In
human anatomy, the
meniscus is a
crescent-shaped piece of
cartilage forming part of the
knee joint. Each knee actually has two menisci: the
medial meniscus, which sits on top of the
tibia on the side of the
leg which faces the other leg, and the
lateral meniscus, which sits on top of that tibia on the outer side of the leg. The menisci form two little cups that the
condyles of the
femur sit in, and perform the function of cushioning the joint.
It is possible to have a knee injury in which one or the other (or both, I guess) menisci are torn and possibly displaced. This is very painful, I kid you not. If part of the cartilage ends up in the wrong place inside the knee joint as a result of this tear, the leg may not straighten completely, and can get locked in a particular position. Did I mention the pain?
Treatment for a torn meniscus sometimes involves simply removing the torn bit (a meniscectomy) but can also involve surgical repair, in which the torn parts are stitched down in place with sutures or with some cute little bioabsorbable arrows that are shot out of a dispenser. The larger the torn fragment, the more likely a surgeon will attempt a repair. Knee joints with cartilage removed don't work very well or last very long.
YMMV, as IANAD.