A baker’s cyst, named after Dr. William Baker, is caused by excess synovial fluid in the popliteal bursa, causing a painful bump on the back of the knee. Treatment options include physical therapy, medication, and surgery. Complications may require immediate medical attention.
A baker’s cyst is not named after the people who bake, but instead derives its name from Dr. William Baker, a 19th-century British physician who described the condition. You may also hear the alternate name of popliteal cyst versus baker’s cyst. The condition can be caused by damage to the knee joint, extensive arthritis, or, in some cases, has no apparent cause. In most cases, the cyst itself expresses itself as a bump on the back of the knee that is often painful and makes it difficult to bend or straighten the knee joint.
People with a baker’s cyst may notice swelling in the back of the knee, which is usually more noticeable when the person is standing. The back of the knee can also be tight and in some cases very painful. Some people get this condition in a milder form, with little or no pain, and with few identifiable causes.
A baker’s cyst forms when the fluid used to lubricate joints, called synovial fluid, is produced in excess. This can cause overloading of pockets of tissue called the bursa, through which fluid passes. In particular, the popliteal bursa located at the back of the knee can become significantly overloaded and expand, creating the cyst.
If you have swelling and pain in the popliteal bursa, you should see a doctor. There are some complications that can occur without medical treatment, and there are other conditions that can resemble a baker’s cyst. For example, the condition could really be a blocked artery or a tumor. General tests to identify popliteal cysts include the use of ultrasound and/or magnetic resonance imaging (MRI) to properly evaluate and diagnose the condition. These can help rule out other potential causes for the swelling behind a knee.
Some circumstances require immediate treatment. If the swelling is very pronounced, the affected leg is red, and there is sharp pain, this could suggest that the cyst has burst and fluid is leaking into the calf. Doctors may need to evaluate and treat this through a variety of methods, often similar to treating a blood clot.
In other cases, the baker’s cyst goes away on its own, and people can get physical therapy with range-of-motion exercises to help reduce pain. It is common to ice the cyst or create a compression wrap around the cyst, and patients with mild to moderate pain can take medications such as ibuprofen. Using crutches and keeping weight on the knee is often advised, and limiting physical activity when the cyst is very painful makes sense.
Sometimes the most important thing to treat is not the cyst, but the underlying cause. If the cyst results from cartilage tears that have leaked extra synovial fluid into the bursa, the injury may require surgery. If arthritis is the problem, doctors work to address the arthritic condition, even if this doesn’t always improve the cyst. Sometimes a baker’s cyst becomes enlarged and requires more aggressive treatment, such as needle aspiration (where fluid is drained from the cyst) or surgical removal of the cyst.
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