Cysts come in all types and sizes. While most people are familiar with cystic acne, epidermoid cysts which are small bumps filled with keratin, and sebaceous cysts which form in sebaceous oil glands of the skin, cysts aren’t always filled with dead skin or oil. Baker’s cysts are a unique type of cyst filled with joint fluid, specifically affecting the knee joint. Baker’s cysts are a type of synovial cyst with a thin film of tissue around the cyst. Ganglion cysts are similar in that they occur at the wrist and ankle joints but they do not have this film of tissue.
Information. A baker’s cyst is a very common condition in which a fluid-filled cyst develops in the popliteal space or the hollow behind the knee joint. Also known as a popliteal cyst, this type of cyst is often related to an issue with the knee joint. Baker’s cysts are not like most cysts as they are filled with synovial fluid which lubricates joints and gives the knee the ability to flex and extend. For some people, a baker’s cyst causes no noticeable symptoms; for others, it can be painful and lead to knee joint stiffness.