Q. I have a Baker's cyst in my right knee. It has been drained twice and recurred. Are there any other treatments for it?
A. Your situation is fairly common. A Baker's cyst (also called a popliteal cyst) is a fluid-filled sac that can develop in the popliteal space, the hollow at the back of the knee joint. It's named for William Morrant Baker, a 19th-century surgeon who first described the condition. The cyst is filled with synovial fluid, a viscous material that lubricates the knee joint, reducing friction among the components of the joint and allowing the knee to flex and extend freely.
There are several ways to treat a Baker's cyst, but it will often recur if the underlying cause hasn't been addressed.
A Baker's cyst may occur as a result of an injury to the knee, such as a tear in a meniscus, or damage to the cartilage from conditions such as rheumatoid arthritis or osteoarthritis. These conditions may cause the synovial cells lining the knee joint to produce excess fluid. If the fluid bulges into the popliteal space, a cyst can develop (see the illustration). The excess fluid can also cause the whole knee to become swollen.
A Baker's cyst forms when excess synovial fluid bulges into the hollow at the back of the knee joint.
A Baker's cyst is often found incidentally during a physical exam or an ultrasound performed for other reasons. It may cause no symptoms at all or just a bulge at the back of the knee, but it can also cause pain, swelling, and joint stiffness. Sometimes the bulge is so large that it's hard to fully bend or straighten the leg.
Baker's cysts aren't dangerous and they may go away on their own. But occasionally they burst, and if that happens, synovial fluid can leak into the calf below, causing pain, swelling, and reddening. These symptoms resemble those produced by a blood clot in the calf, deep vein thrombosis (DVT), a serious condition that requires immediate treatment. That's why it's important to find the source of the problem right away. (A painless Doppler ultrasound of the calf can rule out DVT.)