Iatrogenic L5 Nerve Injury Following Decortication of the Sacral Ala in Posterolateral Lumbosacral Fusion Surgery

Abstract

Study Design: Cadaver study. Objectives: To investigate the risk of the L5 nerve injury following sacral ala decortication performed during lumbosacral posterolateral fusion surgery. Methods: Fourteen fresh cadaver pelvises were dissected through an anterior approach and the L5 nerves on both sides were explored and macroscopically examined by direct observation. Then, the corticotomy of the sacral ala was performed at 0°, 20°, and 30° angles to the sagittal plane through the posterior approach. The site of sacral ala decortication was checked on each side and its distance to the L5 nerve root was measured. Results: The tip of the osteotome was in the danger zone (5 mm medial to 5 mm lateral to the L5 nerve) in all cases (100%) where the osteotome had 0° angle to the sagittal plane. For those with a 20° angle, the osteotome tip laid in the danger zone in 83% and intermediate zone (between 6 to 15 mm lateral to the nerve) in 17% of cases. For those with a 30° angle, the tip was in the safe zone (>15 mm lateral to the nerve) in all cases (100%). Conclusion: Osteotomy of the sacral ala with <30° angle to the sagittal plane risks injury to the L5 nerve; whereas osteotomy angle >30° would not cause any injury to the nerve. It should be considered as a possible cause of iatrogenic L5 nerve injury in patients undergoing posterolateral lumbosacral fusion.