A Biomechanical Analysis of the Effects of Resorption Cavities on Cancellous Bone Strength

Abstract

We evaluated the effects of resorption cavities on cancellous bone strength using computational methods. Adding cavities to cancellous bone caused reductions in strength and stiffness that were greater than expected from the associated changes in bone volume and more pronounced when cavities were targeted to regions of high tissue strain. The amount of bone turnover in the skeleton has recently been implicated as a factor influencing bone strength. One mechanism proposed to explain this effect is that resorption cavities reduce the effective thickness of trabeculae and modify local stress distributions leading to reduced mechanical performance of the entire structure. In this study, we tested the plausibility of this mechanism. High-resolution finite element models were created from muCT images of 16 vertebral cancellous bone samples, as well as from images of the samples in which cavities had been added digitally-either at regions of high strain (targeted) or placed at random on the bone surface (nontargeted). The effect of resorption cavities on predicted bone strength and stiffness was evaluated by comparing the relationships between mechanical properties and bone volume fraction among the three groups (the original images, those with nontargeted cavities, and those with targeted cavities). Addition of resorption cavities modified the relationship between mechanical properties and bone volume fraction in the finite element models such that, for a given bone volume fraction, stiffness and yield strength were reduced compared with the original images (p < 0.05). The differences in yield strength-volume fraction relationships between the original models and those with targeted cavities were significantly greater than those between the original models and those with nontargeted cavities (p < 0.05). None of the differences in predicted mechanical properties per unit bone volume fraction could be accounted for by 3D measures of microarchitecture. Resorption cavities may influence cancellous bone strength and stiffness independent of their effect on bone volume. The effects of cavities on bone mechanical performance relative to bone volume are greater when cavities are targeted to regions of high strain and cannot be predicted using standard microarchitecture measures.