Interval-Based International Multicenter Validation of the Distal Radius and Ulna Classification for Growth Velocity and Curve Progression in Adolescent Idiopathic Scoliosis

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Study Design Prospective international multicenter observational cohort study. Objective To evaluate the relationships among distal radius and ulna (DRU) classification, growth velocity, and scoliosis progression patterns in adolescent idiopathic scoliosis (AIS) using longitudinal interval-based analyses in a multinational Asian cohort. Methods Patients aged 10–18 years with AIS were prospectively enrolled from multiple Asian centers. DRU classification, Sanders classification, Risser stage, standing height, and Cobb angle were assessed at approximately 4–6-month intervals. Only observations obtained before brace treatment or surgery were included. Height velocity and Cobb progression velocity were calculated between consecutive visits. Stage-specific patterns were evaluated using boxplots, nonparametric analyses, and mixed-effects models adjusted for age, sex, and baseline Cobb angle. Results Among 329 enrolled patients, 236 patients contributing 618 longitudinal intervals met eligibility criteria. Mean age was 13.5 years, and mean baseline Cobb angle was 24.0°. Height velocity peaked at Radius stage 6 (0.62 cm/month) and Ulnar stage 5 (0.68 cm/month). Cobb progression velocity was greatest at Radius stage 6 (0.31°/month); among adequately represented Ulnar stages, progression velocity was greatest at stage 5 (0.27°/month). Spearman analyses showed only very weak correlations between skeletal maturity stage and Cobb progression velocity. Mixed-effects analyses suggested nonlinear progression patterns, with increased progression velocity at earlier to intermediate maturity stages. Conclusions DRU classification demonstrated stage-dependent progression patterns, with peak scoliosis progression generally occurring approximately one DRU stage after peak height velocity. These findings suggest that DRU classification may help identify skeletal maturity phases associated with accelerated scoliosis progression in AIS.