Volumetric wear assessment of retrieved metal-on-metal hip prostheses and the impact of measurement uncertainty

In hip replacement the use of hard bearing materials, which have been shown to have lower wear rates than traditional metal-UHMWPE couples, has been encouraged in an effort to extend component life-in-service. With a view to further extending this period of joint activity metal-on-metal hip resurfacings have been developed which allow for implantation into younger and more active patients. However, these bearings have recently been the subject of a MHRA device alert due to unexplained hip pain and reported soft tissue reactions and indeed are under investigation having been shown to exhibit high failure rates. This has highlighted the need for a traceable metrological approach to the quantification and characterization of in vivo wear as currently there is no standard dedicated to the measurement of such wear.