Popliteal cyst mimicking thrombophlebitis as the first indication of knee disease.

Five patients, none of whom were previously known to have knee disease, developed leg swelling which was misdiagnosed as thrombophlebitis. Four were treated with anticoagulants and one developed a large calf hematoma requiring fasciotomy. The primary physicians failed to appreciate evidence of knee disease in these patients, although the rheumatology consultant found knee effusion, and a popliteal cyst was found by arthrography or ultrasonography in every case. The occurrence of popliteal cyst as the first sign of knee disease emphasizes the importance of careful examination of the knee in all patients with a clinical picture of thrombophlebitis.