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The Journal of Bone and Joint Surgery (American) 86:1000-1006 (2004)
© 2004 The Journal of Bone and Joint Surgery, Inc.

A Comparison of the Microarchitectural Bone Adaptations of the Concave and Convex Thoracic Spinal Facets in Idiopathic Scoliosis

Kevin G. Shea, MD1, Tyler Ford, BS2, Roy D. Bloebaum, PhD2, Jacques D'Astous, MD3 and Howard King, MD4

1 Intermountain Orthopaedics, 600 North Robbins Road, Suite 400, Boise, ID 83702. E-mail address: kgshea{at}aol.com
2 Bone and Joint Research Laboratory, Veterans Administration Salt Lake City Health Care System, Salt Lake City, UT 84148
3 Department of Orthopedics, University of Utah School of Medicine, 50 North Medical Drive, Salt Lake City, UT 84132
4 St. Luke's Children's Hospital, Bannock Avenue, Boise, ID 83702

Investigation performed at St. Luke's Children's Hospital, Boise, Idaho, the Shriners Hospital for Children, Salt Lake City, and the Bone and Joint Research Laboratory, Veterans Administration Hospital, Salt Lake City, Utah

The authors did not receive grants or outside funding in support of their research or preparation of this manuscript. They did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

Presented as a poster exhibit at the Annual Meetings of the Orthopaedic Research Society on February 13-17, 2002, in Dallas, Texas; the Pediatric Orthopaedic Society of North America on May 2-5, 2002, in Salt Lake City, Utah; and the Scoliosis Research Society on September 18-21, 2002, in Seattle, Washington.

Background: A limited number of studies have assessed the changes in bone microarchitecture in spinal facets with use of light microscopy but not with use of electron microscopy techniques. The purpose of this study was to analyze the facets in patients with scoliosis to determine whether there are differences in the bone microarchitecture of contralateral facets at the same anatomic level.

Methods: In eight patients undergoing posterior spinal arthrodesis for the treatment of idiopathic scoliosis, biopsy specimens of facet pairs at matched anatomic levels were obtained from three locations: (1) the curve apex, (2) one level cephalad to the apex, and (3) one level caudad to the apex. The facets were analyzed for cortical bone porosity and thickness with use of scanning electron microscopy and National Institutes of Health imaging software. The concave and convex facets were compared with use of a paired t test.

Results: The mean porosity (and standard deviation) for the concave and convex facets was 16.5% ± 5.8% and 24.1% ± 6.2%, respectively. Those on the convex side were significantly more porous than those on the concave side (p ≤ 0.03). The mean cortical width for the concave and convex facets was 798 ± 266 µm and 377 ± 124 µm, respectively. The concave facets had a significantly thicker cortex than did the convex facets (p < 0.01).

Conclusions: These results suggest that scoliotic deformities apply eccentric forces to spinal facets and that the concave and convex portions of the curve are subject to compression and tension forces, respectively. This analysis complements previous investigations of bone microarchitecture in animal models with use of a known compression-tension environment, and it suggests that the spinal facets remodel in a manner consistent with Wolff's law.

Clinical Relevance: Future studies of human spinal facets in scoliosis offer the opportunity to further define the microarchitectural response of human bone. Additional study will be necessary to determine whether these eccentric microarchitectural changes represent a secondary response to abnormal loading in the spine or whether an underlying pathological process in bone is a primary factor in the generation of scoliotic deformities. Further understanding of bone-remodeling in scoliosis may help to validate animal models and provide insight into the pathophysiology of scoliosis.


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