Clinical and radiologic outcomes and complications of unilateral S2AI screw fixation in adult spinal deformity surgery: a retrospective cohort study.

Background: Adult spinal deformity (ASD) poses challenges in achieving optimal spinal alignment, often necessitating rigid lumbosacral fixation. Traditional iliac screw instrumentation has limitations, such as prominent screws, which has led to the exploration of alternative techniques, including sacral-alar-iliac (S2AI) screws. However, S2AI screws have been associated with significant sacroiliac joint pain, as the screw trajectory passes through the normal sacroiliac joint. This study evaluates the feasibility, outcomes, and complications of unilateral S2AI screw fixation in ASD surgery.

Methods: A retrospective review of 80 consecutive ASD patients undergoing unilateral S2AI screw fixation was conducted. This study included patients with a mild-to-moderate sagittal deformity, spine flexibility and a normal pelvic incidence who received unilateral lumbopelvic fixation with an S2AI screw. Clinical and radiographic data were analyzed, including pre- and postoperative measurements, complications, and patient-reported outcomes.

Results: Among the 80 patients, 72 (90%) were women and the mean age was 68.7±6.7 years. Postoperative radiographic improvements were substantial. Complications included screw loosening, proximal junctional kyphosis, infection, S2AI screw-related pain and rod breakage. The overall complication rate was 21%, and the L5/S1 fusion rate at the 2-year follow-up was 95%.

Conclusions: Unilateral S2AI screws appear effective for lumbopelvic fixation in patients with mild to moderate sagittal deformity, achieving outcomes comparable to bilateral fixation. The proposed patient categorization can guide surgical decision-making by aligning fixation methods with patient characteristics. Limitations include the retrospective design and small sample size, underscoring the need for further research to validate these findings and assess the comparative effectiveness of fixation techniques.