Overview

A Baker's cyst is a fluid-filled cyst that causes a bulge and a feeling of tightness behind your knee. The pain can get worse when you fully flex or extend your knee or when you're active.

A Baker's cyst, also called a popliteal (pop-luh-TEE-ul) cyst, is usually the result of a problem with your knee joint, such as arthritis or a cartilage tear. Both conditions can cause your knee to produce too much fluid, which can lead to a Baker's cyst.

Although a Baker's cyst may cause swelling and make you uncomfortable, treating the probable underlying problem usually provides relief.

Symptoms

In some cases, a Baker's cyst causes no pain, and you may not notice it. If you do have signs and symptoms, they might include:

• Swelling behind your knee, and sometimes in your leg
• Knee pain
• Stiffness and inability to fully flex the knee

Your symptoms may be worse after you've been active or if you've been standing for a long time.

When to see a doctor

If you have pain and swelling behind your knee, see your doctor. Though unlikely, a bulge behind your knee may be a sign of a condition more serious than a fluid-filled cyst.

Causes

A lubricating fluid called synovial (sih-NO-vee-ul) fluid helps your leg swing smoothly and reduces friction between the moving parts of your knee.

But sometimes the knee produces too much synovial fluid, resulting in buildup of fluid in an area on the back of your knee (popliteal bursa), causing a Baker's cyst. This can happen because of:

• Inflammation of the knee joint, such as occurs with various types of arthritis
• A knee injury, such as a cartilage tear

Complications

Rarely, a Baker's cyst bursts and synovial fluid leaks into the calf region, causing:

• Sharp pain in your knee
• Swelling in the calf
• Sometimes, redness of your calf or a feeling of water running down your calf

These signs and symptoms closely resemble those of a blood clot in a vein in your leg. If you have swelling and redness of your calf, you'll need prompt medical evaluation to rule out a more serious cause of your symptoms.

Diagnosis

A Baker's cyst can often be diagnosed with a physical exam. However, because some of the signs and symptoms of a Baker's cyst mimic those of more-serious conditions, such as a blood clot, aneurysm or tumor, your doctor may order noninvasive imaging tests, including:

• Ultrasound
• X-ray
• Magnetic resonance imaging (MRI)

Treatment

Sometimes a Baker's cyst will disappear on its own.  However, if the cyst is large and causes pain, your doctor may recommend the following treatments:

• Medication. Your doctor may inject a corticosteroid medication, such as cortisone, into your knee to reduce inflammation. This may relieve pain, but it doesn't always prevent recurrence of the cyst.
• Fluid drainage. Your doctor may drain the fluid from the knee joint using a needle. This is called needle aspiration and is often performed under ultrasound guidance.
• Physical therapy. Icing, a compression wrap and crutches may help reduce pain and swelling. Gentle range-of-motion and strengthening exercises for the muscles around your knee also may help to reduce your symptoms and preserve knee function.

If possible, doctors treat the underlying cause of the cyst. If your doctor determines that a cartilage tear is causing the overproduction of synovial fluid, he or she may recommend surgery to remove or repair the torn cartilage.

Baker's cysts associated with osteoarthritis usually improve with treatment of the arthritis. Surgical intervention is rarely needed.

Lifestyle and home remedies

If your doctor determines that arthritis is causing the cyst, he or she may advise you to take some or all of the following steps:

• Follow the R.I.C.E. principles. These letters stand for rest, ice, compression and elevation. Rest your leg. Ice your knee. Compress your knee with a wrap, sleeve or brace. And elevate your leg when possible, especially at night.
• Try over-the-counter pain-relieving medications. Drugs such as ibuprofen (Advil, Motrin IB, others), naproxen sodium (Aleve, others), acetaminophen (Tylenol, others) and aspirin can help relieve pain. Follow the dosing instructions on the package. Don't take more than the recommend dosage.
• Reduce your physical activity. Doing so will reduce irritation of your knee joint. Your doctor can offer you guidance on how long you need to reduce your activity levels, and he or she may be able to suggest alternative forms of exercise you can do in the meantime.

Preparing for an appointment

Here's some information to help you prepare for your appointment.

What you can do

• Write down symptoms you have, including any that may seem unrelated to the reason for which you scheduled the appointment.
• Write down key personal information, including recent life changes.
• List all medications, vitamins and supplements you're taking.
• Write down questions to ask your doctor.

Your time with your doctor may be limited, so preparing a list of questions can help you make the most of your time together. For a Baker's cyst, some basic questions to ask your doctor include:

• What caused this cyst to develop?
• What tests do I need? Do these tests require special preparation?
• Is a Baker's cyst temporary or long lasting?
• What treatments are available, and which do you recommend?
• What side effects can I expect from treatment?
• What steps can I take on my own that might help?
• Do I need to limit my activity? If so, how much and for how long?
• I have other health conditions. How can I best manage these conditions together?

Don't hesitate to ask other questions.

What to expect from your doctor

Your doctor is likely to ask you a number of questions, such as:

• When did your symptoms begin?
• Do you feel pain or stiffness all the time, or does the pain come and go with activity?
• Does your knee swell, feel unstable or lock?
• How severe are your symptoms?
• Does anything seem to improve your symptoms?
• What, if anything, appears to worsen your symptoms?