What is a joint and what is joint replacement surgery?

The ends of two bones, connected together by ligament tissues, form a joint. For example, your hip is a ball and socket joint, formed by the upper end of the femur or thigh bone (the ball) and a part of the pelvis called the acetabulum (the socket). Your knee joint is formed by the tibia or shin bone and the femur. Joint replacement is used to treat painful, arthritic knees, hips, and shoulders; an arthritic joint is prepared by removing worn and damaged joint surfaces and replacing or resurfacing the joint surfaces with a metal and plastic artificial joint.