A total hip replacement (THR) - also called a hip arthroplasty- is a surgical procedure that re-forms the hip joint. In THR, the head of the femur (the bone that extends from the hip to the knee) is removed along with the surface layer of the socket in the pelvis (the two large bones that rest on the lower limbs and support the spinal column).

• The head of the femur, which is situated within the pelvis socket, is replaced with a metal ball and stem. This stem fits into the shaft of the femur.
• The socket is replaced with a plastic or a metal and plastic cup.

For nearly a century, doctors have been putting various materials into diseased and painful hip joints to relieve pain. Up until the 1960s, outcomes had been unreliable. At that time, the metal ball and plastic socket for the replacement of the hip joint was introduced. Today, the artificial components used in THR are stronger and more designs are available.

There are many different shapes, sizes, and designs of artificial components of the hip joint. For the most part these are composed of chrome, cobalt, titanium, or ceramic materials. Some surgeons are also using custom-made components to improve the fit in the femur.

The hip is a ball-and-socket joint comprised of the following structures:

• Head of the femur
• Acetabulum of the Pelvis
• Ligaments of the hip joint

The head of the femur or "ball" of the hip joint articulates or moves within the cup-like "socket" called the acetabulum of the pelvic bone. Together, these structures are referred to as a "ball and socket" joint. The femoral head and acetabulum are covered by a specialized surface called articular cartilage . This allows smooth and painless motion of the hip joint.

Several strong ligaments help hold the head of the femur within the acetabulum. They are named according to their attachments: