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Pronated what?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by wdd, Mar 12, 2017.

  1. wdd

    wdd Well-Known Member


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    Don't ask me why but suddenly, upon reading the phrase, "maximally pronated patient" I had the feeling that the language was too far from describing what was going on. What does it mean to have a 'patient' who is maximally everted, abducted and dorsiflexed? Why is the phrase so far away from describing what's going on?

    If the idea of a maximally pronated patient is difficult for me is the much used "pronated foot" that much better?

    Is the "foot" everted, dorsiflexed and abducted?

    As the term is commonly used to describe the foot of a person who is standing with their foot/feet flat on the ground it seems to me that the answer to the above questions is no?

    If the "foot" is not pronated what is pronated and why isn't it stated clearly?

    Bill
     
  2. Rob Kidd

    Rob Kidd Well-Known Member


    Insomuch as one believes in the theory of what you have just quoted, the answer is that "the joint" is pronated. Since these things happen at a joint, not a functional unit such as a foot, one must go back to basics; it is the joint. Having said that, one assumes that we are talking about the subtalar joint; there is, of course, no such thing in terms of structural entities. It amuses/bemuses (choose your own adjective) that vast numbers of pods fail to understand this. The subtalar joint, as I am quite sure that you understand, is a composite of two separate joints, one part of which is also a part of the so-called midtarsal joint. Easy? No. Nothing about foot anatomy is easy. Rob
     
  3. wdd

    wdd Well-Known Member

    So would "pronated subtalar and midtarsal joint/s" or even "pronated STJ/MTJ" be more accurate and acceptable descriptive terms which recognise the complexity of structure and function of these bones of contention?

    Bill
     
  4. efuller

    efuller MVP

    When I've seen feet that people describe as pronated with only looking at them from across the room, the things that I usually see are a heel that rests more lateral relative to center of the ankle, marked talar adduction, forefoot abduction on the rearfoot, and low arch height. A lot of things addressed in the foot posture index. It is unfortunate that those findings have been termed pronated, because when you see those things, you don't necessarily know the position of joints of the foot. There may be some correlation with joint position, but it is not 100%. A lot of those findings will also correlate with a medially deviated STJ axis. I would bet that there is a better correlation with medial STJ axis position, than there is with joint position. Those physical findings could mean that there is a high pronation moment from the ground.

    Eric
     
  5. HansMassage

    HansMassage Active Member

    Laying face down on my massage table.
    But to stay on topic my study is the reflexes that occur in one part of the body to compensate for movement in another part of the body. Therefor is the client chronically in a posture that inhibits the supinators and or facilitates the pronators.
    So in my discipline I would say the client has a maximum loss of the capacity to supinate the medial arch.
     
  6. wdd

    wdd Well-Known Member

    Using the example of the Foot Posture Index (FPI) might help me to get a little nearer to what I think is a more accurate description of what's going on.

    In the online User Guide and Manual August 2005 the following definition of the FPI is given in the introduction.

    "The foot posture index (FPI) is a diagnostic clinical tool aimed a quantifying the degree to which the foot can be considered to be in a pronated, supinate or neutral position."

    As "All observations are made with the subject standing in a relaxed angle and base of gait, double limb support, static stance position" it seems that Podiatric biomechanical definitions of supinated and pronated, with respect to foot posture cannot easily be applied?

    As you say Eric, a number of different things contribute to foot posture but hey, so far we haven't got a definition of the word posture.

    Let me try this one, I've just made up, on for size. "Posture is a position of a body or part of a body and is dependent upon both structural and functional characteristics of the body or part of the body."

    The FPI by using the words pronated, supinated and neutral seems to ignore the structural aspect of posture or at least by not clearly stating the structural contribution to posture encourages others to ignore the structural/functional relationship.

    It seems to me that, with respect to the FPI, when using Podiatric definitions of pronated and supinated the 'foot' is not in a supinated or pronated position. Whatever supination or pronation has taken place is at at some specific joint/s within the foot and the other part of the posture is due to structural features affecting things like, the angles and positions of axes of motion and the relative positions of bones to one another and the relative position of bones to their axes of motion plus movements that have taken place at other joints in the foot and lower limb allowing the plantar aspect to rest on the ground.

    I am now asking myself how the description of the FPI would have to be modified to more clearly identify what it is describing and what value there would be in confining terms like "pronated" to describing the everted, abducted, dorsiflexed position of a foot resulting from motion at joint of the foot having supinatory/pronatory axes of motion.

    Then again maybe nothing needs to be changed? Maybe the current popular use of the terms pronated patient, pronated foot and supinated foot are good enough? Oops I need to stop I'm losing my conviction.

    Bloody hell did I write all that! I think I need to lie down for a little while to recover.

    Bill
     
  7. The terms "pronation" and "supination" should be reserved only for discussing the motions of the subtalar joint in the lower extremity. The terms "pronation" and "supination" should not be used to describe the motions of the midtarsal joint since the midtarsal joint does not have a discrete or constrained joint axis, that the subtalar joint seems to have. In other words, it is very easy for the midtarsal joint to dorsiflex, abduct and invert which is not a true pronation range of motion (i.e. pronation is dorsiflexion, adbuction and eversion).

    I defined subtalar joint rotational position as being the position of the subtalar joint within the subtalar joint's range of motion (e.g. maximally pronated, neutral position, maximally supinated, 2 degrees from maximally pronated, etc). I defined subtalar joint axis spatial location as being the three-dimensional of the subtalar joint axis relative to another point of reference (e.g. medially deviated, laterally deviated). Therefore, it is very possible for a foot with a high degree of "rearfoot varus deformity" and a limited subtalar joint range of motion to be "maximally pronated" but still have "supination instability" during weightbearing activities (Kirby KA: Subtalar joint axis location and rotational equilibrium theory of foot function. JAPMA, 91:465-488, 2001).

    Therefore, one must not confuse "maximally pronated at the subtalar joint" to indicate that the individual may have increased risk of symptoms caused by excessive subtalar joint pronation moments, since excessive subtalar joint pronation moments are more likely caused by an abnormally medially deviated subtalar joint spatial location than are caused by a maximally pronated subtalar joint. Hope that makes sense.
     
  8. wdd

    wdd Well-Known Member

    I have often wondered why there is no name to describe any triplane motion other than supination and pronation? But the more I think about it, in the context of this thread possibly it's time to do away with the words pronation and supination and develop a simplified (I hope) system that can incorporate more information and reduces confusion.

    OK, here goes. The single plane motions we have are abduction/adduction, dorsiflexion/plantarflexion, inversion/eversion. If I contract that to ab/ad, do/pl, in/ev it's still clear? In fact do/pl could be contracted to d/p and in/ev to i/e and still contain no inherent confusion?

    So the motions involved in pronation could be written as "abed" and the movements involved in supination could be written as "padi". Then midtarsal joint motion could be described as "abid" and "adep".

    To differentiate between a posture/position resulting from structure (s) or function (f). Hallux valgus or hallux abductovalgus would then become hallux fadse. In a situation where a posture has both structural and functional components sf could be added as a prefix, e.g. Calcaneal sfe or in the case of uncertainty sf?e.

    It sounds nonsensical at the moment and I am sure would need a bit/ lot more consideration but there might be something in it?

    Bill
     
  9. Rob Kidd

    Rob Kidd Well-Known Member

    Oh you word smith you!
     
  10. efuller

    efuller MVP

    When I first read about the foot posture index, I had a hard time reconciling those measurements to joint positions. However, I did have clinical instructors who talked about pronated and supinated feet. By osmosis, the majority of students would pick up a sense of what a pronated foot looked like and what a supinated foot would look like. However, you could have a foot that was at its end of range of motion in the direction of pronation of the STJ and it would look like a "supinated" foot. So, clearly when talking about a supinated foot, the community was not thinking about joint position. In my opinion, a better way to think about the shape of the foot is to think about which foot types are more likely to have pronation related problems and which feet are more likely to have supination related problems. The postural findings in the foot posture index are mostly things that will affect the position of the STJ axis relative to the weight bearing surface. The greater talar adduction there is, the more likely there will be a medially deviated STJ axis. The reason that a foot that is "pronated", using the FPI criteria, is that it will tend to have a higher pronation moment from the ground. This means it is more likely to have pronation related problems. It is not the position of the bones that causes the problems, it is the stress on the anatomical structures. A higher pronation moment from the ground will cause higher stress on the structures that resist pronation. It's not the pronation that hurts, it is the stopping of pronation that hurts. We should be thinking about forces and not position. I think what those that called feet pronated or supinated were intuitively seeing was pronation stress and supination stress. Looking at STJ axis position and rotational equilibrium could resolve this problem of supinated looking feet that are maximally pronated at the STJ. This is how posture is likely to affect pathology.

    Eric
     
  11. wdd

    wdd Well-Known Member

    One of many gifts.

    But seriously, for someone writing off the top of his head even I was surprised by the emergence of the nice little mnemonics "abed" and "padi".
    All I have to do now is remember them?

    Bill
     
  12. Rob Kidd

    Rob Kidd Well-Known Member

    Whenever I here the word "index" with respect to linear dimensions my alarm bells go off. And this is for two fundamental, though unconnected reasons. First is the relationship of size and shape; any attempt to remove the "quantity of size" by indexing is naive to say the least. It assumes a Y=MX+C relationship (ie a straight line) which simply does not exist in biology, though many issues may closely approximate to it. The real issue is that bivariate relationships equate to Y=BX to the K (exponent) as in Julian Huxley's bivariate allometry equation. That is, there are no straight lines in biology. The other issue is that the indexing of data frequently buggers up the distribution profile. That is, even if the two (or more than two) data groups may have been normally distributed before, the indexing process may may stuff that up. Normal distribution is an assumed critera for much of standard statistics such and t test or any of its multivariate progressions such as principal components analysis and canonical variates analysis.

    Those people using the foot posture index should be well aware of these two issues, and recognise there shortcomings. I have never heard this referred to.

    References available for those that want. Rob
     
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