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The problem with that is that the STJ is pronated in midstance and for the heel to now lift off the groun, moving into active propulsion, the STJ must now supinate. According to Kevin K and Simon, we need a supination moment to get us to this point and that would require a force medial to the STJ Axis.
The only way that I see this happening is if 1) the 1st ray dorsiflexion stiffness high (stable 1st ray) 2) the 1st ray is allowed to plantaflex with minimal restriction (use of a cutout or kinetic wedge modification) and 3) the peroneas longus functions as it should and keeps the 1st metahead against the ground - hence allowing high gear propulsion, and a functioning windlass.
4) would be re: the calcaneocuboid joint locking up - that would be done either with a high dosrsiflexion stiffness of the lateral rays 4and 5 or with a FF valgus post 3-5 or reverse morton's extension etc.
So, we kind of end up back where Craig started right?
respectfully;
Bruce

Quote: Simon
[What I said is that Norm Murphy said if the CoP was MOVING MEDIALLY so too was the STJ AXIS. This does not mean they are in the same position, just that they are travelling in the same direction. I can say this for a fourth time if it helps.]

Please say it a few more times for me Simon, it makes me hot!
So once again I ask you and Kevin, is the Axis moving as you have now said several times?

Quote: Simon
[Normal CoP progression in which environment?; at what gait speed?; pivoting and changing direction? Bruce life isn't as simple as that even BM held this view. Moreover, how do you explain the Hughes et al. data which showed many subjects, being asymptomatic and yet apparently using "low-gear". Where is the published data to support your contention here?]

Ah yes, I was wondering how long it would take for you to ask me to provide published data!
Sorry Simon, never read the Hughes paper, and from Craig's quote he didn't seem to feel it mattered to the discussion. I'd have to read it myself to know for sure. I can say this much about the data of Hughes, I would completely agree that many patient's functioning in Low Gear would and could be asymptomatic. Would this not also be true if they were functioning with severely medially displaced STJ Axis?

Seriously though. I respect your STJ axis theory and I feel it has added tons to where we are going with foot biomechanics (bx) is that what the abreviation is for? Not sure.
But, you need to explain how to get a higher supination moment in the forefoot area, like I did in ThanH's post.
Like it or not, many will feel that the best way to get a higher supination moment in the FF is to use a varus post not just at the heel, but all the way to the 1st mpj like Rothbart!
Craig has suggested another way, which is to add a FF valgus post, which works as well, and even better with a 1st ray cutout/kinetic wedge etc.
Cheers;
Bruce

Bruce:

Let me comment and add to your reasons why STJ supination may occur during late midstance and propulsion:

1) First ray dorsiflexion stiffness is high (This would tend to increase the ground reaction force (GRF) plantar to the first metatarsal head which would tend to shift the center of pressure (CoP) more medially and thereby increase the STJ supination moment.)

2) The first ray is allowed to plantarflex with minimal restriction (This will be caused by an increased STJ supination moment from some other source or by a normal to higher medial longitudinal arch height. However, once the hallux dorsiflexion starts normally occuring because of these factors, the first ray plantarflexion that results will shift the CoP medially which will increase the STJ supination moment.)

3) The peroneus longus functions as it should (The peroneus longus causes a STJ pronation moment due to its lateral position to the STJ axis but it also functions to increase the first ray dorsiflexion stiffness which will tend to shift the CoP medially which will, in turn, cause an increase in STJ supination moment. However, the net change in STJ moments because of these counteropposing moments from peroneus longus contractile activity is probably in favor of a slight increase in STJ pronation moment.)

4) The calcaneo-cuboid joint locking up (I don't really know what "calcaneo-cuboid joint locking" means. "Calcaneo-cuboid locking", along with "midtarsal joint locking" is terminology we should now discard since it can't be precisely defined. However, it is true that if the lateral column is bearing sufficient weight in late midstance on the 4th and 5th metatarsal heads there will be an increased STJ pronation moment due to the more lateral positioning of the CoP. Surprisingly, however, this may produce increased STJ supination and increased ankle plantarflexion during propulsion and increased duration of propulsive phase of gait. This paradoxical result of an increase in GRF on the lateral column causing more STJ supination during propulsion is probably due to the gastrocnemius-soleus complex having increased magnitude and duration of contractile activity during propulsion since the presence of adequate GRF plantar to the 4th and 5th metatarsal heads allows this increased contractile activity of the gastrocnemius-soleus complex without concomitantly causing lateral instability of the foot during propulsion.)


Other factors that may increase STJ supination moment and/or decrease STJ pronation moment during late midstance and propulsion:

A) Increased contractile activity of the posterior tibial, flexor digitorum longus, flexor hallucis longus, gastrocnemius and/or soleus muscles.

B) Decreased contractile activity of the peroneus brevis muscle.

C) More medial positioning of the CoP in the forefoot.

D) More lateral positioning of the STJ axis.

E) More medially directed GRF vector such as is caused by genu valgum deformity (Van Gheluwe B, Kirby KA, Hagman F: Effects of simulated genu valgum and genu varum on ground reaction forces and subtalar joint function during gait. JAPMA, 95:531-541, 2005).

And finally, Bruce, yes, the STJ axis is continually moving in space relative to the plantar foot during the gait cycle (Kirby KA: Subtalar joint axis location and rotational equilibrium theory of foot function. JAPMA, 91:465-488, 2001). The STJ axis translates medially and internally rotates with STJ pronation and translates laterally and externally rotates with STJ supination. The three dimensional motions of the STJ axis closely follows the three dimensional motions of the talar neck (i.e. anterior exit point of STJ axis) relative to the posterior-lateral calcaneus (i.e. posterior exit point of STJ axis).

I believe that many of the observations that and you and Howard Dananberg have made and have lectured on can be integrated quite nicely with the STJ axis-rotational equilibrium theory as I have tried to demonstrate above with my comments.

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

I'm not quite sure what is meant by not working. Or not working as well. A function of the windlass is to add dorsiflexion stiffness to the first ray. Another function is to create a supination moment at the STJ, and possibly create a supination motion. I could theorize more functions, but I will talk about these. In the picture of the right foot the first met head is off of the ground and the STJ is in a much more supinated position. The functions, that I just stated, are not needed in this foot. There is redundancy in the foot and the function of dorsiflexion stiffness is, in the right foot, now needed in the lateral column. The foot is in a quite supinated position and a supination moment from some other source must have been present to get it into this position. The windlass may not be "functioning" in the right foot but it does not need to when the foot is in the position that it is in.

Eric

What I meant by not working is what you said - ie if you look at the picture of the right foot during propulsion (and ignore all the high gear/low gear stuff), the first MPJ of that foot is not dorsiflexing fully, so windlass not fully established ... but take your point that it may not need to be (but the foot was symptomatic).

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Craig Payne
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Eric;
Just because the foot may be in a somewhat supinated position it does not mean that the foot is propulsing optimally or without pain.

As Simon pointed out, the foot is actually pronating when the hallux is fully dorsiflexed and the windlass is fully engaged and the foot is functioning in high gear propulsion.

The supinated position of the foot in the picture is still in a low gear propulsion mode and will not be functioning optimally and is primed for tissue stress over time.

Cheers.
Bruce

Bruce, Craig, Eric and Colleagues:

Looking at Craig's 14 y/o patient makes me think that this lad has midfoot pain that is made worse by subtalar joint (STJ) pronation and its secondary effects on the midtarsal/midfoot joints and the pain is made better by STJ supination. In addition to the mechanisms suggested by Craig and others, I would also offer that this patient is walking with a more supinated gait pattern in propulsion (evidenced by the low gear push-off) due to pain in his foot. This abnormal gait pattern, or antalgic gait pattern (i.e. limp) may have secondarily, over time, caused his sacroiliac and low back pain. Once the proper orthosis was made for him that generated sufficient external STJ supination moment on the foot and he no longer needed to generate internal STJ supination moments to have his foot be less painful, the orthosis not only improved his pain but also improved his gait.

The point that Eric was making regarding the windlass is a good one. If the patient is so supinated in late midstance and propulsion that propulsion is occurring off the 2nd-5th digits, then the windlass will not be fully functioning. In addition to what Eric said, if the foot is pronating at the STJ in late midstance but has good STJ axis location and good medial longitudinal arch (MLA) height, then the windlass will probably function normally, even though the STJ is pronating abnormallly in late midstance. However, if the STJ is pronating abnormally in late midstance but has a medial STJ axis location and a low MLA height, then functional hallux limitus will likely result and reduced windlass function may occur.

The possible explanations for the exact mechanical scenario in this 14 y/o boy's foot is, of course, made much more complex when a pain avoidance behavior (i.e. antalgic gait) is used during gait. An antalgic gait pattern makes gait examination techniques, whether visual, via pressure-sensing insoles/mats, force plates or 2D or 3D gait analysis much more difficult to interpret since normal muscular contractile activity and temporal patterns are not occurring. Therefore, I don't think that we can be certain of why this child is walking the way he his, since there are many possibly explanations given the limited information presented.

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

Both the right foot and the left foot are primed for tissue stress. The left foot will have excessive load on the medial forefoot and the the right foot will have excessive load laterally after heel lift. From the pictures, if the patient continued to walk this way then I would expect medial column pain in the left foot and lateral column pain in the right foot. The windlass activivation does not magically make the foot immune to stress. In fact if there is a high pronation moment at the time of high medial weight bearing, the windlass will not create enough supination moment to cause motion. This would lead to high stress within the structures of the windlass.

Bruce just becaue the foot is pronated does not mean that it is propulsing optimally and without pain.

In my opinion, optimum push off would have even pressure across the metatarsal heads. Of course, there are exceptions to this.

Eric Fuller

Dear Craig

There is a very valid osteopathic saying that allies to EVERYONE who deals with another.

Tight joints ache Loose joints PAIN. ie Hypermobile joints pain and hypOmobile joints ache. Did anyone ask if the other foot ached? I bet NOT and I would like to bet that the joint mobility of both feet was NOT looked at!

PAul Conneely
www.musmed.com.au

There was no history, present or current of any pain, aches or discomfort in the more pronated foot (I kept probing and asking as I felt as though there should have been). I would normally compare joint motions in both feet and would have noted any difference at the time, but its been a while since I seen this boy, so do not really recall.

__________________
Craig Payne
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As hypermobile as both feet looked, the trigger for the most pronated foot shouldhave been found behind the knee, where his fibular head has been driven. I have ween watching this one for a while...Bojen Moller is one of my favorites. He has it almost right and,in contradiction to what Kevin K. says, is nowhere near snake oil. Kevin K. made a statement that there is no reason for the COM to change side during gait. Did I misunderstand that? If not, why does an F-scan make a sin curve during normal gait. More to ths topic, why do you thing the normal foot has a parabolicmet head shape? To create angular momentum. Then all of this momentum hits this huge 1st met, and it is turned into vertical lift. The Com has to be raised in the center of gravity to "feed" the spine. The COP, with the COM following - or maybe hte other way around - DOES shift from one foot to the other to get this loft. If you do not see this in your patient, then the foot is already broken down. As for High gear/low gear, I just described low gear. In high gear, there is no need for angular momentum because the indvidual is in full run moded and energy storage and return is via fascia and other soft tissue. When will we stop using pathologial feet as our "norms" and simply consider how the foot is put together and functions in synergy with the rest of the body. The feet are the gateway to energy transfer to the spine, they have alot of moving parts with a lot of joints that WILL fail under either extreme force or long term-low load. You all know this. Why is is so hard to grasp that the fett, then are most likely to fail? They take ALL of the force generated by sagital plane COM lift and filter it to make the rest of the kinetic chain work. Of course the are the first to go. The body can adapt and keep you walking....maybe not as efficiently...and high gear may well be just as efficient for a long time after the foot begins to fail simply because the foot is not the primary mode of force transfer in high gear, as stated above. Bojen-Moller was no idiot, he was ahead of his time....and ours, apparently.

Kevin M

I don't think f-scan measures centre of mass position. If you are referring to the COM analyis software which goes with the system, I thought the sign wave is supposed to be the vertical displacement of the COM, not the lateral displacement?

It rarely is parabolic: see the independant work of Demp and Robbins.

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

Hey Simon,

It may be. If Bruce Williams were lurking out there he could tell us, but i thought it followed COP from one side to the other and a break in the "normal" sin pattern had some meaning. It should now be painfully obvious that I know nothing about how the machine really works. :-)

Thanks, Simon,
Kevin M

Sorry to not get this in on the first one, Simon,

You wrote: It rarely is parabolic: see the independant work of Demp and Robbins.

While I appreciate that, I hope to soon have some work finished that demonstrates the opposite. Evne in cadavers, If I cut the tendons so that I can get every joint congruent, the met heads fall into a parabola. If the lat cun disengages from the NAV and Cuboid, leaving the medial and lat columns to opperate independently, the 1st met head, with the second and third following, increase their distance froma given point on the plantar surface of the calcaneus. In other words, of the foot pronates - at all - the parabola is lost. On a naturally high-arched person, they could appear to have normal arches, but demonstrate what i describe. I haven't gathered enough data to run my mouth just yet, but it sure is looking suspicious.

Cheers,
Kevin M

Craig,

I have enjoyed all the comments on this post.

Now that it is 2008, do you have more to say about pressure patterns and the gearing mechanism of the foot in propulsion?

My experience with F-scan pressure studies suggests that the low gear pattern may include the hallux. Whay say you?

Michael DeBrule DPM
Marshall, MN

Michael,

Now, nearly 2 years later, I still think high gear-low gear propulsion is a very weak and misleading concept that has little mechanical significance.

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

thank so much craig for this well explained concept of high gear and low gear.
Now, i understood how it works.

cheers

__________________
***E L L E***

Craig and all

This thread resurfaced and I had not read it before (or could not remember reading it before) so I read it this time. It is a long discussion so I hope I don't go over too much that already has been said.

For a start I had not previously read BM high low gear theory although I thought I knew the concept. In fact I didn't. Previously I thought it was to do with the high gear of the hallux windlass versus the low gear of the lesser digit windlass action.
But having read Craigs summary I see it is not. From Craigs description I see it is to do with lever / moment arm lengths of the 1st 2nd MPJ axis versus the moment arm of the 3rd-5th MPJ axis relative to the achilles tendon insertion. IE the 3rd - 5th is shorter. Therefore since power = moments * angular velocity the shorter moment arm potentially will produce less power for propulsion. Therefore the theory is that the CoP moves across the foot lateral to medial so that potential propulsive power is at its optimum. Also the secondary purpose of directing the forward progression the correct direction onto the next step ie toward the medial.


This is a convenient theory but may I propose some other alternatives.

1) The CoP or CoF (centre of force) that is commonly spoken of is that of vertical force as characterised by a pressure mat. The true CoF also has a horizontal component. Therefore CoP can be anywhere on the foot and still direct the CoM medially during propulsion.

2) The body doesn’t need to do anything, it is allowed or tends to to follow the line of least resistance perhaps. The switch is just a natural progression. Due to the mechanics of the foot and the nature of foot placement in 'normal' (I prefer the term 'standard') walking the CoP must go from lateral to medial. If it does not some other force must be applied to stop its natural standard course. IE the foot remains supinated. Therefore the low gear propulsion is an effect of non-standard mechanics and not the cause.
(Which is basically what Eric said and Simon showed, I think, IE the foot/stj will remain pronated and in the high gear position until there is some other supination moment acting on it)

3) In the reference frame of the foot the CoP may be deviating to the medial but in the global reference frame there could be zero or far less medial deviation if the foot is abducted ie toe out, which it usually is. Therefore the CoP does not deviate because it needs to rather the CoP naturally progresses to the medial foot and the higher propulsive forces are bourne by the more massive structure of the 1st ray and MLA. In this case even though the CoP deviates to the medial, in the foot reference frame, the CoM is not necessarily being directed medially.

4) As Kevin said the anatomical position and the compliance of the rays will determine the position and relative transverse displacement over time of the CoP.

5) Assessment of 2D single camera photography of 3D events can have confounding elements that make evaluation of the action of interest unreliable.

6) Do any studies compare the GRF difference and power output between lateral foot push off and medial foot push off? Is there any difference in CoM velocity or is power loss at the ankle compensated for by increased power at the contralateral hip as in unilateral Transmetatarsal amputees. TMA subjects do have decreased ankle power output but it is not clear if this is due to a short foot or antalgic response to chages in forces. Only those amputations that are above the MPJ's have low power, if the MPJ head is intact then power output is very similar to normal. Wouldn't this be the same for low gear push off?

7) If you have a short lever you can increase the force and achieve the same power output. Antalgic response to higher forces may cause gait compensations and therefore low gear push off becomes less propulsive to avoid tissue damage.

Bruce wrote
This seems to make sense at first but I would say that if the foot is propulsive in the low gear position then it is because of compensation for some other pathology and the supinated position itself will not necessarily lead to excessive internal tissue stress.
If the patient just walks slowly then they may not increase tissue stress to a pathological level. If the compensation was for say, a hallux rigidus and the clinician, only viewing the low gear push off, added a valgus forefoot wedge and restored the high gear push of. How would this affect foot pathology? Wouldn’t the patient be worse off.


I would take the view that the lateral or low gear push off is an alternative to the natural progression of the gait cycle where push off is on the medial or high gear side. It is a compensation for pathology or anatomical variation and not a pathological condition itself. Propulsive power may be less but not necessarily and the CoM direction onto the next step is not necessarily sub optimal. The clinical presentation of a low gear / lateral push off may be a good clue to diagnosis but is not a direct indicator of pathology itself.

Just my view for what its worth,

Cheers Dave

"Propulsion is via met heads one & two (ie BM's high gear or transverse axis) ... a good thing.

Propulsion is via met heads 2 to 5 (ie BM's low gear or oblique axis) ... a bad thing.

Here is the picture above marked with SiliconCoach drawing tool to illustrate this":

More on this one!

Has there been any research conducted on using video analysis to look at propulsion in this way? By this I mean High gear vs Low gear and the application of video analysis to this theory. Practitioners have used silicon coach to better view medial or lateral toe off. This technique seems mainly anecdotal....I would like to use anything in the literature on this in some research of my own. Very interesting thread!

Regards podpup

Craig, for the 'oblique axis' to be the 'path of least resistance' then the counter rotatory force to the force applied by the achilles tendon (ATF) must be greater in the 'transverse axis' scenario, assuming the ATF is equivalent for both 'axes'. Why would this be so? If respective ATF's = counter ATF's then difference in lever arm lengths wouldn't account for it. Thanks, mark c

Moreover, this assumes that there are two rotational axes, in reality there are five, one for each MTPJ. The dorsiflexion stiffness of each digit will be important- see Spooner's Test . I know Eric Fuller has spoken about this previously and the assumption of constant velocities etc. Perhaps he'll chime in here...

__________________
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."

from post #16 of this thread

Just because you have a longer lever arm does not mean a faster velocity of push off. An erroneus assumption of constant angular velocity has been made. With high gear push off ground reaction force has a longer lever arm to resist ankle joint plantar flexion. So much greater force would have to be present in the tendon, with long gear push off, to have the same angular velocity as a short gear push off. We do not know Achilles tendon tension, so we cannot conclude that high gear is automatically faster. A real world example. Get on your bicycle pointed up a slight incline and put the bike in the lowest gear and in the highest gear and start pedaling. In the high gear you might not be able to move the pedals because the resistance is so high. This may be the case for the foot. In the lowest bike gear you will certainly, be able to move the pedals, but you may not be able to go very fast. As you try different gears, you may find one that is optimal for speed. We don't know where the "gearing" of the foot is in relation to optimal speed production.

Cheers,

Eric Fuller