Pigmented villonodular synovitis (PVNS) is a condition that most commonly occurs in the knee joint but can also affect other joints in the body. PVNS occurs when the synovium (knee joint lining) overgrows to the point that it causes pain, swelling, mechanical symptoms and sometimes arthritis. Synovium is a thin layer of tissue that lines the joint and synthesizes joint fluid which facilitates smooth joint motion. If an individual suffers from pigmented villonodular synovitis, the synovium produces excess fluid, which causes the join to swell and makes movement painful. Pigmented villonodular synovitis of the knee typically occurs in individuals ranging in ages 20-50; nearly 80% of all PVNS cases occur in the knee joint. PVNS can occur as an isolated lesion or growth (localized) or present as a widespread diffuse pattern. Doctor Riley J. Williams, orthopedic knee specialist serving Manhattan, Brooklyn, New York City, NY and surrounding areas has extensive experience in diagnosing and treatment knee PVNS and other joint related conditions.