Féline-Orthopédique : A case of synovial osteochondromatosis in a cat

Castrated male cat, 10 years. Calmer since 6 months, reluctant to jump.

There is a decreased range of motion of the right stifle and a mild joint swelling.

Radiography: Right stifle ML view
There are triangular well defined mineralized opacities visible superimposed onto the joint space and most likely corresponding to mineralized menisci. Several other mineralized opacities are seen superimposed onto the joint capsule most likely. These correspond to intra and periarticular mineralizations of the synovial membrane.
There is a moderate osteoarthrosis associated: osteophyte on the apex of the patella and around the fabellae.

Synovial osteochondromatosis is a metaplasia of the synovial membrane. The membrane is differentiating in cartilaginous tissue that can become isolated and loose in the joint space. This cartilaginous structures can eventually mineralize. The number, size of loose bodies and their structure are variable.
This disease is infrequently seen in cats and rarely in dogs.