Midtarsal Joint Equilibrium Theory

We must remember that midtarsal joint motion doesn't include midfoot joint motion also. Therefore, it seems somewhat unrealistic to only be discussing midtarsal joint function especially when the latest bone-pin research shows considerable motion at the other midfoot joints also.

In answer to Simon's question, when both the heel and forefoot are in contact with the ground, it makes sense to me that any movement of the rearfoot in one plane will have a complementary opposite motion of the forefoot, as long as the plantar calcaneus and all the plantar metatarsal heads remain in contact with the ground (i.e. midstance only). Why? Because the rearfoot and forefoot are directly attached to each other at the midtarsal joint!

Stabilization of the proximal aspect of the rearfoot on the ground at the plantar calcaneus and stabilization of the distal aspect of the forefoot on the ground at the plantar metatarsal heads when combined with the distal aspect of the rearfoot and the proximal aspect of the forefoot undergoing the same three dimensional displacements at the midtarsal joint level (because they are attached to each other) means that the forefoot and rearfoot will always be moving anti-phase to each other, as long as the plantar calcaneus and plantar metatarsal heads remain stable on the ground during those movements.

 

I have not used our modified vector coding technique in other pathologies yet, although there seems to be some potential. There are variations of this technique, e.g. Continuous relative phase (CRP). Some of this work has been done in the UMASS and Unv Delaware labs. The CRP technique is a bit different as it incorporates a velocity component. It is a bit more difficult to conceptualize. We recently published a paper on comparing CRP and vector coding. Variability in kinematic coupling assessed by vector coding and continuous
relative phase

Ross H. Miller, Ryan Chang, Jennifer L. Baird, Richard E.A. Van Emmerik, Joseph Hamill. Journal of Biomechanics 43 (2010) 2554–2560

 

It's not to say that pathology (e.g. plantar fasciitis) does not exhibit ANY anti-phase motion. Both healthy and plantar fasciitis exhibit anti-phase motion. The method that I put forth determines the number of anti-phase movements. We found that healthy feet exhibited MORE frequent anti-phase. This method highlights that anti-phase motions occur, along with others. It informs us about how the kinematics are unfolding - something we can't see from traditional time series. With the blind eye, you really can't determine how 'many' anti-phase movements are occurring across stance phase - although that would be really cool if we could.

You're very welcome. Thanks for having me. I think you are citing some of my abstract work from PFOLA? At the time we had limited numbers and these were prelim findings. These are the dangers of reporting data too early at a conference, unfortunately. The data that I speak of now are the final data set. 22 healthy and 22 plantar fasciitis.

My perspective on the matter is inspired by the work of Elftman, Bojsen moller, and others on 'locking of the midtarsal joint.' In fact, I proposed the use of this modified vector coding method particularly to examine this theory. They discuss (although somewhat vaguely at times) that forefoot pronation along with rearfoot supination stabilizes the foot - These are anti-phase movements. When this anti-phase motion is absent, the foot is not an 'effective lever.' In my data, it appeared that more anti-phase movements were associated with a healthy foot - a more effective lever. That's what I really mean when I say "more fluid movements transfer." I'll be more clear in the paper.


Also please note that in my work I have modeled a medial forefoot segment. Someone mentioned that they were uncomfortable with a whole forefoot, and some of the recent work suggest that a 2 segment forefoot is more appropriate. I originally had proposed a whole forefoot, but later altered the model to utilize a medial forefoot due to these newer findings about the forefoot. Again, I hope to get these data and details out soon.

 

Hi everyone
I started to integrate Nestor's articles into biomechanics classes over the last 3-4 years.
I am wondering if you were in the classroom can you simplify these concepts without losing the undergrad?

 

Here the abstract Ryan refers

to.

 

Ive written a post/reply/question to this 3 times now

Heres 4

Always seems a little exact to me there must be time when no motion occurs I would have thought - but maybe you can expand a little Kevin.

For this to be so the MTJ would always need to be in a certain spartial location in relation the motion occuring at the STJ, and if this is so then the MTJ axis is really not that independent to the STJ.

Simon has worked with me to show that something like COP can cause in-phase and anti-phase motion around the MTJ and STJ axis, which I beleive we were discussing when the foot was in midstance ( correct me if I´m wrong Simon). Which lead us and Jeff and I looked at again last night I think Nester indicated that mutiple motions of single, two or three plane could occur at a mutiple of compination at the midtarsal, and that the use of Supination and pronation at the midtarsal joint may not be the best way forward

We have also discuused quickly that it maybe to do with when and where in-phase and anti-phase motion is occuring - but if it is always anti-phase during midstance knowing the motion at the STJ will give us the motion at the MTJ and as I said will define the position of the MTJ axis to allow these motion - it reduces the indepdence factor of the MTJ.

Maybe this is the rebirth of the Forefoot Varus post.

Notsure if there is a question in there but looking for some expansion of ideas as there is conflicting information re in-phase and anti-phase motions at the MTJ and STJ

 

How does the lack of frontal plane coupling reported by Pohl influence this?

Here's a screen shot of a 3D model I built this morning, hopefully I'll be able to use it to demonstrate the effects of discreet GRF vectors about the axes. (just a shame you can't upload .avi files here.)

 

Kevin wrote:

Simon and Michael:

I figured that when I used the word always, that you would get pretty excited about it. Would like to see you prove me wrong.:drinks

 

It not about proving you wrong Kevin, it's about trying to explore the science and improve our understanding of the complexities of foot biomechanics. So, how do you think the lack of frontal plane coupling reported by Pohl will influence your contention?

 

My weekend for heading to the hills in a couple of hours- well ocean in this case. No computer at the cabin, so will be add anything to the discussion in a positive or negative set.

To me there seems to many viariables - but if we take the force thats driving the STJ and work from there.

In our COP examples we have shown the areas where COP would cause both in-phase and anti-phase single plane motion.

In these 2 pictures we have shown that COP vector moments when they occur in various area will in-phase or anti-phase. Where the areas outlined by colour are in phase motions at the MTJ and STJ . The picture on the left inversion and eversion and the right dorsiflexion and plantarflexion

The problem for me is that there are so many variables acting internal and external and that the axis due these variable are always moving and finding new equilibrium points and that the MTJ axis has greater variables in position to the STJ axis.

So I guess I´m saying where do you start this FEM ?

 

ooops, forgot the attachment:


I still think we should look at the axial positions that Nester derived from kinematic data to inform our discussions, but for now I've modelled X,Y and Z MTJ axes, green line is the STJ. Next week I'll add some external force vectors and show their three-dimensional relationship's to these axes. I may have to post it up on you tube though so you can see the model being rotated to get a better feel for it. After that I'll start segmenting the model....

 

I'm looking at this from a theoretical standpoint and believe that what I have stated earlier about the necessity for anti-phase motion in the rearfoot and forefoot during midstance is a basic reality of any mechanically coupled system such as the human foot. I believe that if we come up with some basic modelling realities of this mechanically coupled rearfoot-forefoot system, such as anti-phase motion must occur during midstance, then we can better understand the experimental results.

If, for example, we were to assume that the midtarsal joint is a single universal joint with a point location within the foot and the rearfoot "hinges" around the plantar heel (e.g. attached to the ground) and forefoot "hinges" around the plantar metatarsal heads (e.g. also attached to the ground) during midstance, then I just cannot see how rearfoot motion cannot affect forefoot motion in an anti-phase fashion. In other words, any motion of the distal aspect of the rearfoot to a new spatial location will also mean that the proximal aspect of the forefoot will also now have moved to the new spatial location of the distal rearfoot. And, since we have given that the proximal plantar rearfoot and distal plantar forefoot have remained "attached" the ground, analogous to universal joints at the plantar foot-ground interface of the rearfoot and forefoot, then anti-phase motions of the rearfoot and forefoot must occur. To me, this basic rigid-body modelling concept is very similar to Chris Nester's proclamation that it is the joint motion that produces the joint axis, not the joint axis that produces that joint motion.

As such, I was hoping that if you, or anyone else, can't provide me with an explanation of why I would be wrong, then we may have come up with a basic mechanical modelling concept for the midtarsal joint that is "something solid to stand on" so that we can progress further with our understanding of this interesting subject.:drinks

 

Fantastic place to start, Simon.

Look forward to the next parts of the discussion.

Have a good weekend Simon, Kevin, Ryan, Jeff well everyone.

 

I think we already have by demonstrating how the net GRF vector may cause either in-phase or anti-phase moment depending upon its spatial relationship to the STJ and MTJ axes. Unless the internal moment is equal to or greater than the external moment, the location of the net GRF vector relative to these axes will determine whether or not the forefoot and rearfoot move in-phase or out of-phase. :drinks

 

Something for the weekend, Sir? Lets say the the net ground reaction force vector is in exactly the same position as the MTJ Z axis (represented by the blue line on the diagram). In other words the blue line is both the MTJ Z axis and the net ground reaction force vector. It might not be easy to see on the diagram, but the green line representing the subtalar joint axis passes medially to this blue line. In the absence of any other forces: what would be the direction of the moments acting on:
a) the STJ axis (green line)
b) the MTJ X axis (yellow line)
c) the MTJ Y axis (red line)
d) the MTJ Z axis (blue line)

Given this would the forefoot move in-phase or anti-phase with the rearfoot?

P.S. Can anyone remind me who published the paper showing the helical axes for the CCJ and TNJ, I thought it was Van Langalaan, but I can't seem to find it.

 

I was away for a week and am trying to catch up. Was there a point where we assumed that the MTJ has fixed axes of rotation? I'm having a hard time looking at the anatomy of the joint and seeing how having a fixed axis is a possibility. It seems like a lot of this discussion is based on the idea that MTJ has a fixed axis. The motion determines the axis. The midtarsal joint is essentially a planar joint with an envelope of motion. It will move in the direction it is pushed and then a new axis of motion is created. This makes it impossible to speak about moments about axes for the midtarsal joint.

An axis of motion is an imaginary line that is often very convenient to use for many things. Mathematically, we can calculate a moment about any arbitrary line. We need to examine where this produces useful information. When we use an axis of rotation for a joint it implies that there is a force couple at that joint with one of the forces of the couple being applied at the axis of rotation. If that doesn't happen, I'm not sure the calculation of moments is valid for prediction of motion.

Cheers,

Eric

 

Eric, I've been waiting for you to comment. We started off looking at the axes for the MTJ that Nester published from his kinematic studies. He basically showed three axial positions in his paper: one for loading response; one for midstance; and one for propulsion- see my earlier posts for a picture of these. Assuming that the axis is in existence as long as there is motion at the MTJ, we can assume that the axis must be changing position constantly to swing between the axial positions which were reported by him at these specific points in time. That is, if the bones making up the MTJ are in constant motion throughout the contact period. Obviously, if there are periods where no motion is occurring the axis may jump in space.

Next, Kevin suggested that we should really assume a Cartesian co-ordinate system of axes for the MTJ, so that we have three orthogonal MTJ axes: X, Y, and Z. Again, Nester had previously talked about this approach too.

I really don't mind how we model this because the point I am trying to make can be made either way, but I lean toward using the kinematically derived position of the net MTJ axis that Nester reported, rather than this X, Y, Z approach. Never-the-less, what we a trying to do, is to model the external moment acting about either the kinematically derived MTJ axis (labelled B in Nester's paper and the diagram I posted on page 1 of this thread) or the X, Y and Z axes and a theoretical STJ axial position at midstance- kind of a quasi-static analysis. So at this instant in time the axes are as stated and the CoP position is as stated (wherever we want it to be in this hypothetical) and the net GRF vector is assumed to be vertical. What I've highlighted is that there are theoretical positions for a centre of pressure in relation to the STJ axis and these MTJ axial positions that should result in either the forefoot moving in the same direction, or in the opposite direction as the STJ.

Please read through the thread. I should welcome your thoughts, but view it as a quasi-static analysis as you did when you looked at CoP position relative to the STJ axis, which is also constantly moving throughout contact period and also only exits when there is motion at the joint. i.e. that the force vector is vertical and that the axes are fixed at this point in time.

 

I thought it was Manter?

 

No, I was thinking of an in-vivo- I think.

 

Like-wise with the modelling that I have presented here. Kevin and all, can you find fault with the approaches that I have taken to modelling the external moment acting simultaneously upon the STJ and MTJ axes that I have presented in this thread? Please, prove me wrong.

Anyway:

Now try this: stand on one leg. Perform a small knee bend- a) first, such that the knee passes medially to the foot; b) next, have the knee pass over the second toe; c) then, have the knee pass laterally to the foot. Does the forefoot move in-phase, i.e. in the same direction as the rearfoot, or, in the opposite direction, i.e. anti-phase?

In me: a) and c)) = frontal plane is in-phase: for a) rearfoot everts, forefoot everts; for c) rearfoot inverts, forefoot inverts (which seems odd since frontal plane motion between the forefoot and rearfoot is not supposed to be coupled (at least during gait) according to Pohl); b) there is little motion of the forefoot on the rearoot, if there is motion it's probably sagittal plane and it's probably anti-phase- the longitudinal arrangement of the plantarfascia seems to resist motion in this situation. Why are these results so? Does the knee position control the in-phase / anti-phase motion of the forefoot on the rearfoot? If so, how?

 

The rearfoot and forefoot can only move anti-phase until the internal tissues tensions create an equilibrium between the anti-phase external moments and the in phase internal moments resisting this motion pattern or vice versa. For example, lets look at the sagittal plane and lets assume an external rearfoot plantarflexion moment and an external forefoot dorsiflexion moment about the STJ and MTJ X axis, initially the forefoot and rearfoot will move in opposite directions with the forefoot dorsiflexing and the rearfoot plantarflexing, before too long the tension in the plantarfascia will increase and arrest any further rearfoot plantarflexion and any further forefoot dorsiflexion, at this time the forefoot and rearfoot will begin to move in phase in the sagittal plane so long as the internal moment is maintained in balance with the external moment. Obviously, active tissues could provide a similar internal moment., e.g. certain plantar intrinsics. In this case tissue stress increases until equilibrium is reached.I guess if the role of achieving equilibrium is shared among the tissues, the stress levels shouldn't reach pathological levels, but if a foot becomes reliant on one tissue too much, pathology will result. Now think about external moments that create in phase motion at the forefoot and rearfoot: is tissue stress going to be higher or lower in this case?

P.S I do realise that this is Kevin's original diagram on page 1 of the thread.



Bed now.

 

Simon:

I think we may be having a terminology problem with what constitutes forefoot eversion. I would define forefoot eversion as the distal forefoot everting relative to the proximal forefoot. Is that what you also would consider to be the proper definition of forefoot eversion? I think you may be describing eversion of the forefoot relative to the ground which would totally change our discusssion. In reading your description above, are we talkiing apples and oranges here?

 

Since we are talking about forefoot to rearfoot motion occurring at the MTJ, I am talking about whether the forefoot everts when the rearfoot everts, so in my example of a small knee bend with the knee passing medial to the foot, both my forefoot and rearfoot evert relative to the cardinal planes (my rearfoot and forefoot move in-phase); both my proximal and distal forefoot evert relative to the MTJ "Y" axis, my heel everts about the STJ axis.

 

Maybe it´s driven from the tibia. Tibia force coupling - hey didn´t we discuss this before in relation to leg stiffness

 

Pint of beer to Simon.

Van Langalaan it seems to be.

Taken from the discussion A kinematical analysis of the tarsal joints: An x-ray photogrammetric study.

 

Simon:

This may be our problem. I believe that we are talking around each other here terminology-wise.

If the foot and forefoot was flat on the ground and then the rearfoot everted and the forefoot stayed flat on the ground, I would say that the forefoot had inverted since I am using the common podiatric convention of describing the motion of the distal forefoot relative to the proximal forefoot, not the motion of the whole forefoot to the ground.

Is this the same convention you are using?

 

Here's the full reference:

Van Langelaan EJ: A kinematical analysis of the tarsal joints: An x-ray photogrammetric study. Acta Orthop. Scand., 54:Suppl. 204, 135-229, 1983.

By the way, this is one of my favorite foot biomechanics research papers of all time.

If you want the full paper (more like a book), I have it available for downloading at my box.net website

http://www.box.net/shared/z9vvdj6lt8

You may contact me privately for the password.

 

As the MTJ is an independent joint could the above example indicate that the Rearfoot has everted and the forefoot has not moved ?

Thats how I am seeing it anyway ... Yes there has been motion at the MTJ and STJ articulation but the motion is occuring at the calcaneous and talus where the navicular and cuboid maybe fixed or not undergoing motion . ??

So in relative terms the Forefoot maybe more inverted relative to the rearfoot but as we are discussing motion we only have motion at the rearfoot . I think ?

 

Pictures speak a thousand words. I've attached a couple of skin mounted markers to a foot: one to the skin overlying the medial calcaneus and one to the skin overlying the medial cuneiform and looked at the frontal plane position and displacement of the these markers when the foot is in relaxed stance; with a small knee bend with the knee passing laterally to the foot (foot inverted); and with a small knee bend with the knee passing medial to the foot (foot everted) . The markers always moved in the same direction (i.e., they moved in-phase) between positions. And the distance differential between them in the frontal plane stayed roughly the same (i.e., they moved in-phase, not anti-phase). I'm assuming Ryan Chang also used skin mounted markers in his study, albeit more sophisticated than mine, but that shouldn't change the way they move. Ryan, a photograph of your marker set-up would be really helpful. If I get time tomorrow, I'll add a third marker at the MTPJ and re-photograph (I actually did it today and it moved in-phase too, I didn't photograph it though). I'll also photograph the displacement of the markers in the sagittal and transverse planes, so you can see what anti-phase movements looks like. I might try and do some dynamic stuff too, it'll be 2D, but the gross movement pattern should be observable- IF, I find time between patients.

Anyway, this is distracting from the point I'm really interested in: is the method I have used previously within this thread to model the axes of the MTJ and STJ relative to a net ground reaction force vector acting at a given centre of pressure position erroneous or valid? Kevin and Eric- you thoughts please.

 

Nice balls, Simon!:drinks

 

I thank you (I got them polished for the photo shoot). I got the gaffer tape from one of the roadie's at the U2 concert last week. So we can be sure we are talking apples and apples, not apples and oranges: in your opinion, is the frontal plane motion between these markers in-phase or anti-phase in this example, Kevin?

 

I went off during today and looked at bone pin studies.

I just could not workout if it´s possible to detect if the motion was in-phase or anti-phase from the Lundgren et al paper - listed below. It shows motion in the body plane clearly. Thought I would post it up for the more learned folks to see if helps solve the midstance phase question.

 

I missed this until now: I wrote:

Kevin, you responded:

Yet according to Pohl, the forefoot and rearfoot are not mechanically coupled in the frontal plane! (http://www.ncbi.nlm.nih.gov/pubmed/16759862) So what would happen if the human foot was uncoupled between forefoot and rearfoot in terms of it's movements in one or more planes? They could move independently- right?

Why do the forefoot and rearfoot move in the same direction (in-phase) in some people, some of the time, and anti-phase (in the opposite directions) in some people, some of the time- what is driving these different motion patterns to be well,... different? Internal + external moments. I've provided an explanation for the difference due to external moments, which I think is valid (if you think it is invalid- please speak up). Can a difference in internal moments explain this too?

I'm finding this thread very thought provoking. Not least since my little experiment seems to suggest that forefoot to rearfoot motion is coupled in the frontal plane, at least during small knee bends .

Thanks for your time, Kevin :drinks

 

In phase.....but I still think we are using different frames of reference here. Once we agree to terminology as to the reference frame used to describe forefoot motion then we will be able to make progress.

 

This is why I want to see Ryan's marker set, so we can see what reference frame he was using. Thanks, Kevin. :drinks

 

Frame of reference is critical when we are discussing forefoot motion. In previous discussions on this subject, I was assuming forefoot motion was the motion of the distal forefoot relative to the proximal forefoot, not a part of the forefoot relative to the ground as you did in your "balls" experiment. Therefore, using one frame of reference, the motion of the forefoot to rearfoot may be in-phase, while using another frame of reference, the motion of the forefoot to rearfoot may be anti-phase.

Time now to set our definitions straight so we can all speak the same language and hopefully make some progress on this subject.

Simon, please define how you think forefoot motion should be described, distal aspect of forefoot relative to distal rearfoot? distal to proximal, single marker relative to ground, multiple markers relative to ground????

 

Kevin, in terms of this discussion it is not how I am describing forefoot motion that is important, it is how Ryan has described it. As for me? I'll put some more balls on tomorrow: some on the proximal forefoot, some on the distal forefoot and some on the rearfoot. We can then see how they move relative to each other and relative to the ground. Today, the rearfoot marker and proximal forefoot marker moved in the same direction relative to each other and relative to the ground in the frontal plane- agreed?

 

In all the other joints of the foot and lower extremity, we typically describe movement as being the distal body segment moving relative to the proximal body segment.

Examples:

Hip flexion: Distal femur moves anteriorly relative to pelvis

Knee extension: Distal shank moves anteriorly relative to femur

Ankle plantarflexion: Distal rearfoot moves plantarly relative to shank

Hallux dorsiflexion: Distal hallux moves dorsally relative to first metatarsal

Now, in the case of the midtarsal joint, shouldn't we also use the same convention? In other words, shouldn't forefoot inversion be defined as inversion of the distal forefoot relative to the rearfoot or should forefoot inversion be defined as inversion of the proximal aspect of the forefoot relative to the ground? In other words, should a proximal forefoot that everts relative to the ground during closed kinetic chain subtalar joint pronation be considered as forefoot eversion, even though, during this motion of the forefoot relative to the rearfoot, the distal forefoot is inverting relative to the rearfoot??

There is no right or wrong in this terminology discussion since there are obviously pros and cons to each reference convention that can be used to describe kinematics of a body segment within the biomechanics research community. However, unless the individual is aware of the reference convention being used by a researcher when a discussion is begun, then confusion will result to many of those involved in the discussion and to many of those trying to follow along with the discussion.

Hopefully, Ryan will chime in here to clear up any confusion about what his definition for "forefoot inversion-eversion", "forefoot plantarflexion-dorsiflexion" and "forefoot adbuction-adduction" actually is.

 

Agreed. And, by the way, good work, Dr. Spooner!

 

Simon's experiment:

I tried Simon's experiment and had the same general observation. Here is the problem. How and where do you measure this motion, especially if you’re attempting to isolate the stj and or the mtj?

In the above experiment, if my forefoot and rearfoot invert and evert equally, there would be no relative inversion or eversion of the forefoot relative to the rearfoot. However, when I pass my knee medial to my foot and my forefoot and rearfoot both evert, if my forefoot everts just one degree less than my rearfoot, that would constitute relative inversion of my forefoot to my rearfoot. How can I measure that? I can't.

During closed chain pronation of the stj, the talus and navicular both adduct and plantarflex. However, because the navicular adducts and plantarflexes slightly less than the talus, it results in relative abduction and dorsiflexion of the navicular as compared to the talus. But if I just looked at the talus to the floor, all I see is talar adduction and plantarflexion. So, if is often necessary to use both the ground and the relative position of osseous segments to describe the motion involved. This is really the essence of being able to describe closed chain motion of the foot.

Jeff