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.