Pigmented Villonodular Synovitis of the Knee: Disease of the Popliteus Tendon and Posterolateral Compartment

The knee joint is the most frequent location for pigmented villonodular synovitis (PVNS). Within the knee, localized PVNS is most commonly situated within the anterior compartment and is rarely found in the posterior compartment. Preoperative diagnosis is often elusive but can be improved with magnetic resonance imaging. We present a case of localized PVNS within the posterolateral compartment of the knee originating from the popliteus tendon that was not found on preoperative examination or radiological imaging.