The effect of diametral clearance, motion and loading cycles upon lubrication of metal-on-metal total hip replacements

Abstract

A study of surface contact and separation of 36mm diameter metal-on-metal joints was undertaken in 25 per cent bovine serum using a hip simulator. A range of diametral clearances from 130 to 170 μm was tested and each joint was subjected to two different dynamic motion and loading walking cycles. One simulation used physiological motion and loading cycles as described by Paul [I], while the other used simplified motion cycles, as described by Barbour et al. [2], and simplified loading. An electrical resistivity technique was used to detect the extent of surface separation throughout a complete walking cycle. The proportion of surface separation per cycle was generally greater in the simplified than in the physiological walking cycle. The latter cycle thus appears to present a more severe condition than the simplified cycle as far as joint lubrication is concerned. No surface separation was observed, for either cycle, with the largest diametral clearance of 170 μm. All of the remaining joints, with smaller diametral clearances, showed surface separation for at least a portion of each walking cycle. The proportion of surface separation per simulated walking cycle generally increased as the diametral clearance decreased.