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What is a Baker’s Cyst? (Hint: It Has Nothing to Do with Baking)

Have you ever heard of a condition called a Baker’s cyst? If you haven’t, it’s okay. Let’s just say it doesn’t have anything to do with baking.

A Baker’s cyst is actually a fluid-filled cyst first described by a 19th century surgeon named William Morrant Baker—hence the baker in the name. According to Leah Hillier, MD, a sports and exercise medicine doctor and family physician at Banner - University Family Medicine Clinic in Phoenix, AZ, they’re pretty common but definitely are worth getting evaluated for.

“A popliteal synovial cyst, commonly referred to as a ‘Baker’s cyst’ is a fluid-filled sac on the back of the knee, located more toward the inside of the knee,” Dr. Hillier said. “Many people with these cysts don’t even realize they have them and can go through life without them ever causing problems. The cysts themselves aren’t harmful, but there are lumps there that can be concerning, so it’s a good idea to have them checked out by your doctor.”

What causes a Baker’s cyst?

Like other joints in our body, our knee joints are covered in synovial fluid. This fluid helps reduce friction between the bones of our knee joints when we move. Sometimes, however, this fluid can overproduce, resulting in an excess amount to build up in the back of the knee.

The most common causes for this excessive fluid to form are due to a degenerative disease within the knee, commonly osteoarthritis and trauma to the knee, such as an injury or fall.

“Up to 40 percent of people with knee osteoarthritis have popliteal cysts, though many of them don’t know they do,” Dr. Hillier said. “The likelihood of developing popliteal cysts increases with age, which isn’t too surprising because people are more likely to have knee arthritis as they get older.”

What symptoms should I look out for?

Typically, you’ll notice a non-painful lump on the back of the knee, although sometimes it can become painful. You may experience swelling and stiffness surrounding your knee. The pain may worsen when the knee is straight and relieved when bent. And occasionally the cyst can break open or become large enough to block blood flow to the lower part of your leg, causing swelling, redness and warmth in the calf. The cyst could also look similar to a blood clot in the leg, which can be dangerous if left untreated.

“Patients (and some healthcare providers) often make the mistake of trying to treat the popliteal cysts in isolation without recognizing that these cysts are actually symptoms of a larger problem within the knee joint,” Dr. Hillier said. “You should always be evaluated by a physician to rule out other issues.”

How is a Baker’s cyst diagnosed?

Popliteal synovial cysts can often be diagnosed with a clinical exam by a qualified physician. In some cases, imaging tests, such as an X-ray or MRI, are used to accurately determine if you have a Baker’s cyst or some other condition.

How is a Baker’s cyst treated?

The good news is that oftentimes these cysts go away on their own. But if it’s causing you problems and pain, “treatment should focus on the underlying cause of the swelling,” Dr. Hillier said.

For osteoarthritis, treatment may include:

  • Physical therapy
  • Weight loss and exercise
  • Knee compression sleeves
  • Pain medications
  • Knee injections

For injuries to the knee, treatment may include:

  • Physical therapy
  • Activity modification
  • Knee compression sleeves
  • Steroid injections

If you’ve exhausted all your options, you may wonder if surgery is on the table. “Sometimes a surgery, specifically a knee replacement, may be appropriate for those with knee osteoarthritis,” Dr. Hillier said. “There are surgeries that can specifically remove cysts, but this should only be done if the underlying problem has been treated and the cyst itself is still causing discomfort.”

Don’t let knee pain go untreated

Knee pain is a common issue that affects many of us at some point in our lives. In some cases, the causes are pretty obvious but other times they’re not. If you are experiencing knee pain, don’t try to walk it off or work through the pain. It’s important to get the right diagnosis and make sure it’s a Baker’s cyst and not something more serious like a tumor or artery aneurysm.

Contact your doctor, so you can be properly evaluated and treated. To find a Banner Health orthopedic specialist near you, visit

Ready to learn more about your joint health? Assess how your knee or hip pain may be impacting your daily life by taking our free Joint Pain Test

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