On the correlation between lesions at the palmar apical articular surface of the third metacarpus and the loading from the proximal sesamoid bones: a preliminary ex vivo study.

Already a lot of studies have been done on the equine fetlock joint to obtain more understanding about why fatal ‘breakdown’ injuries in this joint would happen so often, particularly in race horses. However, there is not much knowledge yet about the biomechanical role of the proximal sesamoid bones (PSB) during the repetitive limb loading as experienced at these high speeds. Therefore, the aim of this study was to evaluate the loading pattern of the PSB on the palmar articular surface of the third metacarpal bone at the evident high-risk use of horses particularly for racing, thus to find a possible biomechanical explanation for the typical and quite often fatal lesions reported to develop from that site. Six forelimbs were harvested from horses which were euthanized for reasons not related to musculoskeletal defects and/or clinical lameness, and thus became the specimens for this study. A materials testing machine was used to ex vivo simulate the forces on the fetlock joint surface as experienced during gallop. Pressure sensitive films were inserted into that joint to measure the pressure, specifically those from the PSB. A linear pressure built-up with increased limb loading was found at the site of the PSB. High pressure points were at similar joint surface locations as to where the typical cartilage lesions would develop. It has thus been suggested that lesions at the palmar apical surface of the third metacarpal bone would be the end result of the intermittent loading from high palmar pressures as arising particularly from the PSB