Establishing Maximal Outcome Improvement Threshold for SRS-22r in Patients With Moderate-to-Severe Spinal Deformity

STUDY DESIGN: Retrospective cohort study. OBJECTIVE: To establish the maximal outcome improvement (MOI) threshold for moderate-to-severe spinal deformity. BACKGROUND: Interpretation of patient-reported outcome measures (PROMs) is often limited by ceiling effects and inadequate consideration of baseline status when determining clinically meaningful thresholds. METHODS: One hundred seven patients who underwent surgery for moderate-to-severe spinal deformity and completed ≥ 2-year follow-up were retrospectively included. The Scoliosis Research Society-22 revised (SRS-22r) was administered preoperatively and at ≥ 2-year follow-up to determine the MOI threshold using the anchor-based method. Anchor questions were derived from the SRS-22r satisfaction domain, with postoperative satisfaction defined as scores ≥ 4 on both questions. The MOI was calculated as the changes in SRS-22r scores relative to the total possible improvement. Receiver operating characteristic (ROC) curve analysis identified the optimal MOI threshold. Logistic regression analysis evaluated predictors associated with achieving the MOI threshold. RESULTS: Significant radiographic and clinical improvements were obtained at ≥ 2-year follow-up. Dissatisfied patients had lower postoperative SRS-22r satisfaction (3.1±0.4 vs. 4.5±0.4, P