Synovial rupture of the knee joint: confusion with deep vein thrombosis.

Four patients were admitted to hospital with a provisional diagnosis of deep vein thrombosis. Arthrography of the knee joint subsequently demonstrated the presence of synovial cysts in all four patients with rupture into the tissues of the calf in two cases. These conditions are difficult to distinguish clincally and radiological investigation may be required to provide the correct diagnosis. Synovial rupture should be suspected in patients with knee effusions who develop acute pain and swelling of the calf, particularly if the patient has rheumatoid arthritis.