What causes different coronal curve patterns in idiopathic scoliosis?

BackgroundAdolescent idiopathic scoliosis (AIS) is a three-dimensional deformity of the spinal column in otherwise healthy adolescents. The underlying mechanisms associated with the spinal deformity development have been explored which delineated the role of the sagittal curvature of the spine. The patterns of the spinal deformity vary between the AIS patients as shown in several classification systems. It remains to further investigate how variations in sagittal profiles result in different coronal plane deformities in AIS and how these deformation patterns are intrinsically different. MethodsA total of 71 Lenke 1 and 52 Lenke 5 AIS patients were included retrospectively. The 3D models of the spine were generated from biplanar radiographs to calculate the clinical spinal parameters, vertebral axial rotations, and the 3D centerline of the spinal curvature. A classification based on the centerlines axial plane projection was developed. The 3D curvature of the centerline was calculated at each point. A 2D elastic rod finite element model (FEM) of the sagittal spinal curvature for each axial subtype was developed to calculate the 3D deformity of the spine under gravity and axial torsion. Differences in the axial clusters clinical parameters, curvature of the spine, and the deformation patterns of the FEM were compared. The characteristics of the sagittal curvature of these axial clusters were determined. ResultsLenke1 was divided into two axial groups (I and II) whereas the Lenke 5 cohort all had the same axial projection pattern (loop shape). T5-T12 kyphosis was significantly different between Lenke1-Group I and the other two groups, p=0.04. The vertebral rotation in both Lenke1-Group I and Lenke 5 had only one maximum value and the FEM deformed in a loop shaped whereas Lenke1-group II showed two maximum values for vertebral rotation and the FEM of the centerline deformed in a lemniscate shape. The ratio of the spinal arc lengths above and below the sagittal inflection points for Lenke1-Groups I and II and Lenke 5 were 0.52, 1.16, and 3.24, respectively. ConclusionVariations in the axial plane projection of the curve were observed within Lenke types. Lenke 1- Group I and Lenke 5 showed similar 3D curve characteristics suggesting one 3D curve whereas Lenke1-Group II, with two 3D curves, behaved differently. The length of the spinal arcs above and below the sagittal inflection point related to the patterns of axial deformity.