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For what its worth here is what I really think tonight, increased GRF beneath the 1st met head resulting from 1st met plantarflexion should increase supination moment regardless of STJ axial position since even if the 1st met head is lateral to the STJ axis, the increased GRF here should draw the COP closer to the STJ axis- see the thread on forefoot valgus wedging. However, what we have to consider is that plantarflexion of the first ray is likely to occur in response to two main drivers: 1> peroneus longus contraction 2> compression on metatarsal head. Peroneus longus functions via a pulley mechanism about the cuboid, the action of peroneus longus at the cuboid will create internal pronation moment and external moment about the STJ axis; the nature of the external moment will depend upon the COP position and net GRF vector's relation to the STJ axial position. These moments about the STJ axis may or may not exceed the change brought about in external moment resulting from shift in COP due to increased GRF under the 1st met head due to 1st met plantarflexion. So the key is the STJ axial position. Something like that- it's late and I've had a tough day! Now, I'm just trying to work out how peroneus longus activity raises the base of the 1st metatarsal as Robert suggests. I can see how compression on the metatarsal via the base of the proximal phalanx could do this due to the inevitable force couple, I just can't see how peroneus longus can do this. Like I said, it's late and I'm tired- maybe tomorrow I'll have more lucid thoughts...... Without plantarflexion of the 1st met, can the windlass work so can we have adequate compression on the the 1st met head without windlass? I guess the ehl, fhl and intrinsics attaching to the hallux could achieve this in the absence of forces from the plantar fascia- rambling now.

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Thinking gobally you can add the CNS into the equation. When there is a high pronation moment from the ground there has to be a high supination moment from some source to counteract the pronation moment from the ground. The CNS is faced with some tough choices in the presence of a medially positoined STJ axis. It has to work that poor posterior tibial muscle and tendon much harder than feet with average STJ axes, or it can allow very high stresses in the anatomical structures that limit STJ pronation. If one of the structures becomes painful the options are worse.

I guess my point is the high tensile forces don't come from the ground, they come from high activation of the muscle from the CNS.

Cheers,

Eric

Don't think motion, think forces and moments. In a standing foot, the posterior tibial tendon tension increases, the STJ supinates, the medial arch rises and the ground reaction force decreases on the first met and the met plantar flexes. The met plantar flexion did not cause the supination moment.

Now to discuss moments at the STJ you should be talking about how forces get applied to the talus and the calcaneus. When you dorsiflex the 1st toe in stance the tension in the fascia increases and the first prox phalanx applies an anterior to posterior force on the metatarsal....then there is an anterior to posterior force from the navicular applied to the talar head at the same time there is an anterior pull at the plantar fascial attachment to the calcaneus. This will cause a supination moment most of the time.

These same forces that cause supination of the STJ will tend to cause plantar flexion of the metatarsal. The geometry is important, but it's the forces that do the work. See my Windlass paper.

Cheers,

Eric

If the first ray plantarflexes, and as a result the ground reaction force (GRF) is increased plantar to first metatarsal head as a result, then this will tend to either decrease the external STJ pronation moment or increase the external STJ supination moment, all other factors being equal. After heel off, probably a bigger factor than first ray plantarflexion in creating external STJ supination moment is the magnitude and duration of gastrocnemius-soleus contractile activity that creates an internal STJ supination moment.

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Sincerely,

Kevin

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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

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I read this a couple of time and it starts to make sense. My question, how does this effect the MTJ . Ie as the PL contract there will be a increase in the external STJ supination moment ( from plantar to lat malleolar and cuboid) , Plantarflexion and increased stability of the 1st met. As the 1st met plantarflexes I´m thinking there will be an external inversion, dorsiflexion and abduction moments on the x,y,and z axis as discussed by nester.

If I´m correct in my thinking this will also have some effect on windlass and what happens at the STJ axis ? or maybe I´m just confused as I´m 2nd guessing my post now....

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Michael Weber

The most common thing about common sense is it´s not very common.

I released now how wrong my statement above was..


I clearing was not thinking thru this fully as the PL pull on the cuboid which is part of the MTJ.

Sorry for not thinking before writting. Bit of theme of my life... anyway.

why is it that we don´t discuss the MTJ . So the PL will effect the stj but it must be very effective on the mtj but in this case people are discussing 1st met, stj axis cop widlass etc but no mention of MTJ motion, moments etc.

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Michael Weber

The most common thing about common sense is it´s not very common.

Gosh what a lot of interesting stuff about the windlass! Thanks to Simon Kevin and Eric for taking the time.

Sorry Eric, Having a hard time with this. Bear with me.

Bit confused here. Are we talking about what happens at heel raise in gait? And if so have I correctly understood that you are saying the PT tension supinating the foot is what casues the 1st met to plantarflex rather than vice versa? and that this is different to what happens here

To return a few steps, and trying to keep it simple for simple folks like me...

Kevin Said
Thats what I thought.

So If the Windlass is inoperative (say bacause the 1st mpj cannot bend), is this supination moment lost?

I'm just trying to understand where in the chain of logic my dodgy link is.

The other thing I'd like to clarify is simons question on HOW the windlass exerts its supination moment. I think I understand the concept that there is force X + on the calc and X - on the base of the 1st at either end. I also understand that this will cause an increased GRF sub 1st met. Where I'm struggling is what happens next.

The downforce on the 1st met is transmitted from body weight which is exerted through the base of the 1st met. Is the counter force not also transferred throught the base of the 1st met?





Thanks
Robert

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Robert Isaacs
Specialist in Biomechanical Therapies
www.Footprintspodiatrysolutions.co.uk.

Robert:

In static stance, a flattened first metatarsal head, by itself, would have no net effect on STJ moments.

However, during walking, if the flattened first metatarsal head caused a restriction in 1st metatarsophalangeal joint (MPJ) dorsiflexion, then the individual has the option of, 1) not decreasing their duration of propulsion by electing to supinate more at the STJ to decrease the ground reaction force (GRF) plantar to the 1st MPJ, 2) reducing the duration of their propulsive phase slightly without further supinating the STJ during propulsion, or 3) drastically reducing the duration of their propulsive phase by pronating their STJ during propulsion.

My guess is that those feet with fairly normal STJ axis spatial location will choose option #1, those feet with more significantly medially deviated STJ axes will choose #2 or #3 due to the central nervous system choosing that particular walking style to A) reduce the pain of walking, and/or B) increase the metabolic efficiency of walking.

As far as your other question is concerned, the windlass exerts its STJ supination moment as follows:

1. Hallux dorsiflexion causes increase in tensile force medial band of central component of the plantar aponeurosis (MBCCPA).

2. Increase in tensile force in MBCCPA causes increase in posteriorly directed compression force on first metatarsal head.

3. The simultaneous occurrence of #1 and #2 cause a rearfoot dorsiflexion moment and first ray plantarflexion moment which together cause a medial longitudinal arch raising moment [the magnitude of which will be dependent on the height of the medial longitudinal arch].

4. Medial longitudinal arch raising moment and posteriorly-directed compression force on the first metatarsal, first cuneiform and navicular will cause increased posteriorly-directed compression force at talo-navicular joint which will tend to push the talus posteriorly, which is one of the components of STJ supination motion. This posterior pushing force on the talar head will be resolved into a STJ supination moment, as long as the STJ axis is not too medially deviated. If the STJ axis is extremely medially deviated, this posterior pushing force will cause a STJ pronation moment.

Hope this helps.

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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
**************************************************

Nicely put.

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The original question was does first met plantar flexion cause STJ supination. What I was trying to do was give an example where the met plantarflexed, but the cause of the plantarflexion was not directly acting on the metatarsal. So, met plantar flexion will tend to correlate with STJ supination because all the bones are connected together, but STJ supination is not necessarily caused by Met plantar flexion. I guess another point I wanted people to think about is what causes the met to plantarflex. If you say that met plantar flexion causes STJ supination then you have to figure out what forces cause the met to plantar flex. This is why I had a hard time with the original question. I couldn't figure out what you thought was causing the met to plantar flex.


In Kevin's comment the source of plantar flexion moment on the metatarsal is missing. Yes if you were to take your fingers and grab the metatarsal with your fingers and twisted in the direction of plantar flexion there would be an increase in ground reaction force under the metatarsal.

Other sources of plantar flexion moment on the metatarsal Include:

tension in the peroneus longus tendon and compression at the met cuneiform joint. Specifically the force couple of a posteriorly directed force from the tendon and an anteriorlly didrected push from the cuneiform acting on the metatarsal.

Tension in the plantar ligament and compression at the joint surface at the met cuneiform ligament

And compression at the 1st mpj and compression at the met cuneiform joint. (Windlass)




The windlass creates different moments at different joints.
At the STJ think about the break in the cyma line in the sagittal plane. (The cyma line was described as a radiologic finding by looking at a lateral view x-ray and drawing a line at the talonavicular joint and the calcaneocuboid joint.) With pronation there is an anterior break of the cyma line where the anterior aspect of the talar head is anterior to the calcaneocuboid joint. With a posterior break of the cyma line the talar head sits posterior to the calcaneo cuboid joint. That was the motion that occurs at the joint. Now we have to think about the forces that cause that motion.

Take a loaded foot in static stance where there is tension in the plantar fascia. The tension of the fascia pulls the proximal phalanx into the first met. The phalanx doesn't go anywhere so there must be no net ant post force. (F = ma, a = 0 ) There must be a force from the metatarsal head acting on the base of the phalanx to maintain ant post equilibrium of the prox phalanx. If there is a force from the met acting on the phalanx there must also be a force from the phalanx acting on the met. (for pictures see my windlass paper or draw them yourself as the pictures help the understanding. Draw the bones separately) The met is not moving so there must a force from the cuneiform acting on the base of the metatarsal. Repeat for all bones back to the talus. So, the supination moment from the windlass comes from an anterior pull at the fascial attachment of the calcaneus and a posterior push from the navicular acting on the talar head.

So, simultaneously the windlass causes a plantar flexion moment acting on the metatarsal and a supination moment at the STJ (in most feet)

If you were to grab the 1st toe and dorsiflex it you would increase tension in the plantar fascia. Increased tension in the fascia will cause an increase in plantar flexion moment acting on the metatarsal. So, as you grab the toe and dorsiflex it you will be increasing plantar flexion moment of the first metatarsal and supination moment at the STJ. In addition the plantar flexion moment on the metatarsal will tend to shift the center of pressure under the foot medial and this will decrease the pronation moment from the ground.

The answer to your question Robert, is in drawing out all the free body diagrams of each bone. Start with the know forces and then estimate the missing forces. I went to the local college bookstore and bought an engineering textbook on statics. I did all the problems at end of the chapters and looked at the answers at the back of the book. It took me a while to work through it. The mistake that I made when teaching was trying to get people to understand what took me more than a month to learn in about four hours of class time. Anyway if you made it all the way through this post you might find the statics textbook fun and entertaining. I found it quite useful.

It reminds me of a story a former student told me. He said he was on top of his roof fixing a TV antenna with his father and his father was having trouble rotating the antenna. My student said he thought of me when he showed his father where to grab the antenna so that it would be easier to rotate it. So, someone else found it useful too.

Cheers,

Eric

Hi Robert
Thank you for the welcome, this is a great blog full of interesting and thought provoking subjects. Regarding your point about a ruptured liagamnet which results in a deformed foot, is probably a challenging question as it is perhaps an extreme situation. If I could for the moment ignore the injury and talk about a somewhat normal foot, if we looked this foot print I sand. We might see that the arch of the foot is somewhat supported by the sand and that the entire plantar aspect would be supported and that possibly there would be a reduced amount of “pronation”. There are other complicating factors such as the base of the 5th metatarsal, which often comes into contact with the firm surface under foot early and therefore forces the mid and forefoot into a quicker pronation movement. So if I was to take a cast it might be better taken over a sand box with the patient partial weight bearing. Does this make any sense?

Robert Stated:

Let us consider for a second how a normal healthy foot with a nice healthy function will appear in relaxed stance. The orientation of the Sub Talar Axis means the centre of mass will tend to come down on the pronation side of the line, so the foot will pronate until something stops it. What structures limit pronation? The Tibial muscles group certainly, but it would not be efficient for them to hold the patient in supination when in relaxed stance. The planter fascia / windlass? Sure but there is not a lot of tension there before heel raise (in most patients). Bony osseous limitation? Hope not, unless you are really arthritic! I contend that in most cases the limiting structure is the Deltoid ligament complex which limits the range generally. And what position will that keep the STJ in? Pretty near the maximally pronated position. It represents a position the foot CAN achieve and little more than that. It does not indicate the degree to which the calc everts during gait 2, 3 . The position of a “normal” healthy, effectively functioning foot during static weight bearing may be closer to maximally pronated than neutral, its is certainly not neutral!

DrSha Replies:
What happens when PERM is reached in stance and lets assume the deltoid, plantar fascia, etc. have reduced or eliminated the STJ from pronating further.
Are there any other structures (areas in the rearfoot) that can then supply additional “overpronation” into the foot or does all pronation exist in the STJ?
A possible example that I suggest is that once the foot has reached PERM, the medial side of the plantar pad (the soft tissue that exists from the plantar osseous calcaneal surface to the skin can collapse under the forces that exist and effectively pronate the rearfoot.

DrSha

Perhaps Admin would be kind enough to move this to the English thread on the same article...

However
This is going to take some explaining. Pronation is a movement of the STJ.

Oh and remind us what PERM is? Sorry, I tend to forget non standard acronyms.

Cheers
Robert

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Robert Isaacs
Specialist in Biomechanical Therapies
www.Footprintspodiatrysolutions.co.uk.

Never mind. Just remembered. Pronation end range of movement wasn't it.

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Robert Isaacs
Specialist in Biomechanical Therapies
www.Footprintspodiatrysolutions.co.uk.

Dennis you're back! Always a pleasure. However your first post after your hiatus and you are straight in where you left off (sigh).

Why don't we leave the PERMs to the hairdressers for now and get your thoughts on the original topic being discussed here

Ian

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