Overview

A Baker's cyst:

• Is a lump behind the knee that is filled with liquid
• Can be painful
• Is usually not serious and doesn't cause lasting damage
• Often improves on its own
• Should be checked by a doctor, because it can be confused with other conditions
• Can be treated in various ways, drained or removed

A Baker's cyst, also called a popliteal cyst, occurs when the knee joint produces too much lubricating fluid called synovial fluid. It may form after an injury or in certain kinds of arthritis. In some cases, it forms for no known reason.

A Baker's cyst forms when a bursa, a sac that acts like a cushion for the the joint, overfills with synovial fluid and expands. This causes the swelling known as a Baker's cyst at the back of the knee.

About half of all cases of Baker's cysts occur in children. The cyst gets its name from a 19th century British doctor, William Morrant Baker, who first described it.

More on Baker's Cysts