Pigmented villonodular synovitis.

Pigmented villonodular synovitis is a proliferative condition of the synovium. Monoarticular involvement, the most common process, occurs in two forms: localized and diffuse. The localized form is characterized by focal involvement of the synovium, with either nodular or pedunculated masses; the diffuse form affects virtually the entire synovium. The localized form has an excellent prognosis and a low recurrence rate when managed surgically. The more common diffuse form has a reported recurrence rate of up to 46%. Although the condition can present in any joint, the knee is the most commonly affected site. Pigmented villonodular synovitis is often aggressive, with marked extra-articular extension. Open synovectomy is the standard method of management. Arthroscopic synovectomy, which has gained popularity, has several advantages over the open technique, but it is associated with higher recurrence rates in diffuse pigmented villonodular synovitis. Synovectomy by any approach, however, may prevent secondary osteoarthritis and subsequent joint arthroplasty. Radiation-induced synovectomy has shown mixed results. Combined surgical and nonsurgical approaches may be necessary, and in some patients, total joint arthroplasty may be the only effective treatment.