What Is A Baker's Cyst (Popliteal Cyst)? What Causes A Baker's Cyst?

A Baker's cyst (Baker cyst), also known as a popliteal cyst is a swelling in the popliteal space - the space behind the knee - causing stiffness and knee pain. The pain typically worsens if the patient fully flexes or extends the knee, or when he/she is moving about. 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).

In most cases, people with a baker's cyst have existing knee joint problems, such as arthritis or a cartilage tear, which causes the knee to produce too much fluid, which may lead to a Baker's cyst.

Most effective relief occurs when the likely underlying problem is treated. Sometimes surgery is needed to drain the cyst.

Baker's cysts affect more women than men, probably because women are more likely to develop rheumatoid arthritis and osteoarthritis. Although people of any age may be affected, most patients are over 40 years of age.

As an open communication with the synovial sac is often maintained, a Baker's cyst is not, by definition, a "true" cyst.

According to Medilexicon's medical dictionary:

Baker cyst is " a collection of synovial fluid that has escaped from the knee joint or a bursa and formed a new synovial fluid-lined sac in the popliteal space; seen in degenerative or other joint diseases that produce increased amounts of synovial fluid."

What are the signs and symptoms of a Baker's cyst (popliteal cyst)?

A symptom is something the patient senses and describes, while a sign is something other people, such as the doctor notice. For example, drowsiness may be a symptom while dilated pupils may be a sign.

Some patients may have no pain and may not even notice the cyst is there.

The signs and symptoms of a Baker's cyst include:

• Swelling or lump behind the knee (the main sign) - this 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
• The knee joint may click or buckle
• The knee joint may lock

When to see a doctor - anybody who experiences pain and swelling behind the knee should see a doctor. A bulge behind the knee may be a sign of a more serious condition, such as an aneurysm or a tumor.

What are the causes of a Baker's cyst (popliteal cyst)?

Our knees are made of bone, tendons and cartilage. The tendons and cartilage need lubrication, which they get in the form of 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 which regulates the flow of synovial fluid.

If the knee produces excessive amounts of synovial fluid there can be an accumulation of it in the popliteal bursa. Accumulation of fluid in the popliteal bursa is a Baker's cyst (popliteal cyst). This accumulation can be caused by:

Inflammation of the knee joint, usually caused by 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 when a gout attack happens.
• 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 becomes hyperactive and attacks normal, healthy tissue. This results in symptoms such as inflammation, swelling, and damage to joints, skin, kidneys, blood, the heart, and lungs.
• 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 - a dry, scaly skin disorder. Doctors believe that it is genetic and is caused by the immune system being mistakenly "triggered", resulting in skin cells being produced too quickly. 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. The synovial membrane (synovium) is attacked, resulting in swelling and pain. If left untreated the arthritis can lead to deformity.
• Septic arthritis - joint inflammation caused by a bacterial infection.

Injury - injury or trauma to the knee, such as a cartilage teat, can lead to a Baker's cyst. Baker's cysts are common among athletes.

Diagnosing a Baker's cyst (popliteal cyst)

A GP (general practitioner, primary care physician) can usually diagnose a Baker's cyst after interviewing the patient and carrying out a physical examination of the knee, especially if there 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 may be ordered:

• An ultrasound scan - an imaging device that utilizes sound waves to create images of the inside of the body.
• A CT (computed tomography) scan - a medical imaging method that employs tomography. Tomography is the process of generating a two-dimensional image of a slice or section through a 3-dimensional object (a tomogram).
• An MRI (magnetic resonance imaging) scan - uses a magnetic field and radio waves to create detailed images of the inside of the body.

What are the treatment options for a Baker's cyst (popliteal cyst)?

Often the Baker's cyst will resolve on its own and no treatment is required. Some self-care techniques may be effective, such as:

• NSAIDs (non-steroidal anti-inflammatory drugs) - medications with analgesic (pain reducing), antipyretic (fever reducing) effects. In higher doses they also have anti-inflammatory effects - they reduce inflammation (swelling). Non-steroidal distinguishes NSAIDs from other drugs which contain steroids, which are also anti-inflammatory. NSAIDs are non-narcotic (they do not induce stupor). Ibuprofen is an NSAID.
• Icepacks - 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 or physical therapist (UK: physiotherapist) may advise how long the patient should rest, as well as suggesting alternative forms of exercise.
• Crutches - these will take the weight off the knee joint and help the patient walk without pain.
• Compression bandages - these help support the knee.

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, or if the self-help techniques did not work, further treatment may be required.

• Corticosteroid injection - a corticosteroid medication, such as cortisone, is injected into the affected knee, reducing inflammation (swelling). Although this relieves pain, it does not reduce the risk of recurrence.
• Physical therapy (UK: physiotherapy) - a qualified physical therapist (UK: physiotherapist) may recommend some gentle strengthening and range-of-motion exercise for the knee muscles. These exercises may help reduce symptoms as well as maintaining the function of the knee.
• Arthroscopy - if there is extensive knee joint damage, perhaps because of a physical injury or some underlying condition, the cyst may have to be surgically removed and the joint repaired.
  
  Arthroscopy is an endoscopic examination of the interior of a joint - the surgeon inspects and treats problems inside a joint using an arthroscope. An arthroscope is a thin, flexible fiberoptic tube (scope) which is inserted into a joint space through a small incision. It has a tiny camera, light source and precision tools attached, so that the surgeon can carry out diagnostic procedures, surgical repairs, as well as draining away excess fluid.
  
  The patient may receive either a local or general anesthetic, depending on whether extensive repair has to be done. Sometimes the procedure is done on an outpatient basis.

What are the possible complications of a Baker's cyst (popliteal cyst)?

A Baker's cyst can burst, resulting in synovial fluid leaking into the calf region. This is extremely rare. If it does occur, 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 fluid will eventually be reabsorbed by the body over a period of up to four 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.