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Foot orthotic calibration - the science

Discussion in 'Biomechanics, Sports and Foot orthoses' started by mike weber, Dec 12, 2010.

  1. Members do not see these Ads. Sign Up.
    Over on another thread which I won´t link to due the nature of the discussions at the moment , there has been some intersting discussion about orthotic calibration.

    It has got me thinking I would like to know more.............

    Simon Spooner wrote an orthotic can only there are ultimately three characteristics of a foot orthosis which can have a direct influence on the foot's kinetics: it's coefficient of friction; it's surface geometry ; it´s stiffness.

    Now if we take a foot which we want to provide a supination Orthoic reaction force too ie external supination moment. Instead of taking an educated guess on how much force to use it might be great to calibrate the device to give the required force- not too much not too little.

    So what would influence the amount of force a device can provide.

    stiffness of the shell
    shape of the shell
    friction of the shell

    What other information would influence the calibration of the shell - the internal and external pronation moments verse the internal and external supination moments - right ?

    So if we take a foot what information would we need to have to know the amount of extra force required to supinate the foot ?

    and then how do we design the device to provide this exact force ? and when might you increase friction verse increase shell stiffness.

    Something that I was thinking about today - if we take a 5 mm bit of poly, put it under load record when it flexs - then take the same poly and heat it and bend it put it under load record when flexs the bent poly should take more load until it bends.

    see picture

    so the same will occur in our device, but is there a hape which becomes less stiffness ?

    Also a request can we keep product names out of the discussion and refer to a device, orthosis, orthotic etc.

    I guess thats a place to start.

    Attached Files:

    • poly.jpg
      File size:
      15.3 KB
  2. Re: orthotic calibration - the science

    Mike, see images attached: first is a device which is lower in the medial longitudinal arch; second is a device with a relatively higher medial longitudinal arch section, both are the same material, both are loaded uniformly with the same load. Note the differences in displacement under load. Kevin wrote a newsletter on this some years ago. In terms of what else is needed: stiffness of the medial longitudinal arch of the foot during dynamic function would be a good start; factors that will influence this: internal moment, joint axial positions, body-weight, arch structure etc.

    Anyway, here's some pretty pictures:

    Attached Files:

  3. Re: orthotic calibration - the science

    Yet, my years of having Kevin as a mentor make me say this: first we need to define what exactly is orthosis calibration? Please define "calibration"... "calibration" in terms of what? Shell width? Root was doing that way back in the day, as I'm sure others were too; calibration in terms of rearfoot posting angle? forefoot posting angle? etc. All been done for years. So when you get someone saying "I'm the first to calibrate", you got to take that with a pinch or seven of salt and a pound or twelve of sales hype, and way too much mass around their waists- right? In answer to the question: "What do we do here?": eat too many doughnuts, and don't take enough physical exercise, by the looks... Nice posture, BTW.

    I've always preferred the term "orthosis optimisation".

    Attached Files:

  4. Re: orthotic calibration - the science

    Orthtosis precription optimisation works for me.
  5. Re: orthotic calibration - the science

    The newsletter which Dr. Spooner refers to was my February 1990 newsletter, titled "Factors Affecting Foot Orthosis Stiffness" which I am providing to all of you below from my first Precision Intricast Newsletter Book.

    I suppose then that since I wrote this newsletter nearly 21 years ago, way before Ed Glaser started marketing his hair-brain idea about MASS insoles, then maybe he wasn't either Wilbur or Orville Wright, but maybe Ed Glaser is more like The Marquis de Bacqueville. :rolleyes:

  6. Admin2

    Admin2 Administrator Staff Member

    Re: orthotic calibration - the science

    I have cut n' pasted some of the messages from that thread:
    (link to other thread)
  7. RobinP

    RobinP Well-Known Member

    I was about to start another thread with this query, then I found this one and hope it is appropriate.

    I was uber impressed with Simon's finite element analysis(FEA) pictures. Rightly or wrongly, I have been utilising varying shell thicknesses in order to reduce shell deformation for a while now. Using CADCAM manufacture makes this very easy. Looking at the pictures, I'm not actually sure that I am reinforcing in the correct areas!:confused:

    However, my question is this; if we increase the thickness of the plastic at a given point on the shell and the shape remains the same, the stiffness in this area will be increased. It will therefore have a greater ability to apply an orthotic reaction force(ORF) to the foot at a given instant in the gait cycle. However, does increasing the stiffness of the shell locally in one area create a stress raiser at different points in the shell (immediately surrounding the reinforced area) and ultimately make the shell weaker at a different given point in the gait cycle than would have been had the thickness been uniform?

    The closest analogy I can think of is of someone wearing a ski boot and the most likely area for the leg to be broken is at the top of the ski boot. Not a great analogy admittedly!

    Pre CADCAM, we used thermoforming plastics which, with the best will in the world, were/are stretched over the cast. The uniformity of thickness is lost but either by default or by design, are the areas in which the plastic stays full thickness the same areas we want reinforced? I don't do any manufacture so I'm not sure of how much thinning takes place into the proximal medail longitudinal and lateral arches. Less than around the heel cup I would presume but the shape of the heel cup provides a degree of rigidity?

  8. Yes. Will post more later.
  9. OK two stress plots one with external post; one ground off under heel cup.

    Attached Files:

  10. EdGlaser

    EdGlaser Active Member

    Re: orthotic calibration - the science

    In your newsletter you write, “The stiffness of a plastic is determined by measuring the deflection of the plastic under varying loads.”

    That is exactly what we measure in our calibration. You however have no measurement so the rest of your newsletter is just a wild guess based on your “expert opinion”.

    Then you say, “With this knowledge, the doctor can tailor into the orthosis the exact stiffness needed to make the best orthosis for the patient.”

    EXACT……with no measurement. OK.

    Sounds like a wild unsubstantiated claim.

    To calibrate you must measure something.

  11. EdGlaser

    EdGlaser Active Member

    Re: orthotic calibration - the science

    We noticed this problem years ago and began welding two pieces of plastic together in the heel area feathered into the MLA. this extra plastic corrects for the extra pressure under the sustentaculum tali that is evident in your model. Add a double thickness of plastic under the heel and into the arch and see what happens. Lessons learned in years of calibration.

  12. EdGlaser

    EdGlaser Active Member

    Re: orthotic calibration - the science

    Being the first to calibrate is being the first to measure.

    That is us.

    Its shell thickness not width.

    If those are the best examples you can give then I am certainly the first. Thank you.

    Thanks for the jabs about my weight. That is the case cracker. You figured it out. My theory is wrong because of a single silhouette still of me.....I am too fat to be right. Your scientific method is better than I suspected. When you guys have nothing left, you throw personal insults. That is a sign of victory for me.

  13. Graham

    Graham RIP

    Ed! I used to use X-T sprint and now I use Performance Rx ( a nylon based shell)! these materials are "calibrated" to a weight range by the manufacturers of the material and then used as such by the labs. This has been done for years and is perhaps the only general form of calibration that is available to us at present.
  14. N.Smith

    N.Smith Active Member

    Just a question: I thought it was about resistance (Supination or Pronation) and not weight which determined material thickness or rigidity. I've seen 70+YO ladies weighing less than 100lbs generate massive amounts of pronation resistance, made them a flexible job and they've crushed it! Filled the MLA with EVA to stop the material flex and they love it! Also seen, 200+pound men that pronate massively with not much supination resistance, malke a firm job because of their size/weight and the job kills them because there's not enough resistance in the material. Same shape, thin it out, allow the foot to move and bingo, orthotic not painful anymore. It was just a question, but what do I know!:bang:

    Also...when the MLA is quite high and cavus, the shape/height makes the material harder. The sharper the arc, the harder it is to make the material flex. So.. if your not measuring force and lets say, TOP, then how do you know the material flexion/thickness needed? Again...it's just a question.:drinks

  15. Neil:

    Don't confuse Ed with facts about how the foot works. He totally ignores the fact that different feet need different types of orthosis reaction forces due to the variability in subtalar joint axis location. I believe he ignores this common clinicial observation and Craig's research supporting this fact (Payne C, Munteaunu S, Miller K: Position of the subtalar joint axis and resistance of the rearfoot to supination. JAPMA, 93(2):131-135, 2003) since this would mean him acknowledging that subtalar joint axis location rotational equilibrium (SALRE) theory is supported by this research. He thinks that he is the first to "calibrate" an orthosis, even though his calibration doesn't take into account that some feet actually need to have an external subtalar joint pronation moment from the orthosis in order to relieve their symptoms and improve their gait function.

    I sat through Mert Root's lectures and even though I didn't totally agree with him, I knew Dr. Root was a scientist wanting to improve things for all podiatrists. When I sit through Ed Glaser's lectures, I not only don't agree with him, I get the impression that all he is concerned with is seeing more people using his company's products, with no real science being involved. The funny thing is that, in his promotional material, Ed claims "MASS Position Theory has been recognized as one of the first credible challenges to the industry standard developed by Root, Orion and Weed." I'm sure that Ed and his employees at Sole Supports share this opinion....the funny thing is....no one else does.
  16. Re: orthotic calibration - the science

    Yes, that's why I do something similar but align it to the STJ axial position. That's also why we wrote our paper on CoP and rearfoot post design that was published in JAPMA. Lessons learned in years of finite element analysis and podiatric biomechanics.
  17. Re: orthotic calibration - the science

    Been measuring shell thickness for nearly 20 years, I'm sure others have been doing this even longer. Thanks Ed.
  18. RobinP

    RobinP Well-Known Member

    Correct me if I am wrong, but are we not still having the same discussion here. The only "callibration" of Sole Support orthoses are of the plastic that is being used to fabricate them. As Graham correctly says, companies have been "callibrating" materials for years - to a weight range. This takes no account of orthoses shaping which adds stiffness(and I'm sure that MASS shaping has plenty of this).

    However, the very simple fact is that Sole Support Orthotics "callibration" is moot. If the patient was to stand on a shaped piece of plastic that could be incrementally made stiffer until the desired kinematic position was acheived, that would be "callibrating" it to the patient - unfortunately, this would be moot as well. The finite element analysis models show that the resistance of the material used for fabrication changes throughout the gait cycle so a static"callibration" is inexact.

    I don't disagree with the desire to callibrate the orthosis to the patient. We've been doing it in an artisan, trial and error, fashion for years. I would trust my knowledge of material properties in combination with a good supination resistance test to "callibrate" an orthosis fo a patient and frankly, I think it would be more relevant than testing a piece of plastic with an air filled bladder. Surely we are trying to acheive something better than this? I don't understand Simon's TOP principle yet (being discussed on another thread) but I guess this is what he is trying to acheive.

  19. EdGlaser

    EdGlaser Active Member

    Re: orthotic calibration - the science

    STJ axial position (single axis guy) in what posture?

  20. Graham

    Graham RIP


    This is off topic. Perhaps you could respond to the calibration points brought up?

  21. Re: orthotic calibration - the science

    One of many axes that need to be considered in the foot, or do you still deny that this axis even exists as you did when you first started writing on podiatry arena? I'll find the posts if you wish. I think the expression you used was along the lines of: "the STJ is non-axial". So I guess you have learned something, at least now you recognise that there is a subtalar joint axis. By "posture" (found your new buzz word I see) do you mean in which weightbearing position of the foot?

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