A fluid-filled cyst behind the knee.

A Baker cyst is usually the result of knee joint conditions, such as arthritis or torn cartilage, that cause the knee to produce too much fluid.

Symptoms, when they occur, may include a bulge and tight feeling behind the knee.

Sometimes a Baker cyst will disappear on its own. Mild symptoms can often be controlled by modifying activities. Other treatment options include pain relief medicines, physical therapy, a cortisone shot or fluid drainage with a needle.