Baker’s cyst (popliteal cyst)

What is a Baker’s cyst?

A Baker’s cyst, also called a popliteal cyst, is swelling caused by knee joint fluid protruding to the back of the knee (popliteal area of the knee). 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 a fluid-filled sac, referred to as a Baker’s cyst. The name is in memory of the surgeon who originally described the condition, William Morrant Baker, who worked at St. Barts Hospital in London in the 19^th century.

What causes a Baker’s cyst?

Baker’s cysts are not uncommon and can be caused by virtually any cause of joint swelling (arthritis). The most common form of arthritis associated with Baker’s cysts is osteoarthritis, also called degenerative arthritis. Baker’s cysts also can result from cartilage tears (such as a torn meniscus), rheumatoid arthritis and other knee problems.

What are symptoms of a Baker’s cyst?

A Baker’s 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’s cysts are usually visible as a bulge behind the knee which is particularly noticeable on standing compared to the other knee. They are generally soft and minimally tender.

Baker’s 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, sometimes giving the inner ankle the appearance of a painless bruise. Baker’s cyst dissection and rupture are frequently associated with swelling of the leg and can mimic phlebitis of the leg.

How is a Baker’s cyst diagnosed?

Baker’s cysts can be diagnosed with the doctor's examination and confirmed by ultrasound, contrast dye into the knee called an arthrogram, or an MRI scan.

How is a Baker’s cyst treated?

Baker’s cysts often go 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 with the condition, 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.