Structuring of parameters for assessing vertebral bone strength by star volume analysis using a morphological filter

Abstract

Based on the relationship between bone strength, trabecular skeletal structure, and bone mineral density (BMD), structure parameters for assessing vertebral bone strength were studied using 18 cancellous bone blocks from the third lumbar vertebra of elderly persons. The trabecular bone pattern of each bone block was binarized into a trabecular skeletal pattern by computed radiography (CR) using a morphological filter. The binarized trabecular skeletal pattern was quantified into a trabecular skeletal pixel percentage (SKP; volume parameter of the trabecular skeletal signal component) and trabecular skeletal star volume (Vt; connection parameter of the trabecular skeletal structure) by star volume analysis. Then, the BMD and elasticity of each bone block were measured by dual X-ray absorptiometry and mechanical tests to determine the correlation between SKP and Vt. In the present study, no significant correlations were observed between BMD and elasticity. Elasticity differed greatly between some bone blocks even though BMD was essentially the same. Grid-like skeletal patterns consisting of vertical and horizontal continuous lines showed higher elasticity. SKP showed higher correlations with elasticity than BMD in subset (n = 2-7) and sumset images, although the fluctuation range was narrow. Meanwhile, Vt showed higher correlations with elasticity than SKP in subset (n = 1-6) and sumset images. Vt showed stronger correlations with elasticity than SKP. This fact indicates that strong relationships exist between the connectivity of trabecular skeletal structure and bone strength. Because the SKP-BMD and Vt-BMD correlations are weak, the influences exerted by SKP and Vt seem to be independent of the influence of BMD on the bone strength of vertebra obtained from persons with advanced age. These results indicate that SKP and Vt obtained by star volume analysis using a morphological filter are effective as structure parameters for analyzing the bone quality of lumbar vertebra.