due to the edge contact and the consequent failure of the fluid film
lubrication [3,16]. In the present study, an extreme inclination
angle of 70° was used. It was hypothesised that the high variation
in MoM wear is due to the fact that the conditions approach the
tribological endurance limit of the MoM device in question.
Regarding the tribological behaviour of prosthetic joints, the
endurance limit is defined here as a combination of (a) devicerelated
parameters such as diameter, clearance, sphericity of
bearing surfaces, and the arc of cup coverage, and (b) operation
conditions, such as load, inclination angle of cup and type of
relative motion. Above the limit the tribological behaviour of the
device is unacceptable, i.e., wear and friction will inevitably – not
only occasionally – be so high that serious damage to the patient
and early failure of the arthroplasty would result. Well below the
limit, the wear and its variation are low [1–3]. In the present study,
the limit was being approached with a combination of 2 kN peak
load and 70° inclination angle. Variation of wear was high. The
limit was clearly exceeded when the peak load was increased to
3 kN. This value simulated obesity [17]. Wear was high and linear
and its variation was low. In other words the tribological endurance
limit of the MoM device in question was exceeded under the
test conditions used.