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

A study of surface contact and separation of 36 mm 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 mum 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 B arbour et nl. [2], and simplified loading. An electrical resistivity techni que was used to detect the extent of surface separation throughout a comple te 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 diam etral clearance of 170 mum. All of the remaining joints, with smaller diame tral clearances, showed surface separation for at least a portion of each w alking cycle. The proportion of surface separation per simulated walking cy cle generally increased as the diametral clearance decreased.