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Relative Importance of STJ Motion

Discussion in 'Biomechanics, Sports and Foot orthoses' started by EdGlaser, Nov 23, 2010.

  1. EdGlaser

    EdGlaser Active Member


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    To evaluate anything is assigning it relative value, merit or importance.

    In the field of foot biomechanics, the STJ axis has been given considerable importance.

    In this thread I would like to give the logic as I presented it at the debate in Chicago.

    I spent a lot of time and effort trying to understand all of the approaches and then stand back and analyze the major differences in theory and approach.

    As far as I can see, Dr. Merton Root, used a brilliant approach, trying to correlate measurable structural differences with the presence of pathology. His discovery of Neutral position was certainly his greatest accomplishment. Some feel that Rootian biomechanics is dying. I do not. After my recent research at the Smithsonian, I have come to the conclusion that Merton Root actually did come up with the correct rotational position around the STJ axis. Understanding that statement will take me considerable explanation. Please allow me to explain.

    Firstly lets examine the magnitude of STJ motion.
     

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  2. EdGlaser

    EdGlaser Active Member

    Root estimates (this may actually be Wright's, Inman's or Isman's data.) that in the ideal gait cycle, the STJ axis should move a total of Six Degrees. This is Six Degrees. It is an incredibly small rotation. I understand that people who over pronate often have more but since an orthotic should be taking us from the existing gait cycle closer to the ideal functional gait cycle. The ROM of the ideal becomes relevant as we approach the ideal for that individual (given their anatomy).
     

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  3. EdGlaser

    EdGlaser Active Member

  4. EdGlaser

    EdGlaser Active Member

    At our recent trip to the Smithsonian, we put together hundreds of STJ's and you could feel where the worn pathway of motion had occurred over a lifetime. Most STJ had a ver limited ROM.
    This one had a little more than usual.

    The next one would hardly move at all.
     

    Attached Files:

  5. EdGlaser

    EdGlaser Active Member

    Dr. Matt Tocheri did his Phd on primate hands and feet and is one of the top experts in this field. He confirmed that a similar lack of ROM is present in most primates including the Mountain Gorilla Foot he is holding.
     

    Attached Files:

  6. EdGlaser

    EdGlaser Active Member

    This is a cadaver study where sensors were attached to the foot bones as pictured below.

    They attempted to simulate a barefoot step. I know that these studies have their limitations. Small "n" etc.

    But the results were surprising.
     

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  7. EdGlaser

    EdGlaser Active Member

    The STJ in this study showed very small frontal plane motion.

    That is really what one would expect given the geometry. Put a talus on its calcaneus and try to move it in the frontal plane. It really just doesn't happen much.
     

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  8. EdGlaser

    EdGlaser Active Member

    What was also surprising was the lack of motion in most of the stance phase of gait.

    The STJ did almost NO rotation between 25% - 90% of the stance phase of gait.
     

    Attached Files:

  9. EdGlaser

    EdGlaser Active Member

    In MASS Theory we have proposed a classification of Postural Zones of the foot based on where the STJ axis has translated during Gait. We have one zone called the Dysfunctional Zone where there is little or no STJ Rotation and where the arch is low enough to cause considerable repetitive impact between the foot and the orthotic. It is the reason, in my mind, that arch fill was invented. There is no real science behind it . Less Warrantees for labs. We have noticed that when an orthotic falls about 3/16" below MASS Posture in its apex, the patient experiences arch pain. We feel that it is due to repetitive impact. That is why high arched devices were always considered uncomfortable. Experience told most doctors, if they gradually raised the arch above arch filled Neutral, it would begin to cause arch pain.
     

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  10. EdGlaser

    EdGlaser Active Member

    So the total rotation of Six degrees occurs before the forefoot is weight bearing at all.

    Only the friction between the heel and the ground is governing this motion. Along with the moments from the GRF and the Force vector coming down the leg.
     

    Attached Files:

  11. EdGlaser

    EdGlaser Active Member

    In the functional zone, when the anterior facet of the STJ is near or is level, the talar head can more easily externally rotate and begin to articulate with the anterior facet. This articulation can effectively block sagittal plane motion between the talus and calcaneus. This way contraction or resistance to further elongation of the Gastroc Soleus will cause ankle axis rotation and more efficient propulsion.
     

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  12. EdGlaser

    EdGlaser Active Member

    This is a video that shows the six degrees of motion in the giant foam bones.
     

    Attached Files:

  13. EdGlaser

    EdGlaser Active Member

    What the STJ lacks in rotation, it more than makes up in translation of the axis.

    From Heel strike to full pronation we have measured substantial changes in STJ sagittal and transverse plane displacement.

    These are videos showing that there could be 30 or more degrees of translation during typical gait.
     

    Attached Files:

  14. EdGlaser

    EdGlaser Active Member

    This forward roll is around an axis that is caused by having a round heel. If you imagine the heel as a tennis ball, any axis that passes through the center of the ball will be a valid axis for heel rocker motion. The heel rocker mechanism was first described by Dr. Perry in
    her book Gait Analysis. John Weed et al described the motion in 1989 in Theorem of Foot Compensation #1.
     

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  15. EdGlaser

    EdGlaser Active Member

    I guess we could call that axis the Heel Rocker Axis of Perry..... or Heel Rocker Axis for short.

    When we took several high speed medial to lateral movies of the foot taking a gait cycle and slowed them down the extent of the STJ axial translation could be roughly estimated.

    In this foot, a marathon runner, the STJ axial translation changed approximately 33 degrees.
     

    Attached Files:

  16. efuller

    efuller MVP

    Ed,
    Remember back to High School English when your teacher said "when you write an essay, state what you're going to say, explain it and give examples/data, and then say what you said." Ed, what are you trying to say? Is it that STJ motion is not very important? In 9 posts you given us a lot of data, but no explanation of where you are going with this. Nice pictures though.

    Eric
     
  17. EdGlaser

    EdGlaser Active Member

    So the six degrees of motion can be considered a simple sagittal plane lock and unlock that typically occurs when the foot is in a supinated posture where the anterior facet is approaching level. It requires a certain degree of postural supination to create its proper effect as a locking mechanism. Subtalar rotation in a more pronated posture therefore will be of limited consequence. It is at the end of STJ ROM and has to fight an uphill climb on a tilted anterior facet for any external rotation to occur.
    Calcaneal eversion can be an additive hurdle to jump, making resupination even more difficult in this posture. Re-Supination Resistance is very high in the over pronated foot at midstance.
     

    Attached Files:

  18. EdGlaser

    EdGlaser Active Member

    But lets examine the major forces entering the foot and their relation to the STJ and Heel Rocker Axes.

    The axes are picture here with the bones semi-transparent.
     

    Attached Files:

  19. EdGlaser

    EdGlaser Active Member

    The STJ axis exits the foot on the posterior lateral calcaneus. The foot ideally heel strikes in Supination which puts the heel slightly inverted. That causes heel strike in most people to occur on the lateral aspect of the heel bone. Ideally, then the GRF passes directly through the STJ axis. Of course this may vary on some bell curve but when you correct the gait cycle, This should be pretty close. The GRF was obviously not intended to have a major moment around the STJ axis.
     

    Attached Files:

  20. EdGlaser

    EdGlaser Active Member

    If we now examine the momentum coming down the leg..... another interesting situation is apparent. The force traveling down the leg and entering the foot near the center of the talar dome passes very close or right through the STJ axis. Again there is little or NO moment arm and therefore moments around the STJ axis are minimal at best.
     

    Attached Files:

  21. EdGlaser

    EdGlaser Active Member

    Just looking at axes and forces it looks like this.
     

    Attached Files:

  22. EdGlaser

    EdGlaser Active Member

    Now lets examine the Moment arms around the Heel Rocker Axis.

    They are Huge by comparison. The Magnitude of difference....doing crude math with crude measurements I estimate between 25 and 100 times the moment occurs with the moment arm of the Heel Rocker as compared with the STJ. That is a sizable magnitude of difference.
     

    Attached Files:

  23. EdGlaser

    EdGlaser Active Member

    That is one very large rotational moment (relatively).
     

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  24. EdGlaser

    EdGlaser Active Member

    But a look at the GRF moment around the Heel Rocker at Heel Strike shows that it is in the same direction......an additional moment additive to the moment caused by the force down the leg.
     

    Attached Files:

  25. EdGlaser

    EdGlaser Active Member

    So, at heel strike the moments created by the major forces entering the foot both pass through or near the STJ axis with tiny moments. Meanwhile the Heel Rocker axis is experiencing, by comparison, massive moments. I would go so far as to say that the STJ axis is purposely placed in an orientation to the foot as to have little or no rotational influence by the major forces that pass through the foot at heel contact and through much of the gait cycle as you look closer.

    Whereas the Heel Rocker axis is pushing hard in the direction of a more flattened foot posture.
     

    Attached Files:

  26. EdGlaser

    EdGlaser Active Member

    But, if the STJ has no eversion, then why do we see the calcaneii everting in pronation?
     

    Attached Files:

  27. EdGlaser

    EdGlaser Active Member

    There are three reasons.

    First, the angle of gait combined with the direction of the heel rocker axis can cause considerable eversion. I may need to make a simple video to explain this better. Just try rotating the imaginary heel rocker axis and see how it effects calcaneal eversion.


    Second, if you take a STJ axis that primarily moves in the transverse plane in supination and then roll the calcaneus forward....a portion of the transverse motion becomes frontal plane.

    Third, the calcaneus is merely being pushed out of the way laterally to yield to the far greater moments occurring around the Heel Rocker Axis.
     
  28. EdGlaser

    EdGlaser Active Member

    My grand daughter is spending the night and I have grandparent fun to have. So I will continue .....there is lots more.......tomorrow.

    Ed

    You might want to hold comments till the end....because I might be getting right to your point.
     
  29. Righto.

    I'm really glad to see this thread! There is some good biomechanical meat here, well laid out and thoughtfully presented. I'm grateful to ed for taking the time.

    I look forward to a sensible and respectful debate at it's conclusion!

    This is much more like it!
     
  30. EdGlaser

    EdGlaser Active Member

    Thank you Robert.

    I have the pleasure of giving out holiday bonuses today. It is always a fun day at our company. I dress up like Santa, we have a free lunch day, give thanks and have a company wide meeting where we recognize the accomplishments of our team members, leaders and executives.

    I will continue this thread this evening. There are a lot more pieces to this puzzle.

    Ed
     
  31. EdGlaser

    EdGlaser Active Member

    Eric,
    Instead of giving you my conclusions, I would rather give you the data and let you draw your own conclusions. At the end, I will tell you what I have gleaned from the data and I accept that each practitioner will come at the data with their own preconceived notions and experience and make up their own minds.

    Ed
     
  32. Griff

    Griff Moderator

    Ed,

    I'll give you one thing dude - you've got some nice slides. Keep em coming!

    Ian
     
  33. EdGlaser

    EdGlaser Active Member

    Single Axis theories by definition ignore the rest of the foot. What about the other 34 joints of the foot? Don't they participate in gait.

    In Dr. Kirby's article: Subtalar Axis Location and Rotational Equilibrium Theory he gives a justification for using one axis: "
     

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  34. EdGlaser

    EdGlaser Active Member

    In this article by Wolf, Nester 'et al. They gathered data to determine the presence of functional rigid units in the foot. Their data showed something different.
     

    Attached Files:

  35. How much ankle plantarflexion from heel strike? According to the graph on p.53 of Perry's book (Gait analysis normal and pathological function), the mean seems to be about 6 degrees.

    How much STJ eversion did Bart van Gheluwe see in elite high-jumpers.
     
  36. EdGlaser

    EdGlaser Active Member

    Sorry that I must go now to get ready for my Santa gig. I wish you all, a happy Thanksgiving. In the US it is a holiday where we give thanks for all of the good things that have happened to us this year. We have a lot to be grateful for.

    I want to personally thank everyone who is reading or contributing to this thread and the arena in general and Dr. Craig Payne for giving us the opportunity to share our ideas on this forum. I wish all of you a happy and healthy year ahead.

    In America we have a lot of liberty. We are free to criticize openly. When I see people arguing, say ....about politics for example.... what I see, is people who care enough about their country to vocalize their opinions. I see patriotism on both sides of the argument. Although I disagree vehemently with what someone says, I will defend to death their right to say it.

    How does this apply. I am glad that there are people, both in agreement and disagreeing about biomechanics because it shows you care. I have always been about one thing....Making People Better. Whether you agree or disagree with my MASS approach we are on the same side...... the side of Helping the Patient. For that I am thankful.

    Ed
     

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  37. EdGlaser

    EdGlaser Active Member

    Because ankle plantarflexion is measured relative to the tibia, and the tibia is moving forward with the forward roll of the calcaneus there will be less measured plantarflexion than one might expect. I agree.

    But you do point out the inherent weakness of choosing any one axis.

    I will review Bart's article. I have seen slow motion videos of some elite high jumpers and the amount of eversion I saw was staggering. It actually is somewhat stomach upsetting to watch. It seems that when enormous moments occur around the heel rocker axis repeatedly, the calcaneus really gains more and more ROM in eversion and the calcaneus can be pushed out of the way.....way way out of the way.
    Certainly some of that motion is occuring at the ankle joint as well.

    Really gotta go now.

    Ed
     
    Last edited: Nov 24, 2010
  38. Or indeed, in trying to maintain that anyone joint is more important than another. Anyway, lets play on for a while...

    So we have 6 degrees at the STJ (sometimes) and 6 degrees at the ankle (sometimes). So that would seem about equal, right?

    What proportion of the eversion range is used in the 1st half of the contact phase in normal walking? What proportion of the plantarflexion range is used in 1st half of the contact phase in normal walking?

    This paper gives some clues regarding eversion: http://www.japmaonline.org/cgi/content/abstract/95/4/376

    Anyone have a figure for the average passive plantarflexion range at the rearfoot?

    I'm guessing that the proportion of the eversion range employed will be greater than the proportion of the passive plantarflexion range employed during this phase of gait. So which is more important? After all, this thread is entitled: "the relative importance of STJ motion", as oppose to: "Ed Glaser attempts to discredit Prof. Kevin Kirby". Right, Ed?
     
  39. David Smith

    David Smith Well-Known Member

    Ed

    I appreciate that you are spending a lot of time in research of a kind, However I feel that you are trying to prove your point rather than carry out unbiased investigation.

    It may be true and observable and repeatable that the saggital plane rotation of the STJ complex may be much greater that the frontal plane rotation (if you want to constrain your variables into a single plane reference system) but it is also true that the frontal plane excursion of the knee becomes greater with knee flexion, However it would be absurd to suggest that to stop knee injuries due to excessive strain of the contralateral ligaments one should brace the knee into a rigid extended position or even restrict or increase the stiffness of knee flexion in anyway. Which is kind of what you suggest regarding the plantarflexion of the STJ.

    Regards Dave
     
  40. Ed, according to Bart's paper he was measuring motion of the calcaneus about the talus. In which case it was the subtalar joint exhibiting these huge eversion ranges of motion and the huge moments he was looking at were about the subtalar joint axis as oppose to this "rearfoot rocker axis" of which you speak.

    "The pronational angular displacement and velocity were calculated for all jumps and reached maximal values close to 30°, respectively 2000°/s." Which is obviously a lot more than the 6 degrees which you picked up from Root- right?.

    P.S. it's been a while since I looked at the seminal works on the STJ axis, can you remind me just how many millimetres translation per degree of rotation was reported to occur between the talus and calcaneus during rotation about it's axis?
     
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