Synovial chondroid metaplasia. The condition has been reported in dogs and horses. In dogs, it is usually monoarticular, with a predilection for the shoulder. In horses, cases have been reported to be bilateral and symmetrical in joints of the rear limbs. In man, recurrence after synovectomy occurs but is uncommon.
Malignant transformation is reported in humans but is rare.
The cause of the condition in both humans and domestic animals is not known. In humans, some cases have been reported to have clonal structural abnormalities and re-arrangements of chromosome 6, suggesting PSC is neoplastic. Interestingly, similar chromosomal abnormalities were found in a synovial chondroma but are not found in classic chondrosarcomas. Their appearance in PSC is usually in absence of any etiologic agent, synovial cell hyperplasia, or other evidence of joint capsule inflammation. The presence of these nodules may contribute to progressive, radiographically detectable, degenerative joint disease.