DEAR MAYO CLINIC: I developed a Baker’s cyst on the back of my knee several months ago. My doctor drained the fluid from it, but now it’s back. What could be causing this? What is the best way to permanently get rid of a Baker’s cyst?
ANSWER: In many cases, a Baker’s cyst is not a stand-alone medical condition. Rather, these cysts often are the result of another underlying problem in the knee joint. In many cases, when the underlying condition is treated, the cyst goes away and it usually doesn’t come back.
Circulating in your knee joint is fluid, called synovial fluid. That fluid lubricates the joint and reduces friction between its moving parts. As it flows through your knee, small amounts of synovial fluid can pass in and out of small sacs, or bursa.
If your knee joint is affected by arthritis, torn cartilage or other irritation within the joint, it may make too much synovial fluid — a condition sometimes known as water on the knee. The excess fluid is often pushed out of the knee joint into the one of the bursae, causing it to enlarge. The result is a Baker’s, or popliteal, cyst. Although these cysts usually are not dangerous, they may be accompanied by uncomfortable symptoms, including swelling, pain and stiffness in the knee.
As in your situation, the typical first step in treating a Baker’s cyst is draining the fluid from it. In about one-third of cases, the cyst does not come back after that, and no further treatment is needed. But if there is an underlying knee problem that’s causing the cyst, and it isn’t treated, having the fluid drained will not be a long-term solution. Most cysts will return over time, unless the other problem is resolved.