More modelling queries

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Can any one help with the following modelling question.
We are already attempting to explain and model ORF (Orthoses Reaction Forces) and some some work has been done on the mechanics of footwear.
However, has anyone done the 'coupling' effect of orthoses and footwear modifications.
For example, how can we model the combined effects of a 4 degree posted foot orthoses or medial skive etc with a medial flare and 4 degree post integrated into the sole unit of footwear.
I understand the math but how do we model the subjectives - fibro fatty pad displacement, shear of the foot on the orthotic, heel counter/heel interface, internal shear of the calc on the fibro fatty pad etc etc.
This is not purely an academic question, as if I wish to provide a supinatory moment to the rearfoot complex, how can I get the correct effect without over cooking it?
Both methods have there pro's and cons and I like to use a combination.

Any ideas greatfully accepted

Cheers

Phil

 

Hi Phil,

I would rather say that some work has been done on the mechanics of orthoses and much more about footwear. Just check the website http://www.uni-essen.de/~qpd800/FWISB/download.html

Regards,

 

To look at fat pad displacement, foot shear on orthosis, etc. together is a very complex model, not a simple model. And these values are not necessarily "subjective" but can be mathematically quantified just like other mechanical parameters can. The problem is getting the instrumentation and data to measure these variables so that a relatively accurate model may be created. Models of the heel fat pad have been done, but not to my knowledge regarding foot orthoses. Keith Rome has done some finite element modelling of the plantar heel fat pad, if my memory serves me correctly.

The models I created to describe the effects of the medial heel skive and Blake inverted orthosis are very basic and have not been validated, but certainly have stood the test of time as far as how they may work to enhance the pronation-controlling ability of the orthosis. Much more research is required. Modelling will become an increasingly more valuable research tool as more work is done in this field of trying to better understand the mechanical function of the foot and lower extremity.

 

Phil,

You indeed have a complex problem. I've thought a lot about this. Essentially you have to choose whether you want undertake the research to validate this very complex model. You have asked how much do these interventions change the moment at the STJ. A much simpler question is to see whether or not there is a change in moment from ground reactive force. There has been some work done in this area already. The nice thing about the tissue stress approach is that it tells you in which direction you should change the moment. You could just live with the idea that how much to push in that direction is an unknown and make changes based on the clinical response. This is what we have been doing for years. There is probably a wide range in the value of change in moment that would be in the therapeutic range. (Therapeutic range = enough to relieve symptoms, but not too much that it causes problems.) In most cases it should not be too hard to find a successful amount.

I can think of some situations where the therapeutic range would be very narrow. For example a person with sinus tarsi pain and a significant amount of tibial varum. A varus heel wedge will help the sinus tarsi pain, but may increase the varus moment at the knee and possibly increase knee pain.

Back to your original question. If you wanted to measure how much change there is in moment with a particular intervention, you could generate a value for how much change there was. Now, you have to know how much change will start to cause pathology in some other structure. There could be a huge variation in how much change in moment will cause pathology. Essentially, what you are getting into is predicting pathology. It will be a long time before we will be able to look at external forces and be able to predict pathology in an uninjured person. Knowing how much change in external force will cause pathology is way beyond that. I would not worry about trying to predict how much correction is too much, and just wait for it to happen and act accordingly.

Cheers,

Eric Fuller

 

Phil

No need for any more modeling research the answer is here at http://www.countrforce.com/archbrace.html. There's science too!

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I think I remember that Valerie from Blue Peter made one in 1969 from an old tea towel and the elastic from a pair of her mums old knickers (and some Sellotape).
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All the best Dave

 

I'm sure the big selling factor is it comes in BLACK or WHITE!!!!!!!
cheers hb

 

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At least this website doesn't claim that it cures infertility as does Brian Rothbart's website. At least this website doesn't have testimonials as does Ed Glaser's website. Which of these three websites is the least ethical?? Anyone care to vote?