The Journal of Bone and Joint Surgery

Image Quiz
Painless Effusion of the Knee¹
A fifty-eight-year-old man was evaluated because of a three-month history of recurrent painless effusion in the left knee. Aspiration of the knee and injection of cortisone had been performed at another institution, but the effusion had recurred after one to two weeks. Physical examination revealed a large effusion in the left knee. Anteroposterior radiographs (made with the patient bearing weight), lateral radiographs, and Merchant radiographs revealed normal tibiofemoral joint spaces and mild patellofemoral osteoarthrosis. Magnetic resonance imaging was performed.
Fig. 1-A	Fig. 1-B	For larger view, click on image
Fig. 1-A. T1-weighted axial magnetic resonance image showing a lesion with high signal intensity (arrows) in the suprapatellar pouch. Fig. 1-B. T2-weighted sagittal magnetic resonance image revealing the mass in the suprapatellar pouch (arrows). The mass has the same signal intensity as fat.
An arthroscopic procedure was performed.
Fig. 2-A	Fig. 2-B	For larger view, click on image
Intraoperative photographs demonstrating the arthroscopic appearance of the lesion. Fig. 2-A. Arthroscopic exploration revealed a villous mass in the suprapatellar pouch. Fig. 2-B. Arthroscopic appearance of the lesion as seen from another location.