Reoperation in Long Lumbar Constructs with and Without Iliac Fixation: A Registry Study.

STUDY DESIGN: Retrospective cohort study. OBJECTIVE: To evaluate the association between iliac fixation and long-term reoperation risk in patients undergoing multilevel lumbosacral fusion for degenerative pathology. SUMMARY OF BACKGROUND DATA: Spinopelvic fixation using iliac screws is commonly employed to improve construct stability in long lumbar fusions involving the sacrum. While biomechanical benefits are well established, clinical evidence regarding long-term reoperation risk and failure mechanisms in degenerative populations remains limited. METHODS: We identified adult patients undergoing primary elective multilevel lumbosacral fusion (>4 levels) between 2009 and 2023 from a large integrated healthcare spine registry by using iliac fixation. Primary outcome was all-cause reoperation. Secondary outcomes included reoperation for adjacent segment disease (ASD), nonunion, and hardware-related complications. We used Multivariable Cox proportional hazards regression models adjusted for patient and surgical factors to evaluate reoperation risk. Time-stratified analyses addressed nonproportional hazards. RESULTS: A total of 1,301 patients were included, including 483 with iliac fixation and 818 without. Mean follow-up was 6.3 years. At 10 years, crude all-cause reoperation incidence was 26.0% with iliac fixation versus 31.1% without. Iliac fixation was associated with reduced long-term all-cause reoperation risk (>1 y) (HR 0.63, 95% CI 0.43-0.92, P=0.018), but not early reoperation risk. Nonunion-related reoperation risk was significantly lower with iliac fixation (HR 0.30, 95% CI 0.13-0.67, P=0.004). No significant differences were observed in ASD-related reoperation risk. CONCLUSIONS: In patients undergoing multilevel lumbosacral fusion for degenerative pathology, iliac fixation was associated with significantly lower long-term reoperation risk, driven primarily by reduced nonunion-related reoperation. These findings support the role of iliac fixation in improving long-term construct durability. LEVEL OF EVIDENCE: III.