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Jeff;

Also despite the moment amount, so to speak, if the STJ is maximally pronated with the heel on the ground when does it matter what the pronation / supination moment ratio is?

I would think it would only be once the ration can be tipped towards supination, which is this example will definitley not remotely start until the heel begins to off load.

Bruce

Bruce

__________________
Bruce E. Williams, D.P.M.
Breakthrough Podiatry

Jeff, you are missing my point. You said:
This is not true.

However, in your first example, you will have influenced the moments at all of the joints of the foot with your Cluffy wedge, regardless of whether or not you sever tendons because you have changed the forces under the foot, viz. the net ground reaction force vector will have been altered in relation to all of the joint axes, therefore the external moments about all of the foots joint axes will have been altered. In response to this change in external moments we may or may not see concomitant change in internal moments. Obviously if you severed the tendons, this will influence the net effect because you will have simultaneously changed both the internal and external moments.

Jeff, I'm not saying that a change in kinematics will not alter the internal and external moments, as it clearly will. I'm just pointing out that you can't say that changing the external moment as this is simply not true. You could say that it may have no kinematic effect, but you can't say that it has no influence, as it will alter the kinetics.

__________________
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"My mission drive is to open up my eyes, 'cause the wicked lies and all the sh!te you say..." http://www.youtube.com/watch?v=V4NW5S1UTPQ

"Science is the antidote to the poison of enthusiasm and superstition."

Bruce:

It is very clear to me that I have repeatedly tried to explain the concepts that you keep asking me about. Maybe Eric, Simon, Craig or Robert could explain it in a better way for you since I am obviously failing in that task.

__________________
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
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When does it matter what the pronation to supination "ration" is? All the time.
Bruce, I can increase internal supination moment without lifting my heel off the floor, simply by contracting my supinatory muscles. Fantastic things, muscles. Especially when working in concert with neural control.

__________________
Who? What? When? Why? Yeah? And? So? What?

"My mission drive is to open up my eyes, 'cause the wicked lies and all the sh!te you say..." http://www.youtube.com/watch?v=V4NW5S1UTPQ

"Science is the antidote to the poison of enthusiasm and superstition."

Fascinating as well that you conciously made that happen despite what the STJ axis was.

Still doesn't explain why a FF valgus post would cause the CNS and muscles to do what what yours did in reference to the example we started out with on this thread though. That seems to remain a paradox.

Regarding the ratio, sorry for the spelling error, don't worry about it.

Bruce

__________________
Bruce E. Williams, D.P.M.
Breakthrough Podiatry

Paradox: (noun) 1. A seemingly contradictory statement that may nonetheless be true.

Paradox: (in the context of the example from earlier in this thread):

To those who don't completely understand subtalar joint axis location/rotational equilibrium theory, it seems contradictory to them that a forefoot valgus wedge could cause increased subtalar joint supination or that a rearfoot varus wedge could cause subtalar joint pronation during the dynamics of gait even though, nonetheless, it is often true that it does and is also true that it is completely consistent with the subtalar joint axis location/rotational equilibrium theory.

__________________
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
**************************************************

Conflict avoidance
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Avoidance is a controversial method of dealing with conflict which attempts to avoid directly confronting the issue at hand. Methods of doing this can include changing the subject, putting off a discussion until later, or simply not bringing up the subject of contention.

For those who contend that SALRE works while avoiding direct questions regarding the mechanics.


Bruce

__________________
Bruce E. Williams, D.P.M.
Breakthrough Podiatry

Actually, Bruce, I think you know me well enough to realize that I tend to not avoid conflict, but rather, to run head first into it. At this point in my life, I enjoy the mental challenge and I find it makes life much more interesting.

Otherwise, I do appreciate your good-natured comeback.

I'll let the others try to better explain things for me from now on for you since I don't think we are making sufficient progress to warrant us taking any more of our time in such fruitless discussion. Maybe when we see each other again at a seminar, we can discuss it further. I honestly don't feel we are that far apart.

__________________
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
**************************************************

Kevin;

Fair enough!

I don't think we are that far apart either and said as much earlier in this discussion.

BTW, you could have at least said "touche"!

Till we meet again!
Bruce

__________________
Bruce E. Williams, D.P.M.
Breakthrough Podiatry

Bruce, I suspect during gait the forefoot valgus wedge is likely to induce medium intensity sural nerve reflex.
http://www.ncbi.nlm.nih.gov:80/pmc/articles/PMC2230764/

The increase in tibialis anterior and medial gastrocnemus activity noted by these workers in association with medium intensity stimulation would seem to explain your paradox.

Further the response observed in association with high intensity stimulation would appear to support a "pain avoidance" mechanism, which Eric has discussed upon numerous occasions.

What this suggest to me is that if we stimulate the lateral aspect of the foot with a medium intensity stimulus, we will see the inversion musculature increase their activity, however if the stimulus is too intense the muscles will cut down activity to draw the foot away from the (painful) stimulus. I believe that much of the indirect neuromotor effect of foot orthoses is due stimulation of cutaneous reflexes in this way. The interesting point about many of these reflexes is that they are phase of gait dependent, eliciting a different motor response depending on when during gait they are stimulated. I hope in the future that we can better understand these reflexes and design our orthoses to specifically target them within our therapeutic strategies.

Hope this helps and makes sense to you.

Kevin, I'm full of ideas- you?

__________________
Who? What? When? Why? Yeah? And? So? What?

"My mission drive is to open up my eyes, 'cause the wicked lies and all the sh!te you say..." http://www.youtube.com/watch?v=V4NW5S1UTPQ

"Science is the antidote to the poison of enthusiasm and superstition."

This one is interesting too. http://jp.physoc.org/content/581/1/99.full.pdf+html
look at the emg activity of soleus when the treadmill was inclined versus declined. What does the forefoot valgus wedge do to the dorsiflexory moment at the ankle joint?

__________________
Who? What? When? Why? Yeah? And? So? What?

"My mission drive is to open up my eyes, 'cause the wicked lies and all the sh!te you say..." http://www.youtube.com/watch?v=V4NW5S1UTPQ

"Science is the antidote to the poison of enthusiasm and superstition."

Bruce:

I would have said "touche" if you had instead of using the example of "conflict avoidance", you used the example of "conflict engagement".

Life would be much too simple without conflict.

__________________
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
**************************************************

Kevin;

Touche.

Bruce

__________________
Bruce E. Williams, D.P.M.
Breakthrough Podiatry

Simon;

I'll try to give those sights a look see tomorrow before traveling.

Thank you for your reply and for mentioning the phases of gait and their interaction within the process.

Bruce

__________________
Bruce E. Williams, D.P.M.
Breakthrough Podiatry

To recount: We are talking about an observation where we have seen increased STJ supination after the addition of a forefoot valgus wedge. Do we all agree that we have seen it?

Bruce questioned why do we get supination of the STJ with a modification that looks like it should increase pronation moment from the ground.

Kevin replied that it was CNS mediated response that created more supination moment from the muscles.

Bruce asked: how do we know this?

Is everybody in agreement so far?

Here is my explanation:
We see supination of the STJ, therefore there must be a net supination moment acting on the STJ. If we added a modification that increased pronation moment from the ground and we see supination of the joint, then there must be some other source of supination moment that is larger than the pronation moment from the ground.

This is simple physics. Newton's second law for angular motion is that the net moment = the moment of inertia x angular acceleration. The direction of the acceleration is in the direction of the moment.

So, now we have to look at the foot and leg for potential sources of supination moment. The muscles are the most likely candidate to respond to an external pronation moment from a forefoot valgus wedge. I can't think of any other source of supination moment to explain the extra supination that is seen with a forefoot valgus wedge. If you don't accept that it is the muscle you either have to say that resupination does not occur or come up with some other source of the supination moment. If it supinates there is a net supination moment.

I hope this helps.

Eric

Jeff,
I still don't think you need to think about forefoot to rearfoot relationships to explain the phenomenon that we are talking about. Forefoot to rearfoot relationship measured in neutral position is not necessarily relevant to explaining how wedging will change the forces from the ground under the foot. In your example, you describe how the foot "compensates" from neutral. However, we need to look at the foot in the position that it stands in. For example, some feet with a rigid forefoot valgus may have an extremely laterally deviated STJ axis and these feet will tend to supinate in stance and have a high amount of force under their lateral column in resting stance position. Conversely, a foot with a measured forefoot valgus could have a medially positioned STJ axis and these feet may have higher forces under the medial forefoot. I don't recall if your father talked about a rigid and flexible forefoot valgus, but others have used that concept when trying to explain the above phenomenon that I feel can be better explained using STJ axis location.


You can also measure a perpendicular forefoot to rearfoot relationship with both feet with medially and laterally deviated STJ axes. These will behave differently.

I agree with Simon's comments about apply forces across multiple joints. A force that could apply moments across multiple joints will simultaneously create a moment about all of those joints. The joint that moves the most will be the one with the greatest net moment. A real life example of this can be seen with a patient seated in a chair with the plantar surface of their foot pointed toward you. Push upward on the fifth metatarsal head. In feet with more medially positioned axes you will see more pronation of the STJ. With feet with a more laterally positioned axis you see less pronation and more ankle dorsiflexion. Now, invert the STJ (which will move the fifth met head closer to the STJ axis.) Now push in the same direction (relative to the body, but not relative to the foot.) and you can find a position of the STJ ( if enough range of motion available) where you will not get any STJ motion and get ankle dorsiflexion. Even though you are pushing distal to the MTJ you are getting motion at more proximal joints in relation to the amount of moment at those joints.

Cheers,

Eric

The moment at the ankle joint is dependent upon the distance from the line of action of the force at the center of pressure to the STJ axis. In standing we can assume the line of action of force is vertical. Two situations, A cluffy wedge with the FHL muscle active and another situation where the EHL muscle is active. With the FHL muscle active there will be a tendency to move the center of pressure more distal. With the EHL more active it will tend to move the center of pressure more proximal. So the effect of the cluffy wedge is dependent on how it changes the location of center of pressure. If the long tendons and the attachments of the sesamoids to the proximal phalanx were cut then the cluffy wedge would probably do very little to change the location of the center of pressure.


The lateral forefoot wedge has two different effects. It will tend to increase the pronation moment at the STJ which will tend to increase tension in the plantar fascia. It will also tend to shift weight from the medial forefoot to the lateral forefoot which will tend to decrease tension in the plantar fascia. Sometimes one is more important than the other.

Does the fascia insert medial to the axis. It crosses the STJ with attachments on both sides. The better question is what kind of moment at the STJ does tension in the fascia produce. Most of the time the sagittal view is the best analysis. With pronation there is a relative anterior shift of the talar head relative to the anterior aspect of the calcaneus. Tension in the fascia will push the met head backwards which pushes the cuneiform, navicular and then the talus backward. This push will tend to supinate the STJ. However, in the transverse plane it is possible to have the forefoot so abducted on the rearfoot that the proximal push on the metatarsal head will cause the talus to adduct (and the leg to internally rotate.) This is pronation of the STJ. This phenomenon was originally described by Jack (the push up test of Jack for flat foot) See my paper on the windlass for diagrams of what I'm saying.

Yes we can leave the MTJ and forefoot to rearfoot relationship out of the discussion.

Respectfully,
Eric