Examining the Outcomes of Multilevel Thoracolumbar Instrumented Fusion Constructs With Concomitant Sacroiliac Joint Fusion Using S2-Alar-Iliac Screws

Study Design: Systematic review. Objective: This systematic review evaluates whether concomitant sacroiliac joint (SIJ) fusion to S2-alar-iliac (S2AI) fixation improves clinical, radiographic, and patient-reported outcomes. Summary of Background Data: Adult spinal deformity (ASD) often leads to long-segment fusions ending at the sacrum. As S2AI screws have become a viable technique for pelvic fixation, concerns about SIJ integrity have prompted growing interest in combining S2AI fixation with concurrent SIJ fusion. Methods: This systematic review aims to evaluate the clinical outcomes of S2AI screw placement in adult spinal deformity surgery with concomitant pelvic fusion. PubMed, SCOPUS, COCHRANE, and Web of Science were queried on March 31, 2025. We excluded case reports, nonhuman studies, technology reviews, nonoperative studies, or studies unrelated to SIA fusion. Functional lumbopelvic outcomes assessed included pelvic incidence (PI), pelvic incidence-lumbar lordosis (PI-LL) mismatch, and preoperative and postoperative visual analog scale (VAS) scores for both lower extremity and back pain. Results: Out of 1412 studies reviewed, 6 retrospective studies met the inclusion criteria. These studies involved 332 patients Frequency weighted mean (FWM) age 63.1±6.7 y; FWM follow-up 704.5±286.9 d comparing S2AI fixation (n=118) and S2AI fixation with SIJ fusion (n=204). Across a cohort of 180 patients (63 with concurrent SI fusion, 117 without concurrent SI fusion), postoperative SIJ pain occurred in 1.6% of fusion patients versus 34.2% of SI fixation-only patients. One study reported that dual S2AI screw constructs versus single S2AI screw constructs were associated with higher fusion rates (23% vs. 65%, P =0.011) and lower rates of rod breakage (0% vs. 12%, P =0.17). Conclusion: Concomitant SIJ fusion during S2AI screw fixation for ASD provides effective stabilization and may support more favorable postoperative outcomes versus isolated S2AI fixation, with dual S2AI screws potentially offering superior results to single screws. Levels of Evidence: Level IV.