Pigmented Villonodular Synovitis Presenting at an Atypical Site: A Case Report.

Pigmented villonodular synovitis (PVNS) is an idiopathic villous overgrowth and pigmentation of the synovial membrane of a single joint. It is an uncommon condition characterized by yellow or yellowish-brown colour due to deposits of cholesterol and hemosiderin, excessive secretion of yellowish-brown synovial fluid, and the formation of brownish chocolate synovial tissue. This condition commonly occurs at the knee joint at the age of 20-50 years.