Wear and lubrication of metal-metal bearings for total hip arthroplasty.

摘要

A major current concern in total hip arthroplasty is the generation of polyethylene wear particles at the articulating surfaces and resulting macrophage-mediated, periimplant osteolysis. There has been revived interest in metal-metal bearings for hip implants because of their potential for improved wear performance. Cobalt chromium molybdenum metal-metal hip implants of two materials (alloy types) and two carbon content levels were custom-manufactured and tested in a hip simulator under various loading conditions. In general, accelerated wear occurred within the first million cycles of testing followed by a decrease in wear rate to low steady-state values. The volumetric wear at three million cycles was up to several orders of magnitude less than the wear of conventional metal-polyethylene hip implants. Increased head-cup clearance and surface roughness resulted in increased wear. Independent effects on wear of material and carbon content were not identified. The low wear may be related to fluid film lubrication at the bearing surfaces. A time-varying elastohydrodynamic lubrication model was developed to predict fluid film thickness for the experimental metal-metal hip implants during simulator testing. Decreased clearance, increased lubricant viscosity, and increased cycle frequency resulted in increased film thickness. A strong independent effect on film thickness of load magnitude was not found. The lambda ratio (of film thickness to combined surface roughness) was used to indicate the extent of fluid film lubrication. For the experimental implants, total wear decreased with increasing lambda ratio. These studies provided important new information on the design and testing parameters that control wear performance and lubrication of metal-metal bearings for hip implants.