Abstract
Introduction
Bearing surfaces used for total hip arthroplasty must have characteristics including bio-compatibility, low friction and low wear rate. Bearing combinations are generally characterised as Soft on Hard/Hard. In general, all newer bearing combinations have reduced wear but may present with other issues that impact on patient outcomes.
Materials
The Australian Orthopaedic Association – National Joint Replacement Registry classifies bearing surfaces into six categories. These are metal on polyethylene, ceramic on polyethylene, metal on metal, ceramic on ceramic, ceramic on metal and a sixth category relating to a small number of procedures where the bearing surface is yet to be classified. 147,422 conventional total hip arthroplasty procedures have been recorded by the Registry between 1 September 1999 and 31 December 2008 and analysis has been performed of the cumulative percentage revision in relation to bearing surface.
Results
In general, metal on polyethylene has the lowest risk of revision compared to all other bearing surfaces and metal on metal has the highest revision rate. The risk of revision, however, does vary depending on head size, with larger head sizes having a lower risk of revision with the exception of metal on metal.
Conclusion
When deciding which bearing surface is suitable for patients it must be emphasised that wear reduction is only one of several considerations when choosing the most appropriate combination.
