User login
Improving Spanning-Knee External Fixator Stiffness: A Biomechanical Study
External fixators are commonly used as a temporizing treatment for periarticular fractures about the knee. Since its inception with a claw used for patellar fractures by Malgaigne in 1853,1 external fixation has evolved to include pin–crossbar constructs. The stiffness of the construct directly affects the rate at which the frames are likely to fail.2 Most external fixation systems have the option for 2 types of pin–bar connectors, pin-to-bar clamps or multipin clamps. The multipin clamps rely on a cluster of multiple pins to connect the longitudinal supports. These clamps use the “bull horn” extensions to connect the pins to bars (Figure 1). The implant manufacturers recommend the use of 2 longitudinal bars when using these clamps. Conversely, single pin-to-bar clamps permit widely spaced pins but multipin clamps do not. Pin-to-bar clamps also tend to allow the longitudinal cross-bars to be placed closer to bone, improving frame stability.1
In the experience of Dr. Reisman, utilization of pin-to-bar clamps has resulted in improved external fixator construct stiffness compared with those using multipin clamps. He has recognized that, in his own practice, a busy level I trauma center where 4 to 5 spanning knee frames are applied daily, fracture stability is improved with the use of pin-to-bar clamps and often with only a single crossbar, resulting in a simpler, low-cost construct. Despite external fixators used for temporary fixation, frames need to be strong enough to maintain fracture length and stabilize the soft-tissue envelope for days to weeks. It is critical that the frame’s stability allows for patient transfers but controls fracture motion until definitive fixation. Despite having both options available in the external fixator set, there are no biomechanical studies that compare the effect of using pin-to-bar clamps or multipin clamps and bull horns on external fixator stiffness.
In this study, we compared the stiffness of 3 different types of spanning knee external fixator configurations, using multi-pin clamps and 2 crossbars, or pin-to-bar clamps with 1 or 2 crossbars. We compared constructs using 2 systems, 1 with 8-mm–diameter and another with 11-mm–diameter crossbars. We hypothesized that constructs assembled with pin-to-bar clamps would have improved bending stiffness compared with constructs using multipin clamps.
Materials and Methods
Three constructs were made under the supervision of Dr. Reisman, a trauma fellowship–trained orthopedic surgeon. The first construct (construct 1) used two 200-mm bars attached to pin-to-bar clamps with a single 450-mm–long spanning bar connecting the 2 segments (Figure 2). The second construct (construct 2) used 2 spanning bars with pin-to-bar clamps. The third construct (construct 3) used multipin clamps proximally and distally with two 450-mm–long spanning bars. Therefore, we tested 2 types of constructs using pin-to-bar clamps and 1 construct with multipin clamps. Four of each construct type were assembled with both 8-mm (Stryker) and 11-mm bars (Synthes), providing 24 testable constructs. For this study, we tested previously used and cleaned external fixation pins, bars, and clamps obtained from our trauma center. All equipment was examined thoroughly for any potential damaged parts.
To simulate the femoral and tibial attachments, two 5-mm–diameter pins were drilled into each of 2 steel cylinders and welded in place. The femoral cylinder (8.3×2.5 cm) had a pin distance of 55 mm, and the tibial cylinder (6.4×2.5 cm) had a pin distance of 32 mm (Figure 3). The pins were welded intosteel cylinders to help prevent any loosening or failure at the pin (ie, metal interface isolating stress to the components). Dr. Desai assembled the constructs and placed them on the cylinders with a distance of 25 mm between the fixator construct and the cylinder, with 306 mm between the femoral and tibial cylinders. The pin diameters, pin spread, pin number, and bar-to-cylinder distance were constant throughout testing with these specifications.
The assembled constructs were tested on a materials testing machine (MTS 858 Mini-Bionix Test System). A compressive force was applied, through a roller, to a flat plate (Figures 4, 5). This allowed the constructs to flex and bend freely without overly stressing the simulated pin-to-bone interface. Using this loading method, we could compare the stiffness of the different assembled constructs. Each assembled construct was tested 4 times sequentially on the MTS machine. There was no pin deformation when the load was applied through the roller to the flat plate, to the cylinder, to the pins, and onto the construct. It was possible to observe that the construct flexed when the load was applied. Load-displacement curves were produced for each test, and the stiffness was calculated from the slope of this curve. Each test was repeated 4 times, and the stiffness was measured from the load-displacement curve each time. The 4 stiffness measurements were averaged for each construct and compared across all constructs, using a Wilcoxon rank sum test for statistical analysis.
Results
Construct Design
Three different construct designs were evaluated using our testing protocol. The mean stiffness differed across all constructs as seen in Figure 6. Of the constructs using the 11-mm–diameter bars, construct 2 had the highest mean stiffness (32.1 +/- 3.7 N/mm), and this stiffness was significantly greater than the mean stiffness for construct 1 (15.3 +/- 1.5 N/mm; P < .05) and construct 3 (18.4 +/- 2.9 N/mm; P< .05). There was no statistically significant difference in stiffness between construct 1 and construct 3.
Of the constructs using 8-mm–diameter bars, construct 2 had the highest mean stiffness (11.5 +/- 2.4 N/mm), and this stiffness was significantly greater than the mean stiffness for construct 1 (5.0 +/- 0.9 N/mm; P < .05). There was no statistically significant difference in stiffness between construct 2 and construct 3 (7.8 +/- 1.9 N/mm) or between construct 1 and construct 3.
Discussion
Although numerous investigators have examined the biomechanical properties of external fixator systems, the effect of pin-to-bar clamps on frame stiffness is unknown. Biomechanical studies have found that uniplanar constructs with multiple bars can provide adequate strength for temporary fixation.3-9 With multiple options within a particular external fixator set, it is ideal to understand the benefit of using one component instead of another.
The main results from this experiment are: (1) constructs with pin-to-bar clamps and 2 crossbars are stiffer than those using multipin clamps and 2 crossbars; (2) constructs with a single crossbar and pin-to-bar clamps are as stiff as constructs using 2 crossbars and multipin clamps.
Figure 6 shows the average stiffness differences between the 8-mm and 11-mm–diameter bar constructs tested in this study. As expected, each 11-mm diameter–bar construct had a higher average stiffness compared with the 8-mm–diameter bar constructs. Across both the 8-mm and 11-mm–diameter bar constructs, construct 2 had a higher stiffness than that of constructs 1 and 3. Furthermore, there was no difference in the stiffness between constructs 1 and 3.
To improve external fixator stiffness, number of pins and optimization of pin spread can improve the strength of the construct.7 When using pin-to-bar clamps, 1 pin should be as close to the fracture as possible, with the second pin as far from the fracture as possible. 7 Multipin clamps, by design, prevent any optimization of pin spread and require a clustered-pin arrangement.
Bar configuration also plays a critical role in construct stiffness. Bar-to-bone distance should be approximately 2 fingerbreadths from the skin to maximize the stiffness of the construct.4,10-14 Multipin clamps use “bull horn” extensions that tend to elevate the bar away from the skin, increasing the distance between the bar and the bone.
A temporary spanning knee external fixator is commonly used for treating high-energy periarticular tibial or femoral fractures. To hold the fracture in an adequately reduced position, the frame must resist the deforming forces inherent with all fractures. A frame that is not adequately stiff will not hold the fracture in the reduced position, even at the time of initial surgery, which negates one of the benefits of placing the patient in the frame. Hence, adequate stiffness of the spanning-knee fixator is critical to the effectiveness of temporary stabilization before permanent fixation.
The results of this study provide evidence for the superiority of pin-to-bar clamps over multipin clamps in optimizing external fixator construct stiffness. At our institution, we almost exclusively use the single pin-to-bar clamps for spanning-knee external fixation. Based on the results of this study, we often use only a single crossbar. The ability to use a single bar greatly reduces the cost of the construct because crossbars can cost from $100 to $150, depending on the manufacturer.
A recent cost analysis of spanning-knee external fixators showed that construct costs can range from $8,000 to $19,000.15 The lower-cost constructs included 2 crossbars while the more expensive constructs had additional bars and multipin clamps. The authors noted that constructs with larger diameter bars and higher overall stiffness resulted in an improved cost per stiffness ratio. The results of this study support our conclusions regarding bar diameter. Additionally, our results show improved stiffness of constructs with pin-to-bar clamps instead of multipin clamps. By limiting the need for an additional bar, using pin-to-bar clamps and a single large diameter crossbar can create a very cost-efficient and rigidly stable construct.
One criticism of this study is the testing of used equipment. All external fixator manufacturers must evaluate and carefully examine any used equipment prior to the resterilization process and potential release to the practitioner for re-use. Our rationale for using used equipment is based on the assumption that the vast majority of patients do not have their external fixators removed because of failure but because of definitive surgical treatment, and the timing of removal does not necessarily follow a predetermined protocol. For example, timing of definitive surgery is usually set by the patient’s general health status, status of the soft tissues, and surgeon availability. Therefore, this equipment was tested with the presumption that the equipment was in the same state as if the patient continued to wear the frame 1 more day. A study testing unused equipment would be the next step in evaluating external fixators.
Another potential criticism of this study is the use of the same pin spread for constructs using pin-to-bar clamps and those using multipin clamps. We established that, to minimize confounding variables, a constant pin spread was necessary. This also mirrors our more common pin configurations for external fixators with pins placed outside the zone of injury. However, a key determinant of external fixator stability is pin spread, and this is a potential benefit to using pin-to-bar clamps over the multipin clamps that require an exact pin spread. Indeed, our results may have shown a larger difference between constructs using the pin-to-bar clamps compared with the multipin clamps had we maximized the pin spread. Future studies may be able to use a fracture model to compare the pin-to-bar clamps and multipin clamps using pin spread to maximize stability.
Conclusion
This study has shown that using pin-to-bar clamps can create strong, stable constructs for temporary external fixation. In particular, constructs made with a single bar and pin-to-bar clamps can produce easily implantable and less expensive constructs that are stiff enough to withstand deformation and allow patient transfers without excessive displacement of the fracture.
1. Behrens F. A primer of fixator devices and configurations. Clin Orthop Relat Res. 1989;241:5-14.
2. Chao EY, Aro HT, Lewallen DG, Kelly PJ. The effect of rigidity on fracture healing in external fixation. Clin Orthop Relat Res. 1989;241:24-35.
3. Schrøder HA, Weeth RE, Madsen T. Experimental analysis of Hoffman external fixation in various mountings. Arch Orthop Trauma Surg. 1985;104(4):197-200.
4. Kempson GE, Campbell D. The comparative stiffness of external fixation frames. Injury. 1981;12(4):297-304.
5. Giotakis N, Narayan B. Stability with unilateral external fixation in the tibia. Strategies Trauma Limb Reconstr. 2007;2(1):13-20.
6. Briggs BT, Chao EY. The mechanical performance of the standard Hoffmann-Vidal external fixation apparatus. J Bone Joint Surg Am. 1982;64(4):566-573.
7. Hipp JA, Edgerton BC, An KN, Hayes WC. Structural consequences of transcortical holes in long bones loaded in torsion. J Biomech. 1990;23(12):1261-1268.
8. Edgerton BC, An KN, Morrey BF. Torsional strength reduction due to cortical defects in bone. J Orthop Res. 1990;8(6):851-855.
9. Huiskes R, Chao E. Guidelines for external fixation frame rigidity and stresses. J Orthop Res. 1986;4(1):68-75.
10. Pettine KA, Chao EY, Kelly PJ. Analysis of the external fixator pin-bone interface. Clin Orthop Relat Res. 1993;(293):18-27.
11. Halsey D, Fleming B, Pope MH, Krag M, Kristiansen T. External fixator pin design. Clin Orthop Relat Res. 1992;(278):305-312.
12. Huiskes R, Chao EY, Crippen TE. Parametric analyses of pin-bone stresses in external fracture fixation devices. J Orthop Res. 1985;3(3):341-349.
13. Behrens F, Johnson W. Unilateral external fixation methods to increase and reduce frame stiffness. Clin Orthop Relat Res.1989;(241):48-56.
14. Mercer D, Firoozbakhsh K, Prevost M, Mulkey P, DeCoster TA, Schenck R. Stiffness of knee spanning external fixation systems for traumatic knee dislocations: a biomechanical study. J Orthop Trauma. 2010;24(11):693-696.
15. Kim H, Russell JP, Hsieh AH, O’Toole RV. Bar diameter is an important component of knee-spanning external fixator stiffness and cost. Orthopedics. 2014;37(7):e671-e677.
External fixators are commonly used as a temporizing treatment for periarticular fractures about the knee. Since its inception with a claw used for patellar fractures by Malgaigne in 1853,1 external fixation has evolved to include pin–crossbar constructs. The stiffness of the construct directly affects the rate at which the frames are likely to fail.2 Most external fixation systems have the option for 2 types of pin–bar connectors, pin-to-bar clamps or multipin clamps. The multipin clamps rely on a cluster of multiple pins to connect the longitudinal supports. These clamps use the “bull horn” extensions to connect the pins to bars (Figure 1). The implant manufacturers recommend the use of 2 longitudinal bars when using these clamps. Conversely, single pin-to-bar clamps permit widely spaced pins but multipin clamps do not. Pin-to-bar clamps also tend to allow the longitudinal cross-bars to be placed closer to bone, improving frame stability.1
In the experience of Dr. Reisman, utilization of pin-to-bar clamps has resulted in improved external fixator construct stiffness compared with those using multipin clamps. He has recognized that, in his own practice, a busy level I trauma center where 4 to 5 spanning knee frames are applied daily, fracture stability is improved with the use of pin-to-bar clamps and often with only a single crossbar, resulting in a simpler, low-cost construct. Despite external fixators used for temporary fixation, frames need to be strong enough to maintain fracture length and stabilize the soft-tissue envelope for days to weeks. It is critical that the frame’s stability allows for patient transfers but controls fracture motion until definitive fixation. Despite having both options available in the external fixator set, there are no biomechanical studies that compare the effect of using pin-to-bar clamps or multipin clamps and bull horns on external fixator stiffness.
In this study, we compared the stiffness of 3 different types of spanning knee external fixator configurations, using multi-pin clamps and 2 crossbars, or pin-to-bar clamps with 1 or 2 crossbars. We compared constructs using 2 systems, 1 with 8-mm–diameter and another with 11-mm–diameter crossbars. We hypothesized that constructs assembled with pin-to-bar clamps would have improved bending stiffness compared with constructs using multipin clamps.
Materials and Methods
Three constructs were made under the supervision of Dr. Reisman, a trauma fellowship–trained orthopedic surgeon. The first construct (construct 1) used two 200-mm bars attached to pin-to-bar clamps with a single 450-mm–long spanning bar connecting the 2 segments (Figure 2). The second construct (construct 2) used 2 spanning bars with pin-to-bar clamps. The third construct (construct 3) used multipin clamps proximally and distally with two 450-mm–long spanning bars. Therefore, we tested 2 types of constructs using pin-to-bar clamps and 1 construct with multipin clamps. Four of each construct type were assembled with both 8-mm (Stryker) and 11-mm bars (Synthes), providing 24 testable constructs. For this study, we tested previously used and cleaned external fixation pins, bars, and clamps obtained from our trauma center. All equipment was examined thoroughly for any potential damaged parts.
To simulate the femoral and tibial attachments, two 5-mm–diameter pins were drilled into each of 2 steel cylinders and welded in place. The femoral cylinder (8.3×2.5 cm) had a pin distance of 55 mm, and the tibial cylinder (6.4×2.5 cm) had a pin distance of 32 mm (Figure 3). The pins were welded intosteel cylinders to help prevent any loosening or failure at the pin (ie, metal interface isolating stress to the components). Dr. Desai assembled the constructs and placed them on the cylinders with a distance of 25 mm between the fixator construct and the cylinder, with 306 mm between the femoral and tibial cylinders. The pin diameters, pin spread, pin number, and bar-to-cylinder distance were constant throughout testing with these specifications.
The assembled constructs were tested on a materials testing machine (MTS 858 Mini-Bionix Test System). A compressive force was applied, through a roller, to a flat plate (Figures 4, 5). This allowed the constructs to flex and bend freely without overly stressing the simulated pin-to-bone interface. Using this loading method, we could compare the stiffness of the different assembled constructs. Each assembled construct was tested 4 times sequentially on the MTS machine. There was no pin deformation when the load was applied through the roller to the flat plate, to the cylinder, to the pins, and onto the construct. It was possible to observe that the construct flexed when the load was applied. Load-displacement curves were produced for each test, and the stiffness was calculated from the slope of this curve. Each test was repeated 4 times, and the stiffness was measured from the load-displacement curve each time. The 4 stiffness measurements were averaged for each construct and compared across all constructs, using a Wilcoxon rank sum test for statistical analysis.
Results
Construct Design
Three different construct designs were evaluated using our testing protocol. The mean stiffness differed across all constructs as seen in Figure 6. Of the constructs using the 11-mm–diameter bars, construct 2 had the highest mean stiffness (32.1 +/- 3.7 N/mm), and this stiffness was significantly greater than the mean stiffness for construct 1 (15.3 +/- 1.5 N/mm; P < .05) and construct 3 (18.4 +/- 2.9 N/mm; P< .05). There was no statistically significant difference in stiffness between construct 1 and construct 3.
Of the constructs using 8-mm–diameter bars, construct 2 had the highest mean stiffness (11.5 +/- 2.4 N/mm), and this stiffness was significantly greater than the mean stiffness for construct 1 (5.0 +/- 0.9 N/mm; P < .05). There was no statistically significant difference in stiffness between construct 2 and construct 3 (7.8 +/- 1.9 N/mm) or between construct 1 and construct 3.
Discussion
Although numerous investigators have examined the biomechanical properties of external fixator systems, the effect of pin-to-bar clamps on frame stiffness is unknown. Biomechanical studies have found that uniplanar constructs with multiple bars can provide adequate strength for temporary fixation.3-9 With multiple options within a particular external fixator set, it is ideal to understand the benefit of using one component instead of another.
The main results from this experiment are: (1) constructs with pin-to-bar clamps and 2 crossbars are stiffer than those using multipin clamps and 2 crossbars; (2) constructs with a single crossbar and pin-to-bar clamps are as stiff as constructs using 2 crossbars and multipin clamps.
Figure 6 shows the average stiffness differences between the 8-mm and 11-mm–diameter bar constructs tested in this study. As expected, each 11-mm diameter–bar construct had a higher average stiffness compared with the 8-mm–diameter bar constructs. Across both the 8-mm and 11-mm–diameter bar constructs, construct 2 had a higher stiffness than that of constructs 1 and 3. Furthermore, there was no difference in the stiffness between constructs 1 and 3.
To improve external fixator stiffness, number of pins and optimization of pin spread can improve the strength of the construct.7 When using pin-to-bar clamps, 1 pin should be as close to the fracture as possible, with the second pin as far from the fracture as possible. 7 Multipin clamps, by design, prevent any optimization of pin spread and require a clustered-pin arrangement.
Bar configuration also plays a critical role in construct stiffness. Bar-to-bone distance should be approximately 2 fingerbreadths from the skin to maximize the stiffness of the construct.4,10-14 Multipin clamps use “bull horn” extensions that tend to elevate the bar away from the skin, increasing the distance between the bar and the bone.
A temporary spanning knee external fixator is commonly used for treating high-energy periarticular tibial or femoral fractures. To hold the fracture in an adequately reduced position, the frame must resist the deforming forces inherent with all fractures. A frame that is not adequately stiff will not hold the fracture in the reduced position, even at the time of initial surgery, which negates one of the benefits of placing the patient in the frame. Hence, adequate stiffness of the spanning-knee fixator is critical to the effectiveness of temporary stabilization before permanent fixation.
The results of this study provide evidence for the superiority of pin-to-bar clamps over multipin clamps in optimizing external fixator construct stiffness. At our institution, we almost exclusively use the single pin-to-bar clamps for spanning-knee external fixation. Based on the results of this study, we often use only a single crossbar. The ability to use a single bar greatly reduces the cost of the construct because crossbars can cost from $100 to $150, depending on the manufacturer.
A recent cost analysis of spanning-knee external fixators showed that construct costs can range from $8,000 to $19,000.15 The lower-cost constructs included 2 crossbars while the more expensive constructs had additional bars and multipin clamps. The authors noted that constructs with larger diameter bars and higher overall stiffness resulted in an improved cost per stiffness ratio. The results of this study support our conclusions regarding bar diameter. Additionally, our results show improved stiffness of constructs with pin-to-bar clamps instead of multipin clamps. By limiting the need for an additional bar, using pin-to-bar clamps and a single large diameter crossbar can create a very cost-efficient and rigidly stable construct.
One criticism of this study is the testing of used equipment. All external fixator manufacturers must evaluate and carefully examine any used equipment prior to the resterilization process and potential release to the practitioner for re-use. Our rationale for using used equipment is based on the assumption that the vast majority of patients do not have their external fixators removed because of failure but because of definitive surgical treatment, and the timing of removal does not necessarily follow a predetermined protocol. For example, timing of definitive surgery is usually set by the patient’s general health status, status of the soft tissues, and surgeon availability. Therefore, this equipment was tested with the presumption that the equipment was in the same state as if the patient continued to wear the frame 1 more day. A study testing unused equipment would be the next step in evaluating external fixators.
Another potential criticism of this study is the use of the same pin spread for constructs using pin-to-bar clamps and those using multipin clamps. We established that, to minimize confounding variables, a constant pin spread was necessary. This also mirrors our more common pin configurations for external fixators with pins placed outside the zone of injury. However, a key determinant of external fixator stability is pin spread, and this is a potential benefit to using pin-to-bar clamps over the multipin clamps that require an exact pin spread. Indeed, our results may have shown a larger difference between constructs using the pin-to-bar clamps compared with the multipin clamps had we maximized the pin spread. Future studies may be able to use a fracture model to compare the pin-to-bar clamps and multipin clamps using pin spread to maximize stability.
Conclusion
This study has shown that using pin-to-bar clamps can create strong, stable constructs for temporary external fixation. In particular, constructs made with a single bar and pin-to-bar clamps can produce easily implantable and less expensive constructs that are stiff enough to withstand deformation and allow patient transfers without excessive displacement of the fracture.
External fixators are commonly used as a temporizing treatment for periarticular fractures about the knee. Since its inception with a claw used for patellar fractures by Malgaigne in 1853,1 external fixation has evolved to include pin–crossbar constructs. The stiffness of the construct directly affects the rate at which the frames are likely to fail.2 Most external fixation systems have the option for 2 types of pin–bar connectors, pin-to-bar clamps or multipin clamps. The multipin clamps rely on a cluster of multiple pins to connect the longitudinal supports. These clamps use the “bull horn” extensions to connect the pins to bars (Figure 1). The implant manufacturers recommend the use of 2 longitudinal bars when using these clamps. Conversely, single pin-to-bar clamps permit widely spaced pins but multipin clamps do not. Pin-to-bar clamps also tend to allow the longitudinal cross-bars to be placed closer to bone, improving frame stability.1
In the experience of Dr. Reisman, utilization of pin-to-bar clamps has resulted in improved external fixator construct stiffness compared with those using multipin clamps. He has recognized that, in his own practice, a busy level I trauma center where 4 to 5 spanning knee frames are applied daily, fracture stability is improved with the use of pin-to-bar clamps and often with only a single crossbar, resulting in a simpler, low-cost construct. Despite external fixators used for temporary fixation, frames need to be strong enough to maintain fracture length and stabilize the soft-tissue envelope for days to weeks. It is critical that the frame’s stability allows for patient transfers but controls fracture motion until definitive fixation. Despite having both options available in the external fixator set, there are no biomechanical studies that compare the effect of using pin-to-bar clamps or multipin clamps and bull horns on external fixator stiffness.
In this study, we compared the stiffness of 3 different types of spanning knee external fixator configurations, using multi-pin clamps and 2 crossbars, or pin-to-bar clamps with 1 or 2 crossbars. We compared constructs using 2 systems, 1 with 8-mm–diameter and another with 11-mm–diameter crossbars. We hypothesized that constructs assembled with pin-to-bar clamps would have improved bending stiffness compared with constructs using multipin clamps.
Materials and Methods
Three constructs were made under the supervision of Dr. Reisman, a trauma fellowship–trained orthopedic surgeon. The first construct (construct 1) used two 200-mm bars attached to pin-to-bar clamps with a single 450-mm–long spanning bar connecting the 2 segments (Figure 2). The second construct (construct 2) used 2 spanning bars with pin-to-bar clamps. The third construct (construct 3) used multipin clamps proximally and distally with two 450-mm–long spanning bars. Therefore, we tested 2 types of constructs using pin-to-bar clamps and 1 construct with multipin clamps. Four of each construct type were assembled with both 8-mm (Stryker) and 11-mm bars (Synthes), providing 24 testable constructs. For this study, we tested previously used and cleaned external fixation pins, bars, and clamps obtained from our trauma center. All equipment was examined thoroughly for any potential damaged parts.
To simulate the femoral and tibial attachments, two 5-mm–diameter pins were drilled into each of 2 steel cylinders and welded in place. The femoral cylinder (8.3×2.5 cm) had a pin distance of 55 mm, and the tibial cylinder (6.4×2.5 cm) had a pin distance of 32 mm (Figure 3). The pins were welded intosteel cylinders to help prevent any loosening or failure at the pin (ie, metal interface isolating stress to the components). Dr. Desai assembled the constructs and placed them on the cylinders with a distance of 25 mm between the fixator construct and the cylinder, with 306 mm between the femoral and tibial cylinders. The pin diameters, pin spread, pin number, and bar-to-cylinder distance were constant throughout testing with these specifications.
The assembled constructs were tested on a materials testing machine (MTS 858 Mini-Bionix Test System). A compressive force was applied, through a roller, to a flat plate (Figures 4, 5). This allowed the constructs to flex and bend freely without overly stressing the simulated pin-to-bone interface. Using this loading method, we could compare the stiffness of the different assembled constructs. Each assembled construct was tested 4 times sequentially on the MTS machine. There was no pin deformation when the load was applied through the roller to the flat plate, to the cylinder, to the pins, and onto the construct. It was possible to observe that the construct flexed when the load was applied. Load-displacement curves were produced for each test, and the stiffness was calculated from the slope of this curve. Each test was repeated 4 times, and the stiffness was measured from the load-displacement curve each time. The 4 stiffness measurements were averaged for each construct and compared across all constructs, using a Wilcoxon rank sum test for statistical analysis.
Results
Construct Design
Three different construct designs were evaluated using our testing protocol. The mean stiffness differed across all constructs as seen in Figure 6. Of the constructs using the 11-mm–diameter bars, construct 2 had the highest mean stiffness (32.1 +/- 3.7 N/mm), and this stiffness was significantly greater than the mean stiffness for construct 1 (15.3 +/- 1.5 N/mm; P < .05) and construct 3 (18.4 +/- 2.9 N/mm; P< .05). There was no statistically significant difference in stiffness between construct 1 and construct 3.
Of the constructs using 8-mm–diameter bars, construct 2 had the highest mean stiffness (11.5 +/- 2.4 N/mm), and this stiffness was significantly greater than the mean stiffness for construct 1 (5.0 +/- 0.9 N/mm; P < .05). There was no statistically significant difference in stiffness between construct 2 and construct 3 (7.8 +/- 1.9 N/mm) or between construct 1 and construct 3.
Discussion
Although numerous investigators have examined the biomechanical properties of external fixator systems, the effect of pin-to-bar clamps on frame stiffness is unknown. Biomechanical studies have found that uniplanar constructs with multiple bars can provide adequate strength for temporary fixation.3-9 With multiple options within a particular external fixator set, it is ideal to understand the benefit of using one component instead of another.
The main results from this experiment are: (1) constructs with pin-to-bar clamps and 2 crossbars are stiffer than those using multipin clamps and 2 crossbars; (2) constructs with a single crossbar and pin-to-bar clamps are as stiff as constructs using 2 crossbars and multipin clamps.
Figure 6 shows the average stiffness differences between the 8-mm and 11-mm–diameter bar constructs tested in this study. As expected, each 11-mm diameter–bar construct had a higher average stiffness compared with the 8-mm–diameter bar constructs. Across both the 8-mm and 11-mm–diameter bar constructs, construct 2 had a higher stiffness than that of constructs 1 and 3. Furthermore, there was no difference in the stiffness between constructs 1 and 3.
To improve external fixator stiffness, number of pins and optimization of pin spread can improve the strength of the construct.7 When using pin-to-bar clamps, 1 pin should be as close to the fracture as possible, with the second pin as far from the fracture as possible. 7 Multipin clamps, by design, prevent any optimization of pin spread and require a clustered-pin arrangement.
Bar configuration also plays a critical role in construct stiffness. Bar-to-bone distance should be approximately 2 fingerbreadths from the skin to maximize the stiffness of the construct.4,10-14 Multipin clamps use “bull horn” extensions that tend to elevate the bar away from the skin, increasing the distance between the bar and the bone.
A temporary spanning knee external fixator is commonly used for treating high-energy periarticular tibial or femoral fractures. To hold the fracture in an adequately reduced position, the frame must resist the deforming forces inherent with all fractures. A frame that is not adequately stiff will not hold the fracture in the reduced position, even at the time of initial surgery, which negates one of the benefits of placing the patient in the frame. Hence, adequate stiffness of the spanning-knee fixator is critical to the effectiveness of temporary stabilization before permanent fixation.
The results of this study provide evidence for the superiority of pin-to-bar clamps over multipin clamps in optimizing external fixator construct stiffness. At our institution, we almost exclusively use the single pin-to-bar clamps for spanning-knee external fixation. Based on the results of this study, we often use only a single crossbar. The ability to use a single bar greatly reduces the cost of the construct because crossbars can cost from $100 to $150, depending on the manufacturer.
A recent cost analysis of spanning-knee external fixators showed that construct costs can range from $8,000 to $19,000.15 The lower-cost constructs included 2 crossbars while the more expensive constructs had additional bars and multipin clamps. The authors noted that constructs with larger diameter bars and higher overall stiffness resulted in an improved cost per stiffness ratio. The results of this study support our conclusions regarding bar diameter. Additionally, our results show improved stiffness of constructs with pin-to-bar clamps instead of multipin clamps. By limiting the need for an additional bar, using pin-to-bar clamps and a single large diameter crossbar can create a very cost-efficient and rigidly stable construct.
One criticism of this study is the testing of used equipment. All external fixator manufacturers must evaluate and carefully examine any used equipment prior to the resterilization process and potential release to the practitioner for re-use. Our rationale for using used equipment is based on the assumption that the vast majority of patients do not have their external fixators removed because of failure but because of definitive surgical treatment, and the timing of removal does not necessarily follow a predetermined protocol. For example, timing of definitive surgery is usually set by the patient’s general health status, status of the soft tissues, and surgeon availability. Therefore, this equipment was tested with the presumption that the equipment was in the same state as if the patient continued to wear the frame 1 more day. A study testing unused equipment would be the next step in evaluating external fixators.
Another potential criticism of this study is the use of the same pin spread for constructs using pin-to-bar clamps and those using multipin clamps. We established that, to minimize confounding variables, a constant pin spread was necessary. This also mirrors our more common pin configurations for external fixators with pins placed outside the zone of injury. However, a key determinant of external fixator stability is pin spread, and this is a potential benefit to using pin-to-bar clamps over the multipin clamps that require an exact pin spread. Indeed, our results may have shown a larger difference between constructs using the pin-to-bar clamps compared with the multipin clamps had we maximized the pin spread. Future studies may be able to use a fracture model to compare the pin-to-bar clamps and multipin clamps using pin spread to maximize stability.
Conclusion
This study has shown that using pin-to-bar clamps can create strong, stable constructs for temporary external fixation. In particular, constructs made with a single bar and pin-to-bar clamps can produce easily implantable and less expensive constructs that are stiff enough to withstand deformation and allow patient transfers without excessive displacement of the fracture.
1. Behrens F. A primer of fixator devices and configurations. Clin Orthop Relat Res. 1989;241:5-14.
2. Chao EY, Aro HT, Lewallen DG, Kelly PJ. The effect of rigidity on fracture healing in external fixation. Clin Orthop Relat Res. 1989;241:24-35.
3. Schrøder HA, Weeth RE, Madsen T. Experimental analysis of Hoffman external fixation in various mountings. Arch Orthop Trauma Surg. 1985;104(4):197-200.
4. Kempson GE, Campbell D. The comparative stiffness of external fixation frames. Injury. 1981;12(4):297-304.
5. Giotakis N, Narayan B. Stability with unilateral external fixation in the tibia. Strategies Trauma Limb Reconstr. 2007;2(1):13-20.
6. Briggs BT, Chao EY. The mechanical performance of the standard Hoffmann-Vidal external fixation apparatus. J Bone Joint Surg Am. 1982;64(4):566-573.
7. Hipp JA, Edgerton BC, An KN, Hayes WC. Structural consequences of transcortical holes in long bones loaded in torsion. J Biomech. 1990;23(12):1261-1268.
8. Edgerton BC, An KN, Morrey BF. Torsional strength reduction due to cortical defects in bone. J Orthop Res. 1990;8(6):851-855.
9. Huiskes R, Chao E. Guidelines for external fixation frame rigidity and stresses. J Orthop Res. 1986;4(1):68-75.
10. Pettine KA, Chao EY, Kelly PJ. Analysis of the external fixator pin-bone interface. Clin Orthop Relat Res. 1993;(293):18-27.
11. Halsey D, Fleming B, Pope MH, Krag M, Kristiansen T. External fixator pin design. Clin Orthop Relat Res. 1992;(278):305-312.
12. Huiskes R, Chao EY, Crippen TE. Parametric analyses of pin-bone stresses in external fracture fixation devices. J Orthop Res. 1985;3(3):341-349.
13. Behrens F, Johnson W. Unilateral external fixation methods to increase and reduce frame stiffness. Clin Orthop Relat Res.1989;(241):48-56.
14. Mercer D, Firoozbakhsh K, Prevost M, Mulkey P, DeCoster TA, Schenck R. Stiffness of knee spanning external fixation systems for traumatic knee dislocations: a biomechanical study. J Orthop Trauma. 2010;24(11):693-696.
15. Kim H, Russell JP, Hsieh AH, O’Toole RV. Bar diameter is an important component of knee-spanning external fixator stiffness and cost. Orthopedics. 2014;37(7):e671-e677.
1. Behrens F. A primer of fixator devices and configurations. Clin Orthop Relat Res. 1989;241:5-14.
2. Chao EY, Aro HT, Lewallen DG, Kelly PJ. The effect of rigidity on fracture healing in external fixation. Clin Orthop Relat Res. 1989;241:24-35.
3. Schrøder HA, Weeth RE, Madsen T. Experimental analysis of Hoffman external fixation in various mountings. Arch Orthop Trauma Surg. 1985;104(4):197-200.
4. Kempson GE, Campbell D. The comparative stiffness of external fixation frames. Injury. 1981;12(4):297-304.
5. Giotakis N, Narayan B. Stability with unilateral external fixation in the tibia. Strategies Trauma Limb Reconstr. 2007;2(1):13-20.
6. Briggs BT, Chao EY. The mechanical performance of the standard Hoffmann-Vidal external fixation apparatus. J Bone Joint Surg Am. 1982;64(4):566-573.
7. Hipp JA, Edgerton BC, An KN, Hayes WC. Structural consequences of transcortical holes in long bones loaded in torsion. J Biomech. 1990;23(12):1261-1268.
8. Edgerton BC, An KN, Morrey BF. Torsional strength reduction due to cortical defects in bone. J Orthop Res. 1990;8(6):851-855.
9. Huiskes R, Chao E. Guidelines for external fixation frame rigidity and stresses. J Orthop Res. 1986;4(1):68-75.
10. Pettine KA, Chao EY, Kelly PJ. Analysis of the external fixator pin-bone interface. Clin Orthop Relat Res. 1993;(293):18-27.
11. Halsey D, Fleming B, Pope MH, Krag M, Kristiansen T. External fixator pin design. Clin Orthop Relat Res. 1992;(278):305-312.
12. Huiskes R, Chao EY, Crippen TE. Parametric analyses of pin-bone stresses in external fracture fixation devices. J Orthop Res. 1985;3(3):341-349.
13. Behrens F, Johnson W. Unilateral external fixation methods to increase and reduce frame stiffness. Clin Orthop Relat Res.1989;(241):48-56.
14. Mercer D, Firoozbakhsh K, Prevost M, Mulkey P, DeCoster TA, Schenck R. Stiffness of knee spanning external fixation systems for traumatic knee dislocations: a biomechanical study. J Orthop Trauma. 2010;24(11):693-696.
15. Kim H, Russell JP, Hsieh AH, O’Toole RV. Bar diameter is an important component of knee-spanning external fixator stiffness and cost. Orthopedics. 2014;37(7):e671-e677.
Medicaid Insurance Is Associated With Larger Curves in Patients Who Require Scoliosis Surgery
Rising health care costs have led many health insurers to limit benefits, which may be a problem for children in need of specialty care. Uninsured children have poorer access to specialty care than insured children. Children with public health coverage have better access to specialty care than uninsured children but inferior access compared with privately insured children.1,2 It is well documented that children with government insurance have limited access to orthopedic care for fractures, ligamentous knee injuries, and other injuries.1,3-5 Adolescent idiopathic scoliosis (AIS) differs from many other conditions managed by pediatric orthopedists, as it may be progressive, with management becoming increasingly more complex as the curve magnitude increases.6 The ability to access care earlier in the disease process may allow for earlier nonoperative interventions, such as bracing. For patients who require spinal fusion, earlier diagnosis and referral to a specialist could potentially result in shorter fusions and preserve distal motion segments. The ability to access the health care system in a timely fashion would therefore be of utmost importance for patients with scoliosis.
The literature on AIS is lacking in studies focused on care access based on insurance coverage and the potential impact that this may have on curve progression.7-9 We conducted a study to determine whether there is a difference between patients with and without private insurance who present to a busy urban pediatric orthopedic practice for management of scoliosis that eventually resulted in surgical treatment.
Materials and Methods
After obtaining institutional review board approval for this study, we retrospectively reviewed the medical records of patients (age, 10-18 years) who underwent posterior spinal fusion (PSF) for newly diagnosed AIS between 2008 and 2012. We excluded patients treated with growing spine instrumentation (growing rods), patients younger than 10 years or older than 18 years at presentation, and patients without adequate radiographs or clinical data, including insurance status. To focus on newly diagnosed scoliosis, we also excluded patients who had been seen for second opinions or whose scoliosis had been managed elsewhere in the past. Patients with syndromic, neuromuscular, or congenital scoliosis were also excluded.
Medical records were checked to ascertain time from initial evaluation to decision for surgery, time from recommendation for surgery until actual procedure, and insurance status. Distance traveled was figured from patients’ home addresses. Cobb angles were calculated from initial preoperative and final preoperative posteroanterior (PA) radiographs. Curves as seen on PA, lateral, and maximal effort, supine bending thoracic and lumbar radiographs from the initial preoperative visit were classified using the system of Lenke and colleagues.10 Hospital records were queried to determine number of levels fused at surgery, number of implants placed, and length of stay. Patients were evaluated without prior screening of insurance status and without prior consultation with referring physicians. Surgical procedures were scheduled on a first-come, first-served basis without preference for insurance status.
Results
We identified 135 consecutive patients with newly diagnosed AIS treated with PSF by our group between January 2008 and December 2012 (Table 1). Sixty-one percent had private insurance; 39% had Medicaid. There was no difference in age or ASA (American Society of Anesthesiologists) score between groups. Mean (SD) Cobb angle at initial presentation was 47.5° (14.3°) (range, 18.0°-86.0°) for the private insurance group and 57.2° (15.7°) (range, 23.0°-95.0°) for the Medicaid group (P < .0001). At time of surgery, mean (SD) Cobb angles were 54.6° (11.7°) and 60.6° (13.9°) for the private insurance and Medicaid groups, respectively (P = .008). There was no difference in curve types (Lenke and colleagues10 classification) between groups (Table 2, P = .83). Medicaid patients traveled a shorter mean (SD) distance for care, 56.3 (57.0) miles, versus 73.7 (66.7) miles (P = .05). There was no statistical difference (P = .14) in mean (SD) surgical wait time from surgery recommendation to actual surgery, 103.1 (62.4) days and 128.8 (137.5) days for the private insurance and Medicaid groups, respectively. The difference between patient groups in mean (SD) number of levels fused did not reach statistical significance (P = .16), 10.3 (2.2) levels for the Medicaid group and 9.7 (2.3) levels for the private insurance group. Mean (SD) estimated blood loss was higher for Medicaid patients, 445.7 (415.9) mL versus 335.1 (271.5) mL (P = .06), though there was no difference in use of posterior column osteotomies between groups. There was no difference (P = .11) in mean (SD) length of hospital stay between Medicaid patients, 2.6 (0.8) days, and private insurance patients, 2.4 (0.5) days.
Discussion
According to an extensive body of literature, patients with government insurance have limited access to specialty care.1,11,12 Medicaid-insured children in need of orthopedic care are no exception. Sabharwal and colleagues13 examined a database of pediatric fracture cases and found that 52% of the privately insured patients and 22% of the publicly insured patients received orthopedic care (P = .013).13 When Pierce and colleagues14 called 42 orthopedic practices regarding a fictitious 14-year-old patient with an anterior cruciate ligament tear, 38 offered an appointment within 2 weeks to a privately insured patient, and 6 offered such an appointment to a publicly insured patient. Skaggs and colleagues4 surveyed 230 orthopedic practices nationally and found that Medicaid-insured children had limited access to orthopedic care; 41 practices (18%) would not see a child with Medicaid under any circumstances. Using a fictitious case of a 10-year-old boy with a forearm fracture, Iobst and colleagues3 tried making an appointment at 100 orthopedic offices. Eight gave an appointment within 1 week to a Medicaid-insured patient, and 36 gave an appointment to a privately insured patient.3
There are few data regarding insurance status and scoliosis care in children. Spinal deformity differs from simple fractures and ligamentous injuries, as timely care may result in a less invasive treatment (bracing) if the curvature is caught early. Goldstein and colleagues9 recently evaluated 642 patients who presented for scoliosis evaluation over a 10-year period. There was no difference in curve magnitudes between patients with and without Medicaid insurance. Thirty-two percent of these patients were evaluated for a second opinion, and the authors chose not to subdivide patients on the basis of curve severity and treatment needed, noting only no difference between groups. There was no discussion of the potential difference between patients with and without private insurance with respect to surgically versus nonsurgically treated curves. We wanted to focus specifically on patients who required surgical intervention, as our experience has been that many patients with government insurance present with either very mild scoliosis (10°) or very large curves that were not identified because of lack of primary care access or inadequate school screening. Although summing these 2 groups would result in a similar average, they would represent a different cohort than patients with curves along a bell curve. Furthermore, it is the group of patients who would require surgical intervention that is so critical to identify early in order to intervene.
Our data suggest a difference in presenting curves between patients with and without private insurance. The approximately 10° difference between patient groups in this study could potentially represent the difference between bracing and surgery. Furthermore, Miyanji and colleagues6 evaluated the relationship between Cobb angle and health care consumption and correlated larger curve magnitudes with more levels fused, longer surgeries, and higher rates of transfusion. Specifically, every 10° increase in curve magnitude resulted in 7.8 more minutes of operative time, 0.3 extra levels fused, and 1.5 times increased risk for requiring a blood transfusion.
Cho and Egorova15 recently evaluated insurance status with respect to surgical outcomes using a national inpatient database and found that 42.4% of surgeries for AIS in children with Medicaid had fusions involving 9 or more levels, whereas only 33.6% of privately insured patients had fusions of 9 or more levels. There was no difference in osteotomy or reoperation for pseudarthrosis between groups, but there was a slightly higher rate of infectious (1.1% vs 0.6%) and hemorrhagic (2.5% vs 1.7%) complications in the Medicaid group. Hospital stay was longer in patients with Medicaid, though complications were not different between groups.
The mean difference in the magnitude of the curves treated in our study was not more than 10° between patients with and without Medicaid, perhaps explaining the lack of a statistically significant difference in number of levels fused between groups. Although the groups were similar with respect to the percentage requiring posterior column spinal osteotomies, we noted a difference in estimated blood loss between groups, likely explained by the fact that a junior surgeon was added just before initiation of the study period, potentially skewing the estimated blood loss as this surgeon gained experience. Payer status has been correlated to length of hospital stay in children with scoliosis. Vitale and colleagues8 reviewed the effect of payer status on surgical outcomes in 3606 scoliosis patients from a statewide database in California and concluded that, compared with patients having all other payment sources, Medicaid patients had higher odds for complications and longer hospital stay. Our hospital has adopted a highly coordinated care pathway that allows for discharge on postoperative day 2, likely explaining the lack of any difference in postoperative stay.16
The disparity in curve magnitudes among patients with and without private insurance is striking and probably multifactorial. Very likely, the combination of schools with limited screening programs within urban or rural school systems,17 restricted access to pediatricians,18,19 and longer waits to see orthopedic specialists20 all contribute to this disparity. It should be noted that school screening is mandatory in our state. This discrepancy may be related to a previously established tendency in minority populations toward waiting longer to seek care and refusing surgical recommendations, though we were unable to query socioeconomic factors such as race and household income.21,22 It is clearly important to increase access to care for underinsured patients with scoliosis. A comprehensive approach, including providing better education in the schools, establishing communication with referring primary care providers, and increasing access through more physicians or physician extenders, is likely needed. Orthopedists should perhaps treat scoliosis evaluation with the same sense of urgency given to minor fractures, and primary care providers should try to ensure that appropriate referrals for scoliosis are made. Also curious was the shorter travel distance for Medicaid patients versus private insurance patients in this study. We hypothesize this is related to our urban location and its large Medicaid population.
Our study had several limitations. Our electronic medical records (EMR) system does not store data related to the time a patient calls for an initial appointment, limiting our ability to determine how long patients waited for their initial consultation. Furthermore, the decision to undergo surgery is multifactorial and cannot be simplified into time from initial recommendation to surgery, as some patients delay surgery because of school or other obligations. These data should be reasonably consistent over time, as patients seen in the early spring in both groups may delay surgery until the summer, and those diagnosed in June may prefer earlier surgery.
Summary
Children with AIS are at risk for curve progression. Therefore, delays in providing timely care may result in worsening scoliosis. Compared with private insurance patients, Medicaid patients presented with larger curve magnitudes. Further study is needed to better delineate ways to improve care access for patients with scoliosis in communities with larger Medicaid populations.
1. Skaggs DL. Less access to care for children with Medicaid. Orthopedics. 2003;26(12):1184, 1186.
2. Skinner AC, Mayer ML. Effects of insurance status on children’s access to specialty care: a systematic review of the literature. BMC Health Serv Res. 2007;7:194.
3. Iobst C, King W, Baitner A, Tidwell M, Swirsky S, Skaggs DL. Access to care for children with fractures. J Pediatr Orthop. 2010;30(3):244-247.
4. Skaggs DL, Lehmann CL, Rice C, et al. Access to orthopaedic care for children with Medicaid versus private insurance: results of a national survey. J Pediatr Orthop. 2006;26(3):400-404.
5. Skaggs DL, Oda JE, Lerman L, et al. Insurance status and delay in orthotic treatment in children. J Pediatr Orthop. 2007;27(1):94-97.
6. Miyanji F, Slobogean GP, Samdani AF, et al. Is larger scoliosis curve magnitude associated with increased perioperative health-care resource utilization? A multicenter analysis of 325 adolescent idiopathic scoliosis curves. J Bone Joint Surg Am. 2012;94(9):809-813.
7. Nuno M, Drazin DG, Acosta FL Jr. Differences in treatments and outcomes for idiopathic scoliosis patients treated in the United States from 1998 to 2007: impact of socioeconomic variables and ethnicity. Spine J. 2013;13(2):116-123.
8. Vitale MA, Arons RR, Hyman JE, Skaggs DL, Roye DP, Vitale MG. The contribution of hospital volume, payer status, and other factors on the surgical outcomes of scoliosis patients: a review of 3,606 cases in the state of California. J Pediatr Orthop. 2005;25(3):393-399.
9. Goldstein RY, Joiner ER, Skaggs DL. Insurance status does not predict curve magnitude in adolescent idiopathic scoliosis at first presentation to an orthopaedic surgeon. J Pediatr Orthop. 2015;35(1):39-42.
10. Lenke LG, Betz RR, Harms J, et al. Adolescent idiopathic scoliosis: a new classification to determine extent of spinal arthrodesis. J Bone Joint Surg Am. 2001;83(8):1169-1181.
11. Alosh H, Riley LH 3rd, Skolasky RL. Insurance status, geography, race, and ethnicity as predictors of anterior cervical spine surgery rates and in-hospital mortality: an examination of United States trends from 1992 to 2005. Spine. 2009;34(18):1956-1962.
12. Newacheck PW, Hughes DC, Hung YY, Wong S, Stoddard JJ. The unmet health needs of America’s children. Pediatrics. 2000;105(4 pt 2):989-997.
13. Sabharwal S, Zhao C, McClemens E, Kaufmann A. Pediatric orthopaedic patients presenting to a university emergency department after visiting another emergency department: demographics and health insurance status. J Pediatr Orthop. 2007;27(6):690-694.
14. Pierce TR, Mehlman CT, Tamai J, Skaggs DL. Access to care for the adolescent anterior cruciate ligament patient with Medicaid versus private insurance. J Pediatr Orthop. 2012;32(3):245-248.
15. Cho SK, Egorova NN. The association between insurance status and complications, length of stay, and costs for pediatric idiopathic scoliosis. Spine. 2015;40(4):247-256.
16. Fletcher ND, Shourbaji N, Mitchell PM, Oswald TS, Devito DP, Bruce RW Jr. Clinical and economic implications of early discharge following posterior spinal fusion for adolescent idiopathic scoliosis. J Child Orthop. 2014;8(3):257-263.
17. Kasper MJ, Robbins L, Root L, Peterson MG, Allegrante JP. A musculoskeletal outreach screening, treatment, and education program for urban minority children. Arthritis Care Res. 1993;6(3):126-133.
18. Berman S, Dolins J, Tang SF, Yudkowsky B. Factors that influence the willingness of private primary care pediatricians to accept more Medicaid patients. Pediatrics. 2002;110(2 pt 1):239-248.
19. Sommers BD. Protecting low-income children’s access to care: are physician visits associated with reduced patient dropout from Medicaid and the Children’s Health Insurance Program? Pediatrics. 2006;118(1):e36-e42.
20. Bisgaier J, Polsky D, Rhodes KV. Academic medical centers and equity in specialty care access for children. Arch Pediatr Adolesc Med. 2012;166(4):304-310.
21. Sedlis SP, Fisher VJ, Tice D, Esposito R, Madmon L, Steinberg EH. Racial differences in performance of invasive cardiac procedures in a Department of Veterans Affairs medical center. J Clin Epidemiol. 1997;50(8):899-901.
22. Mitchell JB, McCormack LA. Time trends in late-stage diagnosis of cervical cancer. Differences by race/ethnicity and income. Med Care. 1997;35(12):1220-1224.
Rising health care costs have led many health insurers to limit benefits, which may be a problem for children in need of specialty care. Uninsured children have poorer access to specialty care than insured children. Children with public health coverage have better access to specialty care than uninsured children but inferior access compared with privately insured children.1,2 It is well documented that children with government insurance have limited access to orthopedic care for fractures, ligamentous knee injuries, and other injuries.1,3-5 Adolescent idiopathic scoliosis (AIS) differs from many other conditions managed by pediatric orthopedists, as it may be progressive, with management becoming increasingly more complex as the curve magnitude increases.6 The ability to access care earlier in the disease process may allow for earlier nonoperative interventions, such as bracing. For patients who require spinal fusion, earlier diagnosis and referral to a specialist could potentially result in shorter fusions and preserve distal motion segments. The ability to access the health care system in a timely fashion would therefore be of utmost importance for patients with scoliosis.
The literature on AIS is lacking in studies focused on care access based on insurance coverage and the potential impact that this may have on curve progression.7-9 We conducted a study to determine whether there is a difference between patients with and without private insurance who present to a busy urban pediatric orthopedic practice for management of scoliosis that eventually resulted in surgical treatment.
Materials and Methods
After obtaining institutional review board approval for this study, we retrospectively reviewed the medical records of patients (age, 10-18 years) who underwent posterior spinal fusion (PSF) for newly diagnosed AIS between 2008 and 2012. We excluded patients treated with growing spine instrumentation (growing rods), patients younger than 10 years or older than 18 years at presentation, and patients without adequate radiographs or clinical data, including insurance status. To focus on newly diagnosed scoliosis, we also excluded patients who had been seen for second opinions or whose scoliosis had been managed elsewhere in the past. Patients with syndromic, neuromuscular, or congenital scoliosis were also excluded.
Medical records were checked to ascertain time from initial evaluation to decision for surgery, time from recommendation for surgery until actual procedure, and insurance status. Distance traveled was figured from patients’ home addresses. Cobb angles were calculated from initial preoperative and final preoperative posteroanterior (PA) radiographs. Curves as seen on PA, lateral, and maximal effort, supine bending thoracic and lumbar radiographs from the initial preoperative visit were classified using the system of Lenke and colleagues.10 Hospital records were queried to determine number of levels fused at surgery, number of implants placed, and length of stay. Patients were evaluated without prior screening of insurance status and without prior consultation with referring physicians. Surgical procedures were scheduled on a first-come, first-served basis without preference for insurance status.
Results
We identified 135 consecutive patients with newly diagnosed AIS treated with PSF by our group between January 2008 and December 2012 (Table 1). Sixty-one percent had private insurance; 39% had Medicaid. There was no difference in age or ASA (American Society of Anesthesiologists) score between groups. Mean (SD) Cobb angle at initial presentation was 47.5° (14.3°) (range, 18.0°-86.0°) for the private insurance group and 57.2° (15.7°) (range, 23.0°-95.0°) for the Medicaid group (P < .0001). At time of surgery, mean (SD) Cobb angles were 54.6° (11.7°) and 60.6° (13.9°) for the private insurance and Medicaid groups, respectively (P = .008). There was no difference in curve types (Lenke and colleagues10 classification) between groups (Table 2, P = .83). Medicaid patients traveled a shorter mean (SD) distance for care, 56.3 (57.0) miles, versus 73.7 (66.7) miles (P = .05). There was no statistical difference (P = .14) in mean (SD) surgical wait time from surgery recommendation to actual surgery, 103.1 (62.4) days and 128.8 (137.5) days for the private insurance and Medicaid groups, respectively. The difference between patient groups in mean (SD) number of levels fused did not reach statistical significance (P = .16), 10.3 (2.2) levels for the Medicaid group and 9.7 (2.3) levels for the private insurance group. Mean (SD) estimated blood loss was higher for Medicaid patients, 445.7 (415.9) mL versus 335.1 (271.5) mL (P = .06), though there was no difference in use of posterior column osteotomies between groups. There was no difference (P = .11) in mean (SD) length of hospital stay between Medicaid patients, 2.6 (0.8) days, and private insurance patients, 2.4 (0.5) days.
Discussion
According to an extensive body of literature, patients with government insurance have limited access to specialty care.1,11,12 Medicaid-insured children in need of orthopedic care are no exception. Sabharwal and colleagues13 examined a database of pediatric fracture cases and found that 52% of the privately insured patients and 22% of the publicly insured patients received orthopedic care (P = .013).13 When Pierce and colleagues14 called 42 orthopedic practices regarding a fictitious 14-year-old patient with an anterior cruciate ligament tear, 38 offered an appointment within 2 weeks to a privately insured patient, and 6 offered such an appointment to a publicly insured patient. Skaggs and colleagues4 surveyed 230 orthopedic practices nationally and found that Medicaid-insured children had limited access to orthopedic care; 41 practices (18%) would not see a child with Medicaid under any circumstances. Using a fictitious case of a 10-year-old boy with a forearm fracture, Iobst and colleagues3 tried making an appointment at 100 orthopedic offices. Eight gave an appointment within 1 week to a Medicaid-insured patient, and 36 gave an appointment to a privately insured patient.3
There are few data regarding insurance status and scoliosis care in children. Spinal deformity differs from simple fractures and ligamentous injuries, as timely care may result in a less invasive treatment (bracing) if the curvature is caught early. Goldstein and colleagues9 recently evaluated 642 patients who presented for scoliosis evaluation over a 10-year period. There was no difference in curve magnitudes between patients with and without Medicaid insurance. Thirty-two percent of these patients were evaluated for a second opinion, and the authors chose not to subdivide patients on the basis of curve severity and treatment needed, noting only no difference between groups. There was no discussion of the potential difference between patients with and without private insurance with respect to surgically versus nonsurgically treated curves. We wanted to focus specifically on patients who required surgical intervention, as our experience has been that many patients with government insurance present with either very mild scoliosis (10°) or very large curves that were not identified because of lack of primary care access or inadequate school screening. Although summing these 2 groups would result in a similar average, they would represent a different cohort than patients with curves along a bell curve. Furthermore, it is the group of patients who would require surgical intervention that is so critical to identify early in order to intervene.
Our data suggest a difference in presenting curves between patients with and without private insurance. The approximately 10° difference between patient groups in this study could potentially represent the difference between bracing and surgery. Furthermore, Miyanji and colleagues6 evaluated the relationship between Cobb angle and health care consumption and correlated larger curve magnitudes with more levels fused, longer surgeries, and higher rates of transfusion. Specifically, every 10° increase in curve magnitude resulted in 7.8 more minutes of operative time, 0.3 extra levels fused, and 1.5 times increased risk for requiring a blood transfusion.
Cho and Egorova15 recently evaluated insurance status with respect to surgical outcomes using a national inpatient database and found that 42.4% of surgeries for AIS in children with Medicaid had fusions involving 9 or more levels, whereas only 33.6% of privately insured patients had fusions of 9 or more levels. There was no difference in osteotomy or reoperation for pseudarthrosis between groups, but there was a slightly higher rate of infectious (1.1% vs 0.6%) and hemorrhagic (2.5% vs 1.7%) complications in the Medicaid group. Hospital stay was longer in patients with Medicaid, though complications were not different between groups.
The mean difference in the magnitude of the curves treated in our study was not more than 10° between patients with and without Medicaid, perhaps explaining the lack of a statistically significant difference in number of levels fused between groups. Although the groups were similar with respect to the percentage requiring posterior column spinal osteotomies, we noted a difference in estimated blood loss between groups, likely explained by the fact that a junior surgeon was added just before initiation of the study period, potentially skewing the estimated blood loss as this surgeon gained experience. Payer status has been correlated to length of hospital stay in children with scoliosis. Vitale and colleagues8 reviewed the effect of payer status on surgical outcomes in 3606 scoliosis patients from a statewide database in California and concluded that, compared with patients having all other payment sources, Medicaid patients had higher odds for complications and longer hospital stay. Our hospital has adopted a highly coordinated care pathway that allows for discharge on postoperative day 2, likely explaining the lack of any difference in postoperative stay.16
The disparity in curve magnitudes among patients with and without private insurance is striking and probably multifactorial. Very likely, the combination of schools with limited screening programs within urban or rural school systems,17 restricted access to pediatricians,18,19 and longer waits to see orthopedic specialists20 all contribute to this disparity. It should be noted that school screening is mandatory in our state. This discrepancy may be related to a previously established tendency in minority populations toward waiting longer to seek care and refusing surgical recommendations, though we were unable to query socioeconomic factors such as race and household income.21,22 It is clearly important to increase access to care for underinsured patients with scoliosis. A comprehensive approach, including providing better education in the schools, establishing communication with referring primary care providers, and increasing access through more physicians or physician extenders, is likely needed. Orthopedists should perhaps treat scoliosis evaluation with the same sense of urgency given to minor fractures, and primary care providers should try to ensure that appropriate referrals for scoliosis are made. Also curious was the shorter travel distance for Medicaid patients versus private insurance patients in this study. We hypothesize this is related to our urban location and its large Medicaid population.
Our study had several limitations. Our electronic medical records (EMR) system does not store data related to the time a patient calls for an initial appointment, limiting our ability to determine how long patients waited for their initial consultation. Furthermore, the decision to undergo surgery is multifactorial and cannot be simplified into time from initial recommendation to surgery, as some patients delay surgery because of school or other obligations. These data should be reasonably consistent over time, as patients seen in the early spring in both groups may delay surgery until the summer, and those diagnosed in June may prefer earlier surgery.
Summary
Children with AIS are at risk for curve progression. Therefore, delays in providing timely care may result in worsening scoliosis. Compared with private insurance patients, Medicaid patients presented with larger curve magnitudes. Further study is needed to better delineate ways to improve care access for patients with scoliosis in communities with larger Medicaid populations.
Rising health care costs have led many health insurers to limit benefits, which may be a problem for children in need of specialty care. Uninsured children have poorer access to specialty care than insured children. Children with public health coverage have better access to specialty care than uninsured children but inferior access compared with privately insured children.1,2 It is well documented that children with government insurance have limited access to orthopedic care for fractures, ligamentous knee injuries, and other injuries.1,3-5 Adolescent idiopathic scoliosis (AIS) differs from many other conditions managed by pediatric orthopedists, as it may be progressive, with management becoming increasingly more complex as the curve magnitude increases.6 The ability to access care earlier in the disease process may allow for earlier nonoperative interventions, such as bracing. For patients who require spinal fusion, earlier diagnosis and referral to a specialist could potentially result in shorter fusions and preserve distal motion segments. The ability to access the health care system in a timely fashion would therefore be of utmost importance for patients with scoliosis.
The literature on AIS is lacking in studies focused on care access based on insurance coverage and the potential impact that this may have on curve progression.7-9 We conducted a study to determine whether there is a difference between patients with and without private insurance who present to a busy urban pediatric orthopedic practice for management of scoliosis that eventually resulted in surgical treatment.
Materials and Methods
After obtaining institutional review board approval for this study, we retrospectively reviewed the medical records of patients (age, 10-18 years) who underwent posterior spinal fusion (PSF) for newly diagnosed AIS between 2008 and 2012. We excluded patients treated with growing spine instrumentation (growing rods), patients younger than 10 years or older than 18 years at presentation, and patients without adequate radiographs or clinical data, including insurance status. To focus on newly diagnosed scoliosis, we also excluded patients who had been seen for second opinions or whose scoliosis had been managed elsewhere in the past. Patients with syndromic, neuromuscular, or congenital scoliosis were also excluded.
Medical records were checked to ascertain time from initial evaluation to decision for surgery, time from recommendation for surgery until actual procedure, and insurance status. Distance traveled was figured from patients’ home addresses. Cobb angles were calculated from initial preoperative and final preoperative posteroanterior (PA) radiographs. Curves as seen on PA, lateral, and maximal effort, supine bending thoracic and lumbar radiographs from the initial preoperative visit were classified using the system of Lenke and colleagues.10 Hospital records were queried to determine number of levels fused at surgery, number of implants placed, and length of stay. Patients were evaluated without prior screening of insurance status and without prior consultation with referring physicians. Surgical procedures were scheduled on a first-come, first-served basis without preference for insurance status.
Results
We identified 135 consecutive patients with newly diagnosed AIS treated with PSF by our group between January 2008 and December 2012 (Table 1). Sixty-one percent had private insurance; 39% had Medicaid. There was no difference in age or ASA (American Society of Anesthesiologists) score between groups. Mean (SD) Cobb angle at initial presentation was 47.5° (14.3°) (range, 18.0°-86.0°) for the private insurance group and 57.2° (15.7°) (range, 23.0°-95.0°) for the Medicaid group (P < .0001). At time of surgery, mean (SD) Cobb angles were 54.6° (11.7°) and 60.6° (13.9°) for the private insurance and Medicaid groups, respectively (P = .008). There was no difference in curve types (Lenke and colleagues10 classification) between groups (Table 2, P = .83). Medicaid patients traveled a shorter mean (SD) distance for care, 56.3 (57.0) miles, versus 73.7 (66.7) miles (P = .05). There was no statistical difference (P = .14) in mean (SD) surgical wait time from surgery recommendation to actual surgery, 103.1 (62.4) days and 128.8 (137.5) days for the private insurance and Medicaid groups, respectively. The difference between patient groups in mean (SD) number of levels fused did not reach statistical significance (P = .16), 10.3 (2.2) levels for the Medicaid group and 9.7 (2.3) levels for the private insurance group. Mean (SD) estimated blood loss was higher for Medicaid patients, 445.7 (415.9) mL versus 335.1 (271.5) mL (P = .06), though there was no difference in use of posterior column osteotomies between groups. There was no difference (P = .11) in mean (SD) length of hospital stay between Medicaid patients, 2.6 (0.8) days, and private insurance patients, 2.4 (0.5) days.
Discussion
According to an extensive body of literature, patients with government insurance have limited access to specialty care.1,11,12 Medicaid-insured children in need of orthopedic care are no exception. Sabharwal and colleagues13 examined a database of pediatric fracture cases and found that 52% of the privately insured patients and 22% of the publicly insured patients received orthopedic care (P = .013).13 When Pierce and colleagues14 called 42 orthopedic practices regarding a fictitious 14-year-old patient with an anterior cruciate ligament tear, 38 offered an appointment within 2 weeks to a privately insured patient, and 6 offered such an appointment to a publicly insured patient. Skaggs and colleagues4 surveyed 230 orthopedic practices nationally and found that Medicaid-insured children had limited access to orthopedic care; 41 practices (18%) would not see a child with Medicaid under any circumstances. Using a fictitious case of a 10-year-old boy with a forearm fracture, Iobst and colleagues3 tried making an appointment at 100 orthopedic offices. Eight gave an appointment within 1 week to a Medicaid-insured patient, and 36 gave an appointment to a privately insured patient.3
There are few data regarding insurance status and scoliosis care in children. Spinal deformity differs from simple fractures and ligamentous injuries, as timely care may result in a less invasive treatment (bracing) if the curvature is caught early. Goldstein and colleagues9 recently evaluated 642 patients who presented for scoliosis evaluation over a 10-year period. There was no difference in curve magnitudes between patients with and without Medicaid insurance. Thirty-two percent of these patients were evaluated for a second opinion, and the authors chose not to subdivide patients on the basis of curve severity and treatment needed, noting only no difference between groups. There was no discussion of the potential difference between patients with and without private insurance with respect to surgically versus nonsurgically treated curves. We wanted to focus specifically on patients who required surgical intervention, as our experience has been that many patients with government insurance present with either very mild scoliosis (10°) or very large curves that were not identified because of lack of primary care access or inadequate school screening. Although summing these 2 groups would result in a similar average, they would represent a different cohort than patients with curves along a bell curve. Furthermore, it is the group of patients who would require surgical intervention that is so critical to identify early in order to intervene.
Our data suggest a difference in presenting curves between patients with and without private insurance. The approximately 10° difference between patient groups in this study could potentially represent the difference between bracing and surgery. Furthermore, Miyanji and colleagues6 evaluated the relationship between Cobb angle and health care consumption and correlated larger curve magnitudes with more levels fused, longer surgeries, and higher rates of transfusion. Specifically, every 10° increase in curve magnitude resulted in 7.8 more minutes of operative time, 0.3 extra levels fused, and 1.5 times increased risk for requiring a blood transfusion.
Cho and Egorova15 recently evaluated insurance status with respect to surgical outcomes using a national inpatient database and found that 42.4% of surgeries for AIS in children with Medicaid had fusions involving 9 or more levels, whereas only 33.6% of privately insured patients had fusions of 9 or more levels. There was no difference in osteotomy or reoperation for pseudarthrosis between groups, but there was a slightly higher rate of infectious (1.1% vs 0.6%) and hemorrhagic (2.5% vs 1.7%) complications in the Medicaid group. Hospital stay was longer in patients with Medicaid, though complications were not different between groups.
The mean difference in the magnitude of the curves treated in our study was not more than 10° between patients with and without Medicaid, perhaps explaining the lack of a statistically significant difference in number of levels fused between groups. Although the groups were similar with respect to the percentage requiring posterior column spinal osteotomies, we noted a difference in estimated blood loss between groups, likely explained by the fact that a junior surgeon was added just before initiation of the study period, potentially skewing the estimated blood loss as this surgeon gained experience. Payer status has been correlated to length of hospital stay in children with scoliosis. Vitale and colleagues8 reviewed the effect of payer status on surgical outcomes in 3606 scoliosis patients from a statewide database in California and concluded that, compared with patients having all other payment sources, Medicaid patients had higher odds for complications and longer hospital stay. Our hospital has adopted a highly coordinated care pathway that allows for discharge on postoperative day 2, likely explaining the lack of any difference in postoperative stay.16
The disparity in curve magnitudes among patients with and without private insurance is striking and probably multifactorial. Very likely, the combination of schools with limited screening programs within urban or rural school systems,17 restricted access to pediatricians,18,19 and longer waits to see orthopedic specialists20 all contribute to this disparity. It should be noted that school screening is mandatory in our state. This discrepancy may be related to a previously established tendency in minority populations toward waiting longer to seek care and refusing surgical recommendations, though we were unable to query socioeconomic factors such as race and household income.21,22 It is clearly important to increase access to care for underinsured patients with scoliosis. A comprehensive approach, including providing better education in the schools, establishing communication with referring primary care providers, and increasing access through more physicians or physician extenders, is likely needed. Orthopedists should perhaps treat scoliosis evaluation with the same sense of urgency given to minor fractures, and primary care providers should try to ensure that appropriate referrals for scoliosis are made. Also curious was the shorter travel distance for Medicaid patients versus private insurance patients in this study. We hypothesize this is related to our urban location and its large Medicaid population.
Our study had several limitations. Our electronic medical records (EMR) system does not store data related to the time a patient calls for an initial appointment, limiting our ability to determine how long patients waited for their initial consultation. Furthermore, the decision to undergo surgery is multifactorial and cannot be simplified into time from initial recommendation to surgery, as some patients delay surgery because of school or other obligations. These data should be reasonably consistent over time, as patients seen in the early spring in both groups may delay surgery until the summer, and those diagnosed in June may prefer earlier surgery.
Summary
Children with AIS are at risk for curve progression. Therefore, delays in providing timely care may result in worsening scoliosis. Compared with private insurance patients, Medicaid patients presented with larger curve magnitudes. Further study is needed to better delineate ways to improve care access for patients with scoliosis in communities with larger Medicaid populations.
1. Skaggs DL. Less access to care for children with Medicaid. Orthopedics. 2003;26(12):1184, 1186.
2. Skinner AC, Mayer ML. Effects of insurance status on children’s access to specialty care: a systematic review of the literature. BMC Health Serv Res. 2007;7:194.
3. Iobst C, King W, Baitner A, Tidwell M, Swirsky S, Skaggs DL. Access to care for children with fractures. J Pediatr Orthop. 2010;30(3):244-247.
4. Skaggs DL, Lehmann CL, Rice C, et al. Access to orthopaedic care for children with Medicaid versus private insurance: results of a national survey. J Pediatr Orthop. 2006;26(3):400-404.
5. Skaggs DL, Oda JE, Lerman L, et al. Insurance status and delay in orthotic treatment in children. J Pediatr Orthop. 2007;27(1):94-97.
6. Miyanji F, Slobogean GP, Samdani AF, et al. Is larger scoliosis curve magnitude associated with increased perioperative health-care resource utilization? A multicenter analysis of 325 adolescent idiopathic scoliosis curves. J Bone Joint Surg Am. 2012;94(9):809-813.
7. Nuno M, Drazin DG, Acosta FL Jr. Differences in treatments and outcomes for idiopathic scoliosis patients treated in the United States from 1998 to 2007: impact of socioeconomic variables and ethnicity. Spine J. 2013;13(2):116-123.
8. Vitale MA, Arons RR, Hyman JE, Skaggs DL, Roye DP, Vitale MG. The contribution of hospital volume, payer status, and other factors on the surgical outcomes of scoliosis patients: a review of 3,606 cases in the state of California. J Pediatr Orthop. 2005;25(3):393-399.
9. Goldstein RY, Joiner ER, Skaggs DL. Insurance status does not predict curve magnitude in adolescent idiopathic scoliosis at first presentation to an orthopaedic surgeon. J Pediatr Orthop. 2015;35(1):39-42.
10. Lenke LG, Betz RR, Harms J, et al. Adolescent idiopathic scoliosis: a new classification to determine extent of spinal arthrodesis. J Bone Joint Surg Am. 2001;83(8):1169-1181.
11. Alosh H, Riley LH 3rd, Skolasky RL. Insurance status, geography, race, and ethnicity as predictors of anterior cervical spine surgery rates and in-hospital mortality: an examination of United States trends from 1992 to 2005. Spine. 2009;34(18):1956-1962.
12. Newacheck PW, Hughes DC, Hung YY, Wong S, Stoddard JJ. The unmet health needs of America’s children. Pediatrics. 2000;105(4 pt 2):989-997.
13. Sabharwal S, Zhao C, McClemens E, Kaufmann A. Pediatric orthopaedic patients presenting to a university emergency department after visiting another emergency department: demographics and health insurance status. J Pediatr Orthop. 2007;27(6):690-694.
14. Pierce TR, Mehlman CT, Tamai J, Skaggs DL. Access to care for the adolescent anterior cruciate ligament patient with Medicaid versus private insurance. J Pediatr Orthop. 2012;32(3):245-248.
15. Cho SK, Egorova NN. The association between insurance status and complications, length of stay, and costs for pediatric idiopathic scoliosis. Spine. 2015;40(4):247-256.
16. Fletcher ND, Shourbaji N, Mitchell PM, Oswald TS, Devito DP, Bruce RW Jr. Clinical and economic implications of early discharge following posterior spinal fusion for adolescent idiopathic scoliosis. J Child Orthop. 2014;8(3):257-263.
17. Kasper MJ, Robbins L, Root L, Peterson MG, Allegrante JP. A musculoskeletal outreach screening, treatment, and education program for urban minority children. Arthritis Care Res. 1993;6(3):126-133.
18. Berman S, Dolins J, Tang SF, Yudkowsky B. Factors that influence the willingness of private primary care pediatricians to accept more Medicaid patients. Pediatrics. 2002;110(2 pt 1):239-248.
19. Sommers BD. Protecting low-income children’s access to care: are physician visits associated with reduced patient dropout from Medicaid and the Children’s Health Insurance Program? Pediatrics. 2006;118(1):e36-e42.
20. Bisgaier J, Polsky D, Rhodes KV. Academic medical centers and equity in specialty care access for children. Arch Pediatr Adolesc Med. 2012;166(4):304-310.
21. Sedlis SP, Fisher VJ, Tice D, Esposito R, Madmon L, Steinberg EH. Racial differences in performance of invasive cardiac procedures in a Department of Veterans Affairs medical center. J Clin Epidemiol. 1997;50(8):899-901.
22. Mitchell JB, McCormack LA. Time trends in late-stage diagnosis of cervical cancer. Differences by race/ethnicity and income. Med Care. 1997;35(12):1220-1224.
1. Skaggs DL. Less access to care for children with Medicaid. Orthopedics. 2003;26(12):1184, 1186.
2. Skinner AC, Mayer ML. Effects of insurance status on children’s access to specialty care: a systematic review of the literature. BMC Health Serv Res. 2007;7:194.
3. Iobst C, King W, Baitner A, Tidwell M, Swirsky S, Skaggs DL. Access to care for children with fractures. J Pediatr Orthop. 2010;30(3):244-247.
4. Skaggs DL, Lehmann CL, Rice C, et al. Access to orthopaedic care for children with Medicaid versus private insurance: results of a national survey. J Pediatr Orthop. 2006;26(3):400-404.
5. Skaggs DL, Oda JE, Lerman L, et al. Insurance status and delay in orthotic treatment in children. J Pediatr Orthop. 2007;27(1):94-97.
6. Miyanji F, Slobogean GP, Samdani AF, et al. Is larger scoliosis curve magnitude associated with increased perioperative health-care resource utilization? A multicenter analysis of 325 adolescent idiopathic scoliosis curves. J Bone Joint Surg Am. 2012;94(9):809-813.
7. Nuno M, Drazin DG, Acosta FL Jr. Differences in treatments and outcomes for idiopathic scoliosis patients treated in the United States from 1998 to 2007: impact of socioeconomic variables and ethnicity. Spine J. 2013;13(2):116-123.
8. Vitale MA, Arons RR, Hyman JE, Skaggs DL, Roye DP, Vitale MG. The contribution of hospital volume, payer status, and other factors on the surgical outcomes of scoliosis patients: a review of 3,606 cases in the state of California. J Pediatr Orthop. 2005;25(3):393-399.
9. Goldstein RY, Joiner ER, Skaggs DL. Insurance status does not predict curve magnitude in adolescent idiopathic scoliosis at first presentation to an orthopaedic surgeon. J Pediatr Orthop. 2015;35(1):39-42.
10. Lenke LG, Betz RR, Harms J, et al. Adolescent idiopathic scoliosis: a new classification to determine extent of spinal arthrodesis. J Bone Joint Surg Am. 2001;83(8):1169-1181.
11. Alosh H, Riley LH 3rd, Skolasky RL. Insurance status, geography, race, and ethnicity as predictors of anterior cervical spine surgery rates and in-hospital mortality: an examination of United States trends from 1992 to 2005. Spine. 2009;34(18):1956-1962.
12. Newacheck PW, Hughes DC, Hung YY, Wong S, Stoddard JJ. The unmet health needs of America’s children. Pediatrics. 2000;105(4 pt 2):989-997.
13. Sabharwal S, Zhao C, McClemens E, Kaufmann A. Pediatric orthopaedic patients presenting to a university emergency department after visiting another emergency department: demographics and health insurance status. J Pediatr Orthop. 2007;27(6):690-694.
14. Pierce TR, Mehlman CT, Tamai J, Skaggs DL. Access to care for the adolescent anterior cruciate ligament patient with Medicaid versus private insurance. J Pediatr Orthop. 2012;32(3):245-248.
15. Cho SK, Egorova NN. The association between insurance status and complications, length of stay, and costs for pediatric idiopathic scoliosis. Spine. 2015;40(4):247-256.
16. Fletcher ND, Shourbaji N, Mitchell PM, Oswald TS, Devito DP, Bruce RW Jr. Clinical and economic implications of early discharge following posterior spinal fusion for adolescent idiopathic scoliosis. J Child Orthop. 2014;8(3):257-263.
17. Kasper MJ, Robbins L, Root L, Peterson MG, Allegrante JP. A musculoskeletal outreach screening, treatment, and education program for urban minority children. Arthritis Care Res. 1993;6(3):126-133.
18. Berman S, Dolins J, Tang SF, Yudkowsky B. Factors that influence the willingness of private primary care pediatricians to accept more Medicaid patients. Pediatrics. 2002;110(2 pt 1):239-248.
19. Sommers BD. Protecting low-income children’s access to care: are physician visits associated with reduced patient dropout from Medicaid and the Children’s Health Insurance Program? Pediatrics. 2006;118(1):e36-e42.
20. Bisgaier J, Polsky D, Rhodes KV. Academic medical centers and equity in specialty care access for children. Arch Pediatr Adolesc Med. 2012;166(4):304-310.
21. Sedlis SP, Fisher VJ, Tice D, Esposito R, Madmon L, Steinberg EH. Racial differences in performance of invasive cardiac procedures in a Department of Veterans Affairs medical center. J Clin Epidemiol. 1997;50(8):899-901.
22. Mitchell JB, McCormack LA. Time trends in late-stage diagnosis of cervical cancer. Differences by race/ethnicity and income. Med Care. 1997;35(12):1220-1224.