The effect of modular tapered fluted stems on proximal stress shielding in the human femur.

The purpose of this study was to show a change in proximal femur surface strains following total hip arthroplasty and after the addition of BoneSource hydroxyapatite bone cement in the proximal region of an instrumented femur and to measure the surface strain on the proximal body. Seven third-generation composite femurs (Pacific Research Laboratories, Vashon, Wash) were instrumented with 12 uniaxial strain gages, 6 gages on the anterior face, and 6 gages on the posterior face of each femur. All femurs exhibited stress shielding since the strains in the proximal region were drastically reduced. There was a large decrease in strain in the mid-shaft region and small changes in strain in the distal region. The surface strains on the modular implant were relatively low.