A cyst is a bag-like growth that contains fluid, air, or other substances. It can grow almost anywhere on the body.

A Baker’s cyst — also called a popliteal cyst — is a fluid-filled cyst on the back of the knee. It can bulge out, causing a feeling of tightness that becomes painful when you extend or flex your knee.

A Baker’s cyst is often caused by a knee joint problem such as arthritis, gout, or a knee injury that causes your knee to produce too much fluid.

Early on, you may have a Baker’s cyst with no symptoms at all. As they form, these fluid-filled bubbles that develop at the back of the knee can cause symptoms like:

  • painless swelling
  • stiffness
  • general discomfort
  • a lump behind the knee that you can feel

A Baker’s cyst will become much more noticeable if it ruptures or bursts. When this happens, the fluid that fills the cyst can leak down into the tissues of your leg. You might even have a sensation of liquid running down the back of your leg.

A ruptured Baker’s cyst can also cause symptoms like:

  • sharp pain in your leg or calf
  • redness
  • inflammation
  • bruising, mostly on the inner ankle

In many cases, a Baker’s cyst requires no treatment at all. A healthcare professional may watch the development of the cyst, but in time, it should go away on its own with the excess fluid from the cyst reabsorbing into your joint tissues.

When treatment is required, the steps you take will depend on how much pain or discomfort the cyst is causing you, and whether the cyst has ruptured.

Treatment before a rupture

Initial treatment of a Baker’s cyst that has not ruptured is usually noninvasive. A doctor or nurse may decide to just watch the cyst and act only if there are complications or increasing discomfort. Some techniques you may use to help reduce symptoms associated with these cysts include:

If these methods don’t do enough to relieve your pain or discomfort, you can ask a healthcare professional about additional treatments, like:

  • Cortisone injections. These steroid injections are directly injected into the joint to reduce swelling.
  • Ultrasound-guided aspiration. Fluid is removed from the cyst with a long needle.

In rare cases, arthroscopy or excision — both surgical options — are performed to permanently remove cysts that keep developing.

Treating a Baker’s cyst rupture

When a Baker’s cyst ruptures, you may feel sharp pain and inflammation, but the fluid from the cyst should be reabsorbed by your body within a few weeks.

A healthcare professional may decide to drain a large cyst before it ruptures, but once it does, the primary treatment focuses on increasing your comfort and reducing pain or swelling.

In rare cases, you may experience complications from a ruptured cyst, like compartment syndrome.

Compartment syndrome develops when pressure increases in a muscle compartment. In the case of a Baker’s cyst, inflammation and accumulated fluid can cause this pressure to rise. There are some nonsurgical options to treat compartment syndrome, but severe cases require surgery.

Self-care and home remedies

When a Baker’s cyst ruptures — or even before a rupture — you can reduce pain and swelling by:

  • applying ice or a cold pack to the affected area
  • keeping your calf elevated
  • taking over-the-counter medications for pain and inflammation
  • using an elastic wrap or brace to support your knee
  • resting
  • avoiding strenuous activity

Most Baker’s cysts develop in adults ages 35 to 70, especially in people with:

Even without these risk factors, Baker’s cysts can develop due to:

  • abnormal structure of the joint space
  • any collection or buildup of synovial fluid (joint fluid)
  • traumas or injuries to the leg
  • herniation (bulging) of the joint capsule

A Baker’s cyst can develop again after treatment, especially if the underlying cause of the cyst was not corrected. Even with surgical treatment, these cysts can return. A study reviewed recurrence rates based on different treatment methods and found that Baker’s cysts returned:

  • 3.1 percent of the time in people who were treated with ultrasound-guided cyst drainage
  • 5.2 percent of the time in people who were treated with surgical excision after ultrasound-guided drainage
  • 40 percent of the time in people who were treated with surgical excision alone

If you have a Baker’s cyst that doesn’t clear up on its own, you should see a doctor. After a physical examination, a doctor might decide to drain (aspirate) the cyst.

A doctor will also want to address the underlying condition that caused the cyst.

If you have a bulge behind your knee, it could be a Baker’s cyst. If the pain and swelling behind your knee results in a swollen, red calf, you could have a ruptured Baker’s cyst.

In either case, it’s a good idea to see a doctor for a proper diagnosis. If it is a Baker’s cyst, your doctor will recommend appropriate treatment. There’s a chance that what you think is a Baker’s cyst could be a more serious condition.