What is Bakers cyst?
Also called a popliteal cyst, this is swelling or fullness in the popliteal fossa with minimal tenderness. Its proposed cause in some individuals involves a communication between the semimembranosus/gastrocnemius bursa and the knee joint. Some have postulated a one-way valve effect in which synovial fluid moves from the knee to the bursa. Baker’s cysts can occur secondary to any process that produces synovial fluid (most commonly RA, osteoarthritis, or trauma). A ruptured cyst can occasionally dissect down the calf and be confused with deep venous thrombosis. Ecchymoses inferior to the medial malleolus of the ankle (Crescent sign) is characteristic. It is diagnosed with ultrasound or arthrography.