Predictors of curve flexibility in adolescent idiopathic scoliosis: a retrospective study of 100 patients.

Curve flexibility in adolescent idiopathic scoliosis (AIS) was one of the major concerns of spinal surgeons since the evolution of surgical correction techniques. In this respect, many tried to identify which criteria denote more rigid curve. In the present study, we aimed toward determining important factors influencing AIS curve flexibility on supine bending films. We assessed radiographs of 100 patients with AIS for direction of curves, number of involved vertebrae, apical vertebral translation and rotation, magnitude of main thoracic curve and T5-T12 kyphosis. Statistical analysis performed via stepwise linear regression model with these variables plus age and sex against flexibility index. According to regression analysis, there was a clear relationship between flexibility indexes (FI) and magnitude of main thoracic curve at all (P<0.001). When we consider flexible curves (FI>50%) against rigid curves, apical vertebral rotation was a major determinant of curve flexibility also (P<0.001). Adolescent idiopathic scoliosis curves with larger Cobb's angle and apical vertebral rotation show less flexibility on supine bending films.