Baker's Cyst

Excerpt

A Baker Cyst, also known as a popliteal or parameniscal cyst, is a fluid-filled sac that forms in the posterior aspect of the knee, typically located between the semimembranosus and medial head of the gastrocnemius.

In adults, Baker's Cysts tend to form in association with degenerative conditions of the knee. One of the most common associations seen is secondary to degenerative meniscal tears. Inflammatory conditions and arthritides are also known causes of popliteal cyst formation. When the cyst forms in association with a meniscal tear, the meniscus serves as a one-way valve and the extruded synovial fluid localizes and consolidates to form a viscous, gel-like material.

In children, popliteal cysts more commonly arise as a primary condition. Unlike adults, popliteal cysts in children arise from a herniated posterior knee joint synovium/capsule.