What Is a Baker's Cyst?

Baker's cysts, also called popliteal cysts, are fluid-filled sacs caused by excess knee-joint fluid.

This common condition can occur with arthritis or injuries that lead to swelling. 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.

This article explains the causes and symptoms of a Baker's cyst and how it is diagnosed and treated.

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.

Baker's cysts can occur with the following conditions:

• Cartilage or meniscus tears or other knee injuries
• Osteoarthritis
• Rheumatoid arthritis
• Infectious arthritis
• Pigmented villonodular synovitis (a condition that causes the thin layer of tissue that lines tissues and joints to thicken and overgrow)

The more severe an injury, such as cartilage tear, is, the greater the volume or size of the Baker's cyst tends to be.

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. Magnetic resonance imaging (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.

Summary

A Baker's cyst is a common fluid-filled lump behind the knee that can occur with conditions that lead to swelling, such as injuries or arthritis. Any swelling and pain behind the knee should be evaluated by a healthcare provider since it can also be a sign of a blot clot.

Treatments for a Baker's cyst depend on the underlying condition that led to the cyst and can involve draining the cyst and icing or elevating the leg. In some cases, surgery may be recommended.