gms | German Medical Science

In total hip arthroplasty (THA) "impingement" is the unfavorable collision of the implant components resulting in liner damage and shear stresses in the acetabular implant/bone interface. The overall goal of this project is to predict the stability of the interface in individual cases of bone defects. This could help surgeons to make confident choices for the best suitable revision implants in difficult cases. The presented work documents an application of the finite element method (FEM) to analyse the shear stress distribution in a fully bonded implant/bone interface.

Using the FEM software ANSYS a finite element model of the femoral and acetabular components and the surrounding acetabular bone was generated. The model is represented by 143,000 equations incorporating non-linear material definition and sliding contact. The model resembles the configuration of a dislocation testing assembly from a preliminary study for validation purpose. After loading with the resultant joint force the model is displacement controlled in a second load case. A typical analysis runs 23 CPU hours.

The model was validated against test data. The distribution of shear stresses was contour plotted over the interface. It was interesting to find unexpectedly high shear stresses in the equatorial direction.

The maximum shear stress compares well with the literature. The pattern of equatorial shear stresses suggests an unsymmetrical lever-out mechanism. Its mechanics could be comprehensibly described through investigating the three-dimensional momentum equilibrium. In future work the validity of modelling without contact definition will be investigated to reduce CPU hours.