Contact Mechanics Analysis and Initial Stability of Press-Fit Metal-on-Metal Hip Resurfacing Prostheses

To ensure potential long-term stability and survivorship for metal-on-metal hip resurfacing prostheses, implant migration would need to be minimised to encourage bone in-growth. This study uses the finite element method to investigate the effects of the surgical press-fit procedure on the bearing and interfacial contact mechanics, and on the initial stability of a metal-on-metal (MOM) hip resurfacing prosthesis. The finite element models simulated the press-fit procedure using different amounts of interference between the cup-bone (1–2mm). The resurfacing prosthesis was implanted anatomically into a 3-D bone model. Resultant hip joint loads were applied to the model through muscle and subtrochanteric forces. Results showed that increasing the friction and the interference between the cup and bone resulted in significant reductions in the relative micromotion between the cup and bone. This would ensure the immediate post-operative stability of the acetabular cup and provide adequate conditions for potential long-term bone in-growth and implant stability. The contact mechanics at the bearing surfaces, which has a large effect on tribological performance, was found to be little affected by changes at the cup-bone interface. These findings are consistent with the general satisfactory short and medium-term clinical results of metal-on-metal hip resurfacing prostheses. This study suggests that interference, friction and a mechanically sound bone structure are important parameters to promote implant stability and support.