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Three bones affect how your knee works: the thigh (femur), shin (tibia), and kneecap (patella). To ensure a secure fit, there are two C-shaped pieces of meniscus cartilage where the bones meet: one on the outer (lateral) half of the knee joint; the other on the inner (medial) half. This cartilage, along with fluid-filled sacks called bursae located at points of greatest friction, also helps absorb shock when you walk.
All of this is held together by ligaments attached at points of high stress. There are ligaments on the inside (medial) and outside (lateral) of the knee that provide stability during side-to-side motion. The cruciate (crossed) ligaments run through the joint between the cartilage and provide back-to-front and front-to-back stability.
When you move, a few large leg muscles also support your knee: the thigh muscles (quadriceps) cross the knee and attach to the top of the shinbone;
there are three hamstrings, one attaching to the outside
of the knee and the other
two to the inside; the calf muscle (gastrocnemius) attaches to the back of the thigh; and finally, a long thin muscle (gracilis) runs from your groin to the inside of your knee.
A band of tendons
(the iliotibial band) runs
from the muscles in your hindquarters (gluteals),
down your thigh, across the knee, and attaches to the outside of the shinbone. This also supports your knee.