Standing CT-based finite element models efficiently identify regions of high mechanical strain in equine metacarpal subchondral bone

Stress fractures are common in racehorses, with the metacarpophalangeal (MCP) joint being the most frequently affected site as it is subjected to high-magnitude and high-rate cyclic loads during training and racing. These loads lead to repeated compressive stresses, resulting in subchondral bone (SCB) sclerosis, fatigue microcracks, and matrix damage that can progress to parasagittal fractures or palmar osteochondral disease (POD). The present study developed joint-specific 3D FE models and slice-based FE models using standing CT images for three trained racehorses, each presenting distinct SCB conditions common in racehorses as identified by their CT images: (1) biaxial sclerotic condylar SCB with no visible lesions: BS, (2) focal lytic SCB with associated sclerosis in the PSG: LGL, and (3) focal lytic SCB with associated sclerosis in the condyles: BCL. Both models predicted similar overall patterns of SCB stress and strain, identifying peak tensile and compressive strains in the PSGs and condyles, while minimal strains were observed over the sagittal ridge. The 3D models predicted a larger volume of highly strained bone compared to slice-based models, particularly in the horse with biaxial sclerosis. Both 3D and slice-based FE models demonstrated strong agreement in identifying the PSG and midcondyles as high-strain regions. The sensitivity analysis showed that variations in input parameters had minimal impact on the results, indicating the robustness of slice-based models. Despite being less detailed, slice-based models were much faster and more straightforward to develop and provided stress and strain patterns comparable to 3D models. These findings suggest that slice-based models offer a valuable tool for rapid assessment of biomechanical behaviour in equine fetlock joints, particularly for identifying regions at high-risk of failure in the clinical setting.