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 ...

. 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 Deep vein thrombosis (DVT) is a type of venous thrombosis involving the formation of a blood clot in a deep vein, most commonly in the legs or pelvis. A minority of DVTs occur in the arms. Symptoms can include pain, swelling, redness, and enla ...

peripheral neuropathy Peripheral neuropathy, often shortened to neuropathy, is a general term describing disease affecting the peripheral nerves, meaning nerves beyond the brain and spinal cord. Damage to peripheral nerves may impair sensation, movement, gland, or or ...

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 w ...

, or

compartment syndrome Compartment syndrome is a condition in which increased pressure within one of the body's anatomical compartments results in insufficient blood supply to tissue within that space. There are two main types: acute and chronic. Compartments of the ...

may occur. Risk factors include other knee problems such as

osteoarthritis Osteoarthritis (OA) is a type of degenerative joint disease that results from breakdown of joint cartilage and underlying bone which affects 1 in 7 adults in the United States. It is believed to be the fourth leading cause of disability in the ...

, meniscal tears, or

rheumatoid arthritis Rheumatoid arthritis (RA) is a long-term autoimmune disorder that primarily affects joints. It typically results in warm, swollen, and painful joints. Pain and stiffness often worsen following rest. Most commonly, the wrist and hands are inv ...

. 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 articul ...

from the

knee joint In humans and other primates, the knee joins the thigh with the human leg, 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 join ...

to the gastrocnemio-semimembranosus bursa, resulting in its expansion. The diagnosis may be confirmed with

ultrasound Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies ...

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 comf ...

. 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 ...

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 so ...

(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 A bruise, also known as a contusion, is a type of hematoma of tissue, the most common cause being capillaries damaged by trauma, causing localized bleeding that extravasates into the surrounding interstitial tissues. Most bruises occur close ...

below the

medial malleolus A malleolus is the bony prominence on each side of the human ankle. Each leg is supported by two bones, the tibia on the inner side (medial) of the leg and the fibula on the outer side (lateral) of the leg. The medial malleolus is the promi ...

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.,

) 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 ...

(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 The gastrocnemius muscle (plural ''gastrocnemii'') is a superficial two-headed muscle that is in the back part of the lower leg of humans. It runs from its two heads just above the knee to the heel, a three joint muscle (knee, ankle and subtalar ...

and the semimembranosus muscles. They are posterior to the medial femoral condyle. 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 The popliteal artery is a deeply placed continuation of the femoral artery opening in the distal portion of the adductor magnus muscle. It courses through the popliteal fossa and ends at the lower border of the popliteus muscle, where it branche ...

aneurysm An aneurysm is an outward bulging, likened to a bubble or balloon, caused by a localized, abnormal, weak spot on a blood vessel wall. Aneurysms may be a result of a hereditary condition or an acquired disease. Aneurysms can also be a nidus ( ...

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

(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 Thrombophlebitis is a phlebitis (inflammation of a vein) related to a thrombus (blood clot). When it occurs repeatedly in different locations, it is known as thrombophlebitis migrans (migratory thrombophlebitis). Signs and symptoms The following s ...

. 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 Signs and symptoms are the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign for example may be a higher or lower temperature than normal, raised or lowered blood pressure or an abnormality showi ...

. 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 inv ...

to reduce inflammation.

Surgical excision Surgery ''cheirourgikē'' (composed of χείρ, "hand", and ἔργον, "work"), via la, chirurgiae, meaning "hand work". is a medical specialty that uses operative manual and instrumental techniques on a person to investigate or treat a pat ...

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 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 c ...

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 Physical therapy (PT), also known as physiotherapy, is one of the allied health professions. It is provided by physical therapists who promote, maintain, or restore health through physical examination, diagnosis, management, prognosis, patien ...

may instruct on

hamstring In human anatomy, a hamstring () is any one of the three posterior thigh muscles in between the hip and the knee (from medial to lateral: semimembranosus, semitendinosus and biceps femoris). The hamstrings are susceptible to injury. In quadrupe ...

stretching to reduce pressure on the Baker's Cyst, and strengthening exercises for the

quadriceps The quadriceps femoris muscle (, also called the quadriceps extensor, quadriceps or quads) is a large muscle group that includes the four prevailing muscles on the front of the thigh. It is the sole extensor muscle of the knee, forming a large ...

and/or the

patellar ligament The patellar tendon is the distal portion of the common tendon of the quadriceps femoris, which is continued from the patella to the tibial tuberosity. It is also sometimes called the patellar ligament as it forms a bone to bone connection when ...

References

External links

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