Meniscus - functional anatomy

The two menisci differ in shape and mobility. Look at this photo of two real meniscus just before being used for transplant. The lateral meniscus (left of photo) is more O-shaped and quite highly mobile, able to slide forwards and backwards with knee movement. There is a tendon (popliteus tendon) passing along one edge, which breaks the attachment to the capsule of the joint, and this adds to the mobility.

The medial meniscus (right of photo) is quite different. It is larger and more C-shaped, and tightly bound to the capsular structures and to the medial collateral ligament along the outer rim. It moves very little with the movement of the knee. It is this inflexibility which leads to the medial meniscus being torn more frequently than the lateral meniscus. The lateral one can move and absorb impact, while the medial one simply rips.