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Quote from PA in an earlier thread.
Why isn't it? Kinetically, what is the difference between 'simple wedging on an insole' and wedging incorporated within a prefab/custom orthoses? I really don't get it, thanks, mark

 

I wish I had an answer; I wrestle with this.
Depends on what you trying to achieve.
eg if you have a, for eg, a post tib tendinopathy and eh aim is to reduce the inversion moment, then simple wedging in some people will do that and in others it won't.... so if you had a full custom orthotic to reduce that inversion moment, then will you get a better, bigger reduction in more people than you would with a 'simple wedging on an insole' or 'wedging incorporated within a prefab/custom orthoses?' ... I don't have an answer

 

Mark, I didn't read the original thread so I'm not sure of the context here. However, if we recognise that foot orthoses "work" by modifying reaction forces at the foot's interface with shoe, ground, whatever... and that foot orthoses can only achieve this directly by virtue of altering the shape of the interface, the stiffness of the interface and the frictional characteristics of the interface then it is easy to realise that unless two devices are identical in respect to all three of these variables then they cannot have identical mechanical effects in terms of modifying the reaction forces at the foot's interface. That is not to say that two devices with different characteristics in respect to these variables cannot both be clinical efficacious.

Here's a little pilot study I did where I looked at the effect of foot orthoses on the shape of the foot. Cast of the foot in-shoe (control), versus cast of the foot in-shoe with low density off-the-shelf insole, versus cast of the foot in-shoe with identically shaped high density insole. Look at how the stiffness of the insole influences the "work-done" on the foot by the orthoses.

 

I liked Simon's reply. I would add that if you want to increase pressure medial to the STJ axis then you can do so better with a device that follows the contours of the foot and presses up into the arch. A flat wedge cannot do that. And, as Craig pointed out, sometimes the wedge is enough and sometimes you need more.

 

Excellent replies by Simon and Eric. We are able to now, with our knowledge of how foot orthoses work, to move away from the overly simplistic notion that foot orthoses "hold the STJ in neutral", "lock the MTJ", and "prevent compensations for foot deformities", as I was taught by the Root et al theorists. Now, with a more scientific understanding of how foot orthoses work, we can say that foot orthoses or in-shoe wedges alter the magnitude, plantar locations and temporal patterns of ground reaction force (i.e. external forces) acting on the plantar foot and that is how they produce their kinetic effects. It is really no more complicated than that, both custom foot orthoses and in-shoe wedges work the same way.

Gone are the days of speaking in ill-defined terms using clinical language that is ambiguous. Even though we still have a few older podiatrists who are so myopic that they still desperately cling to the antiquated ideas that foot orthoses work by "holding the STJ in neutral", "locking the MTJ", and "preventing compensations for foot deformities", and will hold their dearly held faulty ideas to their graves, the rest of the podiatry profession, thanks to individuals like Dr. Simon Spooner and Eric Fuller, are gradually being led into the realm of real biomechanics and scientific research. Say goodbye to podiatric biomechanics myths. Hello science and clear reasoning.

Thank goodness for that!

 

Thank you Messrs Payne, Spooner, Fuller and Kirby