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Compliancy in foot orthoses query

Discussion in 'Biomechanics, Sports and Foot orthoses' started by markjohconley, May 13, 2016.

  1. markjohconley

    markjohconley Well-Known Member


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    As the 'MLA' section of the foot orthoses deforms under load does that entail lengthening of the anterior medial 'corner' of the foot orthoses and would that possibly irritate the 1st MPJ (or 2nd MPJ in an orthosis with a 1st ray cutout).

    When Prof Kirby talks of the medial anterior corner 'binding' with the shoe upper and causing discomfort to the patient (Precision Intracast Newsletters, 2009-2013, p.74) is this what is involved, an impediment to orthoses lengthening?
    mark
     
  2. s the 'MLA' section of the foot orthoses deforms under load does that entail lengthening of the anterior medial 'corner' of the foot orthoses and would that possibly irritate the 1st MPJ

    and the reason why a device is generally finishing 1cm behind the 1st MTPJ positive cast.

    of course you may want a longer device in certain treatment plans
     
  3. Ian Drakard

    Ian Drakard Active Member

    You may also find there is a bit of leeway because if the MLA section of the orthotic is deforming the MLA of the foot itself may be elongating.
     
  4. markjohconley

    markjohconley Well-Known Member

    Ian, thanks; should have been obvious, mark

    Gents any thoughts on discussing ramp angle instead of drop, which seems relatively useless considering different sized footwear?
     
  5. efuller

    efuller MVP

    It's really hard turning around imprecise terminology. I've spent a lot of effort on trying to wipe out hypermobility, I don't know if I have the motivation to fight the ramp vs. drop battle. If shoe manufacturers design their shoes with height difference between heel and forefoot regardless of foot length then drop seems to be the correct term. It does make sense that they should be proportional and use ramp. But then you would have to figure out what the ideal amount of ramp is for the average person.

    Eric
     
  6. markjohconley

    markjohconley Well-Known Member

    Goodaye Eric, didn't realise i was, which term(s) are imprecise? I thought 'drop' and 'ramp (angle)' were the appropriate terms used by the 'running community', certainly used in this website by the most respected authors. 'Pitch' is the term used by footwear manufacturers, no? so would use that term if i was conversing to a footwear manufacturer.
    I haven't used 'hypermobility' since i read prof Kirby's posts years ago.
    Didn't say I knew how to work out the ideal ramp for an individual, just it was useless to attempt to work out the drop for anyone if not taking into account the size of the shoe, mark
     
  7. Mark, I don't think Eric was criticising you personally. It's basic trigonometry which you are applying here so obviously if the "opposite" length is maintained, but the "adjacent" length varies, then the tangent of the angle will vary too. What is being called the "ramp angle, is the slope of the hypotenuse.
     
  8. markjohconley

    markjohconley Well-Known Member

    Simon, thanks, and I thought the 'ramp angle' was the angle of one of the non-90 degree corners, which would be constant (for all shoe sizes) unlike drop (pitch).
    If my post read that way I sincerely apologise to Dr Fuller, who of all the learned contributors, on this website, has educated me the most, and I note continues to do for other podiatrists in need of biomechanical comprehension, all the best, mark
     
  9. markjohconley

    markjohconley Well-Known Member

    Simon I misread your post in my haste. So it is the angle, which i thought it was. I obviously haven't made my posts comprehensible.

    So, if you proposed a study to ascertain which slope of the insole/midsole gave an ideal kinetic result (not sure how to phrase it) you wouldn't be able to use 'heel to forefoot drop' as a variable, as it differs in different shoe sizes, but 'ramp angle' could be used as a variable. I'm ignoring the subject specificity and activity specificity here just for the argument.
    It's not the heel drop to forefoot drop that would be responsible for the outcomes, per se, it would be the ramp angle, yes?, mark
     
  10. Yes, but there is more to it than that. You've also got the heel seat angle, toe-spring and all the other variables of the last.
     
  11. markjohconley

    markjohconley Well-Known Member

    Right, as in good point hadn't thought of that; how do the athletic footwear manufacturers settle on a specific sole (sagittal plane) geometry? do they have studies to justify their choices, mark and thanks
     
  12. efuller

    efuller MVP

    Hi Mark,
    Simon was right I wasn't criticizing you. I was agreeing with you that there is some imprecision in all the terms that are used. I just didn't have the energy to fight that battle.

    As to your question of is there an optimum ramp/pitch/drop. Shoe makers would be thinking about population optimum rather than individual optimum. For an individual there is likely to be a wide range of heel heights/drop etc. that would not correlate with injury. People after all are quite adaptable. The injury that you would get from too little drop will be different than from too much. For example, with too little drop there would be tendancy toward arch strain as the length of time that the heel will be shorter with too little drop. There would be a tendency toward ankle sprains with increased drop.

    The shoemaker has to balance too little with too much for the entire population. I am not aware of any studies that have looked at this. The study would probably have to have a very large number of subjects to find the optimal drop/ramp. There were anecdotal reports of increased injuries with Earth shoes that had a negative heel. There could easily be enough individuals with limited ankle dorsiflexion that some drop/ramp could lower the incidence of arch strain for the population. The problem for the shoemakers is there might be some trend where it becomes uncool, or perceived as unnatural, to have some drop in your shoes. ;)

    Eric
     
  13. Ian Drakard

    Ian Drakard Active Member

    Hi Mark, I think in terms of discussion there's a couple of factors. Mechanically it proabably is better to talk about the drop or ramp angle but it's much easier to talk about the absolute height!

    The other consideration is the relative difference a given heel drop makes across shoe sizes compared to the change in height.

    A 10mm drop with heel to ball length of 150mm is approx 3.81 degrees angle. A 10mm drop at 200mm heel ball is 2.86 degrees. Is less than a degree significant in the sagital plane? Depends on the individual.

    A small change in absolute drop height will have a bigger effect- a change from 10mm to 5mm drop will obviously halve the angle so 1.9 degrees at 150mm heel/ball.

    From a manufacturing point of view I can also see it's easier to keep the heel drop the same across a size range.

    Sorry if this is rambling a bit
    Ian
     
  14. markjohconley

    markjohconley Well-Known Member

    Thanks Ian, so significance is not worth worrying about; good point, I hadn't actually done the sums, thanks again, mark
     
  15. And the step to step variation in the sagittal plane angulation of the ground is....... never been worth worrying about.
     
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