Extraarticular pigmented villonodular synovitis: a cause for failed knee arthroscopy.

Arthroscopic treatment of diffuse pigmented villonodular synovitis of the knee is reported to have low recurrence rates and morbidity. The purpose of the current study was to evaluate demographic information, clinical symptoms, treatment parameters, and functional outcome in a group of 38 consecutive patients referred to the authors' hospital with persistent extraarticular diffuse pigmented villonodular synovitis of the knee after arthroscopic synovectomy. There were 23 males and 15 females with an average age of 31.7 years (range, 11-65 years) at the time of arthroscopy. All had an average of 1.7 (range, 1-5) arthroscopies. Thirty-four of 38 (89.5%) patients had some improvements of their symptoms after arthroscopic synovectomy, but all had worse symptoms and function at the latest followup of 3.63 years (range, 0.25-19.5 years). Although arthroscopic synovectomy offered some short-term relief, a critical review of prior reports and the data in the current study suggest poor outcomes in patients who have extraarticular diffuse pigmented villonodular synovitis of the knee after arthroscopic synovectomy. Magnetic resonance imaging is recommended for accurate staging of the disease and for long-term followup after arthroscopic treatment.