Large Localized Pigmented Villonodular Synovitis of the Knee Presenting with Patellar Dislocation: A Case Report and Surgical Technique

Localized pigmented villonodular synovitis (PVNS) of the knee joint is a rare condition that results in the development of a tumor. The tumor is slowly progressive but sometimes causes mechanical symptoms. We herein report a rare case involving a 21-year-old woman who presented with patellar dislocation. Magnetic resonance imaging revealed a large focus of localized PVNS at the patellofemoral joint and medial patellar gutter causing lateral subluxation of the patella. Arthroscopy showed a hypervascular synovial tumor extending from the medial patellar gutter to the patellofemoral joint. Arthroscopic resection and medial retinacular plication were performed. The patient’s patellar dislocation resolved with no recurrence of instability.