What Is a Baker's Cyst?

If you have a lump behind your knee that's filled with fluid and causes a feeling of tightness, it might be a Baker's cyst. Doctors also call it a popliteal cyst.

What Causes It?

Swelling in the knee. This happens when the fluid that lubricates your knee joint increases. When pressure builds up, fluid squeezes into the back of the knee and it creates the lump or cyst.

It’s common with all forms of arthritis. A Baker’s cyst can also be brought on by a sports-related injury or blow to the knee. Gout is another common cause. That’s a type of arthritis that results from the build-up of uric acid -- a waste product -- in the blood.

What Are the Symptoms?

You may not have any. If you do, they might include swelling behind your knee and maybe in your leg, knee pain, and stiffness.

Sometimes, the cysts break open (rupture). This can cause pain, swelling, and bruising on the back of your knee and calf. The pain might get worse when you fully extend your knee or when you’re active.

Baker’s cysts are more common in women than in men. That’s because women are more likely to develop osteoarthritis and rheumatoid arthritis. They also tend to affect people over 40, but anyone can get them -- including children.

How Do I Know If I Have a Baker’s Cyst?

See your doctor if you have any of the symptoms listed above and they’re causing problems.

He’ll examine you to rule out conditions that are more serious, like a blood clot (deep vein thrombosis). He may also order an imaging test, like an ultrasound or MRI, to get a better look.

What’s the Treatment?

You may not need any. Baker’s cysts aren’t dangerous and tend to go away on their own. In the meantime, try these at-home remedies to ease your pain and make yourself more comfortable:

  • Keep it cold. Apply a cold pack to the affected area. It’ll help keep the swelling down. A compression wrap might also help.
  • Relieve pain. For pain (and to reduce inflammation), take an over-the-counter medication, like ibuprofen.
  • Rest your leg. Keep it raised above heart level when possible. This will keep down swelling. Use a cane or crutch when you walk to keep pressure off your leg.

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If these at-home treatments don’t work, see your doctor. He may recommend one of the following:

  • Steroids. These can help reduce inflammation.
  • Aspiration. Your doctor can drain the cyst. He’ll likely do it with the aid of an ultrasound. This treatment may not work if your case is severe.
  • Surgery. If you’re in serious pain, or if the cyst makes it hard for you to move your knee, this might be an option. But it’ll only work if your doctor also treats the issue that caused the Baker’s cyst to begin with, such as arthritis.

If your leg turns red or starts to swell, see your doctor right away. This could mean your Baker’s cyst has ruptured.

Can I Prevent a Baker’s Cyst?

Possibly -- by preventing knee injuries in the first place. Wear the right shoes when you work out. Be sure to warm up before you exercise. And if you do get a knee injury, take care of it right away. See your doctor if it doesn’t get better.

WebMD Medical Reference Reviewed by William Blahd, MD on December 28, 2016

Sources

SOURCES:

Mayo Clinic: “Diseases and Conditions: Baker’s Cyst.”

John Hopkins Arthritis Center: “Baker’s Cysts and Fullness in the Back of the Knee.”

Gov.UK: “Baker’s Cyst.”

Harvard Medical School: “Ask the Doctor: How Do You Treat a Baker’s Cyst?”

Orthopedics: “Popliteal Cysts: A Current Review.”

Saint Luke’s Health System: “Baker’s Cyst.”

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