Direct evidence of lubrication in ceramic-on-ceramic total hip replacements

A study of surface contact and separation of ceramic-on-ceramic joints was undertaken in 25 per cent bovine serum using a hip simulator. An electrical resistivity technique was used to detect the extent of surface separation throughout a complete walking cycle. The femoral and acetabular components were coated in a thin conducting film of titanium nitride to allow applicat ion of the resistivity technique to non-conducting ceramic. Surface separation of the acetabular and femoral components was detected th roughout each simulated walking cycle. Fluctuations in the applied voltage across the joint were observed which could not be attributed to elastohydro dynamic or squeeze-film lubrication effects. The probable cause of the volt age fluctuations was brief and occasional contact between the surfaces caus ed by a combination of asperity contact and subsequent detachment of the co nductive coating.