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"Original Root Postulate" on the Midtarsal Joint

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Kevin Kirby, Jun 6, 2013.

  1. "I'll get me lab coat".
     
  2. rdp1210

    rdp1210 Active Member

    OK, Simon, this is not about nationalism. This isn't the academic olympics, so let's drop who's living in whatever artificial political boundaries that have or will exist. :boxing:

    I do apologize if I sounded sarcastic in asking you for a treatise. I really did want you to expound on how the quote from Nester was being appied by yourself. This quote seems to be very general. It seems that it could apply to Whitman theory, Root theory, Schuster theory, Phillips theory, Spooner theory, or just about anybody else.

    You say that you take a tissue stress approach. As I read Root, I see lots and lots of things about tissue stress, starting from page one with the definition of the normal foot. I don't see anything in that definition about neutral, pronated, supinated, etc. It just says that a normal foot is any foot that allows you to function over a lifetime with a minimum of stress, deformity, injury, etc. Do you agree with this definition?

    Please respond to the following questions in regards to tissue stress.
    1. Does heel vertical in stance minimize tissue stress? Why or why not? (I'm not going to quibble right now about the definition of calcaneal bisection, we'll just be mathematicians by assuming that it does exist)
    2. Do you agree with Lovett & Cotton that people should not be standing with the rearfoot maximally pronated? Why or why not?
    3. Should muscle function be optimized to functioning around its resting length?
    4. Do you agree with the Dananberg postulate that the first MTPJ should dorsiflex as much as possible to minimize stress to the spine?

    I could go on, with a lot more questions, but I'll wait for you to answer these first.
    Now Nester talks about lots of variation, the question that he doesn't answer is whether all of these variations can function without injury? He says the variations are normal, though he fails to define the word normal. As you know, I have maintained that the foot, leg, body, will do everything possible to put all 5 metatarsal heads on the ground in stance. Lots and lots of variations exist that can do this. Are all of these variations going to produce minimal stress or give equal results?

    I do believe first and foremost that I am very tuned into tissue stress (and orthotic stress). I was practicing tissue stress analysis long before Eric wrote anything about it. Today I HAVE TO BE even more tissue stress oriented because of the large percentage of my patients who are high risk diabetic. Do I apply Root principles? Yes! Do I applly sagittal plane theory? Yes! Do I look at STJ axis? Yes! Do I look at the pedobarograph results? Yes! Do I consider frictional forces? Yes! Am I incorporating the principles of Owings? Yes!

    I was going to write a long dissertation on how Root et al changed the face of podiatry, but will leave that for another thread when we've got more time to :deadhorse: .

    Best wishes,
    Daryl
     
  3. OK Daryl, I'll play:
    1) Depends on the individual and the surface characteristics upon which they are standing etc. I presume you meant static stance, otherwise the additional caveat of it depends on the specifics of the additional motor task should be included.
    2) see 1) above
    3) See 1) above, with the addition of it depends on the neuromotor task.
    4) I don't think that Dananberg postulated that the first MTPJ should dorsiflex as much as possible to minimize stress to the spine, viz. this is a straw man argument.

    That's the beauty of variation, both in terms of genotype and the environment and the interaction between these two, Daryl. Or, do you think there is one biomechanical solution for all genotypes in all environments?

    So, my turn:
    1. In which dynamic situations and in which activities of daily living, and in which individuals, and upon which surface characteristics does heel vertical in stance minimize tissue stress?
    2. In which individuals and in which environmental situations do you agree with Lovett & Cotton that people should not be standing with the rearfoot maximally pronated? Why or why not?
    3. In which dynamic situations and in which activities of daily living, and in which individuals, and upon which surface characteristics should muscle function be optimized to functioning around its resting length?
    4. Did Dananberg postulate that the first MTPJ should dorsiflex as much as possible to minimize stress to the spine?

    I think the expression you are now looking for is: "touche", Daryl. BTW, you didn't answer my previous questions before you posed your own, above. ~And it is all about "academic olympics", we're all here for the academic debate and mental workout- right? Isn't that why it's called Podiatry Arena? Through such debate we learn and grow. As opposed to "podiatry come on here and try to sell your wears"?
     
  4. Simon:

    Am I safe to assume that you have now resumed your normal level of postings per day on Podiatry Arena after your brief spring hiatus?:rolleyes:
     
  5. I just hope I'm providing quality as well as quantity to the readership.
     
  6. Of course, Dr. Spooner. Your postings.....as long as they don't degenerate into lyrics to a song I never heard of....are always excellent sources of information.;)
     
  7. These are excellent comments above from Simon and are thoughts that I agree with 100%.

    Foot orthoses work by altering the magnitudes, locations and temporal patterns of ground reaction force on the plantar foot. The biomechanical effects of foot orthoses may either be direct mechanical or neuromotor effects, meaning that the foot orthosis may either push on the foot and the foot will respond by moving in the direction of the push from the orthosis (i.e. direct mechanical effect) or the foot will respond by moving in a direction that is not predicted by its direct mechanical effects on the foot, thereby suggesting a central nervous system motor response to the orthosis (i.e. neuromotor effect).

    A three-dimensional model of the plantar foot (e.g. negative cast of the foot, optical scan) is helpful, but not absolutely necessary for the skilled clinician to produce positive changes in the kinetics and kinematics of gait of their patients with some form of in-shoe modification that also alters the magnitudes, locations and temporal patterns of ground reaction force on the plantar foot. In other words, pads and modified over-the-counter insoles placed inside shoes also have the mechanical potential to exert profound effects on gait kinetics and gait kinematics, just as custom foot orthoses.

    Dr. Root and his colleagues certainly provided us all with a useable and practical place to begin to understand foot and lower extremity biomechanics and use foot orthosis therapy to help our patients. Some of what he and his colleagues taught was accurate and useful, however some of what he taught was also inaccurate and was not the most effective way of understanding the biomechanics of the foot and lower extremity and treating patients with mechanically-based pathologies of the foot and lower extremity.

    It is up to the current generation of podiatrists, foot-health clinicians and researchers to devise improvements in foot and lower extremity biomechanics theory and treatment for our patients, that Dr. Root and his colleagues worked so hard to provide to us during their lifetimes. Our patients deserve our continued efforts at improving the treatments we use on them on a daily basis.

    However, it is also not productive to continually try and defend a previous researcher's or clinician's ideas especially when there is no research evidence to support their ideas and plenty of research evidence to refute their ideas. This "clinging to old ideas" does not help stimulate progress within a medical profession, but only retards the flow of ideas that need to be continually analyzed, tested and researched to improve the care for our patients.

    Let's work together to improve the care for our patients, continue to pay respect to those before us that have made positive impacts on our medical profession, but also not assume that the ideas of someone that we greatly respect are always true. We must always question our beliefs if we are to progress as a medical profession. Good science demands it.
     
  8. Jeff Root

    Jeff Root Well-Known Member

    Kevin, I agree with everything you said in your post, including that which I just quoted. That is why I ask Robert Kidd "In your opinion, how has science changed the way in which podiatrists now examine, diagnose and treat foot conditions? Please be as specific as possible". Theories are great but where the rubber meets the road is contained in my question to Robert. I see these areas becoming more fragmented in terms of how individual clinicians approach things. If science were truly at work here, wouldn't we see some streamlining with respect to examination, diagnosis and treatment?
     
  9. Jeff:

    You may want to Thomas Kuhn's book on "The Structure of Scientific Revolutions". Eric Fuller introduced me to this book years ago and it certainly applies to the where we are now in podiatric biomechanics. Eric and I coauthored a chapter in a book that is due to be published within the next month (at least that is what the editor said last week) where we also talk about this idea.
     
  10. Daryl:

    So, let me summarize your stories.

    If I am criticizing the Root Functional Orthotic, you say:

    However, if we are discussing the fact that Root wasn't the first one to create foot orthoses that were shaped to the plantar foot, wasn't the first clinician to use thermoplastic orthoses, wasn't the first one to end the orthosis shell at the metatarsal necks, was 38 years too late to be the first physician to describe negative casting using strips of plaster, and that he possibly wasn't as responsible for the "orthosis revolution" as many authors have claimed him to be, you then say:

    That is very convenient, Daryl, for you to use different stories to keep Mert Root at the top of the world of podiatric biomechanics as long as possible.

    If we criticize his Root Functional Orthosis for being limited in design you say he wasn't responsible for the thermoplastic orthotic, but if we criticize that he possibly wasn't as important in developing the worldwide foot orthosis industry, you then conjure up images of George Bailey, Clarence Odbody and Pottersville, like no one would have ever figured out how to make a "functional foot orthosis" if Mert Root had never been born.

    So which one is it? You can't have it both ways, Daryl. Was the Root Functional Orthotic an original design that spawned the worldwide orthosis industry, or was it just another form of a thermoplastic orthosis that had already been done years before by clinicians in other countries or in other parts of the United States before Mert Root started lecturing and writing about it?
     
  11. Rob Kidd

    Rob Kidd Well-Known Member

    Jeff, its not a question of science changing, or not changing the manner in which podiatrist now examine, diagnose and treat, it is a question what is scientifically correct, and what is flawed. I don't actually practice very often, so I would always refer this to someone who does. However I do teach functional anatomy from time to time, and if fact have just finished a semester at Central Queensland Uni. When I taught the hindfoot and its joint axes, I took great pains to note that two functional units - subtalar and midtarsal, share three morphologically separate joints. That is, the structural and functional units do not agree. There are two possible explanations for this. 1) the foot is so highly evolved (which it is), that the original structural units are much modfied in terms of function, or 2) the function models are wrong. For the last 30 years, I have taught that it is to be expected that the two axes model of the midtarsal joint is highly likely to change, but I did not predict what that change may be. It seems to me that the change process that I and others have predicted for a very long time, is now underway.

    The structural/functional issues are ones that I addressed is some detail when I was a PhD student many moons ago. Rob
     
    Last edited: Jun 12, 2013
  12. blinda

    blinda MVP

    Without distracting from the invaluable content of this thread, can I just say; `No!` Prof Kirby ;), but only with regard to song lyrics....the rest is making for great practitioner consumption, from all contributors. Great discussion :drinks
     
  13. Anyway, now that we've had our trip back to the 60's, lets get back to modern biomechanics.....

    Mike had previously and insightfully written:

    Eric replied:
    In response to this I wrote:
    I should be interested to hear Eric, Kevin, Daryl, Jeff and anyone else respond to this. It negates Nester's previous work in which the rigid body assumption between the navicular and cuboid was endorsed. Good scientist- admitting he was wrong. But where does this leave the educator's attempting to teach midfoot biomechanics? Let's move it on...
     
  14. Jeff Root

    Jeff Root Well-Known Member

    Simon,

    During closed chain stj pronation, as the head of the talus adducts relative to the long axis of the calcaneus and as the body of the calcaneus simultaneously everts, I would think that the frontal and transverse plane motion between the cuboid and navicular would play a significant role in converting the foot into a mobile adaptor. In other words, the head of the talus adducts taking with it the navicular. But the navicular doesn’t adduct as much as the navicular, so this results in some relative abduction of the navicular relative to the talus. However, both bones are adducting relative to the ground. It’s just that the navicular adducts less than the talus. Simultaneously, the calcaneus everts along with the cuboid as the navicular inverts. I believe this contributes to foot splay during closed chain pronation.

    When we examine pathological feet, we get a clue into this mechanism. For example, if we look at the osseous relationship of an individual with advanced adult acquired flatfoot, we see adduction of the talus (and a wider T-C angle), eversion of the calcaneus and varus rotation of the navicular. This adaptive condition results in the medial prominence (bulging) of the head of the talus and the navicular and the everted heel that are common adaptive changes with AAFF. The varus rotation of the navicular causes the navicular tuberosity to point from a plantar/medial direction to a more medial direction, which is why it becomes so medially prominent. In my estimation, these are just gross exaggerations of the normal motions of these bones. I think these motions are clinically significant, especially when they occur in excess and contribute to osseous migration over time (i.e. functional adaptation).
     
  15. rdp1210

    rdp1210 Active Member


    Fair enough Kevin,

    BTW, thanks for answering my question about your current casting technique. One question remaining, do you dorsiflex the ankle joint to 90 deg, and do you care whether the plantar foot is perpendicular to the ground when casting?

    In regards to the people you mentioned as having taught you casting (Drs. John Weed, Ron Valmassy, Chris Smith, John Marczalec, Lester Jones, Bill Sanner, Rich Blake) I also worked with each of these people when I was in school. All were taught by Mert Root, but each also developed their own little caveats and modifications. Rich Blake and I were team mates when we were also taught by Mert at his office. I still remember what a small ROM Rich had in his STJ; made it a little difficult to find neutral position; yet, Mert made us learn to do it with our eyes closed, and without touching the TNJ. Though Mert did write a book on casting, yet each of the disciples, with their little variations which they passed on to their trainees, and as a result it has been almost impossible to 100% standardize the orthotic casting process. I'm reviewing again right now McPoil's article in 1987, on the relationship of talar neck rotation to forefoot alignment, and there are several questions I have, that he does not make fully clear, one being how he did a plaster casting of the foot with no skin on it. When I took casting lessons from John Marzalec and Les Jones in school, they utilized much more force in pronating the MTJ than Mert did when I took lessons from him. There has yet to be a paper produced on how the shape of the orthotic changes with varying degrees of pronatory force on the MTJ.

    While I seem to be characatured by many as some type of blind nonprogressive Root disciple, yet I have tried to analyze many different ideas as to why they work, both those in the pre-root and post-root age. I feel that I am not unlike you, I keep incorporating more and more ideas from various sources to make the perfect orthotic every time. I was even ready to accept Glaser's ideas if he could have made an orthotic for either myself or my wife that didn't cripple us. The fact is that the older I get, the more respect (not less) I get for Mert Root.

    Now you challenged me that I was trying to have my cake and eat it too. On the surface, it may look like that. So I will try to put it in perspective. I think there are two aspects of Root: one is theory and the other is practice application. We assume that if the application isn't perfect, then the theory must also be wrong, and visa versa. The Root-bashing crowd often use a trebuchet to throw the biggest stone and totally smash him into the ground, instead of carefully using a scalpel to tease away truth and error. You have to remember I was a first hand witness to the challenge by Milt Wille on osseous locking. I have spent a lifetime trying to live up to the challenge by Dr. Wille, to put the mechanics into biomechanics.

    As I have tried to analyze Root's teachings, comparing them with those from the past, the one thing I can say that appears to be truly original from Mert Root was what I now call the Root Postulate. This is Root theory. He erroneously continue to use the term "locking" even though he removed the term "osseous locking" from his 1977 text. The only thing even close to the application of the Root Postulate is Steindler 1929, with his shoe wedges. You can find things throughout the literature before him on just about everything else. I find that Lovett and Cotton almost word for word described the STJ neutral position. Perkins put out an a great article on the effect and treatment of forefoot varus, and even used the term (1948).

    From the Root Postulate came a methodology of casting that was unique. My reading of the Lee paper on the history of Root, shows that his teachers were using the Levy mold which involved a semi WB technique. If someone can come up with another person before Root that was utilizing his NWB technique, I'd love to get hold of the paper. Other aspects, including materials, and dimensions of orthotics were nothing new. As I've pointed out before, Root was no different than anyone else in starting with what he was taught, beginning practice, and finding failures, doing some additional reading and incorporating ideas from that, and then developing some additional ideas (kind of like Kevin Kirby).

    When we look at Root, we have to look at not just at his theory and practice, we also have to look at his influence and effect. Yesterday, a check of scholar.google.com showed that Root's volume 2 book has been cited 611 times. I would say that is a very extensive effect on the biomechanics world. And it's not just the American authors that are citing him, there hasn't been any other podiatrist who has been as widely cited in the biomechanics literature internationally. Was there an orthotic industry before Root? Not really as almost all practioners made their own orthotics. Did he directly build it? No. Did he inspire other people to build it? I would say that he had more influence on such than any other one person. There are lots of local heros throughout the world, and I don't want to say anything bad about any of them. (You remember one of my local heroes, Bud Collins.) But in terms of shear effect, whether it be good or not, few have equaled Root (Dalt McGlamery is one). I know you've done a lot, travelled more than Root, maybe given more lectures, but still you and I are both Root products. We're both still using the basic Root Postulate, though it's mechanism isn't fully understood. (BTW I've also experimented a little with force up and down on the medial column too for select patients).

    Please don't think that I want to canonize everything Root said nor am I saying that everything shouldn't be questioned. What I am saying is give due credit where it's due. Could you do a Kirby skive on a flat piece of insole and have it have the effect as the orthotic you make? How about the same effect on an orthotic in which the patient contracted the anterior tibialis during the casting procedure? Does the plantar shape of the orthotic matter in any way as long as it has Kirby skive? When you start ordering Glaser orthotics, then I'll say that you consider the Root Postulate dead.

    BTW - I did review again, for Simon's sake, Shepard's 1951 paper and his statement about the MTJ being uniaxial has absolutely no basis in experiment. He paints a picture of it being similar to the Hicks OAMTJ. Also reviewed again GK Rose's paper, and noted his reliance on Manter's work. I realize that he is a contemporary of Root, but I don't see much progress from Whitman's 1885 paper. So Simon, I really doubt that we'd be where we are today with just what was happening on the East side of the Atlantic. Not saying I don't enjoy reading these peoples' work and that they aren't intelligent, probably both better thinkers than me.

    Best wishes,
    Daryl
     
  16. rdp1210

    rdp1210 Active Member



    Simon,

    I think we need Erin Ward to weigh in on this as well as he is one of the best informed. I have been maintaining for quite some time that there is significant cuneiform-navicular joint motion and that in some people the CNJ motion can contribute more to the inversion of the forefoot against the rearfoot than the MTJ. Don't think that it could contribute much to the transverse motion, and not a lot more to the sagittal plane motion. I think you read the paper several years ago I did on the contribution of the first CNJ to total first ray motion during propulsion.

    I will review the paper again before making comments on it. Also we need to look at all the papers on the subject. It's hard to believe that a syndesmotic joint moves more than a diarthrodial joint. Maybe you can explain that. Also with no MTJ model to teach, maybe we should return to the Levy mold for all our orthotics. Will make more comments later.

    Have a good evening,
    Daryl
     
  17. Great reply, Daryl.:good:

    Your perspective is certainly unique since you, like I, had personal contact with Mert and his students during our formative years. [Did you graduate from CCPM in 1980?]. There are not many of us left who are still teaching actively who had the pleasure and honor of being taught directly from these individuals that learned directly from Mert Root and John Weed.

    By the way, Daryl, I love having you here on Podiatry Arena. I'm having more fun now on Podiatry Arena than I have had in years....mostly because of you and Simon and these discussions we have been having the last week or so.:drinks
     
  18. I load the Achilles tendon with sufficient force to stabilize the midtarsal and midfoot joints (i.e. position of loaded equilibrium) which generally amounts to about 10 pounds of force. I am never worried about ankle joint rotational position during casting since the position of negative casting will be a direct reflection of the dorsiflexion stiffness of the ankle.

    In other words, in those ankles with high dorsiflexion stiffness, that 10 pounds of dorsiflexion loading force on the forefoot may produce an ankle joint that is 10 degrees plantarflexed. In those ankles with low dorsiflexion stiffness, that 10 pounds of dorsiflexion loading force on the forefoot may produce an ankle joint that is 10 degrees dorsiflexed.

    Hope that helps.:drinks
     
  19. How we describe midtarsal and midfoot biomechanics gets down to how accurate and complicated we want the foot model to be and what the purposes the foot model is being used for.

    For example, of course, the navicular and cuboid rotate and translate independently of each other during weightbearing activities. However, do they rotate and translate together enough to allow them to be effectively modeled as being a single functional unit? I think so, for most purposes. In other words, for the podiatry student, I believe these two bones should be considered as one functional unit, but also with an understanding that slight motion does occur between these two bones during gait.

    If you need more accuracy, however, you will need a much more complex model. However, as accuracy increases, the ability to use rigid body assumptions for even single bones of the foot go straight out the window. For example, given the bendable nature of long bones, such as the metatarsals, since we know that the metatarsals flex during weightbearing activities so that the proximal and distal aspects of the bones are really not moving in the same direction as each other at all times, we can not consider metatarsals as being rigid bodies either, in reality.

    Do you now see the problem with trying to be too accurate in modeling? What starts happening with using more complex models is that even though reality is becoming more closely approached , the models become so complex that basic ideas, ideas that are very clinically useful, can't be taught to the average podiatrist who has a basic understanding of foot biomechanics without them being confused. Therefore, it is often helpful to simplify foot models, including those of the midtarsal and midfoot joints, in order to make progress in teaching and understanding important basic concepts in foot biomechanics; concepts that otherwise could not be readily taught using more complex models.

    Now, to move forward, what can we definitely say, given the prior research to date, and along with a firm understanding of rigid body dynamics, about the midtarsal and midfoot joints?

    1. There is no single oblique midtarsal joint (MTJ) axis.
    2. There is no single longitudinal MTJ axis.
    3. If the talus and calcaneus are accepted as being one rigid body and the navicular and cuboid are accepted as being another rigid body, then there can be only one instantaneous axis of the MTJ at any point in time. Research has shown the MTJ axis to be constantly rotating and translating in space during gait.
    4. However, if the talus, calcaneus, navicular and cuboid are accepted as all being rigid bodies by themselves, then, at any point in time, there will be four simultaneously occurring MTJ axes (CA-CU, CA-NA, TA-CU and TA-NA) which also likely are constantly rotating and translating in space during gait relative to each other.
    5. The axis of motion of any of these MTJ axes are dependent on both the external and internal forces acting across these joint axes at any instant in time whch are, in turn, partially determined by the geometry of the structural components of the midtarsal joints and midfoot joints.
    6. There is a range of midfoot and MTJ stiffness from one individual to another in each direction of motion that will determine the most likely path of motion at each joint of the midfoot and midtarsal joint (theoretical, but biologically plausible and biomechanically reasonable).
    7. All midtarsal joint and midfoot joint motions should be described using three orthogonal reference axes, rather than just one axis of motion, as proposed by Nester and Findlow for the midtarsal joint in 2006 (Nester CJ, Findlow AH: Clinical and experimental models of the midtarsal joint. Proposed terms of reference and associated terminology. JAPMA, 96:24-31, 2006). This allows description of the kinetics and kinematics of each joint of the midtarsal joint and midfoot joint at any instant in time and does not require the antiquated concept of a two fixed, simultaneously-occurring axes of motion for the midtarsal joint.
    8. The plane of the forefoot relative to the rearfoot is not just due to subtalar and midtarsal joint position and motion, but is largely also due to midfoot joint position and motion.

    Time for bed now, but maybe tomorrow I will add more.:cool:
     
  20. I can't follow your logic here, Daryl. If we don't have model for the MTJ, then we should be using 1950's rubber butter foot orthoses?

    Who says we don't have a model for the MTJ? That the two axis model which Root was a proponent of lacks validity and is inaccurate, doesn't mean we should forget everything we have learned in despite of this model now being rejected, as you appear to be suggesting.
     
  21. that is the sort of stuff that I missed in the last 12 months of PA .

    you read sit back and think :drinks the four simultaneously occurring MTJ axes (CA-CU, CA-NA, TA-CU and TA-NA) especially
     
  22. Daryl, if you could get Erin to contribute here that would be great. Maybe someone could give the Nester and Tony Arndt a nudge too?

    With regard to a syndesmotic joint displaying greater motion during dynamic function than a diarthrodial joint, I should imagine this could be easily explained by differences in the loading forces being applied about each of the joints during the given dynamic function.

    One thing we do need to be cautious of regarding interpretation of the dynamic cadaver data and tarsal mobility is that within the dynamic cadaver studies, the intrinsic muscles of the foot were not being recruited. There is little doubt in my mind that the action of these muscles modulates midfoot stiffness and relative motion between the tarsals.
     
  23. rdp1210

    rdp1210 Active Member


    Thanks, Kevin,
    Next time we get together, we ought to try both casting the same person and get a scan of the casts so we can compare. I'll talk to Norm Murphy about how we can measure the dorsiflexion force that we apply. I'm in the same opinion about the Achilles tension, except I may use less force. I try to dorsiflex the lateral column with slightly more force than I think the forefoot weighs. And I don't worry about the ankle joint. Is your lab using any sort of digital system yet?

    :drinks 7Up

    Have a great day
    Daryl
     
  24. One of the reasons I am so interested in this midtarsal joint thread is that my last four months of Precision Intricast Newsletters were titled:

    February 2013: The Midtarsal Joint: Reference Axes and Joint Constraint Mechanisms

    March 2013: Muscles and Ligaments of the Medial-Lateral Midtarsal Joint Axis

    April 2013: Rotational Equilibrium of the Vertical Midtarsal Joint Reference Axis

    May 2013: Biomechanics of the Anterior-Posterior Midtarsal Joint Reference Axis

    These should all be ready for reading in my fourth Precision Intricast book to be published in early 2014.
     
  25. The real question is does the difference between two pounds of pushing force and ten pounds of pushing force on the lateral metatarsals make any difference in the shape of the negative cast and, ultimately, the function of the patient's orthoses.

    Here is what I have found. The harder the push on the lateral column, then the more everted (or less inverted) will be the forefoot to rearfoot relationship of the resultant negative cast. This is why I often also manipulate the load on the medial column while loading the lateral column during negative casting to get the shape of the foot that should make the best foot orthosis for my patients.
     
  26. Look forward to reading them and the rest of your book, Kevin. :drinks

    In the meantime, here's a link to where we discussed midtarsal joint equilibrium theory back in 2010: http://www.podiatry-arena.com/podiatry-forum/showthread.php?t=54294
     
  27. Daryl:

    I agree with Simon on this comment.

    Who says just because we have ruled out the antiquated concept of the longitudinal and oblique midtarsal joint (MTJ) axes that are simultaneously occurring as being reality that was taught by Mert Root and John Weed (and myself for some years) to thousands upon of thousands of podiatry students and podiatrists, does not mean that we have "no MTJ model to teach".

    Furthermore, how does your perceived lack of an accurate model of the MTJ invalidate any of the numbers of scientific peer-reviewed studies that show that foot orthoses not only effectively alter the kinematics and kinetics of gait but also are therapeutically very effective for patients. The answer? It doesn't.

    I believe Chris Nester's more recent in-vivo bone pin research, combined with Van Langelaan's research from three decades ago clearly points to the fact that the midtarsal joint is very complicated and involves continually rotating and translating multiple joint axes. Now that we are no longer spending our energy trying to understand how two MTJ axes, the longitudinal and oblique, can somehow coexist as two axes of motion that don't move in space and allow the same bones to move in two different directions, all at the same time, we now can free our minds to consider the reality of how the MTJ truly does work.

    A new model must be able to not only focus on the kinematics of the MTJ, which has been the focus of Chris Nester's research, but also must, and I believe more importantly, focus on the kinetics of the MTJ, which has been my focus of interest over the past few decades. I believe that using simplified models of the load-deformation characteristics of the medial and lateral longitudinal arches, such as the leaf-spring model I discussed earlier, is the key to developing a greater understanding of the kinetics of the MTJ and midfoot joints, or how the external and internal forces and moments acting across them work together to produce normal and abnormal foot function.

    In addition, I believe using Nester's three orthogonal reference axes of the MTJ, and also applying these concepts to the midfoot joints, can be easily used to teach how motions and moments in three body planes can explain any pathology of the MTJ and midfoot. In addition, when combined with the subtalar joint axis location/rotational equilibrium theory and the known construction of the foot and lower extremity, these concepts can then be used to explain most, if not all, mechanically-based pathologies of the foot and lower extremity.

    So, Daryl, I don't think any of us will somehow need to regress back to using plaster puddle casts and cork and leather foot orthoses just because the antiquated idea of simultaneously occurring, fixed axis oblique and longitudinal MTJs have been refuted and replaced by better models to describe the MTJ. However, by ridding podiatry of these old and worn-out concepts, we will be able to move forward, using more accurate terminology and ideas that have already been around for decades within the International Biomechanics Community to explain how the midtarsal and midfoot joints work during weightbearing activities.
     
  28. Jeff Root

    Jeff Root Well-Known Member

    With that much force, how can you not pronate the stj at the same time unless you squeeze the margins of the calcaneus with your opposite hand in order to resist stj pronation?
     
  29. Why should it be a problem if you do pronate the subtalar joint during casting? How will it change the shape of the cast?
     
  30. Jeff:

    Increased force plantar to the lateral column will create an external subtalar joint (STJ) pronation moment that will be counterbalanced by an equal and opposite internal STJ supination moment from Achilles tendon tension acting medial to the STJ axis during negative casting. This is why, when negative casting in a patient with a normal STJ axis location, that you can press lateral to the STJ axis but still have the patient's foot not pronate due to the increase in force lateral to the STJ axis from your manual pushing forc. In fact, in patients with very lateral STJ axes, increased force on the 4th and 5th metatarsal heads will tend to cause STJ supination, not STJ pronation.

    Only in very medially deviated STJ axis patients is excessive STJ pronation a problem with increased force under the lateral column in negative casting. In these special cases, the tendency for STJ pronation during negative casting is easily remedied by either slightly angulating the angle of manual push on the lateral column more medially and/or by manually stabilizing the tibia within the patient's transverse plane relative to the supporting table.
     
  31. Jeff Root

    Jeff Root Well-Known Member

    It's only a problem when you don't want to pronate the stj. So when Kevin takes a stj neutral cast, how does he keep the stj from pronating while applying ten pounds of pronation force to the forefoot distal to the mtj?
     
  32. But how would it change the shape of the cast if you pronated the foot say 2 degrees, 5 degrees or 10 degrees from neutral? Moreover, when the person stands, there is going to be whole lot more than 10 pounds of force to the forefoot distal to the MTJ- right?
     
  33. Jeff Root

    Jeff Root Well-Known Member

    If you apply ten pounds of force to the plantar aspect of the 4th and 5th met heads, how can you not pronate the stj? In order for the stj not to pronate in that situation, you would also need to be applying some adduction force to counterbalance the pronation moment at the stj caused by the eversion force, since eversion is a component of stj pronation.
     
  34. Jeff Root

    Jeff Root Well-Known Member

    That's not the question. The question is how can you maintain the stj in neutral while applying a strong pronation force to the forefoot in an effort to get more pronation at the mtj?
     
  35. Here's a question: given that the in-vivo bone pin studies show that "motion that was previously attributed to the midtarsal joint and rearfoot was most likely taking place between the cuneiforms, the navicular, and cuboid." and that the Blackwood study indicated that rearfoot position did not significantly alter the motion at the midtarsal joint (CCJ, TNJ), how does this impact on the concepts of forefoot varus and valgus as defined by Root?
     
  36. I appreciate that this may have not been the original question, Kevin has given his response to this already, but I'm interested to know the answer to the question I subsequently posed: viz. what difference does it make whether the subtalar joint is maintained in neutral during casting or not to the shape of the cast? Remember, all we are capturing during casting is an initial shape.
     
  37. Jeff Root

    Jeff Root Well-Known Member

    Not a all. FF varus and valgus can only be determined with the stj in the neutral position, just like we use a standard anatomical position to describe basic anatomy. That's like saying, if I fully flex my elbow, then my hand is no longer distal to my elbow. But since we relate proximal and distal to the standard anatomical position, my hand is always distal to my elbow. Root noted that ff to rf relationship changes with stj position.
     
  38. Jeff Root

    Jeff Root Well-Known Member

    In some feet, there is a significant shape change in the plantar contour of the foot as you move away from stj neutral and in other feet, not as much. Significant changes do occur at the mtj in most feet. Just measure ff to rf relationship with the stj maximally supinated, neutral and then maximally pronated. Very often, there are big difference in ff to rf angle!
     
  39. Yeah, but given that STJ position doesn't change the range of motion at the midtarsal joints (CCJ, TNJ), why can FF varus and valgus only be determined with the STJ in neutral? I thought that forefoot varus and valgus were fixed osseous deformities at the midtarsal joint (CCJ and TNJ). Is it that these "deformities" were measured between a "heel bisection" and the plane of the metatarsal heads in Vol.1? Moreover, it was described that they compensated around the "oblique and longitudinal midtarsal joint axes" in Vol. 2, isn't it far more likely that the tarsal articulations of the midfoot involving the cuneiforms et al. are where such compensation takes place? Indeed, as your dad noted that forefoot to rearfoot relationships change with STJ position, but the Blackwood data suggests that this was not occurring at the MTJ (CCJ, TNJ).

    Given the range of motion available at all the joints of the midfoot, how can we even validly measure the existence of forefoot varus / valgus, whether the subtalar joint is in "neutral" or not? Now, I'm not saying that it forefoot valgus and varus do or do not exist, but if they are fixed osseous deformities occurring at the level of the midtarsal joint, then clearly your father had no way of assessing these in-vivo, any more than we could easily assess these today.
     
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