Tuesday, March 20, 2012

Wear Analysis report for explanted hip (connie's hip.) part 2 of 2.

This a continuation of the post yesterday on my hip explant: http://www.mydepuyhiprecall.com/2012/03/wear-analysis-report-for-explanted-hip.html

I wanted to address the source of the baseline data for the statements made re the amount of metals which were deposited in my body as a result of the depuy metal on metal hip wear over 5 years.  Yesterday I addressed the test results.  Today,  I will look at the methods.

In order to determine if I had a "heavily worn" explant, something had to be used as a base comparable  data to draw that conclusion.  The group in England whom I posted about previously  wrote the first peer reviewed paper for validating the results of the assessment of volumetric wear of retrieved metal on metal hip components: http://www.mydepuyhiprecall.com/2012/03/three-video-interviews-of-triumvirate.html  

This paper  was: "Volumetric wear assessment of failed meal-on-metal hip resurfacing prostheses by Lord, Langton, Nargol and Joyce.   Systems of mechanical and systems engineering at Newcastle University in Newcastle upon Tyne in England.  Published in WEAR 2011.

There are only a handful of studies offering ex vivo studies (measurement outside the body).  the bottom line is that you need a high precision coordinate measuring machine with very high precision in order to draw any reliable "wear" conclusions.  Further, you need to be able to verify the accuracy of these readings.  Most of the prior methodologies delivered results which varied from 55% to 10% error rates.This methodology described below in the abstract resulted in wear rate validation to within .5mm3 for their measurements.

This paper provided a method for calculating volumetric wear of retrieved MoM resurfacing hip prostheses using a combination of co-ordinate measuring machine data and Matlab.  A validation study was included and the method was applied to 54 retrieved hip resurfacing components to assess in vivo wear. 

They used this approach on my hip not for resurfacing as resurfacing was not available through Depuy in the US but rather for measuring wear in an ASR depuy MoM hip.

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