Determining the minimal clinically important difference of angle of trunk rotation for monitoring conservatively treated adolescent idiopathic scoliosis.

Abstract

The angle of trunk rotation (ATR) is widely used in the clinical follow-up of adolescent idiopathic scoliosis (AIS); however, the minimal clinically important difference (MCID) has not been clearly defined. This study aimed to determine treatment-specific MCID values for ATR in conservatively treated AIS patients. This retrospective cohort study included 316 AIS patients treated with brace plus exercise or exercise alone. Radiographic outcomes at 6 months were classified as improvement (ΔCobb ≤ - 5°), stabilization (- 5° < ΔCobb < + 5°), or worsening (ΔCobb ≥ + 5°). Receiver operating characteristic (ROC) analyses were performed to determine optimal ΔATR cut-off values for clinically meaningful improvement and worsening in the overall cohort and separately by treatment group. In the overall cohort, ΔATR showed good discriminative ability for improvement (AUC = 0.778) and worsening (AUC = 0.777). The optimal cut-offs were ΔATR ≤ - 1.5° for improvement and ΔATR ≥ + 0.5° for worsening. In subgroup analyses, the improvement threshold was ΔATR ≤ - 1.5° in the exercise-only group and ≤ - 4.5° in the brace-plus-exercise group. For radiographic worsening, the optimal thresholds were ΔATR ≥ + 0.5° in the exercise-only group and ≥ - 2.5° in the brace-plus-exercise group. Treatment-specific ΔATR thresholds provide clinically meaningful benchmarks for monitoring both improvement and worsening, supporting the use of ATR as a practical radiation-free follow-up parameter in AIS management.