Foot Orthoses = matrix of wedges?

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A foot orthosis, whether custom or prefabricated, is a matrix of wedges. Do any of those wedges not exert a 'significant' force on the bones of the foot? Are there wedges in this matrix which are expendable? Yes English was my worst subject. Any thoughts, mark c.

 

Expendable? Probably, hence you can achieve positive clinical outcomes using "simple" flat insole bases with added rearfoot and/ or forefoot wedging.

Think also of the Rose Schwartz meniscus.

 

If a patient has symptoms, we need to change moments to reduce the force in the tissues that are painful. However you want to define a "foot orthoses", all they all do is apply a force to change the moments. .... its just that some types are more effective than others in different circumstances that others are.

Mark - good to see the boot camp got you thinking --- thats what its all about!

 

Simon,
I agree there are probably some expedable portions to the contour of a device. It got me thinking though. Do you need to have a matrix of wedges or could you have a series of "more flexible" or less rigid portions in your device.

I guess I am asking directly about your FEA modelling. Do you think one day there will be a school of thought where we don't invert/evert (or wedge in any form in any direction) anything on our devices but have a series of varying thicknesses along the orthotic device in order to achieve a preferred pathway?

Was good to see/meet everyone at PFOLA.
Cheers
Phil

 

Now I think about it, even if a foot orthoses is just a matrix of wedges, there is also the comfort issue of the wedges being incoporated into a contoured device.

 

Thoughts now i've finished the washing-up
- the term array would be more apt than matrix.
- 'Expendable' as in 'considered not worth having'.
- 'Rose Schwartz meniscus', not quite Simon but thanks.
- I appreciate the comfort issue; would met domes, 1st ray cutouts and heel skives also affect perceived comfort, as these are modifications to the contour (of the plantar foot shape)?
- As in-shoe pressure analysis shows different regions of the orthosis exert different magnitudes of force, therefore regions of the orthosis differ in import.
- Why i'm revisiting this topic is the poor intra and inter repeatability of casting; at least fixed components of known size/shape would eliminate this.
Now for bed, goodnight all (or at least the one or two who haven't assigned me to the 'IGNORE LIST' and peruse this post), Mark C

 

"You can't get there from here" REM

 

If we took a series of cubes of equal dimension but of varying stiffness and stuck them together in the shape of an insole we would effectively have a flat insole, not a matrix of inclined planes, that could be used to redirect CoP. However, once loaded the various cube elements would compress relative to the load applied and the cube stiffness something like:
deflection = force/ stiffness

Hence you would, under load, still have a series of inclined planes.

I think that both wedging and "smart shell design" will be used in combination.

 

...and the more I think about it....there are now two studies that have shown comfort on initial issue of orthotic is a predictor of outcomes ... so comfort of a contoured device is obviosuly of some importance.

(I will start a new thread on this another time, but one published orthoses outcome study showed, as a secondary outcome measure, that comfort was a predictor; another yet to be published study also showed the same thing ... will try to collate the info and post back another day)

 

BTW If CoP path is of "ultimate" significance it's should be relatively simple to create a "normal" CoP path using this concept.

 

At the Boot Camp, I moaned about all these others getting patents and trademarks. I am off to the patent office now to patent this:

:morning:

 

Simon,
What I mean is, FOR EXAMPLE, if a 'region', that being lateral to the assessed stj axis, contributes to the pronatory moments and in this patient a reduction in same should prove beneficial, then the corresponding region of the orthosis could be 'reduced' as it is of no importance in 'correcting' the moments about the stj axis.
REM? my ignorance extends to acronyms
thanks for the replies, mark c

 

Could this contribute to the mystifying 'success' of prefab's?

 

Any chance of a link to these studies??? I think from memory one of them at least was from Nigg's group at Calgary.... but I could be wrong.
On this topic I have to say that it is one area of our profession that frustrates me- the tendency to say to patients that 'you will get used to it ' if the orthosis is uncomfortable.
My experience is that few people who wince with discomfort when they first put on their orthoses have good outcomes... and those who still cannot wear their devices for more than a couple of hours after 6 weeks... um... I think there may be a problem.

 

My feeling would be that the devices do not work by being comfortable, but they don't work well unless they are...
Why do you say say prefabs are more comfortable??? Is that what you are saying?

 

Nigg spoke about it at SMA mtg in Adelaide last month --- I just have not got to have closer look at publication; the other one is from Bill Vicenzino at U of Q and is not close to being published, but I hope to get something quotable from him to start a thread.

 

Craig, hi, no what I was thinking of was the prefab's surprisingly 'good' results, in say Karl Landorf and Ann-Marie Keenan's study, and Craig Payne's team's findings.
I hypothesise that the smooth contours of the prefab's may contribute to their relative success, mark c

 

'spect someone will.

Mark- http://www.youtube.com/watch?v=eXscBQ9HHKE&feature=related

 

Absolutely. But the orthotic would need to hold the "unwanted" area of the foot off the ground or at least minimize GRF in this area. Really what we want is an orthoses which directs the CoP right?

If we took a flat insole and stuck a domed brass thumb tack in it this will create an area of high pressure which will draw the CoP toward it. If we could exert enough pressure we could possibly pull the CoP right onto it. Now insert a whole series of tacks of the right stiffness/ height to create enough pressure on the plantar surface of the foot to guide the CoP through the entire contact phase. This is what I was saying with my cube insole / smart shell. Trouble is you might have to push real hard- this might be real uncomfortable. Also the internal moment might be fighting against you. Patent pending.igs:

 

Craig

Sorry to burst your patent idea but I already have patent pending on this concept.
Don't want to give too much away but the device allows for different densities of inserts to be placed under the MLA and LLA along with conventional posting underneath.
The idea is based on modifying the COP within an insole but from a patients perspective it allows them to change the 'comfort' of the insole. Also the inserts allow the calcaneal angle to be modified - bit like the interpod but one shell can be modified rather than buying multiple orthos.
This has been done in many ways and there are lots of existing patents out there. The trick was to design something unique - it looks as though we have managed it.
Hope fully we should be in production early 2008.

Cheers

Phil

 

...oh damn! At least I won't have to worry any more about Simon coming and beating me up for stealing his idea :empathy:

 

Thanks Simon, gotya

 

netizens

:morning:Following this very interesting discussion I would add many specialty shoe design already capture these principles within their infrastructure of different polymers. Being Friday, I would have to say "the end is neigh for the humble foot orthoses."

igs:

toeslayer

 

If you really want to redirect CoP you have put those tacks pointy end up. I was going to patent that idea where you have a tack with an 1/8" long point pointy end up into 1/8" EVA in the medial arch on top of a plastic device. I ended up not patenting it because I was a little worried about liability issuses.

Athough, I'm sure that this device would show a change in the path of center of pressure. As long as the patient wasn't neuropathic.

Cheers,

Eric

 

Eric, while I agree with your point about pointy points, there is more than one way to skin a cat. I start at the nose and peel

 

Are these orthoses in production now?

 

Hopefully will be lauchned in March 2010 - fingers crossed.

Phil