Adolescent idiopathic scoliosis (AIS) is a three-dimensional structural deformation of the spine in which spinal rotation causes initial deformity resulting in rib cage distortion and vertebral wedging. Progression of vertebral wedging could be attributed to abnormal vertebral growth and could be related to the precarious coronal balance [1,2].

Deformation progresses with asymmetrical loading during skeletal maturation according to the Hueter-Volkmann law [3,4]. Several authors have shown that deformation becomes more severe as the Cobb angles increase, and by three-dimensional morphometric analyses demonstrated that those deformations are greatest in the apical vertebral body [[5], [6], [7]]. A previous longitudinal study revealed that intervertebral disc wedging affects curve progression before and during the growth spurt, but that the vertebral wedge contributed most to curve progression after the growth spurt [8]. Many reports have analyzed intervertebral disc wedging [1,2,8,9], but only a few evaluated vertebral wedging [4,6,10,11].

Most anatomical morphological studies have been limited to imaging modalities such as X-rays [4,9,10] and magnetic resonance imaging (MRI) [6]. However, it is difficult to obtain accurate reconstructed images with radiographs or MRI. On the other hand, computed tomography (CT) provides high-resolution three-dimensional image construction, but no reports have evaluated vertebral wedging using CT, and the associated factors and the effect of vertebral wedging in AIS are unknown.

The purpose of the present study was to investigate the associated factors for coronal vertebral wedging in AIS patients with a main thoracic curve type using a series of CT images to evaluate the impact of vertebral wedging on curve flexibility.