What is the minimum effective wearing dosage of orthotic intervention in adolescent idiopathic scoliosis?

PURPOSE: This study aimed to estimate the minimum effective orthosis-wearing time (MEWT) needed to prevent curve progression and reduce surgical risk in adolescent idiopathic scoliosis (AIS). METHODS: This retrospective study analyzed 281 patients with AIS who completed orthotic treatment. Compliance was measured using both objective temperature sensors and subjective self-reports, categorized into four daily wear-time levels: 0 to 6, 6 to 12, 12 to 18, and 18 to 24 h. Treatment outcomes at endpoint were classified as improvement (> 5° decrease), stabilization (± 5°), deterioration (> 5° increase), or surgical deterioration (Cobb angle > 50° or requiring surgery). Associations between compliance and outcomes were examined, and MEWT thresholds were estimated within risk-stratified subgroups based on baseline clinical risk factors. RESULTS: Patients wearing orthoses for 0 to 6 and 6 to 12 h/day showed significantly lower improvement rates and higher deterioration rates than those in the 12 to 18 and 18 to 24 h/day groups. No significant differences in treatment outcomes were observed between the 12 to 18 and 18 to 24 h/day groups, nor between the 0 to 6 and 6 to 12 h/day groups. Risk-stratified logistic regression models showed that MEWT estimates for curve deterioration ranged from 9.3 to 21.6 h/day, depending on target risk (20% to 5%) and Risser sign. For surgical deterioration, MEWT estimates at the 5% target risk ranged from 8.1 to 20.6 h/day. However, for patients with Risser 0 and a baseline Cobb angle > 30°, the model-derived MEWT estimates for target risks of 2% or lower exceeded 24 h/day and were therefore considered clinically infeasible. CONCLUSIONS: Although orthosis wear of 12 h per day or more was associated with better outcomes in group-level comparisons, MEWT is not uniform and varies by baseline clinical risk factors. Integrating objective compliance monitoring with risk-adapted targets may support personalized orthotic prescriptions, facilitate shared decision-making, and optimize treatment effectiveness.