Baker's cyst infection: case report and review.

A Baker’s (popliteal) cyst is a distention of the gastrocnemius–semimembranous bursa of the knee, which communicates with the posterior portion of the joint capsule. It usually appears in the popliteal fossa as a painless swelling. In adults it is nearly always secondary to pathological changes in the knee joint that cause an effusion. Occasionally the cyst becomes so large that it ruptures, spilling synovial fluid into the surrounding tissues, with a clinical presentation that mimics acute thrombophlebitis. Infection of a popliteal cyst is an uncommon complication usually associated with septic arthritis. We report such a rare case and review the world literature.