Reinforcement of lumbosacral instrumentation using S1-pedicle screws combined with S2-alar screws.

OBJECTIVE: Increasing construct stability of lumbosacral instrumentations using S2-ala screws as an alternate to iliac screws. INDICATIONS: Revision surgery after failed lumbosacral fusion; long instrumentations to the sacrum; L5-S1 fusion without anterior support. CONTRAINDICATIONS: Lack of sacral bone stock. SURGICAL TECHNIQUE: Midline approach. The entry point for S2-ala screws is caudal to the posterior S1 foramen and close to the lateral sacral crest. Screw tract preparation for S2-ala screws necessitates 30-45° angulation in the axial plane. Biplanar fluoroscopy with inlet and outlet views ensure screw accuracy. With S2-ala screws, bicortical fixation is the goal. POSTOPERATIVE MANAGEMENT: Patients are mobilized under the surveillance of physiotherapists on day 1 and released from the hospital after 10 days. Clinical and radiographic controls are performed at 6, 12 and 24 months. RESULTS: Retrospective review of 80 patients undergoing S2-ala screw fixation. Main diagnosis was degenerative lumbar instability, adult scoliosis, high-grade listhesis, and nonidiopathic scoliosis. In 66% of patients, the instrumentation using S2-ala screws was part of a major lumbosacral revision surgery. Follow-up averaged 26 months. There were no deaths or major neurovascular complications. First time fusion rate at L5-S1 was greater than 90%. Eight patients (10%) experienced a complication which could be related to the S2-ala screws. Out of 160 S2-ala screws, 16 screws were judged to cause focal irritation and were removed, indicating a survival rate of 90% for the S2-ala screw.