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 intensity of exercise and by location within a joint. Relationships between histology and mechanical behaviour were identified in 2-year-old horses undergoing 19 weeks of high-intensity treadmill training or low-intensity exercise and then compared between groups. Dorsal and palmar test sites were identified on radial, intermediate, and third carpal articular surfaces after euthanasia. The mechanical properties of cartilage were determined with an automated creep indentation apparatus as previously described for equine cartilage. Cartilage morphology was assessed with use of sections stained with haematoxylin and eosin and toluidine blue. Dorsal cartilage was less permeable, thinner, and had a loss of chondrocyte alignment compared with palmar cartilage. 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 trained animals were significantly less stiff than that from gently exercised animals, and the former had reduced superficial toluidine blue staining compared with that from the gently exercised group. These results indicate that topographical and exercise-related differences exist in the morphology and mechanical properties of carpal cartilage and suggest that strenuous training may lead to deterioration of cartilage at sites with a high clinical incidence of lesions.