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A Baker’s cyst (or Baker cyst), also known as a popliteal cyst, is a swelling in the popliteal space, the space behind the knee. It causes stiffness and knee pain.
The pain caused by the cyst typically worsens if the patient fully flexes or extends the knee, or moves around.
The condition, which has nothing to do with baking, is named after the British surgeon who first described it, Dr. William Morrant Baker (1838-1896).
A Baker’s, or popliteal, cyst is a painful swelling that develops behind the knee. It is filled with fluid.
Symptoms include pain and stiffness as well as popping, clicking, creaking, or locking in the knee joint.
A Baker’s cyst will commonly resolve on its own, and no treatment is required.
Some self-care techniques may be effective, such as:
- Icepacks: This can be useful in reducing inflammation. Make sure there is no direct contact with ice on skin.
- Resting: The knee needs to rest; it must not be exposed to irritation. A doctor may advise how long the patient should rest, as well as suggesting alternative forms of exercise.
- Crutches: These take the weight off the knee joint and help the patient walk without pain.
- Compression bandages: These help support the knee. Compression bandages are available for purchase online.
Ibuprofen, a common over the counter medication, is an NSAID.
In most cases, if there is an underlying cause, the doctor will treat the cause rather than the cyst itself. If the swelling is particularly large and painful, further treatment may be required:
- Corticosteroid injection: This reduces inflammation and relieves pain, but it does not reduce the risk of recurrence.
- Physical therapy: A qualified physical therapist may recommend some gentle strengthening and range-of-motion exercise for the knee muscles. These exercises can help reduce symptoms as well as maintaining the function of the knee.
- Arthroscopy: Extensive knee joint damage, possibly due to a physical injury or some underlying condition, may mean that the cyst must be surgically removed and the joint repaired. The surgeon inspects and treats problems inside a joint using an arthroscope, a thin, flexible fiber-optic tube which is inserted into the joint through a small incision.
Baker’s cysts affect more women than men, probably because women develop rheumatoid arthritis and osteoarthritis more often.
Although people of any age may be affected, most patients are over 40 years.
Some patients may have no pain and may not even notice the cyst is there. However, the signs and symptoms of a Baker’s cyst can include:
- swelling or lump behind the knee that is more evident when standing and comparing one knee to the other. It may feel like a water-filled balloon
- knee pain
- calf pain
- accumulation of fluid around the knee
- clicking, locking, or buckling of the knee joint
The knee is made of bone, tendons, and cartilage. The tendons and cartilage need lubrication, which they get from synovial fluid – it helps the legs move smoothly and reduces friction.
There are various pouches, called bursae, in each knee, through which the synovial fluid circulates. Between the popliteal bursa – a pouch at the back of the knee – and the knee joint, there is a valve-like system that regulates the flow of synovial fluid.
If the knee produces too much synovial fluid, there can be an accumulation of it in the popliteal bursa.
This can be caused by an inflammation of the knee joint, usually due to an underlying condition, such as:
- Gout – levels of uric acid in the blood rise until the level becomes excessive (hyperuricemia), causing urate crystals to build up around the joints. This causes inflammation and severe pain.
- Hemophilia – an inherited medical condition where the blood does not clot properly, leading to internal bleeding and joint damage.
- Lupus – an autoimmune disease where the body’s immune system attacks normal, healthy tissue.
- Osteoarthritis – a form of arthritis caused by inflammation, breakdown, and the eventual loss of cartilage in the joints – the cartilage wears down over time.
- Psoriasis – some patients also experience pain and inflammation in their joints.
- Reactive arthritis – a chronic (long-term) type of arthritis with inflamed joints, inflammation of the eyes, and inflammation of the genital, urinary, or gastrointestinal system.
- Rheumatoid arthritis – an inflammatory form of arthritis.
- Septic arthritis – joint inflammation caused by a bacterial infection.
- Injury – injury or trauma to the knee, such as a cartilage tear, can lead to a Baker’s cyst; they are common among athletes.
A doctor can usually diagnose a Baker’s cyst after interviewing the patient and carrying out a physical examination of the knee, especially if there is an underlying health condition.
Sometimes, additional diagnostic tests may be ordered to rule out other conditions, such as an aneurysm or a tumor.
The following non-invasive tests might be carried out:
Gentle exercise might help to extend or maintain the range of motion of the knee and to strengthen the muscles around the knee.
These may also may help relieve symptoms and maintain knee function.
A doctor or physical therapist can advise on suitable exercises.
Existing knee issues are the most significant risk factor. Most effective relief comes from treating the underlying problem.
A Baker’s cyst can burst, resulting in synovial fluid leaking into the calf region. This is extremely rare. If a Baker’s cyst bursts, the patient will probably experience:
- severe and sharp pain in the knee
- inflammation (swelling)
- the calf region may become red
- there may be a sensation of water trickling down the calf
The body will eventually reabsorb the fluid over a period of up to 4 weeks. Doctors may prescribe painkillers to control the pain. Redness in the calf region may also be a sign of a blood clot in a vein. Patients with such signs should see their doctor immediately.