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Hip Arthroplasty

Anchoring Concepts

The hip arthroplasty has improved within the last 20 years not only in the survival rates of the implants but also in the design of the implants. The previous changes of the hip prosthesis in the sixties were in the different forms of the implant without having any respect to the introduction of forces into the thigh bone (femur).

Nowadays the concept and philosophy of the implants is important due to the design of the implant can help to save bone. With an intelligent concept of the load transfer of the prosthesis into the femur it is possible to keep more bone healthy.

The ideal solution for this problem is given by the nature. All technical solutions are less ideal.

The current anchoring concepts are shown in the following graphics. Historically the hip implants were impacted into the distal part of the femur. This requires certain length and design (Fig. 1d). The distal part of the implant has to transfer all the loads into the femur with the effect that the upper part of the femur gets less strong. This weakness makes this solution not ideal because the primary implantations are revised statistically after 15 to 20 years. The second implant in the same hip needs also enough bone to be stable fixed in the thigh bone. Weak bones make the revisions in the hip joint not easy. Fig. 1b shows a shorter system that tries to be fixed in the upper part of the femur. Nevertheless the distal part of that systems generate similar situations as with long stems.

The hip resurfacing devices (Fig. 1a), that just replace the femoral head and leaves the femoral neck untouched. This is the most anatomical way to introduce the forces into the femur. But these hip resurfacing devices have meanwhile very high revision rates. This makes this concept not easy to survive in the markets.

Fig. 1b shows the force introduction with the most newest concept, so called short hip stems. These stems have the advantages that they can be implanted really less invasive due to they are just short. They keep the anatomical elasticity of the femur and they introduce the forces in the upper part of the femur. This makes this concept very attractive for young and active patients but also for the surgeons due to the possible revision after the service life time is easier and does not require real revision stems. The current standard implants with the normal length can be used to revise the short stems.