A Baker's cyst, also known as a popliteal cyst, is a pocket of joint fluid that forms a lump behind the knee. Often a Baker's cyst is painless, but occasionally this pocket of fluid can tear open and drain into the tissues of the lower leg, causing pain and swelling.
When swelling and pain increase, the best approach is to avoid activities such as squatting or kneeling. Wrapping the knee may help reduce swelling. Occasionally, fluid may be drained from the knee, and the person may be given a steroid injection. In cases of restricted mobility or persistent pain, surgery to remove the cyst may be recommended.
WebMD Medical Reference from Healthwise