The largest joint in the body, the knee is also one of the most complex. The knee may be described as a modified hinge joint, similar to the hinge on a door. However, the knee not only bends back and forth like a hinge, it has a complex rotational component that occurs with flexion and extension of the knee.

The knee is a major weight-bearing joint that is held together by muscles, ligaments, and other important soft tissue. Cartilage is the material inside the joint that provides shock absorption to the knee during weight-bearing activities such as walking or stair climbing. Below is an illustration of knee anatomy with its major bones, ligaments and muscles appropriately labeled. Bones The bones of the knee are the femur (thigh bone), tibia (shin bone) and patella (kneecap). The femur and tibia meet to form a hinge with the patella

Ligaments
Ligaments hold the knee together and give it stability. The medial (inner) collateral ligament (MCL) and outer (lateral) collateral ligament (LCL) limit sideways motion of the knee. The posterior and anterior cruciate ligaments (PCL and ACL) limit forward motion of the knee bones, keeping them stable.

Cartilage
Two structures known as menisci sit between the femur and the tibia and act as cushions or shock absorbers for the knee.