Does the coronal deformity angular ratio affect bracing outcome in adolescent idiopathic scoliosis?

Purpose: To examine if coronal deformity angular ratio (C-DAR) serves as a predictor for progression to surgical magnitude in patients with Adolescent Idiopathic Scoliosis (AIS) treated with thoracolumbar sacral orthosis (TLSO).

Methods: Patients with AIS, prescribed a full-time TLSO, Cobb angle 20-40°, Risser 0-2, who wore the brace ≥ 12.9 h and reached skeletal maturity/surgery were included retrospectively. C-DAR was defined as the Cobb angle divided by the number of vertebrae in the curve, yielding a larger value in short curves. The association between C-DAR and the risk of progression to surgical magnitude (> 45°) was assessed. Secondly, we evaluated the association between pre-treatment Cobb angle and in-brace correction on the risk of progression to > 45°.

Results: We included 165 patients with a mean Cobb angle of 30 ± 6°. Of these, 46/165 (28%) progressed ≥ 6° and 26/165 (16%) reached surgical magnitude at the end of treatment. C-DAR was a significant predictor for risk of progression to surgical magnitude with an OR of 1.9 (CI 1.2-2.9) per unit increase in C-DAR. A threshold value of 5.15 was established and demonstrated an OR 5.9 (CI 2.1-17.9) for curve progression to a surgical magnitude. Likewise, pre-treatment Cobb angle showed a significant OR 1.3(CI 1.2-1.4) per degree increase in Cobb, whereas in-brace % correction showed OR 0.96 (CI 0.93-0.98).

Conclusion: C-DAR is an independent predictor for progression to a surgical magnitude in AIS patients treated with bracing. Patients with a higher C-DAR should be counseled to help set realistic expectations regarding the likelihood of curve progression despite compliance with brace wear.