The tribological behaviour of different clearance MOM hip joints with lubricants of physiological viscosities

Abstract

Clearance is one of the most influential parameters on the tribological performance of metal-on-metal (MOM) hip joints and its selection is a subject of considerable debate. The objective of this paper is to study the lubrication behaviour of different clearances for MOM hip joints within the range of human physiological and pathological fluid viscosities. The frictional torques developed by MOM hip joints with a 50 mm diameter were measured for both virgin surfaces and during a wear simulator test. Joints were manufactured with three different diametral clearances: 20, 100, and 200 microm. The fluid used for the friction measurements which contained different ratios of 25 percent newborn calf serum and carboxymethyl cellulose (CMC) with the obtained viscosities values ranging from 0.001 to 0.71 Pa s. The obtained results indicate that the frictional torque for the 20 microm clearance joint remains high over the whole range of the viscosity values. The frictional torque of the 100 microm clearance joint was low for the very low viscosity (0.001 Pa s) lubricant, but increased with increasing viscosity value. The frictional torque of the 200 microm clearance joint was high at very low viscosity levels, however, it reduced with increasing viscosity. It is concluded that a smaller clearance level can enhance the formation of an elastohydrodynamic lubrication (EHL) film, but this is at the cost of preventing fluid recovery between the bearing surfaces during the unloaded phase of walking. Larger clearance bearings allow a better recovery of lubricant during the unloaded phase, which is necessary for higher viscosity lubricants. The selection of the clearance value should therefore consider both the formation of the EHL film and the fluid recovery as a function of the physiological viscosity in order to get an optimal tribological performance for MOM hip joints. The application of either 25 per cent bovine serum or water in existing in vitro tribological study should also be revised to consider the relevance of clinic synovial fluid viscosities and to avoid possible misleading results.

The Performance of Mixed Manufacturer Metal On Metal Total Hip Replacements

“…This difference can be explained in part by the lower clearance (40µm less) of the Adept joints ( Table 4). The Adept clearance is high enough to overcome any fears around deformation during insertion [35] and high friction due to lubricant starvation [36], but low enough to reduce the volume lost as a result of the running in wear associated with higher clearance joints [17,37].…”

Development of a Synthetic Synovial Fluid for Tribological Testing

“…There are many different approaches to mimic the synovial fluid, most of them based on HA [25,28,35,38,39], carboxy methyl cellulose [40][41][42], polyvinylpyrrolidone [43] or polysaccharides (sodium alginate and gellan gum) [44,45] together a with single type of protein or with proteins from bovine serum. With these substances, the viscosity could be increased to values similar as in the synovial fluid [35,39,41,[43][44][45].…”

Retrieval Analysis And Principal Variable Analysis Of 127 M2a-38 Mm™ Metal On Metal Hip Replacements

“…The cohort of M2a-38mm™ components reviewed in this study showed no evidence of equatorial contact and the high wall thickness of the acetabular cups likely precluded this as a factor. Hu et al (22) also expressed concern about the lubricant starvation of low clearance bearings if the synovial fluid viscosity were higher than that of the 25% bovine serum used in simulator studies. While this could have been an issue, it is not present in the results for the NW group.…”