A bursa is a fluid filled sac that acts as a cushion between tendons, bones, and skin to reduce friction. A Baker’s cyst is an abnormal swelling of a bursa located in the space behind the knee (the popliteal space). The cyst connects to the membrane covering the knee joint.
There is no definite cause for a Baker’s cyst. However, the cysts can occur when the lining of the knee joint produces too much fluid, as in rheumatoid arthritis, or after an injury to the knee.
You may have pain, swelling, or a feeling of fullness in the area behind the knee. Excess swelling may also decrease the amount that your knee is able to bend.
Your doctor will examine your knee and may find a bulge in the back of your knee. You may need to have an MRI to help your doctor determine if you have a Baker’s cyst. A Baker’s cyst may also be visible on an ultrasound of the lower leg and knee.
The initial discomfort of a Baker’s cyst may be treated by wearing an elastic bandage. You doctor may prescribe anti-inflammatory medications, the cyst may be drained, or an operation may be performed to remove the cyst. There at times when the cyst goes away on its own. If the cyst is not causing bothersome symptoms, it may not be treated.
Information obtained from The Sports Medicine Patient Advisor by Pierre Rouzier, MD