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Mid-tarsal Joint biomechanics?

Discussion in 'Teaching and Learning' started by guinue, Sep 19, 2012.

  1. guinue

    guinue Member

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    I am guinue who is 2nd year Podiatry student.

    I have one question about mid-tarsal joint biomechanic.

    Does subtalar joint supination directly lead to mid-tarsal joint pronation(osseous locking eversion) from mid-stance to propulsive toe-off phase?

    Or Does subtalar joint supination 'just' decrease range of motion of mid-tarsal joint, then indirectly lateral ground reaction force(GRF) leads to mid-tarsal joint pronation(eversion)?

    Or both subtalar joint supination and indirect GRF contribute on mid-tarsal joint pronation from mid-stance to propulsive toe-off phase?

    With textbooks, I still found not clear about this concept.

    Can anyone help me?


  2. Admin2

    Admin2 Administrator Staff Member

  3. David Smith

    David Smith Well-Known Member

    What is a Guinue? is it a 1st year who's been given a good seeing to by the sports master behind the bike sheds? Gooey Newy:dizzy: oh no can't be since your a second year, maybe its a novel recipe for a chocolate brownie topped with caramel, are you a baker?. Or maybe you come out of a magic lamp when rubbed ah yeah and if your rubbed to much you'll be a gooey newy Genie eh!:D MAGIC!


    Sorry couldn't resist,

    Forget about locking, forget about joints, imagine a very wide plastic 30cm rule. Thru one axis it is very compliant and flexible and thru the other it is very stiff and rigid. Lets say you hold it parallel to the ground so it is flexible to bending moments in the saggital plane and rigid in the transverse plane and you can twist it in the frontal plane by applying torsion at either end.

    As you twist the rule it becomes stiffer to the applied torsion and at some point your maximum applied force will be matched by the stiff torsional resistance of the rule i.e. max applied moments = maximum resisting moments. But now also the stiffness to bending will be increased in the saggital plane and the stiffness to bending in the transverse plane will decrease.

    This is because of changes in the second moment of area(sma), which is changed by the twisting action, as the thin or narrow sma gets greater the wide sma reduces.

    Wiki explains 2nd area of moment well enough so:
    Second moment of area means:
    The second moment of area, also known as "moment of inertia of plane area", "area moment of inertia", or "second area moment", is a property of a cross-section that can be used to predict the resistance of a beam to bending and deflection around an axis that lies in the cross-sectional plane. The stress in, and deflection of, a beam under load depends not only on the load but also on the geometry of the beam's cross-section: larger values of second moment cause smaller values of stress and deflection. This is why beams with larger second moments of area, such as I-beams, are used in building construction in preference to other beams with the same cross-sectional area.

    So the larger the second moment of area the stiffer the beam is to bending moments applied. (I beam T beam ) Bend your rule (which is a flat beam) about different axes and discover which has the greatest moment of area. Can you say which is the largest sma? Yes! good.;)

    Apply this to the foot and you'll get the basic theory on how it gets stiffer and more flexible depending on how its loaded relative to its second moment of area at the time of interest.

    Regards Dave Smith
  4. Other than the fact that I'm wondering if you've been on the happy tablets today, Dave- this above and the running economy gag, both in the same day ;), I like what you are saying. I'm reminded of the twisted beam model which, if memory serves, Saraffian discussed. He modelled the foot as a flat beam with a twist within it. I'll pull out my copy of Saraffian tomorrow (thanks Labguy) and take another look as it's been a while since I read this. But if the starting position has a "twist" in the beam, we unwind in one direction of motion and increase the "wind" in the other direction. Just want to check the direction of twist that Saraffian gives for the relaxed foot.
  5. 7Pod7

    7Pod7 Active Member

    David Smith,

    Is there any literature on biomechanics out there where I can revisit what you are teaching here. It sounds very realistic model ie applied science.

    The locking/unlocking of MTJ never sat quite comfortably with me. A little too abstract.:dizzy:


  6. David Smith

    David Smith Well-Known Member


    Teaching is not my objective in that I don't say this is what you must believe but rather presenting you with an idea for you to evaluate and decide how useful it is for your purposes.

    This model, when applied to the foot, was from my own inventive mind and in response to Guinue's question. As you can see, Simon has referenced Saffarian as another proponent of this model and with luck Simon will post some literature soon.

    The general principle is one that can be found in many engineering texts and one taught by the excellent Prof Nicol at Strathclyde Uni using large foam blocks with lines drawn on it to intuitively show the cross sectional deformation.

    Obviously this simple model allows the question to be explored in an intuitive way without introducing confusing variables (even tho in the real world model they may be very important) This could be likened to a statistical regression model in many ways. Whereby we manipulate the variables to a convenient curve in order to predict or explain a generally expected outcome or trend.

    Guinue wanted to understand the influence of torsional moments or twisting, i.e. GRF versus muscle action, in the longitudinal axis of the foot in terms of the deformation of the foot about the joints of interest i.e. the mid tarsal joints.

    Guinue was also asking if there is a change in the foot mid tarsal stiffness when the pronated STJ is compared to the supinated STJ in open chain i.e. non weight bearing. This introduces confusing concepts of reference frames and which reference frame you are talking about when assessing stiffness.

    If you invert the STJ open chain then effectively there is little change in the stiffness using a reference frame that rotates with the foot but if you use the fixed reference frame of the ground with a fixed direction of applied force then the stiffness does change. This would be the same with the 30cm rule example and is what we see in the example earlier.

    However, we cannot assess bending or torsional stiffness with only one applied force, as in the open chain model, we need two applied forces at least. As soon as we apply two forces we are, to all intents and purposes, assessing as a closed chain model.

    You might be think, well when you invert/supinate the STJ the calcaneo-cuboid joint rotates around the talo-navicular joint and this change in relative position means that the joint is stiffer if a force is applied to dorsiflex the mid foot. Now first you have to determine what you mean by dorsiflex and what direction that is relative to the new foot position as compared to the original position of a everted or pronated STJ. This is confusing and if the force is applied from the same direction on both inverted and everted positions then what reference frame are you using and where are the axes or joints of interest.

    The 30 cm rule example makes all this much simpler and I believe represents a sufficiently realistic model as to be useful for practical application.

    regards Dave Smith
  7. I had a quick look in Sarrafian this morning and he basically talking about the "lamina pedis" which as you can see is Dave's 30cm ruler with a twist in it. http://books.google.co.uk/books?id=...=0CCEQ6AEwAA#v=onepage&q=lamina pedis&f=false


    Attached Files:

  8. I believe both Eric Fuller and I have also commented on this idea that the midtarsal joint dorsiflexion stiffness within the sagittal plane is largely determined by the dorsal to plantar thickness of the midtarsal-midfoot ioints, rather than by some imaginary crossing of "joint axes" as suggested by Elftman in 1960 (Elftman H: The transverse tarsal joint and its control. Clin. Orthop., 16:41-44, 1960).

    Here is an excerpt from a Precision Intricast Newsletter I wrote in May 2008 regarding the dorsiflexion stiffness of the midtarsal joint and the concept that increased dorsal to plantar thickness of the midtarsal/midfoot will increase midtarsal joint dorsiflexion stiffness (Kirby KA: Foot and Lower Extremity Biomechanics III: Precision Intricast Newsletters, 2002-2008. Precision Intricast, Inc., Payson, AZ, 2009, p. 128).

    This topic really deserves a complete paper of its own. I'll consider this when things slow down a bit.
  9. If one thinks of the foot as a piece of lumber that simply resists deformation when loads are applied, then the dorsiflexion stiffness of the foot will increase with the cube of the dorsal to plantar thickness of the foot at the midtarsal-midfoot.

  10. 7Pod7

    7Pod7 Active Member

    Simon Spooner & David Smith,

    Many Thanks for the visual and Text Reference. I assume one of you at least has the text book-how strongly do you recommend it in context of biomechanics of the foot. Thinking of acquiring it.


  11. It's not a biomechanics book per se, but it is probably the best book on anatomy of the foot.
  12. 7Pod7

    7Pod7 Active Member

    I noticed ch10 about function of foot and maybe cross sectional area would be about biomechanics. I'm thinking that a great revision of anatomy would spruse up my diagnostic skills as well. What do you recon?
  13. If you can afford it, you can't have enough books in your library.
  14. 7Pod7

    7Pod7 Active Member

    Right in both accounts. Just want to splurge a little from a Tax Refund.
    One shop wants $400, another just under $200.
    One more question;
    Any excellent Biomechanics texts to check out on the web you're familiar with?


  15. Kevin's 3 volumes- http://www.dpmlab.com/html/bookreview.html
  16. 7Pod7

    7Pod7 Active Member

    Right. I saw these advertised on PodArena and meant to check them out a little while ago. Had other goals then and now they disappeared. Are they available in any other outlets?

  17. No, follow the link.
  18. 7Pod7

    7Pod7 Active Member

    Many Thanks for all the info,

  19. guinue

    guinue Member

    Thank you very much.

    Thanks to this thread, I knew that there were a variety of mechanism of midtarsal joint (eg, a dorsal plus plantar thickness theory).

    I really appreciate for all threads.

  20. David Smith

    David Smith Well-Known Member


    Have you looked at this thread yet 'the wring theory'



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