SYNOVIAL OSTEOCHONDROMATOSIS
The principal difference with diagnosis on PVNS is synovial osteochondromatosis.
whenever PVNS is considered as a differential diagnosis, synovial osteochondromatosis (SOC) should also be considered.
The disease occurs in a very similar age group and a
similar clinical presentation to PVNS.
Both conditions are non malignant synovial metaplasias.
Phases of involvement are identified of both conditions although these are more obvious in SOC.

Three phases are described,
      • the early active phase which is predominantly a synovitis,
      • the late active phase when calcification begins
      • quiescent phase

where the synovitis has regressed and the patient may be left without effusion or obvious synovitis but with lose intra-articular calcific and ossific bodies.
The imaging findings vary with these three different phases.

The plain film is the first step in the differentiation from SOC from PVNS.
Small areas of punctate or
occasionally, large conglomerate areas of calcification.
Erosions are significantly less common than in PVNS
consequently the absence of erosions in the presence of calcification is typical.

Difficulties with early disease which is predominantly synovial hyperplasia
Seen in approximately 10% of patients.
In addition early calcification may be obscured by the overlying bone.
CT may be helpful