A popliteal cyst, also called a Baker's cyst, is a soft, often painless bump that develops on the back of the knee. A cyst is usually nothing more than a bag of fluid. These cysts occur most often when the knee is damaged due to arthritis, gout, injury, or inflammation in the lining of the knee joint. Surgical treatment may be successful when the actual cause of the cyst is addressed. Otherwise, the cyst can come back again.

Symptoms :
The symptoms caused by a popliteal cyst are usually mild. You may have aching or tenderness with exercise or your knee may feel unsteady, as though it's going to give out. You may feel pain from the underlying cause of the cyst, such as arthritis, an injury, or a mechanical problem with the knee, for instance a tear in the meniscus. Along with these symptoms, you may also see or feel a bulge on the back of your knee. Anything that causes the knee to swell and more fluid to fill the joint can make the cyst larger. It is common for a popliteal cyst to swell and shrink over time.

Sometimes a cyst will suddenly burst underneath the skin, causing pain and swelling in the calf. A ruptured popliteal cyst gives symptoms just like those of a blood clot in the leg, called thrombophlebitis. For this reason, it is important to determine right away the cause of the pain and swelling in the calf. Once the cyst ruptures, the fluid inside the cyst simply leaks into the calf and is absorbed by the body. In this case, you will no longer be able to see or feel the cyst. However, the cyst will probably return in a short time.