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Primary implant stability

There are several different designs of endoprostheses. They may be categorized into cemented and non-cemented systems. By cementing the stem of the femoral component, the space between the prosthesis and the internal surface of the bone is completely filled. This kind of interlocking is said to have a form fit connection. However, cementing makes a stem revision much more difficult than revision of non-cemented systems; also bony defects may be more extensive. Usually, non-cemented stems do not offer an almost perfect form fit immediately after implantation. Rather, the mechanical contact occurs at discrete areas in the contacting surfaces (press fit). Only when the bone grows into the surface of the implant can secondary stability be achieved. Therefore primary stability is of paramount importance to allow secondary stability to occur.

With the measurement system shown here, different load scenarios can be applied. Using inductive sensors (resolution 0.1 Ám) the 3-dimensional motions of the implant and the bone can be measured. Thus the quality and degree of frictional connection of non-cemented prostheses can be characterized.

The standardized methods enable comparison of different implants due to their characteristic of implant fixation pattern. Apart from a large number of prostheses with normal stem length, short, revision as well as tumor stems have been characterized in a defined model of femoral defects. Not only the characterization of prostheses already on the market but also the characterization of prototypes influence the development of new products.

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