Tuesday, December 13, 2011

Evaluating the Hip Explant: What are we searching for in an explant analysis? (part 2 of 2)

This post is about the question:  What is the bottom line we are looking for in examining the explants?

In the process of screening evaluation lab methodology for the purpose of understanding what happened to the hip implant, the following points have been raised  about the exam protocol which was attached as exhibit A in the explant preservation and examination order issued by the MDL:

(1) There is  no requirement to obtain  exact wear measurements on the implant which will tell the patient at the end, how much metal went into their body.


(2) co-ordinate measuring machines  specified in the MDL order give wear volumes  and out-of-roundness machines  give wear depths, however the procedure appears to ignore the use of such machines for wear measurements.

(3) Instead, the procedure suggests studying articulating surfaces of failed hips by eye, and evaluating them qualitatively to determine the damage to them. 
  • In reviewing the summary of the requested inspection and capabilities, this is what they are requesting in the order:
    • photography of components as received
    • photography of the decontaminated components
    • Macro and sterocommicroscopic exam of each component
      • general shape, staining etc
    • Metrology
      • using a coordinated measurement machine (CMM) to do surface profiling for measurement to engineering drawings
      • Surface finish measurement.
(4)  There is no dimensional measurements requested in the procedure for the taper adapter or for the taper of the hip stem.  It has been demonstrated  that a loss of metal from these junctions contributes to the higher failure rate seen with the ASR XL – recently announced as a 29% revision rate at 6 years in the 2011 National Joint Registry for England and Wales.  Such dimensional measurements would again help to quantify how much metal has been released from the taper and has gone into a patient’s body.

xxxxxxxx
  • I can see in this order that  there are suggested machines to use during this evaluation by the MDL/Depuy agreement but I do not see any where in the exhibit a srequest to report  how much metal went into the patient's body as a result of this hip wear.  Here is the equipment recommended for use though:
    • digital camera with certain specs
    • Optical steromicroscope
The optical microscope, often referred to as the "light microscope", is a type of microscope which uses visible light and a system of lenses to magnify images of small samples. Optical microscopes are the oldest design of microscope and were possibly designed in their present compound form in the 17th century. Basic optical microscopes can be very simple, although there are many complex designs which aim to improve resolution and sample contrast. Historically optical microscopes were easy to develop and are popular because they use visible light so the sample can be directly observed by eye. The stereo or dissecting microscope is an optical microscope variant designed for low magnification observation or a sample using incident light illumination rather than transillumination. It uses two separate optical paths with two objectives and two eyepieces to provide slightly different viewing angles to the left and right eyes. In this way it produces a three-dimensional visualization of the sample being examined.

    • Coordinate measurement machine
A coordinate measuring machine (CMM) is a device for measuring the physical geometrical characteristics of an object. This machine may be manually controlled by an operator or it may be computer controlled. Measurements are defined by a probe attached to the third moving axis of this machine. Probes may be mechanical, optical, laser, or white light, amongst others. 
They are often used for:
  • Dimensional measurement
  • Profile measurement
  • Angularity or orientation measurement
  • Depth mapping
  • Digitizing or imaging
  • Shaft measurement
    • contact profilometer
Profilometer is a measuring instrument used to measure a surface's profile, in order to quantify its roughness.

xxx

As you all know, I have no science training whatsoever. I am merely sharing information  and observations that I find in my investigation for my own case.  I agree with the observation that what I want to know from the "wear analysis" is how much metal has gone into my body.  If the current protocol recommended by the MDL doesn't provide that answer, that is a problem.

Apparently, there are a few labs in the world that have the equipment capable of rendering the measurement which results in the answer to the question:  how much metal has gone into the person's body.  The equipment required to do that is a high precision coordinate measuring machine coupled with customized software written to determine the ware volumes (exact measurements).

As I uncover additional information on this subject, I will let you know.  I have a few weeks off over the holiday and was planning on focusing on the DNA testing but I need to finish this exploration first.

No comments:

Post a Comment