Diseases & Conditions

Baker Cyst

Overview, Causes, & Risk Factors

A Baker's cyst is an abnormal collection of joint fluid inside a sac that is located behind the knee.

What is going on in the body?

Bursae are sacs located in and around joints. They are normal and they contain fluid. These sacs and the joint fluid help to reduce friction and wear on the bones and muscles. In some people, an abnormal outpouching from these sacs may form in the back of the knee. This outpouching is known as a Baker's cyst. These cysts usually form due to some type of knee irritation or injury and may cause symptoms.

What are the causes and risks of the condition?

In children, this condition seems to occur for no reason and is not related to knee irritation. In adults, Baker's cysts are commonly due to:

  • a common type of arthritis, known as osteoarthritis. Other forms of arthritis, such as rheumatoid arthritis, may also cause this condition.
  • increased fluid in the knee. This is called an effusion, and can be due to infection and other causes,
  • injury to the knee. This is usually a cartilage tear