How does an artificial hip joint work?

The design of hip endoprostheses is based on the human hip joint. Just like natural hip joints, it too comprises an acetabulum and a femoral head which is positioned on the stem of the prosthesis.

The artificial prosthesis components are made of different materials:

Today metal alloys are frequently used; titanium alloys in particular are popular due to their good tolerance and durability. In addition, prosthesis components made of ceramic and special plastic polymers are used which imitate the lubricative cartilage layer found in human joints. The surgeon will decide which materials to use depending on the patient's anatomy.

Depending on the disease and patient, the following different types of prostheses can be used: total endoprosthesis, partial endoprosthesis or a hip surface replacement.

Total endoprosthesis: in the majority of cases, the complete diseased hip joint is replaced. An artificial acetabular cup replaces the damaged acetabulum. The deformed femoral head together with the femoral neck are exchanged for an artificial femoral head which sits on the prosthesis stem. This is referred to as a total endoprosthesis.

Partial endoprosthesis: If the cartilage layer in the acetabulum is in good condition (for example after a femoral neck fracture), this does not need to be replaced. In such cases, only the femoral head and the femoral neck are replaced with an artificial femoral head on a prosthesis stem. Following the operation, the artificial femoral head sits in the natural acetabulum. This is referred to as partial endoprosthesis or hemi-endoprosthesis.

Hip surface replacement: with this method, only the damaged joint surface is replaced and lined with a metal spherical cup. The prosthesis thus comprises an artificial acetabular cup and a cup for the natural femoral head. Both components are made of metal and fit perfectly into each other. This is referred to as a cup prosthesis. This complex technique has only been around for a few years and to date only limited findings are available as to the longevity and tolerance of this type of prosthesis.