What is a Baker's cyst?

A Baker's cyst, or popliteal cyst, is a fluid-filled lump or swelling behind the knee. It is usually caused by excess fluid that comes from the knee joint.

People with a Baker's cyst might also have arthritis or an injury such as a torn cartilage in their knee.

What are the symptoms of a Baker's cyst?

If the cyst is small, you might not notice it.

Otherwise, you may have aching, a swelling or lump behind your knee, feel pressure when you straighten your leg, or stiffness or tightness in your knee.

How is a Baker's cyst diagnosed?

A doctor can often diagnose a Baker's cyst by examining the knee and shining a torch through the lump to see whether it is filled with fluid. They might order an x-ray to check for arthritis in the knee, which may be causing the problem.

You might also have an ultrasound or MRI scan.

How is a Baker’s cyst treated?

If a child has a painless Baker’s cyst, it can usually be left alone. In children, most Baker’s cysts disappear eventually without treatment.

Adults can ease any pain from a Baker’s cyst with cold packs, or by taking paracetamol or anti-inflammatory medications and using crutches to take weight off the knee.

The pain may also ease with physical activities such as walking, swimming or Tai Chi. If you are overweight, losing weight may help.

Taking supplements or wearing a brace is unlikely to help with symptoms.

If you have a troublesome Baker's cyst, your doctor may suggest it can be drained under ultrasound guidance and injected with corticosteroids, which has been shown to result in significant improvements and a low chance of the cyst coming back.

If the cyst is associated with arthritis or a knee injury, then treating these conditions can help. Another treatment is physiotherapy using hot or cold packs and exercises to keep the knee strong and mobile.

For some people, surgery is needed to fix the cause. For example, repairing a torn cartilage might help. Removing the cyst alone is not helpful, as it usually comes back unless the underlying cause is addressed.

Your doctor can advise you on the treatment options that are best for you.

What are the possible complications of a Baker’s cyst?

Occasionally Baker’s cysts become infected or grow bigger.

Sometimes a Baker’s cyst ruptures or bursts beneath the skin, causing pain and swelling in the calf. In this case, your doctor may want to rule out a serious problem such as a blood clot (deep vein thrombosis).