Baker’s cyst, also known a popliteal cyst, is a small fluid-filled lump that forms on the back of the knee joint. A cyst is a closed, sac-like structure filled with synovial fluid. It may range in size and may not cause a great deal of pain or discomfort, but it can lead to tightness and restricted movements. Pain may intensify with the increase of fluid in the cyst.


Synovial fluid is a clear, thick liquid that normally lubricates and circulates through the cavities in your knee joints. Sometimes the knee produces an excess of synovial fluid which escapes the joint capsule causing fluid to the build up in the back of the knee. Baker’s cyst is more common in people suffering from degenerative joint disease, or osteoarthritis. However, it can also be the result of an injury such as a torn meniscus or inflammation of the knee joint.


In some cases, a Baker’s cyst can be felt as a small bulge behind the knee that is soft and tender. Further, it can be associated with knee pain, tightness and stiffness behind the knee, especially when the knee is extended or fully flexed. The swelling behind the knee may increase and limit activities that involve a bent knee. If swelling is severe, the pressure can be quite painful.


A Baker’s cyst often doesn’t need treatment and will go away on its own. If swelling increases in size and causes severe pain, physical therapy may be recommended. It can increase the range of motion and strengthen the muscles surrounding the knee joint.  A compression wrap and/or ice may help reduce swelling and discomfort.

Moreover, if physical therapy does not resolve the discomfort, your doctor may drain the fluid by inserting a needle into the knee joint, a process known as aspiration. In some cases, aspiration provides only temporary relief as the cyst may reoccur.


For some adults, a torn meniscus may be the underlying cause for the Baker’s cyst. If this is the case, your physician will perform arthroscopic surgery to repair the meniscal tear, which will remove the condition creating the cyst.