Abstract
Purpose of Study:
To look at the difference in metal ion levels using Ceramic on Metal (COM) and Metal on Metal (MOM) bearings in Total Hip Replacements, comparing the results between well placed and poorly placed cups.
Methods:
Metal ion levels using the ICP-MS method of assay have been studied as part of a prospective randomised trial between 4 different bearing combinations. The ion levels have been raised in the COM and MOM bearings. Metal ions are not raised in the Ceramic on Ceramic (COC) and Ceramic on X linked Poly(COP) bearings, showing that no other material in the study prosthesis aside from the bearing surfaces contribute to raised ion levels. Cup inclination and cup anteversion has been measured in all patients.
Results:
At 3 year follow-up the Cobalt and Chrome levels are significantly lower with the COM bearing than the MOM bearing when both well and poorly placed cups are included, and seem to be returning to normal pre-operative levels. Taking cups put in in Lewinnik's safe zones, then the Chrome levels are similar between the two bearings, but the Cobalt levels remain raised in the MOM bearing.
Conclusion:
Cobalt and Chrome levels are significantly lower in COM bearings than MOM bearings when cups are not placed in the ideal position. This represents an added advantage in the use of COM bearings as compared to MOM bearings.
