A hierarchical classification of adolescent idiopathic scoliosis: Identifying the distinguishing features in 3D spinal deformities

Abstract

This study aimed to identify the differentiating parameters of the spinal curves’ 2D projections through a hierarchical classification of the 3D spinal curve in adolescent idiopathic scoliosis (AIS). A total number of 103 right thoracic left lumbar pre-operative AIS patients were included retrospectively and consecutively. A total number of 20 non-scoliotic adolescents were included as the control group. All patients had biplanar X-rays and 3D reconstructions of the spine. The 3D spinal curve was calculated by interpolating the center of vertebrae and was isotropically normalized. A hierarchical classification of the normalized spinal curves was developed to group the patients based on the similarity of their 3D spinal curve. The spinal curves’ 2D projections and clinical spinal measurements in the three anatomical planes were then statistically compared between these groups and between the scoliotic subtypes and the non-scoliotic controls. A total of 5 patient groups of right thoracic left lumbar AIS patients were identified. The characteristics of the posterior-anterior and sagittal views of the spines were: Type 1: Normal sagittal profile and S shape axial view. T1 is leveled or tilted to the right in the posterior view. Type 2: Hypokyphotic and a V shape axial view. T1 is tilted to the left in the posterior view. Type 3: Hypokyphotic (only T5-T10) and frontal imbalance, S shape axial view. T1 is leveled or tilted to the right, and 3 frontal curves. Type 4: Flat sagittal profile (T1-L2), slight frontal imbalance with a V shape axial view, T1 tilted to the left. Type 5: flat sagittal profile and forward trunk shift with a proximal kyphosis and S shape axial view. T1 is leveled or tilted to the right. In conclusion, a hierarchical classification of the 3D scoliotic spine allowed identifying various distinguishing features of the spinal curves in patients with a right thoracic curve in an orderly fashion. The subtypes’ characteristics resulting from this 3D classification can be identified from the pairs of the frontal and sagittal spinal curves i.e. X-rays in right thoracic AIS patients.

What causes different coronal curve patterns in idiopathic scoliosis?

“…This centerline was isotropically normalized in a way that all the spines have the same heights while modifying the antero-posterior and lateral coordinates by the same factor. The reliability of this method in evaluating the 3D spinal curves was shown previously [3,15].…”

“…As shown previously, the axial projection of the curve carries important information for surgical and non-surgical management of the right thoracic AIS [6,[8][9][10]. It was also shown that the sagittal profile strongly relate to the patterns of axial deformation using mechanics of deformation in an elastic rod [3,11,12]. Here, it is studied if the axial projection of the curve varies within the Lenke types and whether that variation relates to the sagittal curvature of the spines within these subtypes.…”

“…It was previously showed that two axial subgroups exist in right thoracic AIS: loops shaped and lemniscate shaped [3,19]. The sagittal curvature of the spine relates to the pattern of the 3D deformity development, particularly the aforementioned axial subgroups of right thoracic AIS [19].…”

“…The current widely-used classification system of AIS, Lenke classification, primarily is based on the curve appearance in the frontal plane, with a minor role for the sagittal plane [2]. 3D curve subtypes have been identified within the Lenke subtypes [3,4]. However, it has not been determined whether the 3D characteristics of the curves follow the current clinical classification of the AIS.…”

“…This system classifies the AIS patients, based on the number of structural curves in the frontal plane to one curve scoliotic types (Lenke1 and Lenke5), twocurve scoliotic types (Lenke 2, 3, and 6), and a three-curve scoliosis (Lenke 4). Threedimensional classification of the curves resulted in more than 6 curve patterns in AIS, sub classifying the patients within the Lenke types [3][4][5]. But it was not determined how different aspects of the 3D curves vary within and between the Lenke types.…”