Metal on Metal Bearings: Better or Worse?


Interesting questions posted by the Dept. of Medical Engineering and Physics at the Royal Perth Hospital in Australia. Notice how they specifically cite the Depuy ASR Hip as an example of problems with the bearings.  Even more interesting, the bulletin was published in March 2010- 5 months BEFORE the official Depuy ASR Hip Implant recall.   

Metal on Metal Bearings:  How Effective?
March 2010
The increase in use of metal-on-metal (MoM) bearings over the past 5 years has been
dramatic. The claimed advantages of low wear and reduced dislocation risk should be balanced
against increased metal ion release and generation of fine metal wear particles. The
Australian Joint Registry (2009) identified MoM bearings, in particular ASR (DePuy) and
Durom (Zimmer) resurfacings, as having higher than average revision rates. In 2008, the FDA
issued a recall on Durom cups because of unacceptable loosening rates. Durom and ASR MoM bearings sent for analysis, show high rates of loosening (41%), extensive wear markings on the articular surfaces, and fine corrosion pitting near the rim of the heads. All components are Co-Cr-Mo alloy but differ in composition and manufacturing (cast or forged). Some of the microstructures revealed carbide precipitation at the grain boundaries – features that can affect wear and mechanical performance. Some questions remain:
• What is the cause of fine corrosion pitting on the bearing surfaces despite excellent
in vitro corrosion resistance?
• What is the relationship between metal hypersensitivity, osteolysis and implant
failure (loosening, infection)?
• Is there a correlation with increased reporting of pseudotumours or ALVAL with
usage of MoM bearings?

This is the link to the 2010 Bioengineering Bulletin PDF.

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