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Scientific Articles   |    
Intervertebral Disc Health Preservation After Six Months of Spinal Growth Modulation
Vidyadhar V. Upasani, MD1; Christine L. Farnsworth, MS2; Reid C. Chambers, BA2; Tracey P. Bastrom, MA2; Gregory M. Williams, PhD3; Robert L. Sah, MD, ScD3; Koichi Masuda, MD1; Peter O. Newton, MD2
1 Department of Orthopaedic Surgery, University of California at San Diego, 350 Dickenson Street, MC 8894, San Diego, CA 92103
2 Department of Orthopedic Surgery, Rady Children's Hospital and Health Center at San Diego, 3030 Children's Way, Suite 410, San Diego, CA 92123. E-mail address for P.O. Newton: pnewton@rchsd.org
3 Department of Bioengineering, University of California at San Diego, 9500 Gilman Drive, MC 0412, La Jolla, CA 92093
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Disclosure: One or more of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of an aspect of this work. In addition, one or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. No author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.

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Investigation performed at the Rady Children's Hospital and Health Center, San Diego, California

Copyright © 2011 by The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2011 Aug 03;93(15):1408-1416. doi: 10.2106/JBJS.J.00247
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Abstract

Background: 

Spinal growth modulation has been proposed as a non-fusion strategy for treatment of idiopathic scoliosis, although the effect of this treatment modality on intervertebral disc health has not been evaluated in detail. The objectives of this in vivo study were to assess the creation of three-dimensional spinal deformity during six months of growth modulation compared with that in sham-surgery controls, and to compare, with use of magnetic resonance imaging (MRI), gross morphological, histological, and biochemical analyses, disc health between control animals and animals treated with a spinal tether.

Methods: 

Six immature Yucatan mini-pigs underwent anterior spinal instrumentation with vertebral screws connected by a polyethylene tether over four consecutive thoracic vertebrae (T8-T11). An additional six animals underwent sham surgery (screw placement only [the control group]). Radiographs were obtained preoperatively, postoperatively, and monthly thereafter during six months of growth. Computed tomography (CT) and MRI studies were performed ex vivo, and the spines were sectioned for histological and biochemical analyses. Multivariate analysis of variance (MANOVA) was used to compare six-month postoperative data between the control and tethered animals, with the alpha level of significance set at 0.05.

Results: 

Radiographs and CT images demonstrated the creation of significant three-dimensional deformity (p < 0.013) in the tethered animals compared with the controls. Macroscopic, MRI, and histological evaluation revealed no signs of disc degeneration, with a bulging gelatinous nucleus pulposus, discrete fibrous anular lamellae, and uniformly hyperintense T2-signal intensity within the nuclei pulposi. Biochemical analysis demonstrated no significant difference in the nuclei pulposus between the tethered and control vertebrae; however, the water content (p < 0.001) of both sides of the anulus fibrosus and the glycosaminoglycan content (p < 0.001) of the left side of the anulus fibrosus differed significantly between the two groups.

Conclusions: 

Six months of spinal growth modulation created significant spinal deformity in all three planes compared with what was found in the sham-surgery controls. Although disc health was qualitatively maintained, quantitative changes in the anulus fibrosus water content and the disc height were observed on the side opposite to the tether. These changes likely represent metabolic responses of the discs to compressive loads generated by the flexible tether.

Clinical Relevance: 

Clinical trials are needed to evaluate the ability of an anterolateral spinal tether to correct deformity while preserving spinal flexibility and intervertebral disc health.

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    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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