Prediction of brace outcome in adolescent idiopathic scoliosis

Abstract

Adolescent idiopathic scoliosis (AIS) is a 3-dimensional deformity of the spine affecting patients from the age of 10, with the tendency for progression in adolescence and after skeletal maturity. Bracing is the standard modality of treatment for patients with a moderately sized curve, but treatment success with bracing varies from patient to patient. This dissertation aims to identify clinically applicable prognostic factors for brace success in AIS and to develop a new prognostic index for guide bracing for AIS patients. A systematic review was conducted to examine the existing predictors of AIS curve progression in both braced and unbraced patients. Cobb angle, curve type, flexibility, and correction rate were found to be predictors of curve progression with strong and consistent evidence. A Cobb angle greater than 25° and curve flexibility greater than 28% were identified as clinically important prognostication thresholds. Several other predictors, including apical vertebral rotation, rib morphology, and pelvic tilt may be promising factors, in view of the surge of new 3-dimensional imaging reconstruction for AIS. A large-scale prospective cohort of braced AIS patients was followed to identify predictors of brace outcome under objectively controlled brace compliance data. High supine flexibility and in-brace correction rate were identified as significant predictors of brace success, with clinically significant cut-offs of 18.1% and 28.8% respectively. A novel Supine Correction Index (SCI), defined as the quotient of division of in-brace correction by supine flexibility, was established as a clinically important predictor of brace outcome with a threshold of 1.21 predicting a 60% reduction of risk of progression. In this dissertation, a comprehensive review of the existing evidence was conducted. Prognostication of brace outcome was optimized with the establishment of clinical thresholds for important brace-specific parameters, with control of known brace predictors. The SCI was identified as a promising predictor of brace outcome for future research.