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Midtarsal Joint Equilibrium Theory

Discussion in 'Biomechanics, Sports and Foot orthoses' started by mike weber, Sep 3, 2010.

  1. Members do not see these Ads. Sign Up.
    I´m with Robert a looksee via the internet would be very intersting epecially around the midtarsal joint equilibrium theory. Kevin if at all possible could I have a look at the lecture notes on that one, or it would make a great thread discussion. As it seems after Nesters et al not much has been written about it in journals.
  2. Re: Competing Theories in Podiatric Biomechanics Seminar

    Here's a segment from my lecture.

    And here's one of my illustrations from the part of the lecture on midtarsal joint rotational equilbrium.

    Hope this is enough to give you a taste of some of the topics I will be lecturing on.

    Attached Files:

  3. Re: Competing Theories in Podiatric Biomechanics Seminar


    You may want to check out my 3rd book and the chapter on "Load-Deformation Characteristics of the Foot" where I discuss midtarsal-midfoot joint mechanics quite a bit, including spring function of the midtarsal-midfoot joints (Kirby KA: Foot and Lower Extremity Biomechanics III: Precision Intricast Newsletters, 2002-2008. Precision Intricast, Inc., Payson, AZ, 2009, pp. 49-60).

    If you want to start a new thread on the subject, I'll try to contribute as time allows.
  4. Re: Competing Theories in Podiatric Biomechanics Seminar

    Kevin, the only thing I think you should be aware of is that if we look at your diagram above we see a foot which has to be in dynamic function in order for there to be an axis of motion at the midfoot, so we must asume a "quasi-static analysis" here. In your diagram the foot is somewhere between forefoot loading and heel lift, maybe midstance. The best research we have for the net midfoot axis during this stage of gait, i.e. that of the Nester, shows an axis which is more longitudinally orientated at this point of the gait cycle than that which you have depicted.

    In the attached diagram the axis labelled "b" represents the axial position that Chris reported at this stage of gait.

    Attached Files:

  5. Re: Competing Theories in Podiatric Biomechanics Seminar


    Actually, Chris Nester and I talked about this years ago when he visited Sacramento (and spent some time at my old house) about 10 years ago. The analysis for rotational equilibrium would be around his "reference axes" of the midtarsal joint individually, yielding three separate sets of equations, one for each cardinal body plane (Nester CJ, Findlow AH: Clinical and experimental models of the midtarsal joint. Proposed terms of reference and associated terminology. JAPMA, 96:24-31, 2006). The illustration provided is only for MTJ equilibrium in the sagittal plane. I was supposed to write the paper for rotational equilibrium about all three reference axes of the MTJ after I finished my paper on SALRE theory, but something called "life" got in the way.:rolleyes::drinks
  6. Re: Competing Theories in Podiatric Biomechanics Seminar

    I don't buy this. We don't do this when we discuss subtalar joint axis (or any other joint axis to my knowledge), so why should we do this here? Further, does it make more sense to orientate the foot about the cardinal planes or about the axis? Orientating about the cardinal planes as you have done, does not make sense to me, as the axis is not perpendicular to any plane at this point in time. Moreover, we can take moments about reference planes, but why determine the axis to be perpendicular to the sagittal plane at the anatomical point that you have? i.e. why did you decide that the axis should piece the talar head?

    Surely it would have been easier to project the MTJ axis to the transverse plane, why did you choose sagittal plane modelling for this, when we usually look at transverse plane moments about the subtalar joint axis?

    There aren't three simultaneous axes of rotation, i.e. one orientated perpendicular to each anatomical plane. There is only one (if we model the midfoot in this way-personally I think we should take separate moment about the calcaneocuboid joint and talar-navicular joint). And if we modelled one axis perpendicular to each anatomical plane, we'd end up with a resultant, as indicated in the diagram that I posted.

    The other thing to note about the diagram I posted from the Nester paper, is that the axial orientations A and C result in neither pronation nor supination.
  7. Re: Competing Theories in Podiatric Biomechanics Seminar

    So, if we have three centre of pressure positions, indicated in the diagram as the black circles labelled 1, 2 and 3 and we take moments about the axis labelled b, assuming a vertical force vector, what would be the moments produced about the axis by each centre of pressure?

    what would be the moments produced about axial positions a and c?

    Attached Files:

  8. Re: Competing Theories in Podiatric Biomechanics Seminar

    P.S. Craig, if you could break off posts no. 12-17 into new thread entitled "rotational equilibrium about the MTJ", that would be stunning.
  9. Craig Payne

    Craig Payne Moderator

    Re: Competing Theories in Podiatric Biomechanics Seminar

    Done. This is the original thread.

    For those coming to the next round of Boot Camps, we do go over this...
  10. Re: Competing Theories in Podiatric Biomechanics Seminar

    And if you are feeling smart take simultaneous moments about the three hypothetical STJ axes labelled i, ii, iii and about the 3 MTJ axis labelled a, b and c and for each of the cop postions 1,2,3

    cop: position 1; mtj: position a; STJ axis i =?
    cop position 2; mtj: position a; STJ axis i =?
    cop position 3; mtj: position a; STJ axis i =?
    cop position 1; mtj: position b; STJ axis i =?
    cop position 1; mtj: position c; STJ axis i =?

    etc etc. if I find the time I'll matrix it.

    Have fun... you'll find some mad things, which I think cause pathology. C'mon Kirby, time we did that work...

    Attached Files:

  11. Re: Competing Theories in Podiatric Biomechanics Seminar


    You don't have to buy it...that's what makes this all so fun and interesting.

    Unfortunately (and fortunately), I'm heading up to our mountain property for a three day vacation with the family in a few hours so I can't spend too much time here and I have three patients waiting for me in the office.

    Let me ask you a question, Simon. If you were to model the kinetics of the hip joint that has multiple axes of rotation (a relatively non-constrained joint), how would you do it?

    I'll be back Monday.
  12. Re: Competing Theories in Podiatric Biomechanics Seminar

    I'd model it in a quasi-static manner: so for any given instant in time I'd look at the axial position and take moments about that axial position. How would you do it? Have fun in the hills.
  13. Re: Competing Theories in Podiatric Biomechanics Seminar

    Thanks Craig. I should be interested to here your thoughts on this...
  14. Re: Competing Theories in Podiatric Biomechanics Seminar

    What if you didn't know what the axial position was at any instant in time? Then how would you do it?
  15. Re: Competing Theories in Podiatric Biomechanics Seminar

    I would use kinematic analysis to derive the instantaneous centres of rotation and couple this with kinetic analysis to derive moments. And that's the key, Nester's subsequent work to the study which you cited did derive instantaneous axes. Hence the diagram that I was able to post.

    But lets assume that we don't know where the axis is. We can take moments about three orthogonal planes, but how can we know what the net moment is unless we simultaneously look at all three orthogonal planes. Indeed how can we know what the axial position is unless we measure the displacement in those planes? I only saw one plane in your diagram, and that diagram made the assumption of an axial position relative to the foots anatomy- why did you assume this axial position relative to the anatomy?
  16. Jeff Root

    Jeff Root Well-Known Member

    Re: Competing Theories in Podiatric Biomechanics Seminar

    One of the biggest challenges in understanding biomechanics is using the cardinal planes on limbs moving in space and joint segments moving relative to those limbs. For example, if you could instantly freeze motion of the mtj and took the final mtj axis from heel lift through toe off, the foot would externally rotate which would abduct the axis, and as the heel rose, the axis would continually become more horizontally oriented or even plantarflexed. Now, take that simple model and add mtj motion so the mtj axis actually changes in space with mtj. How can you relate it to the cardinal planes? It becomes very difficult.
  17. Jeff Root

    Jeff Root Well-Known Member

    Not to change the subject, but I bet Kevin's wife will really appreciate the fact that Simon got Kevin's mind going on this just before a three day trip with no internet access! Really got him relaxing now!!!
  18. Jeff, you know Kevin and I have been good friends for many years now, and he has always been a great mentor to me throughout this time, yet the online discussions we have together where I learn the most are those in which we challenge each other, sometimes I get burnt, sometimes I don't... we'll see how this one runs... I got the upper hand 'cause he's getting old now and running to the hills every weekend. ;):morning::drinks
  19. Simon I´m following along and if no one answers your question I´m on it and get a excel sheet done, but a little 4 day old man called Oliver I coming home today with his mum and we will see how the sleep thing goes for both.

    a very tired guy at work catching up on devices before Monday aahhhhh the life of a single prac who makes his on orthotics.
  20. Congratulations.
  21. Thanks Simon, pretty amazing last few days.

    For anyone who has not read the papars written by Nester et al on the midtarsal joint here they are.
  22. Ive been going over this and instead of an excel sheet I thought that it would sum up Simons question.

    When the COP is medial to an axis it will cause a supination moment.

    When the COP is lateral to an axis it will cause a pronation moment.

    When the COP is inline (?) to an axis it will cause neither a pronation or supination moment.

    thus we can have COP cause pronation moments at the MTJ and STJ joints dependent on the relationship of the axis to COP.

    we can also have COP cause supination moments at the MTJ and STJ joints dependent on the relationship of the axis to COP.

    we can also have COP cause a supination moment at the MTJ joint and Pronation moment at the STJ joint dependent on the relationship of the axis to COP.

    We can also have COP cause a Pronation moment at the MTJ joint and a Supination moment at the STJ joint dependent on the relationship of the axis to COP.

    We could also have COP cause neither a pronation or supination moment at both the MTJ and STJ joints or at one and not the other

    I think that covers all options.

    I also have been consideing this - If we look at patient related issues that have a cause of increased tension of the plantar intrinsics and Plantar fascia, if we have COP causing opposite Moments at the MTJ and STJ joints which leads to motion of these joints, the tension in the plantar foot should increase.

    ie take a rubber band pull it out it take X newtons of force to pll the rubber band y distance.

    now twist it once and the force to pull the rubber band y distance will be x+z.
  23. Define pronation and supination, then take another look at the MTJ axes, then tell me what component motions you'll get from each
  24. Pronation = inversion + plantarflexion + adduction

    Supination = eversion + dorsiflexion + abduction

    ie triplane motion.

    aahhh I see your point ( I hope ) A and C axis will mean that the axis plane dominance will mean motion is mainly available in a single plane not all three and therefore the sagittal plane motion of dorsiflexion and plantarflexion at the midtarsal joint will more likely to occur from the COP than triplane motion in your example.

    MALRE theory going to be a brain workout I think.
  25. Not quite, Mike:

    pronation = eversion dorsiflexion and abduction
    supination = inversion plantarflexion and adduction

    Take another look at those axial positions, will you get the combinations of movement listed above with all these axial orientations a, b, c?
  26. Silly mistake put the pronation , supination on the wrong group of motions, feel abit dumb now.

    I need to think about this, due to the joint make up of the midtarsal joint being very different to the STJ, so off to think and maybe a nap.
  27. Simon I know I said I would lay off this as not to reduce the qualilty of the thread , but it´s doing my nut in.

    The above is taken from Nester et al papers that I posted above - clinical and experimential models of the midtarsal joint.

    But if we have a look at your picture it seems to me that we can get mutiple different motions and that Supination and Pronation are really not the best terms to be used re midtarsal joints. We should be using reference to the x,y,z axis and depending on where the force vector comes from (espically considering the COP example) Distal or proximal to the MTJ axis different Moments and strength of Vector will occur. So we may get more in the z axis and less in the x,y - which will be important.

    We can alos get different compinations of motions, ie we may get plantarflexion and eversion moments occuring at the same time.

    Hope that makes sense,
    if not somebody put me down.
  28. For example, axis c will give inversion, dorsiflexion and abduction or eversion, plantarflexion and adduction. By definition these movements are neither pronation, nor supination. As they are new triplane motions, I should like to call them spoonation and noopsation- only joking.

    What you do need to remember is that the motion created these axes, not the other way round.
  29. Thanks Simon.

    So it will be important to reference individual motions.

    It could be that the midtarsal joint axis as all axis are fluid, but is could be much more fluid than say the STJ axis - ie a medial STJ axis will be generally medially deviated , generally .

    Also is it only motion or do moments help to define the midtarsal joint axis?
  30. Motion is driven by moments, BUT if there is no motion, there is no axis. So if we have moments acting about the MTJ axis which are in equilibrium and the joint is static, there will be no axis.

    The MTJ is "less constrained" than the STJ so there will be a larger envelope for the axial positions.
  31. Next we need to think about forefoot to rearfoot coupling and direction of power flow...
  32. During my melt down over the last 24 hours, this had crossed my mind. But I thought I would read - Kevins MTJ kinematics: Motion v´s stiffness thread again.
  33. And it is because of the relative non-constraint of the midtarsal joint (MTJ), especially when compared to the relatively highly constrained subtalar joint (STJ) that it will be impractical, if not highly unlikely, that we will be able to determine the kinetics of the MTJ by assigning it a single spatial axis location, unless that axis has first been determined by a time-consuming 3D kinematic analysis. This is why the three reference axes of the MTJ are so important since they allow the kinetics of any of the hundreds of potential axis locations of the MTJ to be determined without first having to determine the kinematics of the MTJ.

    In the illustration I provided in the second posting of this thread, I showed the medial-lateral reference axis of the MTJ so I could more clearly discuss the forces acting across the MTJ within the sagittal plane. Two more illustrations could also be provided showing the kinetics of the anterior-posterior MTJ reference axis for kinetics in the frontal plane and the dorsal-plantar MTJ reference axis for kinetics in the transverse plane. In this fashion, the highly compliant MTJ, that moves in the direction of the external forces acting on it, with little regard to a "set axis of motion", can be easily analyzed, as long as it is understood that the axis is extremely variable and not relatively constrained, as is the ankle joint and STJ.

    Here is a video I put up on YouTube over a year ago to show how variable the axis of the MTJ can be.

    [Motion of the midtarsal joint does not occur about a single axis or two axes as has been taught for the last 30+ years within podiatric biomechanics. The midtarsal joint, rather, has a constantly moving axis of motion that is dependent on the prevailing external forces acting across it and the prevailing internal forces acting within it from the muscles, ligaments and joint surfaces, at that instant in time. In the foot shown, the MTJ is clearly seen to be a relatively unconstrained joint; a joint that allows motion around an infinite number of moving axes, not around one or two joint axes.]
    Last edited by a moderator: Sep 22, 2016
  34. Try these Mike, I'm particularly interested in the third in the list which talks about in-phase versus out-of-phase motion of the forefoot relative to the rearfoot, see if you can relate this to centre of pressure position relative to the STJ axis and the MTJ axis.


    How's fatherhood suiting you?
  35. Hi Simon Fatherhood pretty good, except that thing called sleep, but Grandma come down to help out so It´s giving us some time to catch-up and I can go to work without falling a sleep when talking to patients.

    Had a nice hangout session with the little man after dinner. But I did lie awake thinking about the MTJ the other night - Bloody gaining more knowledge thing.

    anyway back to the MTJ - I tried to open link 3 and the website could not be found.
  36. Yeah weird. Sleeping now is easy, enjoy it while you can- it gets worse. Try the pdf below:

    Attached Files:

  37. Found link 3 on the Vault thread - http://people.umass.edu/ryanc/aboutme/Chang_PFOLA_07_Syllabus%20vfinal.pdf I need to do a PFOLA meeting I think.

    So any COP which causes greater forefoot dorsiflexion and eversion of the MTJ on the STJ maybe a issue in increased tension of the Plantarfascia.

  38. But a question if I may. we are talking about a microsecond of time with joint position, axis and COP always changing and adjusting - can these microseconds cause that much tension force on the Plantar fascia ?
  39. So, look at the STJ axial position, then look at the MTJ axial position, then look at the centre of pressure position relative to these. Sometimes it will result in anti-phase moments, sometimes it will result in in-phase moment. My point being that anti-phase is more stress inducing. This is what I wanted you to see in the diagrams I posted, but we got lost in motion about axes instead. Still it's all learning- right? Just like having a child in your house.
  40. Forces and axial position determine the moments, moments determine the motion, motion determines the axial position, load determines the stress, deformation determines the strain. Simples...;)

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