What is a Baker's cyst?
A person with a Baker's cyst has a small sac or pouch under the skin, behind the knee joint. The wall of the cyst is formed by the lining of the knee joint. This lining holds slippery fluid inside the joint, called the synovial fluid. The synovial fluid lubricates the joint, so that the joint surface can slide easily as the joint moves.

What are the symptoms of a Baker's cyst?
Common symptoms of a Baker's cyst include swelling behind the knee that often extends into the calf. Other symptoms include knee pain, calf pain, and tenderness and warmth behind the knee.

How does the doctor treat a Baker's cyst?
Treatment for a Baker's cyst includes knee rest, elevation, and nonsteroidal anti-inflammatory medications. Some larger cysts may be treated with corticosteroid injections or surgery.