Study worthy of comments, questions and debate!

[Harrison]

Slack posted a very interesting abstract of a study in the Article Library:

Biomechanical Effect Constraint Lumbar TDR (FEA): :Spine May 20 2009

Please read it carefully! He bolded certain parts of the conclusion for a reason. I am ranting a bit as no one has commented yet.

Here's why: if this study remains uncontested, and valid, it may have significant ramifications for us patients...if not already. As well, these design differences may matter more in lumbar implants, where stresses are more pronounced than the cervical spine. If patients have arthritic or diseased facets, all the more reason for concern. Just my opinion, and that's all.

PS: We've discussed this many times. Use the search utility to find more subjects; e.g. search using charite and prodisc (or pro disc) in the topic title.

[Harrison]

^ for comments...

[jchebert1979]

I guess the question to ask with this study whether you agree or disagree with it is, are the results reproducable?

Also I would have to ask what are the results of increased loading to the surrounding bones and ligaments. How much until the load becomes unbearable and causes symptoms and what are those symptoms? Just because there is an increased load does not mean that it WILL cause damage. It may or may not and that needs to be established before drawing any conclusions.

Also I'm not sure if the conclusion is paraphrased or not, but I really hate to read any source of information where loaded words are used.

For example the phrase "By the result of this study it is obvious that implanted...." is loaded. The same point could have been reached by saying "The results show that....". By pointing out to me that the results are obvious it shifts the focus from the actual results to the fact that they are unquestionable.

[Harrison]

J, you raise a good point. While these "obvious" differences in artificial disc designs are easily identified by these study researchers, their findings may not be so obvious to the very people that have received the artificial disc implants! When one is not performing this R & D stuff for work every day...it is most definitely not obvious. The main point I am focusing on here is the crucial differences between artificial disc designs.

I think the competition between academic institutions, device companies and docs will continue to frustate us with conflicting findings for some time...but it will not last forever. This, I am sure.

[daveinaustin]

There was no quantitative analysis in the conclusion. As previously mentioned, "By the result of this study it is obvious that implanted segment with AD has large range of motion and suffers from increased loading to surrounding bone and ligaments" is much too subjective, and shows the bias that the authors had before even starting their research.

Increased loading over various axial positions is critical. There needs to be substantive, quantitative analysis showing a significant, increased load over specific, various axial positions to warrant any purpose for this study. Measuring stress and strain over two dimensions is simple. However, they need to demonstrate and quantify over three dimensions. Even then, there is a huge difference on the strain and loading caused from either static or dynamic motion from each axial motion. Once a body is in a static position, the reflex arc causes a rapid trigger between flexors and extenders, which need to be taken into consideration, and can reduce the impact of the load.

Bottom line. I'd expect more. The conclusion demonstrated a lack of any scientific principal to warrant further discussion.

Sorry, I sound rather harsh. It's probably a good thing I didn't become a professor after all. My graduate students would have had their work cut out for them before I'd pass any thesis or dissertation!

[annapurna]

This was a FEA, finite element analysis, of the spine. The results of such an analysis are always reproducible; it's whether or not the assumptions used to create the model are realistic, that is the primary concern. Also, FEA always produces a quantifiable answer; interpretation of that answer is typically the subject of hours of arguments, depending upon the criticality of the result and the number of hours available in which to argue before the final answer is due. As for the language, I'd strongly suspect that we're suffering from the English as a second language problem as I've seen the same problem at work numerous times.

Bottom line, the abstract doesn't give enough information to cause you to believe or disbelieve this paper and it will take expert analysis to decide if the assumptions they made in making their models were accurate or bogus.

[daveinaustin]

> As for the language, I'd strongly suspect that we're suffering from the English as a second language problem as I've seen the same problem at work numerous times.

Agreed, there could be a translation issue. Hence, it is critical for research study abstracts to be based on brief, quantitative data rather than qualitative wording.

I have a personal rant in which it appears (to me) that over the past 20 years, more research studies has moved away from the basics. Language interpretation has always been a barrier in research. Ok. I'll admit it. I'm getting older and a bit grumpier!

Just my $0.02.

-Dave