication year, sample size, mean age, mean follow-up duration, type of treatment (conservative vs surgical), ability to return to original level of play, time required to return to original form, and complications (Tables 1, 2).

Results

Nonoperative Management

Four of the 5 included studies implemented only conservative therapy for their patients.^4,7-9 The average duration these patients were followed for during treatment and rehabilitation was 26.3 months. Malcolm and colleagues⁷ followed patients for 8 months, the shortest length among the 4 conservative studies in this review. Leland and colleagues8 followed patients for 17 months, and Nagda and colleagues⁹ had the longest length of observation of 36 months (range 12 to 82 months).Schickendantz and colleagues⁴ followed patients for >12 months, but the exact duration was not specified. In order to calculate the average duration of observation, each patient was assigned a duration of 12 months.

Of the 30 patients included in this review, 29 were treated conservatively. All of the included studies consisted of male patients. The mean age was 26.8 years (range 22 to 28.1 years). Of the 29 injuries treated conservatively, there were 2 LD tendon avulsions, 4 TM tendon avulsions, 1 LD and TM tendon avulsion, 7 LD intramuscular strains, 9 TM intramuscular strains, and 6 LD and TM intramuscular strains.

Treatment Protocol

The various treatment and rehabilitation programs used for the conservative patient population all followed a similar pathway. After initial injury, a rest period focused on stretching was implemented. Patients were started on steroid or anti-inflammatory medications, cryotherapy, or other therapeutic modalities. Once pain-free and full range of motion was achieved, patients began the strength and throwing components of the rehabilitation program. Reoccurrence of symptoms would halt the throwing component of the rehabilitation program until symptoms improved. Patients were progressed through a return-to-throw program and once they could throw off the mound and achieve their preinjury velocity, strength, and range of motion, they were cleared to return to competitive pitching.

In the senior author’s (MSS) practice, all throwers are managed with the same nonoperative protocol.⁴ Initial treatment consists of short periods of rest and symptom control via the application of cryotherapy, among other modalities. Restoration of preinjury range of motion is achieved with active-assisted stretching exercises. As range of motion begins approaching pre-injury levels, strength training is initiated with isometric strengthening of the LD and TM progressing to resistance exercises. Exercising the abdominal core, strengthening the lower body, and cardiovascular conditioning are focal points of the rehabilitation period. Once patients regain preinjury shoulder strength and range of motion without pain, they begin a throwing program that consists of 4 weeks of long toss followed by 2 weeks of throwing from the pitching mound. After completion of the throwing program, the patient is allowed to return to competitive pitching. For patients who did not suffer season-ending injury, the average time required to return to play was 99.8 days (range 72.3 to 182.6 days).

Complications and Reinjury

The patients in Leland and colleagues⁸ and Malcolm and colleagues⁷ did not suffer any complications or reinjuries. In Schickendantz and colleagues⁴, all but 3 of the 10 patients were able to return to full speed pitching by 3 months. The other 3 required 4, 6, and 10 months. The patient that required 10 months tore both his LD and TM and the patient that required 6 months tore his TM and was never able to regain his pre-injury throwing velocity. None of the TM tears had a recurrence, while 1 LD tear had a recurrence of injury 6 months after returning to competitive pitching. This patient was successfully treated with 6 weeks of conservative rest and rehabilitation.

In Nagda and colleagues⁹, 2 athletes suffered injury recurrence. One athlete with a LD strain suffered 2 subsequent LD strains, 4 months and 1 year after initial injury. The other athlete with a LD avulsion suffered a subsequent TM avulsion 13 months after initial injury. One pitcher who had an LD and TM strain suffered a superior labrum anterior and posterior (SLAP) tear and was never able to return to his prior level of play.

Surgical Treatment

Only 1 of the 5 included studies utilized surgical repair for their patient.¹⁰ The single patient suffered an avulsion injury of the distal LD tendon and its insertion on the humerus. The LD tendon was retracted approximately 5 cm from the distal humeral insertion. The TM was not involved. Eight days post-injury, the patient underwent surgical repair.¹¹ Postoperatively, the patient started passive range of motion after 2 weeks and active range of motion after 6 weeks. He started throwing at 12 weeks and returned to play at 30 weeks after he had returned to his preinjury form in regards to muscle strength, pitch control, and velocity. The patient was able to resume pitching at a high level in MLB.

Discussion

Overhand throwing athletes, especially professional baseball players, have to constantly deal with a variety of shoulder injuries.^12,13 Currently, there is minimal literature on isolated TM and LD injuries. As a result, there is still debate about the optimal treatment method for these injuries, especially in athletes who compete at the highest level. In order to treat isolated injuries of these muscles, it is important to understand their anatomic relationship, as these 2 muscles are intimately associated. The LD originates from the thoracolumbar spine and inserts on the proximal humerus between the pectoralis<hl name="2"/> major and TM tendons. The TM originates from the scapula and, similar to the LD, inserts on the proximal humerus. In an anatomic study, the TM tendon inserted into the LD tendon before its humeral insertion in the majority of cadavers.^14,15

The LD is responsible for extension, adduction, and internal rotation of the humerus. The TM, while not as extensively studied, is believed to also contribute to extension, adduction, and internal rotation of the humerus.¹⁶ As Jobe and colleagues⁵ demonstrated, the LD is vital during the acceleration phase of pitching. While they were unable to make any conclusions about the role of the TM during the pitching cycle, it is reasonable to hypothesize that these 2 muscles work together. While it is thought that these 2 muscles work as a unit, it is significant to note that a professional pitcher can sustain an isolated injury to the TM without injury to the LD, and vice versa. This questions whether these 2 muscles work more independently than once thought. One hypothesis is that the physical size of the LD provides protection from injuries that the smaller TM cannot overcome. This is a potential area of further research.

The most common findings in patients with TM injuries include swelling, bruising, tenderness of the proximal arm, and limitations of shoulder range of motion in abduction, flexion, and external rotation. There is also weakness when resistance is applied against internal rotation and extension. Similar to the TM, common findings in patients with LD injuries include pain in the posterior shoulder, bruising, and weakness when resistance is applied against internal rotation of the shoulder. Pitchers are often able to pinpoint the occurrence of their acute pain during a specific time in the game. They commonly experience a pulling sensation and sometimes even feel a “pop” in their shoulder followed by an acute onset of pain and stiffness in the posterior aspect of the axilla. These injuries seem to be associated with the pitcher throwing a “breaking ball,” a pitch that requires greater shoulder rotation since it changes trajectory while traveling towards home plate. Despite the clear role of the LD and hypothesized role of the TM in the pitching sequence, there has been limited research on the optimal treatment of isolated injuries of these muscles in MLB pitchers. The majority of studies in this review opted for conservative treatment for both LD and TM injuries. The only study that presented a surgical option was for a LD avulsion injury.

Athletes undergoing either conservative or surgical treatment required a significant period of recovery and rehabilitation before they were able to compete at the professional level. In Leland and colleagues⁸, it took about 10 to 12 weeks of rehabilitation for both pitchers to return to pitching against competition. In Schickendantz and colleagues⁴, barring any complications or injury recurrence, it took patients 12 weeks to return to their preinjury level. In Malcolm and colleagues⁷, magnetic resonance imaging after 8 weeks showed marked recovery, and shortly after the pitcher was able to return to the pitching rotation. In Nagda and colleagues⁹, the time lost to injury ranged from 7 weeks to an entire season. Of the 9 pitchers who were lost for the season, 6 had avulsion injuries. The other 3 consisted of an LD strain, TM strain, and LD plus TM strain.⁹ In this study, it seems that avulsion injuries had a more significant impact on patient recovery. On average, it took 35.6 days after injury for players to begin throwing. In contrast, it took an average of 65.5 days after an avulsion injury for players to begin throwing. Ellman and colleagues¹⁰ included the only surgically repaired injury, and it was for an avulsion of the LD tendon. In the surgical case, it took slightly longer for the pitcher to return to preinjury form. It took him 12 to 16 weeks to begin light throwing and his full return to pitching took about 20 to 30 weeks. Since muscle strains and tendon avulsions are significantly different injuries in regards to the type of soft tissue damage and healing potential, they may require different treatment strategies. An avulsion injury may require more aggressive intervention, whereas a strain may only require conservative rehabilitation. Ultimately, there does not seem to be a significant benefit of one treatment option compared to the other. The majority of conservatively managed pitchers were able to return to previous form in a reasonable time frame. While each rehabilitation protocol was slightly different, multiple studies advocated for rehab programs that centered around the following goals: slowly progressing pitchers to light throwing once their pain resolved, followed by long throwing, then throwing off of the mound, and finally returning to competitive pitching. It is important to discuss with patients that rehabilitation generally takes 12 to 16 weeks before they are able to fully return to pitching against competition and that rest should immediately follow any recurrence of pain or stiffness. Once those symptoms resolve, patients may continue the rehabilitation protocol.

As with any form of treatment, there are risks involved. This holds true for both conservative and nonconservative therapy for LD and TM injuries. One risk of nonoperative treatment of an LD avulsion is the development of strength deficits in the muscle.¹⁷ While this deficit may go unnoticed in a recreational athlete, it may be more pronounced in a professional athlete, especially since the LD of a professional baseball pitcher is more active on electromyography during the acceleration phase of the pitching cycle compared to a recreational athlete.¹⁸ Another risk of conservative treatment of an LD avulsion is jeopardizing the potential for future surgery. As a result, some advocate for early surgical intervention of an acute LD avulsion.^19,20 Others, however, recommend conservative management with subsequent surgical intervention if conservative measures fail. One caveat is that surgical intervention to restore the original anatomy may become difficult after a certain period of time due to the buildup of scar tissue. Surgical intervention also has associated risks, such as nerve injury, infection, vascular damage, persistent pain, and the buildup of large amounts of scar tissue. It is important to discuss these risks with patients when deciding on a treatment option.

LD and TM avulsion and tears typically present after an acute event in throwing athletes. There are a number of case reports published that demonstrate successful outcomes with both nonoperative management²¹ and operative repair of LD injuries in non-throwing athletes such as competitive water skiers,^22,23 steer wrestlers,²⁴ professional wrestlers,²⁵ and recreational rock climbers.²⁶ The 5 studies included in this review were the first ones to present LD and TM injuries in MLB pitchers. They discussed the outcomes of mainly conservative and surgical management of LD and TM avulsion and tears. Unfortunately, there remains a limited number of cases on the treatment of these injuries in highly competitive throwing athletes. Further research is required to elucidate the advantages and disadvantages of operative vs nonoperative treatment. The goal of this review is to provide clinicians with a concise summary of the current literature so that they may offer some evidence to their patients when discussing appropriate treatment plans.

Upper extremity injuries are very common in pitchers in amateur and professional baseball. The vast majority involving labral or rotator cuff pathology.^1-3 While uncommon, injuries to the latissimus dorsi (LD) (Figure) and teres major (TM) have been reported in Major League Baseball (MLB) pitchers.⁴ Jobe and colleagues⁵ demonstrated the role of the LD during the various phases of pitching. The LD is most active during the acceleration phase and remains active during the deceleration phase and follow-through.⁶ Anatomically, the TM lies posterior to the LD separated by bursal tissue. The tendon fibers converge and unite along their lower borders, leading to a synergistic mechanism of action.

Due to the rarity of LD and TM injuries, literature on the pathology and appropriate treatments for these injuries is limited. The goal of this review is to present the current literature on professional baseball players who have undergone either nonsurgical treatment or surgery for LD and TM strains and/or avulsion injuries. This review will ultimately assist clinicians when deciding on the optimal treatment method for professional baseball players.

Methods

We performed an extensive Medline database search with the following search algorithm: ([latissimus OR latissimus dorsi OR teres major] AND baseball). The search returned 20 citations. Inclusion criteria consisted of clinical studies that focused on professional baseball pitchers with TM and/or LD injuries that underwent either conservative nonsurgical treatment or surgical repair. There was no exclusion based on the type of injury present, such as avulsion vs strain. Any study with amateur athletes or athletes from other sports such as handball or rugby were excluded. Due to the limited amount of data available, the majority of included studies were case reports and case series.

Based on these parameters, 5 articles met criteria for inclusion. Of the 5 included studies, 3 were case reports and 2 were case series. From the eligible articles, the following information was obtained: publication year, sample size, mean age, mean follow-up duration, type of treatment (conservative vs surgical), ability to return to original level of play, time required to return to original form, and complications (Tables 1, 2).

Results

Nonoperative Management

Four of the 5 included studies implemented only conservative therapy for their patients.^4,7-9 The average duration these patients were followed for during treatment and rehabilitation was 26.3 months. Malcolm and colleagues⁷ followed patients for 8 months, the shortest length among the 4 conservative studies in this review. Leland and colleagues8 followed patients for 17 months, and Nagda and colleagues⁹ had the longest length of observation of 36 months (range 12 to 82 months).Schickendantz and colleagues⁴ followed patients for >12 months, but the exact duration was not specified. In order to calculate the average duration of observation, each patient was assigned a duration of 12 months.

Of the 30 patients included in this review, 29 were treated conservatively. All of the included studies consisted of male patients. The mean age was 26.8 years (range 22 to 28.1 years). Of the 29 injuries treated conservatively, there were 2 LD tendon avulsions, 4 TM tendon avulsions, 1 LD and TM tendon avulsion, 7 LD intramuscular strains, 9 TM intramuscular strains, and 6 LD and TM intramuscular strains.

Treatment Protocol

The various treatment and rehabilitation programs used for the conservative patient population all followed a similar pathway. After initial injury, a rest period focused on stretching was implemented. Patients were started on steroid or anti-inflammatory medications, cryotherapy, or other therapeutic modalities. Once pain-free and full range of motion was achieved, patients began the strength and throwing components of the rehabilitation program. Reoccurrence of symptoms would halt the throwing component of the rehabilitation program until symptoms improved. Patients were progressed through a return-to-throw program and once they could throw off the mound and achieve their preinjury velocity, strength, and range of motion, they were cleared to return to competitive pitching.

In the senior author’s (MSS) practice, all throwers are managed with the same nonoperative protocol.⁴ Initial treatment consists of short periods of rest and symptom control via the application of cryotherapy, among other modalities. Restoration of preinjury range of motion is achieved with active-assisted stretching exercises. As range of motion begins approaching pre-injury levels, strength training is initiated with isometric strengthening of the LD and TM progressing to resistance exercises. Exercising the abdominal core, strengthening the lower body, and cardiovascular conditioning are focal points of the rehabilitation period. Once patients regain preinjury shoulder strength and range of motion without pain, they begin a throwing program that consists of 4 weeks of long toss followed by 2 weeks of throwing from the pitching mound. After completion of the throwing program, the patient is allowed to return to competitive pitching. For patients who did not suffer season-ending injury, the average time required to return to play was 99.8 days (range 72.3 to 182.6 days).

Complications and Reinjury

The patients in Leland and colleagues⁸ and Malcolm and colleagues⁷ did not suffer any complications or reinjuries. In Schickendantz and colleagues⁴, all but 3 of the 10 patients were able to return to full speed pitching by 3 months. The other 3 required 4, 6, and 10 months. The patient that required 10 months tore both his LD and TM and the patient that required 6 months tore his TM and was never able to regain his pre-injury throwing velocity. None of the TM tears had a recurrence, while 1 LD tear had a recurrence of injury 6 months after returning to competitive pitching. This patient was successfully treated with 6 weeks of conservative rest and rehabilitation.

In Nagda and colleagues⁹, 2 athletes suffered injury recurrence. One athlete with a LD strain suffered 2 subsequent LD strains, 4 months and 1 year after initial injury. The other athlete with a LD avulsion suffered a subsequent TM avulsion 13 months after initial injury. One pitcher who had an LD and TM strain suffered a superior labrum anterior and posterior (SLAP) tear and was never able to return to his prior level of play.

Surgical Treatment

Only 1 of the 5 included studies utilized surgical repair for their patient.¹⁰ The single patient suffered an avulsion injury of the distal LD tendon and its insertion on the humerus. The LD tendon was retracted approximately 5 cm from the distal humeral insertion. The TM was not involved. Eight days post-injury, the patient underwent surgical repair.¹¹ Postoperatively, the patient started passive range of motion after 2 weeks and active range of motion after 6 weeks. He started throwing at 12 weeks and returned to play at 30 weeks after he had returned to his preinjury form in regards to muscle strength, pitch control, and velocity. The patient was able to resume pitching at a high level in MLB.

Discussion

Overhand throwing athletes, especially professional baseball players, have to constantly deal with a variety of shoulder injuries.^12,13 Currently, there is minimal literature on isolated TM and LD injuries. As a result, there is still debate about the optimal treatment method for these injuries, especially in athletes who compete at the highest level. In order to treat isolated injuries of these muscles, it is important to understand their anatomic relationship, as these 2 muscles are intimately associated. The LD originates from the thoracolumbar spine and inserts on the proximal humerus between the pectoralis<hl name="2"/> major and TM tendons. The TM originates from the scapula and, similar to the LD, inserts on the proximal humerus. In an anatomic study, the TM tendon inserted into the LD tendon before its humeral insertion in the majority of cadavers.^14,15

The LD is responsible for extension, adduction, and internal rotation of the humerus. The TM, while not as extensively studied, is believed to also contribute to extension, adduction, and internal rotation of the humerus.¹⁶ As Jobe and colleagues⁵ demonstrated, the LD is vital during the acceleration phase of pitching. While they were unable to make any conclusions about the role of the TM during the pitching cycle, it is reasonable to hypothesize that these 2 muscles work together. While it is thought that these 2 muscles work as a unit, it is significant to note that a professional pitcher can sustain an isolated injury to the TM without injury to the LD, and vice versa. This questions whether these 2 muscles work more independently than once thought. One hypothesis is that the physical size of the LD provides protection from injuries that the smaller TM cannot overcome. This is a potential area of further research.

The most common findings in patients with TM injuries include swelling, bruising, tenderness of the proximal arm, and limitations of shoulder range of motion in abduction, flexion, and external rotation. There is also weakness when resistance is applied against internal rotation and extension. Similar to the TM, common findings in patients with LD injuries include pain in the posterior shoulder, bruising, and weakness when resistance is applied against internal rotation of the shoulder. Pitchers are often able to pinpoint the occurrence of their acute pain during a specific time in the game. They commonly experience a pulling sensation and sometimes even feel a “pop” in their shoulder followed by an acute onset of pain and stiffness in the posterior aspect of the axilla. These injuries seem to be associated with the pitcher throwing a “breaking ball,” a pitch that requires greater shoulder rotation since it changes trajectory while traveling towards home plate. Despite the clear role of the LD and hypothesized role of the TM in the pitching sequence, there has been limited research on the optimal treatment of isolated injuries of these muscles in MLB pitchers. The majority of studies in this review opted for conservative treatment for both LD and TM injuries. The only study that presented a surgical option was for a LD avulsion injury.

Athletes undergoing either conservative or surgical treatment required a significant period of recovery and rehabilitation before they were able to compete at the professional level. In Leland and colleagues⁸, it took about 10 to 12 weeks of rehabilitation for both pitchers to return to pitching against competition. In Schickendantz and colleagues⁴, barring any complications or injury recurrence, it took patients 12 weeks to return to their preinjury level. In Malcolm and colleagues⁷, magnetic resonance imaging after 8 weeks showed marked recovery, and shortly after the pitcher was able to return to the pitching rotation. In Nagda and colleagues⁹, the time lost to injury ranged from 7 weeks to an entire season. Of the 9 pitchers who were lost for the season, 6 had avulsion injuries. The other 3 consisted of an LD strain, TM strain, and LD plus TM strain.⁹ In this study, it seems that avulsion injuries had a more significant impact on patient recovery. On average, it took 35.6 days after injury for players to begin throwing. In contrast, it took an average of 65.5 days after an avulsion injury for players to begin throwing. Ellman and colleagues¹⁰ included the only surgically repaired injury, and it was for an avulsion of the LD tendon. In the surgical case, it took slightly longer for the pitcher to return to preinjury form. It took him 12 to 16 weeks to begin light throwing and his full return to pitching took about 20 to 30 weeks. Since muscle strains and tendon avulsions are significantly different injuries in regards to the type of soft tissue damage and healing potential, they may require different treatment strategies. An avulsion injury may require more aggressive intervention, whereas a strain may only require conservative rehabilitation. Ultimately, there does not seem to be a significant benefit of one treatment option compared to the other. The majority of conservatively managed pitchers were able to return to previous form in a reasonable time frame. While each rehabilitation protocol was slightly different, multiple studies advocated for rehab programs that centered around the following goals: slowly progressing pitchers to light throwing once their pain resolved, followed by long throwing, then throwing off of the mound, and finally returning to competitive pitching. It is important to discuss with patients that rehabilitation generally takes 12 to 16 weeks before they are able to fully return to pitching against competition and that rest should immediately follow any recurrence of pain or stiffness. Once those symptoms resolve, patients may continue the rehabilitation protocol.

As with any form of treatment, there are risks involved. This holds true for both conservative and nonconservative therapy for LD and TM injuries. One risk of nonoperative treatment of an LD avulsion is the development of strength deficits in the muscle.¹⁷ While this deficit may go unnoticed in a recreational athlete, it may be more pronounced in a professional athlete, especially since the LD of a professional baseball pitcher is more active on electromyography during the acceleration phase of the pitching cycle compared to a recreational athlete.¹⁸ Another risk of conservative treatment of an LD avulsion is jeopardizing the potential for future surgery. As a result, some advocate for early surgical intervention of an acute LD avulsion.^19,20 Others, however, recommend conservative management with subsequent surgical intervention if conservative measures fail. One caveat is that surgical intervention to restore the original anatomy may become difficult after a certain period of time due to the buildup of scar tissue. Surgical intervention also has associated risks, such as nerve injury, infection, vascular damage, persistent pain, and the buildup of large amounts of scar tissue. It is important to discuss these risks with patients when deciding on a treatment option.

LD and TM avulsion and tears typically present after an acute event in throwing athletes. There are a number of case reports published that demonstrate successful outcomes with both nonoperative management²¹ and operative repair of LD injuries in non-throwing athletes such as competitive water skiers,^22,23 steer wrestlers,²⁴ professional wrestlers,²⁵ and recreational rock climbers.²⁶ The 5 studies included in this review were the first ones to present LD and TM injuries in MLB pitchers. They discussed the outcomes of mainly conservative and surgical management of LD and TM avulsion and tears. Unfortunately, there remains a limited number of cases on the treatment of these injuries in highly competitive throwing athletes. Further research is required to elucidate the advantages and disadvantages of operative vs nonoperative treatment. The goal of this review is to provide clinicians with a concise summary of the current literature so that they may offer some evidence to their patients when discussing appropriate treatment plans.

NEW ORLEANS—Disease progression during moderately advanced multiple sclerosis (MS) is amnesic to prior disease activity, according to researchers reporting at the ACTRIMS 2016 Forum. Lower relapse rates and greater persistence on higher-efficacy immunomodulatory therapy after reaching Expanded Disability Status Scale (EDSS) steps 3, 4, and 6 are associated with a decreased risk of accumulating further disability. “Highly effective disease-modifying therapy can mitigate the disability accrual after reaching confirmed EDSS steps of 3, 4, and 6,” said Nathaniel Lizak, BMedSc(Hons), MBBS, of Monash University in Clayton, Australia, and the University of Melbourne, and his research colleagues.

Three large cohort studies have previously examined factors influencing disability accumulation in moderately advanced MS, Dr. Lizak and colleagues noted, but these studies yielded contradictory conclusions. “The effect of therapy during this disease stage remains unclear,” the researchers said.

Dr. Lizak and colleagues sought to identify modifiers of disability trajectories in moderately advanced MS, including disease activity and immunomodulatory therapy during the early and moderately advanced stages of MS. They hypothesized that individual disability trajectories are not homogenous and can be predicted based on demographic and clinical characteristics.

The researchers analyzed epochs between EDSS steps 3 to 6, 4 to 6, and 6 to 6.5. Patients with relapse-onset MS, six-month confirmed progression to the initial EDSS step (baseline), and 12 months pre-baseline follow-up were identified in MSBase, a large international observational MS cohort study. Multivariable survival models examined the impact of relapse rate and proportion of time treated (prior to and during each epoch), age and disease duration at baseline, and progression to the outcome EDSS (6 or 6.5). Sensitivity analyses varying outcome definition and inclusion criteria also were conducted.

For the 3 to 6, 4 to 6, and 6 to 6.5 epochs, 1,560, 1,504, and 1,231 patients were identified, respectively. Pre- and post-baseline disability trajectories showed large coefficients of variance (0.85 to 0.92 and 1.95 to 2.26, respectively) and did not correlate. Probability of reaching the outcome EDSS was not associated with pre-baseline variables, but was increased by higher relapse rates during each epoch (hazard ratios, 1.58 to 3.07). Greater proportion of each epoch treated with higher-efficacy therapies was associated with lower risk of the outcome EDSS (hazard ratios, 0.27 to 0.68). These results were confirmed by sensitivity analyses.

“These observations justify treatment even after moderately advanced disability has been attained,” Dr. Lizak and colleagues concluded.

NEW ORLEANS—Disease progression during moderately advanced multiple sclerosis (MS) is amnesic to prior disease activity, according to researchers reporting at the ACTRIMS 2016 Forum. Lower relapse rates and greater persistence on higher-efficacy immunomodulatory therapy after reaching Expanded Disability Status Scale (EDSS) steps 3, 4, and 6 are associated with a decreased risk of accumulating further disability. “Highly effective disease-modifying therapy can mitigate the disability accrual after reaching confirmed EDSS steps of 3, 4, and 6,” said Nathaniel Lizak, BMedSc(Hons), MBBS, of Monash University in Clayton, Australia, and the University of Melbourne, and his research colleagues.

Three large cohort studies have previously examined factors influencing disability accumulation in moderately advanced MS, Dr. Lizak and colleagues noted, but these studies yielded contradictory conclusions. “The effect of therapy during this disease stage remains unclear,” the researchers said.

Dr. Lizak and colleagues sought to identify modifiers of disability trajectories in moderately advanced MS, including disease activity and immunomodulatory therapy during the early and moderately advanced stages of MS. They hypothesized that individual disability trajectories are not homogenous and can be predicted based on demographic and clinical characteristics.

The researchers analyzed epochs between EDSS steps 3 to 6, 4 to 6, and 6 to 6.5. Patients with relapse-onset MS, six-month confirmed progression to the initial EDSS step (baseline), and 12 months pre-baseline follow-up were identified in MSBase, a large international observational MS cohort study. Multivariable survival models examined the impact of relapse rate and proportion of time treated (prior to and during each epoch), age and disease duration at baseline, and progression to the outcome EDSS (6 or 6.5). Sensitivity analyses varying outcome definition and inclusion criteria also were conducted.

For the 3 to 6, 4 to 6, and 6 to 6.5 epochs, 1,560, 1,504, and 1,231 patients were identified, respectively. Pre- and post-baseline disability trajectories showed large coefficients of variance (0.85 to 0.92 and 1.95 to 2.26, respectively) and did not correlate. Probability of reaching the outcome EDSS was not associated with pre-baseline variables, but was increased by higher relapse rates during each epoch (hazard ratios, 1.58 to 3.07). Greater proportion of each epoch treated with higher-efficacy therapies was associated with lower risk of the outcome EDSS (hazard ratios, 0.27 to 0.68). These results were confirmed by sensitivity analyses.

“These observations justify treatment even after moderately advanced disability has been attained,” Dr. Lizak and colleagues concluded.

NEW ORLEANS—Disease progression during moderately advanced multiple sclerosis (MS) is amnesic to prior disease activity, according to researchers reporting at the ACTRIMS 2016 Forum. Lower relapse rates and greater persistence on higher-efficacy immunomodulatory therapy after reaching Expanded Disability Status Scale (EDSS) steps 3, 4, and 6 are associated with a decreased risk of accumulating further disability. “Highly effective disease-modifying therapy can mitigate the disability accrual after reaching confirmed EDSS steps of 3, 4, and 6,” said Nathaniel Lizak, BMedSc(Hons), MBBS, of Monash University in Clayton, Australia, and the University of Melbourne, and his research colleagues.

Three large cohort studies have previously examined factors influencing disability accumulation in moderately advanced MS, Dr. Lizak and colleagues noted, but these studies yielded contradictory conclusions. “The effect of therapy during this disease stage remains unclear,” the researchers said.

Dr. Lizak and colleagues sought to identify modifiers of disability trajectories in moderately advanced MS, including disease activity and immunomodulatory therapy during the early and moderately advanced stages of MS. They hypothesized that individual disability trajectories are not homogenous and can be predicted based on demographic and clinical characteristics.

The researchers analyzed epochs between EDSS steps 3 to 6, 4 to 6, and 6 to 6.5. Patients with relapse-onset MS, six-month confirmed progression to the initial EDSS step (baseline), and 12 months pre-baseline follow-up were identified in MSBase, a large international observational MS cohort study. Multivariable survival models examined the impact of relapse rate and proportion of time treated (prior to and during each epoch), age and disease duration at baseline, and progression to the outcome EDSS (6 or 6.5). Sensitivity analyses varying outcome definition and inclusion criteria also were conducted.

For the 3 to 6, 4 to 6, and 6 to 6.5 epochs, 1,560, 1,504, and 1,231 patients were identified, respectively. Pre- and post-baseline disability trajectories showed large coefficients of variance (0.85 to 0.92 and 1.95 to 2.26, respectively) and did not correlate. Probability of reaching the outcome EDSS was not associated with pre-baseline variables, but was increased by higher relapse rates during each epoch (hazard ratios, 1.58 to 3.07). Greater proportion of each epoch treated with higher-efficacy therapies was associated with lower risk of the outcome EDSS (hazard ratios, 0.27 to 0.68). These results were confirmed by sensitivity analyses.

“These observations justify treatment even after moderately advanced disability has been attained,” Dr. Lizak and colleagues concluded.

NEW ORLEANS—Meningeal B-cell infiltrates may be the main source of inflammatory or cytotoxic molecules that are released into the CSF to cause cortical tissue injury in progressive multiple sclerosis (MS), according to a study described at the ACTRIMS 2016 Forum. The proinflammatory CSF profile of patients with high levels of gray matter damage significantly differs from that of patients with low levels of gray matter damage, thus suggesting that measuring levels of meningeal B-cell infiltrates may be a useful approach for patient stratification at disease onset.

Gray matter damage is the best correlate of the accumulation of physical and cognitive deficits and one of the main substrates of disability progression in MS, according to the researchers. New advanced imaging techniques enable a more accurate estimation of the load of gray matter demyelination and brain atrophy, thus suggesting that increased levels of gray matter pathology play a crucial role in more rapid progressive outcome. Investigators have proposed meningeal B-cell infiltrates as the main source of the intrathecal inflammatory or cytotoxic milieu in the CSF that may mediate and exacerbate the gradient of tissue injury in the adjacent gray matter.

Roberta Magliozzi, PhD, of the University of Verona in Italy, and colleagues undertook a study to identify specific biomarkers and imaging tools to predict and monitor gray matter pathology and its association with MS progression. The investigators performed advanced MRI imaging of gray matter damage and an extensive protein analysis of CSF for 70 patients with MS and 12 controls. Dr. Magliozzi’s group also analyzed molecular expression in paired meningeal and CSF samples from 20 postmortem cases of secondary progressive MS and 10 control cases to verify whether inflammatory mediators expressed by the meningeal infiltrates are released into the CSF.

The researchers observed that a pronounced proinflammatory CSF profile, including overexpression of CXCL13, CXCL12, CCL19, CCL21, IL6, IL10, APRIL, BAFF, TNF, TNFR1, LIGHT, IFN-γ, gray matter-CSF, and MMP2, was strictly associated with increased gray matter pathology and disease progression in patients with MS. The proinflammatory CSF profile suggested lymphoid-neogenesis, B-cell and plasmablast or plasma-cell involvement, and a TNF-mediated inflammatory response. A pattern of increased regulatory molecules, including IFNα, IFNβ, IFNλ, CCL22, and CCL25, was associated with a lower level of gray matter pathology. Consistent with this finding, the investigators detected increased expression of CXCL13, CXCL9, TNF, IFNγ, LTα, LTβ, IL10, IL16, and IL12p40 in the meninges and CSF samples of postmortem cases of secondary progressive MS with a higher level of meningeal inflammation and gray matter demyelination.

NEW ORLEANS—Meningeal B-cell infiltrates may be the main source of inflammatory or cytotoxic molecules that are released into the CSF to cause cortical tissue injury in progressive multiple sclerosis (MS), according to a study described at the ACTRIMS 2016 Forum. The proinflammatory CSF profile of patients with high levels of gray matter damage significantly differs from that of patients with low levels of gray matter damage, thus suggesting that measuring levels of meningeal B-cell infiltrates may be a useful approach for patient stratification at disease onset.

Gray matter damage is the best correlate of the accumulation of physical and cognitive deficits and one of the main substrates of disability progression in MS, according to the researchers. New advanced imaging techniques enable a more accurate estimation of the load of gray matter demyelination and brain atrophy, thus suggesting that increased levels of gray matter pathology play a crucial role in more rapid progressive outcome. Investigators have proposed meningeal B-cell infiltrates as the main source of the intrathecal inflammatory or cytotoxic milieu in the CSF that may mediate and exacerbate the gradient of tissue injury in the adjacent gray matter.

Roberta Magliozzi, PhD, of the University of Verona in Italy, and colleagues undertook a study to identify specific biomarkers and imaging tools to predict and monitor gray matter pathology and its association with MS progression. The investigators performed advanced MRI imaging of gray matter damage and an extensive protein analysis of CSF for 70 patients with MS and 12 controls. Dr. Magliozzi’s group also analyzed molecular expression in paired meningeal and CSF samples from 20 postmortem cases of secondary progressive MS and 10 control cases to verify whether inflammatory mediators expressed by the meningeal infiltrates are released into the CSF.

The researchers observed that a pronounced proinflammatory CSF profile, including overexpression of CXCL13, CXCL12, CCL19, CCL21, IL6, IL10, APRIL, BAFF, TNF, TNFR1, LIGHT, IFN-γ, gray matter-CSF, and MMP2, was strictly associated with increased gray matter pathology and disease progression in patients with MS. The proinflammatory CSF profile suggested lymphoid-neogenesis, B-cell and plasmablast or plasma-cell involvement, and a TNF-mediated inflammatory response. A pattern of increased regulatory molecules, including IFNα, IFNβ, IFNλ, CCL22, and CCL25, was associated with a lower level of gray matter pathology. Consistent with this finding, the investigators detected increased expression of CXCL13, CXCL9, TNF, IFNγ, LTα, LTβ, IL10, IL16, and IL12p40 in the meninges and CSF samples of postmortem cases of secondary progressive MS with a higher level of meningeal inflammation and gray matter demyelination.

NEW ORLEANS—Meningeal B-cell infiltrates may be the main source of inflammatory or cytotoxic molecules that are released into the CSF to cause cortical tissue injury in progressive multiple sclerosis (MS), according to a study described at the ACTRIMS 2016 Forum. The proinflammatory CSF profile of patients with high levels of gray matter damage significantly differs from that of patients with low levels of gray matter damage, thus suggesting that measuring levels of meningeal B-cell infiltrates may be a useful approach for patient stratification at disease onset.

Gray matter damage is the best correlate of the accumulation of physical and cognitive deficits and one of the main substrates of disability progression in MS, according to the researchers. New advanced imaging techniques enable a more accurate estimation of the load of gray matter demyelination and brain atrophy, thus suggesting that increased levels of gray matter pathology play a crucial role in more rapid progressive outcome. Investigators have proposed meningeal B-cell infiltrates as the main source of the intrathecal inflammatory or cytotoxic milieu in the CSF that may mediate and exacerbate the gradient of tissue injury in the adjacent gray matter.

Roberta Magliozzi, PhD, of the University of Verona in Italy, and colleagues undertook a study to identify specific biomarkers and imaging tools to predict and monitor gray matter pathology and its association with MS progression. The investigators performed advanced MRI imaging of gray matter damage and an extensive protein analysis of CSF for 70 patients with MS and 12 controls. Dr. Magliozzi’s group also analyzed molecular expression in paired meningeal and CSF samples from 20 postmortem cases of secondary progressive MS and 10 control cases to verify whether inflammatory mediators expressed by the meningeal infiltrates are released into the CSF.

The researchers observed that a pronounced proinflammatory CSF profile, including overexpression of CXCL13, CXCL12, CCL19, CCL21, IL6, IL10, APRIL, BAFF, TNF, TNFR1, LIGHT, IFN-γ, gray matter-CSF, and MMP2, was strictly associated with increased gray matter pathology and disease progression in patients with MS. The proinflammatory CSF profile suggested lymphoid-neogenesis, B-cell and plasmablast or plasma-cell involvement, and a TNF-mediated inflammatory response. A pattern of increased regulatory molecules, including IFNα, IFNβ, IFNλ, CCL22, and CCL25, was associated with a lower level of gray matter pathology. Consistent with this finding, the investigators detected increased expression of CXCL13, CXCL9, TNF, IFNγ, LTα, LTβ, IL10, IL16, and IL12p40 in the meninges and CSF samples of postmortem cases of secondary progressive MS with a higher level of meningeal inflammation and gray matter demyelination.

Throwing and batting each require repetitive motions that can result in injuries unique to baseball. Fortuantely, advances in operative and nonoperative treatments have allowed players to return to competition after sustaining what previously would have been considered a career-ending injury. Once a player has been deemed ready to return to throwing or hitting, a comprehensive, multiphased approach to rehabilitation is necessary to reintroduce the athlete back to baseball activities and avoid re-injury. This article reviews the biomechanics of both throwing and hitting, and outlines the phases of rehabilitation necessary to allow the athlete to return to competition.

Throwing

Biomechanical Overview

The overhead throwing motion is complex and involves full body coordination from the initial force generation through the follow-through phase of throwing. The “kinetic chain”—the concept that movements in the body are connected through segments culminating with the highest energy in the final segment—is paramount to achieving the force and energy needed for throwing.^1-8 The kinetic chain begins in the lower body and trunk and transmits the energy distally to the shoulder, elbow, and hand, ending with kinetic energy transfer to the ball.^3-5,7 The progression of motion through the kinetic chain during throwing includes stride, pelvis rotation, upper torso rotation, elbow extension, shoulder internal rotation, and wrist flexion. Disruptions in this chain due to muscle imbalance or weakness can lead to injury downstream, particularly in the upper extremity.^3,7,9

The importance of the kinetic chain can be highlighted in the 6 phases of throwing motion. These include wind-up, early arm cocking, late arm cocking, arm acceleration, arm deceleration, and follow-through (Figure 1).^1,2,9,10

The wind-up phase starts with initiation of motion and ends with maximal knee lift of the lead leg; its objective is to place the body in an optimal stance to throw.^3-5,7 There are minimal forces, torques, and muscle activity in the upper extremity during this phase, but up to 50% of throw speed is created through stride and trunk rotation.⁶ During the early cocking phase, the thrower keeps his stance foot planted and drives his lead leg towards the target, while bringing both arms into abduction. This is coupled with internal rotation of the stance hip, external rotation of the lead hip, and external rotation of the throwing shoulder. This creates linear velocity by maximizing the length of the elastic components of the body. Elbow, wrist, and finger extensors are also contracting during this phase to control elbow flexion and wrist hyperextension.³

The late cocking phase begins when the lead foot contacts the ground and ends with maximum shoulder external rotation.^3-5 Lead foot contact is followed by quadriceps contraction to decelerate and stabilize the lead leg. This is followed by rotation of the pelvis and upper torso. The result is energy transfer to the throwing arm with a shear force across the anterior shoulder of 400 N.⁴ The shoulder stays in 90° of abduction, 15° of horizontal adduction, and externally rotates to between 150° and 180°. This produces a maximum horizontal adduction moment of 100 N^.m and internal rotation torque of 70 N^.m.⁴ Simultaneously, the elbow generates maximum flexion and a 65 N^.m varus torque.⁷ Forces about the elbow are generated to resist the large angular velocity experienced (up to 3000°/second). This places an extreme amount of valgus stress along the medial elbow, particularly on the ulnar collateral ligament. The shoulder girdle and rotator cuff muscles simultaneously act to stabilize the scapula and glenohumeral joint.

The arm acceleration phase is from maximal shoulder external rotation until ball release.^3-5 In this phase, the thrower flexes his trunk from an extended position, returning to neutral by the time of ball release while the lead leg straightens. The shoulder stays abducted at 90° throughout while the rotator cuff internal rotators and scapular stabilizers contract to explosively internally rotate the shoulder, creating a maximal internal rotation velocity greater than 7000°/second by ball release.^1,4,7 The elbow also begins to extend, reaching maximum velocity during mid-acceleration phase from a combination of triceps contraction and torque generated from rotation at the shoulder and upper trunk.³ Finally, the wrist flexors contract to move the wrist to a neutral position from hyperextension as the ball is released.

During arm deceleration, the shoulder achieves maximum internal rotation until reaching a neutral position and horizontally adducts across the body. This is controlled by contraction of the shoulder girdle musculature; the teres minor has the highest activity.^3,4 The greatest forces produced during the throwing motion act at the shoulder and elbow during deceleration and can contribute to injury.² These include compressive forces of greater than 1000 N, posterior shear forces of 400 N, and inferior shear forces of 300 N.^4,7

The final phase, the follow-through phase, starts at shoulder maximum internal rotation and ends when the arm assumes a balanced position across the trunk. Lower extremity extension and trunk flexion help distribute forces throughout the body, taking stress away from the throwing arm. The posterior shoulder musculature and scapular protractors contribute to continued deceleration and muscle firing returns to resting levels. This complex motion of throwing fueled by the kinetic chain lasts less than 2 seconds and can result in ball release speeds as high as 100 miles per hour.^3,4

Return to Throwing: Principles

Nonoperative and postoperative rehabilitation programs allow restoration of motion, strength, static and dynamic stability, and neuromuscular control. The initiation of an interval throwing program (ITP) is based on the assumption that tissue healing is complete and a complete physical examination has been conducted to the treating physician’s approval.¹¹ An ITP progressively applies forces along the kinetic chain in a controlled manner through graduated throwing distances, while minimizing the risk of re-injury.

Reinold and colleagues¹² described guidelines that were used in the development of the ITP.¹² These factors include: (1) The act of throwing a baseball involves the transfer of energy from the feet up to the hand and therefore careful attention must be paid along the entire kinetic chain; (2) gradual progression of interval throwing decreases the chance for re-injury; (3) proper warm-up; and (4) proper throwing mechanics minimizes the chance of re-injury.

Variability. Unlike traditional rehabilitation programs that advance an athlete based on a specific timetable, the ITP requires that each level or phase to be completed pain-free or without complications prior to starting the next level. Therefore, an ITP can be used for overhead athletes of varying skill levels because progression will be different from one athlete to another. It is also important to have the athlete adhere strictly to the program, as over-eagerness to complete the ITP as quickly as possible can increase the chance of re-injury and thus slow the rehabilitation process.¹²

Warm-up. An adequate warm-up is recommended prior to initiating ITP. An athlete should jog or cycle to develop a light sweat and then progress to stretching and flexibility exercises. As emphasized before, throwing involves nearly all the muscles in the body. Therefore, all muscle groups should be stretched beginning with the legs and working distally along the kinetic chain.

Mechanics. Analysis, correction, and maintenance of proper throwing mechanics is essential throughout the early phases of rehabilitation and ITP. Improper pitching mechanics places increased stress on the throwing arm, potentially leading to re-injury. Therefore, it would be valuable to have a pitching coach available to emphasize proper mechanics throughout the rehabilitation process.

The Interval Throwing Program

For a PDF patient handout that summarizes the phases of this program, see Appendix 1.

Phase 1. We have adopted the ITP as described by Reinold and colleagues.¹² Phase begins with the overhead athlete throwing on flat ground. He or she begins tossing from 45 feet and gradually progresses to 60, 90, 120, 150, and 180 feet.

As discussed earlier, it is critical to use proper mechanics throughout the ITP. The “crow hop” method simulates a throwing act and helps maintain proper pitching mechanics. Crow hop has 3 components: hop, skip, and throw. Using this technique, the pitcher begins warm-up throws at a comfortable distance (generally 30 feet) and then progresses to the distance as indicated on the ITP. The athlete will then need to perform each step 2 times, with 1 day of rest between steps, before advancing to the next step. The ball should be thrown with an arc and have only enough momentum to reach the desired distance.

For example, Step 1 calls for the athlete to perform 2 sets of 25 throws at 45 feet, with adequate rest (5 minutes) between sets. This step will be repeated following 1 day of rest. If the athlete demonstrates the ability to throw at the prescribed distance without pain, he or she can progress to Step 2, which calls for 3 sets of 25 throws at 45 feet. If pain is present at any step, the thrower returns to the previous asymptomatic step and can progress once he is pain-free.

Positional players are instructed to complete Phase 1 prior to starting position-specific drills. Pitchers, on the other hand, are instructed to stop once they reach and complete 120 feet. They will then progress to tossing at progressive distances of 60, 90, and 120 feet, followed by throwing at 60 feet 6 inches with normal pitching mechanics, initiating straight line throws with little to no arc.

Phase II (Throwing off the Mound). Once a pitcher completes Phase 1 without pain or complications, he is ready to begin throwing off the mound. The same principle remains in Phase 2: pitchers must complete each step pain-free before advancing to the next stage. Pitchers should first throw fastballs at 50% effort and progress to 75% and 100% effort. Because athletes often find it difficult to gauge their own effort, it is important to emphasize the importance of strictly adhering to the program. Fleisig and colleagues¹³ studied healthy pitchers’ ability to estimate their throwing effort. When targeting 50% effort, athletes generated ball speeds of 85% with forces and torque approaching 75% of maximum. A radar gun may be valuable in guiding effort control.

As the player advances through Phase 2, he will increase the volume of pitches as well as the effort in a gradual manner. The player may introduce breaking ball pitches once he demonstrates the ability to throw light batting practice. Phase 2 concludes with the pitcher throwing simulated games, progressing by 15 throws per workout.

Hitting

Biomechanics Overview

The mechanics of hitting a baseball can be broken down into 6 phases: the preparatory phase, stance phase, stride phase, drive phase, bat acceleration phase, and follow-through phase.¹⁴ While progressing through a return-to-play protocol, it is important to understand and teach the player proper swing mechanics during each phase in order to minimize the risk of re-injury (Figure 2).

The preparatory phase occurs as the player positions himself into the batter’s box. This phase is highly individualized, depending on each player’s personal preference. Though significant variability in approach exists, there are 3 basic stances a player can take in preparation to bat. In the closed stance, the batter’s front foot is positioned closer to the plate than the back foot. A more popular stance is the open stance, where the player’s back foot is placed closer to the plate than the front foot. The square batting stance is the most common stance. This stance is where both feet are in line with the pitcher and parallel with the edge of the batter’s box. Most authors agree that the square stance is the optimal position because it provides batters the best opportunity to hit pitches anywhere in the strike zone and limits compensatory or extra motion to their swing.¹⁵

Once the player begins the swing, he has entered the loading period, which is divided into the stance, stride, and drive phases. The loading period, also known as coiling or triggering, begins as the athlete eccentrically stretches agonist muscles and rotates the body away from the incoming ball. The elastic energy stored during this stretching is released during the concentric contraction of the same muscles and transferred through the entire kinetic chain as different segments of the body are rotated; it culminates in effort directed at hitting the baseball.¹⁶

In each phase of the loading period, certain critical motions should be monitored and corrected in order to return the player to his previous level of competition. Stride length has been shown to be critical in the timing of a batter’s swing. A short stride length can cause early initiation of the swing, while a longer stride can produce delayed activation of hip rotation. As the player enters the drive phase, he should have increased elbow flexion in the back elbow compared to the front elbow. The bat should be placed at a position approximately 45° in the frontal plane, and the bat should bisect the batter’s helmet. The back elbow should be down, both upper extremities should be positioned close to the hitter’s body, and the proximal interphalangeal joints of the hands should align on the handle of the bat. Athletic trainers and coaches should be aware that subtle compensations due to deficits during these movements could cause injury during the swing by disrupting the body’s natural motion.

The bat acceleration phase occurs from maximal bat loading through striking the ball. In this time, the linear force that has been exerted by the player must be transferred into rotational force through the trunk and upper extremities. When the lead leg contacts the ground, the player has created a closed kinetic chain, where the elastic energy gathered during the loading period is used to produce segmental rotation beginning in the hips and rising through the trunk and out to the arms and hands, finally producing contact with the baseball.¹⁶ To produce effective bat velocity, each segment must rotate in a sequential manner. If the upper extremities reach peak velocity before any lower segment, then the player has lost the ability to efficiently transfer kinetic energy up the kinetic chain.

Finally, the follow-through phase occurs after contact with the baseball and ends with complete deceleration, completing the swing. In order to achieve optimal effort, full hip rotation is needed, which is aided by rotation of the trail foot. Both hips and back laces should face the pitcher upon completion of the swing producing maximum power output.¹⁵

Return to Hitting: Principles

As with the initiation of the ITP, an interval hitting protocol (IHP) is designed to begin only after the player has been assessed on impairment measures, physical performance measures, and self-assessment.¹⁷ The player should have minimum to no pain, have no tenderness to palpation, and show adequate range of motion and strength to meet the demands of performing a full hitting cycle.¹² It is recommended that before beginning a return-to-play protocol, the involved extremity should be at least 80% as strong as the uninvolved extremity.¹⁸ Physical measures challenging an athlete’s ability to perform tasks specific to hitting a baseball must also be considered through standardized examinations of the involved area.¹⁹ Finally, the athlete’s self-perception of functional abilities must be taken into account. This gives a subjective account of what the hitter perceives they are able to perform, providing useful insight into whether they are mentally prepared to participate in the protocol.

Like the ITP, progression through the IHP is also based on the player’s level of pain and soreness rather than following a specific timetable (Table). The program features a 1 day on, 1 day off schedule during which the player completes 1 step per day. The athlete must remain pain-free to progress to the next step and monitor his level of soreness during their workout. If pain or soreness persists, the player should rest for 2 days and be reevaluated upon return.¹⁷

The same principles of proper warm-up and mechanics apply in the IHP. An athlete should jog or cycle for a minimum of 10 minutes and perform stretching exercises focused on both upper and lower extremity muscles, as batting involves whole body movement. As the athlete progresses through the IHP, having a hitting coach to analyze, correct and maintain proper swing mechanics is valuable in enhancing performance as well as decreasing risk of re-injury.

The Interval Hitting Program

For a PDF patient handout that summarizes the phases of this program, see Appendix 2.

Phase 1 (Dry Swings). Only the most basic fundamentals are stressed during this phase. The player should focus on properly moving from one phase of the swing to the next, without the goal of hitting the baseball. Trainers should measure critical points in the swing and correct deficits early.

Phase 2 (Batting Off a Tee). In this phase, the player is reintroduced to batting at low intensity with a fixed position target. The initial steps have the batter swing in a position of greatest comfort and natural movement, while the final steps in this phase test the athlete’s range of motion and confidence in the previous, healed injury.

Phase 3 (Soft Toss). As the player progresses to this phase, a baseball with trajectory is used to simulate differences in placement of pitches used during a game. As the hitter is able to pick up differences in target position, his performance and confidence should both increase.²⁰ The coach should sit about 30 feet away, facing the hitter at an angle of 45°, and toss the ball in an underhand motion.

Phase 4 (Simulated Hitting). In this phase, the player and coach should focus on the timing of sequential body movements in order to elicit proper loading and force production. With the randomized pitch delivery and increased velocity, the hitter will practice against pitches similar to those delivered in competition.

Conclusion

Interval throwing and hitting programs are designed to allow the athlete to return to competition through a gradual, stepwise program. This permits the player to prepare his body for the unique stresses associated with throwing and hitting. The medical personnel should familiarize themselves with the philosophy of the interval throwing and hitting programs and individualize them to each athlete. Emphasis on proper warm-up, mechanics, and effort control is paramount in expediting return to play while preventing re-injury.

Throwing and batting each require repetitive motions that can result in injuries unique to baseball. Fortuantely, advances in operative and nonoperative treatments have allowed players to return to competition after sustaining what previously would have been considered a career-ending injury. Once a player has been deemed ready to return to throwing or hitting, a comprehensive, multiphased approach to rehabilitation is necessary to reintroduce the athlete back to baseball activities and avoid re-injury. This article reviews the biomechanics of both throwing and hitting, and outlines the phases of rehabilitation necessary to allow the athlete to return to competition.

Throwing

Biomechanical Overview

The overhead throwing motion is complex and involves full body coordination from the initial force generation through the follow-through phase of throwing. The “kinetic chain”—the concept that movements in the body are connected through segments culminating with the highest energy in the final segment—is paramount to achieving the force and energy needed for throwing.^1-8 The kinetic chain begins in the lower body and trunk and transmits the energy distally to the shoulder, elbow, and hand, ending with kinetic energy transfer to the ball.^3-5,7 The progression of motion through the kinetic chain during throwing includes stride, pelvis rotation, upper torso rotation, elbow extension, shoulder internal rotation, and wrist flexion. Disruptions in this chain due to muscle imbalance or weakness can lead to injury downstream, particularly in the upper extremity.^3,7,9

The importance of the kinetic chain can be highlighted in the 6 phases of throwing motion. These include wind-up, early arm cocking, late arm cocking, arm acceleration, arm deceleration, and follow-through (Figure 1).^1,2,9,10

The wind-up phase starts with initiation of motion and ends with maximal knee lift of the lead leg; its objective is to place the body in an optimal stance to throw.^3-5,7 There are minimal forces, torques, and muscle activity in the upper extremity during this phase, but up to 50% of throw speed is created through stride and trunk rotation.⁶ During the early cocking phase, the thrower keeps his stance foot planted and drives his lead leg towards the target, while bringing both arms into abduction. This is coupled with internal rotation of the stance hip, external rotation of the lead hip, and external rotation of the throwing shoulder. This creates linear velocity by maximizing the length of the elastic components of the body. Elbow, wrist, and finger extensors are also contracting during this phase to control elbow flexion and wrist hyperextension.³

The late cocking phase begins when the lead foot contacts the ground and ends with maximum shoulder external rotation.^3-5 Lead foot contact is followed by quadriceps contraction to decelerate and stabilize the lead leg. This is followed by rotation of the pelvis and upper torso. The result is energy transfer to the throwing arm with a shear force across the anterior shoulder of 400 N.⁴ The shoulder stays in 90° of abduction, 15° of horizontal adduction, and externally rotates to between 150° and 180°. This produces a maximum horizontal adduction moment of 100 N^.m and internal rotation torque of 70 N^.m.⁴ Simultaneously, the elbow generates maximum flexion and a 65 N^.m varus torque.⁷ Forces about the elbow are generated to resist the large angular velocity experienced (up to 3000°/second). This places an extreme amount of valgus stress along the medial elbow, particularly on the ulnar collateral ligament. The shoulder girdle and rotator cuff muscles simultaneously act to stabilize the scapula and glenohumeral joint.

The arm acceleration phase is from maximal shoulder external rotation until ball release.^3-5 In this phase, the thrower flexes his trunk from an extended position, returning to neutral by the time of ball release while the lead leg straightens. The shoulder stays abducted at 90° throughout while the rotator cuff internal rotators and scapular stabilizers contract to explosively internally rotate the shoulder, creating a maximal internal rotation velocity greater than 7000°/second by ball release.^1,4,7 The elbow also begins to extend, reaching maximum velocity during mid-acceleration phase from a combination of triceps contraction and torque generated from rotation at the shoulder and upper trunk.³ Finally, the wrist flexors contract to move the wrist to a neutral position from hyperextension as the ball is released.

During arm deceleration, the shoulder achieves maximum internal rotation until reaching a neutral position and horizontally adducts across the body. This is controlled by contraction of the shoulder girdle musculature; the teres minor has the highest activity.^3,4 The greatest forces produced during the throwing motion act at the shoulder and elbow during deceleration and can contribute to injury.² These include compressive forces of greater than 1000 N, posterior shear forces of 400 N, and inferior shear forces of 300 N.^4,7

The final phase, the follow-through phase, starts at shoulder maximum internal rotation and ends when the arm assumes a balanced position across the trunk. Lower extremity extension and trunk flexion help distribute forces throughout the body, taking stress away from the throwing arm. The posterior shoulder musculature and scapular protractors contribute to continued deceleration and muscle firing returns to resting levels. This complex motion of throwing fueled by the kinetic chain lasts less than 2 seconds and can result in ball release speeds as high as 100 miles per hour.^3,4

Return to Throwing: Principles

Nonoperative and postoperative rehabilitation programs allow restoration of motion, strength, static and dynamic stability, and neuromuscular control. The initiation of an interval throwing program (ITP) is based on the assumption that tissue healing is complete and a complete physical examination has been conducted to the treating physician’s approval.¹¹ An ITP progressively applies forces along the kinetic chain in a controlled manner through graduated throwing distances, while minimizing the risk of re-injury.

Reinold and colleagues¹² described guidelines that were used in the development of the ITP.¹² These factors include: (1) The act of throwing a baseball involves the transfer of energy from the feet up to the hand and therefore careful attention must be paid along the entire kinetic chain; (2) gradual progression of interval throwing decreases the chance for re-injury; (3) proper warm-up; and (4) proper throwing mechanics minimizes the chance of re-injury.

Variability. Unlike traditional rehabilitation programs that advance an athlete based on a specific timetable, the ITP requires that each level or phase to be completed pain-free or without complications prior to starting the next level. Therefore, an ITP can be used for overhead athletes of varying skill levels because progression will be different from one athlete to another. It is also important to have the athlete adhere strictly to the program, as over-eagerness to complete the ITP as quickly as possible can increase the chance of re-injury and thus slow the rehabilitation process.¹²

Warm-up. An adequate warm-up is recommended prior to initiating ITP. An athlete should jog or cycle to develop a light sweat and then progress to stretching and flexibility exercises. As emphasized before, throwing involves nearly all the muscles in the body. Therefore, all muscle groups should be stretched beginning with the legs and working distally along the kinetic chain.

Mechanics. Analysis, correction, and maintenance of proper throwing mechanics is essential throughout the early phases of rehabilitation and ITP. Improper pitching mechanics places increased stress on the throwing arm, potentially leading to re-injury. Therefore, it would be valuable to have a pitching coach available to emphasize proper mechanics throughout the rehabilitation process.

The Interval Throwing Program

For a PDF patient handout that summarizes the phases of this program, see Appendix 1.

Phase 1. We have adopted the ITP as described by Reinold and colleagues.¹² Phase begins with the overhead athlete throwing on flat ground. He or she begins tossing from 45 feet and gradually progresses to 60, 90, 120, 150, and 180 feet.

As discussed earlier, it is critical to use proper mechanics throughout the ITP. The “crow hop” method simulates a throwing act and helps maintain proper pitching mechanics. Crow hop has 3 components: hop, skip, and throw. Using this technique, the pitcher begins warm-up throws at a comfortable distance (generally 30 feet) and then progresses to the distance as indicated on the ITP. The athlete will then need to perform each step 2 times, with 1 day of rest between steps, before advancing to the next step. The ball should be thrown with an arc and have only enough momentum to reach the desired distance.

For example, Step 1 calls for the athlete to perform 2 sets of 25 throws at 45 feet, with adequate rest (5 minutes) between sets. This step will be repeated following 1 day of rest. If the athlete demonstrates the ability to throw at the prescribed distance without pain, he or she can progress to Step 2, which calls for 3 sets of 25 throws at 45 feet. If pain is present at any step, the thrower returns to the previous asymptomatic step and can progress once he is pain-free.

Positional players are instructed to complete Phase 1 prior to starting position-specific drills. Pitchers, on the other hand, are instructed to stop once they reach and complete 120 feet. They will then progress to tossing at progressive distances of 60, 90, and 120 feet, followed by throwing at 60 feet 6 inches with normal pitching mechanics, initiating straight line throws with little to no arc.

Phase II (Throwing off the Mound). Once a pitcher completes Phase 1 without pain or complications, he is ready to begin throwing off the mound. The same principle remains in Phase 2: pitchers must complete each step pain-free before advancing to the next stage. Pitchers should first throw fastballs at 50% effort and progress to 75% and 100% effort. Because athletes often find it difficult to gauge their own effort, it is important to emphasize the importance of strictly adhering to the program. Fleisig and colleagues¹³ studied healthy pitchers’ ability to estimate their throwing effort. When targeting 50% effort, athletes generated ball speeds of 85% with forces and torque approaching 75% of maximum. A radar gun may be valuable in guiding effort control.

As the player advances through Phase 2, he will increase the volume of pitches as well as the effort in a gradual manner. The player may introduce breaking ball pitches once he demonstrates the ability to throw light batting practice. Phase 2 concludes with the pitcher throwing simulated games, progressing by 15 throws per workout.

Hitting

Biomechanics Overview

The mechanics of hitting a baseball can be broken down into 6 phases: the preparatory phase, stance phase, stride phase, drive phase, bat acceleration phase, and follow-through phase.¹⁴ While progressing through a return-to-play protocol, it is important to understand and teach the player proper swing mechanics during each phase in order to minimize the risk of re-injury (Figure 2).

The preparatory phase occurs as the player positions himself into the batter’s box. This phase is highly individualized, depending on each player’s personal preference. Though significant variability in approach exists, there are 3 basic stances a player can take in preparation to bat. In the closed stance, the batter’s front foot is positioned closer to the plate than the back foot. A more popular stance is the open stance, where the player’s back foot is placed closer to the plate than the front foot. The square batting stance is the most common stance. This stance is where both feet are in line with the pitcher and parallel with the edge of the batter’s box. Most authors agree that the square stance is the optimal position because it provides batters the best opportunity to hit pitches anywhere in the strike zone and limits compensatory or extra motion to their swing.¹⁵

Once the player begins the swing, he has entered the loading period, which is divided into the stance, stride, and drive phases. The loading period, also known as coiling or triggering, begins as the athlete eccentrically stretches agonist muscles and rotates the body away from the incoming ball. The elastic energy stored during this stretching is released during the concentric contraction of the same muscles and transferred through the entire kinetic chain as different segments of the body are rotated; it culminates in effort directed at hitting the baseball.¹⁶

In each phase of the loading period, certain critical motions should be monitored and corrected in order to return the player to his previous level of competition. Stride length has been shown to be critical in the timing of a batter’s swing. A short stride length can cause early initiation of the swing, while a longer stride can produce delayed activation of hip rotation. As the player enters the drive phase, he should have increased elbow flexion in the back elbow compared to the front elbow. The bat should be placed at a position approximately 45° in the frontal plane, and the bat should bisect the batter’s helmet. The back elbow should be down, both upper extremities should be positioned close to the hitter’s body, and the proximal interphalangeal joints of the hands should align on the handle of the bat. Athletic trainers and coaches should be aware that subtle compensations due to deficits during these movements could cause injury during the swing by disrupting the body’s natural motion.

The bat acceleration phase occurs from maximal bat loading through striking the ball. In this time, the linear force that has been exerted by the player must be transferred into rotational force through the trunk and upper extremities. When the lead leg contacts the ground, the player has created a closed kinetic chain, where the elastic energy gathered during the loading period is used to produce segmental rotation beginning in the hips and rising through the trunk and out to the arms and hands, finally producing contact with the baseball.¹⁶ To produce effective bat velocity, each segment must rotate in a sequential manner. If the upper extremities reach peak velocity before any lower segment, then the player has lost the ability to efficiently transfer kinetic energy up the kinetic chain.

Finally, the follow-through phase occurs after contact with the baseball and ends with complete deceleration, completing the swing. In order to achieve optimal effort, full hip rotation is needed, which is aided by rotation of the trail foot. Both hips and back laces should face the pitcher upon completion of the swing producing maximum power output.¹⁵

Return to Hitting: Principles

As with the initiation of the ITP, an interval hitting protocol (IHP) is designed to begin only after the player has been assessed on impairment measures, physical performance measures, and self-assessment.¹⁷ The player should have minimum to no pain, have no tenderness to palpation, and show adequate range of motion and strength to meet the demands of performing a full hitting cycle.¹² It is recommended that before beginning a return-to-play protocol, the involved extremity should be at least 80% as strong as the uninvolved extremity.¹⁸ Physical measures challenging an athlete’s ability to perform tasks specific to hitting a baseball must also be considered through standardized examinations of the involved area.¹⁹ Finally, the athlete’s self-perception of functional abilities must be taken into account. This gives a subjective account of what the hitter perceives they are able to perform, providing useful insight into whether they are mentally prepared to participate in the protocol.

Like the ITP, progression through the IHP is also based on the player’s level of pain and soreness rather than following a specific timetable (Table). The program features a 1 day on, 1 day off schedule during which the player completes 1 step per day. The athlete must remain pain-free to progress to the next step and monitor his level of soreness during their workout. If pain or soreness persists, the player should rest for 2 days and be reevaluated upon return.¹⁷

The same principles of proper warm-up and mechanics apply in the IHP. An athlete should jog or cycle for a minimum of 10 minutes and perform stretching exercises focused on both upper and lower extremity muscles, as batting involves whole body movement. As the athlete progresses through the IHP, having a hitting coach to analyze, correct and maintain proper swing mechanics is valuable in enhancing performance as well as decreasing risk of re-injury.

The Interval Hitting Program

For a PDF patient handout that summarizes the phases of this program, see Appendix 2.

Phase 1 (Dry Swings). Only the most basic fundamentals are stressed during this phase. The player should focus on properly moving from one phase of the swing to the next, without the goal of hitting the baseball. Trainers should measure critical points in the swing and correct deficits early.

Phase 2 (Batting Off a Tee). In this phase, the player is reintroduced to batting at low intensity with a fixed position target. The initial steps have the batter swing in a position of greatest comfort and natural movement, while the final steps in this phase test the athlete’s range of motion and confidence in the previous, healed injury.

Phase 3 (Soft Toss). As the player progresses to this phase, a baseball with trajectory is used to simulate differences in placement of pitches used during a game. As the hitter is able to pick up differences in target position, his performance and confidence should both increase.²⁰ The coach should sit about 30 feet away, facing the hitter at an angle of 45°, and toss the ball in an underhand motion.

Phase 4 (Simulated Hitting). In this phase, the player and coach should focus on the timing of sequential body movements in order to elicit proper loading and force production. With the randomized pitch delivery and increased velocity, the hitter will practice against pitches similar to those delivered in competition.

Conclusion

Interval throwing and hitting programs are designed to allow the athlete to return to competition through a gradual, stepwise program. This permits the player to prepare his body for the unique stresses associated with throwing and hitting. The medical personnel should familiarize themselves with the philosophy of the interval throwing and hitting programs and individualize them to each athlete. Emphasis on proper warm-up, mechanics, and effort control is paramount in expediting return to play while preventing re-injury.

Throwing and batting each require repetitive motions that can result in injuries unique to baseball. Fortuantely, advances in operative and nonoperative treatments have allowed players to return to competition after sustaining what previously would have been considered a career-ending injury. Once a player has been deemed ready to return to throwing or hitting, a comprehensive, multiphased approach to rehabilitation is necessary to reintroduce the athlete back to baseball activities and avoid re-injury. This article reviews the biomechanics of both throwing and hitting, and outlines the phases of rehabilitation necessary to allow the athlete to return to competition.

Throwing

Biomechanical Overview

The overhead throwing motion is complex and involves full body coordination from the initial force generation through the follow-through phase of throwing. The “kinetic chain”—the concept that movements in the body are connected through segments culminating with the highest energy in the final segment—is paramount to achieving the force and energy needed for throwing.^1-8 The kinetic chain begins in the lower body and trunk and transmits the energy distally to the shoulder, elbow, and hand, ending with kinetic energy transfer to the ball.^3-5,7 The progression of motion through the kinetic chain during throwing includes stride, pelvis rotation, upper torso rotation, elbow extension, shoulder internal rotation, and wrist flexion. Disruptions in this chain due to muscle imbalance or weakness can lead to injury downstream, particularly in the upper extremity.^3,7,9

The importance of the kinetic chain can be highlighted in the 6 phases of throwing motion. These include wind-up, early arm cocking, late arm cocking, arm acceleration, arm deceleration, and follow-through (Figure 1).^1,2,9,10

The wind-up phase starts with initiation of motion and ends with maximal knee lift of the lead leg; its objective is to place the body in an optimal stance to throw.^3-5,7 There are minimal forces, torques, and muscle activity in the upper extremity during this phase, but up to 50% of throw speed is created through stride and trunk rotation.⁶ During the early cocking phase, the thrower keeps his stance foot planted and drives his lead leg towards the target, while bringing both arms into abduction. This is coupled with internal rotation of the stance hip, external rotation of the lead hip, and external rotation of the throwing shoulder. This creates linear velocity by maximizing the length of the elastic components of the body. Elbow, wrist, and finger extensors are also contracting during this phase to control elbow flexion and wrist hyperextension.³

The late cocking phase begins when the lead foot contacts the ground and ends with maximum shoulder external rotation.^3-5 Lead foot contact is followed by quadriceps contraction to decelerate and stabilize the lead leg. This is followed by rotation of the pelvis and upper torso. The result is energy transfer to the throwing arm with a shear force across the anterior shoulder of 400 N.⁴ The shoulder stays in 90° of abduction, 15° of horizontal adduction, and externally rotates to between 150° and 180°. This produces a maximum horizontal adduction moment of 100 N^.m and internal rotation torque of 70 N^.m.⁴ Simultaneously, the elbow generates maximum flexion and a 65 N^.m varus torque.⁷ Forces about the elbow are generated to resist the large angular velocity experienced (up to 3000°/second). This places an extreme amount of valgus stress along the medial elbow, particularly on the ulnar collateral ligament. The shoulder girdle and rotator cuff muscles simultaneously act to stabilize the scapula and glenohumeral joint.

The arm acceleration phase is from maximal shoulder external rotation until ball release.^3-5 In this phase, the thrower flexes his trunk from an extended position, returning to neutral by the time of ball release while the lead leg straightens. The shoulder stays abducted at 90° throughout while the rotator cuff internal rotators and scapular stabilizers contract to explosively internally rotate the shoulder, creating a maximal internal rotation velocity greater than 7000°/second by ball release.^1,4,7 The elbow also begins to extend, reaching maximum velocity during mid-acceleration phase from a combination of triceps contraction and torque generated from rotation at the shoulder and upper trunk.³ Finally, the wrist flexors contract to move the wrist to a neutral position from hyperextension as the ball is released.

During arm deceleration, the shoulder achieves maximum internal rotation until reaching a neutral position and horizontally adducts across the body. This is controlled by contraction of the shoulder girdle musculature; the teres minor has the highest activity.^3,4 The greatest forces produced during the throwing motion act at the shoulder and elbow during deceleration and can contribute to injury.² These include compressive forces of greater than 1000 N, posterior shear forces of 400 N, and inferior shear forces of 300 N.^4,7

The final phase, the follow-through phase, starts at shoulder maximum internal rotation and ends when the arm assumes a balanced position across the trunk. Lower extremity extension and trunk flexion help distribute forces throughout the body, taking stress away from the throwing arm. The posterior shoulder musculature and scapular protractors contribute to continued deceleration and muscle firing returns to resting levels. This complex motion of throwing fueled by the kinetic chain lasts less than 2 seconds and can result in ball release speeds as high as 100 miles per hour.^3,4

Return to Throwing: Principles

Nonoperative and postoperative rehabilitation programs allow restoration of motion, strength, static and dynamic stability, and neuromuscular control. The initiation of an interval throwing program (ITP) is based on the assumption that tissue healing is complete and a complete physical examination has been conducted to the treating physician’s approval.¹¹ An ITP progressively applies forces along the kinetic chain in a controlled manner through graduated throwing distances, while minimizing the risk of re-injury.

Reinold and colleagues¹² described guidelines that were used in the development of the ITP.¹² These factors include: (1) The act of throwing a baseball involves the transfer of energy from the feet up to the hand and therefore careful attention must be paid along the entire kinetic chain; (2) gradual progression of interval throwing decreases the chance for re-injury; (3) proper warm-up; and (4) proper throwing mechanics minimizes the chance of re-injury.

Variability. Unlike traditional rehabilitation programs that advance an athlete based on a specific timetable, the ITP requires that each level or phase to be completed pain-free or without complications prior to starting the next level. Therefore, an ITP can be used for overhead athletes of varying skill levels because progression will be different from one athlete to another. It is also important to have the athlete adhere strictly to the program, as over-eagerness to complete the ITP as quickly as possible can increase the chance of re-injury and thus slow the rehabilitation process.¹²

Warm-up. An adequate warm-up is recommended prior to initiating ITP. An athlete should jog or cycle to develop a light sweat and then progress to stretching and flexibility exercises. As emphasized before, throwing involves nearly all the muscles in the body. Therefore, all muscle groups should be stretched beginning with the legs and working distally along the kinetic chain.

Mechanics. Analysis, correction, and maintenance of proper throwing mechanics is essential throughout the early phases of rehabilitation and ITP. Improper pitching mechanics places increased stress on the throwing arm, potentially leading to re-injury. Therefore, it would be valuable to have a pitching coach available to emphasize proper mechanics throughout the rehabilitation process.

The Interval Throwing Program

For a PDF patient handout that summarizes the phases of this program, see Appendix 1.

Phase 1. We have adopted the ITP as described by Reinold and colleagues.¹² Phase begins with the overhead athlete throwing on flat ground. He or she begins tossing from 45 feet and gradually progresses to 60, 90, 120, 150, and 180 feet.

As discussed earlier, it is critical to use proper mechanics throughout the ITP. The “crow hop” method simulates a throwing act and helps maintain proper pitching mechanics. Crow hop has 3 components: hop, skip, and throw. Using this technique, the pitcher begins warm-up throws at a comfortable distance (generally 30 feet) and then progresses to the distance as indicated on the ITP. The athlete will then need to perform each step 2 times, with 1 day of rest between steps, before advancing to the next step. The ball should be thrown with an arc and have only enough momentum to reach the desired distance.

For example, Step 1 calls for the athlete to perform 2 sets of 25 throws at 45 feet, with adequate rest (5 minutes) between sets. This step will be repeated following 1 day of rest. If the athlete demonstrates the ability to throw at the prescribed distance without pain, he or she can progress to Step 2, which calls for 3 sets of 25 throws at 45 feet. If pain is present at any step, the thrower returns to the previous asymptomatic step and can progress once he is pain-free.

Positional players are instructed to complete Phase 1 prior to starting position-specific drills. Pitchers, on the other hand, are instructed to stop once they reach and complete 120 feet. They will then progress to tossing at progressive distances of 60, 90, and 120 feet, followed by throwing at 60 feet 6 inches with normal pitching mechanics, initiating straight line throws with little to no arc.

Phase II (Throwing off the Mound). Once a pitcher completes Phase 1 without pain or complications, he is ready to begin throwing off the mound. The same principle remains in Phase 2: pitchers must complete each step pain-free before advancing to the next stage. Pitchers should first throw fastballs at 50% effort and progress to 75% and 100% effort. Because athletes often find it difficult to gauge their own effort, it is important to emphasize the importance of strictly adhering to the program. Fleisig and colleagues¹³ studied healthy pitchers’ ability to estimate their throwing effort. When targeting 50% effort, athletes generated ball speeds of 85% with forces and torque approaching 75% of maximum. A radar gun may be valuable in guiding effort control.

As the player advances through Phase 2, he will increase the volume of pitches as well as the effort in a gradual manner. The player may introduce breaking ball pitches once he demonstrates the ability to throw light batting practice. Phase 2 concludes with the pitcher throwing simulated games, progressing by 15 throws per workout.

Hitting

Biomechanics Overview

The mechanics of hitting a baseball can be broken down into 6 phases: the preparatory phase, stance phase, stride phase, drive phase, bat acceleration phase, and follow-through phase.¹⁴ While progressing through a return-to-play protocol, it is important to understand and teach the player proper swing mechanics during each phase in order to minimize the risk of re-injury (Figure 2).

The preparatory phase occurs as the player positions himself into the batter’s box. This phase is highly individualized, depending on each player’s personal preference. Though significant variability in approach exists, there are 3 basic stances a player can take in preparation to bat. In the closed stance, the batter’s front foot is positioned closer to the plate than the back foot. A more popular stance is the open stance, where the player’s back foot is placed closer to the plate than the front foot. The square batting stance is the most common stance. This stance is where both feet are in line with the pitcher and parallel with the edge of the batter’s box. Most authors agree that the square stance is the optimal position because it provides batters the best opportunity to hit pitches anywhere in the strike zone and limits compensatory or extra motion to their swing.¹⁵

Once the player begins the swing, he has entered the loading period, which is divided into the stance, stride, and drive phases. The loading period, also known as coiling or triggering, begins as the athlete eccentrically stretches agonist muscles and rotates the body away from the incoming ball. The elastic energy stored during this stretching is released during the concentric contraction of the same muscles and transferred through the entire kinetic chain as different segments of the body are rotated; it culminates in effort directed at hitting the baseball.¹⁶

In each phase of the loading period, certain critical motions should be monitored and corrected in order to return the player to his previous level of competition. Stride length has been shown to be critical in the timing of a batter’s swing. A short stride length can cause early initiation of the swing, while a longer stride can produce delayed activation of hip rotation. As the player enters the drive phase, he should have increased elbow flexion in the back elbow compared to the front elbow. The bat should be placed at a position approximately 45° in the frontal plane, and the bat should bisect the batter’s helmet. The back elbow should be down, both upper extremities should be positioned close to the hitter’s body, and the proximal interphalangeal joints of the hands should align on the handle of the bat. Athletic trainers and coaches should be aware that subtle compensations due to deficits during these movements could cause injury during the swing by disrupting the body’s natural motion.

The bat acceleration phase occurs from maximal bat loading through striking the ball. In this time, the linear force that has been exerted by the player must be transferred into rotational force through the trunk and upper extremities. When the lead leg contacts the ground, the player has created a closed kinetic chain, where the elastic energy gathered during the loading period is used to produce segmental rotation beginning in the hips and rising through the trunk and out to the arms and hands, finally producing contact with the baseball.¹⁶ To produce effective bat velocity, each segment must rotate in a sequential manner. If the upper extremities reach peak velocity before any lower segment, then the player has lost the ability to efficiently transfer kinetic energy up the kinetic chain.

Finally, the follow-through phase occurs after contact with the baseball and ends with complete deceleration, completing the swing. In order to achieve optimal effort, full hip rotation is needed, which is aided by rotation of the trail foot. Both hips and back laces should face the pitcher upon completion of the swing producing maximum power output.¹⁵

Return to Hitting: Principles

As with the initiation of the ITP, an interval hitting protocol (IHP) is designed to begin only after the player has been assessed on impairment measures, physical performance measures, and self-assessment.¹⁷ The player should have minimum to no pain, have no tenderness to palpation, and show adequate range of motion and strength to meet the demands of performing a full hitting cycle.¹² It is recommended that before beginning a return-to-play protocol, the involved extremity should be at least 80% as strong as the uninvolved extremity.¹⁸ Physical measures challenging an athlete’s ability to perform tasks specific to hitting a baseball must also be considered through standardized examinations of the involved area.¹⁹ Finally, the athlete’s self-perception of functional abilities must be taken into account. This gives a subjective account of what the hitter perceives they are able to perform, providing useful insight into whether they are mentally prepared to participate in the protocol.

Like the ITP, progression through the IHP is also based on the player’s level of pain and soreness rather than following a specific timetable (Table). The program features a 1 day on, 1 day off schedule during which the player completes 1 step per day. The athlete must remain pain-free to progress to the next step and monitor his level of soreness during their workout. If pain or soreness persists, the player should rest for 2 days and be reevaluated upon return.¹⁷

The same principles of proper warm-up and mechanics apply in the IHP. An athlete should jog or cycle for a minimum of 10 minutes and perform stretching exercises focused on both upper and lower extremity muscles, as batting involves whole body movement. As the athlete progresses through the IHP, having a hitting coach to analyze, correct and maintain proper swing mechanics is valuable in enhancing performance as well as decreasing risk of re-injury.

The Interval Hitting Program

For a PDF patient handout that summarizes the phases of this program, see Appendix 2.

Phase 1 (Dry Swings). Only the most basic fundamentals are stressed during this phase. The player should focus on properly moving from one phase of the swing to the next, without the goal of hitting the baseball. Trainers should measure critical points in the swing and correct deficits early.

Phase 2 (Batting Off a Tee). In this phase, the player is reintroduced to batting at low intensity with a fixed position target. The initial steps have the batter swing in a position of greatest comfort and natural movement, while the final steps in this phase test the athlete’s range of motion and confidence in the previous, healed injury.

Phase 3 (Soft Toss). As the player progresses to this phase, a baseball with trajectory is used to simulate differences in placement of pitches used during a game. As the hitter is able to pick up differences in target position, his performance and confidence should both increase.²⁰ The coach should sit about 30 feet away, facing the hitter at an angle of 45°, and toss the ball in an underhand motion.

Phase 4 (Simulated Hitting). In this phase, the player and coach should focus on the timing of sequential body movements in order to elicit proper loading and force production. With the randomized pitch delivery and increased velocity, the hitter will practice against pitches similar to those delivered in competition.

Conclusion

Interval throwing and hitting programs are designed to allow the athlete to return to competition through a gradual, stepwise program. This permits the player to prepare his body for the unique stresses associated with throwing and hitting. The medical personnel should familiarize themselves with the philosophy of the interval throwing and hitting programs and individualize them to each athlete. Emphasis on proper warm-up, mechanics, and effort control is paramount in expediting return to play while preventing re-injury.

Major league baseball (MLB) is one of the most popular sports in the United States, with an average annual viewership of 11 million for the All-Star game and almost 14 million for the World Series.¹ MLB has an average annual revenue of almost $10 billion, while the net worth of all 30 MLB teams combined is estimated at $36 billion; an increase of 48% from 1 year ago.² As the sport continues to grow in popularity and receives more social media coverage, several issues, specifically injuries to its players, have come to the forefront of the news. Injuries to MLB players, specifically pitchers, have become a significant concern in recent years. The active and extended rosters in MLB include 750 and 1200 athletes, respectively, with approximately 360 active spots taken up by pitchers.³ Hence, MLB employs a large number of elite athletes within its organization. It is important to understand not only what injuries are occurring in these athletes, but also how these injuries may be prevented.

Epidemiology

Injuries to MLB players, specifically pitchers, have increased over the past several years.⁴ Between 2005 and 2008, there was an overall increase of 37% in total number of injuries, with more injuries occurring in pitchers than any other position.⁵ While position players are more likely to sustain an injury to the lower extremity, pitchers are more likely to sustain an injury to the upper extremity.⁵ The month with the most injuries to MLB players was April, while the fewest number of injuries occurred in September.⁵ One injury that has been in the spotlight due to its dramatically increasing incidence is tear of the ulnar collateral ligament (UCL). Several studies have shown that the number of pitchers undergoing ulnar collateral ligament reconstruction (UCLR), commonly known as Tommy John surgery, has significantly increased over the past 20 years (Figure 1).^4,6 Between 25% to 33% of all MLB pitchers have undergone UCLR.

While the number of primary UCLR in MLB pitchers has become a significant concern, an even more pressing concern is the number of pitchers undergoing revision UCLR, as this number has increased over the past several years.⁷ Currently, there is some debate as to how to best address the UCL during primary UCLR (graft type, exposure, treatment of the ulnar nerve, and graft fixation methods) because no study has shown one fixation method or graft type to be superior to others. Similarly, no study has definitively proven how to best manage the ulnar nerve (transpose in all patients, only transpose if preoperative symptoms of numbness/tingling, subluxation, etc. exist). Unfortunately, the results following revision UCLR are inferior to those following primary UCLR.^4,7,8 Hence, given this information, it is imperative to both determine and implement strategies aimed at minimizing the need for revision.

Risk Factors for Injury

Although MLB has received more media attention than lower levels of baseball competition, there is relatively sparse evidence surrounding injury risk factors among MLB players. The majority of studies performed have evaluated risk factors for injury in younger baseball athletes (adolescent, high school, and college). The number of athletes at these lower levels sustaining injuries has increased over the past several years as well.⁹ Several large prospective studies have evaluated risk factors for shoulder and elbow injuries in adolescent baseball players. The risk factors include pitching year-round, pitching more than 100 innings per year, high pitch counts, pitching for multiple teams, geography, pitching on consecutive days, pitching while fatigued, breaking pitches, higher elbow valgus torque, pitching with higher velocity, pitching with supraspinatus weakness, and pitching with a glenohumeral internal rotation deficit (GIRD).^10-17 The large majority of these risk factors are essentially part of a pitcher’s cumulative work, which consists of number of games pitched, total pitches thrown, total innings pitched, innings pitched per game, and pitches thrown per game. One prior study has evaluated cumulative work as a predictor for injury in MLB pitchers.¹⁸ While there were several issues with the study methodology, the authors found no correlation between a MLB pitcher’s cumulative work and risk for injury.

Given our current understanding of repetitive microtrauma as the pathophysiology behind these injuries, it remains unclear why cumulative work would be predictive of injury in youth pitchers but not in MLB pitchers.¹⁶ Several potential reasons exist as to why cumulative work may relate to risk of injury in youth pitchers and not MLB pitchers. Achieving MLB status may infer the element of natural selection based on technique and talent that supersedes the effect of “cumulative trauma” in many players. In MLB pitchers, cumulative work is closely monitored. In addition, these players are only playing for a single team and are not pitching competitively year-round, while many youth players play for multiple teams and may pitch year-round. To combat youth injuries, MLB Pitch Smart has developed recommendations on pitch counts and days of rest for pitchers of all age groups (Table).¹⁹ While data do not yet exist to clearly demonstrate the effectiveness of these guidelines, given the risk factors previously mentioned, it seems that these recommendations will show some reduction in youth injuries in years to come.

Some studies have evaluated anatomic variation among pitchers as a risk factor for injury. Polster and colleagues²⁰ performed computed tomography (CT) scans with 3-dimensional reconstructions on the humeri of both the throwing and non-throwing arms of 25 MLB pitchers to determine if humeral torsion was related to the incidence and severity of upper extremity injuries in these athletes. The authors defined a severe injury as those which kept the player out for >30 days. Overall, 11 pitchers were injured during the 2-year study period. There was a strong inverse relationship between torsion and injury severity such that lower degrees of dominant humeral torsion correlated with higher injury severity (P = .005). However, neither throwing arm humeral torsion nor the difference in torsion between throwing and non-throwing humeri were predictive of overall injury incidence. While this is a nonmodifiable risk factor, it is important to understand how the pitcher’s anatomy plays a role in risk of injury.²⁰ Understanding nonmodifiable risk factors may be helpful in the future to risk stratify, prognosticate, and modulate modifiable risk factors such as cumulative work.

Elbow

Injuries to the elbow have become more common in recent years amongst MLB players, although the literature regarding risk factors for elbow injuries is sparse.^4,6 Wilk and colleagues²¹ performed a prospective study to determine if deficits in glenohumeral passive range of motion (ROM) increased the risk of elbow injury in MLB pitchers. Between 2005-2012, the authors measured passive shoulder ROM of both the throwing and non-throwing shoulder of 296 major and minor league pitchers and followed them for a median of 53.4 months. In total, 38 players suffered 49 elbow injuries and required 8 surgeries, accounting for a total of 2551 days spent on the disabled list (DL). GIRD and external rotation insufficiency were not correlated with elbow injuries. However, pitchers with deficits of >5° in total rotation between the throwing and non-throwing shoulders had a 2.6 times greater risk for injury (P = .007) and pitchers with deficits of ≥5° in flexion of the throwing shoulder compared to the non-throwing shoulder had a 2.8 times greater risk for injury (P = .008).²¹ Prior studies have demonstrated trends towards increased elbow injury in professional baseball pitchers with an increase in both elbow valgus torque as well as shoulder external rotation torque; maximum pitch velocity was also shown to be an independent risk factor for elbow injury in professional baseball pitchers.^10,11 These injuries typically occur during the late cocking/early acceleration phase of the pitching cycle, when the shoulder and elbow experience the most significant force of any point in time during a pitch (Figure 2).¹⁷ At our institution, there are several ongoing studies to determine the relative contributions of pitch velocity, number, and type to elbow injury rates. Prospective studies are also ongoing at other institutions.

Shoulder

Shoulder injuries are one of the most common injuries seen in MLB players, specifically pitchers. Similar to the prior study, Wilk and colleagues²² recently performed a prospective study to determine if passive ROM of the glenohumeral joint in MLB pitchers was predictive of shoulder injury or shoulder surgery. As in the previous study, the authors’ measured passive shoulder ROM of the throwing and non-throwing shoulder of 296 major and minor league pitchers during spring training between 2005-2012 and obtained an average follow-up of 48.4 months. The authors found a total of 75 shoulder injuries and 20 surgeries among 51 pitchers (17%) that resulted in 5570 days on the DL. While total rotation deficit, GIRD, and flexion deficit had no relation to shoulder injury or surgery, pitchers with <5° greater external rotation in the throwing shoulder compared to the non-throwing shoulder were more than 2 times more likely to be placed on the DL for a shoulder injury (P = .014) and were 4 times more likely to require shoulder surgery (P = .009).²² The authors concluded that an insufficient side-to-side difference in external rotation of the throwing shoulder increased a pitcher’s likelihood of shoulder injury as well as surgery.

Other

One area that has not received as much attention as repetitive use injuries of the shoulder and elbow is acute collision injuries. Collision injuries include concussions, hyperextension injuries to the knees, shoulder dislocations, fractures of the foot and ankle, and others.²³ Catchers and base runners during scoring plays are at a high risk for collision injury. Recent evidence has shown that catchers average approximately 2.75 collision injuries per 1000 athletic exposures (AE), accounting for an average of 39.1 days on the DL per collision injury.²³ However, despite these collision injuries, catchers spend more time on the DL from non-collision injuries (specifically shoulder injuries requiring surgical intervention), as studies have shown 19 different non-collision injuries that accounted for >100 days on the DL for catchers compared to no collision injuries that caused a catcher to be on the DL for >100 days.²³ The position of catcher is not an independent risk factor for sustaining an injury in MLB players.⁵

Preventative Measures

Given that recent evidence has identified certain modifiable risk factors, largely regarding shoulder ROM, for injuries to MLB pitchers, it stands to reason that by modifying these risk factors, the number of injuries to MLB pitchers can be decreased.^21,22 However, to the authors’ knowledge, there have been no studies in the current literature that have clearly demonstrated the ability to prevent injuries in MLB players. Based on the prior studies, it seems logical that lowering peak pitch velocity and ensuring proper shoulder ROM would help prevent injuries in MLB players, but this remains speculative. Stretching techniques that have been shown to increase posterior shoulder soft tissue flexibility, including sleeper stretches and modified cross-body stretches, as well as closely monitoring ROM may be helpful in modifying these risk factors.^24-26

Although the number of collision injuries is significantly lower than non-collision repetitive use injuries, MLB has implemented rule changes in recent years to prevent injuries to catchers and base runners alike.^23,27 The rule change, which went into effect in 2014, prohibits catchers from blocking home plate unless they are actively fielding the ball or are in possession of the ball. Similarly, base runners are not allowed to deviate from their path to collide with the catcher while attempting to score.²⁷ However, no study has analyzed whether this rule change has decreased the number of collision injuries sustained by MLB catchers, so it is unclear if this rule change has accomplished its goal.

Outcomes Following Injuries

One of the driving forces behind injury prevention in MLB players is to allow players to reach and maintain their full potential while minimizing time missed because of injury. Furthermore, as with any sport, the clinical outcomes and return to sport (RTS) rates for MLB players following injuries, especially injuries requiring surgical intervention, can be improved.^4,28,29 Several studies have evaluated MLB pitchers following UCLR and have shown that over 80% of pitchers are able to RTS following surgery.^4,30 When critically evaluated in multiple statistical parameters upon RTS, these players perform better in some areas and worse in others.^4,30 However, the results following revision UCLR are not as encouraging as those following primary UCLR in MLB pitchers.⁷ Following revision UCLR, only 65% of pitchers were able to RTS, and those who were able to RTS pitched, on average, almost 1 year less than matched controls.⁷ Unfortunately, results following surgeries about the shoulder in MLB players have been worse than those about the elbow. Cohen and colleagues28 reported on 22 MLB players who underwent labral repair of the shoulder and found that only 32% were able to return to the same or higher level following surgery, while over 45% retired from baseball following surgery. Hence, it is imperative these injuries are prevented, as the RTS rate following treatment is less than ideal.

Future Directions

Although a concerted effort has been made over the past several years to mitigate the number of injuries sustained by MLB players, there is still significant room for improvement. New products are in development/early stages of use that attempt to determine when a pitcher begins to show signs of fatigue to allow the coach to remove him from the game. The mTHROW sleeve (Motus Global), currently used by several MLB teams, is an elastic sleeve that is worn by pitchers on their dominant arm. The sleeve approximates torque, velocity, and workload based upon an accelerometer positioned at the medial elbow and sends this information to a smart phone in real time. This technology theoretically allows players to be intensively monitored and thus may prevent injuries to the UCL by preventing pitchers from throwing while fatigued. However, elbow kinematic parameters may not change significantly as pitchers fatigue, which suggests that this strategy may be suboptimal. Trunk mechanics do change as pitchers become fatigued, opening up the possibility for shoulder and elbow injury.^17,31,32 Further products that track hip-to-shoulder separation and trunk fatigue may be necessary to truly lower injury rates. However, no study has proven modifying either parameter leads to a decrease in injury rates.

Conclusion

Injuries to MLB pitchers and position players have become a significant concern over the past several years. Several risk factors for injury have been identified, including loss of shoulder ROM and pitch velocity. Further studies are necessary to determine the effectiveness of modifying these parameters on injury prevention.

Major league baseball (MLB) is one of the most popular sports in the United States, with an average annual viewership of 11 million for the All-Star game and almost 14 million for the World Series.¹ MLB has an average annual revenue of almost $10 billion, while the net worth of all 30 MLB teams combined is estimated at $36 billion; an increase of 48% from 1 year ago.² As the sport continues to grow in popularity and receives more social media coverage, several issues, specifically injuries to its players, have come to the forefront of the news. Injuries to MLB players, specifically pitchers, have become a significant concern in recent years. The active and extended rosters in MLB include 750 and 1200 athletes, respectively, with approximately 360 active spots taken up by pitchers.³ Hence, MLB employs a large number of elite athletes within its organization. It is important to understand not only what injuries are occurring in these athletes, but also how these injuries may be prevented.

Epidemiology

Injuries to MLB players, specifically pitchers, have increased over the past several years.⁴ Between 2005 and 2008, there was an overall increase of 37% in total number of injuries, with more injuries occurring in pitchers than any other position.⁵ While position players are more likely to sustain an injury to the lower extremity, pitchers are more likely to sustain an injury to the upper extremity.⁵ The month with the most injuries to MLB players was April, while the fewest number of injuries occurred in September.⁵ One injury that has been in the spotlight due to its dramatically increasing incidence is tear of the ulnar collateral ligament (UCL). Several studies have shown that the number of pitchers undergoing ulnar collateral ligament reconstruction (UCLR), commonly known as Tommy John surgery, has significantly increased over the past 20 years (Figure 1).^4,6 Between 25% to 33% of all MLB pitchers have undergone UCLR.

While the number of primary UCLR in MLB pitchers has become a significant concern, an even more pressing concern is the number of pitchers undergoing revision UCLR, as this number has increased over the past several years.⁷ Currently, there is some debate as to how to best address the UCL during primary UCLR (graft type, exposure, treatment of the ulnar nerve, and graft fixation methods) because no study has shown one fixation method or graft type to be superior to others. Similarly, no study has definitively proven how to best manage the ulnar nerve (transpose in all patients, only transpose if preoperative symptoms of numbness/tingling, subluxation, etc. exist). Unfortunately, the results following revision UCLR are inferior to those following primary UCLR.^4,7,8 Hence, given this information, it is imperative to both determine and implement strategies aimed at minimizing the need for revision.

Risk Factors for Injury

Although MLB has received more media attention than lower levels of baseball competition, there is relatively sparse evidence surrounding injury risk factors among MLB players. The majority of studies performed have evaluated risk factors for injury in younger baseball athletes (adolescent, high school, and college). The number of athletes at these lower levels sustaining injuries has increased over the past several years as well.⁹ Several large prospective studies have evaluated risk factors for shoulder and elbow injuries in adolescent baseball players. The risk factors include pitching year-round, pitching more than 100 innings per year, high pitch counts, pitching for multiple teams, geography, pitching on consecutive days, pitching while fatigued, breaking pitches, higher elbow valgus torque, pitching with higher velocity, pitching with supraspinatus weakness, and pitching with a glenohumeral internal rotation deficit (GIRD).^10-17 The large majority of these risk factors are essentially part of a pitcher’s cumulative work, which consists of number of games pitched, total pitches thrown, total innings pitched, innings pitched per game, and pitches thrown per game. One prior study has evaluated cumulative work as a predictor for injury in MLB pitchers.¹⁸ While there were several issues with the study methodology, the authors found no correlation between a MLB pitcher’s cumulative work and risk for injury.

Given our current understanding of repetitive microtrauma as the pathophysiology behind these injuries, it remains unclear why cumulative work would be predictive of injury in youth pitchers but not in MLB pitchers.¹⁶ Several potential reasons exist as to why cumulative work may relate to risk of injury in youth pitchers and not MLB pitchers. Achieving MLB status may infer the element of natural selection based on technique and talent that supersedes the effect of “cumulative trauma” in many players. In MLB pitchers, cumulative work is closely monitored. In addition, these players are only playing for a single team and are not pitching competitively year-round, while many youth players play for multiple teams and may pitch year-round. To combat youth injuries, MLB Pitch Smart has developed recommendations on pitch counts and days of rest for pitchers of all age groups (Table).¹⁹ While data do not yet exist to clearly demonstrate the effectiveness of these guidelines, given the risk factors previously mentioned, it seems that these recommendations will show some reduction in youth injuries in years to come.

Some studies have evaluated anatomic variation among pitchers as a risk factor for injury. Polster and colleagues²⁰ performed computed tomography (CT) scans with 3-dimensional reconstructions on the humeri of both the throwing and non-throwing arms of 25 MLB pitchers to determine if humeral torsion was related to the incidence and severity of upper extremity injuries in these athletes. The authors defined a severe injury as those which kept the player out for >30 days. Overall, 11 pitchers were injured during the 2-year study period. There was a strong inverse relationship between torsion and injury severity such that lower degrees of dominant humeral torsion correlated with higher injury severity (P = .005). However, neither throwing arm humeral torsion nor the difference in torsion between throwing and non-throwing humeri were predictive of overall injury incidence. While this is a nonmodifiable risk factor, it is important to understand how the pitcher’s anatomy plays a role in risk of injury.²⁰ Understanding nonmodifiable risk factors may be helpful in the future to risk stratify, prognosticate, and modulate modifiable risk factors such as cumulative work.

Elbow

Injuries to the elbow have become more common in recent years amongst MLB players, although the literature regarding risk factors for elbow injuries is sparse.^4,6 Wilk and colleagues²¹ performed a prospective study to determine if deficits in glenohumeral passive range of motion (ROM) increased the risk of elbow injury in MLB pitchers. Between 2005-2012, the authors measured passive shoulder ROM of both the throwing and non-throwing shoulder of 296 major and minor league pitchers and followed them for a median of 53.4 months. In total, 38 players suffered 49 elbow injuries and required 8 surgeries, accounting for a total of 2551 days spent on the disabled list (DL). GIRD and external rotation insufficiency were not correlated with elbow injuries. However, pitchers with deficits of >5° in total rotation between the throwing and non-throwing shoulders had a 2.6 times greater risk for injury (P = .007) and pitchers with deficits of ≥5° in flexion of the throwing shoulder compared to the non-throwing shoulder had a 2.8 times greater risk for injury (P = .008).²¹ Prior studies have demonstrated trends towards increased elbow injury in professional baseball pitchers with an increase in both elbow valgus torque as well as shoulder external rotation torque; maximum pitch velocity was also shown to be an independent risk factor for elbow injury in professional baseball pitchers.^10,11 These injuries typically occur during the late cocking/early acceleration phase of the pitching cycle, when the shoulder and elbow experience the most significant force of any point in time during a pitch (Figure 2).¹⁷ At our institution, there are several ongoing studies to determine the relative contributions of pitch velocity, number, and type to elbow injury rates. Prospective studies are also ongoing at other institutions.

Shoulder

Shoulder injuries are one of the most common injuries seen in MLB players, specifically pitchers. Similar to the prior study, Wilk and colleagues²² recently performed a prospective study to determine if passive ROM of the glenohumeral joint in MLB pitchers was predictive of shoulder injury or shoulder surgery. As in the previous study, the authors’ measured passive shoulder ROM of the throwing and non-throwing shoulder of 296 major and minor league pitchers during spring training between 2005-2012 and obtained an average follow-up of 48.4 months. The authors found a total of 75 shoulder injuries and 20 surgeries among 51 pitchers (17%) that resulted in 5570 days on the DL. While total rotation deficit, GIRD, and flexion deficit had no relation to shoulder injury or surgery, pitchers with <5° greater external rotation in the throwing shoulder compared to the non-throwing shoulder were more than 2 times more likely to be placed on the DL for a shoulder injury (P = .014) and were 4 times more likely to require shoulder surgery (P = .009).²² The authors concluded that an insufficient side-to-side difference in external rotation of the throwing shoulder increased a pitcher’s likelihood of shoulder injury as well as surgery.

Other

One area that has not received as much attention as repetitive use injuries of the shoulder and elbow is acute collision injuries. Collision injuries include concussions, hyperextension injuries to the knees, shoulder dislocations, fractures of the foot and ankle, and others.²³ Catchers and base runners during scoring plays are at a high risk for collision injury. Recent evidence has shown that catchers average approximately 2.75 collision injuries per 1000 athletic exposures (AE), accounting for an average of 39.1 days on the DL per collision injury.²³ However, despite these collision injuries, catchers spend more time on the DL from non-collision injuries (specifically shoulder injuries requiring surgical intervention), as studies have shown 19 different non-collision injuries that accounted for >100 days on the DL for catchers compared to no collision injuries that caused a catcher to be on the DL for >100 days.²³ The position of catcher is not an independent risk factor for sustaining an injury in MLB players.⁵

Preventative Measures

Given that recent evidence has identified certain modifiable risk factors, largely regarding shoulder ROM, for injuries to MLB pitchers, it stands to reason that by modifying these risk factors, the number of injuries to MLB pitchers can be decreased.^21,22 However, to the authors’ knowledge, there have been no studies in the current literature that have clearly demonstrated the ability to prevent injuries in MLB players. Based on the prior studies, it seems logical that lowering peak pitch velocity and ensuring proper shoulder ROM would help prevent injuries in MLB players, but this remains speculative. Stretching techniques that have been shown to increase posterior shoulder soft tissue flexibility, including sleeper stretches and modified cross-body stretches, as well as closely monitoring ROM may be helpful in modifying these risk factors.^24-26

Although the number of collision injuries is significantly lower than non-collision repetitive use injuries, MLB has implemented rule changes in recent years to prevent injuries to catchers and base runners alike.^23,27 The rule change, which went into effect in 2014, prohibits catchers from blocking home plate unless they are actively fielding the ball or are in possession of the ball. Similarly, base runners are not allowed to deviate from their path to collide with the catcher while attempting to score.²⁷ However, no study has analyzed whether this rule change has decreased the number of collision injuries sustained by MLB catchers, so it is unclear if this rule change has accomplished its goal.

Outcomes Following Injuries

One of the driving forces behind injury prevention in MLB players is to allow players to reach and maintain their full potential while minimizing time missed because of injury. Furthermore, as with any sport, the clinical outcomes and return to sport (RTS) rates for MLB players following injuries, especially injuries requiring surgical intervention, can be improved.^4,28,29 Several studies have evaluated MLB pitchers following UCLR and have shown that over 80% of pitchers are able to RTS following surgery.^4,30 When critically evaluated in multiple statistical parameters upon RTS, these players perform better in some areas and worse in others.^4,30 However, the results following revision UCLR are not as encouraging as those following primary UCLR in MLB pitchers.⁷ Following revision UCLR, only 65% of pitchers were able to RTS, and those who were able to RTS pitched, on average, almost 1 year less than matched controls.⁷ Unfortunately, results following surgeries about the shoulder in MLB players have been worse than those about the elbow. Cohen and colleagues28 reported on 22 MLB players who underwent labral repair of the shoulder and found that only 32% were able to return to the same or higher level following surgery, while over 45% retired from baseball following surgery. Hence, it is imperative these injuries are prevented, as the RTS rate following treatment is less than ideal.

Future Directions

Although a concerted effort has been made over the past several years to mitigate the number of injuries sustained by MLB players, there is still significant room for improvement. New products are in development/early stages of use that attempt to determine when a pitcher begins to show signs of fatigue to allow the coach to remove him from the game. The mTHROW sleeve (Motus Global), currently used by several MLB teams, is an elastic sleeve that is worn by pitchers on their dominant arm. The sleeve approximates torque, velocity, and workload based upon an accelerometer positioned at the medial elbow and sends this information to a smart phone in real time. This technology theoretically allows players to be intensively monitored and thus may prevent injuries to the UCL by preventing pitchers from throwing while fatigued. However, elbow kinematic parameters may not change significantly as pitchers fatigue, which suggests that this strategy may be suboptimal. Trunk mechanics do change as pitchers become fatigued, opening up the possibility for shoulder and elbow injury.^17,31,32 Further products that track hip-to-shoulder separation and trunk fatigue may be necessary to truly lower injury rates. However, no study has proven modifying either parameter leads to a decrease in injury rates.

Conclusion

Injuries to MLB pitchers and position players have become a significant concern over the past several years. Several risk factors for injury have been identified, including loss of shoulder ROM and pitch velocity. Further studies are necessary to determine the effectiveness of modifying these parameters on injury prevention.

Major league baseball (MLB) is one of the most popular sports in the United States, with an average annual viewership of 11 million for the All-Star game and almost 14 million for the World Series.¹ MLB has an average annual revenue of almost $10 billion, while the net worth of all 30 MLB teams combined is estimated at $36 billion; an increase of 48% from 1 year ago.² As the sport continues to grow in popularity and receives more social media coverage, several issues, specifically injuries to its players, have come to the forefront of the news. Injuries to MLB players, specifically pitchers, have become a significant concern in recent years. The active and extended rosters in MLB include 750 and 1200 athletes, respectively, with approximately 360 active spots taken up by pitchers.³ Hence, MLB employs a large number of elite athletes within its organization. It is important to understand not only what injuries are occurring in these athletes, but also how these injuries may be prevented.

Epidemiology

Injuries to MLB players, specifically pitchers, have increased over the past several years.⁴ Between 2005 and 2008, there was an overall increase of 37% in total number of injuries, with more injuries occurring in pitchers than any other position.⁵ While position players are more likely to sustain an injury to the lower extremity, pitchers are more likely to sustain an injury to the upper extremity.⁵ The month with the most injuries to MLB players was April, while the fewest number of injuries occurred in September.⁵ One injury that has been in the spotlight due to its dramatically increasing incidence is tear of the ulnar collateral ligament (UCL). Several studies have shown that the number of pitchers undergoing ulnar collateral ligament reconstruction (UCLR), commonly known as Tommy John surgery, has significantly increased over the past 20 years (Figure 1).^4,6 Between 25% to 33% of all MLB pitchers have undergone UCLR.

While the number of primary UCLR in MLB pitchers has become a significant concern, an even more pressing concern is the number of pitchers undergoing revision UCLR, as this number has increased over the past several years.⁷ Currently, there is some debate as to how to best address the UCL during primary UCLR (graft type, exposure, treatment of the ulnar nerve, and graft fixation methods) because no study has shown one fixation method or graft type to be superior to others. Similarly, no study has definitively proven how to best manage the ulnar nerve (transpose in all patients, only transpose if preoperative symptoms of numbness/tingling, subluxation, etc. exist). Unfortunately, the results following revision UCLR are inferior to those following primary UCLR.^4,7,8 Hence, given this information, it is imperative to both determine and implement strategies aimed at minimizing the need for revision.

Risk Factors for Injury

Although MLB has received more media attention than lower levels of baseball competition, there is relatively sparse evidence surrounding injury risk factors among MLB players. The majority of studies performed have evaluated risk factors for injury in younger baseball athletes (adolescent, high school, and college). The number of athletes at these lower levels sustaining injuries has increased over the past several years as well.⁹ Several large prospective studies have evaluated risk factors for shoulder and elbow injuries in adolescent baseball players. The risk factors include pitching year-round, pitching more than 100 innings per year, high pitch counts, pitching for multiple teams, geography, pitching on consecutive days, pitching while fatigued, breaking pitches, higher elbow valgus torque, pitching with higher velocity, pitching with supraspinatus weakness, and pitching with a glenohumeral internal rotation deficit (GIRD).^10-17 The large majority of these risk factors are essentially part of a pitcher’s cumulative work, which consists of number of games pitched, total pitches thrown, total innings pitched, innings pitched per game, and pitches thrown per game. One prior study has evaluated cumulative work as a predictor for injury in MLB pitchers.¹⁸ While there were several issues with the study methodology, the authors found no correlation between a MLB pitcher’s cumulative work and risk for injury.

Given our current understanding of repetitive microtrauma as the pathophysiology behind these injuries, it remains unclear why cumulative work would be predictive of injury in youth pitchers but not in MLB pitchers.¹⁶ Several potential reasons exist as to why cumulative work may relate to risk of injury in youth pitchers and not MLB pitchers. Achieving MLB status may infer the element of natural selection based on technique and talent that supersedes the effect of “cumulative trauma” in many players. In MLB pitchers, cumulative work is closely monitored. In addition, these players are only playing for a single team and are not pitching competitively year-round, while many youth players play for multiple teams and may pitch year-round. To combat youth injuries, MLB Pitch Smart has developed recommendations on pitch counts and days of rest for pitchers of all age groups (Table).¹⁹ While data do not yet exist to clearly demonstrate the effectiveness of these guidelines, given the risk factors previously mentioned, it seems that these recommendations will show some reduction in youth injuries in years to come.

Some studies have evaluated anatomic variation among pitchers as a risk factor for injury. Polster and colleagues²⁰ performed computed tomography (CT) scans with 3-dimensional reconstructions on the humeri of both the throwing and non-throwing arms of 25 MLB pitchers to determine if humeral torsion was related to the incidence and severity of upper extremity injuries in these athletes. The authors defined a severe injury as those which kept the player out for >30 days. Overall, 11 pitchers were injured during the 2-year study period. There was a strong inverse relationship between torsion and injury severity such that lower degrees of dominant humeral torsion correlated with higher injury severity (P = .005). However, neither throwing arm humeral torsion nor the difference in torsion between throwing and non-throwing humeri were predictive of overall injury incidence. While this is a nonmodifiable risk factor, it is important to understand how the pitcher’s anatomy plays a role in risk of injury.²⁰ Understanding nonmodifiable risk factors may be helpful in the future to risk stratify, prognosticate, and modulate modifiable risk factors such as cumulative work.

Elbow

Injuries to the elbow have become more common in recent years amongst MLB players, although the literature regarding risk factors for elbow injuries is sparse.^4,6 Wilk and colleagues²¹ performed a prospective study to determine if deficits in glenohumeral passive range of motion (ROM) increased the risk of elbow injury in MLB pitchers. Between 2005-2012, the authors measured passive shoulder ROM of both the throwing and non-throwing shoulder of 296 major and minor league pitchers and followed them for a median of 53.4 months. In total, 38 players suffered 49 elbow injuries and required 8 surgeries, accounting for a total of 2551 days spent on the disabled list (DL). GIRD and external rotation insufficiency were not correlated with elbow injuries. However, pitchers with deficits of >5° in total rotation between the throwing and non-throwing shoulders had a 2.6 times greater risk for injury (P = .007) and pitchers with deficits of ≥5° in flexion of the throwing shoulder compared to the non-throwing shoulder had a 2.8 times greater risk for injury (P = .008).²¹ Prior studies have demonstrated trends towards increased elbow injury in professional baseball pitchers with an increase in both elbow valgus torque as well as shoulder external rotation torque; maximum pitch velocity was also shown to be an independent risk factor for elbow injury in professional baseball pitchers.^10,11 These injuries typically occur during the late cocking/early acceleration phase of the pitching cycle, when the shoulder and elbow experience the most significant force of any point in time during a pitch (Figure 2).¹⁷ At our institution, there are several ongoing studies to determine the relative contributions of pitch velocity, number, and type to elbow injury rates. Prospective studies are also ongoing at other institutions.

Shoulder

Shoulder injuries are one of the most common injuries seen in MLB players, specifically pitchers. Similar to the prior study, Wilk and colleagues²² recently performed a prospective study to determine if passive ROM of the glenohumeral joint in MLB pitchers was predictive of shoulder injury or shoulder surgery. As in the previous study, the authors’ measured passive shoulder ROM of the throwing and non-throwing shoulder of 296 major and minor league pitchers during spring training between 2005-2012 and obtained an average follow-up of 48.4 months. The authors found a total of 75 shoulder injuries and 20 surgeries among 51 pitchers (17%) that resulted in 5570 days on the DL. While total rotation deficit, GIRD, and flexion deficit had no relation to shoulder injury or surgery, pitchers with <5° greater external rotation in the throwing shoulder compared to the non-throwing shoulder were more than 2 times more likely to be placed on the DL for a shoulder injury (P = .014) and were 4 times more likely to require shoulder surgery (P = .009).²² The authors concluded that an insufficient side-to-side difference in external rotation of the throwing shoulder increased a pitcher’s likelihood of shoulder injury as well as surgery.

Other

One area that has not received as much attention as repetitive use injuries of the shoulder and elbow is acute collision injuries. Collision injuries include concussions, hyperextension injuries to the knees, shoulder dislocations, fractures of the foot and ankle, and others.²³ Catchers and base runners during scoring plays are at a high risk for collision injury. Recent evidence has shown that catchers average approximately 2.75 collision injuries per 1000 athletic exposures (AE), accounting for an average of 39.1 days on the DL per collision injury.²³ However, despite these collision injuries, catchers spend more time on the DL from non-collision injuries (specifically shoulder injuries requiring surgical intervention), as studies have shown 19 different non-collision injuries that accounted for >100 days on the DL for catchers compared to no collision injuries that caused a catcher to be on the DL for >100 days.²³ The position of catcher is not an independent risk factor for sustaining an injury in MLB players.⁵

Preventative Measures

Given that recent evidence has identified certain modifiable risk factors, largely regarding shoulder ROM, for injuries to MLB pitchers, it stands to reason that by modifying these risk factors, the number of injuries to MLB pitchers can be decreased.^21,22 However, to the authors’ knowledge, there have been no studies in the current literature that have clearly demonstrated the ability to prevent injuries in MLB players. Based on the prior studies, it seems logical that lowering peak pitch velocity and ensuring proper shoulder ROM would help prevent injuries in MLB players, but this remains speculative. Stretching techniques that have been shown to increase posterior shoulder soft tissue flexibility, including sleeper stretches and modified cross-body stretches, as well as closely monitoring ROM may be helpful in modifying these risk factors.^24-26

Although the number of collision injuries is significantly lower than non-collision repetitive use injuries, MLB has implemented rule changes in recent years to prevent injuries to catchers and base runners alike.^23,27 The rule change, which went into effect in 2014, prohibits catchers from blocking home plate unless they are actively fielding the ball or are in possession of the ball. Similarly, base runners are not allowed to deviate from their path to collide with the catcher while attempting to score.²⁷ However, no study has analyzed whether this rule change has decreased the number of collision injuries sustained by MLB catchers, so it is unclear if this rule change has accomplished its goal.

Outcomes Following Injuries

One of the driving forces behind injury prevention in MLB players is to allow players to reach and maintain their full potential while minimizing time missed because of injury. Furthermore, as with any sport, the clinical outcomes and return to sport (RTS) rates for MLB players following injuries, especially injuries requiring surgical intervention, can be improved.^4,28,29 Several studies have evaluated MLB pitchers following UCLR and have shown that over 80% of pitchers are able to RTS following surgery.^4,30 When critically evaluated in multiple statistical parameters upon RTS, these players perform better in some areas and worse in others.^4,30 However, the results following revision UCLR are not as encouraging as those following primary UCLR in MLB pitchers.⁷ Following revision UCLR, only 65% of pitchers were able to RTS, and those who were able to RTS pitched, on average, almost 1 year less than matched controls.⁷ Unfortunately, results following surgeries about the shoulder in MLB players have been worse than those about the elbow. Cohen and colleagues28 reported on 22 MLB players who underwent labral repair of the shoulder and found that only 32% were able to return to the same or higher level following surgery, while over 45% retired from baseball following surgery. Hence, it is imperative these injuries are prevented, as the RTS rate following treatment is less than ideal.

Future Directions

Although a concerted effort has been made over the past several years to mitigate the number of injuries sustained by MLB players, there is still significant room for improvement. New products are in development/early stages of use that attempt to determine when a pitcher begins to show signs of fatigue to allow the coach to remove him from the game. The mTHROW sleeve (Motus Global), currently used by several MLB teams, is an elastic sleeve that is worn by pitchers on their dominant arm. The sleeve approximates torque, velocity, and workload based upon an accelerometer positioned at the medial elbow and sends this information to a smart phone in real time. This technology theoretically allows players to be intensively monitored and thus may prevent injuries to the UCL by preventing pitchers from throwing while fatigued. However, elbow kinematic parameters may not change significantly as pitchers fatigue, which suggests that this strategy may be suboptimal. Trunk mechanics do change as pitchers become fatigued, opening up the possibility for shoulder and elbow injury.^17,31,32 Further products that track hip-to-shoulder separation and trunk fatigue may be necessary to truly lower injury rates. However, no study has proven modifying either parameter leads to a decrease in injury rates.

Conclusion

Injuries to MLB pitchers and position players have become a significant concern over the past several years. Several risk factors for injury have been identified, including loss of shoulder ROM and pitch velocity. Further studies are necessary to determine the effectiveness of modifying these parameters on injury prevention.