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.
With that in mind, your next step should be to work with your doctor to determine what is actually going on in your knee. X-rays or a magnetic resonance imaging (MRI) exam can reveal arthritis, tears or other problems with the cartilage within the joint. If an underlying problem is discovered, then you can pursue treatment options for that condition.
In rare cases, a Baker’s cyst may not go away despite treatment of an underlying medical condition in the knee joint. Surgery to remove the cyst may be an option in such a situation, but it is rarely necessary.
While you’re investigating and treating the underlying cause of the cyst, take steps to decrease swelling inside your knee joint. That may include moving to a lower-impact exercise routine, regularly putting ice on your knee and using a compression sleeve. This should help relieve discomfort, as well as keep the cyst from getting bigger.
Also, be aware that in addition to symptoms of knee swelling, pain and stiffness, in some cases a Baker’s cyst can rupture, resulting in sudden calf pain and swelling. A ruptured Baker’s cyst may be mistaken for a blood clot in the leg, or deep vein thrombosis, a serious condition that requires immediate medical treatment. It can be hard to tell the two conditions apart based on appearance. If you have swelling associated with pain in your calf, seek medical attention right away. — Diane Dahm, M.D., Orthopedic Surgery, Mayo Clinic, Rochester, Minn.