Effect of increased load on the wear of a large diameter metal-on-metal modular hip prosthesis with a high inclination angle of the acetabular cup

• Large diameter metal-on-metal (MoM) hip prostheses have disappointed clinically.
• Hip simulator studies have shown unexplained variation in wear, causing uncertainty.
• High variation took place when the endurance limit of the MoM device was approached.
• When the limit was exceeded, wear was linear and high, and its variation was low.
• Below the limit under ‘normal’ test conditions, the wear and its variation were low.

In some earlier hip simulator studies of large-diameter metal-on-metal (MoM) hip prostheses high, unexplained variation in wear has been observed. In the present study it was found that high variation occurs when the tribological endurance limit of the MoM device in question is being approached. When the limit is exceeded, high wear takes place uniformly, and the variation is low. Below the limit, both the wear and its variation are low. The endurance limit was exceeded by increasing the peak load from 2 kN to 3 kN, to simulate obesity. The acetabular cup inclination angle was high, 70°. Potential clinical wear problems can be predicted by hip simulator studies provided that relevant adverse test conditions are included.