Estimation of Changes in Mechanical Bone Quality by Multi-scale Analysis with Remodeling Simulation

Abstract

Mechanical bone quality and its related load-supporting function at the macro-scale is a result of adaptation, which is achieved by trabecular bone remodeling at the microscale. The increase in fracture risk in patients with osteoporosis is a clear example of this structure/function relationship, where decreased bone mass as a result of structural changes during remodeling leads to changes in the stress distribution of trabecular bone. This stress distribution is closely associated with the morphology and orientation of the nano-scale biological apatite (BAp) crystallite - the main factor determining bone quality. It is therefore important to evaluate both the changes in mechanical bone quality and bone mass when predicting fracture risk. We propose a computational model of remodeling and multi-scale stress analysis of trabecular bone based on homogenization techniques, considering the mechanical properties of the BAp crystallite orientation to be anisotropic. We first identified morphological changes in healthy and osteoporotic cases, and then performed a multi-scale stress analysis for the remodeled osteoporotic trabecular bone to elucidate changes in mechanical bone quality leading to fracture risk. Our results demonstrate that the load-supporting function of remodeled bone correlates with mechanical adaptability to external loads through remodeling, despite a progressive decrease in bone mass. These findings suggest the potential to use changes in mechanical bone quality as a predictor of fracture risk. The availability of these simulation methods for bone quality evaluation is discussed.