A Subluxing Knee Mass

Abstract

A 44-year-old woman was referred for right knee pain that had been present for a year, and magnetic resonance imaging (MRI) findings revealed pigmented villonodular synovitis (PVNS). The patient had no other significant medical history and no other musculoskeletal or constitutional symptoms. Findings of the physical examination were normal except for the striking observation of a hard nodular mass that appeared to sublux from the anterior knee laterally upon knee extension (Video 1). MRI of the knee revealed a nodular mass measuring approximately 2.5 cm craniocaudad, 1.5 cm anteroposterior, and 2.7 cm in the transverse direction (Figure 1). Increased signal intensity was observed on the fat-suppressed T2-weighted images, and similar signal intensity was observed on corresponding T1-weighted images. A small amount of fluid in the semimembranosus bursa was seen, likely representing mild bursitis. Otherwise, cartilaginous surfaces were intact, and no evidence was found of ligament or menisci abnormalities or arthritic changes. PVNS is a hypertrophic synovial process characterized by villonodular proliferation and hemosiderin pigmentation [1,2]. Initially, PVNS was not believed to possess the potential for malignancy, but Layfield et al [3] have described rare cases of malignant PVNS. PVNS is a relatively uncommon disease with an estimated annual incidence of 1.8 cases per 1 million persons. Localized intra-articular involvement almost exclusively involves the knee and represents approximately 6% of all cases. Clinical symptoms vary depending on the location of the lesion but frequently present as a slowly progressive, painful, soft tissue mass that rarely causes joint dysfunction. The treatment of choice is surgical resection via arthroscopy [4].