Contact area and pressure distribution changes of the equine third carpal bone during loading

Changes in contact area and pressure distribution with loading were evaluated on the proximal articulating surface of the equine third carpal bone using safranin-O dye staining and pressure sensitive film techniques. A significant increase in percentage contact area resulted as the applied load was increased from 3115 to 9000 N (54.93% +/- 7.99 vs 61.43% +/- 7.37 respectively, P = 0.016). The area in contact shifted towards the dorsal aspect of both the radial and intermediate facets of the third carpal bone. Changes were also detected in the mean pressure under the same loading conditions. There was a significant increase (P < 0.05) in the mean pressure on the dorsomedial to dorsolateral aspect of the radial facet and the dorsomedial to middle-lateral aspect of the intermediate facet with increased loading. A trend towards an increase (P < 0.10) in mean pressure was detected on the middle-medial aspect of the radial facet and the middle-medial to palmar-lateral aspect of the intermediate facet. There was no significant increase (P > 0.05) in mean pressure with an increase in load from 3115 to 9000 N at the palmar aspect of either facet. The increase in contact area and mean pressure with loading in the most dorsal and dorsomedial aspect of the radial facet may explain the large amount of third carpal bone trauma seen in this location in racing horses.