Clinical Outcomes of S2 Alar-Iliac (S2AI) Screw Technique in The Treatment of Severe Spinal Sagittal Imbalance: A Retrospective 2-Year Follow-Up Study

Abstract

Background The treatment of adult spinal deformity (ASD) remains a significant challenge, especially in elderly patients. This study aimed to evaluate the outcomes of the S2AI screw technique in the treatment of severe spinal sagittal imbalance with a minimum 2-year follow-up. Methods From January 2015 to December 2018, 23 patients with severe degenerative thoracolumbar kyphosis who underwent placement of S2AI screws for long segment fusion were retrospectively reviewed. Patients were divided into group A (no mechanical complications, 13 cases) and group B (with mechanical complications, 10 cases) according to the occurrence of mechanical complications at the last follow-up. Radiographic parameters were compared between groups preoperatively, 1 month postoperatively, and at the last follow-up. Risk factors for mechanical complications were analyzed. Results The incidence of mechanical complications was 43.5%, and the revision rate was 17.4%. At 1 month postoperatively, sagittal correction was better in group A than in group B (P<0.05). The lumbar lordosis (LL), pelvic incidence minus lumbar lordosis (PI-LL), T1 pelvic angle (TPA), and sagittal vertical axis (SVA) of both groups at the last follow-up were significantly different from corresponding values at 1 month postoperatively (P<0.05), and the sagittal correction was partially lost. Pearson correlation analysis revealed that the occurrence of mechanical complications was associated with sacral slope (SS), LL, PI-LL, and global alignment and proportion (GAP) score at 1 month postoperatively. Conclusion A high incidence of mechanical complications was observed in long-segment corrective surgery with the S2AI screw technique for severe spinal sagittal imbalance. Inadequate sagittal correction is a risk factor for the development of mechanical complications.