Distribution of mechanical strain in equine distal metacarpal subchondral bone: A microCT-based finite element model

Microdamage accumulation and adaptation of subchondral bone subjected to intensive cyclic loading are important processes associated with catastrophic bone failure, and joint degeneration in athletic humans and racehorses. At the tissue-level, they lead to a spatial variation in bone tissue mineral density (TMD) which affects the response of the bone to mechanical load. Quantifying the spatial distribution of mechanical load within the subchondral bone is critical for understanding the mechanism of the joint failure. Previously, a gradient of TMD and mechanical properties has been reported under unconfined compression in osteochondral plugs. In the present study, we used micro computed tomography (μCT)-based finite element (FE) models of cartilage-bone to investigate the gradient of strain in the subchondral bone (SCB) from the third metacarpal (MC3) condyle of racehorses under simulated in situ compression. Non-destructive mechanical testing of specimens under high-rate compression provided the apparent-level modulus of SCB. FE models were analysed using unconfined and confined boundary conditions. Unconfined FE-predicted apparent-level gradient of modulus across the SCB thickness correlated well with the experimental results (R2 ​= ​0.72, p ​< ​0.05). The highest strain occurred in the most superficial SCB (0.5–2.5 ​mm deep to the cartilage-bone interface) under the simulated in-situ compression through articular cartilage. The findings of this study provide an estimation for the spatial distribution of mechanical strain within SCB in-situ in the presence of heterogeneous bone tissue which is commonly observed in joints subjected to intensive cyclic loading.