Biomedical and General Engineering Department
BS in Biomedical Engineering
Improper positioning of the acetabular cup has been shown to contribute to issues such as high wear rates and dislocations in total hip replacements. The differences in contact mechanics due to varying orientation of the acetabular cup may also significantly affect strain distribution in the femur. This study examined these effects of acetabular orientation changes and their contribution to stress shielding using finite element analysis. A solid model of a cementless total hip implant was obtained using 3D point scanning and implanted virtually into a femur solid model. The implanted femur model was imported into ABAQUS and loaded with a 1000 N force perpendicular to the surface of the femoral head in 13 orientations varying in inclination and anteversion. Strain values were taken from 6 locations along the proximal medial and lateral diaphysis of the femur. Analysis of these strain values found that strain decreased with increased inclination. Strain was also shown to increase and decrease on the lateral and medial side, respectively, for increasing anteversion. With an orientation change of 5.7º resulting in a strain difference of 30.9%, strain demonstrated sensitivity to orientation. From these results, it was concluded that acetabular cup orientation influences stress shielding which is determined by strain distribution. Therefore, greater emphasis is needed on obtaining the correct acetabular cup orientation during implantation surgery to prevent stress shielding effects and device failure.