Micro-Architectural Bone Adaptations in Scoliotic Spinal Facets

PURPOSE: The purpose of this study was two-fold: 1) to analyze the facets in scoliosis patients to determine if there are differences in the microscopic morphology of contra-lateral facets, and 2) to determine if these differences in morphology are consistent with bone responses to eccentric compression and tension environments.

METHODS: IRB approval and informed consent was obtained. Idiopathic scoliosis patients underwent posterior fusion. In 8 patients, matched anatomic level facet pair biopsies were obtained from 3 levels: 1) curve apex, 2) one level above the curve apex and, 3) one level below the curve apex. The facets on the concave and convex sides were considered to be under compression and tension respectively. The facets were analyzed by scanning electron microscopy for cortical bone porosity and thickness using NIH imaging software. The data was tested for normality and a Paired t-test was used to determine significance.

RESULTS: The porosity for the compression and tension facets was 16.5 ± 5.8% and 24.1 ± 6.2% respectively. The tension side was significantly more porous then the compression side (P < 0.03). The average cortical width for the compression and tension facets was 798 ± 266 mm and 377 ± 124 µm respectively. The compression facets had a significantly thicker cortex then the tension 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 micro-architecture in animal models using a known compression/tension environment. Future studies of human facets in scoliosis offer the opportunity to further define the micro-architectural response of human bone to eccentric stress environments. Additional study will be necessary to determine if these eccentric micro-architectural changes in bone represent a secondary response to abnormal loading in the spine, or if an underlying pathological process in bone is a primary factor in the generation of scoliosis deformities. Further understanding of bone remodeling in scoliosis may help validate animal models and provide insight into the pathophysiology of scoliosis.