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Transverse plane rotations of the hip driving the pronation/supination movement of the foot

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Brian A. Rothbart, Nov 8, 2011.

  1. Brian A. Rothbart

    Brian A. Rothbart Active Member

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    Inman and Close (The Action of the Ankle Joint. Prosthetic Devices Research Project, Series 11, issue 22. 1952) were the first to publish on (I believe) the correlation between the transverse plane rotations of the hip driving the pronation/supination movement within the subtalar joint (I.e., Hip Drive). Inman later discussed the link between leg rotation and movement within the subtalar joint. (The Joints of the Ankle, Chapter 9, The Subtalar Joint. Williams & Wilkins 1976).

    This research is the keystone to understanding (defining) normal vs abnormal pronation (in my opinion).

  2. efuller

    efuller MVP

    Re: Henke's Original Paper on STJ Axis

    The hip rotates over the stance leg femur. There are three possible situations. 1. The hip musculature is retarding rotation (And this will create and external rotation moment on the leg). 2. The muscles of the hip are not acting in the transverse plane on the leg and the pelvis movement over the stance leg is from the momentum of the body. 3. The muscles of the hip are acting to increase the speed of rotation of the pelvis over the femur (and this would cause an internal rotation moment on the femur.) Newton's 1st law for every action there is an equal and opposite reaction. In different circumstances each of these possiblities will occur. For, example instead of walking straight ahead, someone could make a right turn by altering pelvis rotation over the stance leg. These moments can be measured by inverse dynamics. Therefore hip drive does not occur 100% of the time. I would bet that it occurs much less often than that.

    We often see late stance phase pronation in some feet. We see late stance phase supination in other feet. It makes much more sense that this motion is controlled by the muscles of the lower leg than by the momentum of the hip. Besides the knee does not support/ transmit transverse plane torque very well. This is the main reason that the hip cannot drive STJ motion.

    I don't see how this defines normal from abnormal pronation.
  3. Brian A. Rothbart

    Brian A. Rothbart Active Member

    Re: Henke's Original Paper on STJ Axis


    In all due respect, I disagree with you. The following very simple demonstration visualizes how the direction of the transverse plane rotations within the pelvis controls the motion within the STJ.

    Standing, rotate your hip clockwise. Note the motion in the STJ: The right foot supinates, the left foot pronates. That is transverse rotation of the pelvis directs (which I refer to as Hip Drive) the motion within the STJ. This is independent of muscular control.

    Read the research that was done at the University Hospital in Berkeley California by Inman and Close. They were dealing with leg amputees after WWII. The problem they were having was trying to put a prosthetic foot at the end of the leg prosthesis. Every time they tried, an ulcer formed where the prosthesis conjoined the stump. But no ulcer formed with they used a peg leg. The question was - Why.

    Ultimately, they discovered the why: The STJ acts as a transducer, absorbing the motion being initiated by the transverse rotations of the hips during ambulation.

    Using a prosthesis with a wooden foot, the transducer becomes the knee joint, hence the formation of the ulcers.

    What does this all have to do with normal pronation - when the motion within the STJ is directed by (I.e, linked to) the transverse plane rotations of the pelvis, the STJ action as a transducer is maximized. When the SJT motion no longer is in sync with the rotations of the pelvis, its action as a transducer are dramatically attenuated. (I refer to this as gravity drive).

    In my research, I have proposed that the definition of normal vs abnormal foot pronation should be based on whether the STJs motion is linked or has escaped the direction of the pelvic rotations. If you go to my research site, you will see examples of this.

  4. efuller

    efuller MVP

    Re: Henke's Original Paper on STJ Axis

    I've done that demonstration with numerous students. If you look at the tendons of the ankle joint, you can see that they contract when you see the motion you describe. Also, you can move your pelvis without moving the STJ, it is not rigidly linked.

    Where does the power come from to rotate the hip to perform this maneuver? The pelvis is in the air, on top of the leg. The foot is on the ground. The power to move the hip has to come from force on the ground. Answer, muscles of the leg.

    When you choose to activate the muscles of the lower leg to create those foot motions you can allow the pelvis to rotate farther before it runs out of range of motion. You still haven't addressed the lack of ability of the knee to transmit torque. Try this experiment, stand on your left foot and attempt to push from right to left a heavy object on the floor, with the toes of your right foot. Can you feel the stress in your knee. If the hip drove the movement in the STJ, you would feel that stress every step.

    This doesn't prove that the hip drives the STJ. Another explanation is that hip muscles are trying move the hip over the stance leg. With a peg leg there is no traction to drive the hip, so it doesn't try when there is a peg leg.

    I would agree that it easier to take longer strides when the leg externally rotates in late stance phase. I have to disagree with the notion that the hip drives the STJ. If the hip drove the STJ how can the STJ "escape" the rotation of the pelvis?

  5. Admin2

    Admin2 Administrator Staff Member

  6. Brian A. Rothbart

    Brian A. Rothbart Active Member


    This discussion is beginning to sound more and more like 'which came first, the chicken or the egg'?

    First, I need to define terminology a little bit better, because I have taken liberties in using the term hip and pelvis interchangeably, which they really are not:

    The hip is the innominate bone, which comprises 3 separate bones (ilium, ischium and pubis).
    The pelvis is comprised of two innominates and the interlinking sacrum.

    When you read my previous two posts, I was using these terms interchangeably. Forgive this misuse of terminology.

    I use the term hip drive which is not technically correct. The correct term would be pelvic drive, because the pelvis moves as a unit on the transverse plane. However, I termed hip drive more than 5 years ago and to change it now would produce some confusion. So let's stick with the term hip drive even though we mean pelvic drive.

    Regarding the foot not being linked to the pelvic rotations, I am unable to move my pelvis without also observing motion in my STJ (the magnitude of the STJ motion increases with the magnitude of the pelvic oscillations).

    More on this later, I need to see a patient.
  7. David Smith

    David Smith Well-Known Member


    I don't get this and other debates that ask the question does the hip drive the foot or vice versa??
    If the trunk has a rotational acceleration then there must be a connection to the ground via the foot providing the force, assuming the subject is not walking on their hands or pushing off a wall etc.
    Therefore there must be some mechanical coupling thru the ankle, knee and hip joints. Therefore these couplings must produce a torque thru the joint and so it tends to move in the direction of the applied moment.
    If there is no acceleration of the trunk then there can be no moments produced at any joint and so there will be no tendency to move in any direction.

    Does anyone not agree with this statement?

    Dave Smith
  8. The interesting bit is the coupling and how it may be influenced. This from one of my slides on kinematics versus kinetics:

    Nigg et al. 1998
    Five inserts identical shape but different materials designed to reduce pronation
    12 subjects heel toe running at 4 m/s
    Foot eversion and tibial rotation measured using skin markers

    Only 1 of the 12 subjects showed reduction in foot eversion and tibial rotation or no change for all conditions
    One subject showed reduction in eversion but increase in tibial rotation in all insoles
    One subject showed a reduction in foot eversion for all insoles conditions, but an increase in tibial rotation for only some

    Attached Files:

  9. Brian A. Rothbart

    Brian A. Rothbart Active Member

    Dear David and Simon,

    David, you said exactly what I was going to say in my last post. This is exactly what I have observed in my research (over the past 40 years) and what many of my compeers have also observed.

    Simon, regarding your citations:

    Nigg paper (1998) was very interesting. He used different materials to reduce pronation. However, pronation is a symptom, not a cause. The question that was not addressed in Nigg's paper (if my memory is correct) was what was the exact cause of the observed hyperpronation. This was one of the main reasons that I dismissed his paper (even given the fact that it was well written and presented).

    Let me expand on this subject a little more. I have written on two embryological abnormal foot structures that will cause the foot to excessively pronate. I treat these foot structures using proprioceptive insoles. However, if the proprioceptive insole that reduces pronation in Rothbarts Foot, is used for a patient having the Preclinical Clubfoot Deformity, that proprioceptive insole will actually increase forefoot pronation.

    Bottom line, you must first determine the cause of the hyperpronation, and address that cause directly. Otherwise the observed results will be misleading. Let me go one step further, in my above example, using the incorrect insole, one would observe a pronation movement at midstance when the tibia was externally rotating. The conclusion would be that there was no coupling between the two (The foot would be pronating when the tibia is externally rotating). However, when one understands gravity drive, this apparent uncoupling becomes understandable.

  10. No Brian, pronation is a movement.
  11. Brian:

    Please define the term "hyperpronation".
  12. Brian A. Rothbart

    Brian A. Rothbart Active Member

    Correct, movement (thanks for picking up the typo error)
  13. Brian A. Rothbart

    Brian A. Rothbart Active Member

    Hyperpronation, what is the definition. Great question. I can only give you my answer based on my research.

    If one accepts hip drive as a valid paradigm, which I do, then defining hyperpronation (abnormal pronation, excessive pronation, or whatever term you wish to use) becomes self apparent:

    Hyperpronation is any closed kinetic chain pronation that occurs when the tibia is externally rotating. Or, if you prefer, any pronation that escapes hip drive.

  14. Brian A. Rothbart

    Brian A. Rothbart Active Member


    Pronation is a movement, but it is also a symptom.

  15. Brian A. Rothbart

    Brian A. Rothbart Active Member

    Here is an example of abnormal (hyperpronation) occuring in a patient with the Primus Metatarsus Supinatus foot structure. Note that the left foot is pronating (frames 2 & 3) when the ipsilateral leg is externally rotating (pelvis is moving in a counterclockwise rotation).

    Note, the abnormal pronation is attenuated by the Windlass Mechanism (frame 4).

    (Again, I use hip and pelvis interchangeably. When in actuality I should only use the term pelvic rotation, not hip rotation).

  16. So, how is it we can treat the pathology without a change in the "symptom"? A fine example of this, again this is a study I use in my kinematics versus kinetics lecture, can be found here: Williams et al, 2003: Effect of Inverted Orthoses on Lower-Extremity Mechanics in Runners. MEDICINE & SCIENCE IN SPORTS & EXERCISE

    Brian, regardless of your idea of pronation being a symptom. How do you explain the variability in coupling observed between and within individuals in the Nigg study?
  17. Brian A. Rothbart

    Brian A. Rothbart Active Member


    I believe the variability in coupling observed in Nigg's study was a function of not first identifying the underlying pathology (cause) and treating that cause directly. Instead they used different types of materials under feet to control the pronation movements. In my previous post I explained how this could produce misleading data.

    Regarding treating a pathology without changing the symptom, you lost me there. Can you be more specific?

  18. efuller

    efuller MVP

    The hip joint is the articulation between the femur and pelvis. I'm ok with calling the pelvis the pelvis. The hip bone is a term I'd rather not use.

    I'm ok with the term. I still doubt that hip drive is significant in powering gait.

    I'm sorry to hear that. I can move my pelvis without moving my STJ. I would hope that most people can, because, the femur can rotate relative to the pelvis around 80 degrees in most people. I will get more appearent rotation of the pelvis relative to the ground if I choose to move my leg in the same direction as the pelvis.

  19. The Williams et al study found that the patients symptoms resolved without a change in joint kinematics, i.e. the rearfoot pronation was not changed by the different types of orthoses provided, yet the pathology resolved with a specific type of orthoses, which did markedly change the kinetics without changing the kinematics. If, as you contend pronation is a symptom of the pathology, you'd think this would change when the pathology was successfully treated. Yet no.

    You miss the point of the Nigg study. Why do some people get increased tibial rotation with decreased rearfoot pronation and why do some people get increased rearfoot pronation with decreased tibial rotation? Saying they didn't address the cause of the pronation is neither here nor there, it about the variation in coupling between the rearfoot and the shank observed with the devices that were provided.
  20. So, with this definition, any closed kinetic chain pronation that occurs when the tibia is not externally rotating is not "hyperpronation"?

    How does the talus rotate internally while the tibia rotates externally?

    Please define "hip drive".
  21. By being de-coupled at the ankle. Which I think was Eric's point. Complete decoupling of the foot to the shank as this suggests is interesting and warrants further thought. I can see it in trauma, I'll need to think on it.... and review the bone pin data again.... There is certainly some slack in the ankle mortice.

    (EDIT) Five minutes thought: To achieve this the foot should have to be driving the talus independently of the leg---------- so the external rotation moment from the tibia has to be greater than the internal rotation moment from the rest of the foot on the talus and there needs to be enough slack in the ankle mortice and soft tissues surrounding the joint to allow this....
  22. Nester et al estimated 10 degrees of transverse plane talar to tibia-fibula "slack" in the ankle mortise. Don't have time now to find the reference.
  23. Don't worry, I know the one, JFAR have it as a freebie. This kind of de-coupling should have to occur at the ankle as the subtalar joint is far too constrained.
  24. I agree, Dr. Spooner.:drinks
  25. Brian A. Rothbart

    Brian A. Rothbart Active Member

  26. Completely irrelevant to the discussion

    "Gravity drive" you say hmmm. And how does this occur?


    And people wonder why I swear. You may think you are, but in my mind you are not answering the questions Brian. And making **** up things like "gravity drive" does not help your cause.
  27. Brian A. Rothbart

    Brian A. Rothbart Active Member

    When the STJ is coupled to the transverse plane rotations of the pelvis, by definition pronation pattern is normal (whatever the degrees of rotation might be).

    When the STJ is decoupled from the transverse plane rotation of the pelvis, we observe abnormal pronation (Pronation movements occuring when the ipsilateral hip is externally rotating).

    I have observed that when the foot escapes hip drive, I find the tibial rotation linked to the talar movement. That is, as goes talus, so goes the tibial. You can imagine what happens in the knee joint (where the tibial and femoral rotations are decoupled). We give it many different names: Oblique Patellar Tracking Pattern, Chrondromalacia, etc. But the end result is a derangement of both function and structure within the knee joint.

    Now, I am aware there are many studies that one could cite that would argue against this, and many studies that would argue for this. So be it. This has been my research experience and what I see clinically over the past 40 years.

  28. So cite 'em, then we might judge each on it's own merit rather than being expected to take your word for it.
  29. Brian A. Rothbart

    Brian A. Rothbart Active Member


    Better idea, you cite them.

    However, I am simply presenting my research.

  30. No Brian, that's not how it works. I have no idea of the research studies of which you referred to, so how could I possibly cite them? Unless you have invented an insole which provides the wearer with the ability to read minds, in which case you'll still need to send me a pair before I can read yours here.

    Or were you just plain old making it up, again? Perhaps in the hope that you wouldn't get called on it? If you did, you'd be able to weasel your way out of by saying something like " why don't you cite it?" I can't cite the references you had in mind Brian because it was you who mentioned them without referencing them. Simple as that. I have no idea what you were talking about.
  31. Brian A. Rothbart

    Brian A. Rothbart Active Member


    Let's start with JR Close and VT Inman, the ones I cited at the beginning of this thread. Apparently, you disagree with their discussion on the coupling between the pelvis and foot. Please do elaborate.

    Then we can discuss the following:

    Gagey P.M., Weber B. (1995) Posturologie; Régulation et dérèglements de la station debout. Masson, Paris.
    Gagey PM, Weber, B. 2005. Posturologie, Elsevier Masson
    Pelissier, J, Blayac JP 1993. Posture, equilibration et medecine de reeducation. Elsevier Masson.
    Souchard PE 2006. RPG. Principles of global postural reeducation. Editorial Paidotribo

    These are textbooks written on Posturology which goes into the different coupling systems in the body.

    After that we can discuss the following:

    Gagey PM. 1986 Postural Disorders. In: Bles W, Brandt Th. Disorders of Posture and Gait. Elsevier. 253-268.
    Gagey PM, Baron JB, Ushio N 1980. Introduction a la posturologie clinique. Agressologie, 21 E 119-124.
    Gagey PM, Toupet M, Heuschen S. 1992. From ankle to hip strategy. In: Posture and gait: control mechanisms. Vol II. 251-154. Woollacott & Horak
    Gagey PM, Gentaz R. 1996. Postural disorders of the body. In: Rehabilitation of the spine. Williams & Wilkins, Baltimore.
    Gentaz, R 1988. L'eil postural. Agressologie, 29, 685-686.
    Gurfinkel VS 1973a. Physical foundations of stabilography. Agressologie, 14, C, 9-14.
    Jongit N, Villeneuve Parpay S, Villeneuve P 1996. Determination des seuils de perception des baroropresseurs plantaires: variations en fonction du sexe dt de l'age. In: Pied equilibre et posture. Frison Roche, Paris 61-65.
    Kavounudijas A, Roll JP, Gilhodes JC Bouquerel A 1998. Responses posturales induites par stimulation vibratoire des afferences cutances plantaires chez l'homme. In: Pied equilibre et rachis, Frison-Roche, Paris.

    These citations do not just deal with foot and pelvis, they deal with the entire body. However, in order to stay within the discussion in this thread, we can limit ourselves to those areas that only deal with the the pelvis and foot, if you wish.

    After these, I have another 100 or so we can discuss including:

    Levens, AS, Inman Vt, Blosser JA 1948. Transverse rotation of the segments of the lower extremity in locomotion. J Bone Joint Surgery 30-A 859.
    Ryker NJ 1952. Glass Walkway Studies of Normal Subjects During Normal Level Walking. Institute Engineering Research. Univer California, Series 11, Issue 20.
    Saunders JB, Inman VT, Eberhart HD. 1953. The major determinants in normal and pathological gait. J Bone Joint Surgry, 35A:543.
    Inman VT, Man RA 1973. Biomechanics of the foot and ankle. In: DuVries Surgery of the Foot. Ed 3. CV Mosby, St Louis.
    Wright DB, Desai SM, Henderson WH. 1964. Action of the subtalar joint and ankle joint complex during the stance phase of walking. J Bone Joint Surgery, 46A:361.


    By the way Simon, when I suggested you that should read my book, you replied: "I rather eat sh-t than read your book" I would be delighted to send you some. Which do you prefer, cow or donkey?

  32. Just your usual bull variety again I see, Brian. That is more than enough to suffice. If you could show me where in this thread that I have stated that I disagree with Close and Inman?

    Rather, you'll go back to find that my objection was and is with your use of the term "symptom" to describe pronation. Which of the references above says "pronation is a symptom" and should only be considered as "abnormal / hyper pronation" when it occurs in association with external rotation of the shank? You have still not addressed the point I made by citing the Wiliams paper. To reiterate: how can pathology be successfully treated without change in the pronation motion if your contention holds that pronation is a symptom? Nor have you addressed the variation in coupling observed in the Nigg study. I'm not sure why you feel the need for deflection. Nor how you expected me to cite references from chapters within obscure French posturology books and biomechanics literature the 1940's-60's which were in your mind, and where your reading of biomechanics literature appears to have ended, Brian. Nothing like being up-to-date. Perhaps if you could attach one of the chapters by Gagey whom you cite repeatedly above so that we may judge for ourselves how this individuals work supports your world view, and examine their research data, Brian?

    I have a copy of Close and Inman at work, if I get chance I'll re-read it tomorrow and tell you the bits I really do disagree with in light of more modern studies. If memory serves they treat the subtalar joint as a mitred hinge joint with its axis fixed in space. This is obviously inaccurate. But as I said, has nothing to do with your concept that pronation is a "symptom" Brian.

    For the record: http://en.wikipedia.org/wiki/Symptom
    Oh and since you bring it up, I'd still rather eat my own turds than read your book. In fact just reading your posts here is, as ever, making me rather sick.
  33. Brian A. Rothbart

    Brian A. Rothbart Active Member

    Oh and since you bring it up, I'd still rather eat my own turds than read your book. In fact just reading your posts here is, as ever, making me rather sick.[/QUOTE] Simon

    I knew there were people that do disgusting things like that (eating their own defectation), but I didn't realize you were one of them Simon. And if reading my posts are making you sick, why are you reading them?

    Putting all that aside and in all due respect, Simon, it appears that you are the one that is (if I can paraphrase you here) trying to weasel out of this discussion. If you recall, I provided you with the opportunity to supply your own citations. You declined with your usual disparaging statements, so I am supplying my own.

    That being said, do re-read Close and Inman. It might help clarify for you the concept of hip drive. And by the way, when the foot is in a closed kinetic chain, its axis of rotation is fixed in space. And Inmans demonstration of the STJ being a mitered (not mitred) hinge connecting the leg to the foot was a visual (if not somewhat overly simplified) presentation of his concept on coupled mechanics. It becomes even more interesting when they extend that concept to the pelvis.

    Regarding which reference(s) state that pronation is a symptom, I am the one suggesting that pronation is a symptom not a cause of pathology. And I am the one that suggests that pronation should only be considered abnormal when it is linked to external pelvic (not shank, which is part of the human leg between the knee and the ankle) rotation.

    Regarding Gagey, don't be lazy. Read his book and then we can discuss it. And by the way, I am sure you remember his remarks regarding my research on another thread (last year). And also the comment by David Simons, co-author of the two volume medical textbook, Myofascial Pain and Dysfunction. Or possibly you have also read Janet Travell's comments on my research.

    So let's get started with Inman. Waiting to hearing your comments.


    PS Any more juvenile or disparaging remarks from you, will terminate our discussion punto. I'm tired of digressing to your level of behavior. It tires me out.
  34. As ever Brian you lack accuracy the key word being ignored was the word "rather". I said I would "rather" eat my own turds than read your book. It was a a comparative statement demonstrating the utter disgust of the thought of reading your book, by my making a comparison with the thought of another utterly disgusting action.

    I'm reading your posts to stop you spreading your bile without challenge.
    Brian re-read the thread. You said that you could cite papers, I asked you to cite them, you told me to cite them instead- utter madness.

    The subtalar joint axis is not fixed in space during dynamic function, Brian. Read past the 1960's
    Yes I know. It is in my opinion a false premise which is the meat of this discussion. I'll ask again, how can pronation be a symptom of pathology when treatment of the pathology and resolution occurs without change in the "symptom" of pronation?
    Seems to be in French.

    As I said, I'll take a look at Close and Inman when I get to work.

    Like that would be some form of punishment for us all Brian :rolleyes::bash: Don't adopt a patronising tone like that or I'll just tell you to **** off. Regarding the word "mitre", we are not all using American bastardisations of the English language.

    Now, answer my questions please then I might see fit to answer yours regarding Close and Inman.

    Regarding Saunders and Inman and their six determinants of gait, you can see from this paper that this premise is now viewed as somewhat questionable http://www-personal.umich.edu/~artkuo/Papers/HMS07.pdf.
  35. Brian A. Rothbart

    Brian A. Rothbart Active Member


    You have a very unappealing personality. There is no sense trying to maintain a meaningful discussion with you. It is just impossible to do.

    Possibly your behavioral deficits are linked to your insecurities. It appears you attempt to intimidate anyone you feel threatened by.

    Be that as it may, NO MAS y adios.

    Professor/Dr Brian A Rothbart

    PS Just to let you know, I will no longer will be replying/reading any of your ravings (sorry, make that posts).
  36. David Smith

    David Smith Well-Known Member


    Lets get back to the nature of joint coupling:

    Let's consider a steering system (without power assistance) on a car. A well designed rack and pinion system without any wear will result in proportional turning between the road wheels and the steering wheel depending on the rack and pinion gearing ratio.

    When there is wear in ball joints and gearing then some of the steering wheel action is not transmitted to the road wheels, this can be called slack in the system. However taking up this slack does not take much force application since there is little resistive force in opposition, unlike in the unworn system with no slack where the main resistive force is from the friction between road wheel tyres and the road.

    So if the wear allows 10dgs of steering wheel slack before its action acts on the road wheels, then this is also true in reverse i.e. the wheels have the same proportion of movement that is not under the control of the steering wheel and so, especially at speed the car can wander or drift all over the road and I'm sure you have all seen the old movies where drivers are constantly compensating for drift by oscillating the steering wheel, this is due to the use of steering boxes that came before rack and pinion. Those old enough will have experienced this wooly steering in their first cars (of course, as we all know in the UK, all American cars still have this problem and that is why they need such wide roads eh!!:D :rolleyes: )

    Anyway! Now the steering wheel having a solid steel drive shaft acting thru the rack and pinion tends to be to harsh and every little road variation is felt thru the steering wheel. So we put a rubber coupling in its length, in fact we experiment with rubber couplings with varying stiffness/elasticity. This will reduce the amount of road variation feed back thru the steering wheel but it will also introduce some slack into the system but in this case it would be better called force or torque attenuation. The amount of attenuation will increase as the rubber bush becomes less stiff and more elastic (in this case I use elastic to mean stretchy or the force / deformation ratio). Therefore if the rubber stretches further fore the same amount of force (or torque) applied then there will be more slack in the system i.e. when stationary the force/torque required to move the road wheels via the steering wheel is high and so with a less stiff rubber coupling the steering wheel will turn further to get to the point where there is enough torque transmission to start turn the road wheels. At speed when the effective friction on the road wheels is reduced then there will be less slack and more control or drive in the coupling between steering wheel and road wheel.

    This same principle can be applied to the joint coupling in the hip, knee, ankle and STJ. Where the coupling is less stiff and more elastic then there will be less drive between the segment units, where there is slack caused by 'poor design / design tolerances' or wear then there is either no drive or full drive when the rigid surfaces from each side of the joint make contact. NB in this situation where the torque is suddenly applied and there is no built in attenuation device then the peak forces become very high and damage to the material will occur / therefore rubber bushes or elastic tissues are desirable in a system such as this.

    So if the coupling between STJ and tibial shank is very elastic then lots of transverse pelvic rotation will result in little STJ rotation and where the coupling is more stiff then there will be more drive or torque transmission between the two segments.

    If the STJ pronation takes up all the slack due to wear and 'poor design/design tolerances' then there could still be 100% torque transmission due to pelvis rotation but it starts from a different anatomical position, just like taking up the 10dgs of slack in the steering system the steering wheel starts to drive the road wheels from a new or different start position. In the foot tho this new position will or may effect the mechanical advantage of the relative levers and that is another consideration outside what I'm think about now.

    any takers?

    Regards Dave Smith
    Last edited: Nov 11, 2011
  37. Dave, if we take the ankle as an example and the bone pin studies of Nester and his Swedish friends, is it really slack in the system or is it just that we'd previously assumed that the frontal plane motion occurred at the STJ and not at the ankle because we didn't really have the means to study it well enough back in the days of Inman?


    See also:
  38. David Smith

    David Smith Well-Known Member


    Partly yes but
    There clearly is coupling between tibial rotation and STJ pronation/supination. I would say that it is a mixture of slack/stiff coupling, elastic coupling and geared coupling and this varies between individuals.

  39. efuller

    efuller MVP

    In terms of hip/pelvis drive of the STJ, looking at Close and Inman is looking at the wrong end of the leg. Even if there were good coupling of the tibia and the STJ, there is still the problem of the other end and the "drive shaft." The knee is really poor at transmitting transverse plane torque and the hip has a huge range of motion in the transverse plane relative to the femur. For the pelvis to the drive the femur, by passive mechanisms, the hip has to be at its end of range of motion. This happens very rarely in walking.


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