What is a Baker’s cyst?

A Baker’s cyst is a fluid-filled swelling that can develop behind the knee. It is also sometimes called a popliteal cyst, as the medical term for the area behind the knee is the popliteal fossa.

The cyst varies in size from a very small cyst to a large cyst that is a few centimetres across. Rarely, a Baker’s cyst can develop behind both knees at the same time.

What causes a Baker’s cyst?

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There are two ways in which a Baker’s cyst may form:
A primary Baker’s cyst – A Baker’s cyst may develop just behind an otherwise healthy knee joint. This type of cyst is sometimes referred to as a primary or idiopathic Baker’s cyst. It is usually common amongst younger people and children.
It is thought that in this type of Baker’s cyst there is a connection between the knee joint and the popliteal bursa behind the knee. This means that synovial fluid from inside the joint can pass into the popliteal bursa and a Baker’s cyst can form.

A secondary Baker’s cyst – Sometimes a Baker’s cyst might develop if there is an underlying problem within the knee, such as arthritis (including osteoarthritis and rheumatoid arthritis), or a tear in the meniscal cartilage that lines the inside of the knee joint. This type of Baker’s cyst is the most common. It is often referred to as a secondary Baker’s cyst.

In a secondary Baker’s cyst, the underlying problem within the knee joint causes too much synovial fluid to be produced within the joint. As a result of this, there will be an increase in pressure inside the knee. This has the effect of stretching the joint capsule. The joint capsule bulges out at the back of the knee, thus forming the Baker’s cyst which is filled with synovial fluid.

Who gets a Baker’s cyst?

A Baker’s cyst occurs mainly in children aged 4 to 7 years and in adults aged between 35 and 70 years old. However, Baker’s cysts are more common amongst the adults than in children. You are more likely to develop a Baker’s cyst if you previously have an underlying problem with your knee.

Arthritis is the most common condition associated with Baker’s cysts. This can include various types of arthritis, such as osteoarthritis, 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 the knee. The cyst may be found by accident when having an investigation done on your knee, such as an MRI scan.

In general, the larger the Baker’s cyst, the more obvious are the 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 might feel a little discomfort around the knee area. It will be difficult to bend your knee with a large Baker’s cyst and the area behind your knee may feel some tightness, especially when you are standing up. Though uncommon, 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.

What is the treatment for a Baker’s cyst?

A Baker’s cyst often gets better and disappears by itself over time. However, it may persist for months or even years before it goes. In a lot of people it causes little in the way of symptoms and no specific treatment is needed.

Treatment of any underlying knee problem

It is important that any underlying knee problem is treated if you have a Baker’s cyst. This may help to reduce the size of the Baker’s cyst and any swelling or pain that it causes. For example, if you have osteoarthritis, a steroid injection into the knee may help to relieve pain and inflammation. This however, does not always stop the cyst from coming back.

If you have an injury to the knee such as a meniscal tear, treating it may help to treat the Baker’s cyst as well.

Treatment to help relieve symptoms
If you have pain and discomfort because of your Baker’s cyst, one or more of the following may be helpful:

  • Support stockings – these provide compression and may help to reduce the swelling.
  • Non-steroidal anti-inflammatory drugs (NSAIDs) – these can help to relieve pain and may also limit inflammation and swelling. Side effects sometimes do occur with NSAIDs. These side effects include stomach pain, and bleeding from the stomach, which are the most serious. Some people with asthma, high blood pressure, kidney failure, and heart failure may not be able to take NSAIDs. So, consult your doctor or pharmacist before taking them.
  • If the cyst ruptures, the fluid from inside the cyst may leak into the calf and cause worse pain. Stronger pain relief medication may be required.
  • Ice treatment – this may also help to reduce swelling and pain. Make an ice pack by wrapping ice cubes in a plastic bag or towel. Apply the ice pack for 10-30 minutes. Less than 10 minutes has little effect. More than 30 minutes may damage the skin.
  • Crutches – it may be necessary to use crutches to move about until your symptoms ease. They help to take the weight off the affected leg while you are walking.
  • Physiotherapy – keeping your knee joint moving and use strengthening exercises to help the muscles around your knee will be helpful.

Other treatments
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 failed to 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.