Baker's cyst or popliteal cyst is an accumulation of joint fluid that forms a cyst behind the knee (popliteal socket).
This swelling is due to an increase in the synovial fluid that lubricates the knee joint.
A large cyst may cause some discomfort or stiffness, but usually has no symptoms. It may feel like a water-filled balloon. Sometimes, the cyst may break open (rupture) and cause pain, swelling, and bruising in the back of the knee and calf.
Diagnosis will be made by a complete history and physical examination without the need for additional radiological tests.
Usually no treatment is necessary. If the cyst is painful, the goal of treatment is to correct the problem that is causing it.
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