Artificial hip joints commonly pair a metal ball and a plastic cup; however the problem of polyethylene wear debris has sparked renewed interest in metal-on-metal joints. For lubrication studies such joints can be modeled as spherical bearings. A finite element code has been developed to carry out modal elastohydrodynamic lubrication analysis of spherical bearings. An operating environment which accurately represents that seen in the human hip was determined. Lubricant film thicknesses were predicted and compared for different designs.
The lubrication analysis indicates elastohydrodynamic lubrication analysis may be necessary. It also suggests that manufacturing tolerances may be important for the success or failure of the metal-on-metal hip replacements.