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Does Gravity Cause Pronation?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Kevin Kirby, Nov 11, 2008.

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    One of the more memorable public discussions that I had with one of the forefathers of Podiatric Biomechanics, Dr. William Orien, occurred at the Root Lab Biomechanics Meeting from about 16 years ago at Lake Tahoe, when Dr. Orien was lecturing to about 70 of us on the subject of treating feet with custom orthoses. During his lecture, he made the statement, "As we all know, gravity always causes pronation". After about 3 seconds of Dr. Orien making that statement, I raised my hand from the audience and said that gravity not only causes pronation but also causes supination, so that to say "gravity always causes pronation" was a misleading and innaccurate statement. [My thought process had been influenced heavily at the time by my observation that individuals with a laterally deviated subtalar joint axis would maximally supinate, rather than pronate, under the influence of gravity and the resultant ground reaction forces on the plantar feet.]

    Getting a little annoyed with me, since I had already publicly questioned Dr. Mert Root for the last few years about some of his theories and ideas at his previous seminars, Dr. Orien said that he didn't know what physics books that I had learned from in school since everyone knew that "gravity caused pronation". I went on to tell Dr. Orien that he would need to wait for my book to come out before he may be able to understand about how gravity may cause both pronation and supination. Talking about this recollection from my past still brings a smile to my face due to the great learning experiences and discussions (some say arguments) I had while attending Dr. Root's lectures and seminars as a young podiatrist.

    Having told this little story, I would be interested to know how many podiatrists still believe that gravity only can cause pronation since "the center of gravity is between the feet and will therefore tend to pull the calcaneus into eversion" (which is what I was taught in podiatry school at CCPM). In other words, how prevalent is this notion that gravity always causes a tendency for subtalar joint pronation and how often is it being taught within the international podiatric biomechanics community? I would be interested to hear from the students, recent graduates and more mature graduates of podiatry school to see whether these ideas are still being discussed and taught within our podiatric medical institutions.

    Thanks in advance for your responses.:drinks
  2. N.Knight

    N.Knight Active Member

    we are not taught about the gavity and root et al theary. We get taught that to be open minded to new thearies

    To be honest i have not read much into the root theary much as we get taught it is dated, so i dont know too much about it, my lectueres seem to be very keen on the work Craig Payne is doing/has done

    just my veiw on how it is taught in the UK at the moment, it would be intresting to see how it is taught in the USA as your system is so different from everyone elses?


  3. Steve The Footman

    Steve The Footman Active Member

    We were taught Root theory in second year in Queensland (Australia). It was raised at the time that much of Root theory had been superceded by other theories although these other theories were not examined until later. I do not remember hearing the statement that " gravity always causes pronation" although I am sure it was suggested that people pronated to the midline after contact. From discussing their study with our podiatry scholarship students it appears that the Root theory is still taught although with much less emphasis when I went through.

    I think another factor might be the direction of force at contact. I have had some patients who had a wide base of gait and had a lateral movement of the foot prior to strike when running. This momentum caused lateral instability and supination after strike. Most runners will strike the ground in varus with the foot moving medially prior to strike to land under their bodies midline. This increases the force causing pronation.

    Absolutes like Dr Orien's statement usually come undone. However I would agree that gravity causes a tendency for pronation... just not always.
  4. javier

    javier Senior Member


    In the earlies 90's, Dr. Root's paradigm was not taught in Spanish Podiatry Schools, neither physics actually; but common sense and a basic physics background tell us that when a force like gravity is applied to a body (foot) it will deform or resist deformation according to its structure (anatomy). Thus, I do not understand how it can be taught that "gravity always causes pronation" since it depends on each one anatomy. Also, GRF is the opposite force to the vector resultant or sum of the gravitational and inertial forces and its beneath your foot.

    I am not involved in podiatry education in my country, but I hope it is not being taught.

    Last edited: Nov 12, 2008
  5. Matt Kimball

    Matt Kimball Member

    I can tell you that at CSU we get taught Root theory as the basis, with the reminder that there are other theories but we don't go into much depth. On placement however, we are exposed to, and have to integrate, our placement supervisor's different thought processes. And from personal experience, in our last few months in the course we seem to have been bombarded by a mix of sales people and well renowned pods giving us their two bobs worth.

    It's all very confusing! As students we like things to be black and white - which biomechanics and orthoses mangement clearly isn't. :wacko: However I'm sure there is common ground with most of the theories out there, I'd like to find them or be pointed in the right direction on how where they've already been found! In getting my head around everything biomechanics I'm currently working on a Keep It Simple Stupid summary of what we know about abnormal lower limb biomechanical function, and how we can use basic orthotic principles to address them. :pigs:

    As a novice I'm sure it'll be full on inaccuracies and inconsistencies, potholes and deadends, so I expect to get whacked for it but watch this space and I'll do my best!

    Sincerely, Matt Kimball.
  6. Matt Kimball

    Matt Kimball Member

    I thought that I should update that last post of mine following some more meaningful study of the literature. More specifically, upon reading Craig Payne and Adam Bird's article "Teaching clinical biomechanics in the context of uncertainty" http://www.japmaonline.org/cgi/reprint/89/10/525 . I've realised that clinical biomechanics shouldn't be black and white. It's as much the student's responsibility to digest and critically evalutate each viewpoint as it is the teacher's responsibility to present them. A KISS principle might be useful to begin with, but we earn our stripes as clinicians when we can call upon a broader base of knowledge, based on all the different theories, and adapt it to each individual case.

    And to answer the original question, I believe we are initially taught that the foot will naturally pronate due to gravity and GRF occurring towards the midline of the body. However in retrospect, this doesn't really make sense, as it really doesn't explain the occurence of a weightbearing supinated foot - whereas the location of the STJ axis can.
  7. efuller

    efuller MVP

    The moment from ground reaction force is determined by the location of center of pressure of ground reaction force (the average point of ground reactive force) relative to the projection of the STJ axis onto the transverse plane.

    All you need to understand the foot is knowledge of the anatomy and understanding of a some physics concepts.

    One other thing for you students out there. An axis is an imaginary line and cannot limit motion, but it convenient to use in some situations.

    Eric Fuller
  8. Ian Linane

    Ian Linane Well-Known Member


    To confirm my ignorance.

    If we are stood on both feet the centre of gravity may well be between the feet. However, in single limb stance or in single limb support (depending where you are in the gait cycle) does not the centre of gravity reach a point where it is more focused in the support foot. If this is the case then the STJ axis position would play a crucial role in the affect of gravity. Or am I confusing this with something else?

  9. Ian:

    Yes, subtalar joint (STJ) axis spatial location will greatly affect the rotational forces (i.e. moments) occurring across the STJ axis in both relaxed bipedal stance and during walking. The center of mass (CoM) of the body is aligned generally between the feet in relaxed bipedal stance. During the midstance phase of walking, the CoM is aligned slightly medial to the stance phase foot. As Eric said, the center of pressure acting on each foot, and the direction of the ground reaction force vector relative to the STJ axis, will determine the STJ moments that are being caused by ground reaction force. So in this way, yes, STJ axis location does play a crucial role in the effects of gravity on the mass of the body.
  10. David Smith

    David Smith Well-Known Member

    Kevin and all

    1st gravity causes everything. In terms of gait and GRF force vectors there can be none without gravity.

    The position of the COG implies nothing obout the direction or magnitude of the forces of origin and is just a convenient summation of all the force vectors.
    The action of an individual segment in the mechanism is soley dependent on the forces acting on it at the point of interest.

    Eric really summed it up neatly


    How true

  11. Some say that pronation occurs because the navicular has to drop to accomodate the internal rotation of the leg.

    Or is it that the leg rotates because gravity causes the navicular to drop?

    Chicken? Egg? Egg? Chicken?

  12. Robert:

    Subtalar joint (STJ) pronation will only occur when the external STJ moments (i.e. ground reaction force) and the internal STJ moments (i.e. interosseous compression forces, ligament, tendon, muscle tensile forces) are added together and their summation equals a net STJ pronation moment. The net STJ pronation moment will then accelerate the STJ into a larger angular velocity of pronation.

    This simplified method of mechanical analysis is the best way to understand the complexity of mechanical variables that may produce pronation and supination motions of the STJ in the human foot during both non-weightbearing and weightbearing activities. When compared to the bewildering assortment of "foot and lower extremity deformities" and other confusing biomechanics theories that I was taught during my student and biomechanics fellowship years at the California College of Podiatric Medicine, this simplified method of mechanical analysis is far superior to both understand and to teach at the podiatry student and clinician level, as long as the student and clinician already comprehend the elementary concepts of Newtonian physics.
  13. Graham

    Graham RIP


    Is this a personal theoretical assumption or a known, scientifically proven fact, when it comes to foot function that is?
  14. Graham:

    It is equally as theoretical as the supposition that using in-shoe pressure analysis gives you a good indication of the function of the foot and gives you a good idea of the internal forces occurring within the foot and lower extremity during weightbearing activities or that functional hallux limitus causes flattening of the longitudinal arch of the foot or that functional hallux limitus causes subtalar joint pronation.

    Good to have you back nipping at my heels, Graham.:drinks
  15. Graham

    Graham RIP


    My pleasure! No offence meant but frank statements made by prominent members such as your self, without clarification such as, "in my opionion", or, "theoretically it would suggest that", suggests absolute truth, and can be missleading. Similar to saying my orthoses are better than yours!

    Which in my opinion they are, theoretically.:drinks
  16. You are right. I hope no one thinks that anything I say should be taken as an "absolute truth"......just my best educated guess at this instant in time.:drinks
  17. Graham

    Graham RIP


    And always stimulating and a pleasure to read and think through.

    Thanks Kevin.:cool:
  18. Will you two stop with the :drinks? You're livers won't hold;).

    Right with you on the moments Kevin. The tricky question (for me) is knowing where those moments come from.

    A movement occurs. Pronation. The foot everts, the navicular drops and the leg rotates.

    Is the internal rotation of the leg something which creates pronation moments across the joint? Or is it the case that the leg is moveing in response to internal rotational moments at the tibia generated by grf moments in the STJ causing pronation. In other words does the leg push the foot into pronation or does the foot pull the leg into rotation?

    Also glad to have you back graham. Have a coffee after all that beer :morning:.;)

    Or else....:dizzy:

  19. efuller

    efuller MVP

    To add my two cents:

    Be careful of the distinction between the center of mass, center of pressure and center of gravity. The center of mass is the average point of mass. The center of gravity is projection of the center of mass onto the ground.

    When describing how forces act on an object you must carefully define the object. So, for the following discussion the foot is defined as the talus and all bones and stuff distal. The center of pressure is the average point of force, in this case, under the foot. Gravity, will affect the foot as the mass is supported by the leg. So the force of gravity (gravitational attraction of the earth and person) will be applied to the foot from the bottom of the tibia. The center of mass does not apply a force to the foot the bottom of the tibia does.

    Ground reaction force occurs because gravity would accelerate the body downward. The ground prevents the body from accelerating downward, therefore ground reaction force is exactly equal to the pull of gravity. This is one area that has confused people trying to understand the biomechanics of the foot for a long time. There is a force from above and a force from below when you examine the foot. The force from above is very close to the STJ axis. The force from below can vary its position relative to the STJ axis.

    One of the mechanical principles you need in addition to the anatomy is free body diagram analysis. This helps you identify where the forces are coming from


    Eric Fuller
  20. efuller

    efuller MVP

    Hi Robert,

    It depends on the input forces and starting position/conditions. If you are standing there and someone grabs your femur and internally rotates it, it will cause and internal rotation moment on the talus. If the foot is held steady, by friction for example, then the pronation moment could come from the leg. On the other hand, if you had a little trap door under the first metatarsal head. You are standing there and the trap door is released, this will cause a lateral shift in the center of pressure under the foot causing an increase in pronation moment from the ground. If range of motion is available, there will be STJ pronation with internal talar rotation. The internal talar rotation would create a moment on the lower leg causing it to internally rotate if the mometn was unopposed.


    Eric Fuller
  21. PodAus

    PodAus Active Member

    Think of a seesaw motion and the associated axis...

    Does gravity cause one side of the seesaw to rise, or does it only make the opposite side lower?

    Or is it GRF's?

    I say both...

    Remove gravity and what is the result? :morning:
  22. Quite. So in the absence of small people grabbing femurs and twisting them how much of this rotational force exists originating proximally during gait?

    I suppose one way we could find out would be to chop somebodies foot off, replace it with a round ended stump ball, put them on a low friction surface (so that the ball could rotate freely on the ground but there was no grf causing rotational movement) and then see how much rotation there was in the femur during gait.

    Any volunteers:eek: :butcher:?

    Its possible that this might affect other gait parameters as well but you get the idea.

    This is connected to my ongoing headache about what volume of supination moments are generated by the glutes and by inference, how significant they are in foot posture.

    Put it this way. Shortly after the the stance leg is planted the contralateral leg starts traveling forward relative to it. Thus the pelvis rotates around that limb and presumably generates some EXTERNAL rotation moments through the hip. This, presumably again, is why the tibial starts to externally rotate just after Foot flat.

    During the first part of stance phase when the tibia is internally rotating is this driven by an active muscular force? Because if not, based on the performance of the tibia after foot flat, one might suppose that the internal rotation is a passive movement.

    Thanks for bearing with me guys.

  23. The external hip rotators obviously have a potential to increase the subtalar joint (STJ) supination moments during the stance phase of gait by their contractile activity. However, I would imagine they have much less potential to increase STJ supination moment compared to the posterior tibial muscle. In addition, in a flatter arched foot, where there is a low inclination angle of the STJ axis, the external hip rotators would have a much more difficult time in generating STJ supination moment compared to a higher arched foot due to the decreased STJ supination moment arm available for rotational forces from GRF within the transverse plane to cause STJ supination moment.

    In other words, the external hip rotators probably play only a minor role in generating STJ supination moment in most individuals.
  24. In
    Always been my position. It would be nice to have a way to measure. I kow a good number of respected colleagues who feel differently!

  25. efuller

    efuller MVP

    It's been a while since I've looked at Winters' inverse dynamic papers. He did measure transevers plane moments. I don't recall off the top of my head what they were.

  26. Johnpod

    Johnpod Active Member

    Hi Guys,

    If we take a loose-wired skeletal foot and set it upon a table top (to save our knees) and hold it in a position close to subtalar neutral we can observe that:

    a) it will display a bony lateral border which in life will be not far removed from the ground surface, and

    b) a raised medial aspect, beneath which is a considerable amount of airspace.

    When we release the model it will invariably (with apologies to Schroeder - and his cat!) fall inwards - i.e. it will pronate upon the surface. This it does under the effect of gravity.

    Now, attach ligaments, muscle, fascia and a leg. Can I ask - is it now different? Has gravity finally been overcome in some biogalactomechanical takeover?

    I sometimes have moments of 'inspiration' in which I beleive that Einstein got it wrong, such is my open-mindedness! Am I having one of those attacks right now? Was Root right, after all? Am I going nuts?

    To mutilate the words of Issac Newton,
    "If I have seen further than most it is because I have seen between those big fellas standing in front...."
  27. Measure navicular height in RCSP, contract external rotators and re-measure.
  28. David Smith

    David Smith Well-Known Member


    Kevin wrote
    you replied
    In human terms there are no absolute truths but when it comes to theory and the probability that the theory in question is true then this one is about as probable as it gets. The chances of of rejecting this hypothisis has a probability of <0.0000000000000000000001.

    Someone, PodAus I think, mentioned a see saw, well the probability that gravity will accelerate one side or the other is within the constraint of distribution of mass about the pivot. How the mass is distributed will determin the forces and moments about the pivot. IE the side with the greatest force and therefore moments, goes down.

    The STJ or any joint of interest is no more complicated than that. The only force (vector) that one needs to consider in terms of foot mechanics is the GRF vector. Whatever other more proximal forces are acting they will determine the position and magnitude of the GRFV and the GRFV will indicate the 3D external moments acting about the joint. Because there is always equilibrium, then all the other forces will act to cause moments to balance the momnets by GRFV. This is why it is important to accept that there is alway equilibrium of forces and moments in a mechanism whether it is in motion or stationary.

    The intuitive visualisation of the GRF vector is difficult, so intuitively, in clinic, we tend look at body motion and attempt to make some assumption about internal forces but because of the many and various variables, I belive this is also difficult and leads to misinterpretation and misunderstanding of basically simple and reliable mechanical principles.

    Last edited: Nov 15, 2008
  29. Dave:

    Good reply to Graham.:good:

    A few weeks ago, I gave a 25 minute lecture at the PFOLA meeting in Vancouver titled "Subtalar Joint Kinetics: A 24 Year Journey of Determining Subtalar Joint Axis Location" in which I reviewed the history of the scientific literature on STJ axis location determination, reviewed the importance of STJ axis location to the kinetics of the foot and lower extremity and to foot orthosis therapy, and reviewed some recent research I am participating in on determining the STJ axis location. After the lecture, I walked out of the lecture hall to get a cup of coffee and one of the keynote speakers at the seminar, a PhD biomechanist that is very well known, said that he had listened to my lecture and said the following to me:
    "I thought your lecture made complete sense and was very straightforward, Kevin. Do podiatrists disagree with the concepts you presented since I can't see much to disagree with?"

    My reply:

    "The problem is that many podiatrists just don't have the background knowledge in biomechanics and are so locked into their older theoretical notions as to how the foot works that they often struggle with the concepts I have been lecturing on for over the past two decades."

    The PhD biomechanist then shook his head in agreement.

    This is a relatively common occurence that a PhD biomechanist has heard that my ideas are controversial within podiatry, goes to hear my lecture for the first time, and then comes up to me and says he doesn't understand why other podiatrists find my ideas so controversial since they make complete biomechanical sense.

    The recent episode here on Podiatry Arena, where an older podiatrist that doesn't understand basic biomechanics terminology tried to convince us that regressing to static descriptions of foot shape using archane architectural terms was somehow an improvement in biomechanics, is a good example of the way many podiatrists view the biomechanics of the foot. It is my firm belief that the way forward for podiatry is not to regress back to the Root model or try to come up with another classification scheme based on external deformities of the foot but rather to try to understand foot mechanics using the same proven concepts and methods that biomechanists and engineers would describe any mechanical system.

    I have always considered that if I have used Newtonian mechanics to base my theories on, then I will be standing on much more solid ground than the others that have not adhered to these very solid mechanical principles when they have conjectured as to how the foot functions. Twenty five years from now, it will be interesting to see which podiatric theory of foot function is still being taught and which theories have been discarded.
  30. efuller

    efuller MVP

    Hi Johnpod
    You describe what happens with rotational equilibrium quite well. The foot model is sitting there in equilibrium. You add a supination moment to place it in neutral positoin. It supinates to a new position where there is more weight bearing laterally. The lateral weight bearing creates a pronation moment that is balanced by your input supination moment. When you let go, your input supination moment is removed, but there is still a pronation moment from the ground. So, in response the pronation moment from the ground causes the STJ to pronate until equilibrium is again achieved. Gravity is involved, but it is a pronation moment that casued the foot to fall back to its original position. Most feet, when you maximally invert them and apply force from the tibia and the ground the foot will tend to stay supinated, because the location of ground reaction is medial to the STJ axis.

    Your description also illustrates a problem with neutral position. Root et al, described neutral position as a position of stability. In this example neutral position is inherently unstable, because you have to hold it in that position.
    There is no good reason to start the description of the foot in what Root et al, described as neutral position. They were right in that to compare feet you should start in the same position of the joint for each foot, but that position does not have to be neutral position.


    Eric Fuller
  31. drsarbes

    drsarbes Well-Known Member

    Interesting Thread.

    For my way of thinking, it may be more accurate to state that Gravity is the force behind the progression of both pronation and supination, as well as just about all other movements on our planet.

    When asked by patients what causes this or that (heel spurs, bunions, arthritis, etc.....) I often tell them that as long as we live on a planet with gravity we are predisposed to these things.
    "will it get worse?" Well yes, unless you're moving to the moon.

    Gravity is the force that causes a supinated foot to become more supinated, a pronated foot to become more pronated, a genu vagum to become more valgus, a scoliosis to become more scoliotic, etc........... or a leaning tree to lean more or a human to go from 6'2" to 6' even.

    To deny any of this is to be unaware of how our world works, how the laws of physics interact with all aspects of our existence (including the laws of gravity)

  32. Johnpod

    Johnpod Active Member

    Hello Eric, thanks for taking the time to answer my post.

    I can totally accept this, but what position of the joint IS then the best position to use as a datum position if we abandon this concept? Presumably Root chose neutral because it is a repeatable position in which the articulating surfaces are congruent - the position from which the subtalar joint can make excursion in either direction. If we consider the case of the 'ideal' human that Root attempted to define, the rotational equilibrium of the left foot would effectively neutralise/cancel out the rotational equilibrium of the right foot. This seems reasonable to postulate since each foot effectively forms half a dome. Bring the feet together and the dome formed is stable under load of the weight vertically above.

    I'd really appreciate your further explanation. I was brought up and cut my teeth on Root et al. (it's me age, you know) and am only too willing to update and integrate more modern thinking into my understanding. Root seemed at one time to explain everything. Many of the latest concepts seem to be more piecemeal?

    much obliged

    Last edited: Nov 16, 2008
  33. Relaxed standing, end of range pronation, end of range supination- take your pick

    Lets hope not because it isn't.

    I remember reading about the two half domes in an antique text that Eric Lee sent to me. Demp has similarly modelled the foot in this way. The idea above is really not very helpful as soon as you explore dynamic function.
  34. efuller

    efuller MVP

    Well, looking at the really big picture, we can question whether or not we need to compare feet. Comparison of feet is important in research. However, it is not so important in treatment. The Root et al. paradigm treated feet by "supporting the deformity." Well, that was one of many interpretations. There were some who said that an orthotic put the foot into neutral position. I think that we can discard the treatment model because "the deformity" is not reproducibly measurable. In measuring forefoot to rearfoot, the heel bisection is not reproducible, the amount of load on the lateral forefoot is not accurately described, and the position of the medial forefoot is variable and not reproducible.

    That is one reason I like the tissue stress approach to treatment of foot pathology. Repetitive mechanical stress will cause damage to an anatomical structure. How stress is applied to that structure can be modeled. That model can also be used to predict what changes in ground reaction force would reduce the stress on the injured structure. The structure can heel when it has less stress applied to it. When you use this approach, you don't have to compare the foot to another foot, or to a "normal" foot.

    For a lot of research, the resting standing position would be a good starting position for comparison of feet. This position will be at least very close to the position of function in gait. It also can be used to determine the position of STJ axis position in the transverse plane in the position of function. I believe that it will be shown that STJ axis position will be an important factor in what kind of pathology a person has.

    If you delve into Root theory more deeply you will see that it does not explain everything. Root et al. tried to explain everything, but there are a lot of holes in the theory. e.g. Two different definitions of normal. One of the normarls is not anywhere near average. The measurement problem mentioned above. The faulty analysis of hypermobility of the first ray and HAV formation. However, the concept of a varus deformity where there is lack of range of motion to get the medial forefoot to the ground is valid. But there is no reason to distinguish between partially compensated forefoot and rearfoot varus.

    Mechanical analysis may seem piecemeal initially. However, if you spend some time with it, just as you spent time with Root theory, you can learn to apply it.

    I hope this helps. Let me know if you want more.

  35. Johnpod

    Johnpod Active Member

    Eric, thanks for taking time out to put this useful post together. I already utilise tissue stress modelling and I am still trying to get to grips with forefoot function, as I'm sure we all are. I must confess that I had begun to think that many of those who rejected Rootian theory simply did not understand it. The detail of your post has helped me to see some of its failings, for which I shall remain grateful.
    -thanks again!
  36. Root was looking for a reference position within the subtalar joint (STJ) range of motion that he could use to compare one foot versus another. He wanted a position that was neither pronated or supinated, so he found a midrange position of the STJ range of motion that he called the "neutral position". I find neutral position to be very useful in comparing one foot to another and in making foot orthoses for my patients. The main problem with the STJ neutral position is that it is not a well-defined position within the range of motion of the joint. In addition, it is difficult for one practitioner to agree with another as to where exactly neutral position is within the range of motion of the STJ unless these practitioners work closely with each other. Therefore, when communicating with another practitioner, using neutral position as your reference datum, the accuracy of the clinician in describing externally apparent anatomical variables is reduced when compared to a situation where STJ neutral position had less interexaminer variability.

    If someone was to ask me what variable was left out of the Root theory that prevented it from being a better system at predicting foot function and foot pathology, I would say that Root neglected the great mechanical signficance of talar head and neck spatial location (i.e. exit point of the STJ axis) to the rest of the foot in his theory. Root focused on the posterior calcaneal position/shape of the rearfoot (not the talar position/shape) to determine foot classification/function and did not consider that the talar head/neck position, and its effects on STJ axis spatial location and STJ kinetics, could have a very significant impact on foot function. In my opinion, this is the main reason why Root theory has limitations in predicting foot function, predicting foot pathology and in prescribing custom foot orthoses.
    Last edited: Nov 18, 2008
  37. Steve The Footman

    Steve The Footman Active Member

    Then how did Root identify STJN position? Isn't palpation of the talar head into the neutral position in relation to the rest of the foot the way it is done? You could conceivably say that this takes into account the talar head in a slight way even if he is not measuring the change from RCSP to NCSP of the talar head itself. I am really unclear on how Root theory identified NCSP.:confused:
  38. He used 2:1 ratio of inversion to eversion.
  39. Steve The Footman

    Steve The Footman Active Member

    Sorry I was taught that in second year but forgot it immediately. A simple 2:1 ratio measurement really makes no sense. Probably why we were taught the palpation method at the same time.
  40. Which begs the questions:
    1) Why wasn't the mid point of the range of motion considered as the neutral position?
    2) If we did take neutral to be mid-point in the range where would the neutral position be in the majority of feet?
    3) Why is rearfoot varus such a common foot type revealed by static foot typing techniques (see Root, Paul Shearer's chapter in Valmassy)?
    4) Where is the zone of optimal stress for the subtalar joint?

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