Association of the GAP score and roussouly-based algorithm with long-term patient-reported outcomes following adult spinal deformity surgery: a systematic review and meta-analysis.

PURPOSE: The Global Alignment and Proportion (GAP) score and Roussouly-based alignment algorithms were originally developed to predict postoperative mechanical complications and outcomes following adult spinal deformity (ASD) surgery. While these frameworks have been extensively studied in relation to mechanical complications, their association with long-term patient-reported outcomes (PROMs) remains incompletely defined. The aim of this study was to systematically review and meta-analyze whether these frameworks are associated with long-term PROMs following ASD surgery. METHODS: PubMed, Embase, and Web of Science were searched from inception through February 2026. Studies were included if they evaluated postoperative alignment using the GAP score and/or a Roussouly-based restoration framework in patients undergoing ASD surgery, reported validated PROMs, and had ≥ 24-month follow-up. Random-effects meta-analyses were performed to pool mean differences (MDs) with 95% confidence intervals (CIs). Study quality was assessed using the Newcastle-Ottawa Scale. RESULTS: Eight retrospective cohort studies were included. ODI was reported in all studies and SRS-22/22r in six. Compared with proportioned alignment, severely disproportioned GAP alignment was associated with worse ODI (MD, 8.08; 95% CI, 1.00-15.20; p = 0.025; I²=71%), whereas moderately disproportioned alignment showed no significant difference (MD, 2.15; 95% CI, - 3.93 to 8.23; p = 0.489; I²=70%). Severe versus moderate disproportion demonstrated worse ODI (MD, 6.71; 95% CI, 3.81-9.62; p < 0.001; I²=0%). For SRS-22r, no significant differences were observed except for worse outcomes in severe versus moderate disproportion (MD, - 0.26; 95% CI, - 0.42 to - 0.10; p = 0.001; I²=24%). Roussouly-based restoration was not associated with significant differences in ODI or SRS-22r. CONCLUSION: Severely disproportioned GAP alignment was associated with worse long-term disability as measured by ODI, whereas moderately disproportioned alignment was not clearly distinguishable from proportioned alignment. Roussouly-based alignment restoration was not consistently associated with improved PROMs. LEVEL OF EVIDENCE: III.