An introduction to hip replacements

There are two main parts to a total hip replacement implant. The femoral component fits into the top of the femur and replaces the ball of the ball-and-socket joint. The acetabular cup sits in the pelvis and replaces the socket. This is shown in the diagram and micrographs below.

Diagram and radiograph of a hip replacement

Diagram and radiograph of a hip replacement

The femoral component is fitted by inserting it into the shaft of the femur, which is prepared by hollowing out a section to fit the stem of the implant. The femoral stem essentially replaces bone in the femur and has a structural role that requires it to match, as closely as possible, the strength and toughness of the natural bone.

The requirements for the femoral head component are that it must have a very particular shape, which fits exactly within the replacement socket, and the surface should have a low coefficient of friction.

The acetabular cup component sits in the hip socket and replaces the worn cartilage. Therefore, this part must itself have a low wear rate and must also minimise wear of the femoral head component.

It is therefore likely that these three components will be made from different materials and choosing materials with the correct properties is very important.