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 a doctor
You should see a doctor if your cyst causes you problems and does not go away. The doctor can usually diagnose a Baker’s cyst by examining your knee and asking about your symptoms.
The doctor 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
It is important that any underlying condition is properly managed as the cyst may go away when the condition causing it has been treated.
Some cases, needle aspiration is required to drain the cyst.
In some rare cases, surgery may be needed to remove it. This is usually done using a type of keyhole surgery called arthroscopy.