Effect of elliptical deformation of the acetabulum on the stress distribution in the components of hip resurfacing surgery

Hip resurfacing surgery is a matter of controversy. Some authors present very good late results of 99% survival outcomes. However, national records of implants point to the series of complications connected with biomechanical flaws of the implant. These results implicate the experimental research on biomechanical properties of HRS. The aim of the research was to define the nature of cooperation between the components of hip resurfacing surgery (HRS) and the influence of the deformation of acetabulum, the size of the implant and the nature of the bone surface on the stress distribution in the acetabulum and the femoral component. The calculations were run with the use of the finite element method (FEM), using the ANSYS bundle for this purpose. Four decrete models of the studied system were made: a model with the elements of the system connected with glue, a perfect spherical model with cooperating surfaces, a model reflecting an elliptical deformation of the acetabulum, and a model with different sizes of the implant. The results indicate that the stress values obtained for models with the ideally spherical acetabulum cannot cause significant deformation of cooperating implants. In the case of loads of the elliptically deformed acetabulum significant point stress concentrations can be observed in the spots of joint. The size of the acetabular and femoral components of HRS has influence on the stress concentration on the internal surface of the acetabulum as well as in the bone tissue surrounding the madrel of the femoral component. Moreover, physical properties of the base surface surrounding the HRS components have influence on the size of stress in the acetabulum and the femoral component.