Baker Cyst
(Popliteal
Cyst)
Medical Author: William C. Shiel Jr., MD, FACP, FACR
Medical Editors: Dennis Lee, MD, and Melissa Conrad Stöppler, MD
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Cyst Symptoms and Causes
Medical Author: Melissa Conrad Stöppler, MD
Medical Editor:
William C. Shiel Jr., MD, FACP, FACR
 A cyst is a closed sac- or bladder-like structure that is
not a normal part of the tissue where it is found. Cysts are common and can
occur anywhere in the body in persons of any age. Cysts usually contain a
gaseous, liquid, or semisolid substance. Cysts vary in size; they may be
detectable only under a microscope or they can grow so large that they displace
normal organs and tissues. The outer wall of a cyst is called the capsule.
Cysts can arise through a variety of processes in the body, including...
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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.
- 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.
Additional resources from WebMD Boots UK on
Baker's Cyst
Last Editorial Review: 2/27/2009
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