Abstract

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 <or= 0.03). The mean cortical width for the concave and convex facets was 798 +/- 266 microm and 377 +/- 124 micro m, 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.