In search of a mechanism for foot orthoses’ effects

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Interesting article in this months Lower Extremity Review. If you look closely Craig has responded at the end:


http://www.lowerextremityreview.com/article/in-search-of-a-mechanism-for-foot-orthoses-effects

What say you?

 

Personally, I was disappointed in this article. To interview six people for this article on how orthoses work and, of those six people, to include only one podiatrist, is an insult to the podiatry profession. Since when have the research PhDs been the only one that knows anything about "how orthoses work"? It would be like doing an article on how bunion surgery works and only interviewing one podiatrist who routinely does the surgery and 5 PhD researchers who have only done experimental cadaver surgery. Doesn't make much sense to me.:butcher::craig:

 

Can't quite agree with you here, Craig.

Foot orthoses can also "work" to "lower the load in the damaged tissues" by reducing compression forces and plantar pressures on both external and internal structures of the plantar foot that may, in turn, 1) heal plantar ulcers, 2) reduce the pain and inflammation in plantar prominences and 3) reduce internal compression forces on injured soft tissue and osseous structures. This involves mechanisms other than "changing joint moments", even though the change in the temporal patterns, magnitudes and locations of ground reaction force acting on the plantar foot may cause a change in joint moments (Kirby KA: "Evolution of Foot Orthoses in Sports", in Werd MB and Knight EL (eds), Athletic Footwear and Orthoses in Sports Medicine. Springer, New York, 2010).

 

I agree with Kevin. The problem with this paper is that not once was the foot orthoses "examined" in its own right, merely the effects foot orthoses have been shown to have on the human body. Yet, if you want to know how foot orthoses work, you need to look at foot orthoses not the human body!

As Kevin has said foot orthoses work by changing the temporal patterns, magnitudes and locations of ground reaction force acting at the foots interface.

As I have said repeatedly now, they can only do this by altering:
1) geometrical characteristics at the foot's interface
2) load/ deformation characteristics at the foots interface
3) frictional characteristics at the foots interface

Sooner or later, researchers are going to need to start examining these three design characteristics in earnest since this is "how" foot orthoses work.

 

I find the neuromodulative effects plausible but I wonder if it is a direct effect or merely as a consequence of the function of the orthosis? Does that make sense Kevin and Simon, is that what you are trying to say? If so, then they completely missed the mark with the title, "mechanism for foot orthoses effects" when we know the mechanism and this article is really more about possible secondary CNS effects brought about by those mechanisms?

Not certain what I have written here to be honest

 

David,
Ultimately foot orthoses can only work in the manner in which Kevin and I have described. While this may result in direct and CNS mediated responses, ultimately foot orthosis can only ever alter the magnitude , timing and distribution of reaction forces at the foot-orthosis interface via variation in geometry, load/ deformation and frictional characteristics at this interface. Anything else is purely psychological. Think about it... What can the foot orthosis do? It's an inert, shaped piece of plastic. It can't send electrical impulses to the muscles to make them fire- right? So any change in muscle activation are a result of the changes in the force pattern and magnitude at the foots interface....... or psychological changes, end of story.

 

David:

I think Simon and I are on the same page here. In addition, I'm sure Craig is on the same page also. However, in my response to Craig's comment, I wanted simply to point out that foot orthoses performs their many therapeutic functions not only by altering joint moments since they can, also, directly redistribute plantar pressures on the plantar foot to provide a therapeutic effect; a therapeutic effect which does not necessarily mean that the foot orthoses are healing the injury by altering joint moments.

Alteration in moments with orthoses can occur both from direct mechanical effects, from the orthosis altering ground reaction forces on the plantar foot, and from neuromotor effects, from the central nervous system altering the efferent signals to the muscles of the locomotor system.

I wrote a Precision Intricast Newsletter in October 2009 titled "DIRECT MECHANICAL AND NEUROMOTOR EFFECTS OF FOOT ORTHOSES".

Here is a segment from that newsletter, that has not been published in book form yet:

Here, also, is the thread I started in early 2009 on the subject: Direct Mechanical and Neuromotor Effects of Foot Orthoses

Too bad "Lower Extremity Review Magazine" didn't get the full story on how foot orthoses work.

 

Here is an experiment that I had Dr. Spooner and his buddy Tony Achilles do on their own foot during a break when I was lecturing at the Biomechanics Summer School back in August 2001 in Oxforshire, UK. (I believe this is the correct date, isn't it Simon?)

Walk barefoot at a relaxed pace over a flat surface and measure the distance that you cover in 10 steps. Repeat this process a total of four times and come up with an average stride length while walking barefoot. Now take two piece of 1/4" (i.e. 6 mm) thick felt and adhere it to the plantar aspect of your first metatarsal heads and perform the same experiment as above, but this time walking with the pads under your first metatarsal heads.

The results of this experiment which are quite repeatable (I've been doing this demonstration for 20+ years with podiatry students and podiatrists) point toward one of the effects of foot orthoses.

Who wants to be the first one to do the experiment, report back with their own personal results and offer a reasonable hypothesis for the change in stride length seen with the first metatarsal pads in place versus the barefoot with no pads condition? Is the effect seen with this pad likely to be more of a direct mechanical effect or a neuromotor effect from the foot orthosis (pad)? What clinical situation does this pad represent that may help us understand why foot orthoses cause certain changes in the kinematics of gait?

 

Kevin, the 'external', they would be? Thanks, Mark

 

Skin.

 

Skin. Aaah

I was attempting to think of, external to the foot, say tibia.

Thanks Prof.

 

Thank you Kevin and Simon. When I read the article I though I was missing something in my reading and after reading Craig's response to the article I was even more confused. The responses have helped affirm my understanding of the mechanism of CFO's.

I would answer Kevin's experiment but I feel I would be cheating given I've spent a little time around here lately....

 

Mark:

Making the distinction between internal structures and external structures of the foot is important in biomechanics since we can directly measure the forces acting on the external structures but can not directly measure the forces acting on the internal structures without surgical intervention. This becomes especially important when we start talking about the effects of foot orthoses having both effects on the external structures of the foot (i.e. skin) and the internal structures (bone, cartilage, ligament, muscle and tendon) of the foot. Many podiatrists and researchers often forget in their discussions of the biomechanical effects of foot orthoses about the fact that foot orthoses can have a very significant effect on the healing of skin ulcerations and on the reduction of symptoms from painful plantar lesions by altering the external forces acting on the plantar foot. It is for this reason is why I made this distinction. I am glad you asked. Good question!