Exercise affects the mechanical properties and histological appearance of equine articular cartilage

Dorsal carpal osteochondral injury is a major cause of reduced performance in horses undergoing high-intensity training. It was hypothesised that the mechanical behaviour and histology of cartilage are influenced by the inten sity of exercise and by location within a joint. Relationships between hist ology and mechanical behaviour were identified in 2-year-old horses undergo ing 19 weeks of high-intensity treadmill training or low-intensity exercise and then compared between groups. Dorsal and palmar test sites were identi fied on radial, intermediate, and third carpal articular surfaces after eut hanasia. The mechanical properties of cartilage were determined with an aut omated creep indentation apparatus as previously described for equine carti lage. Cartilage morphology was assessed with use. of sections stained with haematoxylin and eosin and toluidine blue. Dorsal cartilage was less permea ble, thinner and had a loss of chondrocyte alignment compared with palmar c artilage Cartilage from strenuously trained horses showed more fibrillation and chondrocyte clusters than did cartilage from gently exercised animals. Dorsal radial carpal cartilage and third carpal cartilage of strenuously t rained animals were significantly less stiff than that from gently exercise d animals, and the former had reduced superficial toluidine blue staining c ompared with that from the gently exercised group. These results indicate t hat topographical and exercise-related differences exist in the morphology and mechanical properties of carpal cartilage and suggest that strenuous tr aining may lead to deterioration of cartilage at sites with a high clinical incidence of lesions.