Naturally occurring osteoarthritis in the metacarpophalangeal joints of wild horses

This study identified changes consistent with osteoarthritis; articular car tilage damage, subchondral bone sclerosis and marginal osteophytes, in the metacarpophalangeal joints of mild New Zealand horses. The articular cartil age lesions were identified by Indian ink staining techniques and histology , The lesions occurred on the proximodorsal aspect of the first phalanx (P1 ) and were more severe on the medial compared to the lateral eminence of th e bone, and their severity increased with age. The bone mineral density of the subchondral bone underlying the cartilage lesions, assessed using conve ntional radiography and dual energy absorptiometry, also increased with age and with severity of the overlying cartilage lesion. Subjective assessment of cabinet radiographs revealed that the subchondral bone sclerosis was gr eater in horses with severe articular cartilage damage. Ossicles, with a di stinct trabecular bone pattern, mere identified at the proximo-dorsal margi n of P1 in 8 specimens from 5 horses from the older age groups (greater tha n age 5 years). The results of this study demonstrate age-related changes consistent with o steoarthritis in the metacarpophalangeal joints of wild horses. There appea rs to be a significant relationship between subchondral bone sclerosis and overlying cartilage degeneration in the proximodorsal aspect of P1. We have identified an age-related osteoarthritic process naturally present in hors es; and postulate that the stresses of racing and training may accelerate t his ageing process.