A Baker's cyst, also called a popliteal cyst, is a fluid-filled swelling that develops at the back of the knee. It is caused by a problem with the knee joint or the tissue behind it.
The swelling may cause:
- pain in the knee and calf
- a build-up of fluid around the knee
- occasional locking or clicking in the knee joint
However, it may cause no symptoms at all other than the lump.
In rare cases, a Baker's cyst can burst (rupture), causing fluid to leak down into your calf. This can cause sharp pain, swelling and redness in your calf.
What causes a Baker's cyst?
Knee damage caused by a sports-related injury or blow to the knee can lead to a Baker's cyst developing.
A Baker's cyst can also be caused by a number of health conditions, including:
- osteoarthritis – usually caused by age-related "wear and tear" of joints, it particularly affects the knees, hips, hands and big toe
- rheumatoid arthritis – a less common but crippling type of arthritis caused by the immune system attacking the joints
- gout – a type of arthritis that usually affects the big toe caused by a build-up of the waste product uric acid in the blood
A Baker's cyst is more common in women than men, probably because women are more likely to develop osteoarthritis and rheumatoid arthritis. It usually develops in people aged over 40, although it can affect people of any age, including children.
When to see your doctor
You should see your doctor if your cyst causes you problems and does not go away. They can usually diagnose a Baker's cyst by examining your knee and asking about your symptoms.
They will also want to know if you have any associated health conditions, such as arthritis.
Further tests may be recommended to rule out other more serious conditions, such as a tumour or aneurysm (a bulge in a section of a blood vessel). These can include an ultrasound scan or a magnetic resonance imaging (MRI) scan.
Treating a Baker's cyst
You can reduce the swelling and relieve any pain using over-the-counter painkillers, bandages or an ice pack (a bag of frozen peas wrapped in a tea towel works well).
It's important that any underlying condition is properly managed as the cyst may go away when the condition causing it has been treated.
In some cases, surgery may be needed to drain the cyst or to remove it.
Read more information about treating a Baker's cyst.
You can treat a Baker's cyst yourself at home. Further treatment is only needed if the cyst stops you using your knee properly or causes pain that doesn't go away.
To treat a Baker's cyst:
- take non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, to reduce swelling and pain in the affected knee
- hold an ice pack to the knee for 10-20 minutes to reduce any swelling – try a bag of frozen peas wrapped in a cloth (never put ice directly on your skin)
- rest your knee joint
- use compression bandages to support your knee joint – you can buy these from a pharmacy
See your doctor for further treatment if your cyst still causes problems after you have tried the treatments above.
One treatment option is to inject corticosteroid medication directly into the affected knee. This helps reduce inflammation and swelling.
Treating a ruptured cyst
In rare cases, a Baker's cyst can burst, causing fluid to leak down into your calf. This can cause sharp pain and swelling in your calf. The fluid will gradually be reabsorbed into the body within a few weeks.
Prescription painkillers – usually a combination of paracetamol and codeine – can be used to control any pain. See your doctor for a prescription.
Surgery to repair damage to the knee
If there is a lot of damage to the knee joint caused by a condition such as osteoarthritis or a physical injury, surgery may be needed to fix the problem with the joint. This is usually done using a type of keyhole surgery called arthroscopy. This allows the surgeon to look inside a joint and repair or remove any damage.