Monday, January 23, 2012

Wear debris dialog based not on the articulating surface between the ball and cup but rather the Trunion/stem

I just thought this interchange on one of the posts was interesting so thought I would post it as some don't go back and read old posts.

I received an article on Trunion ware from someone who sent in an  unpublished paper.  Here is a brief summary of what I got from the paper which I suppose will be published at some point.

As a background to this post:

Last week I was speaking with the hospital Path department who are responding to requests to have the explants sent for examination. When I asked what parts she had of my explant, I expected her to say:

  • Ball
  • Acetablum
  • Taper/Stem/trunion (I think these are all the same.)
She left out the Taper/Stem. I was kind a curious as to why that didn't get replaced when the MRI had shown some issues with the tissue surrounding the stem. I have to ask my surgeon when I see him. The lady in the path lab said quite a few of the explants did have the stem/taper removed so of course I was curious about that comment as well.

Results from the Tunion study:

Paper can be found here (note/no author and no publication so I am not sure of the origin of this paper.  One of the readers sent it to me.)  http://www.jbjs.org.uk/media/55176/27749-resub.pdf

 have had a chance to read it now. Seems consistent with the comments on other papers re the wear debris generated from the trunion/taper/stem.

the key things I got out of this paper:

after reviewing 111 of the component hips, the tapers/stem/trunion from 3 manufactures (Dupuy, Smith and Nephew and Zimmer) findings follow  :

-showed that 102 of the 111 stems showed signs of corrosion.
-corrosion did not influence the levels of Co or Cr in the blood (interesting)
-seems that the study claims this was the first study to quantify the severity of the MOM THR devices
-claims also that this was the largest analysis of retrieved ASR MOM hips performed to date.
-their hypothesis was that the ASSR device would demonstrate more corrosion than the other two hips given its recall I guess. This was not the case however according to this unpublished paper.

Most important point was that the paper overall supported the view that the head-trunnion junction is a significant source of material loss and thus may be a contributor towards the accumulation of the metal ions in the blood.

All very interesting.

Connie

3 comments:

  1. Hi Connie, I've been thinking about this article since I sent it for reference. It seems the larger diamer heads show a slightly higher rate of issues with the trunnion corrosion issue. Of interest, have you seen any theories about galvanic corrosion between the Co/Cr and the titanium alloy used for the stem. I'm thinking the synovial fluid would make a great electolyte and set up an accelerated corrosive environment. It might be interesting to see if any other readers have seen or had any thoughts. I wonder why we haven't heard much about the trunnion issue sooner. I know there are many people that have not responded well after revision so the Co/Cr release from bearing wear, once the ASR cup and ball have been removed, should have given a positive result but hasn't always. Any thoughts?

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    Replies
    1. Oh and I did forget the concept that the paper specifically highlighed the corrosion in large diameter MOM implants.

      Thanks for pointing that out!

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  2. I have a similar question: Why was this issue not raised as a replacement part or possiblity during the revsion? I raised it because I had been sent the information.

    The issue has been raised since the mid 90's as your bibliography shows in the medical literature and I know many research guys talk about it in thier lectures.

    I am afraid electrolyte discussions are a bit over my head so I can't comment on that. By chance did you see that big finding published in Science in the Dec 23rd issue? That was pretty interesting about the Carbon: MOM implants generate substance similar to industrial lubricant: graphite carbon? I did a post on that a few weeks ago. just type in graphite carbon in the search box. Sure you'll find it.

    In terms of your question about the Co/Cr and the titanimum alloy comparitives, I would refer you to a study that was published in the journal of Biomechnics in 2011 which is not contained in your bibliography for some reason. Hope this helps.

    xxxx

    J Biomech. 2011 Jun 3;44(9):1747-51. Epub 2011 Apr 30.

    Influence of material coupling and assembly condition on the magnitude of micromotion at the stem-neck interface of a modular hip endoprosthesis.

    Jauch SY, Huber G, Hoenig E, Baxmann M, Grupp TM, Morlock MM.


    Source

    Biomechanics Section, TUHH Hamburg University of Technology, Denickestr 15, 21073 Hamburg, Germany. sabrina.jauch@tuhh.de


    Abstract

    Hip prostheses with a modular neck exhibit, compared to monobloc prostheses, an additional interface which bears the risk of fretting as well as corrosion. Failures at the neck adapter of modular prostheses have been observed for a number of different designs. It has been speculated that micromotions at the stem-neck interface were responsible for these implant failures. The purpose of this study was to investigate the influence of material combinations and assembly conditions on the magnitude of micromotions at the stem-neck interface during cyclic loading. Modular (n = 24) and monobloc (n = 3) hip prostheses of a similar design (Metha, Aesculap AG, Tuttlingen, Germany) were subjected to mechanical testing according to ISO 7206-4 (F(min) = 230N, F(max) = 2300N, f = 1Hz, n = 10,000 cycles). The neck adapters (Ti-6Al-4V or Co-Cr29-Mo alloy) were assembled with a clean or contaminated interface. The micromotion between stem and neck adapter was calculated at five reference points based on the measurements of the three eddy current sensors. The largest micromotions were observed at the lateral edge of the stem-neck taper connection, which is in accordance with the crack location of clinically failed prostheses. Titanium neck adapters showed significantly larger micromotions than cobalt-chromium neck adapters (p = 0.005). Contaminated interfaces also exhibited significantly larger micromotions (p < 0.001). Since excessive micromotions at the stem-neck interface might be involved in the process of implant failure, special care should be taken to clean the interface prior to assembly and titanium neck adapters with titanium stems should generally be used with caution.

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