what is a Baker's cyst?

A Baker's cyst forms a bump in the lower part of the hollow of the knee. It is caused by an accumulation of synovial fluid (effusion) in a bulge (cyst) of the knee joint capsule. Those affected have colloquially “water in their knees”. Baker's cyst is usually caused by damage to the knee joint , such as osteoarthritis or damage to the joint cartilage (meniscus). The body tries to compensate for such impairments by producing more synovial fluid.

With wear-related (degenerative) diseases of the knee joint (osteoarthritis of the knee), many sufferers suffer from pain and dysfunction. Some, however, hardly notice the change. A Baker's cyst itself does not generally cause any symptoms. However, it can press on muscles, nerves and / or vessels and thereby trigger health problems. As the cyst grows in size, impairment becomes more likely.

If the damage in the knee joint is repaired, a Baker cyst often regresses on its own. If this is not the case, it can be treated directly. However, surgery is rarely necessary. The Baker cyst got its name from the English surgeon William Morrant Baker, who was the first to recognize damage to the knee joint as the cause of the cyst (1877) and who described the connection (publication 1885).

By definition, a cyst is a body cavity that has been formed by certain circumstances and usually does not exist. Cysts can develop in various tissues and are usually filled with fluid, less often with air. A Baker's cyst forms out of the joint capsule in the knee . Usually the joint is already damaged.

The visible bulge usually occurs on the inside of the leg in the lower area of ​​the hollow of the knee (poplitea) and upper calf. The cyst lies between or on the muscles attached to the side of the knee and is often connected to the joint by a stalk. The Baker cyst is also called a popliteal cyst because of its location and is filled with synovial fluid.

Causes of a Baker's Cyst

• mostly wear-related (degenerative) damage to the knee joint
• Injuries, especially of the joint cartilage (meniscus)
• Baker's cysts are very rarely congenital

Symptoms of a Baker's cyst

The often outwardly visible and palpable symptom of a Baker's cyst is a swelling or bump on the inside of the leg in the area of ​​the lower hollow of the knee . This is the bulge (cyst) of the posterior capsule of the knee joint. The Baker cyst itself does not usually cause pain. Depending on its size, however, it can press on other tissues, nerves and blood vessels and cause discomfort. The size of a Baker's cyst depends heavily on the amount of stress on the knee and the time it takes for it to develop. 

If the already damaged knee joint is stressed, the body produces more synovial fluid as a buffer so that bones and cartilage do not rub against each other too much. If the joint capsule has given in to the resulting increase in pressure inside and a Baker's cyst has formed, it becomes larger as a result of stress. Because the knee forms more and more synovial fluid, which is also pressed out of the joint capsule into the cyst when the leg moves. You can feel the fluid movements in the cyst . If the leg is spared, the Baker's cyst can shrink and the swelling decreases.

To prevent the Baker's cyst from growing again, the cause of the cyst formation must be corrected. Especially since a Baker cyst, once it has formed, slowly but steadily enlarges even without stress. The larger the cyst becomes, the more likely it is to trigger feelings of pressure, pain, and damage to neighboring tissues, as well as restricted mobility. If the Baker's cyst presses on the popliteal vein, it can also cause thrombosis .

Bending the knee with Baker's cyst in particular causes pain and is often difficult. A large cyst can cause circulatory disorders and abnormal sensations or numbness in the lower leg when it presses on vessels and nerves.

If a Baker's cyst is too large or stressed too much, it can burst. In the case of a so-called rupture, the cyst wall can no longer withstand the pressure and tears open (ruptures). The synovial fluid then gets into the surrounding tissue, especially the lower leg muscles, and causes inflammation and further pain.

Baker's cyst: swelling on the inside of the leg below the hollow of the knee due to a bulging of the posterior capsule of the knee. Depending on its size, the Baker cyst can press on other tissues, nerves and blood vessels

In some Baker cysts, the duct (stem) between the cyst and the joint capsule acts like a valve. The synovial fluid gets into the cyst, but cannot return. It accumulates more and more, the cyst is getting bigger and bigger and threatens to burst. In other Baker's cysts, the connection to the joint recedes. This can also cause the internal pressure to become so great that the cyst can easily rupture.

A burst Baker's cyst can cause synovial fluid from the knee to reach the ankle. The whole lower leg swells up and permanent tissue damage can occur. A ruptured Baker cyst is an emergency and should be treated promptly. In the worst case, there is a risk of a lower leg amputation in the event of nerve and vascular damage.

Causes of a Baker's Cyst

Each joint is surrounded by a shell - the joint capsule - which consists of a connective tissue-like cell structure. It stabilizes the joint and produces the synovial fluid on the inside. This serves as a lubricant for the joint and prevents function-impairing friction in healthy, young people. It also contains important nutrients for the articular cartilage.

A Baker's cyst usually forms when the knee joint is damaged or the capsule is weakened for other reasons. The causes are often injuries, in particular meniscus or other cartilage damage, inflammation ( arthritis / rheumatism ) or severe signs of wear and tear (osteoarthritis). As the signs of wear and tear increase with age, Baker's cysts are more common in the elderly . In principle, however, such a cyst can form at any age.

When a joint is damaged, friction usually arises. To counteract this, the body produces more synovial fluid as a mechanical buffer. As the fluid increases, so does the pressure in the joint capsule and on the envelope. The tissue of the knee joint capsule is weaker at the back than at the front, where it is generally more heavily stressed. If the pressure inside from the large amount of fluid becomes too great, the back of the capsule gives way and a fluid-filled bulge forms in the hollow of the knee, the Baker's cyst. If the causal joint damage can be repaired, a Baker cyst often regresses spontaneously.

There are several types of Baker's cyst. Primary cysts are less common and are more likely to occur in younger patients. Sometimes they are congenital, but they rarely cause discomfort. The cause is unknown (idiopathic). Secondary Baker's cysts are more common, the causes described above. Most cysts have a permanent connection between the sac and the joint capsule . They are called distension cysts. However, there are also so-called dissection cysts in which the connection is interrupted or regressed, but the fluid-filled body cavity remains.

Treatment of a Baker's cyst

How to get rid of a Baker cyst and what exactly to do for it depends on the stage of the cyst and the personal requirements of the person concerned. If a Baker cyst does not cause any symptoms, it does not necessarily have to be treated. Cysts can also regress spontaneously, i.e. by themselves. Incidentally, the symptoms, especially existing pain, should be treated first. For this, various pain relievers and anti-inflammatories can be taken or injected by the doctor.

In addition to non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and diclofenac, so-called Cox-2 inhibitors and, if necessary, cortisone are available for treating Baker's cysts. Cortisone can be injected directly into the damaged knee joint to stop inflammatory processes there. If severely damaged joint cartilage is the cause of the Baker's cyst, injected hyaluronic acid can also help the knee joint in the long term.

The real treatment for a Baker's cyst is treating its cause, the knee injury, joint wear, or inflammation. Otherwise, a Baker's cyst will very likely fill up again and again and cause discomfort.

There are drug therapies for inflammation. Damage to the joint can also be treated surgically, for example with an arthroscopy (minimally invasive procedure). The aim is always to repair the joint damage that causes Baker's cyst and to stabilize the knee. Physiotherapy or occupational therapy has a supportive effect.

If treatment of the knee can correct the cause of Baker's cyst , the cyst will often resolve on its own . If this does not happen, the doctor can puncture it. A Baker's cyst rarely needs to be removed surgically .

Therapies for Baker's cyst

• Medications (pain relievers and anti-inflammatories)
• Cooling, massages (not the cyst directly!), Bandaging, taping
• physical therapy
• Hyaluronic acid
• Correction of the causing joint damage through a minimally invasive procedure (arthroscopy)
• Puncture of the cyst, possibly thermotherapy with electricity
• surgical removal of the cyst  @ READ MORE When a Side Effect Occurs?