Utility of The Novel Supine Correction Index For Predicting Brace Outcomes In Adolescent Idiopathic Scoliosis

Abstract

Objectives: To assess the predictive ability of morphological predictors in predicting brace outcome in patients with adolescent idiopathic scoliosis (AIS) and to establish a novel supine correction index for guiding brace treatment. Methods: A prospective cohort of braced patients with AIS between December 2016 and December 2018 was recruited and followed up until weaning. Patients were braced according to the Scoliosis Research Society bracing criteria. Patients who were lost to follow-up or had incomplete radiographic records were excluded. Baseline radiological data were obtained from pre-brace standing posteroanterior and lateral whole-spine radiographs, supine radiographs, and immediate in-brace posteroanterior and lateral standing radiographs. Cobb angles, supine flexibility, and in-brace correction rate were obtained and used to predict curve progression at the end of follow-up, defined by ≥5° increase of Cobb angle via univariate and multivariable logistic regressions. The supine correction index (SCI) was defined as the ratio between correction rate and flexibility. Receiver operating characteristic (ROC) curve analysis was performed to assess the optimal thresholds for flexibility, correction rate and SCI in predicting lower risk of progression, defined by a change in Cobb angle ≥5° or incidence of surgery. Odds ratios (ORs) and 95% confidence intervals (CIs) were reported where appropriate. Results: A total of 207 patients, with mean±standard deviation age of 12.8±1.2 years at recruitment, were included. The baseline Cobb angle was similar (p=0.374) between progressed (32.7°±10.7) and stable patients (31.4°±6.1). High supine flexibility (OR, 0.947; 95% CI, 0.910–0.984; p=0.006) and correction rate (OR, 0.926; 95% CI, 0.890–0.964; p<0.001) were significantly predictive of lower incidence of progression after adjusting for Cobb angle, Risser sign, curve type, menarche status, distal radius, and ulna grading and brace compliance. Factors related to shoulder imbalance and coronal imbalance were not significantly predictive of brace outcomes. ROC curve analysis identified a cut-off of 18.1% for flexibility (sensitivity=0.682, specificity=0.704) while a cut-off of 28.8% is found for correction rate (sensitivity=0.773, specificity=0.691) in predicting lower risk of curve progression. Cut-off for SCI was found to be 1.21 by ROC curve analysis (sensitivity=0.583, specificity=0.591), and an SCI greater than 1.21 is significantly predictive of a lower risk of progression (OR, 0.4; 95% CI, 0.251–0.955; p=0.036). Conclusions: High supine flexibility (18.1%) and correction rate (28.8%) predict a lower risk of curve progression. An SCI of 1.21 was found predictive of bracing outcomes in patients with AIS. This is a guide for achieving the target correction rate during brace fabrication to optimize brace outcomes.