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Three-Dimensional Characterization of Torsion and Asymmetry of the Intervertebral Discs Versus Vertebral Bodies in Adolescent Idiopathic Scoliosis

Schlösser, Tom P.C. MD*; van Stralen, Marijn PhD; Brink, Rob C. BSc*; Chu, Winnie C. W. MD; Lam, Tsz-Ping FRCSEd§; Vincken, Koen L. PhD; Castelein, René M. MD, PhD*; Cheng, Jack C. Y. MD, FRCSEd§

doi: 10.1097/BRS.0000000000000467
Deformity

Study Design. Cross-sectional study.

Objective. To compare the relative contribution of the vertebral bodies and intervertebral discs with the 3-dimensional spinal deformity in adolescent idiopathic scoliosis.

Summary of Background Data. There is an ongoing discussion about the causal role of skeletal growth processes in the etiopathogenesis of adolescent idiopathic scoliosis. Contradictory findings have been reported on the individual contribution of the vertebral bodies as compared with the discs to the coronal deformity. As far as we know, the true 3-dimensional deformity of the discs and vertebral bodies have not yet been described.

Methods. High-resolution computed tomographic scans of 77 patients with severe adolescent idiopathic scoliosis were included. Torsion and anterior-posterior and right-left asymmetry of each individual vertebral body and intervertebral disc were studied from T2 to L5, using semiautomatic analysis software. True transverse sections were reconstructed along the anterior-posterior and right-left axis of all endplates. These “endplate-vectors” were calculated semiautomatically, taking rotation and tilt into account. Torsion was defined as the difference in axial rotation between 2 subsequent endplates. Asymmetry was defined as the relative anterior-posterior or right-left height difference of the discs and the vertebrae.

Results. There were at least 3 times more torsion, anterior overgrowth, and coronal wedging in the discs than in the vertebrae in the thoracic as well as in the (thoraco) lumbar curves (P < 0.001). These values correlated significantly with the Cobb angle (r ≥ 0.37; P < 0.001). Anterior overgrowth and coronal asymmetry were greater in the apical regions whereas torsion was most pronounced in the transitional segments between the curves.

Conclusion. The discs contribute more to 3-D deformity than the bony structures, and there is significant regional variability. This suggests an adaptive rather than an active phenomenon.

Level of Evidence: 2

The relative contribution of the vertebral bodies and the discs to the 3-dimensional deformity in adolescent idiopathic scoliosis was analyzed on computed tomographic scans. The discs contributed at least 3 times more to the spinal deformity than the vertebrae, and there are regional differences, suggesting that this deformation is an adaptation rather than a generalized active growth process.

*Department of Orthopedic Surgery, University Medical Center Utrecht, Utrecht, the Netherlands

Image Sciences Institute, University Medical Center Utrecht, Utrecht, the Netherlands; and

Departments of Diagnostic Radiology and Organ Imaging and

§Orthopaedics and Traumatology, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, Hong Kong.

Address correspondence and reprint requests to René M. Castelein, MD, PhD, Department of Orthopedic Surgery, G05.228, University Medical Center Utrecht, PO Box 85500, 3508 GA Utrecht, The Netherlands; E-mail: R.M.Castelein@umcutrecht.nl.

Acknowledgment date: February 24, 2014. Revision date: April 11, 2014. Acceptance date: May 22, 2014.

The manuscript submitted does not contain information about medical device(s)/drug(s).

Alexandre Suerman, MD/PhD program, an unrestricted Medtronic research grant and the Anna Foundation/NOREF funds were received to support this work.

Relevant financial activities outside the submitted work: grants/grants pending.

© 2014 by Lippincott Williams & Wilkins