What is a Baker cyst?

A Baker cyst is swelling caused by fluid from the knee joint protruding to the back of the knee. The back of the knee is also referred to as the popliteal area of the knee. A Baker cyst is sometimes called a popliteal cyst. When an excess of knee joint fluid is compressed by the body weight between the bones of the knee joint, it can become trapped and separate from the joint to form the fluid-filled sac of a Baker cyst. The name of the cyst is in memory of the physician who originally described the condition, the British surgeon William Morrant Baker (1839-1896).

What causes a Baker cyst?

Baker cysts are not uncommon and can be caused by virtually any cause of joint swelling (arthritis). The excess joint fluid (synovial fluid) bulges to the back of the knee to form the Baker cyst. The most common type of arthritis associated with Baker cysts is osteoarthritis, also called degenerative arthritis. Baker cysts can occur in children with juvenile arthritis of the knee. Baker cysts also can result from cartilage tears (such as a torn meniscus), rheumatoid arthritis, and other knee problems.

What are symptoms of a Baker cyst?

A Baker cyst may cause no symptoms or be associated with knee pain and/or tightness behind the knee, especially when the knee is extended or fully flexed. Baker cysts are usually visible as a bulge behind the knee that is particularly noticeable on standing and when compared to the opposite uninvolved knee. They are generally soft and minimally tender.

Baker cysts can become complicated by protrusion of fluid down the leg between the muscles of the calf (dissection). The cyst can rupture, leaking fluid down the inner leg to sometimes cause the appearance of a painless bruise on the inner ankle. Baker cyst dissection and rupture are frequently associated with swelling of the leg and can mimic phlebitis of the leg. A ruptured Baker cyst typically causes rapid-onset swelling of the leg.

How is a Baker cyst diagnosed?

Baker cysts can be diagnosed by the doctor's examination and confirmed by radiological testing (either ultrasound, injection of contrast dye into the knee followed by imaging, called an arthrogram, or MRI scan) if necessary.

How is a Baker cyst treated?

Baker cysts often resolve with removal of excess knee fluid in conjunction with cortisone injection. Medications are sometimes given to relieve pain and inflammation.

When cartilage tears or other internal knee problems are associated, surgery can be the best treatment option. During a surgical operation the surgeon can remove the swollen tissue (synovium) that leads to the cyst formation. This is most commonly done with arthroscopic surgery.

Baker Cyst At

A Glance

• A Baker cyst is swelling caused by fluid from the knee joint protruding to the back of the knee.
• Baker cysts are not uncommon and can be caused by virtually any cause of joint swelling (arthritis).
• A Baker cyst may cause no symptoms or be associated with knee pain and/or tightness behind the knee, especially when the knee is extended or fully flexed.
• Baker cysts can rupture and become complicated by protrusion of fluid down the leg between the muscles of the calf (dissection).
• Baker cysts can be treated with medications, joint aspiration and cortisone injection, and surgical operation, usually arthroscopic surgery.

Reference:

Primer on the Rheumatic Diseases. Springer, edited by John H. Klippel, et al., 2008

Kelley's Textbook of Rheumatology, W B Saunders Co, edited by Shaun Ruddy, et al., 2000.

Last Editorial Review: 2/27/2009

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