Baker's Cyst

What is a Baker cyst?

A Baker 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 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 most common form of arthritis associated with Baker cysts is osteoarthritis, also called degenerative arthritis. 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 which is particularly noticeable on standing and comparing 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 give the inner ankle the appearance of a painless bruise. Baker cyst dissection and rupture are frequently associated with swelling of the leg and can mimic phlebitis of the leg.

How is a Baker cyst diagnosed?

Baker cysts can be diagnosed with the doctor's examination and confirmed by radiological testing (either ultrasound, contrast dye into the knee called arthrogram, or MRI scan).

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.