The wear of hip replacements can be dependent on serum protein levels and the swing-phase load during the gait cycle. We hypothesise that these effects may be associated with changes in the lubrication and friction of the joint. The aim of this study was to assess the effect of the lubrication regime and lubricant on the friction of metal-on-metal (MOM) and ceramic-on-ceramic (COC) THRs. Increasing the swing-phase load led to decreased fluid film thickness and an increase in friction, in both MOM and COC bearings. Increasing the protein concentration of the lubricant, decreased the friction of MOM THRs. Friction testing of COC bearings demonstrated an increase in friction as the protein concentration increased. The change in lubricating film thickness explains differences in friction and wear as the swing-phase load is changed for a given lubricant. However, when we change the lubricant composition, protein boundary lubrication effects dominate, this influences friction and wear differently in MOM and COC THRs.

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