Baker's cyst

A Baker's cyst, also known as a popliteal cyst, is a type of fluid collection behind the knee. Often there are no symptoms. If symptoms do occur these may include swelling and pain behind the knee, or knee stiffness. If the cyst breaks open, pain may significantly increase with swelling of the calf. Rarely complications such as deep vein thrombosis, peripheral neuropathy, ischemia, or compartment syndrome may occur. Risk factors include other knee problems such as osteoarthritis, meniscal tears, or rheumatoid arthritis. The underlying mechanism involves the flow of synovial fluid from the knee joint to the gastrocnemio-semimembranosus bursa, resulting in its expansion. The diagnosis may be confirmed with ultrasound or magnetic resonance imaging (MRI). Treatment is initially with supportive care. If this is not effective aspiration and steroid injection or surgical removal may be carried out. Around 20% of people have a Baker's cyst. They occur most commonly in those 35 to 70 years old. It is named after the surgeon who first described it, William Morrant Baker (1838–1896).