A Baker's cyst, also known as a popliteal cyst, is a type of fluid collection behind the

knee In humans and other primates, the knee joins the thigh with the leg and consists of two joints: one between the femur and tibia (tibiofemoral joint), and one between the femur and patella (patellofemoral joint). It is the largest joint in the hu ...

. Often there are no symptoms. If symptoms do occur these may include swelling and pain behind the knee, or knee stiffness. If the cyst breaks open, pain may significantly increase with swelling of the calf. Rarely complications such as deep vein thrombosis, peripheral neuropathy,

ischemia Ischemia or ischaemia is a restriction in blood supply to any tissue, muscle group, or organ of the body, causing a shortage of oxygen that is needed for cellular metabolism (to keep tissue alive). Ischemia is generally caused by problems wi ...

, or compartment syndrome may occur. Risk factors include other knee problems such as osteoarthritis,

meniscal tear A tear of a meniscus is a rupturing of one or more of the fibrocartilage strips in the knee called meniscus (anatomy), menisci. When doctors and patients refer to "torn cartilage" in the knee, they actually may be referring to an injury to a meni ...

s, or rheumatoid arthritis. The underlying mechanism involves the flow of

synovial fluid Synovial fluid, also called synovia, elp 1/sup> is a viscous, non-Newtonian fluid found in the cavities of synovial joints. With its egg white–like consistency, the principal role of synovial fluid is to reduce friction between the articular ...

from the

knee joint In humans and other primates, the knee joins the thigh with the leg and consists of two joints: one between the femur and tibia (tibiofemoral joint), and one between the femur and patella (patellofemoral joint). It is the largest joint in the hu ...

to the

gastrocnemio-semimembranosus bursa The knee bursae are the fluid-filled sacs and synovial pockets that surround and sometimes communicate with the knee joint cavity. The bursae are thin-walled, and filled with synovial fluid. They represent the weak point of the joint, but also pr ...

, resulting in its expansion. The diagnosis may be confirmed with ultrasound or

magnetic resonance imaging Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio wave ...

(MRI). Treatment is initially with

supportive care Symptomatic treatment, supportive care, supportive therapy, or palliative treatment is any medical therapy of a disease that only affects its symptoms, not the underlying cause. It is usually aimed at reducing the signs and symptoms for the comfor ...

. If this is not effective aspiration and

steroid A steroid is a biologically active organic compound with four rings arranged in a specific molecular configuration. Steroids have two principal biological functions: as important components of cell membranes that alter membrane fluidity; and a ...

injection or surgical removal may be carried out. Around 20% of people have a Baker's cyst. They occur most commonly in those 35 to 70 years old. It is named after the surgeon who first described it,

William Morrant Baker William Morrant Baker (20 October 1839, Andover, Hampshire, England – 3 October 1896, Pulborough, Sussex) was an English physician and surgeon. He first described the condition now known as Baker's cyst. Life William Morrant Baker was the son ...

(1838–1896).

Signs and symptoms

Symptoms may include swelling behind the knee, stiffness, and pain. If the cyst breaks open, pain may increase, and there may be swelling of the calf. Rupture of a Baker's cyst may also cause bruising below the medial malleolus of the ankle (Crescent sign).

Cause

In adults, Baker's cysts usually arise from almost any form of knee

arthritis Arthritis is a term often used to mean any disorder that affects joints. Symptoms generally include joint pain and stiffness. Other symptoms may include redness, warmth, swelling, and decreased range of motion of the affected joints. In som ...

(e.g., rheumatoid arthritis) or

cartilage Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck an ...

(particularly a meniscus) tear. Baker's cysts in children do not point to underlying joint disease. Baker's cysts arise between the tendons of the medial head of the gastrocnemius and the semimembranosus muscles. They are posterior to the

medial femoral condyle Medial may refer to: Mathematics * Medial magma, a mathematical identity in algebra Geometry * Medial axis, in geometry the set of all points having more than one closest point on an object's boundary * Medial graph, another graph that repre ...

. The synovial sac of the knee joint can, under certain circumstances, produce a posterior bulge, into the popliteal space, the space behind the knee. When this bulge becomes large enough, it becomes palpable and cystic. Most Baker's cysts maintain this direct communication with the synovial cavity of the knee, but sometimes, the new cyst pinches off. A Baker's cyst can rupture and produce acute pain behind the knee and in the calf and swelling of the

calf muscles Calf most often refers to: * Calf (animal), the young of domestic cattle. * Calf (leg), in humans (and other primates), the back portion of the lower leg Calf or calves may also refer to: Biology and animal byproducts *Veal, meat from calves *C ...

Diagnosis

Diagnosis is by examination. A Baker's cyst is easier to see from behind with the patient standing with knees fully extended. It is most easily palpated (felt) with the knee partially flexed. Diagnosis is confirmed by ultrasonography, although if needed and there is no suspicion of a popliteal artery aneurysm then aspiration of synovial fluid from the cyst may be undertaken with care. An MRI image can reveal presence of a Baker's cyst. An infrequent but potentially life-threatening complication, which may need to be excluded by blood tests and ultrasonography, is a deep vein thrombosis (DVT). Quick assessment of the possibility of DVT may be required where a Baker's cyst has compressed vascular structures, causing leg edema, as this sets up conditions for a DVT to develop. A burst cyst commonly causes calf pain, swelling and redness that may mimic thrombophlebitis. Popliteal Cyst in situ.jpg, A specimen from a cadaver of a Baker's cyst in popliteal space Image:Bakerzyste MRT ax.jpg, Baker's cyst on axial MRI with communicating channel between the semimembranosus muscle and the medial head of the gastrocnemius muscle. Image:Bakerzyste1 MRT sag.jpg, Baker's cyst on MRI, sagittal image Image:Bakerzyste2 MRT sag.jpg, Baker's cyst on MRI, sagittal image

Treatment

Baker's cysts usually require no treatment unless they are symptomatic. It is very rare that the symptoms are actually coming from the cyst. In most cases, there is another disorder in the knee (arthritis, meniscal (cartilage) tear, etc.) that is causing the problem. Initial treatment should be directed at correcting the source of the increased fluid production. Often rest and leg elevation are all that is needed. If necessary, the cyst can be aspirated to reduce its size, then injected with a

corticosteroid Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex of vertebrates, as well as the synthetic analogues of these hormones. Two main classes of corticosteroids, glucocorticoids and mineralocorticoids, are involv ...

to reduce inflammation. Surgical excision is reserved for cysts that cause a great amount of discomfort to the patient. A ruptured cyst is treated with rest, leg elevation, and injection of a corticosteroid into the knee. Baker's cysts in children, unlike in older people, nearly always disappear with time, and rarely require excision.

Ice pack therapy Cryotherapy, sometimes known as cold therapy, is the local or general use of low temperatures in medical therapy. Cryotherapy may be used to treat a variety of tissue lesions. The most prominent use of the term refers to the surgical treatment, s ...

may sometimes be an effective way of controlling the pain related to Baker's cyst. Heat is also commonly used. A knee

brace Brace(s) or bracing may refer to: Medical * Orthopaedic brace, a device used to restrict or assist body movement ** Back brace, a device limiting motion of the spine *** Milwaukee brace, a kind of back brace used in the treatment of spinal cur ...

can offer support giving the feeling of stability in the joint.

Exercise

Many activities can put strain on the knee, and cause pain in the case of Baker's cyst. Avoiding activities such as squatting, kneeling, heavy lifting, climbing, and even running can help prevent pain. Despite this, some exercises can help relieve pain, and a physiotherapist may instruct on hamstring stretching to reduce pressure on the Baker's Cyst, and strengthening exercises for the quadriceps and/or the patellar ligament.

References

External links

* {{Soft tissue disorders, state=collapsed Musculoskeletal disorders Wikipedia medicine articles ready to translate