Condition Basics

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.

What causes it?

A Baker's cyst is caused when excess joint fluid is pushed into one of the small sacs of tissue behind the knee. When this sac fills with fluid and bulges out, it is called a cyst. The excess fluid is usually caused by conditions such as rheumatoid arthritis or osteoarthritis that irritate the knee. It may also be caused by an injury.

What are the symptoms?

Often a Baker's cyst causes no pain. You may not notice symptoms unless the cyst becomes very large or it bursts. 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 it 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 ultrasound or an MRI, to see a picture of the inside of your knee.

How is a Baker's cyst 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 give you 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, fluid is drained with a needle or the Baker's cyst is removed by surgery.

How can you care for yourself at home?

• Rest your knee as much as possible.
• Ask your doctor if you can take an over-the-counter pain medicine, such as acetaminophen (Tylenol), ibuprofen (Advil, Motrin), or naproxen (Aleve). Be safe with medicines. Read and follow all instructions on the label.
• Use a cane, a crutch, a walker, or another device if you need help to get around. These can help rest your knees.
• If you have an elastic bandage, 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.
• Stay at a healthy weight. Being overweight puts extra strain on your knee.