How Serious Is a Baker's Cyst?

Baker's cysts are fluid-filled sacs caused by excess knee-joint fluid.

This common condition occurs when excess fluid produced by the lining of the knee joint pushes through the back part of the joint capsule (the fibrous tissue surrounding the joint), forms a cyst and protrudes into the back area of the knee, known as the popliteal fossa. A Baker's cyst may also be referred to as a "popliteal cyst."

If you have osteoarthritis or rheumatoid arthritis, you may be familiar with this painful condition. Fortunately, there are treatment remedies available for Baker's cysts, depending on the cause.

Causes

Baker's cysts have nothing to do with actual bakers; they're named for William Morrant Baker, the British surgeon who first discovered them. Anyone can develop a Baker's cyst, especially after a knee injury or due to a chronic knee condition.

Simply put, a Baker's cyst can develop after the joint capsule becomes damaged or weakened. It's caused by swelling in the knee from arthritis or an injury, such as a cartilage tear or a meniscus tear.

It's important to verify whether your condition is, in fact, a Baker's cyst, since other serious conditions can have the same symptoms—notably deep vein thrombosis, a dangerous type of blood clot.

Symptoms

A Baker's cyst can be soft to the touch and slightly tender. You may have no symptoms other than a visible bulge behind the knee or a tight feeling that something is behind the knee. When you extend your knee, this can make a Baker's cyst tighter or more painful.

A Baker's cyst can actually swell or shrink. It also can burst underneath the skin, and the symptoms of a burst Baker's cyst are very much like those associated with blood clots: redness and pain in the calf. The fluid from the ruptured cyst is absorbed by the body. When this happens, the Baker's cyst temporarily disappears, but it usually comes back.

Diagnosis and Treatment

A physical examination is usually all that is needed to diagnose a Baker's cyst. MRIs or ultrasounds can be used to confirm that the cyst is fluid-filled, as opposed to solid.

Depending on the underlying condition that causes it, a Baker's cyst can be treated without surgery in most cases. Nonsurgical treatment can include:

• Draining the fluid from the cyst using a needle and syringe
• Cortisone injection to reduce inflammation
• Rest
• Elevating the leg
• Icing to reduce inflammation
• Physical therapy regimen to control swelling
• Treating the underlying condition

A study published in 2020 showed that radiosynoviorthesis (a nonsurgical technique that uses radioactive agents to restore the joint lining) could significantly reduce the volume of Baker's cysts.

Surgical removal of a Baker's cyst is an option if you find the cyst painful or particularly bothersome. Even after it is surgically removed, a Baker's cyst may recur. In most cases, however, treatment of the injury that caused the Baker's cyst will alleviate symptoms and reduce the likelihood that it will recur.