• Rob C Brink, Jelle F Homans, Schlösser Tom P C TPC Department of Orthopaedic Surgery, G05.228, University Medical Center Utrecht, P.O. Box 85500, 3508 GA, Utrecht, The Netherlands., Marijn van Stralen, Koen L Vincken, Lin Shi, Chu Winnie C W WCW Department of Imaging and Interventional Radiology, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, Hong Kong., Max A Viergever, René M Castelein, and Cheng Jack C Y JCY Department of Orthopaedics and Traumatology, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, Hong Kong..
• Department of Orthopaedic Surgery, G05.228, University Medical Center Utrecht, P.O. Box 85500, 3508 GA, Utrecht, The Netherlands. r.c.brink@umcutrecht.nl.
• Eur Spine J. 2019 Dec 1; 28 (12): 3044-3052.

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. These slides can be retrieved under Electronic Supplementary Material.

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