Popliteal synovial cysts, also known as Baker’s cysts, are a common occurrence in adults and children [1,2]. They present as swelling in the popliteal fossa due to enlargement of the gastrocnemius-semimembranosus bursa, which lies between these two muscles on the medial side of the fossa slightly distal to the center crease in the back of the knee .
Popliteal cysts in adults are often secondary to degenerative or inflammatory joint disease or joint injury; they usually communicate with the adjacent knee joint space, especially in older patients with knee pathology. Communicating cysts contain synovial fluid. In children, popliteal cysts are usually a primary process, arising directly from the gastrocnemius-semimembranosus bursa; they do not communicate with the joint space. (See 'Popliteal (Baker's) cyst in children' below.)
The epidemiology, pathogenesis, clinical features, diagnosis, and management of popliteal (Baker’s) cyst will be presented here. The clinical and radiographic evaluation of knee pain is reviewed separately. (See "General evaluation of the adult with knee pain" and "Knee bursitis" and "Traumatic causes of acute knee pain and injury in the child or adolescent athlete" and "Radiologic evaluation of the acutely painful knee in adults" and "Radiologic evaluation of the chronically painful knee in adults".)
Most popliteal cysts are asymptomatic and are detected incidentally by an imaging study performed for some other reason. They tend to occur in adults from ages 35 to 70 .
In general, the prevalence of popliteal cysts varies based upon the imaging technique used, the age of the patient population, and/or whether the cyst is secondary or primary.