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Talking like an engineer

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Asher, Oct 28, 2008.

  1. Asher

    Asher Well-Known Member

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    Hi there

    Previous threads have encouraged us to think more like an engineer. I have been doing this but when it comes to my patient notes, I am generally using the same old descriptions, like flat feet and excess pronation.

    In an attempt to explain myself in my patient notes in a more appropriate manner, I have a few of the descriptions I often use listed below. I would like to get used to using descriptions that show that I am thinking and talking more like an engineer as these sound sub-par.

    Flat feet
    High arches
    Hyperpronated at stance
    Excess pronation during gait
    Tight calf
    Flexible plantarflexed first ray ( I now say complaint)
    Rigid plantarflexed first ray (I now say stiff)

    I believe it is proper to describe things as ‘increased stiffness’ or 'increased pronation moments' but to me, it seems weird to say that because saying ‘increased’ means you are comparing it to something. What are you comparing it to, normal feet, I doubt it? But I am so no authority so would like some guidance please.

    Any advice would be appreciated.
  2. efuller

    efuller MVP

    An engineer still has to describe the anatomy.

    These are still good. If you want more description you could measure the height of the arch to be more accurate. There are some engineering characteristics that are related to arch height, but a convenient short hand to describe these engineering charactaristics is high arch or low arch. (The charactaristic is related to the joist effect. A board that is loaded vertically will be stiffer with its longest surface vertical as opposed horizontal) A foot with less dorsal plantar thickness will tend to be more flexible than a thicker dorsal to plantar thickness foot.

    I don't know what hyperpronated is. Again, you can describe the anatomy. For example you could describe the position of the talus relative to the foot. You could describe the position center of the leg relative to the center of the heel.

    It took me a while to realize that when some of my instructors in podiatry school were talking about STJ pronation, they were including midtarsal joint forefoot abduction on the rearfoot. So it is important to make the distinction of which joint you are talking about. Or combining them together you could describe rotation of the leg relative to the foot.

    When talking about pronation, you can be talking about the velocity of pronation, the total range of motion of pronation, the furthest everted position and even the pronation moment from the ground. You could talk about one of or more than one of those pronation measures. You could also talk about the timing of the proantion. Is it occurring around the time of forefoot loading, or is it occurring around the time of heel off (late midstance pronation).

    Excessvie is a tricky word. Normal is a tricky word. (Excessive would be more than normal, but what is normal.) That said, I agree with Root et al that the ideal gait would have external leg rotation relative to the foot between full forefoot loading and heel off. However, this is still a value judgement without any evidence that I'm right.

    More thoughts later.
  3. Rebecca:

    I am careful in my medical charts to use terminology that would be consistent with the prevailing medical terminology of my community, and not use strictly mechanical/engineering terminology. I tend to decrease the usage of mechanical/engineering terminology in my medical charts because these medical-legal documents need to be understood by other physicians, claims adjusters, and attorneys. However, when I am writing on Podiatry Arena or writing for the podiatric community, I "switch gears" to the most unambiguous terminology that allows me to communicate my ideas with optimum clarity. So basically, I speak several "languages" depending on the audience that I am communicating with and depending on the intended purpose of the document I am preparing.

    By the way, the term "hyperpronated", in my opinion, is worse than the term "hypermobility". Why not just say "excessively pronated"?
  4. Admin2

    Admin2 Administrator Staff Member

  5. efuller

    efuller MVP

    Some more thoughts:

    First ray rigidity is such a functional thing. Does the first ray bear significant load in stance. (The ray includes the hallux in my definition.) One of the Root et al theories had that a rigid plantar flexed first ray would cause STJ supination in compensation for that. I'm not so sure about what causes what in this case. The first metatarsal head will be medial to the STJ axis in a laterally deviated STJ axis foot and it will be lateral to the STJ axis in a medially deviated axis foot. So, depending on where the STJ axis is, force on the first met head will do different things in different feet. In a more medially deviated axis foot the force on the first met head will cause STJ pronation, if there is range of motion available additional pronation motion will tend to increase the force sub first met head. With this situation, over time, the rigid 1st met could be strained and become more "flexible" or have increased range of motion.

    This is leading to one of the problems I have with just concentrating on stiffness of the 1st ray and of the ankle (tight calf). This could be a whole other thread.

    Stiffness is a measure of motion relative to the force applied. If you plantar flex the ankle maximally and then apply a force to the bottom of the foot, you will dorsiflex the ankle until stiffness increases. We still need to assess where this stifness increase occurs. In the old thinking we looked at whether or not this stiffness occured before or after the plantar surface of the foot was 10 degree dorsiflexed relative to perpendicular. The problem we still have is how stiff (how much force to apply) when we take the measure. The ankle joint will have an increase in stiffness at some point, it may be 20 degrees dorsiflexed. So, the position of the ankle (or first ray) is in when it becomes stiffer is functionally important.

    Under the old paradigm we looked at what caused the increase in stiffness. I think this still important. The increase in stiffness could be from the gastroc, soleus or bony impingement. And this is at the "end of range of motion." This doesn't examine the fact that there can be variable stiffness because of variation of the activation of the muscle. You can choose to toe walk some of the time. However, I still feel there is some clinical relevence to the passive end or range of motion (position of increase in stiffness) of the ankle. So, to answer the charting question you could say there is an increase in stiffness at 5 degrees of dorsiflexion.

    You asked this question in regards to charting. This is an interesting thought. What do we do with the information that we chart. One thing we do is chart so we won't be accused of insurance fraud (in the states anyway.) Since we are in the biomechanics sports part of the arena, I'll concentrate on that. We chart so that we don't have to repeat the same thought process over again. "What was I thinking?" If the treatment did not work sometimes we should repeat the whole process over again. Another reason that we chart is that we want to be able to defend against a lawsuit. So, we chart so that we can remember what our thought process was in what was done to treat the patient. So, we need to look at the measurements and observations in terms of how they effect what we did.

    A lot of what I do is based on STJ axis position, so I usually document that relative to an average axis location. If I'm making an orthotic I will measure arch height, otherwise I won't chart it. If I had a lift I will chart limited ankle dorsiflexion. (I still haven't shifted over to stiffness on this one.) I certainly will chart which anatomical structure hurts. I usually do not chart 1st ray stiffness. I will chart that I added a reverse Morton's extension of if there is a long 2nd I'll chart that and use a valgus wedge. If I have to replace the top cover a year later I will know what needs to be done and why.

    That is an interesting question. What findings do people find important to chart and why?

    Eric Fuller
  6. Asher

    Asher Well-Known Member

    Hi Eric

    Fair enough


    Hmm, I've been using that one for years, I'm embarrased to say!

    Instead of having to write all this down, doing the Foot Posture Index will give you all this information.

    Thanks Eric.

    My initial question in regard to 'charting' as you call it, refers mainly to performing a quick and basic but informative mechanical assessment of the foot, not so much for a full biomechanical assessment.

    I think I'm going to go with the FPI a bit more than I do currently and expand on that if anything relevant shows itself.


  7. Asher

    Asher Well-Known Member


    I'm more comfortable now in describing what I see in relatively non-engineer terms. But I think it would be appropriate in my charting 'Diagnosis' or 'Thoughts at this stage' section to talk more like an engineer.

    For example, instead of saying: Plantarfasciitis caused by flat feet and tight calf.

    I could say: Plantarfasciitis due to increased tesile force in plantarfascia caused by ... (just realised I don't know how to explain why flat feet increase plantarfascia tensile force)... and increased rearfoot plantarflexion moments of tight calf.

    I realise this sounds a bit over the top, but this engineering stuff doesn't come all that naturally to me and I want to keep thinking like an engineer so I don't lose it. Please help! :eek:


  8. Rebecca:

    When I was in my Biomechanics Fellowship in '84-'85, I would write as much as I could about the foot mechanics of my paitnets in their charts to help me think through why the patients had a more pronated foot or had their symptoms, for example. This, I think, did help me with my thought processes and the further development of my theories. Whether you write your thoughts in your patient's charts, or write on Podiatry Arena or for some other podiatry publication, the more you write and think about the subject, the better you will get at doing it.

    Flatter medial longitudinal arch contours will increase plantar fascia tensile force since a flatter foot will need increased plantar tension in its plantar ligaments and plantar fascia in order to maintain equilibrium of the arch contour when compared to a higher arched foot. Think of it as the flatter foot having increased rearfoot plantarflexion moment and as having increased forefoot dorsiflexion moment when compared to the higher arched foot.
  9. Asher

    Asher Well-Known Member

    I have re-read the Anterior Cavus thread where Kevin suggested instead of saying limited AJ dorsiflexion, we could more accurately be reporting the Ankle-foot dorsiflexion stiffness. The dorsiflexion that occurs could be coming from any one or combination of the midfoot joints and / or from stretch in the gastroc-soleus complex. How much is coming from where? When I test nwb AJ dorsiflexion, if it doesn't reach 10 degrees, I chart 'tight calf' ... that is so wrong. But I would be right in saying 'high ankle-foot dorsiflexion stiffness'. And this is the clinically relevant measure, is it not?

    I pretty much only look at what is relevant to the patients problem, be it a corn, plantarfasciitis or whatever. I look at:
    o Structural things (adductovarus toe, arch height / contour, plantarflexed 1st ray, anterior cavus, metatarsal length)
    o ROM / stiffness things (tight calf, is plantarflexed 1st ray stiff or compliant, is anterior cavus stiff or compliant)
    o Kinetic measurements (Jack's test and supination resistance test)

    and then put all that together to see what forces could be causing the symptoms and what I can do to reduce those detrimental forces.

  10. Asher

    Asher Well-Known Member

    Understood Kevin, thank you.
  11. Asher

    Asher Well-Known Member

    How do I explain the effects of a tibial varum on the subtalar joint - like an engineer?

    Left to my own devices, I would say something like: Tibial varum causing a more lateral heel strike which leads to increased STJ pronation. STJ functioning at end of pronation range.

    Thanks for any help.

  12. efuller

    efuller MVP

    Hi Rebecca,

    This is more geometry than physics. Tibial varum doesn't really change the moment from ground reaction force about the STJ axis. What it does do is decrease the amount of eversion range of motion. Therefore, the STJ will tend to sit closer to the end of range of motion in the direction of pronation. There is increased liklihood of compressive force in the floor of sinus tarsi, but you should still look to see if in static stance the STJ is at its end of range of motion.

    I hope this helps.

  13. Graham

    Graham RIP


    Seeing as there is no correlation between static measurements of: Tibia to ground, heel to ground, and tibia to heel, and stance position and/or dynamic function/compensation, how important is an apparent tibial varum when considering dynamic function and treatment protocols?

  14. Rebecca:

    Tibial varum will, basically, tilt the whole foot into a more inverted posture which will invert the rearfoot and forefoot relative to the ground. An inverted calcaneus, when barefoot, will cause the plantar calcaneus to be more medial to the STJ axis so this will increase STJ supination moment. An inverted forefoot will cause the lateral forefoot to hit the ground sooner which will cause an increase in STJ pronation moment. Therefore, with these mechanical factors in mind, with increased tibial varum, one might expect increased lateral shoe wear, earlier STJ pronation motion, but a more stable rearfoot (due to the more inverted calcaneus) that tends to resist the tendency to have a significantly medially deviated STJ axis.
  15. efuller

    efuller MVP

    There is a problem with inaccuracy of measurement in terms of calcaneal motion relative to the leg and leg to ground. However, the concept is still valid. At some point you run out of range of motion as you attempt to evert the foot. However, the available range of motion in static stance is probably very loosely corelated with the magnitude of tibial varum. So, I would not consider tibial varum vary important. I would consider a measurement that I call maximum eversion height much more important. The maximum eversion height is the hieght off of the ground of the lateral forefoot when the patient is asked to evert their foot without moving their leg. Some folks can get inches, some folks can't budge it off of the ground.

  16. bob

    bob Active Member


    You want to talk like an engineer?

    Check this out:

    Fred'll 'ave yer talkin' like an engineer in no time at all, 'appen!

    Eeee, by 'eck!
  17. Asher

    Asher Well-Known Member

    Hi Eric,

    Thank you for your reply. Could you please explain two things that I don't understand.

    OK, so you are saying that tibial varum doesn't change kinetics (force) at the STJ, it changes kinematics (motion). I can accept that. But I don't understand how tibial varum reduces the amount of STJ eversion that occurs.

    Now it sounds like you are saying that the STJ will pronate more towards pronation.

    Can you explain further? Thanks!

  18. Asher

    Asher Well-Known Member

    Hi Kevin,

    I am properly confused, could you please explain further?

    I think I'm missing something here. Do you mean more lateral. Something more lateral to the STJ axis would increase the STJ supination moment.

    Why earlier STJ pronation motion? What do you mean by more stable rearfoot?

    Thank you Kevin.
  19. Asher

    Asher Well-Known Member

    Hi Eric

    I can't see why the 'maximum eversion height test' is more revealing than identifying the presence and extent of tibial varum. The maximum eversion height test is not an indicator of STJ pronation range only, it involves movement within the midfoot also. I use it when I am contemplating a valgus forefoot extension to see whether it would be tolerated, but can't see why I would use it to tell me anything about the STJ.

    Thanks for any advice you can give me.

  20. efuller

    efuller MVP

    I can see why my statement confused you. I didn't talk about eversion of what relative to what. I'm talking about eversion of the calcalaneus to the ground. Tibial varum will decrease the amount of available eversion of the calcaneus relative to the ground. With increased tibial varum there will be less eversion of the calcaneus available because the STJ will be in a more pronated position.

    The above was talking about calcaneus to leg pronation.

    Does that help?

  21. efuller

    efuller MVP

    Hi Rebecca,

    Again, Kevin and I were writing a little fast and did not say what relative to what. When talking about STJ moments you need to know two things: the positoin of the STJ axis and the position of ground reaction force. So with increased tibial varum there is a tendancy to increased inversion of the whole lower leg. With inversion of the whole lower leg the contact point with the ground will be more medial and the STJ axis will be more lateral. That will increase supination moment.

    I'm not sure what Kevin meant by earlier STJ motion.

  22. efuller

    efuller MVP

    When John Weed taught, at CCPM, the measurements of tibial varum, calcaneal eversion to leg and calcaneal eversion to ground we would often calculate whether or not the STJ was at the end of its range of motion. As a student, and then as a clinical instructor I would actually try and use these measurements to calculate and see if they came out right. It became very frustrating because of the measurement error. Then I thought about what the purpose of the measurements. What do you do with the information?

    The foot functions differently when at the end of range of motion of the STJ. You are much more likely to get sinus tarsi pain if the STJ is at the end of range of motion than if it's not at the end of range of motion.

    Also, the measurements were important in prescription writing variables. A person could have a forefoot valgus and a rearfoot varus (or a large degree of tibial varum). The forefoot valgus would tend to supinate the STJ away from the end of range of motion and the rearfoot varus would tend to put the STJ toward the end of range of motion of pronation. Using the calculations from the measurements you could not figure out the eversion of the forefoot off of the ground even with perfect measurements. This is important for the amount of forefoot valgus intrinsic post in your orthotic. Too much forefoot valgus post will cause sinus tarsi pain by attempting to get more eversion out of the STJ and forefoot than there is available range of motion.

    Why not look right at the foot for the available range of motion. That is what maximum eversion height is. At the same time, if you are looking from behind the person, you can observe calcaneal motion. If the calcaneus does not evert it is maximally pronated. You may see internal leg rotation without calcaneal eversion when there is MTJ motion, but not STJ motion. So, maximum eversion height does tell you something about the STJ.

    I have to admit that I do think tibial varum is important in a slightly different way. The position of the center of the knee relative to the position of the center of pressure under the foot will determine the frontal plane moment acting on the knee. When you shift the center of pressure under the foot to change STJ moments, you are also changing the frontal plane moment on the knee. If someone has a large amount of tibial varum and pronation related problems, you can increase frontal plane moment at the knee and cause knee pain as you reduce symptoms in the foot.

    Those are clilnical decisions that I make that involve tibial varum. Do you use the tibial varum measurement to make any other decisions?


    Last edited: Nov 28, 2008
  23. Probably the best way to analyze the effects of a structural deformity such as tibial varum is to look at its effect on the foot compared to a vertical tibia. When compared to a vertical tibia, having a tibial varum deformity will increase the inverted position of both the rearfoot and the forefoot relative to the ground. When the rearfoot is inverted, then the inferior aspect of the calcaneus (where ground reaction force (GRF) acts) becomes more medially positioned relative to the superior aspect of the calcaneus (where the subtalar joint (STJ) axis is located). Because of this inverted rearfoot position, the medial calcaneal tubercle becomes more medially positioned relative to the STJ axis so that now, when GRF acts on the plantar calcaneus in the tibial varum deformity, there will increased STJ supination moment when compared to a vertical tibia.

    However, a complicating factor with tibial varum is that the inverted forefoot that results will tend to cause an increase in STJ pronation moment since now the GRF acts more laterally on the forefoot at initial contact of the foot with the ground. The increase in laterally positioned GRF on the forefoot causes an increased STJ pronation moment which will, nearly always, be of greater magnitude than the STJ supination moment resulting from the inverted rearfoot. As a result, the net external STJ moment (i.e. from GRF) at the instant of forefoot contact in the limb with a tibial varum deformity will be a STJ pronation moment which will cause an acceleration of STJ pronation, unless there is an internal STJ supination moment that is resisting this external STJ pronation moment. Pronation will continue to occur until the medial forefoot contacts the ground and balances out the STJ moments or pronation will continue until some other internal source of STJ supination (i.e. posterior tibial muscle tensile force, sinus tarsi compression force) stops the pronation of the foot.

    Below is an illustration from a newsletter I wrote on this subject over 10 years ago, in much greater detail, in my November 1998 Precision Intricast Newsletter titled "Effects of Tibial Varum and Rearfoot Varus on Foot Function" (Kirby KA: Foot and Lower Extremity Biomechanics II: Precision Intricast Newsletters, 1997-2002. Precision Intricast, Inc., Payson, AZ, 2002, pp. 123-126).

    Hope this helps.
    Last edited by a moderator: Nov 30, 2008

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