Incidence and outcomes of spinopelvic fixation loosening following adult spinal deformity surgery

PURPOSE: To identify the incidence and clinical outcomes of spinopelvic fixation loosening following surgical correction of adult spinal deformity (ASD). METHODS: A single-institution retrospective cohort of 152 consecutive patients meeting inclusion criteria who underwent long-segment fusion with pelvic fixation for correction of ASD was reviewed. Pelvic screws were assessed on follow-up post-operative standing radiographs for evidence of loosening. Surgical revision of spinal instrumentation served as the primary outcome. PROMIS Pain Interference and Physical Function T-Scores were assessed as secondary outcomes among the subset of cases (n = 92) with available scores. RESULTS: Pelvic screw loosening was appreciated in 25 cases (16.4%) with initial evidence of loosening identified a median 1.1 years (Q1: 0.8, Q3: 2.5) following surgery. Loosening of pelvic screws (OR 3.0, 95% CI 1.2-7.3, p = .017) was associated with significantly increased odds of eventual instrumentation revision surgery, including specifically surgical revision of spinopelvic fixation (OR 5.5, 95% CI 1.6-18.5, p = .006). 4 of 26 cases (15%) with S2-Alar-Iliac (S2AI) screws required revision surgery compared to 37 of 126 cases (29%) without S2AI screws. PROMIS T-Scores were significantly worse for patients requiring instrumentation revision surgery but did not differ between cases with and without loosening. CONCLUSION: Loosening of spinopelvic fixation occurs frequently following correction of ASD and can develop years following surgery. While distal construct screw loosening may be appreciated incidentally at follow-up, loosening of pelvic screws was associated with significantly increased odds of eventual instrumentation revision surgery.