Imaging

Physeal separation of the distal humerus in a newborn is a rare and severe injury that requires immediate treatment. This fracture was reported as an extremely rare complication of cesarean section.¹ The correct diagnosis can be established by clinical and radiologic findings. However, this injury can be easily overlooked and misdiagnosed. Presentation often involves swelling, tenderness, and agitation with movement of the elbow.

We report a case in which neonatal physeal separation of the distal humerus occurred during cesarean section. The diagnosis was based on clinical and radiologic/arthrographic findings and treated with closed reduction and percutaneous fixation. The patient’s guardian provided written informed consent for print and electronic publication of this case report.

Case Report

A full-term (40-week gestation) male neonate weighing 3690 g was born through cesarean section at the mother’s request. Apgar score was 9 at 1 minute and 10 at 5 minutes. The vertex position of the fetus was confirmed with preoperative ultrasonography. This was the mother’s first pregnancy and an in vitro fertilization. On his second day of life, the patient was referred to the orthopedic department for evaluation of local swelling and diminished spontaneous motion of the right elbow.

Examination revealed local tenderness and swelling in the anterior and lateral aspects of the elbow. Passive elbow range of motion (ROM) caused agitation, and elbow instability was present. A complete neurovascular examination was performed, and neurovascular injury and compartment syndrome were ruled out. Hematologic workup showed no signs of septic arthritis. Radiographs showed posteromedial displacement of the humeroulnar joint. The patient was placed in a long-arm splint, and no reduction was attempted initially.

The patient was taken to the operating room the same day. With the patient under general anesthesia, an arthrogram of the right elbow was obtained. It showed posteromedial displacement of the distal humeral epiphysis (Figure 1A). Closed reduction was performed, and the quality of the reduction was confirmed by intraoperative imaging. Percutaneously, a single 2-mm Kirschner wire (K-wire) was placed in an oblique fashion from the inferolateral aspect of the distal fragment to the contralateral metaphysis of the humerus (Figure 1B). The patient was put in a long-arm splint with the elbow flexed at 90° and the forearm in midpronation.

Follow-up visits were scheduled for 1 week, 3 weeks, and 5 weeks after surgery. Three weeks after surgery, callus formation was confirmed, and the K-wire was removed. Five weeks after surgery, the long-arm splint was removed.

At 6-month follow-up, the patient was pain-free and had full elbow ROM, and radiographs (Figures 2A, 2B) confirmed anatomical restoration of the fracture.

Discussion

Madsen² reported the incidence of birth-related long-bone fractures, including fractures of the humerus, the femur, and the tibia (< 0.1%). According to that review, only 1 of 105,119 patients sustained traumatic physeal separation of the distal humerus.

Different mechanisms have been described for this rare fracture. As the physeal region is the weakest part of the distal humerus, it is prone to injury by rotational shear forces,^3,4 hyperextension of the elbow, or a backward thrust on the forearm with the elbow flexed.⁵ Excessive traction applied during cesarean delivery might cause physeal separation, which was the possible cause in the present case. Most patients have a complicated birth history.

This injury should be suspected in an irritable newborn with swelling, tenderness, and reduced mobility of the upper extremity. Osteomyelitis and septic arthritis should be considered in the differential diagnosis. Brachial plexus injury and dislocation of the elbow joint should also be kept in mind. Child abuse and metabolic bone diseases (eg, osteogenesis imperfecta) should also be considered.

Anteroposterior and lateral plain radiographs of the elbow usually establish the diagnosis. Alteration of humeroulnar alignment and displacement of the proximal forearm are the key points leading to the diagnosis.

The cartilaginous part of the distal humerus and humeroulnar alignment can be demonstrated by ultrasonography.⁶ Magnetic resonance imaging (MRI) can be helpful in diagnosis but is seldom required,⁷ and the sedation or general anesthesia used is a disadvantage. Arthrography is useful not only in diagnosis but in determining the quality of the reduction.⁸ An arthrogram may show that open reduction is unnecessary.

Treatment differs widely. In neonates, who have a tremendous healing capability, this fracture almost always heals uneventfully. An effective treatment method is closed reduction and cast immobilization. However, valgus malalignment and limited elbow ROM were noted in 5% of the patients treated with this method.⁴

Jacobsen and colleagues⁴ reported on 6 neonates who sustained traumatic separation of the distal epiphysis of the humerus at birth and who were treated with casting with or without closed reduction. The authors described good results. One patient had varus malalignment, which was attributed to fragment internal rotation caused by rotational instability.

As our patient’s instability was noted during surgery, we performed percutaneous pinning after arthrography-assisted closed reduction. We considered using 2 lateral pins for fixation, but, after the first pin was placed, fluoroscopic stress testing with the patient under anesthesia demonstrated adequate stability. A second, smaller pin could have been used to control rotation, if needed. Medial pin placement that avoids the ulnar nerve is difficult in the newborn elbow; medial pins should probably be avoided in the newborn, if possible.

Early diagnosis and treatment are essential. Late diagnosis was reported to lead to complications such as varus deformity and restriction of joint ROM.⁴

Our patient healed without any complications and achieved full ROM. Long-term follow-up is needed to diagnose any physeal bar that might lead to secondary deformities.

Conclusion

Cesarean section is reported to reduce birth complications, but it might cause fractures of the femur and humerus.¹ Avoiding application of excessive traction to the forearm can prevent physeal separation of the distal humerus. This entity should be kept in mind as a potential complication of cesarean section. Arthrography is helpful in treatment and may help avoid unnecessary open reduction.

Physeal separation of the distal humerus in a newborn is a rare and severe injury that requires immediate treatment. This fracture was reported as an extremely rare complication of cesarean section.¹ The correct diagnosis can be established by clinical and radiologic findings. However, this injury can be easily overlooked and misdiagnosed. Presentation often involves swelling, tenderness, and agitation with movement of the elbow.

We report a case in which neonatal physeal separation of the distal humerus occurred during cesarean section. The diagnosis was based on clinical and radiologic/arthrographic findings and treated with closed reduction and percutaneous fixation. The patient’s guardian provided written informed consent for print and electronic publication of this case report.

Case Report

A full-term (40-week gestation) male neonate weighing 3690 g was born through cesarean section at the mother’s request. Apgar score was 9 at 1 minute and 10 at 5 minutes. The vertex position of the fetus was confirmed with preoperative ultrasonography. This was the mother’s first pregnancy and an in vitro fertilization. On his second day of life, the patient was referred to the orthopedic department for evaluation of local swelling and diminished spontaneous motion of the right elbow.

Examination revealed local tenderness and swelling in the anterior and lateral aspects of the elbow. Passive elbow range of motion (ROM) caused agitation, and elbow instability was present. A complete neurovascular examination was performed, and neurovascular injury and compartment syndrome were ruled out. Hematologic workup showed no signs of septic arthritis. Radiographs showed posteromedial displacement of the humeroulnar joint. The patient was placed in a long-arm splint, and no reduction was attempted initially.

The patient was taken to the operating room the same day. With the patient under general anesthesia, an arthrogram of the right elbow was obtained. It showed posteromedial displacement of the distal humeral epiphysis (Figure 1A). Closed reduction was performed, and the quality of the reduction was confirmed by intraoperative imaging. Percutaneously, a single 2-mm Kirschner wire (K-wire) was placed in an oblique fashion from the inferolateral aspect of the distal fragment to the contralateral metaphysis of the humerus (Figure 1B). The patient was put in a long-arm splint with the elbow flexed at 90° and the forearm in midpronation.

Follow-up visits were scheduled for 1 week, 3 weeks, and 5 weeks after surgery. Three weeks after surgery, callus formation was confirmed, and the K-wire was removed. Five weeks after surgery, the long-arm splint was removed.

At 6-month follow-up, the patient was pain-free and had full elbow ROM, and radiographs (Figures 2A, 2B) confirmed anatomical restoration of the fracture.

Discussion

Madsen² reported the incidence of birth-related long-bone fractures, including fractures of the humerus, the femur, and the tibia (< 0.1%). According to that review, only 1 of 105,119 patients sustained traumatic physeal separation of the distal humerus.

Different mechanisms have been described for this rare fracture. As the physeal region is the weakest part of the distal humerus, it is prone to injury by rotational shear forces,^3,4 hyperextension of the elbow, or a backward thrust on the forearm with the elbow flexed.⁵ Excessive traction applied during cesarean delivery might cause physeal separation, which was the possible cause in the present case. Most patients have a complicated birth history.

This injury should be suspected in an irritable newborn with swelling, tenderness, and reduced mobility of the upper extremity. Osteomyelitis and septic arthritis should be considered in the differential diagnosis. Brachial plexus injury and dislocation of the elbow joint should also be kept in mind. Child abuse and metabolic bone diseases (eg, osteogenesis imperfecta) should also be considered.

Anteroposterior and lateral plain radiographs of the elbow usually establish the diagnosis. Alteration of humeroulnar alignment and displacement of the proximal forearm are the key points leading to the diagnosis.

The cartilaginous part of the distal humerus and humeroulnar alignment can be demonstrated by ultrasonography.⁶ Magnetic resonance imaging (MRI) can be helpful in diagnosis but is seldom required,⁷ and the sedation or general anesthesia used is a disadvantage. Arthrography is useful not only in diagnosis but in determining the quality of the reduction.⁸ An arthrogram may show that open reduction is unnecessary.

Treatment differs widely. In neonates, who have a tremendous healing capability, this fracture almost always heals uneventfully. An effective treatment method is closed reduction and cast immobilization. However, valgus malalignment and limited elbow ROM were noted in 5% of the patients treated with this method.⁴

Jacobsen and colleagues⁴ reported on 6 neonates who sustained traumatic separation of the distal epiphysis of the humerus at birth and who were treated with casting with or without closed reduction. The authors described good results. One patient had varus malalignment, which was attributed to fragment internal rotation caused by rotational instability.

As our patient’s instability was noted during surgery, we performed percutaneous pinning after arthrography-assisted closed reduction. We considered using 2 lateral pins for fixation, but, after the first pin was placed, fluoroscopic stress testing with the patient under anesthesia demonstrated adequate stability. A second, smaller pin could have been used to control rotation, if needed. Medial pin placement that avoids the ulnar nerve is difficult in the newborn elbow; medial pins should probably be avoided in the newborn, if possible.

Early diagnosis and treatment are essential. Late diagnosis was reported to lead to complications such as varus deformity and restriction of joint ROM.⁴

Our patient healed without any complications and achieved full ROM. Long-term follow-up is needed to diagnose any physeal bar that might lead to secondary deformities.

Conclusion

Cesarean section is reported to reduce birth complications, but it might cause fractures of the femur and humerus.¹ Avoiding application of excessive traction to the forearm can prevent physeal separation of the distal humerus. This entity should be kept in mind as a potential complication of cesarean section. Arthrography is helpful in treatment and may help avoid unnecessary open reduction.

Physeal separation of the distal humerus in a newborn is a rare and severe injury that requires immediate treatment. This fracture was reported as an extremely rare complication of cesarean section.¹ The correct diagnosis can be established by clinical and radiologic findings. However, this injury can be easily overlooked and misdiagnosed. Presentation often involves swelling, tenderness, and agitation with movement of the elbow.

We report a case in which neonatal physeal separation of the distal humerus occurred during cesarean section. The diagnosis was based on clinical and radiologic/arthrographic findings and treated with closed reduction and percutaneous fixation. The patient’s guardian provided written informed consent for print and electronic publication of this case report.

Case Report

A full-term (40-week gestation) male neonate weighing 3690 g was born through cesarean section at the mother’s request. Apgar score was 9 at 1 minute and 10 at 5 minutes. The vertex position of the fetus was confirmed with preoperative ultrasonography. This was the mother’s first pregnancy and an in vitro fertilization. On his second day of life, the patient was referred to the orthopedic department for evaluation of local swelling and diminished spontaneous motion of the right elbow.

Examination revealed local tenderness and swelling in the anterior and lateral aspects of the elbow. Passive elbow range of motion (ROM) caused agitation, and elbow instability was present. A complete neurovascular examination was performed, and neurovascular injury and compartment syndrome were ruled out. Hematologic workup showed no signs of septic arthritis. Radiographs showed posteromedial displacement of the humeroulnar joint. The patient was placed in a long-arm splint, and no reduction was attempted initially.

The patient was taken to the operating room the same day. With the patient under general anesthesia, an arthrogram of the right elbow was obtained. It showed posteromedial displacement of the distal humeral epiphysis (Figure 1A). Closed reduction was performed, and the quality of the reduction was confirmed by intraoperative imaging. Percutaneously, a single 2-mm Kirschner wire (K-wire) was placed in an oblique fashion from the inferolateral aspect of the distal fragment to the contralateral metaphysis of the humerus (Figure 1B). The patient was put in a long-arm splint with the elbow flexed at 90° and the forearm in midpronation.

Follow-up visits were scheduled for 1 week, 3 weeks, and 5 weeks after surgery. Three weeks after surgery, callus formation was confirmed, and the K-wire was removed. Five weeks after surgery, the long-arm splint was removed.

At 6-month follow-up, the patient was pain-free and had full elbow ROM, and radiographs (Figures 2A, 2B) confirmed anatomical restoration of the fracture.

Discussion

Madsen² reported the incidence of birth-related long-bone fractures, including fractures of the humerus, the femur, and the tibia (< 0.1%). According to that review, only 1 of 105,119 patients sustained traumatic physeal separation of the distal humerus.

Different mechanisms have been described for this rare fracture. As the physeal region is the weakest part of the distal humerus, it is prone to injury by rotational shear forces,^3,4 hyperextension of the elbow, or a backward thrust on the forearm with the elbow flexed.⁵ Excessive traction applied during cesarean delivery might cause physeal separation, which was the possible cause in the present case. Most patients have a complicated birth history.

This injury should be suspected in an irritable newborn with swelling, tenderness, and reduced mobility of the upper extremity. Osteomyelitis and septic arthritis should be considered in the differential diagnosis. Brachial plexus injury and dislocation of the elbow joint should also be kept in mind. Child abuse and metabolic bone diseases (eg, osteogenesis imperfecta) should also be considered.

Anteroposterior and lateral plain radiographs of the elbow usually establish the diagnosis. Alteration of humeroulnar alignment and displacement of the proximal forearm are the key points leading to the diagnosis.

The cartilaginous part of the distal humerus and humeroulnar alignment can be demonstrated by ultrasonography.⁶ Magnetic resonance imaging (MRI) can be helpful in diagnosis but is seldom required,⁷ and the sedation or general anesthesia used is a disadvantage. Arthrography is useful not only in diagnosis but in determining the quality of the reduction.⁸ An arthrogram may show that open reduction is unnecessary.

Treatment differs widely. In neonates, who have a tremendous healing capability, this fracture almost always heals uneventfully. An effective treatment method is closed reduction and cast immobilization. However, valgus malalignment and limited elbow ROM were noted in 5% of the patients treated with this method.⁴

Jacobsen and colleagues⁴ reported on 6 neonates who sustained traumatic separation of the distal epiphysis of the humerus at birth and who were treated with casting with or without closed reduction. The authors described good results. One patient had varus malalignment, which was attributed to fragment internal rotation caused by rotational instability.

As our patient’s instability was noted during surgery, we performed percutaneous pinning after arthrography-assisted closed reduction. We considered using 2 lateral pins for fixation, but, after the first pin was placed, fluoroscopic stress testing with the patient under anesthesia demonstrated adequate stability. A second, smaller pin could have been used to control rotation, if needed. Medial pin placement that avoids the ulnar nerve is difficult in the newborn elbow; medial pins should probably be avoided in the newborn, if possible.

Early diagnosis and treatment are essential. Late diagnosis was reported to lead to complications such as varus deformity and restriction of joint ROM.⁴

Our patient healed without any complications and achieved full ROM. Long-term follow-up is needed to diagnose any physeal bar that might lead to secondary deformities.

Conclusion

Cesarean section is reported to reduce birth complications, but it might cause fractures of the femur and humerus.¹ Avoiding application of excessive traction to the forearm can prevent physeal separation of the distal humerus. This entity should be kept in mind as a potential complication of cesarean section. Arthrography is helpful in treatment and may help avoid unnecessary open reduction.

Chordomas persist as one of the rarer malignancies, accounting for approximately 1% to 4% of primary bone cancers.¹ When chordomas occur, these tumors localize predominantly in the sacrococcygeal region.² In addition to the urgency for addressing a relatively fast-growing tumor, the anatomical complexity of this area complicates the potential treatments. Furthermore, because of the lack of definitive symptoms, diagnosis is often difficult and typically occurs later in the disease progression.³ An aggressive treatment approach is often warranted because of the biologically aggressive nature of this disease. Full or partial sacrectomy is often the only option that offers the possibility of a long-term cure.⁴ A sacrectomy is a destructive procedure that can lead to mechanical instability depending on the extent of the surgical resection. When the entire sacrum is removed, there is an obvious need for lumbar-pelvic fixation; however, traditionally, partial sacrectomy procedures have been successfully performed without the need for instrumentation.^3,4

This report describes the case of a patient with a noninstrumented sacrectomy procedure distal to the S2 foramen that resulted in an insufficiency fracture. The patient provided written informed consent for print and electronic publication of this case report.

Case Report

A 66-year-old woman presented with severe lower back pain of a month’s duration. Her pain was localized to the coccyx area and did not radiate to the lower legs. Although the pain could not be elicited by palpation, pain occurred when sitting and increased when standing for prolonged periods. Three weeks prior to the patient’s initial office visit, she noticed transient constipation and urinary retention. She denied any fever, chills, nausea, vomiting, unexplained weight loss, weight gain, and abdominal pain. There were no motor deficits in the lower limbs. Sensation was intact in the lower limbs except for the posterior aspect of the left leg down to the popliteal fossa, where light touch perception was absent. She recalled the loss of sensation in this area 20 years earlier, and it had neither progressed nor abated since then. She had a history of osteoarthritis and had been diagnosed with degenerative disc disease 20 years ago.

A radiographic review of her lumbar spine showed significant spinal stenosis and degenerative disease of the lumbar spine on non–contrast-enhanced magnetic resonance imaging (MRI). The MRI also revealed a large, soft-tissue mass at the S3-S4 level, eroding most of the S3 vertebral body and extending into the S4 vertebral body. The MRI images used for this analysis were insufficient in providing a complete portrayal of the entire mass. Because of these uncertainties, contrast-enhanced and non–contrast-enhanced pelvic MRIs were taken. The MRI analyses identified a mass density replacing the lower sacrum and upper coccyx that was bright in intensity on T2 and dim on T1 sequences. Sagittal imaging measurements were 5.9×2.5 cm and 4.4 cm right-to-left on coronal imaging. The mass extended beyond the involved sacrococcygeal segments and dorsally beyond the normal cortical margin of the sacrum and coccyx (Figures 1A, 1B). Next, a computer tomographic–guided needle biopsy through a posterior paraspinal approach was obtained. The biopsy consisted of fragments of a malignant neoplasm consistent with physaliferous cells. The specimen was positive for pankeratin, keratin AE1/AE3, epithelial membrane antigen, and S100 protein. This supported a diagnosis of a sacral chordoma. An en bloc sacrectomy at S2; lumbar laminectomy at L5, S1, and S2; and thecal sac transection at the S3 nerve roots were planned.

Surgical Procedure

The patient was placed in the prone position after a colostomy and harvesting of a rectus flap in the supine position. A midline incision was made from the spinous process of L5 down through the tip of the coccyx, and soft tissues were elevated while maintaining hemostasis. The most distal part of the coccyx was transected, and using a combination of electrocautery and paraspinal elevators, rectal and peritoneal tissues were elevated off the ventral component of the coccyx until a hand could easily reach the bifurcation of the iliac vessels. Electrocautery transected paraspinal muscles at the S1 and S2 levels while the more cranial paraspinal musculature was elevated to allow for a laminectomy. The spinous processes were removed from L5 and the sacrum with a Leksell rongeur. A high-speed burr thinned the dorsal lamina components of L5, S1, and the leading edge of S2. The L5, S1, and S2 nerve roots were identified. The gluteal muscles were elevated and the sacral coccygeal ligaments were transected. After identifying the sciatic notches, the S2 nerves exiting the foramen were identified, followed out through the sciatic notch, and a wire was passed through this region. Three 2-0 silk ties were applied to the exposed portion of the S3 and S4 nerve roots, and the nerves were transected because they were integrally involved with the tumor. Using a series of high-speed burrs and osteotomes, lateral cuts were made through the sciatic notch. The sacrum was osteotomized at the S2 sacral foramen through the anterior component with an osteotome, while a hand protected the ventral structures. The remaining parts of the S3 and S4 dorsal nerve roots were transected. An incision through the peritoneum was made to access the rectus flap, and a plastic surgeon closed the wounds and secured the flap. 

Postoperative Course

The patient’s final pathology confirmed a chordoma with negative margins. Postoperatively, the rectus flap became ischemic and a wound infection developed. It was irrigated, débrided, and treated with vacuum-assisted closure (VAC), in addition to perioperative antibiotic administration. An abdominal computed tomography (CT) scan did not show any fistula, and her wound remained healthy, pink, and viable as her VAC was changed every 3 days. Because the patient’s nutritional status was compromised, she started nutritional supplements in addition to a regular diet. Physical therapy was prescribed and the patient began bladder training with self-catheterization after a failed voiding trial attempt. After 2 months of convalescence, the patient had mobilized well and had progressed to walking without an ambulatory aide.

At her third postoperative month, the patient noted new onset of extreme pain in the groin and left thigh regions. The patient was examined and appeared to have a stable neurological exam. She had reproducible pain with a FABER (Flexion, Abduction, External Rotation, and Extension) test. MRI showed increased signal on short tau inversion recovery (STIR) sequences and T2-weighted images that was consistent with a left sacral ala stress fracture with a vertically oriented fracture line (Figures 2A, 2B). The patient was asked to begin utilizing a walker for ambulatory assistance, but her weight-bearing status was not changed. Over the course of 3 months, the patient noted a resolution of her pain. All postoperative MRI images confirmed the patient to be disease-free; and in addition, all of her follow-up radiographs showed a stable pelvic ring (Figures 3A, 3B). At her 2-year follow-up, the patient remained disease- and pain-free.

Discussion

Full discussions of the mechanical considerations of a partial sacrectomy have been described previously^5-8; however, surgeons typically consider the need for lumbar-pelvic stabilization when the surgical resection requires a violation of the S1 body. Approximately two-thirds of sacral tumors occur at or below the level of the S2 body.⁸ These lesions of the caudal sacrum can sometimes be effectively resected with transverse partial sacrectomy. Great care is taken to resect only the portion of the sacrum necessary for local disease control, sparing as much of the sacroiliac joint and as many of the lumbosacral nerve roots as possible.

Under normal conditions, the sacroiliac articulation is stabilized by both its geometric interface and its extraordinarily strong ligaments. This spatial arrangement conveys stability primarily against caudal migration of the sacrum. The sacroiliac, sacrotuberous, sacrospinous, and lumbosacral ligaments, which are among the strongest ligaments in the body, primarily act to provide stability to the pelvic ring by preventing diastasis. The combination of these factors renders the spinopelvic segment especially stable. Previously, 2 biomechanical studies that specifically looked at extreme loading patterns to better understand the need for lumbar-pelvic instrumentation predicted a fracture pattern when there was an inability of the base of the sacral ala to resist shear.^8,9 This is precisely where our patient’s insufficiency fracture occurred.

To our knowledge, this is the first reported in vivo evidence of this fracture pattern. While this patient’s potential history of osteoporosis may have elevated or contributed to her risk for fracture, her preoperative bone densitometry, with T scores of -1.0 on the left and right femur necks and 0.8 on her L1-L4 anteroposterior spine, would argue against this risk factor. None of these values represent a truly osteoporotic patient. It would appear that our patient sustained the fracture pattern predicted by Hugate and colleagues.⁸

The edema seen on the MRI most likely represents a fracture; however, sacroiliitis and infection are also potential diagnoses. Because there was no tumor in this region on the preoperative scans, we thought that a residual tumor was unlikely. The signal changes seen on T2 MRI sequences represent edema. The use of a bone scan that detects healing bone may have been a useful additional study to confirm this fracture as opposed to sacroiliitis. A CT scan would have been a potentially useful study to provide detail of fracture displacement and the overall fracture pattern. Standing plain radiographs are best for viewing fracture displacement with weight-bearing.

Surgeons contemplating performing partial sacrectomies should bear in mind that, even with preservation of the S1 body, a potential for fracture exists as evidenced by our patient. In our opinion, this patient did not require instrumentation but a more gradual rehabilitation program.

Chordomas persist as one of the rarer malignancies, accounting for approximately 1% to 4% of primary bone cancers.¹ When chordomas occur, these tumors localize predominantly in the sacrococcygeal region.² In addition to the urgency for addressing a relatively fast-growing tumor, the anatomical complexity of this area complicates the potential treatments. Furthermore, because of the lack of definitive symptoms, diagnosis is often difficult and typically occurs later in the disease progression.³ An aggressive treatment approach is often warranted because of the biologically aggressive nature of this disease. Full or partial sacrectomy is often the only option that offers the possibility of a long-term cure.⁴ A sacrectomy is a destructive procedure that can lead to mechanical instability depending on the extent of the surgical resection. When the entire sacrum is removed, there is an obvious need for lumbar-pelvic fixation; however, traditionally, partial sacrectomy procedures have been successfully performed without the need for instrumentation.^3,4

This report describes the case of a patient with a noninstrumented sacrectomy procedure distal to the S2 foramen that resulted in an insufficiency fracture. The patient provided written informed consent for print and electronic publication of this case report.

Case Report

A 66-year-old woman presented with severe lower back pain of a month’s duration. Her pain was localized to the coccyx area and did not radiate to the lower legs. Although the pain could not be elicited by palpation, pain occurred when sitting and increased when standing for prolonged periods. Three weeks prior to the patient’s initial office visit, she noticed transient constipation and urinary retention. She denied any fever, chills, nausea, vomiting, unexplained weight loss, weight gain, and abdominal pain. There were no motor deficits in the lower limbs. Sensation was intact in the lower limbs except for the posterior aspect of the left leg down to the popliteal fossa, where light touch perception was absent. She recalled the loss of sensation in this area 20 years earlier, and it had neither progressed nor abated since then. She had a history of osteoarthritis and had been diagnosed with degenerative disc disease 20 years ago.

A radiographic review of her lumbar spine showed significant spinal stenosis and degenerative disease of the lumbar spine on non–contrast-enhanced magnetic resonance imaging (MRI). The MRI also revealed a large, soft-tissue mass at the S3-S4 level, eroding most of the S3 vertebral body and extending into the S4 vertebral body. The MRI images used for this analysis were insufficient in providing a complete portrayal of the entire mass. Because of these uncertainties, contrast-enhanced and non–contrast-enhanced pelvic MRIs were taken. The MRI analyses identified a mass density replacing the lower sacrum and upper coccyx that was bright in intensity on T2 and dim on T1 sequences. Sagittal imaging measurements were 5.9×2.5 cm and 4.4 cm right-to-left on coronal imaging. The mass extended beyond the involved sacrococcygeal segments and dorsally beyond the normal cortical margin of the sacrum and coccyx (Figures 1A, 1B). Next, a computer tomographic–guided needle biopsy through a posterior paraspinal approach was obtained. The biopsy consisted of fragments of a malignant neoplasm consistent with physaliferous cells. The specimen was positive for pankeratin, keratin AE1/AE3, epithelial membrane antigen, and S100 protein. This supported a diagnosis of a sacral chordoma. An en bloc sacrectomy at S2; lumbar laminectomy at L5, S1, and S2; and thecal sac transection at the S3 nerve roots were planned.

Surgical Procedure

The patient was placed in the prone position after a colostomy and harvesting of a rectus flap in the supine position. A midline incision was made from the spinous process of L5 down through the tip of the coccyx, and soft tissues were elevated while maintaining hemostasis. The most distal part of the coccyx was transected, and using a combination of electrocautery and paraspinal elevators, rectal and peritoneal tissues were elevated off the ventral component of the coccyx until a hand could easily reach the bifurcation of the iliac vessels. Electrocautery transected paraspinal muscles at the S1 and S2 levels while the more cranial paraspinal musculature was elevated to allow for a laminectomy. The spinous processes were removed from L5 and the sacrum with a Leksell rongeur. A high-speed burr thinned the dorsal lamina components of L5, S1, and the leading edge of S2. The L5, S1, and S2 nerve roots were identified. The gluteal muscles were elevated and the sacral coccygeal ligaments were transected. After identifying the sciatic notches, the S2 nerves exiting the foramen were identified, followed out through the sciatic notch, and a wire was passed through this region. Three 2-0 silk ties were applied to the exposed portion of the S3 and S4 nerve roots, and the nerves were transected because they were integrally involved with the tumor. Using a series of high-speed burrs and osteotomes, lateral cuts were made through the sciatic notch. The sacrum was osteotomized at the S2 sacral foramen through the anterior component with an osteotome, while a hand protected the ventral structures. The remaining parts of the S3 and S4 dorsal nerve roots were transected. An incision through the peritoneum was made to access the rectus flap, and a plastic surgeon closed the wounds and secured the flap. 

Postoperative Course

The patient’s final pathology confirmed a chordoma with negative margins. Postoperatively, the rectus flap became ischemic and a wound infection developed. It was irrigated, débrided, and treated with vacuum-assisted closure (VAC), in addition to perioperative antibiotic administration. An abdominal computed tomography (CT) scan did not show any fistula, and her wound remained healthy, pink, and viable as her VAC was changed every 3 days. Because the patient’s nutritional status was compromised, she started nutritional supplements in addition to a regular diet. Physical therapy was prescribed and the patient began bladder training with self-catheterization after a failed voiding trial attempt. After 2 months of convalescence, the patient had mobilized well and had progressed to walking without an ambulatory aide.

At her third postoperative month, the patient noted new onset of extreme pain in the groin and left thigh regions. The patient was examined and appeared to have a stable neurological exam. She had reproducible pain with a FABER (Flexion, Abduction, External Rotation, and Extension) test. MRI showed increased signal on short tau inversion recovery (STIR) sequences and T2-weighted images that was consistent with a left sacral ala stress fracture with a vertically oriented fracture line (Figures 2A, 2B). The patient was asked to begin utilizing a walker for ambulatory assistance, but her weight-bearing status was not changed. Over the course of 3 months, the patient noted a resolution of her pain. All postoperative MRI images confirmed the patient to be disease-free; and in addition, all of her follow-up radiographs showed a stable pelvic ring (Figures 3A, 3B). At her 2-year follow-up, the patient remained disease- and pain-free.

Discussion

Full discussions of the mechanical considerations of a partial sacrectomy have been described previously^5-8; however, surgeons typically consider the need for lumbar-pelvic stabilization when the surgical resection requires a violation of the S1 body. Approximately two-thirds of sacral tumors occur at or below the level of the S2 body.⁸ These lesions of the caudal sacrum can sometimes be effectively resected with transverse partial sacrectomy. Great care is taken to resect only the portion of the sacrum necessary for local disease control, sparing as much of the sacroiliac joint and as many of the lumbosacral nerve roots as possible.

Under normal conditions, the sacroiliac articulation is stabilized by both its geometric interface and its extraordinarily strong ligaments. This spatial arrangement conveys stability primarily against caudal migration of the sacrum. The sacroiliac, sacrotuberous, sacrospinous, and lumbosacral ligaments, which are among the strongest ligaments in the body, primarily act to provide stability to the pelvic ring by preventing diastasis. The combination of these factors renders the spinopelvic segment especially stable. Previously, 2 biomechanical studies that specifically looked at extreme loading patterns to better understand the need for lumbar-pelvic instrumentation predicted a fracture pattern when there was an inability of the base of the sacral ala to resist shear.^8,9 This is precisely where our patient’s insufficiency fracture occurred.

To our knowledge, this is the first reported in vivo evidence of this fracture pattern. While this patient’s potential history of osteoporosis may have elevated or contributed to her risk for fracture, her preoperative bone densitometry, with T scores of -1.0 on the left and right femur necks and 0.8 on her L1-L4 anteroposterior spine, would argue against this risk factor. None of these values represent a truly osteoporotic patient. It would appear that our patient sustained the fracture pattern predicted by Hugate and colleagues.⁸

The edema seen on the MRI most likely represents a fracture; however, sacroiliitis and infection are also potential diagnoses. Because there was no tumor in this region on the preoperative scans, we thought that a residual tumor was unlikely. The signal changes seen on T2 MRI sequences represent edema. The use of a bone scan that detects healing bone may have been a useful additional study to confirm this fracture as opposed to sacroiliitis. A CT scan would have been a potentially useful study to provide detail of fracture displacement and the overall fracture pattern. Standing plain radiographs are best for viewing fracture displacement with weight-bearing.

Surgeons contemplating performing partial sacrectomies should bear in mind that, even with preservation of the S1 body, a potential for fracture exists as evidenced by our patient. In our opinion, this patient did not require instrumentation but a more gradual rehabilitation program.

Chordomas persist as one of the rarer malignancies, accounting for approximately 1% to 4% of primary bone cancers.¹ When chordomas occur, these tumors localize predominantly in the sacrococcygeal region.² In addition to the urgency for addressing a relatively fast-growing tumor, the anatomical complexity of this area complicates the potential treatments. Furthermore, because of the lack of definitive symptoms, diagnosis is often difficult and typically occurs later in the disease progression.³ An aggressive treatment approach is often warranted because of the biologically aggressive nature of this disease. Full or partial sacrectomy is often the only option that offers the possibility of a long-term cure.⁴ A sacrectomy is a destructive procedure that can lead to mechanical instability depending on the extent of the surgical resection. When the entire sacrum is removed, there is an obvious need for lumbar-pelvic fixation; however, traditionally, partial sacrectomy procedures have been successfully performed without the need for instrumentation.^3,4

This report describes the case of a patient with a noninstrumented sacrectomy procedure distal to the S2 foramen that resulted in an insufficiency fracture. The patient provided written informed consent for print and electronic publication of this case report.

Case Report

A 66-year-old woman presented with severe lower back pain of a month’s duration. Her pain was localized to the coccyx area and did not radiate to the lower legs. Although the pain could not be elicited by palpation, pain occurred when sitting and increased when standing for prolonged periods. Three weeks prior to the patient’s initial office visit, she noticed transient constipation and urinary retention. She denied any fever, chills, nausea, vomiting, unexplained weight loss, weight gain, and abdominal pain. There were no motor deficits in the lower limbs. Sensation was intact in the lower limbs except for the posterior aspect of the left leg down to the popliteal fossa, where light touch perception was absent. She recalled the loss of sensation in this area 20 years earlier, and it had neither progressed nor abated since then. She had a history of osteoarthritis and had been diagnosed with degenerative disc disease 20 years ago.

A radiographic review of her lumbar spine showed significant spinal stenosis and degenerative disease of the lumbar spine on non–contrast-enhanced magnetic resonance imaging (MRI). The MRI also revealed a large, soft-tissue mass at the S3-S4 level, eroding most of the S3 vertebral body and extending into the S4 vertebral body. The MRI images used for this analysis were insufficient in providing a complete portrayal of the entire mass. Because of these uncertainties, contrast-enhanced and non–contrast-enhanced pelvic MRIs were taken. The MRI analyses identified a mass density replacing the lower sacrum and upper coccyx that was bright in intensity on T2 and dim on T1 sequences. Sagittal imaging measurements were 5.9×2.5 cm and 4.4 cm right-to-left on coronal imaging. The mass extended beyond the involved sacrococcygeal segments and dorsally beyond the normal cortical margin of the sacrum and coccyx (Figures 1A, 1B). Next, a computer tomographic–guided needle biopsy through a posterior paraspinal approach was obtained. The biopsy consisted of fragments of a malignant neoplasm consistent with physaliferous cells. The specimen was positive for pankeratin, keratin AE1/AE3, epithelial membrane antigen, and S100 protein. This supported a diagnosis of a sacral chordoma. An en bloc sacrectomy at S2; lumbar laminectomy at L5, S1, and S2; and thecal sac transection at the S3 nerve roots were planned.

Surgical Procedure

The patient was placed in the prone position after a colostomy and harvesting of a rectus flap in the supine position. A midline incision was made from the spinous process of L5 down through the tip of the coccyx, and soft tissues were elevated while maintaining hemostasis. The most distal part of the coccyx was transected, and using a combination of electrocautery and paraspinal elevators, rectal and peritoneal tissues were elevated off the ventral component of the coccyx until a hand could easily reach the bifurcation of the iliac vessels. Electrocautery transected paraspinal muscles at the S1 and S2 levels while the more cranial paraspinal musculature was elevated to allow for a laminectomy. The spinous processes were removed from L5 and the sacrum with a Leksell rongeur. A high-speed burr thinned the dorsal lamina components of L5, S1, and the leading edge of S2. The L5, S1, and S2 nerve roots were identified. The gluteal muscles were elevated and the sacral coccygeal ligaments were transected. After identifying the sciatic notches, the S2 nerves exiting the foramen were identified, followed out through the sciatic notch, and a wire was passed through this region. Three 2-0 silk ties were applied to the exposed portion of the S3 and S4 nerve roots, and the nerves were transected because they were integrally involved with the tumor. Using a series of high-speed burrs and osteotomes, lateral cuts were made through the sciatic notch. The sacrum was osteotomized at the S2 sacral foramen through the anterior component with an osteotome, while a hand protected the ventral structures. The remaining parts of the S3 and S4 dorsal nerve roots were transected. An incision through the peritoneum was made to access the rectus flap, and a plastic surgeon closed the wounds and secured the flap. 

Postoperative Course

The patient’s final pathology confirmed a chordoma with negative margins. Postoperatively, the rectus flap became ischemic and a wound infection developed. It was irrigated, débrided, and treated with vacuum-assisted closure (VAC), in addition to perioperative antibiotic administration. An abdominal computed tomography (CT) scan did not show any fistula, and her wound remained healthy, pink, and viable as her VAC was changed every 3 days. Because the patient’s nutritional status was compromised, she started nutritional supplements in addition to a regular diet. Physical therapy was prescribed and the patient began bladder training with self-catheterization after a failed voiding trial attempt. After 2 months of convalescence, the patient had mobilized well and had progressed to walking without an ambulatory aide.

At her third postoperative month, the patient noted new onset of extreme pain in the groin and left thigh regions. The patient was examined and appeared to have a stable neurological exam. She had reproducible pain with a FABER (Flexion, Abduction, External Rotation, and Extension) test. MRI showed increased signal on short tau inversion recovery (STIR) sequences and T2-weighted images that was consistent with a left sacral ala stress fracture with a vertically oriented fracture line (Figures 2A, 2B). The patient was asked to begin utilizing a walker for ambulatory assistance, but her weight-bearing status was not changed. Over the course of 3 months, the patient noted a resolution of her pain. All postoperative MRI images confirmed the patient to be disease-free; and in addition, all of her follow-up radiographs showed a stable pelvic ring (Figures 3A, 3B). At her 2-year follow-up, the patient remained disease- and pain-free.

Discussion

Full discussions of the mechanical considerations of a partial sacrectomy have been described previously^5-8; however, surgeons typically consider the need for lumbar-pelvic stabilization when the surgical resection requires a violation of the S1 body. Approximately two-thirds of sacral tumors occur at or below the level of the S2 body.⁸ These lesions of the caudal sacrum can sometimes be effectively resected with transverse partial sacrectomy. Great care is taken to resect only the portion of the sacrum necessary for local disease control, sparing as much of the sacroiliac joint and as many of the lumbosacral nerve roots as possible.

Under normal conditions, the sacroiliac articulation is stabilized by both its geometric interface and its extraordinarily strong ligaments. This spatial arrangement conveys stability primarily against caudal migration of the sacrum. The sacroiliac, sacrotuberous, sacrospinous, and lumbosacral ligaments, which are among the strongest ligaments in the body, primarily act to provide stability to the pelvic ring by preventing diastasis. The combination of these factors renders the spinopelvic segment especially stable. Previously, 2 biomechanical studies that specifically looked at extreme loading patterns to better understand the need for lumbar-pelvic instrumentation predicted a fracture pattern when there was an inability of the base of the sacral ala to resist shear.^8,9 This is precisely where our patient’s insufficiency fracture occurred.

To our knowledge, this is the first reported in vivo evidence of this fracture pattern. While this patient’s potential history of osteoporosis may have elevated or contributed to her risk for fracture, her preoperative bone densitometry, with T scores of -1.0 on the left and right femur necks and 0.8 on her L1-L4 anteroposterior spine, would argue against this risk factor. None of these values represent a truly osteoporotic patient. It would appear that our patient sustained the fracture pattern predicted by Hugate and colleagues.⁸

The edema seen on the MRI most likely represents a fracture; however, sacroiliitis and infection are also potential diagnoses. Because there was no tumor in this region on the preoperative scans, we thought that a residual tumor was unlikely. The signal changes seen on T2 MRI sequences represent edema. The use of a bone scan that detects healing bone may have been a useful additional study to confirm this fracture as opposed to sacroiliitis. A CT scan would have been a potentially useful study to provide detail of fracture displacement and the overall fracture pattern. Standing plain radiographs are best for viewing fracture displacement with weight-bearing.

Surgeons contemplating performing partial sacrectomies should bear in mind that, even with preservation of the S1 body, a potential for fracture exists as evidenced by our patient. In our opinion, this patient did not require instrumentation but a more gradual rehabilitation program.

Pelvic injuries account for 3% of all skeletal fractures.¹ Injury to the sacroiliac (SI) joint is frequently associated with unstable pelvic ring fractures, which are potentially life-threatening injuries. Surgical fixation of these injuries is preferred to nonoperative treatment given the potential for improved reduction and early mobilization and weight-bearing, thereby decreasing perioperative morbidity and improving functional outcome.²

The classic method of surgical fixation of the SI joint consisted of open reduction and internal fixation. This method carried a substantial risk for large dissection, iatrogenic nerve injury, and increased blood loss to the already traumatized patient.³ Percutaneous fixation allows for a shorter operating time, decreased soft-tissue stripping, and decreased blood loss compared with a traditional open procedure.⁴ However, posterior pelvic anatomy is complex and variable, and reports have found screw misplacements as high as 24%⁵ and neurologic complication rates up to 18%.^6-9 

Various imaging modalities, including fluoroscopy,⁵ computed tomography (CT),^6-7 fluoroscopic CT, and computer-assisted techniques^5,9 have been used to achieve proper screw placement. Conventional fluoroscopy is the standard for intraoperative screw placement. However, acceptable reduction of the SI joint and proper implantation of the screws without perforation of the neural foramina is challenging, especially when coupled with difficulties of fluoroscopic imaging and variations in pelvic anatomy. 

Sacral dysplasia has been reported to occur in up to 20% to 40% of the population and has significant implications in patients indicated for iliosacral screw placement.¹⁰ Incorrect placement of iliosacral screws may result in iatrogenic neurovascular complications.^11-13 Malpositioned screws using fluoroscopic guidance have been reported in 2% to 15% of patients with an incidence of neurologic compromise between 0.5% and 7.7%. As little as 4° of misdirection can result in damage to neurovascular structures.¹⁴

At our institution, we routinely obtained postoperative CT to evaluate the placement of SI screws. The objective of this retrospective study is to evaluate the rate of revision surgery of percutaneous SI screw fixation, to determine whether CT is an accurate tool for evaluation of the reduction and the need for revision surgery, and to decide if any violation of the neural foramina is safe.

Materials and Methods

After institutional review board approval, we retrospectively reviewed and evaluated medical records and radiographs of all patients who sustained unstable pelvic ring fractures between July 1, 2005, and June 30, 2010. We identified all patients who were treated with closed reductions and percutaneous iliosacral screw fixation, according to the method described by Routt in 1995.⁴ We excluded all pelvic fractures in patients who underwent open reduction for the posterior injury or did not have percutaneous SI screws placed, those with spinal injury, and those without follow-up. Of the 46 patients who met the inclusion criteria were 26 men and 20 women with a mean age of 42 years (range, 16 to 73 years). Motor vehicle accidents accounted for 13 cases; 19 were crush injuries and 14 were falls from height. Seventeen patients (37%) met the radiographic criteria for sacral dysmorphism. Forty-two of the 46 patients were polytrauma patients with associated musculoskeletal injuries and/or abdominal, chest, or head injuries.

Six patients presented with some neurologic deficit at the time of injury; all fractures were closed. The initial imaging study included plain anteroposterior (AP), inlet, and outlet radiographs of the pelvis and a pelvic CT scan. Using the classification of Young and Burgess,¹⁵ there were 3 vertical shear injuries, 13 lateral compression–type injuries, 17 anterior-posterior–type injuries, 7 sacral fractures, and 6 combination- or unclassifiable-type pelvic injuries. Of the sacral fractures, there were 3 Denis zone 1, 3 Denis zone 2, and 1 Denis zone 3. 

The pelvic CT scan included the entire pelvis from the ilium to the ischial tuberosities. Each scan consisted of either a 5.0-mm or a 2.5-mm sequential axial image. A picture archiving and communication system (PACS) workstation using Centricity version 2.1 (GE Medical Systems, Waukesha, Wisconsin) was used to analyze each scan with a bone algorithm. On PACS, each initial displacement was characterized by the amount of SI joint widening at the level of the S1 and was measured using digital calipers.   

Surgery

Mean time to surgery was 4 days (range, 2 to 15 days) after the injury. A total of 51 SI screws were implanted in 46 patients. We achieved closed reduction of the posterior pelvic ring by various techniques, including compression with percutaneous partially threaded screw fixation. In the cases in which the posterior ring lesion was associated with a pure pubic symphysis disruption, the anterior pelvis was initially reduced and stabilized with small-fragment plate fixation (Synthes, Inc, Paoli, Pennsylvania). The posterior complex was stabilized with 1 screw in 41 patients, 2 cases required a transiliac screw, and 2 screws (S1 and S2) were placed in each of the remaining 3 cases. Definitive stabilization of the posterior pelvis was achieved with percutaneous, partially threaded 7.3- or 7.5-mm–diameter cannulated screws (Synthes, Inc, and Zimmer Inc, Warsaw, Indiana, respectively) in 42 fractures and 6.5-mm screws (Synthes, Inc) in 4 fractures. In 11 cases where the fracture was through the sacrum, fully threaded cannulated screws were used to avoid compression. Screw insertion was performed under fluoroscopic guidance with inlet, outlet, and lateral sacral views. One of 2 fellowship-trained trauma surgeons performed the surgeries. Rehabilitation plans were customized to each patient based on concomitant injuries. 

Postoperative Assessment

AP, lateral sacral, and inlet and outlet postoperative radiographs were taken in all cases within 24 hours after surgery. Pelvic CT was also obtained within 24 hours of surgery to review reduction and screw placement.

Using the measurement tool on the PACS system, we measured the penetration of the screw into the foramen. Screws were graded as intraosseous (completely contained within the sacral bone), skived (less than 2 mm of partial penetration into the S1 foramen), or extruded (the screw not contained by the bone). Screw penetration of the S1 was evaluated on the radiographic images as well as the axial images of the CT scans.

After surgery, the senior orthopedic resident and attending surgeon performed and documented detailed neurologic evaluations. They reviewed the medical record for neurologic deficit following surgical fixation.   

Results

The mean follow-up time was 12 months (range, 8 months to 2 years). Two patients expired secondary to associated injuries. There were no early deaths related to the pelvic surgery. Stable fixation, including bone or ligamentous healing, as well as full weight-bearing status, was noted in every case. No case exhibited loss of reduction or implant failure or infection.

According to Matta’s criteria of anatomic reduction within 1 cm, all patients were found to have satisfactory reductions.⁷ Six of 46 patients had documented preoperative neurologic deficits. After percutaneous screw fixation, 10 of 46 patients had postoperative neurologic deficit, 2 of which were unchanged from preoperative evaluation. Of the 8 patients with new/altered postoperative neurologic deficit, CT showed neural foramen penetration greater than 2.1 mm in only 2 patients. Both patients underwent screw revision, resulting in improved neurologic deficit. The remaining 4 patients did not have foramen penetration and improved their neurologic function over the course of 2 weeks with return to presurgical status by 6 weeks without necessitating screw removal.

Twenty-three of the 51 screws (45%) had some violation of the S1 foramen on the CT. There were 17 patients with dysmorphic sacrums in which 21 S1 screws were placed. Eleven of  21 (52%) screws showed some penetration of the S1 foramen on CT. There were 29 patients with normal sacral morphology in which 30 S1 screws were placed. Twelve of 30 (40%) screws penetrated the S1 foramen. All violations were in the superior one-third position of the foramen. Two of 46 (4%; 1 with dysmorphism, 1 without) had a new neurologic deficit associated with the surgery (Table). CT showed sacral foramen penetration, and both screws were revised with a better neurologic examination.

High-resolution CTs were obtained in 32 patients, while 14 patients underwent the standard 5.0-mm–cut CTs. Of the 32 patients in which a 2.5-mm high-resolution CT was obtained, 20 (62.5%) had evidence of screw penetration (Figures 1, 2). All violations of the S1 neural foramen were in the superior portion of the foramen. 

When compared with patients who had a 5.0-mm CT, the patients who underwent a high-resolution CT were more likely to show neural foramen penetration (P = .3). The average screw penetration into the S1 neural foramen measured 3.3 mm (range, 1.6-5.7 mm) in dysmorphic sacrum and 2.7 mm  (range, 1.4-7 mm) in normal sacrum. However, in our study, any foramen penetration of less than 2.1 mm on CT did not result in neurologic deficit.  

Discussion

Pelvic fractures are fairly common and represent approximately 5% of all trauma admissions and 3% of all skeletal fractures nationwide.¹ The current treatment for SI disruption is either nonoperative or operative. Surgical fixation is technically demanding and surgeons often need a long learning curve to acquire the demanding technique because of the limitations of radiographic visualization of the relevant landmarks.¹⁶

Letournel¹⁷ developed the technique for iliosacral screw fixation for the treatment of posterior pelvic ring injuries, where 1 or 2 large screws (6.5-7.3 mm in diameter) are inserted under fluoroscopic guidance through the ilium, across the SI articulation, and into the superior sacral vertebral bodies using percutaneous techniques. Currently, the standard procedure to accomplish the percutaneous placement of iliosacral screws derives mainly from the technique described by Matta with the C-arm fluoroscopy visualizing the pelvis in 3 views: strict AP, inlet, and outlet views.⁷

Routt and colleagues⁴ recommend a strict lateral view of the sacrum, particularly when crossing the narrow zone of the sacral alar. They reported high union rates and accurate placement of the screws.⁴ There are limitations to the use of biplanar fluoroscopy because the intraoperative images are not orthogonal, with the average arc (67º) between the ideal inlet and outlet. However, because of the variability in sacral anatomy, CT guidance was recommended by others.^2,6,8,18 Operating in a CT suite had other complications. Misinterpretation of CT led to “in-out-in” screws, which resulted in neurapraxia. 

In our study, we used the technique described by Matta and colleagues for placement of the screws and performed a postoperative CT to evaluate screw placement and to assess pelvic reduction.⁷ We had a high penetration rate using CT, which increased with better resolution, even though none of the radiographs showed any obvious evidence of misplacement of the screws. Ebraheim and colleagues⁶ described the relationship of the S1 nerve root in its neural foramen and found it to be approximately 8.7 mm inferior and 7.8 mm medial to the starting point for a pedicle screw. Given these numbers, it is possible that a large amount of skiving can be tolerated contingent on an adequate reduction of the SI joint. 

Because of our high rates of skiving and low rates of neurologic deficit, a new “safe zone” for screw insertion can be expanded to include skiving of the S1 neural foramen up to 3 mm without fear of nerve root injury. However, drilling and screw insertion at higher speeds can also cause neurologic injury secondary to thermal injury or soft tissue being caught up in a rotating drill/screw. 

Evaluation of placement of percutaneous SI screw placement in our study resulted in neural foramen penetration in 43% of SI screws, which is higher than other studies.^14,19,20 Our study showed that screw penetration up to 2 mm does not correlate with neurologic deficit. Iatrogenic neurologic deficit secondary to perforation of the foramina occurred in only 1 patient. Penetration of the foramina in all cases was in the superior portion of the foramen. We propose that there is a safe zone within the S1 neural foramen, and small amounts of penetration in the superior one-third of the foramen on axial CT images do not correlate with neurologic deficit. This potential safe zone is predicated on adequate reduction of the SI joint. 

Neural foramen penetration shown on postoperative CT does not necessarily correlate with neurologic deficit. A postoperative CT is not indicated unless there are findings of a postoperative nerve injury. Our ideal screw placement skives the superior S1 foramen allowing for a larger screw diameter in a safe zone.

CT-guided placement has been proposed; however, concerns about radiation exposure, cost, and feasibility with similar outcomes compared with fluoroscopic-guided screw placement has resulted in its falling out of favor.

Iatrogenic nerve injuries are reported to occur in 0% to 6% of all percutaneous SI screw placement.^14,21 Risk factors for iatrogenic nerve injury while using fluoroscopic guidance include sacral morphologic abnormalities, presence of intestinal gas, or contrast.²² Although these may be minimized with proper use of fluoroscopy, obtaining anatomic reduction as well as a thorough understanding of the pelvic morphology, the surgeon must be prepared to obtain further studies, such as a CT scan, if there is postoperative neurologic deficit.

Based on our findings, we do not routinely obtain a postoperative CT for SI screw placement, unless there is concern for malreduction or there is neurologic deficit. We also believe that up to 2 mm of foramen penetration is safe and does not result in neurologic deficit.

Pelvic injuries account for 3% of all skeletal fractures.¹ Injury to the sacroiliac (SI) joint is frequently associated with unstable pelvic ring fractures, which are potentially life-threatening injuries. Surgical fixation of these injuries is preferred to nonoperative treatment given the potential for improved reduction and early mobilization and weight-bearing, thereby decreasing perioperative morbidity and improving functional outcome.²

The classic method of surgical fixation of the SI joint consisted of open reduction and internal fixation. This method carried a substantial risk for large dissection, iatrogenic nerve injury, and increased blood loss to the already traumatized patient.³ Percutaneous fixation allows for a shorter operating time, decreased soft-tissue stripping, and decreased blood loss compared with a traditional open procedure.⁴ However, posterior pelvic anatomy is complex and variable, and reports have found screw misplacements as high as 24%⁵ and neurologic complication rates up to 18%.^6-9 

Various imaging modalities, including fluoroscopy,⁵ computed tomography (CT),^6-7 fluoroscopic CT, and computer-assisted techniques^5,9 have been used to achieve proper screw placement. Conventional fluoroscopy is the standard for intraoperative screw placement. However, acceptable reduction of the SI joint and proper implantation of the screws without perforation of the neural foramina is challenging, especially when coupled with difficulties of fluoroscopic imaging and variations in pelvic anatomy. 

Sacral dysplasia has been reported to occur in up to 20% to 40% of the population and has significant implications in patients indicated for iliosacral screw placement.¹⁰ Incorrect placement of iliosacral screws may result in iatrogenic neurovascular complications.^11-13 Malpositioned screws using fluoroscopic guidance have been reported in 2% to 15% of patients with an incidence of neurologic compromise between 0.5% and 7.7%. As little as 4° of misdirection can result in damage to neurovascular structures.¹⁴

At our institution, we routinely obtained postoperative CT to evaluate the placement of SI screws. The objective of this retrospective study is to evaluate the rate of revision surgery of percutaneous SI screw fixation, to determine whether CT is an accurate tool for evaluation of the reduction and the need for revision surgery, and to decide if any violation of the neural foramina is safe.

Materials and Methods

After institutional review board approval, we retrospectively reviewed and evaluated medical records and radiographs of all patients who sustained unstable pelvic ring fractures between July 1, 2005, and June 30, 2010. We identified all patients who were treated with closed reductions and percutaneous iliosacral screw fixation, according to the method described by Routt in 1995.⁴ We excluded all pelvic fractures in patients who underwent open reduction for the posterior injury or did not have percutaneous SI screws placed, those with spinal injury, and those without follow-up. Of the 46 patients who met the inclusion criteria were 26 men and 20 women with a mean age of 42 years (range, 16 to 73 years). Motor vehicle accidents accounted for 13 cases; 19 were crush injuries and 14 were falls from height. Seventeen patients (37%) met the radiographic criteria for sacral dysmorphism. Forty-two of the 46 patients were polytrauma patients with associated musculoskeletal injuries and/or abdominal, chest, or head injuries.

Six patients presented with some neurologic deficit at the time of injury; all fractures were closed. The initial imaging study included plain anteroposterior (AP), inlet, and outlet radiographs of the pelvis and a pelvic CT scan. Using the classification of Young and Burgess,¹⁵ there were 3 vertical shear injuries, 13 lateral compression–type injuries, 17 anterior-posterior–type injuries, 7 sacral fractures, and 6 combination- or unclassifiable-type pelvic injuries. Of the sacral fractures, there were 3 Denis zone 1, 3 Denis zone 2, and 1 Denis zone 3. 

The pelvic CT scan included the entire pelvis from the ilium to the ischial tuberosities. Each scan consisted of either a 5.0-mm or a 2.5-mm sequential axial image. A picture archiving and communication system (PACS) workstation using Centricity version 2.1 (GE Medical Systems, Waukesha, Wisconsin) was used to analyze each scan with a bone algorithm. On PACS, each initial displacement was characterized by the amount of SI joint widening at the level of the S1 and was measured using digital calipers.   

Surgery

Mean time to surgery was 4 days (range, 2 to 15 days) after the injury. A total of 51 SI screws were implanted in 46 patients. We achieved closed reduction of the posterior pelvic ring by various techniques, including compression with percutaneous partially threaded screw fixation. In the cases in which the posterior ring lesion was associated with a pure pubic symphysis disruption, the anterior pelvis was initially reduced and stabilized with small-fragment plate fixation (Synthes, Inc, Paoli, Pennsylvania). The posterior complex was stabilized with 1 screw in 41 patients, 2 cases required a transiliac screw, and 2 screws (S1 and S2) were placed in each of the remaining 3 cases. Definitive stabilization of the posterior pelvis was achieved with percutaneous, partially threaded 7.3- or 7.5-mm–diameter cannulated screws (Synthes, Inc, and Zimmer Inc, Warsaw, Indiana, respectively) in 42 fractures and 6.5-mm screws (Synthes, Inc) in 4 fractures. In 11 cases where the fracture was through the sacrum, fully threaded cannulated screws were used to avoid compression. Screw insertion was performed under fluoroscopic guidance with inlet, outlet, and lateral sacral views. One of 2 fellowship-trained trauma surgeons performed the surgeries. Rehabilitation plans were customized to each patient based on concomitant injuries. 

Postoperative Assessment

AP, lateral sacral, and inlet and outlet postoperative radiographs were taken in all cases within 24 hours after surgery. Pelvic CT was also obtained within 24 hours of surgery to review reduction and screw placement.

Using the measurement tool on the PACS system, we measured the penetration of the screw into the foramen. Screws were graded as intraosseous (completely contained within the sacral bone), skived (less than 2 mm of partial penetration into the S1 foramen), or extruded (the screw not contained by the bone). Screw penetration of the S1 was evaluated on the radiographic images as well as the axial images of the CT scans.

After surgery, the senior orthopedic resident and attending surgeon performed and documented detailed neurologic evaluations. They reviewed the medical record for neurologic deficit following surgical fixation.   

Results

The mean follow-up time was 12 months (range, 8 months to 2 years). Two patients expired secondary to associated injuries. There were no early deaths related to the pelvic surgery. Stable fixation, including bone or ligamentous healing, as well as full weight-bearing status, was noted in every case. No case exhibited loss of reduction or implant failure or infection.

According to Matta’s criteria of anatomic reduction within 1 cm, all patients were found to have satisfactory reductions.⁷ Six of 46 patients had documented preoperative neurologic deficits. After percutaneous screw fixation, 10 of 46 patients had postoperative neurologic deficit, 2 of which were unchanged from preoperative evaluation. Of the 8 patients with new/altered postoperative neurologic deficit, CT showed neural foramen penetration greater than 2.1 mm in only 2 patients. Both patients underwent screw revision, resulting in improved neurologic deficit. The remaining 4 patients did not have foramen penetration and improved their neurologic function over the course of 2 weeks with return to presurgical status by 6 weeks without necessitating screw removal.

Twenty-three of the 51 screws (45%) had some violation of the S1 foramen on the CT. There were 17 patients with dysmorphic sacrums in which 21 S1 screws were placed. Eleven of  21 (52%) screws showed some penetration of the S1 foramen on CT. There were 29 patients with normal sacral morphology in which 30 S1 screws were placed. Twelve of 30 (40%) screws penetrated the S1 foramen. All violations were in the superior one-third position of the foramen. Two of 46 (4%; 1 with dysmorphism, 1 without) had a new neurologic deficit associated with the surgery (Table). CT showed sacral foramen penetration, and both screws were revised with a better neurologic examination.

High-resolution CTs were obtained in 32 patients, while 14 patients underwent the standard 5.0-mm–cut CTs. Of the 32 patients in which a 2.5-mm high-resolution CT was obtained, 20 (62.5%) had evidence of screw penetration (Figures 1, 2). All violations of the S1 neural foramen were in the superior portion of the foramen. 

When compared with patients who had a 5.0-mm CT, the patients who underwent a high-resolution CT were more likely to show neural foramen penetration (P = .3). The average screw penetration into the S1 neural foramen measured 3.3 mm (range, 1.6-5.7 mm) in dysmorphic sacrum and 2.7 mm  (range, 1.4-7 mm) in normal sacrum. However, in our study, any foramen penetration of less than 2.1 mm on CT did not result in neurologic deficit.  

Discussion

Pelvic fractures are fairly common and represent approximately 5% of all trauma admissions and 3% of all skeletal fractures nationwide.¹ The current treatment for SI disruption is either nonoperative or operative. Surgical fixation is technically demanding and surgeons often need a long learning curve to acquire the demanding technique because of the limitations of radiographic visualization of the relevant landmarks.¹⁶

Letournel¹⁷ developed the technique for iliosacral screw fixation for the treatment of posterior pelvic ring injuries, where 1 or 2 large screws (6.5-7.3 mm in diameter) are inserted under fluoroscopic guidance through the ilium, across the SI articulation, and into the superior sacral vertebral bodies using percutaneous techniques. Currently, the standard procedure to accomplish the percutaneous placement of iliosacral screws derives mainly from the technique described by Matta with the C-arm fluoroscopy visualizing the pelvis in 3 views: strict AP, inlet, and outlet views.⁷

Routt and colleagues⁴ recommend a strict lateral view of the sacrum, particularly when crossing the narrow zone of the sacral alar. They reported high union rates and accurate placement of the screws.⁴ There are limitations to the use of biplanar fluoroscopy because the intraoperative images are not orthogonal, with the average arc (67º) between the ideal inlet and outlet. However, because of the variability in sacral anatomy, CT guidance was recommended by others.^2,6,8,18 Operating in a CT suite had other complications. Misinterpretation of CT led to “in-out-in” screws, which resulted in neurapraxia. 

In our study, we used the technique described by Matta and colleagues for placement of the screws and performed a postoperative CT to evaluate screw placement and to assess pelvic reduction.⁷ We had a high penetration rate using CT, which increased with better resolution, even though none of the radiographs showed any obvious evidence of misplacement of the screws. Ebraheim and colleagues⁶ described the relationship of the S1 nerve root in its neural foramen and found it to be approximately 8.7 mm inferior and 7.8 mm medial to the starting point for a pedicle screw. Given these numbers, it is possible that a large amount of skiving can be tolerated contingent on an adequate reduction of the SI joint. 

Because of our high rates of skiving and low rates of neurologic deficit, a new “safe zone” for screw insertion can be expanded to include skiving of the S1 neural foramen up to 3 mm without fear of nerve root injury. However, drilling and screw insertion at higher speeds can also cause neurologic injury secondary to thermal injury or soft tissue being caught up in a rotating drill/screw. 

Evaluation of placement of percutaneous SI screw placement in our study resulted in neural foramen penetration in 43% of SI screws, which is higher than other studies.^14,19,20 Our study showed that screw penetration up to 2 mm does not correlate with neurologic deficit. Iatrogenic neurologic deficit secondary to perforation of the foramina occurred in only 1 patient. Penetration of the foramina in all cases was in the superior portion of the foramen. We propose that there is a safe zone within the S1 neural foramen, and small amounts of penetration in the superior one-third of the foramen on axial CT images do not correlate with neurologic deficit. This potential safe zone is predicated on adequate reduction of the SI joint. 

Neural foramen penetration shown on postoperative CT does not necessarily correlate with neurologic deficit. A postoperative CT is not indicated unless there are findings of a postoperative nerve injury. Our ideal screw placement skives the superior S1 foramen allowing for a larger screw diameter in a safe zone.

CT-guided placement has been proposed; however, concerns about radiation exposure, cost, and feasibility with similar outcomes compared with fluoroscopic-guided screw placement has resulted in its falling out of favor.

Iatrogenic nerve injuries are reported to occur in 0% to 6% of all percutaneous SI screw placement.^14,21 Risk factors for iatrogenic nerve injury while using fluoroscopic guidance include sacral morphologic abnormalities, presence of intestinal gas, or contrast.²² Although these may be minimized with proper use of fluoroscopy, obtaining anatomic reduction as well as a thorough understanding of the pelvic morphology, the surgeon must be prepared to obtain further studies, such as a CT scan, if there is postoperative neurologic deficit.

Based on our findings, we do not routinely obtain a postoperative CT for SI screw placement, unless there is concern for malreduction or there is neurologic deficit. We also believe that up to 2 mm of foramen penetration is safe and does not result in neurologic deficit.

Pelvic injuries account for 3% of all skeletal fractures.¹ Injury to the sacroiliac (SI) joint is frequently associated with unstable pelvic ring fractures, which are potentially life-threatening injuries. Surgical fixation of these injuries is preferred to nonoperative treatment given the potential for improved reduction and early mobilization and weight-bearing, thereby decreasing perioperative morbidity and improving functional outcome.²

The classic method of surgical fixation of the SI joint consisted of open reduction and internal fixation. This method carried a substantial risk for large dissection, iatrogenic nerve injury, and increased blood loss to the already traumatized patient.³ Percutaneous fixation allows for a shorter operating time, decreased soft-tissue stripping, and decreased blood loss compared with a traditional open procedure.⁴ However, posterior pelvic anatomy is complex and variable, and reports have found screw misplacements as high as 24%⁵ and neurologic complication rates up to 18%.^6-9 

Various imaging modalities, including fluoroscopy,⁵ computed tomography (CT),^6-7 fluoroscopic CT, and computer-assisted techniques^5,9 have been used to achieve proper screw placement. Conventional fluoroscopy is the standard for intraoperative screw placement. However, acceptable reduction of the SI joint and proper implantation of the screws without perforation of the neural foramina is challenging, especially when coupled with difficulties of fluoroscopic imaging and variations in pelvic anatomy. 

Sacral dysplasia has been reported to occur in up to 20% to 40% of the population and has significant implications in patients indicated for iliosacral screw placement.¹⁰ Incorrect placement of iliosacral screws may result in iatrogenic neurovascular complications.^11-13 Malpositioned screws using fluoroscopic guidance have been reported in 2% to 15% of patients with an incidence of neurologic compromise between 0.5% and 7.7%. As little as 4° of misdirection can result in damage to neurovascular structures.¹⁴

At our institution, we routinely obtained postoperative CT to evaluate the placement of SI screws. The objective of this retrospective study is to evaluate the rate of revision surgery of percutaneous SI screw fixation, to determine whether CT is an accurate tool for evaluation of the reduction and the need for revision surgery, and to decide if any violation of the neural foramina is safe.

Materials and Methods

After institutional review board approval, we retrospectively reviewed and evaluated medical records and radiographs of all patients who sustained unstable pelvic ring fractures between July 1, 2005, and June 30, 2010. We identified all patients who were treated with closed reductions and percutaneous iliosacral screw fixation, according to the method described by Routt in 1995.⁴ We excluded all pelvic fractures in patients who underwent open reduction for the posterior injury or did not have percutaneous SI screws placed, those with spinal injury, and those without follow-up. Of the 46 patients who met the inclusion criteria were 26 men and 20 women with a mean age of 42 years (range, 16 to 73 years). Motor vehicle accidents accounted for 13 cases; 19 were crush injuries and 14 were falls from height. Seventeen patients (37%) met the radiographic criteria for sacral dysmorphism. Forty-two of the 46 patients were polytrauma patients with associated musculoskeletal injuries and/or abdominal, chest, or head injuries.

Six patients presented with some neurologic deficit at the time of injury; all fractures were closed. The initial imaging study included plain anteroposterior (AP), inlet, and outlet radiographs of the pelvis and a pelvic CT scan. Using the classification of Young and Burgess,¹⁵ there were 3 vertical shear injuries, 13 lateral compression–type injuries, 17 anterior-posterior–type injuries, 7 sacral fractures, and 6 combination- or unclassifiable-type pelvic injuries. Of the sacral fractures, there were 3 Denis zone 1, 3 Denis zone 2, and 1 Denis zone 3. 

The pelvic CT scan included the entire pelvis from the ilium to the ischial tuberosities. Each scan consisted of either a 5.0-mm or a 2.5-mm sequential axial image. A picture archiving and communication system (PACS) workstation using Centricity version 2.1 (GE Medical Systems, Waukesha, Wisconsin) was used to analyze each scan with a bone algorithm. On PACS, each initial displacement was characterized by the amount of SI joint widening at the level of the S1 and was measured using digital calipers.   

Surgery

Mean time to surgery was 4 days (range, 2 to 15 days) after the injury. A total of 51 SI screws were implanted in 46 patients. We achieved closed reduction of the posterior pelvic ring by various techniques, including compression with percutaneous partially threaded screw fixation. In the cases in which the posterior ring lesion was associated with a pure pubic symphysis disruption, the anterior pelvis was initially reduced and stabilized with small-fragment plate fixation (Synthes, Inc, Paoli, Pennsylvania). The posterior complex was stabilized with 1 screw in 41 patients, 2 cases required a transiliac screw, and 2 screws (S1 and S2) were placed in each of the remaining 3 cases. Definitive stabilization of the posterior pelvis was achieved with percutaneous, partially threaded 7.3- or 7.5-mm–diameter cannulated screws (Synthes, Inc, and Zimmer Inc, Warsaw, Indiana, respectively) in 42 fractures and 6.5-mm screws (Synthes, Inc) in 4 fractures. In 11 cases where the fracture was through the sacrum, fully threaded cannulated screws were used to avoid compression. Screw insertion was performed under fluoroscopic guidance with inlet, outlet, and lateral sacral views. One of 2 fellowship-trained trauma surgeons performed the surgeries. Rehabilitation plans were customized to each patient based on concomitant injuries. 

Postoperative Assessment

AP, lateral sacral, and inlet and outlet postoperative radiographs were taken in all cases within 24 hours after surgery. Pelvic CT was also obtained within 24 hours of surgery to review reduction and screw placement.

Using the measurement tool on the PACS system, we measured the penetration of the screw into the foramen. Screws were graded as intraosseous (completely contained within the sacral bone), skived (less than 2 mm of partial penetration into the S1 foramen), or extruded (the screw not contained by the bone). Screw penetration of the S1 was evaluated on the radiographic images as well as the axial images of the CT scans.

After surgery, the senior orthopedic resident and attending surgeon performed and documented detailed neurologic evaluations. They reviewed the medical record for neurologic deficit following surgical fixation.   

Results

The mean follow-up time was 12 months (range, 8 months to 2 years). Two patients expired secondary to associated injuries. There were no early deaths related to the pelvic surgery. Stable fixation, including bone or ligamentous healing, as well as full weight-bearing status, was noted in every case. No case exhibited loss of reduction or implant failure or infection.

According to Matta’s criteria of anatomic reduction within 1 cm, all patients were found to have satisfactory reductions.⁷ Six of 46 patients had documented preoperative neurologic deficits. After percutaneous screw fixation, 10 of 46 patients had postoperative neurologic deficit, 2 of which were unchanged from preoperative evaluation. Of the 8 patients with new/altered postoperative neurologic deficit, CT showed neural foramen penetration greater than 2.1 mm in only 2 patients. Both patients underwent screw revision, resulting in improved neurologic deficit. The remaining 4 patients did not have foramen penetration and improved their neurologic function over the course of 2 weeks with return to presurgical status by 6 weeks without necessitating screw removal.

Twenty-three of the 51 screws (45%) had some violation of the S1 foramen on the CT. There were 17 patients with dysmorphic sacrums in which 21 S1 screws were placed. Eleven of  21 (52%) screws showed some penetration of the S1 foramen on CT. There were 29 patients with normal sacral morphology in which 30 S1 screws were placed. Twelve of 30 (40%) screws penetrated the S1 foramen. All violations were in the superior one-third position of the foramen. Two of 46 (4%; 1 with dysmorphism, 1 without) had a new neurologic deficit associated with the surgery (Table). CT showed sacral foramen penetration, and both screws were revised with a better neurologic examination.

High-resolution CTs were obtained in 32 patients, while 14 patients underwent the standard 5.0-mm–cut CTs. Of the 32 patients in which a 2.5-mm high-resolution CT was obtained, 20 (62.5%) had evidence of screw penetration (Figures 1, 2). All violations of the S1 neural foramen were in the superior portion of the foramen. 

When compared with patients who had a 5.0-mm CT, the patients who underwent a high-resolution CT were more likely to show neural foramen penetration (P = .3). The average screw penetration into the S1 neural foramen measured 3.3 mm (range, 1.6-5.7 mm) in dysmorphic sacrum and 2.7 mm  (range, 1.4-7 mm) in normal sacrum. However, in our study, any foramen penetration of less than 2.1 mm on CT did not result in neurologic deficit.  

Discussion

Pelvic fractures are fairly common and represent approximately 5% of all trauma admissions and 3% of all skeletal fractures nationwide.¹ The current treatment for SI disruption is either nonoperative or operative. Surgical fixation is technically demanding and surgeons often need a long learning curve to acquire the demanding technique because of the limitations of radiographic visualization of the relevant landmarks.¹⁶

Letournel¹⁷ developed the technique for iliosacral screw fixation for the treatment of posterior pelvic ring injuries, where 1 or 2 large screws (6.5-7.3 mm in diameter) are inserted under fluoroscopic guidance through the ilium, across the SI articulation, and into the superior sacral vertebral bodies using percutaneous techniques. Currently, the standard procedure to accomplish the percutaneous placement of iliosacral screws derives mainly from the technique described by Matta with the C-arm fluoroscopy visualizing the pelvis in 3 views: strict AP, inlet, and outlet views.⁷

Routt and colleagues⁴ recommend a strict lateral view of the sacrum, particularly when crossing the narrow zone of the sacral alar. They reported high union rates and accurate placement of the screws.⁴ There are limitations to the use of biplanar fluoroscopy because the intraoperative images are not orthogonal, with the average arc (67º) between the ideal inlet and outlet. However, because of the variability in sacral anatomy, CT guidance was recommended by others.^2,6,8,18 Operating in a CT suite had other complications. Misinterpretation of CT led to “in-out-in” screws, which resulted in neurapraxia. 

In our study, we used the technique described by Matta and colleagues for placement of the screws and performed a postoperative CT to evaluate screw placement and to assess pelvic reduction.⁷ We had a high penetration rate using CT, which increased with better resolution, even though none of the radiographs showed any obvious evidence of misplacement of the screws. Ebraheim and colleagues⁶ described the relationship of the S1 nerve root in its neural foramen and found it to be approximately 8.7 mm inferior and 7.8 mm medial to the starting point for a pedicle screw. Given these numbers, it is possible that a large amount of skiving can be tolerated contingent on an adequate reduction of the SI joint. 

Because of our high rates of skiving and low rates of neurologic deficit, a new “safe zone” for screw insertion can be expanded to include skiving of the S1 neural foramen up to 3 mm without fear of nerve root injury. However, drilling and screw insertion at higher speeds can also cause neurologic injury secondary to thermal injury or soft tissue being caught up in a rotating drill/screw. 

Evaluation of placement of percutaneous SI screw placement in our study resulted in neural foramen penetration in 43% of SI screws, which is higher than other studies.^14,19,20 Our study showed that screw penetration up to 2 mm does not correlate with neurologic deficit. Iatrogenic neurologic deficit secondary to perforation of the foramina occurred in only 1 patient. Penetration of the foramina in all cases was in the superior portion of the foramen. We propose that there is a safe zone within the S1 neural foramen, and small amounts of penetration in the superior one-third of the foramen on axial CT images do not correlate with neurologic deficit. This potential safe zone is predicated on adequate reduction of the SI joint. 

Neural foramen penetration shown on postoperative CT does not necessarily correlate with neurologic deficit. A postoperative CT is not indicated unless there are findings of a postoperative nerve injury. Our ideal screw placement skives the superior S1 foramen allowing for a larger screw diameter in a safe zone.

CT-guided placement has been proposed; however, concerns about radiation exposure, cost, and feasibility with similar outcomes compared with fluoroscopic-guided screw placement has resulted in its falling out of favor.

Iatrogenic nerve injuries are reported to occur in 0% to 6% of all percutaneous SI screw placement.^14,21 Risk factors for iatrogenic nerve injury while using fluoroscopic guidance include sacral morphologic abnormalities, presence of intestinal gas, or contrast.²² Although these may be minimized with proper use of fluoroscopy, obtaining anatomic reduction as well as a thorough understanding of the pelvic morphology, the surgeon must be prepared to obtain further studies, such as a CT scan, if there is postoperative neurologic deficit.

Based on our findings, we do not routinely obtain a postoperative CT for SI screw placement, unless there is concern for malreduction or there is neurologic deficit. We also believe that up to 2 mm of foramen penetration is safe and does not result in neurologic deficit.