The knee bursae are the fluid-filled sacs and synovial pockets that surround and sometimes communicate with the knee joint cavity.

The bursae are thin-walled, and filled with synovial fluid.

They represent the weak point of the joint, but also provide enlargements to the joint space.

[1] They can be grouped into either communicating and non-communicating bursae or, after their location – frontal, lateral, or medial.

In front, there are five bursae: Laterally there are four bursae:[2] Medially, there are five bursae: