Topic Overview

What is a Baker's cyst?

A Baker's cyst is a pocket of fluid that forms a lump behind the knee. It is also called a popliteal cyst. See a picture of a Baker's cyst.

What causes a Baker's cyst?

Baker's cysts in children often involve the bursa, a small sac of fluid behind the knee. The bursa may join with the sac that cushions the knee bones (synovial sac) to form a cyst.

Arthritis is the most common cause in adults, but a Baker's cyst also can be caused by a knee injury. The swelling from these problems causes fluid to build up in your knee. The cyst forms when the fluid pushes out in the back of the knee.

What are the symptoms?

Often a Baker's cyst causes no pain. When symptoms occur, they may include:

• Tightness or stiffness behind the knee.
• Swelling behind the knee that may get worse when you stand.
• Slight pain behind the knee and into the upper calf. You are most likely to feel this when you bend your knee or straighten it all the way.

Sometimes the pocket of fluid behind the knee can tear open and drain into the tissues of the lower leg. This can cause swelling and redness in that part of the leg.

How is a Baker's cyst diagnosed?

Your doctor will examine your knee and ask you questions about your past health and when the pain and swelling started. Your doctor may order tests, such as an MRI, to see a picture of the inside of your knee.

How is it treated?

A Baker's cyst may go away on its own.

If arthritis or another problem is causing the Baker's cyst, your doctor may treat that problem. This usually makes the pain and swelling of a Baker's cyst go away.

If a cyst does not go away, or if it is causing a lot of pain, your doctor may drain the fluid with a needle. You also may be given a shot of steroid medicine to reduce swelling. You may need to use a cane or crutch and wrap your knee in an elastic bandage. In rare cases, a Baker's cyst is removed by surgery.

There are things you can do at home to help you feel better.

• Rest your knee as much as you can.
• Take over-the-counter medicines to reduce pain and swelling. These include ibuprofen (Advil, Motrin) and naproxen (Aleve).
• Use a cane, crutch, walker, or another device if you need help to get around. These can help rest your knee.
• If you wear an elastic bandage around your knee, make sure it is snug but not so tight that your leg is numb, tingles, or swells below the bandage. Loosen the bandage if it is too tight.
• Follow your doctor's instructions about how much weight you can put on your knee.
• Stay at a healthy weight. Being overweight puts extra strain on your knee.