E-Poster Presentation 30th Australian and New Zealand Bone and Mineral Society Annual Scientific Meeting 2020

Microdamage accumulation and adaptation of subchondral bone (SB) subjected to intensive cyclic loading are associated with catastrophic bone failure in athletic horses. At the tissue-level, they lead to a spatial variation in bone mineral density (BMD), affecting the mechanical response of the bone. We used CT-based finite element (FE) modelling to investigate the effect of BMD variation at the joint-level. CT images were taken from the MC3 joint of a standing racehorse. Sesamoid bones were rotated in the sagittal plane to simulate the mid-stance position during galloping where the maximum compression occurs (Fig.A). A single slice through the joint was cropped to develop FE models. The metacarpal condyle, sesamoid bones and cartilage were segmented based on their grey scale. The area between sesamoids was segmented as the intersesamoidian cartilage. Mesh volume was exported to ABAQUS. A BMD-based elastic modulus (E) was assigned to bone to estimate a gradient of E in the proximal SB based on our previous studies on explants from distopalmar condyles (Fig.C). 15 MPa compression was applied to the intersesamoidian cartilage. Stresses were compared to those of the same model with a homogenous E. The homogenous model exhibited peak stresses and strains at the parasagittal grooves with the orientation mostly parallel to the joint surface (Fig.D). The heterogenous model also predicted peak stresses and strains at the joint surface (Fig.E). However, within focal lytic areas stress was lower, with high surrounding stresses where focal sclerosis was observed. High stresses correspond to areas of sclerosis consistent with modelling in response to the loading environment, however this was not the case for the strain measurements suggesting that the relationship between CT data and material properties need further investigation. Future FE models of horses with various CT-identified lesions and longitudinal scans would better explain the MC3 stress fractures.