Longitudinal patient-reported outcomes after spinal fusion for adolescent idiopathic scoliosis: recovery trajectories and insights into surgical timing.

PURPOSE: Health-related quality-of-life (HRQOL) assessment provides insight into patient's subjective experiences that complement traditional clinical and radiological indicators. This study aims to characterize individual variability in long-term HRQOL recovery trajectories after spinal fusion for severe adolescent idiopathic scoliosis (AIS) and to identify preoperative and surgical factors associated with baseline HRQOL and the rate of improvement. METHODS: This retrospective longitudinal cohort study included 388 patients with severe AIS (Cobb angle ≥ 45°) who underwent spinal fusion (mean age at surgery 15.3 ± 2.1 years). A total of 1,539 longitudinal SRS-22r and Spinal Appearance Questionnaire (SAQ) records with up to > 20 years of follow-up were analyzed. Hierarchical multilevel growth models with random intercepts and random slopes (cubic time polynomial) were used to model recovery trajectories. Preoperative patient-reported outcome measures (PROM) level, age at surgery (continuous), sex, and curve magnitude were evaluated as trajectory moderators. "Good recovery" was defined as final-visit SRS-22r composite score ≥ 4.0 or SAQ mean score ≤ 4.2. Marginal and conditional R2 quantified explained variance; partial-effects plots illustrated predicted probabilities. RESULTS: Substantial individual variability existed; the population-average trajectory explained only 18% of variance in SRS-22r and 23% in SAQ scores. Preoperative PROM level was the strongest moderator (additional 54-58% variance explained), with patients having moderate baseline disability showing the greatest and most rapid gains. Younger age at surgery significantly hastened recovery (p < 0.01). Most postoperative HRQOL improvement occurred within the first 4 years (SRS-22r) and 6 years (SAQ), after which scores plateaued at normative levels with no significant long-term decline. CONCLUSION: Preoperative PROM levels and younger age at surgery are dominant, modifiable moderators of both baseline HRQOL and subsequent postoperative recovery speed. These trajectory-based findings support individualized, patient-centered surgical timing discussions rather than rigid chronological thresholds and facilitate shared decision-making that aligns postoperative HRQOL gains with key psychosocial and educational milestones.