Ruptured Baker's cyst: a radiological diagnosis.

Rupture of a Baker's cyst may mimic thrombophlebitis of the leg clinically. Differentiation of these two entities is important because of therapeutic implications. A history of previous disease involving the knee, especially rheumatoid arthritis, or the finding of joint effusion are suggestive of the diagnosis of ruptured Baker's cyst. This may be confirmed by arthrography. We describe a series of eight patients with the "pseudothrombophlebitis" syndrome. Arthrography showed seven as having a ruptured Baker's cyst, while in one an intact cyst was found.