Increased Lateral Waist to Thoracolumbar Height Ratio Correlates With Improved In-brace Correction

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BACKGROUND: Bracing is the primary non-operative treatment for adolescent idiopathic scoliosis (AIS), with in-brace correction (IBC) being a key predictor of long-term success. Although BMI has been linked to bracing outcomes, it fails to capture important aspects of body habitus, such as fat distribution and torso shape, that influence brace fit and force transmission. This study aims to evaluate a novel radiographic measure, the lateral waist-to-height (WH) ratio, as a more accurate predictor of IBC in AIS patients. METHODS: A retrospective review of AIS patients treated with Rigo-style braces between 2014 and 2024 at a single institution was conducted. Thoracolumbar (TL) height and waist width at the iliac crest were measured on AP and lateral radiographs to calculate WH ratios. Linear regression evaluated associations between IBC and BMI, WH ratios, and TL height change. Multivariate regression adjusted for major curve angle and curve apex. RESULTS: The study included 209 females (mean age 11.4±2.1 y, BMI 17.7±2.8). Mean pre-brace major curve angle was 28.2±7.3 degrees, with average IBC of 64.8%±31.6%. Lateral WH ratio correlated positively with IBC ( R =0.21, P =0.014), representing a weak but statistically significant correlation. By contrast, BMI and AP ratio did not demonstrate significant associations with IBC. In multivariate analysis, both major curve angle ( P <0.001) and lateral WH ratio ( P =0.009) were independent predictors of IBC. CONCLUSIONS: Lateral WH ratio offers a more holistic representation of body habitus than BMI and is independently associated with in-brace correction. These findings suggest that the lateral WH ratio may provide additional insight into brace fit and initial correction, warranting further study to determine its potential role in predicting long-term bracing outcomes in AIS. LEVEL OF EVIDENCE: Level III.

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