The meniscus is a pad of cartilage between the two bones that form the knee. There are actually two menisci in the knee: one on the inside (medial) and one on the outside (lateral).
The menisci act as a support for the knee and bear the load of the weight on the joint. They serve as the contact area between the thigh and leg bones, helping to distribute pressure within the knee joint.
Without the meniscus, there is an immediate increase in joint contact pressure. This change in the distribution of pressure causes changes in the knee joint. The bones become flatter, and the joint space gets smaller. If enough of the meniscus is removed, further changes in the joint can occur with a less favorable outcome.