Anatomy of a Knee
The knee joint is comprised of three bones: the femur (thigh bone), the patella (knee cap), and the tibia (shin bone). It can be divided into the medial compartment, the side of your knee that is closest to the center of your body; the lateral compartment, the side of your knee to the outside of your body; and the patellofemoral compartment, which is the area behind the knee cap.
The end of each of these bones is covered with a layer of smooth, glossy, elastic tissue known as articular cartilage. Cartilage protects the bones while allowing the joint to glide smoothly. It also acts as a shock absorber. Cartilage has no nerve or blood supply. If damaged or injured, it may be difficult for it to heal or repair itself.