Abstract
PurposeTo define the longitudinal rotation axis around which individual vertebrae rotate, and to establish the various extra- and intravertebral rotation patterns in thoracic adolescent idiopathic scoliosis (AIS) patients, for better understanding of the 3D development of the rotational deformity.MethodsSeventy high-resolution CT scans from an existing database of thoracic AIS patients (Cobb angle: 46°–109°) were included to determine the vertebral axial rotation, rotation radius, intravertebral axial rotation, and local mechanical torsion for each spinal level, using previously validated image processing techniques.ResultsFor all levels, the longitudinal rotation axis, from which the vertebrae rotate away from the midline, was localized posterior to the spine. The axis became closer to the spine at the apex: apex, r = 11.5 ± 5.1 cm versus two levels above (radius = 15.8 ± 8.5 cm; p < 0.001) and beneath (radius = 14.2 ± 8.2 cm; p < 0.001). The vertebral axial rotation, intravertebral axial rotation, and local mechanical torsion of the vertebral bodies were largest at the apex (21.9° ± 7.4°, 8.7° ± 13.5° and 3.0° ± 2.5°) and decreased toward the neutral, junctional zones (p < 0.001).ConclusionIn AIS, the vertebrae rotate away around an axis that is localized posterior to the spine. The distance between this axis and the spine is minimal at the apex and increases gradually to the neutral zones. The vertebral axial rotation is accompanied by smaller amounts of intravertebral rotation and local mechanical torsion, which increases toward the apical region. The altered morphology and alignment are important for a better understanding of the 3D pathoanatomical development of AIS and better therapeutic planning for bracing and surgical intervention.Graphic abstractThese slides can be retrieved under Electronic Supplementary Material.
Highlights
Despite many years of dedicated research into its cause, no single etiological mechanism has been established for adolescent idiopathic scoliosis (AIS) [1, 2]
The vertebral axial rotation is accompanied by a smaller amount of intravertebral axial rotation and local mechanical torsion, increasing towards the apical region
In severe idiopathic scoliosis the apex rotates away from its original position around a longitudinal rotation axis that is localized far posterior to the spine
Summary
Despite many years of dedicated research into its cause, no single etiological mechanism has been established for adolescent idiopathic scoliosis (AIS) [1, 2]. Insight in the rotation mechanism of the different vertebrae within the curve and whether the rotation is mainly local (located within the vertebra: intravertebral axial rotation and local mechanical torsion), or a rotation of the whole segment (vertebral axial rotation) are important to help understand possible mechanisms of scoliosis development and a better description of the altered anatomy. This knowledge could give more insights in the treatment of scoliosis, since reduction and restoration of the rotational deformity is one of the treatment goals. The objective of this study is to systematically (according to the Scoliosis Research Society 3D Terminology of Spinal Deformity [18]) define all different extra- and intravertebral patterns of spinal rotation in the axial plane in idiopathic scoliosis patients: the vertebral axial rotation and the rotation radius, as well as the intravertebral axial rotation (the rotation between the vertebral body and posterior elements) and the local mechanical torsion (between the upper and lower endplate)
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