A Misplaced S2 Alar-Iliac Screw Causing L5 Spinal Nerve Injury: A Report of a Rare Case

Although neurovascular structures, including the superior gluteal artery, sciatic nerve, obturator nerve, internal iliac vein and artery, and lumbosacral plexus, are at risk when S2 alar-iliac (S2AI) screws are used, no cases of nerve injuries have been reported. An 84-year-old man was referred to our institute with persistent left sciatica for seven months after undergoing salvage surgery using S2AI screws for deep surgical site infection from a previous posterior interbody fusion surgery at L5-S1. Based on the radiographic and diagnostic selective nerve root block findings, a diagnosis of left L5 radiculopathy was suspected due to the left S2AI screw being caudally misplaced and severely protruding into the pelvic cavity. The patient underwent surgical replacement of the left S2AI screw. The patient was discharged eight days postoperatively, with a resolution of the left leg pain. At the three-month follow-up, no recurrent pain was reported. To the best of our knowledge, this is the first reported case of a misplaced S2AI screw causing L5 spinal nerve injury. If the screw is inserted caudally and deviates into the pelvic cavity, in front of the sacroiliac joint, the L5 nerve running in this region may be damaged.