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Our leader (and my boss) has been interviewed for an article in Podiatry Today. Coments also from Chris Nester and Bruce Williams - its a good read.
Link to article.
Anyone want to disagree with them?? :)

Good to see that Craig and Chris are being included more frequently in the US podiatry periodicals as experts on orthoses and biomechanics. The question, however, remains...... do the US podiatrists really care about orthoses and biomechanics, or are they more worried about proper CPT coding and about the next new bunion procedure or new surgical hardware item that they will get a chance to implant into one of their patients' feet?!

__________________
Sincerely,

Kevin

**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College

e-mail: kevinakirby@comcast.net

Private Practice:
107 Scripps Drive, Suite 200
Sacramento, CA 95825 USA
My location

Voice: (916) 925-8111 Fax: (916) 925-8136
**************************************************

Great article, and I appreciate Kevin questions. Certainly would not want to put my head over the parapet to disagree! However, I still find myself uncertain as to why we are surprised by the amounts of motion in other joints in the foot and may only start to look at their impact on gait more recently.

Surely part of the hindrance in our grasping the mechanics of the foot is that we seem to have divorced it from its most suitable terrain - a surface to which it has to be multiply adaptable.

e.g.

1. Is the windlass mechanism as significant on a grassy knoll surface where, barefoot, the joints have opened in such a way as to render resupination obsolete as the foot uses the natural support of the surface as a lever to propel itself rather than becoming a rigid lever?

2.Again, it seems there have been times when we have focused upon the lack of the foot becoming a rigid lever. Perhaps we need to look more at why the foot is not allowed to function in its main capacity (my simplistic view) as a multiple adapting mechanism.

3. The capacity of the MTJ to open, temporarily, may be a vital feature in foot mechanics on rougher terrain

I can understand the need on a uniformly hard flat surface for there to be a consistent first ray that planatarflexes sufficently, for there to be resupination via windlass. This would make sense if we were designing a mechanism that integrates and responds in function with the rest of the human structure that had also been designed to function only on a hard flat surface. However, our current foot is not such a type.

Hobby horse I know - maybe I am not killing of the biomechanics terminology as badly though!!

Ian

The tissue stress aproach can take into account the terrain. I would agree that STJ neutral biomechanics does rely on describing the foot relative to a flat hard surface and this is a problem.

No matter what surface the foot stands on the force from above, body weight, and the force from below, Ground Reaction Force, are going to be the same. (Exception for moon and space station) If you try and jump the forces will increase. The terrain will effect the location and the distribution of force.

In order for the foot to aid in propulsion in a jump, the windlass will be needed to add rigidity to the foot so that the foot and ankle can add more power to make a better jump. This is regardlass of the surface.

Eric

I don't know how a surface that is external to the foot could possibly generate the internal forces and moments within the foot to make it a more "rigid lever". A grass surface does not "render resupination obsolete." Supination of the STJ is necessary not only to allow the foot to have increased forefoot dorsiflexion stiffness but also to allow the transverse plane motions at the pelvis and hip during late midstance and propulsion to be synchronous and in the same directions as the transverse plane motions of the femur and tibia which, in turn, allows optimum efficiency of walking mechanics.

I was taught that pronation was the cause of the foot not becoming a "rigid lever" in propulsion. I was also taught that the foot needed pronation in early stance phase to become a "mobile adaptor". I believe this is still widely taught in podiatry schools worldwide.

As Eric said, the windlass effect aids in increasing the internal rigidity of the foot by increasing the forefoot dorsiflexoin stiffness. This will be the case whether the foot is walking on a hard, flat surface or on any other surface. However, supination of the STJ during propulsion is not all caused by the windlass effect! STJ supination during propulsion is also caused by external rotation moments on the hip from proximal muscles and by STJ supination moments from PT, FDL, FHL and gastrocnemius-soleus contractile activity. In support of this, patients that have had 1st MPJ fusions have great supination in propulsion, but have no windlass since they can't dorsiflex their hallux!! So let's not get too overexcited about needing the windlass effect of hallux dorsiflexion for normal supination of the STJ in propulsion. The windlass effect is not necessary since there are other equally important forces at work during this stage of gait that also cause STJ supination moments.

__________________
Sincerely,

Kevin

**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College

e-mail: kevinakirby@comcast.net

Private Practice:
107 Scripps Drive, Suite 200
Sacramento, CA 95825 USA
My location

Voice: (916) 925-8111 Fax: (916) 925-8136
**************************************************

Hi Kevin and Eric

Thanks for the reply.

I understand the role of other factors generating pronation and the need for the windlass in adding rigidy and consequent increase in power when we want to jump. My query has been about these factors always in relation to a specific surface occupying our attention too much in our understanding of foot function.

I still think this is a significant weakness in our attempts to understand foot function and if ignored could lead to a recurrence of an overly didactic approach to learning biomechanics that I originally experienced. For example what is an efficient barefoot function waking on various types of sandy surfaces? What is an efficient foot function walking barefoot in rugged or jungle terrain as some indiginous people do? There a many occasions when a stepping (not steppage) type of gait is required

I know these are not original questions but there are times when I read material that is suggestive of a holy grail of biomechanics as to understanding the ideal foot function but always in relation to a specific surface.

Now Eric, space station gait - do I sense a niche market for gravity inducing functional foot orthoses???!!!

Again thanks for the reply.

Cheers
Ian

Ian,

I understand your point. This was something I gave some thought to during my PhD studies. The phenomenom of varying biomechanical function in varying environmental circumstances is best described thus:

P = (a function of) G + E + (G x E) + i

Where:
P = phenotype
G = genotype
E= environment
i = measurement error

So for a given quantitative trait (P), say Hallux Dorsiflexion during gait; the measured angle is dependent upon the individuals genotype and the environmental interaction.

I called this Spooner's quantitative genetic theory of foot function

__________________
Science is the antidote to the poison of enthusiasm and superstition

My location

I'm just glad to see that someone actually read it!
Sincerely;
Bruce

Thanks Simon

Still trying to get my first degree so a PhD is many miles way!!

Apart from the equation did you draw any other conclusions?

Cheers
Ian

Tough questions, Ian. Function is a tough word to define, so it is difficult to answer your question. Efficiency is also tough to defiine. What may help you is understanding the concept of joint power. Power is the change in energy. When a leg is lifted it gains potential energy. Or it can gain kinetic energy if it moves. The joint that creates the movement or change in position of a segment of the body can be determined by looking at its joint power through inverse dynamics. David Winter has an excellent book on this. (Joint power is joint moment x joint angular velocity)

Say you have to step over a log. You have to lift your leg, so you leg needs to gain some potential energy. To lift your leg you can use your hip flexors and/or your ankle plantar flexors. Of course a combination of the two can be used. If you use more of one you need less of the other to reach the height you need to clear the log. I'm not really sure how to determine what proportion of ankle lift versus hip lift is more efficient.

In walking, regardless of the terrain, you have to make the back leg become the front leg, by swinging at the hip, and this requires the addition of energy to the leg. The ankle has a much longer lever arm of force applied to the leg to generate moment at the hip. So, it might be more efficient to use ankle push to add energy to the swing leg. However, this would put more stress on the foot and this could cause injury to the foot. So again a way to measure efficiency is difficult to find.

Cheers,

Eric