Finite Element Investigation of the Effects of the Cup Orientation on Implant Load-bearing in Total Hip Resurfacing

Metal-On-Metal hip resurfacing technique is becoming widely accepted as a viable alternative to other forms of total hip replacements. The technique has many proven benefits in terms of ease of the surgical operation, operation outcome and subsequent revisions. However, recent reports suggest that there is an effect caused by the different femoral implant and acetabular cup relative orientations on the release of debris into the blood stream. These reports suggest that an “optimum” orientation needs to be sought. The search for an “optimum” position to reduce wear of the metallic components has been explored clinically and experimentally, however, there are no reports to explain the mechanical mechanisms behind an “optimum” position or lack thereof. In this paper, a finite element analysis (FEA) was conducted to investigate the effect of the acetabular cup orientation on the implant behavior under weight-bearing load. The FEA model incorporates all the components of the Birmingham Hip Resurfacing implant along with the bone tissue. A wide range of anteversion and inclination angles were investigated and the effect of these orientations on the contact and von Mises stresses in the implant for a one-legged stance position was studied. The results of this study suggest that, in the onelegged stance loading configuration, the optimum ranges for inclination and anteversion angles associated with the least contact stresses between the femoral component and cup of the implant are 50 to150 and 400 to 450 respectively. These findings agree with the reported clinical and experimental results and add insight on the mechanical drivers behind the optimum orientation.