Effect of head size on wear properties of metal-on-metal bearings of hip prostheses, and comparison with wear properties of metal-on-polyethylene bearings using hip simulator

• When metal insert diameter in metal-on-metal bearing was smaller than 44 mm, wear loss was reduced with increasing insert diameter.
• The increase in wear loss was observed for 48 mm insert by increasing in rotation moment.
• Decreasing tendency of contact pressure is calculated using the Hertzian equation conformed to change in wear loss.
• On the other hand, the wear loss for cross-linked ultrahigh-molecular-weight polyethylene insert and Co–Cr–Mo articular head was small.

The effects of articular head size on the wear losses of the metal insert and articular head for a metal-on-metal bearing were examined using a hip simulator manufactured to satisfy ISO 14242-1. The wear properties of metal-on-metal and metal-on-polyethylene bearings were also compared under the same conditions. The total wear losses of the metal insert and articular head decreased with increasing diameter of the metal insert in the range from 28 to 44 mm. The total wear loss was greater for a diameter of 48 mm than for a diameter of 44 mm. When the articular metal insert diameter was smaller than 44 mm, the wear loss was reduced because the contact surface pressure increased with increasing metal insert diameter. However, the increase in wear loss observed for the 48-mm-diameter insert might have been due to the considerable increase in the rotation moment with increasing insert diameter. The tendency of decreasing contact pressure calculated using the Hertzian contact stress equation nearly conformed to the change in wear loss. On the other hand, the wear loss of an artificial hip joint consisting of a cross-linked ultrahigh-molecular-weight polyethylene insert (UHMWPE) and a Co–Cr–Mo articular head was small.