Localized pigmented villonodular synovitis of the knee: report of two cases of fat pad involvement.

The localized form of pigmented villonodular synovitis (PVNS) is a rare pathological entity characterized by a limited involvement of the synovium. The knee is most commonly affected. In the knee joint, the disorder generally presents as a nodular, pedunculated lesion protruding into the articular cavity. The lesion is usually revealed by mechanical symptoms such as locking. We report on two cases of localized PVNS that involved the patellar fat pad, an extremely rare area of involvement. Mechanical symptoms were not present. In one case, the lesion reached considerable dimensions without interfering with joint function. Arthroscopic treatment was easily performed. No recurrence was observed at 1-year follow up.