A New Entry Point and Trajectory for Iliac Bolt Fixation in Patients Undergoing Long Fusion to the Sacrum

Abstract

Introduction Osteotomy of the posterior superior iliac spine for preparation of traditional iliac screw entry point exposes the cancellous bone of the inner ilium and causes loss of circumferential cortical starting point which may compromise biomechanical stability. For this reason, traditional iliac screws may not provide the desired primary stability especially in osteopenic and osteoporotic patients. We describe a new free-hand technique with a starting point located at the posterior inferior iliac spine (PIIS), which does not require any decortication for entry and courses very close to the rigid subcortical bone over sciatic notch while providing a low profile fixation and easier connection with S1 screw. The aim of this study is to evaluate the result of this new iliac bolt fixation technique. Patients and Methods A total of 26 patients (21 F and 5 M) having lumbopelvic fixation with the new technique were reviewed. The new entry point is located at the midpoint of PIIS. Lateral cortex of distal iliac wing is exposed subperiosteally and sciatic notch was palpated for safe trajectory. Screw trajectory is intended to be parallel to the outer cortex of ilium, passing 1 to 1.5 cm above the sciatic notch. PIIS provides a rigid circumferential cortical starting point for entrance and trajectory through thick cortical iliac bone over sciatic notch which provides very strong screw purchase even in osteopenic and osteoporotic spine. New entry point also enables easier connection to S1 screw. Free-hand technique eliminates radiation exposure. Pre-op, post-op, and follow-up X-rays were reviewed for the radiological data. Results Mean age was 63.6 years (range, 19–84 years) and mean follow-up was 14 months (range, 12–18 months). Mean screw length was 93.46 mm (range, 80–110 mm). Screw diameters were 8.5 mm in 22 patients and 7.5 mm in 4 patients. Lumbosacral fusion was achieved in all the cases. There were no neurovascular injuries related to the sciatic nerve and gluteal artery during screw placement. There were no implant failures or screw breakage at end of final follow-up. Conclusion This new technique seems to be a viable option in patients undergoing fusion to the sacrum for iliac bolt fixation. PIIS provides a circumferential cortical starting point and low profile fixation with stronger screw purchase especially in osteoporotic patients.