Establishing Maximal Outcome Improvement Threshold for SRS-22r in Patients With Moderate-to-Severe Spinal Deformity: An Anchor-Based Analysis With a Minimum of Two-Year Follow-Up.

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 <0.001) and subtotal scores (3.7±0.4 vs. 4.0±0.3, P <0.001). The determined MOI threshold for the SRS-22r score was 43.5%. Adolescents demonstrated a significantly higher mean MOI percentage than adults (50.3% vs. 42.8%, P =0.001), although the proportion achieving the MOI threshold was comparable between groups (73.4% vs. 62.8%, P =0.242). Male sex (OR=0.8, P =0.022) and surgical complications (OR=0.7, P <0.001) significantly decreased the likelihood of achieving the MOI threshold. Conversely, preoperative neurological deficits were associated with increased odds of meeting this threshold (OR=1.6, P =0.041).

CONCLUSIONS

The MOI threshold for the SRS-22r in moderate-to-severe spinal deformity was 43.5%. Male sex and perioperative complications were negative predictors, whereas preoperative neurological deficits increased the probability of achieving clinically meaningful improvement.