Pigmented villonodular synovitis of the knee: diagnosis and treatment.

Pigmented villonodular synovitis (PVNS) of the knee is a benign but locally aggressive disease of synovial proliferation that occurs in localized nodular and diffuse villous growth patterns. Although inflammatory and neoplastic causes have been hypothesized, etiology remains unknown. Presenting as unilateral knee pain and swelling, PVNS mimics other knee ailments. Radiographs are often unremarkable, whereas magnetic resonance imaging may show characteristic intra-articular masses with signal dropout on T2-weighted sequences. Pigmented villonodular synovitis is surgically treated with open or arthroscopic total or partial synovectomy. High recurrence rates are associated with all treatments of diffuse PVNS. Complications of open synovectomy include arthrofibrosis and wound breakdown. Total arthroscopic synovectomy is technically demanding but can be advantageous. Transcondylar notch views, accessory posterior portals, and the posterior transseptal portal maximize arthroscopic access to the posterior knee. Intra-articular radioisotope injection and external beam radiation may be beneficial adjuvant therapy for extensive diffuse and recurrent PVNS of the knee.