A Baker’s cyst, also called a popliteal cyst, is usually the result of a problem within your knee joint, such as arthritis or a cartilage tear. There is an extravasation of synovial fluid, normally found within your knee, into the back of your knee that collects almost as if there is a one way valve where the fluid cannot drain back into your knee joint.
A lubricating fluid called synovial fluid helps your leg swing smoothly and reduces friction between the moving parts of your knee.
But, sometimes the knee produces too much synovial fluid, resulting in buildup of fluid in an area on the back of your knee (popliteal bursa), causing a Baker’s cyst. This can happen because of:
Inflammation of the knee joint, such as occurs with various types of arthritis
A knee injury, such as a cartilage tear
In some cases, a Baker’s cyst causes no pain, and you may not even notice it. If you do experience signs and symptoms, you may notice:
- Swelling behind your knee, and sometimes in your leg
- Knee pain
Your symptoms may be worse after you’ve been active, or even if you’ve just been standing for a long time.
The Baker’s cyst can be drained and occasionally cortisone or a sclerosing agent such as dextrose can be injected with the hope to stop fluid from reaccumulating. True treatment will involve identifying and treating the knee pathology that lead to fluid accumulation.