Baker's Cyst (Popliteal Cyst)

A Baker's (popliteal) cyst is a fluid-filled cyst on the back of the knee.

A Baker's 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 the knee. A Baker's cyst is sometimes referred to as a popliteal cyst or a Baker cyst.

When an excess of knee joint fluid (synovitis) 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's 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).

Baker's 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 Baker's cyst. The most common type of arthritis associated with Baker's cysts is osteoarthritis, also called degenerative arthritis. Baker's cysts can occur in children with juvenile arthritis of the knee. Baker's cysts also can result from cartilage tears (such as a torn meniscus), rheumatoid arthritis, and other knee problems.

Risk factors for a Baker's cyst include a torn meniscus, knee arthritis (including osteoarthritis and rheumatoid arthritis), and knee joint injury.

A Baker's cyst may cause no symptoms or be associated with knee pain and/or tightness, and stiffness behind the knee, especially when the knee is extended or fully flexed. Baker's 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. Sometimes there can be a mild decrease in the range of motion of the knee.

Baker's cysts can become complicated by the spread 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 under the inner ankle. Baker's cyst dissection and rupture are frequently associated with swelling of the leg and can mimic phlebitis of the leg. A ruptured Baker's cyst typically causes rapid-onset swelling of the leg with bruising around the ankle.

Doctors who treat Baker's cysts include general primary care physicians, orthopedists, and rheumatologists.

Baker's cysts can be diagnosed by the doctor's examination and confirmed by imaging tests (either ultrasound, injection of contrast dye into the knee followed by imaging, called an arthrogram, or MRI scan) if necessary. Health care professionals can rule out other causes of swelling behind the knee (including deep vein thrombosis, popliteal aneurysm, and neuroma) using these imaging tests.

Baker's cysts often resolve with aspiration (removal) of excess knee fluid in conjunction with a cortisone injection. Medications are sometimes given to relieve pain and inflammation, including over-the-counter anti-inflammatory drugs.

When cartilage tears or other internal knee problems are associated, physical therapy or surgery can be the best treatment option. During a surgical operation (typically by arthroscopy using an arthroscope), the surgeon can remove the swollen tissue (synovium) that leads to the cyst formation. This is most commonly done with arthroscopic surgery. Physical therapy is often done in the recovery period.

Home remedies, prior to medical evaluation, include cold applications, resting, and avoiding overuse or injury to the involved knee.

Recovery time depends on the form of treatment rendered. With medications or injections into the knee, recovery can be rapid, within days to weeks. If surgical repair is done, recovery generally takes one to three months.

Complications of a Baker's cyst include blood clotting in the involved leg, as well as rupture of the Baker's cyst, causing swelling and pain of the leg and bruising discoloration of the ankle.

Depending on the cause of Baker's cyst, the outlook is generally very good. Baker's cysts caused by chronic arthritis can be prone to recur in the long term.

There is no prevention for a Baker's cyst except minimizing any underlying arthritis disease.