Osteoarthritis results from the deterioration of cartilage in joints. Cartilage is the tough material that covers the ends of bones, providing a smooth gliding surface. In the knee joint, where the thigh bone (femur) meets the shinbone (tibia), there are three places where bones make contact. One of them is on the inside (nearest the opposite knee, referred to as medial) and one is on the outside (farthest from the opposite knee, referred to as lateral). The kneecap (patella) is the third point of contact.