Aspect-Related Mechanical Properties of the Cortical Bone in the Third Metacarpal Bone of Mares

Complete fractures of the third metacarpal bone (MC III) diaphysis pose a significant clinical challenge, prompting advanced veterinary medicine to utilize constitutive and biomechanical modeling to better understand bone behavior. This study aims to compare the elastic modulus of the MC III cortical bone, supported by measurements of cortical bone thickness and relative density, across the dorsal, lateral, medial, and palmar aspects of the MC III, as well as to evaluate the cortical bone’s response to compressive forces applied in different directions. Given the bone structure can exhibit sex-related differences, MC III bones were isolated from six equine cadaver limbs collected exclusively from mares and imaged using computed tomography (CT) to measure thickness and density. Cortical bone samples were collected from the four aspects of the MC III and subjected to mechanical testing followed by the elastic modulus calculation. Bone thickness and elastic modulus varied across the MC III aspects. Thinner cortical bone on the palmar aspect coincided with a lower sample reaction force-based elastic modulus in the externo-internal direction and a lower axial compression force elastic modulus in the proximo-distal direction. Regardless of the MC III aspect, the cortical bone demonstrated greater resistance to compressive forces when loaded in the vertical plane than in the horizontal plane. The returning of different values in mechanical tests depending on the direction of loading may be attributed to the anisotropic behavior of the cortical bone, which may implicate the increased risk of complete fractures of the MC III diaphysis due to a kick from another horse or a fall, rather than from training or competition-related overload.