Would initial thoracic correction be a key factor in orthotic intervention for adolescent idiopathic scoliosis with double-curve?

PURPOSE: To investigate the influence of in-orthosis correction on treatment outcomes of adolescent idiopathic scoliosis (AIS) with double-curve, and to explore baseline radiographic features associated with achieving high in-orthosis correction. METHODS: This retrospective study analyzed 101 skeletally immature patients with double-curve AIS treated with customized thoracic-lumbar-sacral orthosis (TLSO). Radiographic measurements from pre-orthosis standing and supine, first in-orthosis, and final out-of-orthosis follow-up visits were analyzed. Initial in-orthosis correction rates for the thoracic and thoracolumbar/lumbar (TL/L) curves were compared. Patients were dichotomized into high (≥ 38.3%) and low (< 38.3%) thoracic correction groups. An exploratory multivariable analysis was performed to identify baseline radiographic features associated with thoracic correction outcomes. RESULTS: Thoracic curves had significantly lower initial in-orthosis correction than TL/L curves (29.3% vs. 38.6%, p < 0.001). High initial thoracic correction was strongly associated with final treatment success for the thoracic curve (p = 0.009), whereas TL/L curve correction was not (p = 0.250). Thoracic curve progression accounted for 90.9% of treatment failures. Patients who achieved high thoracic correction had nearly eight times the odds of achieving high TL/L correction (OR = 7.89, 95% CI: 2.97-20.90). Five radiographic factors were found to be associated with high correction: greater pre-orthosis lumbar lordosis, higher thoracic and TL/L supine flexibility, lesser thoracic apical sagittal wedging, and a smaller increase in rib-vertebral angle difference (RVAD) from standing to supine. The model showed good discriminatory capacity within the cohort (AUC = 0.862). CONCLUSION: In AIS with double-curve, inadequate in-orthosis thoracic correction is strongly associated with treatment failure. A set of baseline radiographic features including favorable sagittal alignment, high flexibility, and rib cage stability are associated with successful thoracic correction, generating hypotheses regarding potential biomechanical factors for this limitation which can also serve as a foundation for future research.