Risks to the superior gluteal neurovascular bundle during percutaneous iliosacral screw insertion: an anatomical cadaver study.
BACKGROUND: Iliosacral screws are a popular technique used to treat complicated injuries of the pelvis. It is well recognized that this technique entails some potentially disabling complications, including damage to vessels and lumbosacral nerves. The recommended insertion site for iliosacral screws into the S1 body lies along the posterior ilium between the greater sciatic notch and the iliac crest. The anatomy and course of the superior gluteal nerve and vessels have been described along the outer aspect of the posterior ilium. Injury to the superior gluteal nerve and vessels has been reported during pelvic surgery, including the insertion of iliosacral screws. The purpose of this study is to assess the risks of injury and proximity of percutaneously inserted iliosacral screws to the superior gluteal nerve and vessels using a cadaver model. MATERIALS AND METHODS: Twenty-nine cadaver pelvises for a total of 58 sides (58 screws) were studied. Percutaneous iliosacral screws were placed into the first sacral bodies using multiplanar fluoroscopic guidance. The superior gluteal neurovascular bundle was then studied via a posterior dissection. Injury to the neurovascular bundle was noted if it occurred, and the distance between the screw head and the neurovascular bundle was measured. Distances from the screw head to the crista glutea, greater sciatic notch, and iliac crest were also measured. RESULTS: The branching pattern of the superior gluteal nerve and vessels after they exit the greater sciatic notch demonstrated considerable variation, but was generally consistent with prior descriptions in most cases. Ten of 58 (18%) iliosacral screws caused injury to the superior branch of the superior gluteal nerve and vessels; 8 neurovascular bundles were impaled and 2 others were partly entrapped between the screw head and the ilium. The mean distance from the head of the iliosacral screws to the deep superior branches of the superior gluteal nerve and vessels was 9.1 mm (+/- 6.8 mm). The mean distances from the screw head to the crista glutea, sciatic notch, and iliac crest were 19.5 mm (+/- 4.9 mm), 33.0 mm (+/- 6.4 mm) and 50.3 mm (+/- 4.6 mm). Of the screws that caused superior gluteal nerve and vessels injury, all were within the "desired" area of insertion. CONCLUSIONS: The deep superior branch of the superior gluteal nerve and vessels, which provides major blood and nerve supply to the G. medius and G. minimus, is at significant risk during the percutaneous placement of iliosacral screws even when "well placed" and soft tissue protecting cannulas are used. The clinical effects of these injuries remain poorly understood.