Experimental evaluation of new concepts in hip arthroplasty

Abstract

In this thesis we evaluated two different hip arthroplasty concepts trough in vitro studies andnumerical analyses.

The cortical strains in the femoral neck area were increased by 10 to 15 % after insertion of aresurfacing femoral component compared to values of the intact femur, shown in an in vitrostudy on human cadaver femurs. There is an increased risk for femoral neck fracture after hipresurfacing arthroplasty. An increase of 10 to 15 % in femoral neck strains is limited, andcannot alone explain these fractures. Together with patient specific and surgical factors,however, increased strain can contribute to increased risk of fracture.

An in vitro study showed that increasing the neck length in combination with retroversion orreduced neck shaft angle on a standard cementless femoral stem does not compromise thestability of the stem. The strain pattern in the proximal femur increased significantly at severalmeasuring sites when the version and length of neck were altered. However, the changes wereprobably too small to have clinical relevance.

In a validation study we have shown that a subject specific finite element analysis is able toperform reasonable predictions of strains and stress shielding after insertion of a femoral stemin human cadaver femurs. The usage of finite element models can be a valuable supplement to in vitro tests of femoral strain pattern around hip arthroplasty.

Finally, a patient case shows that bone resorption around an implant caused by stressshielding can in extreme cases lead to periprosthetic fracture.