The pQCT “Bone Strength Indices” (BSIs, SSI). Relative mechanical impact and diagnostic value of the indicators of bone tissue and design quality employed in their calculation in healthy men and pre- and post-menopausal women

Abstract

The pQCT-assessed Bone Strength Indices (BSI’s, SSI) depend on the product of a “quality” indicator, the cortical vBMD (vCtD), and a “design” indicator, one of the cross-sectional moments of inertia or related variables (MIs) in long bones. As the MIs vary naturally much more than the vCtD and represent different properties, it could be that the variation of the indices might not reflect the relative mechanical impact of the variation of their determinant factors in different individuals or circumstances. To understand this problem, we determined the vCtD and MI’s in tibia scans of 232 healthy men and pre- and post-MP women, expressed in SD of the means calculated for each group, and analyzed the independent influence of 1 SD unit of variation of each factor on that of the indices by multiple correlations. Results showed: 1. that the independent influence of the MIs on the indices was generally larger than that of the vCtD, and 2. that in post-MP women the influence of the vCtD was larger than it was in the other groups. This confirms the view that inter-individual variation of vCtD is comparatively small, and that mechanical competence of human bone is mostly determined by ‘design’ factors.