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Efficacy of wedges

Discussion in 'Biomechanics, Sports and Foot orthoses' started by markjohconley, Dec 19, 2009.

  1. markjohconley

    markjohconley Well-Known Member

    Members do not see these Ads. Sign Up.
    To the young podiatrist who doesn't believe a therapeutic effect can be had from the use of judiciously placed wedges, what is a rearfoot skive but a wedge!
  2. Mark:

    ......and your point is..........???:confused::wacko::santa2:
  3. markjohconley

    markjohconley Well-Known Member

    Good evening Kevin, my point was directed to the podiatrist who, though using rearfoot skives herself, doubted the effect on forces that simple heel (and 3/4 length) wedges can have, and all the best to you and your family, and all the other posters and theirs for christmas, mark
  4. markjohconley

    markjohconley Well-Known Member

    I was also hoping it would elicit a response from the thinkers in the forum, mark
  5. Phil Wells

    Phil Wells Active Member


    Just to throw something into the mix re Medial Skives, is it possible that sometimes its mode of action is to apply a dorsiflexory force\moment to the medial aspect of the calcaneus.

    E.g. by reducing calcaneal plantarflexion, the mechanism of hysteresis via the plantar aponeurosis ( the ability of a structure to return energy to a system) is increased = improved hicks windlass mechanism = less frontal plane excursion of the calcaneus = the skive worked.
    This may also be the mode of action for the rearfoot post - it elevates the medial calcaneus.

    Very subjective reasoning but it does make some sense. (may also explain the great variation in orthoses design having similar positive clinical outcomes)

    What do you think?

  6. Hi Mark, just in from snow clearing, been thinking about your question and how to respond so here goes.

    here my option.

    A skive is a type of wedge. And the young pod had it wrong, but that´s is not saying that a eva wedge and a rearfoot skive will act the same way on the foot and have the same therapeutic result they may, they may not.

    So 1 yes a skive is a type of wedge.
    2 can a therapeutic effect be had from a Judiciously placed wedge yes.

    But they will have some similar but some different ways of causing that therapeutic effect.

    Hope that makes sense and helps for Monday coffee.
  7. Phil
    I think that Craig has mention something along the lines of what you said as well in a post somewhere.

    If we consider the STJ axis in the sagittial plane the Dorsiflexion and plantarflexion are important and Simon, Robert, Kevin have discussed it here.


    is that what you had in mind. I must have read that thread 15 times still getting stuff out of now.
  8. Mark:

    I believe a better question would be:

    Does a varus rearfoot wedge have the same biomechanical effect as a medial heel skive?

    My answer would be that the varus rearfoot wedge and medial heel skive would have similar effects at causing an increase in the external STJ supination moment. However, since the foot orthosis acts over a greater surface area on the plantar foot than does the varus rearfoot wedge, it will not only have greater potential to affect foot kinetics and kinematics but will also be more comfortable for the individual since the plantar pressures at the heel will be reduced with the foot orthosis versus the varus wedge due to the greater surface area of contact with the plantar foot.
  9. efuller

    efuller MVP


    I've got a few mechanical nits to pick.

    I don't see how a medial heel skive applies a dorsiflexory moment or force. The mechanism of action of a varus heel wedge is to shift the center or pressure under the foot more medially. This will decrease the pronation moment or increase the supination moment.

    What do you mean when you are talking about "the mechanism of hysteresis via the plantar aponeurosis"? That's a new one to me.


  10. Griff

    Griff Moderator

    Some of the literature on wedging attached

    Attached Files:

  11. Eric in a thread about Achilles tedonitis that someone had done a study on, they discussed the used of Medial Skrive tech. Simon was saying that he could not remember the last time he used a medial skive when treating Achilles tendonitis Kevin said that a skive will provide a type of heel lift. Is this not a Dorsiflex moment on the medial aspect of the calc ?
  12. Michael:

    Dorsiflexion is a sagittal plane motion and inversion is a frontal plane motion. In order to have a dorsiflexion moment on the calcaneus, the heel wedge would need to working in the sagittal plane, not the frontal plane.
  13. Hi Kevin I get the planes of motion which why I linked the thread on high low stj axis to Phil to see if that what he was after.

    It´s a bit late here maybe not thinking straight but by lifting the medial aspect of the calc with a medial skrive yes mostly there is a change in frontal plane movement. I would this there is some sagittal plane movement.

    Here what you wrote in the tread I mention before, the last line of the quote got me thinking that there is some sagittal plane movement as well.

    Sorry if I´m abit confused.

  14. markjohconley

    markjohconley Well-Known Member

    Does a medial heel skive (wedge) increase the total GRF under the posterior end of the calcaneus or just move part thereof from lateral to medial? Wouldn't it take an increase (or decrease) in total GRF under the posterior end, not just a transfer, to affect the sagittal plane moments, and if it were an increase wouldn't it result in increased calcaneal PLANTARFLEXORY moments?
  15. Phil Wells

    Phil Wells Active Member


    My thinking is as follows -
    The calcaneal angle is a measure of a bisection of the plantar surface of the medial aspect of the calc relative to the supporting structure in the sagittal plane. (Can't recall the reference re this measure but I think it was surgical related.)
    This angle has been claimed to show to links (maybe tenuous due to the research bias) to injury - if large degrees of a sagittal plane excursion were seen from the semi weightbearing position to the fully weight bearing position - then this may be an indicator of risk of injury. However I cannot comment on the researchers conclusions, only the measures and its relevance to this thought pattern.

    If a medial skive is applying a force to the medial aspect of a foot that has large amounts of this calcaneal plantarflexion, then I feel that its mode of action is primarily a dorsiflexory ORF than in any other plane!

    The hysteresis term is based on a work learned on the Staff Uni Biomech course - Tissue stress module. I do have the references somewhere that refer to 2 high hysteresis systems of the foot (Tendo achilles and heel fatty pad) and one low system (the PA).
    When we modelled this using simple engineering software and mimicked the changes in the PA length dependant of the Calc angle, then changes were seen in the PA's ability to return energy back in to the foot.

    I have got this wrong?


  16. Phil:

    The type of hysteresis you are talking about here is elastic hysteresis which can be defined as follows:

    A common way of teaching about elastic hysteresis is to diagram the stress-strain curve of a material that is first loaded and then unloaded, tracing its path along the stress-strain curve. Materials will develop a "hysteresis loop", where the loading curve and unloading curves do not match up exactly. The area between the loading and unloading curves represents being the heat lost to deformation of the material (see illustration below). If the material was linearly elastic and obeyed Hooke's Law, then there would be no hysteresis loop.

    One wouldn't typically try to develop a free-body diagram of a mechanical problem like a varus heel wedge or a medial heel skive by talking about the hysteresis of a material since hysteresis is a dynamic concept, not a static concept. I think you are over-complicating and confusing a relatively easy topic by trying to introduce a concept like hysteresis to explain how a simple varus heel wedge may work. [For those that are interested, Phil's abbreviation of PA, that he unfortunately forgot to define in his posting, I believe refers to plantar aponeurosis, though I am not exactly sure since he didn't define it.]

    A simple free body diagram model or similar type of static model will show that a varus heel wedge will not only increase the ground reaction force (GRF) on the medial calcaneus but also will decrease the GRF on the lateral calcaneus, in the frontal plane. Within the sagittal plane, the varus heel wedge will tend to cause the ankle and calcaneus to plantarflex due to the extra thickness of material plantar to the heel that the varus heel wedge possesses.

    Let's not make these concepts any more complicated than they really are.:drinks

    Attached Files:

  17. Phil Wells

    Phil Wells Active Member


    Will be sure to annotate plantar aponeurosis (PA) in future as things can to far along the abbreviation track if we are not diligent!
    Re static verse dynamic, surely most people would assume that a rearfoot post or medial skive are dynamic applications via an orthoses shell.
    Free body diagrams are ok for theoretically modelling but in the clinical situation the application of dynamic principles are far more important.
    Regarding complicating matters, I don't think this is true.
    If we break down medial skives and rearfoot wedges as prescriptions that add extra material to the shell of an orthoses - especially foam based shells - then in reality they are creating asymmetrical heel raises - medial or lateral depending on the prescription.
    If we use solid mechanical functions such as hysteresis, then this may start to explain why most orthoses work no matter what approach is used - MASS, DC Inverted, Root, etc. It also fits within the term ZOOS as described by Dr. Simon Spooner. e.g Small mechanical interruptions to the foots ability to return energy back into the overall gait system that can be correct by an orthotic.
    I am not trying to invent the wheel but to try and explain why orthoses may work. I am also not trying to negate SALRE or the tissue stress approach, just add another way of looking at things from a different mechanical view point.
    To put it into context, I have worked in the manufacture of orthoses for over 10 years, designed/made over 15,000 pairs and seen 100's of different practitioners use very different approaches. They all had success (based on the amount that were returned) but no common approach was easily identified. However most of them did add height to the heel in some form.


  18. Phil:

    A dynamic approach is often times the best approach in explaining the function of dynamic activities, such as walking and running, especially when we start to try to examine energy conservation, angular acceleration of segments, joint powers, etc. However, I have always believed that podiatry students and podiatrists find that the static approach is much more simple to understand since it is so much less complicated than the dynamic approach when attempting to model the human foot and lower extremity.

    Over the past 20+ years of writing my scientific articles and books on foot and orthosis biomechanics, and also in my Thought Experiments here on Podiatry Arena, I have mostly used static analysis to explain relatively complicated foot geometry issues since I have found that using static models and free body diagrams allow seemingly complicated issues to be explained quite neatly and with little confusion. In addition, for the past decade I have considered using quasi-static analysis as another way to simplify the complexities of dynamics by using the principles of static analyses and equilibrium, but analyzing the activity multiple times during the gait cycle (almost like multiple snapshots of the activity) as a way to simplify and better understand how the foot and lower extremity work.

    I realize that you are a very knowledgeable podiatrist and I respect your opinions and experience in the foot orthosis lab business. However, I believe that using the dynamics of energy loss, or hysteresis, of the plantar aponeurosis as a way to explain the biomechanical effect of varus heel wedges or medial heel skives may overly complicate a discussion that should be very straightforward using static analysis.

    However, I have certainly been wrong before so I will step back now and allow you to more fully explain to me, and the others following along here on Podiatry Arena, how you can use the concept of hysteresis in the plantar fascia, Achilles tendon and heel fat pad to better explain how varus heel wedges and medial heel skives can change the function of the foot and lower extremity. I eagerly wait for your reply and to be further educated.:drinks
  19. efuller

    efuller MVP

    If you compare the position of the standing foot with no heel lift to the same foot standing on the heel lift, the foot on the heel lift is in a more plantar flexed position. I still don't see how this can possibly cause a dorsiflexion moment.

    When trying to determine moments on structures you can do a free body diagram analysis. In a free body digram analysis you draw in all the known forces and then calculate the unknown forces by knowing that when the system is in equilibrium the net force and net moment equal 0. If you had a wedge that was thick posterior and tapered to 0 thickness at the anterior edge that was even with the anterior aspect of the calcaneal tubercle, then you could make the case that the center of pressure was shifted posteriorly and this could increase the plantar flexion moment on the calcaneus. This is not a varus wedge.


  20. Thanks Eric I go draw some picture over the holidays and see where we get from there.
  21. markjohconley

    markjohconley Well-Known Member

    Thanks Kevin for the reply,
    No worries, with you, but

    as long as the change in forces reduces the 'pathological' stress

    which surely reduces the 'therapeutic' forces acting at the heel, no?, mark
  22. All,

    As ever Mark has started a thought provoking thread. A few questions to hone our thinking:

    What influence does our rearfoot wedge have on the tension in the Achilles tendon and plantar fascia?

    What factors affect hysteresis in tendon / ligament?

    What difference does active versus passive tension in the musculo-tendinous unit make to the stress / strain curve?
  23. Phil Wells

    Phil Wells Active Member


    I'll have a crack at explaining my thought patterns re hysteresis and energy return via orthoses.

    Point #1 - Fatigue
    Non-fatigued foot = optimum muscle power generation transmitted into the gait cycle
    Fatigued foot = a reduction in the above due to muscle fatigue with increased tendon stress due to the cross section of a tendon decreasing due to it lengthening = the foot stretches/lengthens = energy loss.
    As the foot fatigues, loading rate increases and the duration of load experienced by ligaments increases = reduced energy return back into the foot.

    The plantar aponeurosis (PA) is a prime example of an energy return structure that would experience increased elongation and strain due to fatigue of the extrinsic musculature - especially posterior tibial muscle - resulting in less elastic strain being stored.
    (Simkin et al (1990) stated that energy storage in the PA was at its best when intermediate calcaneal angles were seen due to prolonged loading = increased tension = energy loss.)

    So back to how an orthoses might function within this model.

    As fatigue occurs the calcaneal angle experiences more migration in the sagittal plane due to fatigue (sorry but I can't find the reference for this - Japanese researchers if I am remembering correctly). This results in lengthening of the PA and energy loss.
    A neutral orthoses that captures the non fatigued angulation of the calcaneus will apply a force to resist excessive calcaneal migration/plantarflexion.
    A rearfoot post or skive will increase this force.

    Additional effects of a orthoses and how it interacts with the shoe also fit this model well.
    The orthotic device - whether foam or polypropylene - will have its own method of returning energy via elastic recoil of the material it is made from.
    Also by filling up the gap between the non-weight bearing structures of the foot and the sole of the shoe, the orthoses will transfer some of the load from the foot into the material of the shoe. The sole unit - unless made of a non yielding material such as leather - will also compress and via recoil return energy.
    By adding material to the orthoses via skives or posting we also increases the potential for elastic recoil of the material it is made from.

    I personally think that 50%+ (Arbitrary figure) of the effect of an orthotic comes from this mechanism and the other 50% coming from the application of specific ORF (Orthotic Reaction Force) to reduce tissue stress via the clinicians skill at prescribing orthoses.

    I welcome any feedback on this as I might have got it totally wrong.


  24. Phil Wells

    Phil Wells Active Member

    What influence does our rearfoot wedge have on the tension in the Achilles tendon and plantar fascia?

    A rearfoot wedge will have an effect at initial heel contact of increasing plantarflexion moments on the ankle = increased stiffness in the TA tendon = better energy storage within the tendon.[/I]

    What factors affect hysteresis in tendon / ligament?

    [Duration of load and tendon cross section[/I]I]

    What difference does active versus passive tension in the musculo-tendinous unit make to the stress / strain curve?[/QUOTE]

    Stress = Force/tendon cross section. Passive verse active load will potentaillly change both.

    Strain = percentage of lengthening so agian the same mechanism - a tendon loaded quickly will act 'stiiffer' than if loaded slowly.

    Does that make sense?



    I'll have a go at these-
  25. Mark:

    Don't know quite what you mean by "therapeutic" forces? The impact force of my foot striking the rear side of a few of the "orthotic salesmen" that like to give me trouble here on Podiatry Arena may be therapeutic for me......and also for my foot...... but may not be so therapeutic for them.:cool::drinks:santa:
  26. markjohconley

    markjohconley Well-Known Member

    A bad choice of words on my part. What I was attempting to describe were the, for example, increased medial heel GRF in a pt with a medially deviated TP STJ axis, that is 'created' with the use of a heel wedge (medial). We're using a wedge to get that shift of COP and 'shift' of GRF, and by using a 'full contour orthoses', isn't that dimished?
    And isn't an orthoses doing what you want if it is comfortable (in neurologically intact pts) and have there been any studies on whether an contoured orthoses is more comfortable than a simple wedge or is this just 'common sense'?

    Must be quite frustrating!
  27. Admin2

    Admin2 Administrator Staff Member

  28. Can I ask a question in reference to what Mark wrote it in red.
    Where Mark wrote increase in GRF Should it not be an Orthotic Reaction Force ORF or a Wedge Reaction Force WRF.

    Which is the best way to reference something like that so it´s correct science ?

  29. I think if you were to speak to anyone outside of the Arena, few would iknow what an orthotic reaction force was, ground reaction force is the term employed most commonly by biomechanists. As long as you define your references.
  30. efuller

    efuller MVP

    You could say force applied to the foot. Or describe a shift in the location of the center of pressure of force applied to the foot.

    GRF is a nice acronym that is fairly well understood by the podiatric community. The difference between orthotic reactive force and ground reactive force is probably not that great. The force applied by the ground to the shoe and the force applied to the orthotic by the shoe and the force applied by the orthotic to the foot will generally only differ by the weight of the objects in between the foot and ground.


  31. Jeff Root

    Jeff Root Well-Known Member

    Sorry if this has been covered, I'm jumping in without reading most of the postings on this subject.

    A heel wedge, assuming it is placed on a flat surface, is a frontal plane wedge (ie skive). A medial heel skive is cut into the medial aspect of the positive cast. The medial heel has an angle of inclination which increases anteriorly as the heel transitions into the medial, longitudinal arch. Therefore, a medial heel skive is a triplane modification. A wedge is a uniplane modification.
    Although a wedge is uniplane, it can produce bi and triplane changes. For example, if you place an inverted wedge under the medial forefoot, it can will invert the forefoot and has the potential to elevate the 1st met head relative to the base of the 1st base. This is an example of a biplane change resulting from a uniplane wedge.


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