A Baker cyst is swelling caused by fluid from the knee joint protruding to the back of the knee. The back of the knee is also referred to as the popliteal area of the knee.
A Baker cyst is sometimes referred to as a popliteal cyst. When an excess of knee joint fluid is compressed by the body weight between the bones of the knee joint, it can become trapped and separate from the joint to form the fluid-filled sac of a Baker cyst.
The name of the cyst is in memory of the physician who originally described the condition, the British surgeon William Morrant Baker (1839-1896).
What causes a Baker cyst?
Baker cysts are not uncommon and can be caused by virtually any cause of joint swelling (arthritis). The excess joint fluid (synovial fluid) bulges to the back of the knee to form the Baker cyst.
The most common type of arthritis associated with Baker cysts is osteoarthritis, also called degenerative arthritis. Baker cysts can occur in children with juvenile arthritis of the knee.
Baker cysts also can result from cartilage tears (such as a torn meniscus), rheumatoid arthritis, and other knee problems.
Who gets a Baker’s cyst?
A Baker’s cyst most commonly occurs in children aged 4 to 7 years and in adults aged 35 to 70 years. However, Baker’s cysts are much more common in adults than in children.
You are more likely to develop a Baker’s cyst if you have an underlying problem with your knee.
Arthritis is the most common condition associated with Baker’s cysts. This can include various different types of arthritis, such as osteoarthritis (most common), rheumatoid arthritis, psoriatic arthritis and gout.
Baker’s cysts may also develop if you have had a tear to the meniscus or to one of the ligaments within the knee, or if you have had an infection within the knee joint.
Does a Baker’s cyst cause any symptoms?
Some people with a Baker’s cyst do not have any symptoms. Also, small cysts may not always be found when a doctor examines your knee.
The cyst may be found incidentally when having an investigation on your knee, such as an MRI scan for some other reason.
In general, the larger the Baker’s cyst, the more likely it is to produce symptoms. You may be able to see or feel the swelling behind your knee.
Sometimes you may also notice that the knee joint itself is swollen. Some people feel an ache around the knee area. It may be difficult to bend your knee if you have a large Baker’s cyst and the area behind your knee may feel tight, especially when you are standing up.
Less commonly, you may feel a sensation of clicking or locking of your knee.
If you have an underlying knee problem such as arthritis, you may also have symptoms related to that, such as knee pain.
Are there any complications that can develop?
The most common complication of a Baker’s cyst is for it to rupture (split open). If this happens, the fluid from inside the cyst can leak out into the calf muscle.
This can cause swelling of the calf. You may also develop itching and redness of the skin of your calf because of irritation caused by the fluid that leaks out from the cyst. About 1 or 2 in 20 Baker’s cysts are thought to rupture.
If a Baker’s cyst ruptures, it can be quite difficult to tell the difference between the ruptured cyst and a deep vein thrombosis (DVT) in the leg. A DVT is a blood clot that forms in a leg vein.
In these cases, it is important that investigations are carried out to exclude a DVT because it can be a serious condition that needs treatment.
Having a Baker’s cyst can also increase your risk of developing a deep vein thrombosis even if the cyst does not rupture.
For this reason, anyone who is found to have a Baker’s cyst should also have a DVT excluded. Similarly, anyone who is found to have a DVT should be examined and investigated for a possible Baker’s cyst. Very rarely, a Baker’s cyst may become infected.
How is a Baker’s cyst diagnosed?
Your doctor may suspect a Baker’s cyst when they examine your knee. The area behind the knee may be swollen. Your doctor may shine a light through the swelling.
If the light passes through it, the swelling is full of fluid. The swelling is therefore a cyst.
An ultrasound scan is a good investigation to show a Baker’s cyst and to help to exclude a DVT at the same time. Sometimes an MRI scan is used to confirm the diagnosis.
How is a Baker cyst treated?
Baker cysts often resolve with aspiration (removal) of excess knee fluid in conjunction with cortisone injection. Medications are sometimes given to relieve pain and inflammation.
When cartilage tears or other internal knee problems are associated, physical therapy or surgery can be the best treatment option.
During a surgical operation, the surgeon can remove the swollen tissue (synovium) that leads to the cyst formation. This is most commonly done with arthroscopic surgery.
There are some other treatment options that are sometimes used:
- Fluid drainage – sometimes your doctor may use a needle to drain excess fluid from your knee joint to help to relieve your symptoms. However, it is common for the Baker’s cyst to re-form over time. Cortisone (steroid) injection – this is sometimes used following fluid drainage, to reduce the pain and inflammation caused by the cyst. It does not prevent it from coming back again.
- Surgery to remove the cyst – this is sometimes done, especially if a cyst is very large or painful and/or other treatments have not worked. Sometimes a keyhole method is used to close off the connection between the
- Baker’s cyst and the knee joint. The cyst is also sometimes removed using open surgery. Surgery may be carried out to treat an underlying problem at the same time – for example, repairing a meniscal tear.
What is the prognosis for a Baker cyst?
Depending on the cause of the Baker cyst, the outlook is generally very good. Those caused by chronic arthritis can be prone to recur.
Is it possible to prevent a Baker cyst?
There is no prevention for a Baker cyst except minimizing any underlying arthritis disease.