Reasons Why You May Experience A Fluid-filled Swelling At The Back Of Your Knee (Baker’s Cyst)

A Baker’s cyst, also called a popliteal cyst, is a fluid-filled swelling that develops at the back of the knee.

It’s caused when the tissue behind the knee joint becomes swollen and inflamed. The swelling and inflammation can cause:

1. pain in the knee and calf

2. a build-up of fluid around the knee

3. occasional locking or clicking in the knee joint.

However, sometimes a Baker’s cyst may not cause any symptoms other than the fluid-filled swelling at the back of the knee.

According to NHS, a Baker’s cyst can sometimes burst (rupture), resulting in fluid leaking down into your calf. This can cause sharp pain, swelling and redness in your calf, but redness can be harder to see on brown and black skin.

What causes a Baker’s cyst?

Knee damage caused by a sports injury or a blow to the knee can lead to a Baker’s cyst developing.

A Baker’s cyst can also sometimes occur if you have a health condition such as:

1. osteoarthritis – usually caused by age-related “wear and tear” of joints; it particularly affects the knees, hips, hands and big toe

2. inflammatory arthritis – including rheumatoid arthritis, which is a less common type of arthritis and is caused by the immune system attacking the joints

3. gout – a type of arthritis that usually affects the big toe and is caused by a build-up of the waste product uric acid in the blood.

Baker’s cysts usually develop in people aged 30 to 70, although they can affect people of any age, including children.

When to see your doctor

See your doctor if you have a lump behind your knee that’s causing problems and does not clear up on its own. They’ll usually be able to diagnose a Baker’s cyst by examining the back of your knee and asking about your symptoms.

Your doctor will ask you whether you have any associated health conditions, such as arthritis.

Tests may be recommended to rule out other more serious conditions, such as a tumour, an aneurysm (bulge in a section of a blood vessel) or DVT (deep vein thrombosis) (a blood clot in one of the deep veins of the body). You may need an ultrasound scan or a MRI scan.

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