Impact of L4 tilt and coronal lumbopelvic alignment on in-brace correction in AIS.

PURPOSE: To evaluate the impact of L4 tilt and coronal lumbopelvic alignment on in-brace correction (IBC) in adolescent idiopathic scoliosis (AIS). METHODS: Seventy-four AIS patients treated with CAD/CAM braces between January 2021 and January 2024 were retrospectively analyzed. Pre-brace and 1-month in-brace radiographs were assessed. Cobb angle, L4 tilt, pelvic obliquity (PO), and IBC percentages were measured. IBC was calculated as the percentage reduction in Cobb angle. Patients were grouped according to L4 tilt (≤ 10° vs. >10°). Correlation and stepwise regression analyses were performed to determine predictors of IBC. RESULTS: L4 tilt showed a significant negative correlation with both lumbar (r = -0.318, p = 0.012) and thoracic IBC (r = -0.538, p = 0.001). PO was also negatively correlated with lumbar (r = -0.348, p = 0.006) and thoracic IBC (r = -0.569, p = 0.001). Patients with L4 tilt ≤10° demonstrated significantly higher lumbar (66.2% vs. 50.8%, p = 0.012) and thoracic (59.1% vs. 40.6%, p = 0.001) correction rates. In stepwise regression analysis, L4 tilt remained the only independent predictor of IBC, explaining 10% of lumbar and 29% of thoracic correction variance. Demographic and skeletal maturity parameters were not significantly associated with IBC. CONCLUSION: Higher L4 tilt is independently associated with reduced in-brace correction, particularly in thoracic curves. Incorporating L4 tilt into routine radiographic assessment may improve prediction of brace effectiveness in AIS.