Twenty cases of equine osteoarthrosis detected at autopsy.

A pathological study was performed on osteoarthrosis detected at autopsy in 20 horses whose ages ranged from 21 days to 17 years old. They were asymptomatic on the joints except in 3 animals, and autopsied after death or sacrificed due to accidental fracture or other diseases. Lesions of osteoarthrosis were recognized in all horses, which tended to increase in incidence and severity according to age. Lesions were concentrated at hinged joints such as the elbow, fetlock, and hock. Synovial fossae and ulcerative lesions were observed on each opposite articular cartilage, forming the so-called mirror image. Linear erosions regarded as a secondary one were frequently observed on the cartilages. Histologically, the lesions were classified into 4 phases, 1) edematous degeneration, 2) crevice formation, focal necrosis, erosion of cartilage, 3) ulcerative changes, 4) regenerative changes of cartilage in foals and proliferation of fibrous or adipose tissue on the denuded subchondral bone in aged horses. By toluidine blue stain, decreased acid mucopolysaccharide was suggested in cartilaginous matrix around the lesions. From the results, it was concluded that the disease was a disorder of articular cartilage accompanied with hypoplasia of articular subchondral bone.