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When Does the Subtalar Joint Resupinate During Walking Gait?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Kevin Kirby, Apr 27, 2015.

  1. There is no single normal gait. However, there is a range of normal gait functions just as there is a range of skin colors that are normal. Would you consider someone with green skin to have a normal shade of skin, or is it abnormal?

    When you see a patient with a steppage gait pattern or with a postiive Trendelenburg gait, do you consider that a normal or abnormal gait pattern??

    When you see someone that has a grossly antalgic gait where no weight is put on the heel on one limb during stance phase while the contralateral limb appears more normal, is that a normal or abnormal gait pattern?
     
  2. What I see is a CNS being as metabolically efficient, avoiding injury and pain to the best of it's ability with what its got. If you like it's "normal gait" for that individual given their own personal G+E + (GxE) + i.

    By range you are inferring a deviation from a mean, means are not good here since the mean is defined as much by the outliers as it is by those within the middle. What is the mean number here: 5 6 6 6 6 6 6 6 7 7 8 10 16 24? 8.9 is our mean, so is that normal even though 8.9 didn't show up once in our data set? Feiss recognised this over a century ago when he was looking at navicular height- strangely enough he concluded that there was no such thing as normal, only variation. The bone pin studies, and best quality biomechanics research we have to date only reaffirm this.

    Question why did the first "subject" score 5? Because their Phenotypic value (p) = 5 due to their unique G+E + (GxE) + i ; why did the last subject score 24? Because their P = 24 due to their unique G+E + (GxE) +i, given that neither of them share the same G nor E, why would we expect their phenotypic value to be the same? Now what if the two "subjects" in question, the first and the last in this data set were monozygotic twins who had been separated at birth, what would that tells us?

    Amen, viva variation. Let's not step backwards by comparing them all to some artificial "normal" criteria. Nor worse, trying to make them fit such a criteria with our therapeutic interventions. Better, we begin to partition the variance between individuals...
     
  3. All the other branches of medicine use normal ranges for parameters ranging from serum glucose, to serum CPK, to bone density, etc. Why does podiatry then, out all the other brances of medicine, have a problem then with establishing normal ranges structural and functional parameters, including gait function, in the foot and lower extremities of their patients?

    Is it because "normal" was represented as "ideal" by Root et al? I think so.

    Here is what "normal range" means to the rest of the medical profession, excluding podiatry:

    Normal Range is also known as Reference Range or Reference Interval or Within Normal Limits (WNL) within the field of medicine.
     
  4. Thought experiment: if we were to "fully" characterise the gait of all the people on the planet right now, what would the gait characteristics of those individuals at the upper and lower extremes of the 95% intervals look like? Now think about all of the possible locomotor tasks all of these people perform during just one day of their life, now think about all of the environments that they could be performing all of these tasks in... If you brain hasn't turned to jam yet, it should have.

    OK, lets make it simpler and make our assessment of "normal" gait on a single gender and country basis, lets take males in Cambodia or Afghanistan as our reference here: in countries such as Cambodia or Afghanistan 5-10% of males between 15-44 have had lower limb amputations due to landmines- how are our 95% confidence intervals for "normal gait" going to look in these populations?

    The UK population in 2013 was around 64 million: "There are over 11 million people with a limiting long term illness, impairment or disability. The most commonly-reported impairments are those that affect mobility, lifting or carrying." https://www.gov.uk/government/publications/disability-facts-and-figures/disability-facts-and-figures - how are these people going to impact our "normal range"?

    Lets say we perform a study in which we fully characterise the gait in 200,000 individuals between the ages of 5 and 80 years, the mean age of subjects in the study is 46 years, we then have an 86 year old patient and fully characterise their gait- are we on safe ground comparing this patient to our "normal" range?

    Why don't we have reference ranges for human gait? No-one has done anywhere near enough big enough studies that encompass the required information. No-one ever will.

    Partition the variance in "normal" gait..... starter for 10: age, gender, mood........... there are hundreds and hundreds of factors we could include.
     
  5. I would say that the scientific studies done to date on the kinematics of the reference ranges of walking gait does give us a good starting point from which to move forward. Just because we don't know everything, and won't ever know everything, this should not then preclude us from endeavoring toward gaining a better understanding of how the bipedal human functions during gait for the benefit of our patients.

    I believe that, therefore, the way forward for us, as a profession, is to start with the available scientific research to date and then redefine to podiatrists around the world that "normal" should mean a "reference range" and not "an ideal", and ,along with the work by those such as Josh Burns with his 1,000 Norms Project, try to put podiatry back on track toward better appreciating what the term "Within Normal Limits" really means in regards to foot and lower extremity structure and foot and lower extremity function during the various weightbearing activities that we all perform during our activities of daily living.
     
  6. Devil's advocate: and where are these 1000 patients being drawn from? And what percentage of the global population >7000000000 is 1000? How many blood pressure measurements were made to provide the medical community with its normal limits for blood pressure, more or less than a 1000 do we think?:drinks

    Here is the DNA map for the UK, http://www.wired.co.uk/news/archive/2012-07/04/genetic-mapping-britain/viewgallery/285522 if none of the subjects in the 1000 norms project are from Devon, can I compare a patient that has their ancestory in Devon UK, to the data the 1000 norms project provides?

    Anyway, the 1000 norms study is still to be commended. Just be aware of the limits of the data it may provide.
     
  7. efuller

    efuller MVP

    I still think we should not be looking for what normal is but rather looking for what factors predict pathology.

    What percentage of people will develop arthritic changes in the first MPJ? We may have evolved to the point where we can reproduce with bipedal gait. However, we have not evolved to the point where bipedal gait will not produce pain in the first mpj. That loss of "spring in your step" is often first MPJ pathology. What percentage of the population has the same range of motion of their 1st MPJ at age 60 that they had at age 18? Will "normal" gait lead to pathology?

    Eric
     
  8. I think we should be looking for what the normal ranges are and looking for what factors predict pathology. These are two distinct parameters, both of which may serve different purposes for clinicians that conservatively and surgically treat foot and lower extremity pathologies.
     
  9. efuller

    efuller MVP

    Not everyone who has a fever is going to die from an infection. A much more medially deviated STJ axis than the average is much more likely to have pronation related pathology. At some point, I suspect, there will be a trade off of treating between treating that medially deviated axis proactively as opposed to waiting for pathology to develop. We are certainly a long way from having any idea where that point is. However, I think that further research along those lines will be more productive than defining a normal gait. Some people with extremely medially deviated STJ axes may have the muscle strength to produce a normal gait when they are 25. However, when they are 50 they may develop problems.



    We don't know yet if those observations are enough to predict pathology. Finding measures and observations that predict pathology should be the goal. If you can add two observations and get a better prediction, I'm fine with that. STJ axis position has been found to be reproducible. That alone will make it more likely that STJ axis will be a better predictor of pathology than the measurements advocated by Root et al.

    I am advocating for finding examination techniques that are repeatable and predictive of pathology. Kevin, when you perform the "classic" measurements, I believe you when you say that you are getting some useful information. After seeing thousands of patients there may be something that you are subconsciously picking up. However, if we want to teach the foot specialists that follow us, we can't pass along what our sub conscious is picking up. However, if we consciously identify a measure and then are able to correlate that with pathology and choose a successful treatment, then we are much better off. We should strive to be at the point where we will be able to say when I make a specific observation, I expect a certain result.

    Eric
     
  10. efuller

    efuller MVP

    Maybe our discussion is a semantic one. Perhaps, I'm saying that we should define the abnormal and not define the normal. This goes back to the question that I asked earlier about what do we do with normal. If we see a foot that is "normal", whatever that is, we do nothing. With surgery, are we trying to make someone more normal. After just having written that, I really get a sense of how vague that statement is. I'm looking for something a little more concrete.

    Eric
     
  11. Once the "normal range" is defined, then any value outside that normal range is considered "not within normal limits" or "abnormal" or "outlying the reference range", or whatever term we agree upon. That is why it is first important to define what we consider to be the "normal range".
     
  12. drhunt1

    drhunt1 Well-Known Member

    What kind of world do we live in, where we throw out all standards, tell our patients there is "no normal", discuss with colleagues nebulous relationships in our quest to treat non-normal, ie., pathology? Pathology itself requires some sort of standard...as do laboratory ranges. Do Cardiologists demise EKG readings, simply because they are developing "new standards"? Do surgeons tell their patients that they're writing a new book on anatomy because the norm is simply no longer sufficient, right before that patient is taken into surgery?

    If you don't know what "normal" is, perhaps it's time to begin at the beginning.
     
  13. The great thing about building statistical models which predict pathology is that we don't necessarilly need to define the undefinable "normal" nor "abnormal" values for a particular independent variable when we employ the model. Instead, we often need to only measure the predictive independent variables and plug them into the model to provide us with a statistical risk of developing that pathology. Nice example of a simple predictive model here: http://www.jospt.org/doi/pdf/10.2519/jospt.2001.31.9.504 to use this model we do not need to decide whether navicular drop is "normal" nor "abnormal" any more than we need to decide whether the subjects gender is "normal" nor "abnormal", we just need plug our observations into the model and do the math.

    Further, we could argue that without good quality predictive models, we cannot begin to understand "normal" from "abnormal". Carrying this thought process on, the same value of a given variable may be "abnormal" in a model which predicts one pathology, yet that same value may be "normal" within a model that predicts a different pathology. This is just another reason why generalised labels of "normal" and "abnormal" just don't work here.
     
  14. efuller

    efuller MVP

    Root et al had two definitions of normal. 1. (paraphrased) normal is when there is no discomfort while performing the activities of daily living. 2. The biophysical criteria of normalcy. One of those criteria was that the normal foot stood in neutral position.

    You could make the case that they didn't know what normal was, because they couldn't pick one definition. We could make the case that any value is within one or two standard deviations of the mean could be defined as normal. So what rationale should we use for choosing which definition of normal to use?

    Let's start at the beginning. Why do we need to know what normal is. If we can't explain why we need a normal then we don't need one. Matt's post above is not an explanation.

    We can look at other measures in medicine and how they choose what is abnormal. Take blood pressure. We know that high blood pressure leads to an increased risk of stroke. So, in that instance, normal is defined by increased risk of pathology. Should we choose what abnormal gait is based on what gait is likely to have increased risk of pathology?

    Eric
     
  15. HansMassage

    HansMassage Active Member

    This thread got more interesting toward the end concerning the difference between left and right foot.
    My observation is that there seems to be a correlation with arm swing and where stress points build up in the arch from supinating from the pronation or posisbly from resisting the pronation.
    The foot opposite the restricted arm swing tending to external rotation and stress at the anterior of the arch while the foot on the side of the restricted arm swing has the stress at the posterior of the arch.
    My goal is to understand an document the adaptive reflexes that develop in avoidance of pain or due to post trauma restrictions.
     
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