Thursday, December 15, 2011

Clarifications on the question: Does the MDL protocol for examining the explants adequately address the key questions?

Well, in short, I still don't know exactly.  Remember, the key question we have as patients is:  tell me how much of this metal has gone into our body.  Part two of this question can be addressed later...( what is the implication of the MoM levels for the last 5 years and what are the long term systemic effects?)

Most of the CMM machines are used to measure a dimension, the distance between two points in space.  This is how  the CMM specified in the MDL (multi district litigation) protocol is to be give the spherical diameter of the femoral head and the spherical diameter of the acetabular cup.  Where is the volume of wear though?

It is now possible with the newer machines to measure many thousands of points accurately so you can take the CMMs dimensional measurements and convert these to a volume.  The first publication related to the ware measurement of these hips was back in 1996..some 15 years ago.  Essentially we are back to the following conclusion from my sources:

*   Need to know how much metal has been removed from the articulating surfaces of the acetabular cup and femoral head of an explanted ASR - this will be a quantitative measurement rather than a qualitative assessment as inferred by the MDL protocol.  Also, the MDL protocol suggests that "wear" can be inferred from scratching.  Scratching is associated with surface topography and not necessarily with wear (loss of material.)

 *   Need to know how much damage has occurred to the taper junction between femoral head and femoral stem and they can use the  CMM to give a wear depth AND wear Volumes not just depth.

I will be interested in seeing how this explant endeavor turns out.


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