Abstract:
Catastrophic injuries of the equine metacarpophalangeal joint are a significant concern for equine practitioners and the public, often leading to retirement or euthanasia of Thoroughbred racehorses. The most common types of these catastrophic injuries include fractures of the proximal sesamoid bones and the lateral condyle of the third metacarpal bone. Given the devastating nature of these injuries and the difficulties in treatment, prevention is paramount, necessitating a thorough understanding of the risk factors and pathogenesis of the underlying disease. This project was initiated to develop a comprehensive finite element model of the equine metacarpophalangeal joint to investigate how bone geometry, as a potential risk factor, influences the stress distribution patterns within the joint.
The study commenced with in vitro experiments to generate extensive data on ligament, tendon, and bone strain, as well as pressure distribution within the joint, crucial for validating the subsequent finite element model. Eight forelimbs from different horses were subjected to loads simulating galloping conditions on an MTS machine. Notably, this phase was the first to measure surface contact pressure between the distal condyles of the third metacarpal bone and the proximal sesamoid bones. A significant finding was a pressure distribution pattern indicating an area of high tension in the parasagittal groove, which could elucidate the high incidence of lateral condylar fractures originating in this specific region.
The second phase involved the development and rigorous validation of a three-dimensional finite element model of the metacarpophalangeal joint, constructed from computed tomography (CT) data. This detailed model incorporated the third metacarpal bone, proximal phalanx, proximal sesamoid bones, and various critical ligaments including the suspensory, collateral, collateral sesamoidean, oblique sesamoidean, and straight sesamoidean ligaments. Different mesh resolutions were tested to ensure model convergence, resulting in a robust model comprising 121,533 nodes, 112,633 hexahedral elements, and 10 non-linear springs. Validation was achieved using both the experimental data from the study's first part and existing literature.
In the final section, the validated finite element model was utilized to explore the effect of varying bone geometry on joint mechanics. The model was morphed using CT data from three distinct horse groups: a control, a horse with a lateral condylar fracture, and the contralateral limb of a fractured horse. The analysis revealed a consistent area of increased stress in the palmar aspect of the parasagittal grooves across all three groups, a region frequently associated with fracture initiation. Furthermore, distinct differences in stress distribution patterns were observed between the control, fractured, and contralateral limb models. These biomechanical variations, particularly in stress distribution patterns influenced by joint geometry, may contribute to the predisposition of certain horses to catastrophic injuries. This study concludes that further biomechanical investigations are crucial to precisely define the parameters that lead to these injurious changes.
