Association Between Vertebral Rotation Pattern and Curve Morphology in Adolescent Idiopathic Scoliosis

Objectives: Although rotation is an important aspect of pathogenesis of adolescent idiopathic scoliosis (AIS), there are no studies demonstrating rotation pattern by directly measuring rotation angle in computed tomography (CT) images. The present retrospective comparative radiographic study was conducted to evaluate the rotation pattern in AIS and its relation to curve morphology and Lenke classification. Methods: The study included 245 patients diagnosed with AIS and evaluated with a preoperative CT scan. Rotation angle of each vertebrae was measured using reconstructed axial CT images. Lenke classification of scoliosis curvature, Cobb angle, location of apical vertebra and end vertebra, level of most rotated vertebra (MRV), and rotational shift vertebra were recorded. Student's t-test, analysis of variance test, and correlation analysis were performed to identify the characteristics of rotation patterns in each Lenke type. Results: The rotation angle of MRV was significantly correlated with the Cobb angle. The level of MRV and rotation angle of MRV demonstrated significant correlation in both the main thoracic curve and lumbar curve, which signified that MRV located near the thoracolumbar junction is related to more severe rotational deformity. The level of MRV was also significantly correlated to the Cobb angle in both the main thoracic curve and lumbar curve. The types of structural curves proximal to major structural curves, such as type 2, 4, and 6, demonstrated more severe rotational and coronal plane deformities as compared with types 1, 3, and 5. Conclusions: Curves with different Lenke types demonstrated different levels of MRV and severity of rotation. The results suggest that different center levels of rotation, signified by MRV, are a factor determining curve morphology. The findings would be a basis of connection between 2-dimensional classification and transverse plane deformity.