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The Unified Theory approach to podiatric biomechanics

Discussion in 'Biomechanics, Sports and Foot orthoses' started by NewsBot, Jul 16, 2009.

  1. NewsBot

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    A Review of the Theoretical Unified Approach to Podiatric Biomechanics in Relation to Foot Orthoses Therapy
    Paul Harradine and Lawrence Bevan
    Journal of the American Podiatric Medical Association Volume 99 Number 4 317-325 2009
  2. I brought up this a little while ago.

    Maybe it might happen ???

    Michael Weber
  3. I have just read the paper by Paul Harradine and Lawrence Bevan titled "A Review of the Theoretical Unified Approach to Podiatric Biomechanics in Relation to Foot Orthoses Therapy". I commend the authors for tackling a very difficult subject and bringing the ideas of three different biomechanics theories together to be discussed in JAPMA. Even though I can't agree with some of the points within the paper and there are a few inaccuracies within the paper, I believe the paper is a must-read for all podiatrists interested in foot and lower extremity biomechanics.

    As far as inaccuracies, the authors of the article state on page 319, paraphrasing from my decade-old paper (Kirby KA: Biomechanics of the normal and abnormal foot. JAPMA, 90:30-34, 2000.), the following: "A moderately pronated foot in stance is considered more of a normal position."

    In fact, what I did say in the my paper about this subject was the following:
    "A foot which functions the most normally during walking gait does not have a subtalar joint (STJ) which is in the neutral position during bipedal standing. In my fifteen years of clinical observations, I have noted that feet which stand in the STJ neutral position are quite likely to have symptoms or clinical findings indicating the presence of abnormal supination moment acting across the STJ axis. In addition, I also consider that feet which stand with the STJ either in or within 1-2 degrees from the maximally pronated position to be abnormal due to the lack of available pronation range of motion for shock absorption. The feet which I have observed to function the most normally during gait have STJs which are in a position approximately midway between the maximally pronated and neutral position of the STJ."

    I think if the authors had changed their sentence to read: "A mildly pronated foot in stance is considered more of a normal position.", I would have no objection to this small part of their paper. No one likes to be misquoted so I thought by making this objection publicly, my true opinions would more known.

    In addition, the authors, when describing tissue stress treatment protocol for plantar fasciitis, say in their paper, on page 323, "Tissue stress theory advocates the use of greater posting and the medial heel skive." This is not necessarily true. I have never stated that patients with plantar fasciitis always need a medial heel skive and, in fact, in my paper on medial heel skive, I discourage the use of the medial heel skive to treat plantar heel pain (Kirby KA: The medial heel skive technique: improving pronation control in foot orthoses. JAPMA, 82: 177-188, 1992). I do not use "greater posting" when using tissue stress theory to treat plantar fasciitis.

    Rather, as I have written numerous times on tissue stress theory, the 3 basic steps of tissue stress theory are to:

    1. Anatomically identify the injured structure.
    2. Determine the abnormal stresses causing the pathology.
    3. Design a treatment plan that will reduce the magnitudes of pathological stresses so that the injury heals, gait function is optimized and no other pathological condition is created.

    Overall, however, I think the paper by Harradine and Bevan will go a long way to improving the recognition of the various theories of foot biomechanics to let the clinician better decide which approach or combination of approaches suits their treatment style the best.
  4. eddavisdpm

    eddavisdpm Active Member

    I think that you have made an important point of clarification in your post that needs greater emphasis. The amount of subtalar joint pronation, in degrees, is not as important a consideration as the amount of the total range of subtalar joint pronation available utilized by the patient in gait/midstance phase. A patient who displays subtalar joint overpronation in midstance near or at the end range of pronation may display greater symptomatology than one with a similar amount of pronation but who is not near the end range of subtalar joint pronation for that patient.

    Observations about the degree of subtalar overpronation seen in a patient in stance and gait need to be related to measurements of the actual subtalar joint range of motion available for the specific patient.

  5. Lawrence Bevan

    Lawrence Bevan Active Member

    Hi Kevin

    You are very generous in your praise! Thank you. I think the paper could be better called "brave" in taking on such scope in summarising and reflecting on the work of the seminal Podiatric biomechanical thinkers of recent times.

    To respond to your points:

    1 We would gladly change the wording of our paper to "mildly pronated" - after all the paper is partly about summing your true sentiment or actual practice. However, given the normal range of pronation (using the Root criteria!) is 10 degrees, the difference between mildly and moderately pronated is small. That said I think I can sense your inference and I don't argue with you. The cheeky side of me thinks that the "Root criteria for normalcy" were that a normal foot could have 2 degrees of varus deformity. If this were compensated for by pronation in stance and gait, would this not amount to being "mildly" pronated??

    2 The example of plantar fascitiis in relation to your use of the medial heel skive was, on reflection, not a good one. However in your many writings you do make many references to using higher degrees of posting, where necessary. No need to defend! Since reading them I do too but in contrast I have heard Howard Dananberg make clear and constant reference to the need for only small (1-2 degrees) of posting. I do this also! What is the reality? Is it literally the case that more than one foot orthotic Rx can help the same person?; are you and Howard (and others) describing things differently but in practice doing the same?; or are your patient groups totally different and thus your practice shouldn't be compared?

  6. Lawrence:

    My point is that I would never say and have never said in any of my lectures to podiatrists, "Feet that function the most normally in gait are moderately pronated." However, I have often said, "Feet that function the most normally in gait stand in relaxed bipedal stance with their subtalar joints approximately midway between the neutral position and the maximally pronated position."

    I hope you can see the very different meaning between these two sentences and why I am concerned that I may now be quoted for years to come by individuals who have only read your paper, and not read my original paper from 2000 (Kirby KA: Biomechanics of the normal and abnormal foot. JAPMA, 90:30-34, 2000), as saying, "Feet that are normal are moderately pronated." I don't want to seem to be too critical but I work very hard at trying to be as clear and concise as possible in my writings on podiatric biomechanics. I just don't want others to be confused as to what I have said and not said in my past lectures, papers, books and book chapters.

    Part of the problem with using the words "moderately pronated" or "mildly pronated" to describe either the resting posture or gait function of a foot is that these terms are ill-defined and ambiguous. For example, when your paper said that a normal foot is "moderately pronated", were you referring to subtalar joint (STJ) rotational position, referring to STJ axis spatial location, or referring to more of an appearance of the foot using multiple criteria such as in the "Foot Posture Index" created by Anthony Redmond? If you notice, in my paper in 2000, I was very clear to make certain the reader realized that I was talking about STJ rotational position when I made the statement about feet that functioned most normally in gait being somewhere about halfway between the STJ neutral and maximally pronated position while in relaxed bipedal stance.

    I made that statement in the 2000 paper and in many of my lectures over the past 20 years to challenge the idea that Root et al had claimed that in order for a foot to be considered as "normal" that the STJ had to be resting in neutral position. Thus, Root et al's inclusion of "STJ neutral" as a part of their eight biophysical criteria for normalcy (Root ML, Orien WP, Weed JH, RJ Hughes: Biomechanical Examination of the Foot, Volume 1. Clinical Biomechanics Corporation, Los Angeles, 1971, p. 34) had set the stage for their STJ neutral theory and their STJ neutral casting position that they advocated and taught as the best way to evaluate and cast the foot during the 1960s, 1970s and 1980s. To me, and others, this is a major flaw with the STJ neutral theory, especially if I am correct that the feet that do function the most normally during gait do not stand in neutral position but rather stand with their feet pronated from the neutral position, as I stated very clearly in my 2000 paper.

    The other reason I use STJ rotational position as a way to correlate joint position to normal gait function is that, if the maximally pronated position of the STJ is used as a reference (since it is more reliable to reproduce the maximally pronated position in standing between examiners than is STJ neutral position), then it becomes very clear that feet that stand in the maximally pronated STJ rotational position function very differently and have different types of clinical problems from those feet that stand closer to the STJ neutral position. Therefore, as I've stated before on Podiatry Arena, I believe that Mert Root and his coworkers (who were all my teachers) would have been wiser to not have used the term "normal" to describe what they considered to be ideal structure but rather should have used the terms "ideal structure" or "optimal structure". In addition, I believe that Root and coworkers should have not focused so heavily on the "neutral" STJ rotational position (i.e. 1/3rds-2/3rds, etc) to determine ideal STJ joint position but rather should have selected a STJ rotational position that is 4-5 degrees supinated from the maximally pronated position as being the ideal rotational position for the STJ in relaxed bipedal stance. These two changes would have given Root et al's theories much more durability in response to the challenges it is currently receiving from the other competing biomechanical theories.

    Thanks for the discussion, Lawrence, and again, it was very good of you and Paul to be "brave" to take on such a daunting task. Good luck and hope to see more of your and Paul's work published in the near future.
    Last edited: Jul 20, 2009
  7. Charlie Baycroft

    Charlie Baycroft Active Member

    Dear All
    IMHO. One of the main problems with developing a single, valid and consistent theory of lower extremity function and dysfunction is the concept of a "normal foot".
    Human feet, like all other parts of the body, exhibit a great range of normal anatomical variation. Congenital or acquired structural abnormalities occur in the feet and legs of some people just as they do in other parts of the body but "variety is the spice of life" and we are mostly uniquely different but still normal.
    From my dim recollection of statistics, abnormal is defined as +/- 2SD from the mean and all characteristics can be plotted on a bell curve where the majority of differences are normal.
    The structure of the human body evolved millions of years ago and our feet and legs must have been admirably suited for fitness for survival in a natural environment. If that were not the case, surely we would not have persisted and thrived on this planet to become the dominant species.
    Our environment has however been greatly modified since the industrial revolution (about 1850) and we now walk mainly on flat hard unnatural surfaces and in modern footwear which are unnatural and "abnormal" in terms of our natural environment.
    If the surface under the foot is natural with a great variety of densities, inclinations and textures, the human foot is admirably capable of adapting to these variations and the force vectors acting on various structures will be constantly changing.
    The foot is wonderfully adaptable and tries to adapt itself to the surface beneath it. If this surface is flat and hard (as inside and under our shoes) the STJ will logically pronate in an attempt to adapt the foot to this flatness.
    Should it do anything else?
    When walking on these monotonously consistent modern surfaces there will be less variation in the direction of force vectors and therefore more persisting loading of and stress in specific structures. This will eventually lead to pain, imbalance and deformity.
    If we seek to have a unified theory for lower extremity function we should first consider the basic paradigm upon which this theory rests.
    If we persist in building our theories on the illogical belief that there is only one type of "mechanically normal" foot and leg we will consistently fail.

    Our modern walking surfaces and footwear induce adaptive subtalar pronation. The foot tries to adapt itself to the surface with which it is in contact.

    Most people's feet cannot become as flat as the inside of their shoes or the pavement they are standing on. When people maximally pronate while standing on a podoscope most of the sole of the foot is still not touching the glass.

    Subtalar pronation continues into midstance and propulsion because GRF does not stimulate mechanoreceptors in the sole of the foot and other lower extremity structures sufficiently to trigger resupination.

    The human body is incredibly resilient and adaptive.

    Pain develops when tissue loading (acute or repetitive) overcomes the resilience of the structure which is loaded.

    Foot orthoses alter the surface beneath the foot. If they create a more physiological and natural interface between the foot and support surface then function will be improved. If they replace one unnatural surface with another symptoms may be relieved (altered kinetics and tissue stress) temporarily but eventually another problem will arise when the redirected forces overcome the resilience of other tissues.

    I also question the idea of "control". What is it with us that we are always seeking to control everything? Joints are present in the body to allow movement. Movement is healthy. The human body has been functioning effectively for millions of years. The human foot and leg are amazingly resilient and adaptive. Our bodies know how to work! We just need to provide an environment in which they can function efficiently. This is especially true of the environment under the foot. Good orthotics provide a more "normal" or natural environment for the foot to function on and bad ones replace one hostile modern environment with yet another.

    Comfort, is the feeling we experience when things are going well. Benno Nigg and others have indicated that comfortable foot orthoses are more likely to improve lower extremity function than uncomfortable ones but some clinicians still ignore their patient's discomfort on the basis that biomechanical theory is superior to the ability of the human body to feel what is good or bad for it.

    In seeking a unified theory for foot orthoses and lower extremity function we should unify it with other aspects of human evolution, anthropology, anatomy, physiology and statistics as well as physics and biomechanics.

    Food for thought.



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