Baker's Cyst

A Baker's cyst is a swelling that forms in the back of the knee. It is a sac-like structure. It is filled with the same fluid that is located in your knee. The fluid located in your knee is necessary because it lubricates the bones and cartilage. It allows them to move over each other more easily.


When the knee becomes injured or has soreness (inflammation) present, more fluid forms in the knee. When this happens, the joint lining is pushed out behind the knee and forms the baker's cyst. This cyst may also be caused by inflammation from arthritic conditions and infections.


A Baker's cyst is most often diagnosed with an ultrasound. This is a specialized picture (like an X-ray). It shows a picture by using sound waves. Sometimes a specialized x-ray called an MRI (magnetic resonance imaging) is used. This picks up other problems within a joint if an ultrasound alone cannot make the diagnosis. If the cyst came immediately following an injury, plain x-rays may be used to make a diagnosis.


The treatment depends on the cause of the cyst. But most of these cysts are caused by an inflammation. Anti-inflammatory medications and rest often will get rid of the problem. If the cyst is caused by an infection, medications (antibiotics) will be prescribed to help this. Take the medications as directed. Refer to Home Care Instructions, below, for additional treatment suggestions.


  • If the cyst was caused by an injury, for the first 24 hours, while lying down, keep the injured extremity elevated on 2 pillows.

  • For the first 24 hours while you are awake, apply ice bags (ice in a plastic bag with a towel around it to prevent frostbite to skin) 3 to 4 times per day for 15 to 20 minutes to the injured area. Then do as directed by your caregiver.

  • Only take over-the-counter or prescription medicines for pain, discomfort, or fever as directed by your caregiver.

Persistent pain and inability to use the injured area for more than 2 to 3 days are warning signs indicating that you should see a caregiver for a follow-up visit as soon as possible. Persistent pain and swelling indicate that further evaluation, non-weight bearing (use of crutches as instructed), and/or further x-rays are needed. Make a follow-up appointment with your own caregiver.

If conservative measures (rest, medications and inactivity) do not help the problem get better, sometimes surgery for removal of the cyst is needed. Reasons for this may be that the cyst is pressing on nerves and/or vessels and causing problems which cannot wait for improvement with conservative treatment. If the problem is caused by injuries to the cartilage in the knee, surgery is often needed for treatment of that problem.


  • Understand these instructions.

  • Will watch your condition.

  • Will get help right away if you are not doing well or get worse.