The Prevalence and Risk Factors for S2 Alar-Iliac Screw Loosening with a Minimum 2-Year Follow-up

Study Design A retrospective cohort study. Purpose: The purpose of this study was to investigate the prevalence and risk factors for S2 alar-iliac (SAL) screw loosening following lumbosacral fixation, with a minimum 2-year follow-up. Overview Literature: Although SAI screws allow surgeons to perform lumbosacral fixation with a low profile and enhanced biomechanical strength, screw loosening following surgery can occur in some cases. However, few studies have investigated the prevalence and risk factors for SAI screw loosening. Methods; This retrospective study included 35 patients (mean age, 72.8 +/- 8.0 years; male, 10; female, 251 who underwent lumbosacral fixation using SAI screws with at least 2 years of follow-up. SAI screw loosening and L5-S bony fusion were assessed using computed tomography. The period for which the screws appeared loose and the risk factors for SAI screw loosening were investigated 2 years after surgery. Results: A total of 7D SAI screws and 70 S1 pedicle screws were inserted. Loosening was observed D.5, 1, and 2 years after surgery in 17 (24.3%1, 35 (50.0%), and 35(50.0%) SAI screws, respectively. Bony fusion rate at L5-S was significantly lower in patients with SAI screw loosening than in those without screw loosening (65.0% vs. 93.3%, p=0.048). The score for CAI screw contact with the iliac cortical hone and the bony fusion rate at L5-S were significantly lower in the loosening group than in the non -loosening group (1.8 +/- 0.5 vs. 2.2 +/- 0.3,p<0.001, respectively). Postoperative pelvic incidence lumbar lorclosis was significantly higher in the loosening group than in the non -loosening group (7.9 degrees +/- 15.4 degrees vs. 0.5 degrees +/- 8.7 degrees,p=0.02, respectively). Conclusicms: SAI screw loosening is closely correlated with pseudoarthrosis at L5-S. Appropriate ion and opt a bar lordosis restoration are important to prevent postoperative complications related to SAI screws.