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Challenging the foundations of the clinical model of foot function

Discussion in 'Biomechanics, Sports and Foot orthoses' started by NewsBot, Jan 31, 2017.

  1. Jeff Root

    Jeff Root Well-Known Member

    How to bisect a heel:
    1. Place STJ in neutral
    2. Palpate the superior medial and lateral aspect of the posterior surface of the calcaneus
    3. Mark a line segment bisecting the distance between the tips of your (the examiner's) fingers
    4. Move inferior and repeat this process several times until the upper parabolic surface of the calcaneus has been bisected and then extend this line segment down the remainder of the posterior surface of the heel without palpation
    Figure 7 illustrates the anatomical prupose of a heel bisection.
     

    Attached Files:

  2. Jeff Root

    Jeff Root Well-Known Member

    How to use a heel bisection to alter the forces acting on the foot:
    The stacked casts below demonstrate how a heel bisection line can be used to alter the mechanical influence of an orthosis on a fairly flat foot. The bottom cast was corrected (balanced) with the heel bisection vertical. The middle cast is the exact same cast but had a medial heel skive applied to it. The top cast is the exact same cast as the middle cast but was inverted 10 degrees. Inverting the cast a prescribed number of degrees allows the practitioner to tailor their orthotic prescription to the needs of the individual patient. As you can see, inverting the heel 10 degrees increases the slope of the heel (heel cup) and increases the height of the medial arch of the cast and the resulting orthosis. Figure 15 is a cross section of the heel cup without and with a medial heel skive.
     

    Attached Files:

  3. mazzopod

    mazzopod Member

    We don’t have labs here in Italy that make orthotics for podiatrists therefore we all make our own orthotics, and have been for the last 35 yrs. As already mentioned I do take measurements during the clinical assessment of my patient, but no necessarily use Root’s Criteria of Normalcy to classify foot pathology. For instance an inverted forefoot that is present once the STJ is placed in its neutral position is commonly called a forefoot Varus according to Root’s classification, but we also know that soft tissue compensation causes a forefoot supinatus which is very difficult to quantify with measurement and requires a very different orthotic prescription compared to a Varus deformity.
    The medially deviated STJ axis with calcaneal eversion or a vertical calcaneus requires a medical heel skive modification to withstand or reduce the pronation moment during weight bearing at the STJ and this has been well discussed by Kevin Kirby and clinical measurements apart from locating the STJ axis are of little use in your orthotic prescription.
    As you say the clinician must prescribe the orthotic and the lab must make what is prescribed .....!
    Please try and understand that we don’t all live in the USA and that we all need to speak a common language and that this arena gives us all over the world an opportunity to learn from the experts that are willing to share their knowledge with us. I thank you for the opportunity and for your responses.
     
  4. efuller

    efuller MVP

    Did John Weed ever write about this? I certainly don't recall the valgus onlay from his lecture sylabus. But, this method still is not using the forefoot to rearfoot measurement made in neutral position to decide how to make the orthotic. It is using trial and error. There is nothing wrong with trial and error. I like the idea of altering an orthotic that does not work the first time. The problem is that theory implies that forefoot to rearfoot measurement accuracy is needed.

    The first option is very close to what I often do. I decide what forefoot to rearfoot measurement that I want to see in the cast and then make that happen.
    The second option is not viable because feet don't invert the amount of inversion there is in the heel bisection.

    The difference between maximum eversion height and forefoot to rearfoot angle is that maximum eversion height is simply translated directly to the positive cast. With forefoot to rearfoot relationship with the STJ in neutral position, the vast majority of the time, is not going to be what it is in the weight bearing foot. Additionally, the maximum eversion height measurement also incorporates the amount of rearfoot varus. With maximum eversion height you don't have to multiple calculations, with multiple sources of error to figure out how big of an intrinsic forefoot valgus post is too big.
     
  5. efuller

    efuller MVP

    Daryl, I don't know where you get the idea that this is about personality. When I have been critical of Root I have not criticized the person. I believe I have always stated the idea that I was criticizing. When I say that the Root prescription writing protocol lacks internal logic, I explained why I think that. You are welcome to pick apart my argument, but saying that is about personality is avoiding the discussion. When I have advocated not taking a particular measurement, I have given reasons why that particular measurement should not be used. I have never said that you shouldn't take any measurements. There is a big difference between saying you should not do a particular measurement and saying you should not do any measurement.

    Daryl, did you see the article I wrote for podiatry today last month? I wrote a list of measurements that could be used for making choices in how to design a custom orthotic.

    I am willing to defend the logic on each of those measurements. If we are going to compare the two prescription writing protocols side by side we need someone who is willing to defend the logic of the Root measurements.

    For example, why is the forefoot to rearfoot relationship taken in STJ neutral position? Why, and how, is this measurement used in writing a prescription for an orthosis when in the vast majority of cases the forefoot to rearfoot relationship with the mtj pronated, in the foot standing on the orthosis, will be different than it is when the foot is in neutral position?
     
  6. rdp1210

    rdp1210 Active Member

    I appreciate everything you've said. Actually, in the US we seldom use the term "forefoot varus" because of the various combinations of true varus vs. supinatus problems. What we usually say is "inverted forefoot deformity." You will find an abstract in "The Foot" that I published in 2014 on the contributions of the medial and lateral column plantarflexion to forming the forefoot-rearfoot relationship. I can honestly say that we still don't fully understand the various types of inverted forefoot deformity. I believe that there are those that are caused by talar neck abberations, but I believe there are many other types of inverted forefoot deformities that we haven't fully separated out. There may be those that should be casted with the first metatarsal plantarflexed and those that shouldn't. I'm still investigating. I've been trying to get our hospital to purchase a 3D weightbearing CT for the past 5 years, but the radiologists still haven't seen the light.

    You will find that I also use STJ axis as part of my total assessment. Please note my 1992 article on it, which was the first independent study to confirm what Kirby was saying, plus give a little more insight as well. I think in that article you will find some other measurements that I utilize today, including the linear as well as the angular alignment of the rearfoot to the leg. I've lectured a little on the linear alignment aspect, but haven't written too much about it. Guess that I will have to do more writing in the future about this aspect of orthotic making.

    I'm extremely glad to see that you're still making your own orthotics. That's where you really start to tease out the Root parts that make total sense, but also start to find points where Root can be improved on and even those that should be changed. I was fortunate to have a father who was a big fan of Root, but was also an independent thinker, and was always trying to improve things. He definitely developed some of his own ideas to add to orthotic making. Those who know me find that I look for the truth. If you read some of the book chapters I've written, you will find that I use a lot of Root, but I've also added a lot of things too. I knew Root personally, I know that is what he expected us all to do.

    Will look forward to further discussions.
    Best wishes,
    Daryl
     
  7. efuller

    efuller MVP

    Daryl, this is interesting. It appears that you are saying that not all inverted forefoot deformities should be treated the same. What measures would you use to decide to treat one inverted forefoot differently from another inverted forefoot? Would you consider maximum eversion height as a measure that would help you decide whether to plantar flex the medial side of the foot when casting?

    The supinatus problem (forefoot to rearfoot changes over time) does make it pretty hard to live in a paradigm where you believe foot problems come from compensation for a deformity. Does the deformity cause the problem, or do forces create the deformity. If the answer is some of the time one and some of the time the other, then do you really need an accurate forefoot to rearfoot measurement. Is a more accurate measurement going to be helpful. I'm not saying that you shouldn't measure it. I'm questioning whether or not the measurement is useful for how we treat patients.
     
  8. Trevor Prior

    Trevor Prior Active Member

    Nice pics Jeff. Visually, the heel skive and inverted orthoses provide a similar shape to the heel cup relative to the foot because of th eangle of th eheel. However, in the inverted device, you also alter the the shape of the arch so one would expect the effect to be different.
     
  9. Jeff Root

    Jeff Root Well-Known Member

    Exactly Trevor. If we want to attempt to focus the influence on the medial heel area, then just use a medial heel skive. If you want to increase the supination moments even more, then invert the cast and possibly use a medial heel skive and/or decrease the medial arch fill to increase the orthotic's arch height even more that it would be by simply inverting the cast.
     
  10. Bless, yet we have absolutely no idea how any foot orthosis prescription variable will alter the reaction forces at the foot-orthosis interface from one patient to the next, in one shoe from another, from one terrain to the next.. Until we stick it under their foot. Sleep tight, y'all. It's an industry built on absolutely bullshit science. Ya' gonna have someone making money out of said industry complaining here, right now.. It's bullshit science, explain to me why I'm wrong...
     
  11. Jeff Root

    Jeff Root Well-Known Member

    Eric, we can clearly see acquired ff inversion in patients with adult acquired flatfoot. The degree of ff inversion can decrease after orthotic therapy reduces STJ pronation (moments) and increases MTJ pronation (moments). By measuring the ff to rf relationship in the foot prior to treatment and then later during orthotic treatment, we can quantify the reduction in the degree of ff to rf inversion. In other words, we can measure reduction forefoot supinatus. By quantifying the degree of the inverted ff condition (or ff deformity if you prefer to cal it that) and by quantifying the reduction in the degree of ff inversion post treatment, we can document that our intervention has produced a positive change in the shape of the foot. In other words, using measurements and math we can demonstrate a positive change provided we have a large enough population to demonstrate a pattern in the reduction of ff supinatus with foot orthoses.
     
  12. Jeff Root

    Jeff Root Well-Known Member

    Simon, you will have to take that up with Kevin since these are all techniques that he discusses the mechanics of and endorses in his books. Kevin has attempted to explain the science behind foot orthotic therapy to the best of his ability. There is no doubt that more research is needed to demonstrate how orthoses work and how these and other orthotic manufacturing techniques effect the foot.
     
  13. mr t

    mr t Active Member

    Hello Simon,

    In what way do you mean that angular relationships don't matter?

    What would your views be on the importance of angular reference to 3D scan positioning and what implications would this positioning have on the manufacturing process?

    I have attached two images. Can you please tell me if you believe one position represents a more logical starting baseline for orthotic surface modifications to be applied? Each negative generated will provide different magnitudes of force across the entire foot orthotic interface.
     

    Attached Files:

  14. Anthony, as you know I was referring to the angular relationships between foot segments in this statement, specifically we were discussing forefoot to rearfoot measurement. But perhaps you can better illucidate as to which part of this statement you don't understand so that I may better be able to help you: "Of course an accurate measure of angular relationship doesn't matter. As long as an orthosis is basically providing reaction force in roughly the right place, in roughly the right direction, at roughly the right time then that's as good as we can ascertain."?

    When I have a positive cast in my hand, I look at it from lots of different angles and hold it at different angles whilst I apply the dressing, Similarly when I use Solidworks I rotate the model and apply working planes depending on what it is I am trying to do. Which plane is the right plane? The one that best suites my needs for the task in hand. Yet, however I rotate the model in real or computer space, the angular relationship between the forefoot and rearfoot section of the model doesn't change unless I make a change to the model itself. In your example you are just rotating the model in space, you are not changing the angular relationships between points on its surface; this being the moot point.

    Taking your two examples, if we milled postive models of the scan that is orientated differently in your CAD system examples, in reality both models would actually be the same when turned into physical objects.

    Returning to my original point: perhaps you can tell me the relationship between the surface angulation of the forefoot to rearfoot in your CAD system and how this changes the angular relationship of the foot orthosis surface and ultimately how this changes the magnitude, position and timing of the GRF vector in each patient? No, didn't think so.

    How do prefabricated device work?

    "Ya' gonna have someone making money out of said industry complaining here, right now.. " QED.
     
  15. rdp1210

    rdp1210 Active Member

    I am bringing that up more as a question than a statement -- it's something we need to further investigate. The idea of forefoot supinatus evolved from the observation that sometimes the inverted forefoot deformity reduced after wearing orthotics for a while and sometimes it didn't. Certainly Paul Scherer has given a lot of thought to this as he has tried to reduce the supinatus component during the casting procedure. There's a lot more research work to be done yet on the entire subject of forefoot to rearfoot relationships, and how they interact. I'm not saying I have all the answers yet. But then again, neither does anyone else writing in this arena.

    Now the question is often posed how this or that measurement affects the treatment. It doesn't always, however when a patient presents themselves to me for what they perceive is a problem, I not only have a duty to treat it, but just as important, if not more so, I have a duty to investigate why it occurred in the first place, what are the primary and what are the secondary etiologies. Many times the measurements I take are for better understanding the mechanisms at work. Let's take an example: a patient stands up and the calcaneus is everted from perpendicular, so I know that all the metatarsal heads are making contact with the ground (though they may not all have the same force under them). So in what mechanism did they all come to make contact with the ground. Did the heel evert as a compensation for the forefoot not being able to evert enough, or did the forefoot undergo an inversion motion from its maximally everted state? At which joint(s) did this inversion occur -- i.e. was it the MTJ, the CNJ, the MCJs? Depending on these motions we may have very different complaints of the patient. In one case hallux valgus may result while in the next patient with same amount of calcaneal eversion we may get no hallux valgus. Please review the chapter I also wrote for the Albert book as I discuss this situation. I am still looking for better methodologies and instruments to measure forefoot to rearfoot positions and motions available with the STJ in various positions.


    Since my last posting, I have completely reviewed your Feb article in Podiatry Today. While I took notes as I read it, it will take me a very long time to post my review of it. In summary, I find very little in the literature to back up many of your statements. I feel that you have an obligation to the community of interest to publish in peer reviewed journals your methodologies and put them up for scrutiny from the community.

    As I read everyone's comments on this forum, I guess I'm the only one here that's willing to say that I don't know it all and I'm still very much in learning mode.
    Daryl
     
  16. Jeff Root

    Jeff Root Well-Known Member

    Hi Anthony,
    You wrote "Can you please tell me if you believe one position represents a more logical starting baseline for orthotic surface modifications to be applied'? I think this aspect of your question was lost in the following discussion. If we accept the following:
    1. When we create a negative cast or scan of the plantar surface to the foot, the physical relationship between the plantar surface of the forefoot and rearfoot is captured in our cast or scan
    2. When we manufacture a functional type foot orthotic from a cast/scan of the foot there will be a point of contact with the supporting surface in both the forefoot and the rearfoot of the cast/scan (note: there are some exceptions to this rule such a rocker bottom foot type)
    3. If we alter the frontal plane orientation of the cast or scan it does not alter the ff to rf relationship in the cast/scan but it does alter the relationship of the ff and rf to the plane of the supporting surface. It also alters where the point of contact on the foot is with supporting surface
    4. When we manufacture a Root type functional orthotic or any device that uses an intrinsic or extrinsic method of positioning the cast/scan in the frontal plane, then I think most of us would agree that alignment B in your pictures above would represent a more logical baseline for orthotic surface modifications because alignment B more closely approximates the functional relationship of the plantar surface of the foot to the supporting surface. Root Lab, at the request practitioners, has manufactured Blake type functional orthoses that were inverted in excess of 45 degrees. These devices require far more physical or virtual modification in order to maintain the inverted alignment of the cast and to alter the contour in order to make these highly inverted devices tolerable.

    In addition, in order to invert a cast/scan of the foot we need a starting or reference point. What is the most logical reference point? A heel bisection that represents the frontal plane orientation of posterior surface of the patient's foot is an excellent reference for orienting a cast/scan of the foot in the frontal plane. Another method is to use the plane of the forefoot in relationship to the plane of the floor as a method for positioning the plantar surface of the foot relative to the plane of the supporting surface. If someone is just eyeballing the cast and orienting it in the frontal plane, then they are either using some sort of visual reference (the general appearance and orientation of the posterior heel for example), they could just position it as it sits or they could just do it randomly. In any case, we know that the frontal plane orientation of the cast influences the nature of the forces acting on the foot from the resulting foot orthosis.
     
  17. But you don't know how; thats what you said previously. What say I make two devices: one I invert 5 degrees and make the resultant device out of 5mm polypropylene, the other I invert by 6 degrees and make the device out of 2mm polypropylene- which one will "influence the nature of the forces" the most and in what way? Lets say I make both devices in 3mm polypropylene, do you honestly think the two devices would result in vastly different clinical outcomes? Roughly the right magnitude, in roughly the right direction at roughly the right time- that's all we need to do (and all we can hope to do given our best knowledge) to the forces acting on the plantar foot with a foot orthosis to get the desired clinical outcome- which is why very few of our patients need made to measure custom foot orthoses. Given the wide range of off the shelf devices available to the clinician and the ease of their modification, very few patients require custom moulded foot orthoses in 2018. A few exceptions, for example the patient with the high risk insensate foot, but generally speaking I'd say there is an off the shelf, prefabricated foot orthosis out there for about 90% of the patients that I see on a day to day basis and given the ability to modify at chair side, the patient can leave there and then with an efficacious device in most cases; no erroneous heel bisection, nor forefoot to rearfoot alignment measurement, no subtalar joint "neutral" required.

    Stop pretending we need degree accurate measurements- that's bullshit science.
     
    Last edited: Mar 16, 2018
  18. Nope, quite happy to admit that every day is a learning day for me. I think the bigger problem here is the vested interest and the dollars at stake.
     
    Last edited: Mar 16, 2018
  19. Why? I ask this seriously. Even if we could measure this with zero error, is it not obvious to you that different people will have different values and that the chances of this being demonstrated as a predictor for any pathology on the basis of the between-subject variability are likely to be minimal given the step to step variability of external and internal moments? I ask you seriously, Daryl given what we know about inter-subject variation, the lack of evidence to support static measures predicting dynamic function and all the published research we have up to 2018- why do you think this might even be important anymore?
     
    Last edited: Mar 16, 2018
  20. Jeff Root

    Jeff Root Well-Known Member

    Are you talking about the vested interest associated with book sales, lecturer honorariums and travel perks, advertising revenue from running a podiatry website, income from practicing podiatry and from selling orthotics that conform to TST and other theories of foot function, income from teaching, income or potential future income associated with conducting and publishing research or income from manufacturing foot orthoses that are sold to practitioners who mark them up and profit from them? Each of us has a vested interest and I'm sure that that influences each of us. I don't think I would have any reason or the ability to participate on the PA if I owned a take out pizza shop and had no vested interest associated with podiatry or foot orthotics. One thing is for sure, I can't identify a single cent that I have made as a result of participating on the PA but I have spent a lot of my time, given away free books and hosted guests as a result of the PA. If there is anyone who has become a customer of Root Lab as a result of my 20 (?) plus years on the PA please identify yourself so that I know that my time has paid off in dividends. I don't think we can identify all vested interests but some are certainly much more apparent than others. Personally I think ego is more of a problem here than any vested interest and I believe it clouds our perspective more than anything else. I can't necessarily exclude myself from that group and neither can several others.
     
  21. Petcu Daniel

    Petcu Daniel Well-Known Member

    Which other type of patients/pathologies, next to the high risk insensate foot, do you think are part of the rest of 10%? A second question is if those 10% will need also custom-made footwear or not.
    Thanks,
    Daniel
     
  22. rdp1210

    rdp1210 Active Member

    Let's see, the dollars at stake! Hmmm! Book income - $0. Laboratory consultation fees - $0. Lecture income - less than $2000/year. Time spent in clinic and in hospital and in doing surgery, mostly on diabetics - 60+ hours/week, including weekends and taking 24h call schedule, straight salary with no bonuses or extra pay. Money for being director of residency program - $0. Money received for developing and then being director of 4th year medical school rotation -- $0. Money received for contributing articles and time to podiatry journals and magazines - $0. Money received for contributing any ideas to PA - $0. Money spent on self funding research plus paying own travel to give presentation - (neg $2000). Gee Simon, I know there's got to be a profit in there somewhere. I've got to get hold of an accountant and find out where my interest and dollars and pounds and euros are. Guess Mert Root should have spent more time teaching us investing than in trying to figure out how the foot works. I'm living comfortably, not asking for more, just grateful for all that I've been able to contribute and hoping to contribute a lot more.
    rdp
     
  23. efuller

    efuller MVP

    So, if you saw a foot with an everted heel why would one assume that this is not the position in which there is the least stress on the foot? Why would one assume that this resting state is a compensation for something? Why would one assume that this foot should start with its MTJ in the maximally everted state?

    Why would one expect these motions to cause pathology? For example, why would any of those motions cause a bunion? Snijders et al have shown that flexion forces at the MPJ create the deformity. How would those motions create flexion forces?

    I keep hearing how Mert Root always said he was still learning. Yet, many people who listened to him felt he was very dogmatic and sounded so sure that he was right. I believe that it is possible to sound dogmatic and still be in learning mode. I call it tissue stress theory because it is still theory. I believe that it is an easily defensible theory and one that can be used to create hypotheses that can be tested. This is one problem with Root theory. What are the testable hypotheses from the theory?

    Daryl I'm looking forward to your critique of the prescription writing protocol. I get that a lot of the theory has not been verified in the literature. Not having literature support hasn't stopped people from using neutral position theory. Just because neutral position theory had a 30 year head start shouldn't mean that we can't compare the two theories side by side.

    Respectfully,
    Eric
     
  24. Jeff Root

    Jeff Root Well-Known Member

    Eric, have you read Kevin's dogmatic statements about Root biomechanics on his Facebook page. Kevin has referred to Dr. Root as being dogmatic. Is this not the pot calling the kettle black?
     
  25. Those individuals who sit at either end of the normal distribution curve for arch height/ "foot shape" i.e. > +/- 2 S.D. from the mean; individuals who've undergone severe trauma/ surgical failure; severe RA etc.. Answer to second question- sometimes.
     
  26. Talking about all of it.
     
  27. rdp1210

    rdp1210 Active Member

     
  28. rdp1210

    rdp1210 Active Member

    There are so many things in this post that it's going to be impossible to answer them all in the time I have this morning. I am not going to apologize for Root's lecturing style. However in private conversations I found him to be very much of a listener. He typified many popular lecturers, including those who are popular today.

    I am informed the other day by Jeff Root that he has the book that his father kept of his clinic patients, recording the measurements. There are over 1500 entries. It is unfortunate that Root didn't publish the actual data from his patients instead of just giving us summary conclusions. However to say that Root sat down at his kitchen table and made this stuff up isn't fair at all. Alas Root lived in an era when much of the literature didn't have the published data to back up the conclusions of the authors, so he was following precedents of his time.

    I don't know where you got the idea that I have ever stated that the MTJ should start in a maximally pronated state. I have never stated that. In fact at the beginning of the stance period of gait the MTJ should be maximally inverted against the rearfoot. An orthosis must have enough torsional flexibility to allow for this. In fact in my current research I have twice been able to break Polydor orthotics, the first one with 75 in-lbs of torque and the second with 70 in-lbs of torque. These fractures originated at the medial side of the heel post, and replicated the morphology of the fractures often seen with acrylics. This tells you that acrylic is NOT rigid, it is very flexible and it has to allow for the MTJ to maximally invert at the beginning of stance. However it has to have enough resilience to then promote the MTJ to start to move toward an everted state to the rearfoot during the midstance period of gait. You will see in my research work at IFAB that many polypropylenes don't have this resilience.

    Now above you say that an everted heel isn't necessarily pathological. First the term pathology is a very nebulous term, because it involves some type of angst for a person. If a person has a bunion but it never hurts, they never wear shoes, is that pathological. Please refer to Root's original definition of "normal foot." The definition is based on conditions that shift. It involves the needs of society, it involves the human perceptions and it involves the length of life. So just as Staheli went without custom arch supports for so many years without pain or limitations of activity with the flattest of feet, should we call his flat feet pathological? Root himself often referred to those partially compensated rearfoot valgus feet as those which didn't need treatment. And interestingly enough he advocated that one should not try to put a patient with a congenital equinus in a neutral orthotic, that limiting too much pronation would actually induce other pathologies. So it's time for the "Root-bashers" to quit bashing Root and start bashing those who call themselves his disciples but advocate only one particular type of treatment.

    However you love to talk about equilibrium around the STJ axis. But lets back up and look at rotational equilibrium of the os calcis. If you study compression mechanics of vertical structures, you know that it is most desirable to have the center of weight above passing through the center of mass of the vertical structure. If you don't you set up a tension on one side and a compression on the other side. If you put a joint in the middle of the structure, you have a more tricky situation of equilibrium of rotational moments. Now let's assume (we have no proof and this needs some research) that the calcaneal bisection line overlies the center of mass of the os calcis. As you review my 1992 paper, I actually measured the linear translation medial and lateral of the calcaneal bisection at two different locations and showed mathematically that the subtalar joint axis cannot pass through the point at the inferior posterior edge of the calcaneal fat pad. So if a person stands up and the center of mass of the os calcis isn't under the center of mass of the tibia, there is natural rotational moment that has to be countered by a force from one source or another. It could be two bones making contact, e.g. the talus making contact with the floor of the sinus tarsi, or it could be the deltoid/spring ligament complex or the posterior tibial tendon. Nevertheless most of the time the STJ pronates to its EROM. Do you want these eversion restraining mechanisms to be under constant stress? I think not. (I don't have the time or space to talk about how the FF is part of the counterbalancing moment creators) You'll remember that Root taught that if the STJ pronates more than 3-4 degrees, it finishes pronating to its EROM. If this is the case, then all the studies that try to correlate the amount of forefoot varus to the degree of rearfoot pronation will show very low correlation coefficients. Such studies are then not proving Root wrong as many claim.



    You say you believe in tissue stress, yet you never pay attention to active muscle length-force curves. Isn't this part of the total package? Can you tell me that the posterior tibial tendon is as strong with the patient striking the ground with the subtalar joint highly pronated? At what point of subtalar joint ROM (and ankle joint ROM) can the posterior tibial tendon exert it's strongest contractile force? At what point in the STJ ROM (and ankle joint ROM) does the passive tension in the PT tendon reach zero? Please explain why the STJ neutral ideal doesn't agree with maximal efficiency of the PT muscle/tendon structure. (I realize that the ankle joint is also involved and a graph of PT tendon efficiency would be a three axis graph, with two independent variables of STJ and ankle joint position). Also don't forget how velocity of pronation would effect the PT strength, so that many orthotics that only slow down velocity also alleviate many symptoms.

    I'm sorry that I don't have more time this morning to write more. I will get to my critique of your article. If you say I don't believe in tissue stress, you're badly misinformed. What I am saying though is that you haven't replaced Root with a different theory. I was practicing the concept of identifying the structures under stress long before you graduated from school, so someone must have taught me something about such long before Tom McPoil coined the term tissue stress theory.

    Take care, will write more when I can,
    Daryl
     
  29. Trevor Prior

    Trevor Prior Active Member

    In the Hallux valgus instance then we may term the asymptomatic as a deformity and the painful as a pathological deformity albeit the terms are not great fro the patient and their perception.

    For the PT tendon, the only position where there is no passive tension, would be the position in which the non weightbearing foot hangs. I would assume this must be prone as when supine, the pressure of the couch on the calf may affect the position of the foot and thus the length of the PT tendon. of course, it will never achieve that position through stance.
     
  30. efuller

    efuller MVP

    [QUiOTE="Jeff Root, post: 390152, member: 214"]Eric, have you read Kevin's dogmatic statements about Root biomechanics on his Facebook page. Kevin has referred to Dr. Root as being dogmatic. Is this not the pot calling the kettle black?[/QUOTE]

    Jeff,
    You should have included a little more of my quote to better show my meaning

    What you quoted with the next sentence.
    I keep hearing how Mert Root always said he was still learning. Yet, many people who listened to him felt he was very dogmatic and sounded so sure that he was right. I believe that it is possible to sound dogmatic and still be in learning mode.

    Yes, it was the pot calling the kettle black. Just because you in learning mode does not mean that you don't know anything. When you talk forcefully about what you currently think, you should be able to show the thought process that got you there. It makes it easier to change your mind in the face of new evidence.

    Respectfully,
    Eric
     
  31. efuller

    efuller MVP

    I got that idea from the text that I quoted right before I asked that question. I will repeat the quote:

    "Did the heel evert as a compensation for the forefoot not being able to evert enough, or did the forefoot undergo an inversion motion from its maximally everted state? At which joint(s) did this inversion occur -- i.e. was it the MTJ, the CNJ, the MCJs?"




    Daryl, when you talk about inversion and eversion of the midtarsal joint it appears that you are accepting the idea that there is a LMTJ axis and not an envelope of motion that can allow there to be LMTJ axis. That aside, I'm having trouble understanding what you are saying here. So, if there is a fracture on the medial side of the orthosis just anterior to the post that would imply there is a downward force from the foot applied to the medial arch of the orthosis. There must be an equal and oppoiste reaction from the orthosis applied to the foot. Woulnd't a force from the orthoic in this location cause inversion of the LMTJ and not eversion as you stated above? How would this ortorsis promote motion toward the everted state of the MTJ?

    Why does the orthosis need flexibility to allow inversion that occurs at heel strike. At this point in gait the anterior tibial muscle is lowering the foot down to the ground and since the attachement is medial to the axis this will cause inversion of the LMTJ as you say. How could an orthotic restrict this inversion?



    There are several problems with your mechanical analsis. It is not the center of mass of the calcaneus that matters. It is the loation of the forces from above and below when you are looking at a stacked colum. The next problem is that the foot, specifically the tibia, talus and calcaneus are not a stacked column. There are the moments from the forefoot to be considered. The calcaneus is part of a tied arch on the medial side and discontinuous beam on the lateral side. The forces in those part of the foot will be much higher than the moment of inertia of the calcaneus. Thirdly, the joint surfaes and the ligaments of the talo calcaneal joint limit the motion in such a way that there are a limited bundle of possible axes of rotation for the STJ. So when there is an upward force on the inferior surface of the calcaneus that is lateral to the central line, this force could still be medial to the location of the STJ axis. So, in your analysis I would expect to see inversion of the calcaneus when you would expect to see eversion. We have commonly tested this when palpating for the location of the STJ axis on clinical exam.

    I often talk about muscle forces. A lot of muscle force/length curves are done with the muscle removed from the body. Those length/ tension graphs are rectangular. That is the muscle has near maximum strength over a fairly wide range of lengths of the muscle belly. So, just because a joint is at its end of range of motion, this does not mean that the muscle cannot create significant force in this position. (This reminds me of the physiology 101 lab back in undergrad where we took a frog gastrocnemius and stimulated it at several different lengths and measured the force with a transducer. )


    The first question is the wrong question to ask. Because muscle can develop force over a variable lengths the question should be can the posterior tibial muscle produce enough force to create STJ supiination when the STJ is maximally pronated and is this significantly different from the middle of the joints range of motion.

    For the second question the answer may be never. If there is passive tension in the peroneal muscles and the posterior tibial muscles they will reach an equilibrium at some point where there will be tension in both muscles.

    Daryl, you make the assumption that PT muscle has significant leverate at the ankle joint. I was doing a research project on tendon excursion with joint motion. (Nigg's paper came out at about that time so I stopped trying to publish it) The PT tendon moves very, very little with ankle joint motion. (this makes sense because the line of action of force of the tendon is very close to the ankle joint axis.)

    Since the muscle belly can develop force over a wide range of its potential lenghths, it should be able to create moment at the maximally pronated position as well as in neutral. It might be an interesting study to see if there is a significant difference in force developement of the PT muscle with different positions of the STJ. Remember, those force / length graphs are for muscles that have been reomved from the body. There is no reason not to believe that maximum force could not be developed at the end of range of the joint when the muscle is in the body. Evolutionarlily this makes sense. You would be less likely to survive if you became weak at the end of range of motion of your joint. The posterior tibial and gastroc soleus muscles cross joints where you commonly function near the end of range of motion of the joint. This is also easy to test. See how much plantar flexion power you can develop with your ankle maximally dorsiflexed.
     
  32. Jeff Root

    Jeff Root Well-Known Member

    Eric, why does talking about inversion and eversion at the MTJ imply that Daryl is talking about the longitudinal axis of the MTJ? We know that the MTJ exhibits triplane motion and that the quantity and direction of motion can vary relative to the cardinal body planes depending on the direction of motion and forces acting at the MTJ. For example, we can talk about inversion and eversion of the foot and the frontal plane motion of the heel that occurs with STJ supination and pronation. When we do this we are not saying that the STJ has a longitudinal axis of motion. What we are saying is that you can evaluate the motion of the foot or of a segment of the foot (posterior heel in this case) relative to the cardinal planes of the body. If during the early midstance phase of gait the calcaneus everts and the talus adducts and plantarflexes while the forefoot is in contact with the supporting surface, this produces relative inversion of the plane of the ff relative to the rearfoot. So we can talk about the frontal plane of motion (inversion and eversion) that occurs during triplane motion without suggesting there is a long axis of motion, but there needs to be motion in the frontal plane in order to have inversion and eversion and there has to be some axis to describe this.
     
  33. efuller

    efuller MVP


    Jeff, here is the part of the post that I replied to.

    Daryl said:
    "In fact at the beginning of the stance period of gait the MTJ should be maximally inverted against the rearfoot. An orthosis must have enough torsional flexibility to allow for this. In fact in my current research I have twice been able to break Polydor orthotics, the first one with 75 in-lbs of torque and the second with 70 in-lbs of torque. These fractures originated at the medial side of the heel post, and replicated the morphology of the fractures often seen with acrylics. This tells you that acrylic is NOT rigid, it is very flexible and it has to allow for the MTJ to maximally invert at the beginning of stance. However it has to have enough resilience to then promote the MTJ to start to move toward an everted state to the rearfoot during the midstance period of gait. You will see in my research work at IFAB that many polypropylenes don't have this resilience."

    With terms like "everted state" it appears that Daryl is assuming an LMTJ. Jeff, I was trying figure out what Daryl was thinking. Perhaps we should let Daryl explain his thinking. I am also interested in hearing Daryl's thoughts onmy treating the MTJ as a planar joint with an envelope of motion. Where the extremes of motion in each direction are limited, in most cases by ligaments. With envelope of motion, when you see rearfoot eversion, you would tend to get more tension in the medial plantar ligaments, and less in the lateral plantar ligaments.
     
  34. Jeff Root

    Jeff Root Well-Known Member

    Eric, I wasn't attempting to answer for Daryl, I was attempting to make a point related to the topic of discussion. To say that the MTJ has a bundle of axes doesn't help much clinically unless it has some form of practical application. When we discuss kinematics we use the cardinal body planes and the plane of the floor as the most common references for describing motion of the foot and the osseous segments of the foot. As a result, referencing the frontal plane motion of the MTJ is essential in discussing MTJ function.
     
  35. efuller

    efuller MVP


    I may not have been clear in my previous post. The bundle of axes was referring to the STJ. The MTJ has an infinite number of potential axes of rotation. As you know, an axis of rotation is an imaginary line that describes the motion that could occur, or has occurred. How, does describing this particular motion help clinically? It's not like you can "lock" motion about an imaginary line.

    Saying that the STJ has a bundle of axes helps clinically in that it shows that motion about the talus and calcaneus is relatively constrained and it can be treated like a hinge like axis in terms of applying moments about that axis.
     
  36. rdp1210

    rdp1210 Active Member

    It doesn't matter if I say LAMTJ or inversion/eversion of the forefoot to the rearfoot, Eric you seem to be unhappy -- you're going to find something to pick at to show that you're right and I'm wrong.

    The classic LAMTJ originally described by Manter (not Root) is an axis that produces basically inversion/eversion motion of between the forefoot and the rearfoot. Manter also noted mild angulation of the axis with the transverse and sagittal planes, which means there are "coupled" planar motions. As I have explained for years -- these are not individual planar motions, they are motions that can be measured as angular motions in the three cardinal body planes.

    So let's get down to settling a basic nomenclature problem, Eric, whose tail you continue to chase. How many axes of motion does the hip joint have? I'm not going to carry this discussion any further until you commit yourself to an answer. Please explain your answer using mathematical concepts. If you want some help, please contact NASA and ask them what the minimum number of thrusters they need on a spacecraft in order to maneuver in any direction. Once we get through this basic concept, then we can move on to further discussion of the MTJ.

    Thanks,
    Daryl
     
  37. Jeff Root

    Jeff Root Well-Known Member

    Describing the motion about an axis helps clinically in a number of ways. For one thing it helps when teaching students how to take a Root type neutral position cast of the foot. We teach them how the foot moves about the STJ (axis) in space and that due to the orientation of the STJ axis, when we adduct the foot it also plantarflexes and inverts and when we abduct the foot it also dorsiflexes and everts. We then teach them how to identify and place the foot in the neutral position at the STJ. Next we can teach them how to pronate the MTJ to resistance during casting. To pronate the MTJ the student needs to be able to appreciate the motion of the forefoot to the rearfoot at the MTJ relative to the cardinal body planes. So we teach them how to abduct, evert and dorsiflex the ff on the rf at the MTJ while maintaining the STJ in the neutral position. Proper casting of the foot is one of the most important clinical skills when making functional type foot orthoses.
     
  38. Jeff Root

    Jeff Root Well-Known Member

    I should also add that Root talked about the clinical significance of individual subject variation the direction of motion (i.e. axis) of the MTJ. He described a technique for moving the ff on the rf at the mtj in order to examine the orientation of the MTJ axis. It can be easily demonstrated clinically that not all feet move the same at the MTJ when you examine the open chain range and direction of motion at the MTJ. Some individuals demonstrate more frontal plane motion (inversion and eversion), more transverse plane motion (adduction and abductio) and more sagittal plane motion (plantarflexion and dorsiflexion) when compared to others. Just as the three dimensional orientation of the STJ axis is clinically significant, so to is the three dimensional orientation of the MTJ axis.
     
  39. Why are you referring to Manters somewhat naive work from 1941, when we have far more sophisticated and more modern descriptions of midfoot function available to us in 2018?

    Let me re-phrase this from my perspective Daryl: It doesn't matter what is published to discredit Root's writings, Jeff/ Daryl you seem to be unhappy -- you're going to find something to pick at to show that Root was right by attempting to find minuscule fault with the modern published research which has demonstrated Root's writing to have been wrong; yet happily accept "research" from 1941 with zero critique.
     
  40. Jeff Root

    Jeff Root Well-Known Member

    Simon, I just gave an example of the clinical significance of evaluating the range and direction of motion at the MTJ that is partially based on Manter's work. I would be interested in hearing a good argument to support the use of a "more sophisticated and more modern descriptions of midfoot function" that demonstrates the clinical relevancy of other models. In other words, how has examination and treatment of the foot been improved as a result of more sophisticated and more modern models of midfoot function.
     
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