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Prescribing Orthoses: Has Tissue Stress Theory Supplanted Root Theory?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Kevin Kirby, Apr 1, 2015.

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  1. For those that don't know Daniel Petcu, he is a very bright Romanian researcher that published a paper in 2012 on Foot Functioning Paradigms that is worth a read for those interested.
     
  2. Petcu Daniel

    Petcu Daniel Well-Known Member

    Dear Dr. Kirby,

    Thank you for your nice words ! My article is only a very pale attempt to popularize in my country all these unknown theories about foot functioning. Probably without any impact! As I said in other threads, here we don't know Root which, according to some opinions from PA, means we can start directly with Tissue Stress Theory. At the end, we finish buying some pressure mats from abroad having some bioengineering CAD solution /models which tell us how to build soft orthotics, finally made by hand by unqualified personnel. In this conditions I understand very well the importance of a powerful educational system based on valid theories!

    Sincerely,
    Daniel
     
  3. Trevor this is more accurate. I was trying to show that joint alignment is not predictive of kinetics. In the example I gave all the alignments were the same, yet depending upon where the centre of pressure at the joint is, may result in different types of loading within the tissues. By understanding the rule of thirds we can begin to predict which tissues might be in tension and which might be in compression. You're right we are not made of concrete, but certain tissues are better at dealing with certain kinds of loads than others. We also need to consider that the stress on a tissue may be too low. Doesn't cartilage require compression in order to stay healthy and viable? I'm thinking sagittal groove and hallux valgus- without compression the exposed cartilage becomes unviable? So if we have one side of the joint which is in tension and not compression.... Just thinking out loud and more about tha ankle now than the stj
     
  4. One can see the comments at the bottom of the article, but I will place my comments here for your convenience.

    "It would appear that the author is stating the symptoms dictate whether or not the prescriber should use a particular type of accommodation or orthotic modification in creating the dispensed orthotic. I thought that was why Dr. Root developed the Root principles approach to designing his orthotics. He tried to envision what pathology was introducing the forces that were inducing the patients complaints. Thus his symptomatic approach to orthotic design to minimize the forces causing the patient's complaints based upon the individual foot design.

    If Tissue Stress Theory has supplanted Root-ian Biomechanics, it is fair to say that we as a profession have failed to discover how the foot actually works as a whole along with its individual components. Tissue Stress Theory takes us back to the old 'bag of tricks' method. If we return to the old approach, I am having trouble understanding how this unifies the profession and keeps us at the leading edge of foot care. Tissue Stress Theory is having to be shouted and touted as the best there has ever been by its creator, and not the profession in general, almost thirteen years after having been introduced. It has yet to become any sort of standard after indoctrination of class after graduating class, at the collegiate level.
    What does that say about the theory? It says just that. Still a theory without proof nor consistency in results."

    Thank you Kevin for referencing my article.

    Paul Clint Jones, DPM

    - See more at: http://www.podiatrytoday.com/prescr...y-supplanted-root-theory#sthash.b3Fj6MCs.dpuf
     
  5. drhunt1

    drhunt1 Well-Known Member

    Kevin-yes, send those newsletters along, I'd be happy to read them. My concern is that by focusing on one problem the practitioner may be missing the bigger picture. As an example, how many times do we see a patient that has developed a Morton's neuroma symptoms secondary to compensation for plantar fascial enthesitis? And then, upon furtber inspection, one finds that the plantar fascial pain was secondary to weight gain and/or low ROM of the STJ? Do you address the patients' immediate concerns or deal with the bigger picture? Pathology based treatment may miss identifying the underlying reason why that pathology exists in the first place....that is my concern. Have fun in Vancouver with Jeff and Darryl.
     
  6. Simon:

    I don't know if we need a "rule of thirds" to predict which tissues will be subjected to tension, compression or shearing forces during weightbearing activities. Simple modelling should be sufficient to accomplish that goal without necessarily using "rules" that can sometimes be "broken".

    In addition, I'm not aware how much cartilage requires compression forces to stay healthy and viable. In fact, in a commonly performed knee surgery, the osteochondral autograft transfer system (OATS) procedure, cartilage-bone plugs are taken from areas of the hyaline cartilage of the knee that do not receive little to any weightbearing load and are placed into areas of damaged knee cartilage.

    Here is an article which reviews hyaline cartilage physiology and surgeries: Cartilage Restoration Part 1, Basic Science, Historical Perspective, Patient Evaluation and Treatment Options

    Also, as far as one side of a joint being in compression and one in tension, I don't think this commonly happens in more common weightbearing activities but rather will occur in more extreme motions of the lower extremity, such as during potential injury-producing motions. Rather, it is more likely that, during more normal weightbearing kinematics, on one side of the knee or ankle joint there is a large increase in joint loading and on the other side of the joint, there a large decrease in joint loading, combined with an increase in tension forces from the ligamentous restraining forces on that side of the joint that is under the least compression load.

    In other words, I doubt that one side of the knee or ankle joint "open ups a gap", where the cartilage surfaces of the joint actually separate, but rather one side of the joint becomes relatively less loaded. Hyaline cartilage does have the ability to compress much, much more than does bone.

    The elastic modulus of cartilage is 0.5 - 0.9 MPa (megapascals) whereas the elastic modulus of cancellous bone is 10.4-14.8 GPa (gigapascals) and the elastic modulus of cortical bone is 18.6-20.7 GPa (Rho Jy, Ashman RB, Turner CH: Young's modulus of trabecular and cortical bone material: ultrasonic and microtensile measurements. J Biomech. 26(2):111-9, 1993).

    [For those following along, 1,000 MPa = 1 GPa.]

    Therefore, for a given load, cartilage probably deforms at least 1,000 times more than will bone meaning that even there exists the potential for considerable "slop" in a joint that has a 4-6 mm thickness of hyaline cartilage that allows it to compress on one side before the other side of the joint "opens up" or "gaps" so that the hyaline cartilagenous surfaces are no longer contacting.

    Also, for those following along, here is a great book chapter on cartilage biomechanics that is worth a read: Cartilage Biomechanics.

    If we are going to be continuing this discussion on cartilage biomechanics, I suggest we open up a new thread on cartilage biomechanics here on Podiatry Arena.:drinks
     
  7. Matt:

    Please send me your private e-mail address so I can forward those newsletters to you: kevinakirby@comcast.net

    I'll be sure to keep Jeff and Daryl in line while I'm up there in Vancouver. Jeff, Daryl and I have all known each other for over three decades so no matter how much we argue here on Podiatry Arena, we still are good old friends when we meet again...that's when the discussions (i.e. arguments) become even more fun for all of us. Can't wait...:drinks
     
  8. Jeff Root

    Jeff Root Well-Known Member

    And we all know what a wild guy Daryl is. Not!:D It will be good to get a taste of a PFOLA conference again. Hopefully we can build on this symposium and have a regular PFOLA conference in the future!

    Jeff
     
  9. Just got to keep Daryl from drinking too many ginger ales in one sitting while we're at the conference...:rolleyes:
     
  10. efuller

    efuller MVP

    The first thing to look at is the history as told by the patient. If the patient says that their MPJ has been hurting since their husband stepped on it... On the other hand if there is no specific event that created the 1st MPJ pain then it must be from the activities of daily living. So, this is where the modeling comes in. In my article on the windlass mechanism, I modeled the first mpj and you can use that model to explain why their would be high loads at the first MPJ. Since the patient is complaining of pain there we can assume the loads were high enough to cause damage. During physical examination, we can increase loads on the MPJ, by compressing the joint and trying to move it, and see if the pain increases.

    So, if we know that increasing the load increases the pain, then decreasing the load should decrease the pain. This is where there is another difference between neutral position theory is different than tissue stress. There is not really a very good connection between neutral position theory and pathology at the first MPJ. (If anyone feels otherwise they are welcome to explain it.) In examining the windlass mechanism the prediction for increasing stress at the first MPJ is a high pronation moment at the STJ, high force under the first metatarsal head and hallux. (Other corroborating physical findings is callus sub first met head and halllux IPJ and hyperextension of the hallux IPJ.)

    A specific foot type where the treatment using tissue stress would differ from neutral position theory is in the foot with extremely laterally deviated STJ axis with first MPJ pathology. In these feet, the peroneal muscles will be constantly active and will be the source of pronation moment at the STJ. So, in this foot the treatment should be designed to increase load on the lateral forefoot, often to the point of trying to pronate the STJ.

    Eric
     
  11. efuller

    efuller MVP

    J Am Podiatr Med Assoc. 2014 Jun 24.
    The Subtalar Joint Axis Palpation Technique: Part 2 - Results on reliability and validity using cadaver feet. Van Alsenoy KK1, D'Août K, Vereecke E, De Schepper J, Santos D.

    True the abduction of the forefoot on the rearfoot (too many toes sign) seen with PT dysfunction is most likely the result of the decreased adduction moment from the muscle. This abduction of the forefoot on the rearfoot will make the STJ axis position more medially deviated. So, medial deviation of the STJ will get often worse with PT dysfunction. However, the theory is that the axis was medially deviated to start with and this is what increased the load on the tendon to the point that caused it to fail. So, if there was no knife wound to the medial ankle, or other similar event, why did the tendon fail under the activities of dailly living? Variation in the position of the STJ axis is a solid theoretical explanation for why some tendons fail and others don't. In the foot with the medially deviated STJ axis, the tendon will have to be under higher loads to produce the same motion.

    Your next question was how do you treat PT dysfunction in a foot with a fixed varus and OA of the midfoot? It depends on what is actively hurting at this point. If you have one of those patients who has a massively thick first met cuneiform joint that is now fused and solid. You can often feel these create a plantar prominence in the medial arch. There may be no pain in that joint. So, under the Root paradigm, you would make a device that would correct the forefoot to rearfoot deformity with an intrinsic forefoot varus post. An intrinsic forefoot varus post will tend to raise the medial longitudinal arch and the plantar prominence will need to be accomodated. So, the treatment is based off of a non weight bearing measurement.

    Under tissue stress, we would want to assess the load under the first metatarsal in stance. John Weed used to describe a test where he would try and get his fingers under the medial or lateral side of the forefoot. If you have a marked fixed forefoot varus, (perhaps this is better termed a fixed supinatus?) you need to know if there is significant load on the first met head. You can't tell this from a non weight bearing forefoot to rearfoot measurement. So, if you can run your fingers under the first met head, and you cannot under the lateral forefoot, you know the center of pressure is very far lateral and this is creating a high pronation moment on the STJ and this could be helped by adding a forefoot varus extension to the orthotic to increase the load on the medial forefoot. With a medially deviated STJ axis, the medial forefoot is still on the lateral side of the axis and pressure here will still cause a pronation moment. However, the center of pressure is moved more medially and the amount of pronation moment will be reduced.

    On the other hand, if there is already high force under the medial forefoot, you probably don't want to increase force under the first met head, because there is a risk increasing the load on the already arthritic joint. (If this joint was fused and non painful then this is somewhat less of a concern.) So, to treat this PT dysfunction foot, you have to look to increase supination moment in other ways than increasing the load on the medial forefoot. A medial heel skive is the first thing to try. Then you could go to medial and lateral flanges, or AFO's etc.

    Eric
     
  12. Kevin,

    How do we model forces in a vertical column and predict at what point the stress changes from compression to tension on one side or the other without knowledge of the rule of thirds? I was trying to show why we cannot look at a foot with a vertical heel bisection when standing on a foot orthosis and make the assumption that if we do this with all our foot orthosis, in all our patients, we can then conclude that we have done a good thing, nor the same thing to everyone. I think the model and the application of the rule of thirds is relevant here. Just because a heel is vertical, the loading of the tissues may be very different- the model I employed shows why.

    I was thinking of this from the back of my memory:

    "Lane (1887), on the other hand, considered the eminence to be not a new growth but a part of the metatarsal that had originally articulated with the phalanx, but which had become exposed as the toe was displaced laterally. He found that the exposed cartilage, out of contact with the phalanx, might become soft and inelastic, and lose its white colour, and that similar degenerative changes might occur in association with the displaced sesamoids. Anderson ( 1891) showed a preparation from an extreme case in which the toe made a right angle with the metatarsal and he also found tissue destruction rather than new formation in the region of the prominence. The detailed anatomical work of Payr (1894) and Heubach (1897) left no doubt that Lane’s theory was correct, but these studies are seldom considered by recent authors."
    http://www.bjj.boneandjoint.org.uk/content/36-B/2/272.full.pdf

    According to Mueller M J, Maluf K S PHYS THER 2002;82:383-403 the effect of reduced stress on cartilage is reduced protoglycen content, reduced cartilage thickness and decreased stiffness while increased stress has the opposite effects.

    Clearly there is change in the contact-stresses at the tibiotalar articulation with "flat-foot" and foot orthoses. The point being the health of cartilage is far more likely to be influenced by compressive forces than are tendons and ligaments, so if we can model the tension and compression about a joint, this helps when we are trying to build a clinical picture. I thought the example you and Eric gave in your chapter regarding genu varum was really helpful in this regard, however, it didn't address the variation in forces that are possible within vertically aligned joint segments, hence I have included it in this discussion. Given that the Root criteria for normalcy relies very much on vertical alignment, I felt that potential variation in kinetics even with such alignment should be exposed; rule of thirds explains this simply.

    BTW this is an excellent little book to give a primer on structural engineering (including rule of thirds), for the non-structural engineer: http://www.amazon.com/Structures-Things-Dont-Fall-Down/dp/0306812835 , his other book is worth reading first for the novice- http://www.amazon.co.uk/The-New-Science-Strong-Materials/dp/0140135979 both can be picked up fairly cheaply on Amazon, e-bay etc
     

    Attached Files:

  13. efuller

    efuller MVP

    Among my classmates, and other recent graduates that I talked to, there was a common refrain. They understood surgery better and better the more they practiced. Biomechanics they understood less and less. Even those students who got good grades in their biomechanics classes would say they did not understand biomechanics. They were able to produce the correct answers for the test without understanding the subject. There is a problem there, and it's not with the students.

    When I was at CCPM, I was teaching these concepts and I had many students tell me what I was teaching them was easier to understand than traditional neutral position theory.


    I don't see how you can make that conclusion from what I wrote. When you apply the same stress to a specific structure in different feet, some will break and some won't. It all depends on whether a specific structure can withstand the load applied. In different feet and with different loads there will be differing amounts of injury. Injury occurs when the load that the structure can handle is exceeded.


    I am trying to make biomechanics easier to understand. The way it was taught when you and I were students is incomplete and confusing.

    I agree that we need to write the prescription that will best serve the patient the first time. If we don't get it right the first time we should use a paradigm that will encourage a change in the prescription rather than just do the same thing over again. I feel that the prescription writing protocol that I use is better than the one that I was taught when I was a student. I think that because I know the thought process that went into both neutral position and tissue stress prescription writing protocols.

    I agree we should have an academic debate on what the best prescription writing protocol is. Matt, until you start agreeing with me, we aren't going have an agreement.;) But, seriously, we need to have the academic debate so that others can look at the debate and make up their own minds who is right and who is wrong. The debaters may never change their minds, but the observers might. Hopefully, the debaters won't get personal and not resort to name calling.

    I agree there should be more research into how treat the problems that we see in our practices. There won't be any research in neutral position theory because of the inherent inaccuracy of the measurements. (calcaneal and leg bisections and forefoot to rearfoot measurements) There also won't be much research into neutral position theory because it is difficult to make predictions with the theory. (So, if neutral position is normal then pathology should happen when feet don't stand in neutral position. I looked at 30 asymptomatic feet and 30 of 30 did not stand in neutral position.) How do you make predictions that can be tested with neutral position theory.

    Matt, you should read Thomas Kuhn's The Nature of Scientific Revolutions. He describes nicely what is happening here. When the majority of a profession believes one thing it sails on nicely until anomalies develop. When anomalies develop new ideas and paradigms are suggested. At this point there is conflict and historically there is either an advancement or change in the old pardigm and it wins or another paradigm takes over.

    There are holes in the Root paradigm. It is really hard to get disciples of the Root paradigm to see the holes. I get accused of nitpicking when I point out holes to some disciples. You have to have an open mind to be able to see the holes to see if there are enough holes to correctly abandon what you once believed.

    One problem that Kuhn noted was that proponents of the old paradigm could not see beyond their current paradigm. Their view of the world was such that they could not see differences between the new and the old paradigms. Matt, you are worried that I am confusing our profession. The profession is already confused by what was taught as biomechanics. It is much more confusing to try and reconcile neutral position biomechanics with tissue stress if you are absolutely convinced that neutral position solves everything, or has the potential to solve everything. I've had students who were not yet fully invested in neutral position biomechanics say that tissue stress made more sense to them than neutral position biomechanics.

    Another thing that Kuhn pointed out was that change in paradigms was usually over generations. It is hard to change the minds of existing practitioners. However, students can look at both paradigms and wonder why did they believe that old stuff. I am not saying that there is no value in the old stuff. The new paradigm has to be able to explain the successes of the old paradigm. There are a lot of successes under the old paradigm, but there are holes in the explanation of those successes. So, we will need hundreds and hundreds of posts to explain to the youngsters why they should switch paradigms.

    Eric
     
  14. Here is a book I read about 25 years ago that really helped explain many things to me when I was trying to understand structural engineering ideas. It has now been reprinted and reissued in a more modern version.

    Why Buildings Stand Up: The Strength of Architecture

    Here's a newer edition of another book by Salvadori I have on my library shelf (I bought mine in 1993) which also helped me understand engineering concepts at a time when I knew practically nothing about engineering.

    Why Buildings Fall Down

    For those of you who want practical examples of the concepts we are talking about in this thread when it comes to world of building bridges, buildings, etc, and in plain English terms, these books are all excellent.
     
  15. Don ESWT

    Don ESWT Active Member

    We are all trying to build the best Mousetrap with cheese, the only problem is that the mouse only wants the cheese

    Mousetrap = Orthotic
    Cheese = Orthotic
    Mouse = Patient

    Life of Brian Movie = Brian standing at the window crowd below = Brian says "We are all individuals"

    Not every one has the same foot/feet, therefore orthotics must be customised to that persons needs.
    You can postulate until you are blue in the face whose right and whose wrong

    Orthotic will vary, pod/pod, lab/lab, technique/technique. What is important is that the orthotic when fitted to the patient that
    1. It contours to the patients foot/feet
    2. It is the correct size
    3. It fits into their NEW footwear. It is pointless to put new orthotics into old footwear as the wear patterns will negate what you are trying to achieve.
    4. You give correct advice on how to wear the new device.
    5. Listen to what the patients needs are, as they have to walk every day with the device that you are fabricating for them.

    Methods for making orthotics
    Palgenate - Thermo-setting - took excellent impression superseded by
    Foam Boxes
    Plaster Bandages - superseded by digital technology
    Gait analysis 2D and 3D superseded by imaging technology
    3D Camera - plantar surface only
    3D Scanning - Plantar surface only
    3D radial arm scanner - leg and foot - all surfaces


    I use 3D imaging to document patients feet by using a radial arm scanner which scans from knee to toe

    If you want to see OUR new radial arm scanner developed for footwear, orthotics and AFO's just gone into production go to -
    Google
    www.localsearch.com.au
    podiatrist
    grafton nsw
    Donald Iain Scott (c) on listing
    watch video it runs for about 50 seconds

    Don Scott
     
  16. rdp1210

    rdp1210 Active Member



    Big problems, Eric, with your discussion of load on the first MTPJ.

    First and foremost is that first MTPJ pain may be a sesamoiditis, or it may be an anatomical or functional hallux limitus. Sesamoiditis pain is due to the first metatarsal being unable to dorsiflex adequately. Functional hallux limitus, on the other hand, is due to the first ray dorsiflexing too much. In the first situation you want to pronate the forefoot against the rearfoot to increase the lateral load. In the second case you want to plantarflex the first ray, i.e. increase the load under the first ray. I find that knowing the relationship of the rearfoot and forefoot to the ground when the STJ is neutral is an essenial part of the equation needed to treat the patient.

    I find it interesting, that you only ever discuss the subtalar joint axis, like it is the only axis that exists in the foot. As I have tried to point out many times before, a force against the forefoot can only exert a moment around the subtalar joint axis if there is stability of the joints between the force and the subtalar joint.

    Daryl
     
  17. I would have thought it can not be Only, but much less depending on the angle, direction etc of the Forefoot force, Excluding of course if the direction of force is in line with the axis of the distal joints, then we would get compression at those joints until it causes a moment at the STJ ( if the force is not inline with the STJ axis of course ) ??

    But certainly I agree we as a profession focus way to much on the STJ especially in theoretical discussions
     
  18. Actuallly, in the review of Kevin's latest book which I submitted for publication in JAPMA over a year ago (yet only just seems lined up for publication- I was only asked for copyright release a couple of weeks ago), I noted how Kevin had addressed the rotational equilibrium about the joints of the ankle, midfoot and forefoot. If memory serves, I made a statement regarding how some had not been able to extrapolate the concepts beyond the STJ and how Kevin had "dotted the i's and crossed the t's" within this volume to make this more explicit.

    I think it would be more accurate to state that a force can only exert a kinematic influence about the subtalar joint axis if there is an adequate level of stiffness of the joints between the applied force and the subtalar joint, don't you Daryl? Since the moment will be simultaneously exerted across all joint axes that the net vector crosses. So unless the net GRF vector is passing negative to the horizontal (it never happens) or directly through the axis and does not cross the projection of the STJ axis neither anteriorly nor posteriorly at a perpendicular distance from the axis, a moment about it will be generated regardless of whether the joints between the point of application are stable or not; I think this was Mike's point earlier. Otherwise, the GRF vector at the forefoot could not generate a knee joint moment unless all of the joints between the point of application and the knee joint axis were "stable"- this just isn't true since the joints between the point of application of the net GRF vector at the forefoot and the knee joint axis are never all simultaneously "stable" during gait (it never happens). Because of this biomechanics researchers are able to derive external moments about the knee joint axis at this and any other time during the gait cycle despite the fact that the joints between the point of application of the net force and the joint axis of interest are never all simultaneously "stable".

    However, strictly speaking unless the STJ is in motion, then there is no joint axis- without an axis there can be no moment. So if we apply a force and the STJ is not in motion, there is no moment because no STJ axis exists at this time.

    Those that want biomechanics simplified are those that are unwilling to learn. See the last paragraph above- I just "learned" myself something.
     
  19. I agree with Simon here. If there is an external force against against the forefoot, by definition, this force will cause a moment about the subtalar joint (STJ) unless the line of action of that force vector is pointing directly through the STJ axis. As Simon stated, as soon as the forefoot has sufficient stiffness to resist motion relative to the rearfoot by the application of an external force acting on the forefoot, by definition, that external force acting on the forefoot must also be simultaneously be exerting a moment across not only the midtarsal joint and the STJ, but also through the ankle joint, knee joint and hip joint, unless that force vector passes directly through one of these joint axes.

    In addition, Daryl, please define what you mean by "stability" since this word is about as useless and ambiguous of a term, from a scientific standpoint, as the word "hypermobile" is. Does stability mean high stiffness, absolutely no motion, only a little motion...what does you mean when you use this term and how would you define it?
     
  20. rdp1210

    rdp1210 Active Member


    You're technically correct, except you have to factor in the moment of inertia of each segment so that results in the angular acceleration around the STJ axis being a lot smaller unless you have adequate stiffness of the distal joints. That's something we could calculate, how much moment is needed to be applied by the soft tissues at a distal joint before you get acceleration around the proximal joint. That brings to mind something that Howard Hillstrom started but didn't finish, and that was measuring the frontal plane stiffness of the forefoot against the rearfoot. As I pointed out quite some time ago, taking a forefoot to rearfoot measurement such as Mert did is a good start, but what we really need is a forefoot to rearfoot angle vs. frontal plane torque curve. When we analyze what Mert Root was doing (he may not have said or even recognized such) but it appears that he was trying to create a stiffness of the midfoot joints so that forces applied distally could create significant joint accelerations around more proximal joints. I realize that this is a simplification, we really need link segment modeling to do a good job of analyzing the moments around all the midfoot joints.

    Thanks,
    Daryl
     
  21. Jeff Root

    Jeff Root Well-Known Member

    Can we discuss this concept by looking at a different set of joints that are less complicated than the STJ and MTJ? If we put a wedge under the hallux, like a Cluffy wedge that is thicker anteriorly and tappers out proximally, will it create a dorsiflexion moment at the ankle joint when it dorsiflexes the hallux say five degrees? Is it not possible that the wedge will create a dorsiflexion moment at the 1st MPJ but not at the ankle joint?

    Now, if we evert the forefoot with a wedge like we dorsiflexed the hallux, is it possible to do this without producing an increased eversion moment at the STJ?

    Jeff
     
  22. Daryl Phillips has left his comments at the end of my article on the Podiatry Today website.

    Prescribing Orthoses: Has Tissue Stress Theory Supplanted Root Theory

     
  23. No, because provided we pick a fixed reference point at our ankle joint we can take moments about this point with and without the cluffy wedge in-situ, and these moments will not be the same even if we take into account the segmental moments of inertia because the external forces acting upon the forefoot within the system will have changed by the addition of the wedging when compared to the conditions without it. Similarly for your everting wedge and moments at the STJ.

    I was wrong when I said previously that we could not have moments without a joint axis, since we can take moments about any point we choose. But thanks for that Jeff, gave my brain a work out- I had to think back to "A" level physics to remember that- took me back nearly 30 years.
     
  24. I think Daryl said that, without the help of Mert, nor a safety net. You didn't need to mention Root in your response Daryl- take the credit yourself. If you want to credit anyone here, credit Newton et al. i.e., the physics guys that allowed us to talk about moments of inertia- I don't recall Root talking about this. There is nothing new in tissue stress, it is simply the application of known physical principles to the body- isn't that what biomechanics is, by definition? The problem I had as an undergraduate student is that the Rootian biomechanics I was taught had an invented language, and didn't discuss physics. As such I found the topic very, very confusing, since I'd previously studied mechanics and what I was being taught was not mechanics nor biomechanics. When i read your STJ paper it sang to me because it discussed biomechanics, from this I found Kevin's papers... the rest as they say...
     
  25. efuller

    efuller MVP

    Daryl you are giving the positional explanation of the pathologies. This is a difference between tissue stress and Neutral position biomechanics. Why does dorsiflexion of the first ray cause a functional hallux limitus? In positional biomechanics the correlation is noted and not explained. Now, let's examine the forces. As the first ray dorsiflexes, the distance between insertions of the plantar fascia at the calcaneus and base of proximal phalanx increases. This tension will increase the compressive forces at the first mpj and will create a plantar flexion moment on the phalanx. The increased compressive forces explain the pain in the MPJ that can occur with functional hallux limitus. The force couple of the tension in the plantar fascia and compression at the joint surface explain why the hallux does not dorisflex. The more force there is on the plantar aspect of the metatarsal head and phalanx the greater tension there will be in the plantar fascia. If the metatarsal is dorsiflexed with minimal force an attempt to dorsiflex the hallux will tend to plantar flex the metatarsal. However, if there is a lot of force on the met, attempts to dorsiflex the toe will be resisted. So, it's not the position that causes the limitus, but the forces that dorsiflex the metatarsal.

    So we agree on the explanation of a sesamoiditis caused by direct high loads on the metatarsal. So, when examining the forces we see that same high forces cause the pathology. Reduction in the forces are what is used to treat the pathology. This is a much simpler and easier to understand explanation than the "positional" biomechanics explanation.

    I discuss the ankle joint axis as well. The STJ and the ankle joints have joint surfaces that lend themselves easily to axis discussion, because the motion follows the axis. We have discussed the MTJ axes in the past. This is a good example of adherents of one paradigm not being able to communicate with adherents of another paradigm. In tissue stress theory we can ignore the midtarsal joint axes. Under tissue stress we can look at just the ligaments and joint surfaces of the midtarsal joint and not worry about the joint axes.

    Other than the ankle and STJ, the axes of motion are not very useful because the ligaments and joint surfaces don't constrain the motion around a single axis. So, any axis we ascribe to any of those joints are just instantaneous centers of rotation and not really useful for anything other than describing motion.

    Eric
     
  26. efuller

    efuller MVP

    The above is from the text that Kevin said was from Daryl's comment on the Podiatry Today website.

    Daryl, we have a problem here. Motions don't create motions. Forces create linear motions and moments, or force couples, create angular motions. Motion, or lack of motion, can be understood within the tissue stress approach.

    Motions, don't really create forces either. When an object is moving a force has to be applied to it to change the motion.

    Eric
     
  27. drhunt1

    drhunt1 Well-Known Member

    And as a non-academic, but a fairly astute clinician, I can safely write that perhaps we DON'T spend enough time looking at the STJ. Perhaps we should focus less on axis of motion, and focus on the bigger picture. After all, this is the source of symptoms for GPs in children, and I believe RLS in adults. Oh, and there's more too...although it will take me awhile to put together.
     
  28. Jeff Root

    Jeff Root Well-Known Member

    Eric,

    Do you have a copy of Normal and Abnormal Function of the Foot? In the index of Normal and Abnormal Function of the Foot, under the heading of Hallux Limitus, there are nineteen sub references within the book:
    Hallux Limitus, 60, 316, 357-375
    1. Caused by abnormal pronation in the rectus foot, 365
    2. Caused by a long 1st metatarsal, 51, 362
    3. Caused by peroneus longus weakness, 218
    4. Caused by restricted plantarflexion of the 1st ray, 363-368
    5. Conservative treatment of, 375
    6. Control of abnormal subtalar joint pronation in, 371
    7. Deformity of, 357-375
    8. Degenerative changes of the 1st metatarsophalangeal joint in, 368-369
    9. Differential diagnosis, 370
    10. Etiology of, 360-363
    11. Functional adaption of bone in, 368
    12. Hyperextension of interphalangeal joint in, 375-376
    13. Objective and methods of treatment of, 370-375
    14. Pathomechanics of, 363-368
    15. Sequelae of, 369-370
    16. Shortening of long 1st metatarsal, 372
    17. Subluxation in, 368
    18. Swing phase function of, 146
    19. Treatment of sequelae associated with, 375-376

    If you don't have a copy of the book, I would be glad to provide you with one so we could discuss the merits of the reasons presented in this book.

    Jeff
     
  29. efuller

    efuller MVP

    I did have a copy. I haven't been able to find it the last two times that I looked for it.

    How many of those don't boil down to: when the first ray is dorsiflexed the MPJ can't dorsiflex. For example, a long first met is more likely to be dorsiflexed to its end of range of motion. That explanation is still correlational. The tissue stress explanation goes beyond that. When the metatarsal is dorsiflexed, the distance between the proximal attachment and the distal attachment of the plantar fascia, into the proximal phalanx, is increased. This will likely lead to increased tension in the fascia that will prevent dorsiflexion of the hallux.

    Eric
     
  30. Eric:

    I think a better way of discussing whether the joints of the foot and lower extremity can be described with joint axes or not is to describe whether joints are relatively constrained or unconstrained.

    The subtalar joint, due to it's tight, short ligaments within the sinus tarsal and tarsal canal, is relatively constrained so the joint axis tends to closely follow the dorsal talar neck. The midtarsal joint, on the other hand, is relatively unconstrained and its axis of motion will depend largely on the external forces and internal forces acting at any instant during gait.

    However, none of the joint axes of foot, lower extremity, or any of the joints of the body can be thought to be only a "single axis"...they are all constantly moving axes, some moving more than others. For modelling purposes, I think it is fairly accurate, and certainly convenient, to model the STJ and ankle joint as having one axis of motion even these two joints have moving, multiple axes of motion. However, I would think the MTJ would be difficult to model accurately that way due to its relatively unconstrained mechanical characteristics and the research evidence for its widely varying angles and spatial locations of instantaneous joint axes (i.e. from Nester's papers).
     
  31. Simon,

    Glad you corrected yourself since I was going to comment that moments will be present across a joint as long as the forces acting across that joint have a moment arm by which to cause a moment.

    In other words, one doesn't need to know exactly where the joint axis is at any instant in time in order to know if there will be a moment produced or not. However, the closer the line of action of the force vector is to pointing toward or through the joint, then the more likely that force vector will produce a minimal moment across that joint.

    Or said another way, one should assume that all forces that act across a joint cause at least some moment across that joint. This is because that the only way a force acting across a joint doesn't cause a joint moment is if that force passes directly through the instantaneous axis of that joint at that instant in time that the force vector is acting.
     
  32. Jeff,

    If a person is standing on the ground and then I pull upward on the hallux with my hand and the hallux doesn't move (i.e. hallux limitus), what will happen?

    What happens is that the force from my hand will cause a 1st MPJ dorsiflexion moment, a first metatarsal-first cuneiform dorsiflexion moment, a first cuneiform-navicular dorsiflexion moment, a talo-navicular dorsiflexion moment and an ankle joint dorsiflexion moment, and all of these dorsiflexion moments will occur simultaneously.

    The force from the hallux can certainly affect the moments acting across the ankle joint. However, whether the ankle joint moves or not in response to that hallux force is dependent on the prevailing external and internal forces acting across the ankle joint at that instant in time.
     
  33. Don ESWT

    Don ESWT Active Member

    If you are moving the hallux are you pushing/pulling or rotating/lever arm
    Is the foot on solid ground or the is the foot only supported by the metatarsal heads?
    Are you the tester standing/kneeling or lying prone?
    If your finger/hand is not powerful enough then use a bigger crowbar
    Do you have your opposite hand passively or aggressively place over the ankle joint to feel movement- perceived or not?
    Are you using a force plate to measure any movement?
    Are you using high sped motion capture to document movement?
    What are the measurements calculated in Newton (What)
    If you do/don't get movement - What have you achieved?
    In theory this may be great but in the real world where we have to earn an income. The patient will ask did it or didn't it move and if so what are you going to do. You have 10 Sec to decide and the move on to the next part of the examination.
    If you isolated the hallux, wouldn't the motion stop at the proximal phalange
    If the person has a Hemiplegia or spasm you may get a negative outcome

    Happy wife= happy peaceful life
    When you are moving a hallux - Remember to always bend at the knees when lifting an object

    Leave it to Sheldon,Leonard,Raj and Howard they will work it out. "BIG BANG THEORY"
     
  34. Petcu Daniel

    Petcu Daniel Well-Known Member

    I want to learn but sometimes I really don't know how or sometimes seems to be impossible/discouraging !
    To explain better I've tried to compare 2 articles which are using similar concepts (as modeling, free body diagrams) but are too different as structure. Both are of a real interest because is treating the subject of tissue stress: one is "The Windlass Mechanism of the Foot A Mechanical Model to Explain Pathology" the other one is "Real-time subject-specific monitoring of internal deformations and stresses in the soft tissue of the foot: A new approach in gait analysis " [ https://www.eng.tau.ac.il/~msbm/resources/J_BIOMECH_39-2673-1689.pdf ]. Lot of questions in my head (!!!) as for example :
    -1. are those articles reflecting the evolution of Tissue Stress Theory ?
    -2. thinking at Hannas Jarvis PhD thesis, does the actual models (Kirby, Fuller) should pass through a validation process as that from Yamitzky et al. article ?
    -3. how much understanding of von Mises stress, FEA, structural analysis,.... will be needed to be able treat pathologies ?
    -4. ...
    Could you make a comparative analysis of these two articles ? Till where should we go with bio-engineering principles in order to have a good rate of success with our prescriptions ?

    Looking forward to read your comments,
    Daniel :bang:
     
  35. Recent comment on my article by Daryl Phillips, DPM:

    My reply:

    And a new comment by Greg Wolfe:

     
  36. efuller

    efuller MVP


    Kevin, I agree with you completely. My post was in response to a question about why I seem to only talk about the STJ axis and don't mention other axes of the foot. I think you and I are in agreement that a theory that describes foot function can be valid and effective and not mention midtarsal joint axes.

    Eric
     
  37. efuller

    efuller MVP

    Daniel, don't get caught up in the name tissue stress theory. Look at the principles that are used within the theory. Some principles. Things break when loaded too much. We can model things to try and understand what loads will break them. We can model things to figure out which treatments will reduce load in them. I think the two articles are both applying the same principles. The focus of my article was modelling the windlass mechanism. The focus of the other article was plantar fat pad properties.

    I'm sorry I don't recall the content of the Jarvis thesis. Could expand what you are referring to in the Jarvis thesis and the Yamitzky paper?

    The first paper cited in the other article by Nigg talks about how good your modeling has to be. In that paper they created 3 models of different complexity that attempted to predict Achilles tendon tension from external measurements. The simplest model was good enough. This is the point here. If your model is good enough to make predictions for your particular use then it is good enough.

    Comparing the two papers: In my paper I did not use much math and I modeled ligaments and tendons as simple non elastic wires. In the other paper they did significant calculations of stresses on structures. With my paper I can make predictions on what treatments will work. To validate the model one would have to try the predicted treatments and see if they were successful. You don't have to go to higher level math to make predictions. Both papers are using finite element analysis. The elements in my paper are very large.

    Practitioners can live at different levels of knowledge and do the same thing. For example on practitioner could work on the level of.. I see a medially deviated STJ axis and posterior tibial dysfunction. I know that this medially deviated STJ axis foot will tend to have a higher pronation moment from the ground and that if I shift the center of pressure under the foot more medially I will reduce the pronation moment on the STJ and this should reduce the load on the posterior tibial tendon and this should allow it to heal. On another level a practitioner could say oh you have posterior tibial dysfunction, I'm going to give you an orthotic with a medial heel skive, because I've heard that is what works. Two different levels of knowledge, same treatment. So, no, you don't have to know finite element analysis to treat patients. You don't have to know models and their predictions. You just have to know what the correct modification is for your particular problem. Knowing modeling will help you modify your treatment when the need arises.

    In keeping with the title of the thread. How many Root theorists can explain why they cast the foot in neutral position? Can someone present the though process on why it is better to cast the foot in neutral position than to not cast the foot in neutral position?

    Eric
     
  38. Petcu Daniel

    Petcu Daniel Well-Known Member

    I'll add next to Javris' thesis [discussed in http://www.podiatry-arena.com/podiatry-forum/showthread.php?t=93943 ] this article http://www.ncbi.nlm.nih.gov/pubmed/17507529 which is concluding that "...Additional well-controlled clinical trials that are methodologically consistent must be conducted to determine the clinical efficacy of orthotic treatment... "

    Which are, in your opinion, the most objective form of validating a model [any model] at the level of clinical practice? What means "have to try" ?

    Respectfully,
    Daniel
     
  39. efuller

    efuller MVP

    With modelling we predict that posterior tibial dysfunction will be helped by a device that has a medial heel skive. So, in a clinical trial you would have to try no orthotic, vs orthotic made from a cast with "vertical" heel vs. orthtoic made from the same cast, but with a medial heel skive, for number of patients with PT dysfunction. Repeat for other pathologies and other orthotic modifications.

    Eric
     
  40. Petcu Daniel

    Petcu Daniel Well-Known Member

    Do we have such a clinical trial ?
    And, if we don't have it, what can we say about medial heel skive, even if the principles and common sense tell us that it should work according to the prediction of the theoretical model ?

    Daniel
     
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