Localized pigmented villonodular synovitis: three cases of intra-articular knee involvement.

Pigmented villonodular synovitis (PVNS) is a relatively uncommon, benign hypertrophy of synovial tissue that mimics numerous intra-articular derangements or neoplasms. Patients with PVNS present with a variety of symptoms. Pigmented villonodular synovitis may exist in other orthopedic pathology, making it a difficult diagnosis without histologic examination. This article presents three unusual cases of localized PVNS involving the knee, including one lesion arising from the popliteal tendon, which is previously unreported in the orthopedic literature. These cases illustrate the protean manifestations of PVNS as well as the variety of methods necessary to treat it. A brief discussion of PVNS including proposed etiologies, clinical presentation, description of the histologic and radiographic characteristics of the lesion, and its treatment are included.