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Foot orthotic device and plantar topography of the foot

Discussion in 'Biomechanics, Sports and Foot orthoses' started by RobinP, Jun 28, 2011.

  1. RobinP

    RobinP Well-Known Member


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    Well put Col

    One thing that I think I have found interesting throughout this thread is that one ultimately wants to be capturing a true representation of the plantar topography of the foot, however that is acheived.

    I'm going to open myself up to a load of criticism here, but I'm not even sure how important that is. I am perfectly happy fitting an orthosis to the foot that bears no resemblance to the plantar topography.

    If I have someone with plantar fasciitis for example, am I really that bothered about the device fitting the plantar contours that accurately?

    In many cases, my answer would be no. Depending on the prescription variable required, I would try to increase the proximal arch height in order to provide a dorsiflexion moment to the rearfoot which causes a forefoot plantarflexion moment - reducing plantar fascia(PF) tension. I would also always have a forefoot valgus wedge to shift COP laterally(except for the 31% who it would do the opposite for ;)) which will reduce PF tension by allowing the 1st ray plantarflexion. I may use a medial heel skive, heel raise, cluffy wedge, all of which potentially reduce PF tension.

    Do I need the exact shape of the bottom of the foot to do this - probably not.
    That being said, there may be a comfort element involved. Are bespoke devices more comfortable than prefabs(is there any research? I don't know the answer to this) If prefabs are considered no less comfortable then one would assume that "inaccurate" capture of the plantar topography makes no difference to comfort and hence compliance.

    In 10 years of being involved in biomechanics, I have had 1 pair of custom devices and they were probably the least comfortable devices and ones that I struggled to wear the most. I use prefabs that companies send me for trials, orthotics that have been made for people who don't come to get them and are going to be thrown out, I've even used my wife's on occasion. They all resolve my PF problems. My favourite pair are some 3 year old vasyli howard danenbergs. And they look nothing like the underside of my foot!

    I'm not naive enough to say that we don't ever need to cast or take a good representation of the foot to prvide a certain prescription variable or provide a force, but I don't think it is as necessary as historically we would be led to believe.

    Open fire...arm the weapons....dispatch Warder Kanajax to brrring back his body.

    Robin

     
  2. Re: POP casting vs Impression box casting

    Going to let you all into a secret...................................................













    Ready?...................................................











    Drum roll..............................................










    The foot changes shape during dynamic function















    and.................................................














    So does the orthosis.


















    That's not to say orthosis topography is not important, it is.
     
  3. Re: POP casting vs Impression box casting

    Depends on the stiffness on the material your using on the importance of better fit to the plantar topography of the foot re comfort - soft not so much the device will deform to the lumps and bumps - poly little deformation to the limps and bumps - uncomfortable outcome

    and whats key Comfort....
     
  4. Re: POP casting vs Impression box casting

    [​IMG]

    I'm not sure thats true though. A foam box captures a true representation of the plantar topography of the foot if used fully WB... and people are not feeling love for that. Its not the TRUE shape people want I don't think. Its the CORRECT shape.

    Perhaps they know the "correct" position. I'm not that clever.

    I asked a question in the sidas thread which none of the new posters had a go at. How do orthoses work. The answer, for many, is still "they hold the foot in the correct position / the position its cast in." This is obviously nonsense. They change the forces acting on the foot. Do they have to be foot shape to do that? Nope.

    Javier asked a vicious question about 5 years ago. To the effect of, "if the foot is a patholgical shape, why are you so keen to capture it?"

    Nah. Sub talar neutral all the way through. So long as the cast was taken in STN of course, and the insole is rigid of course. Don't know where you got a crazy Idea like that Simon. Too many disco biscuits in the 80s coming home to roost I reckon.
     
  5. Re: POP casting vs Impression box casting

    The foot has variable load/deformation characteristics across it's interface with the orthosis. The orthosis has variable load/ deformation characteristics across it's interface with the foot. When the two come together they both deform until static equilibrium is reached. Which one deforms the most, depends on which is stiffer at that point. This leads to distinct changes in the distribution of forces at the foot-orthosis interface and will vary with time during gait. It also influences the exchange of energy between the two, but lets not get too complex yet. Ultimately, in a tissue stress paradigm it is the internal forces acting on the tissues at the time of static equilibrium which is key.

    Shape and load/deformation characteristics are inter-related, but is it more important to optimise the interface shape, or the load/deformation characteristics at the interface? This bring us to the kinematic versus kinetic argument. Shape is related to position which is the kinematic view of foot orthosis function. Load/ deformation is related to force, which is the kinetic view of orthosis function. Ultimately, the two are inseparable- "I am the weaver": Hicks

    http://www.muzu.tv/gb/biffyclyro/many-of-horror-when-we-collide-music-video/605715/
     
  6. Re: POP casting vs Impression box casting

    And where the point is?

    Or not on reflection.
     
  7. RobinP

    RobinP Well-Known Member

    Re: POP casting vs Impression box casting

    But not for the reason that it needs to capture an exact replica of the plantar topography of the foot.

    The topography of the orthosis determines it's load deformation charcteristics and hence is one element of the orthosis reaction force(ORF) at a given point. If that ORF is appropriate to reducing tissue stress, does the matching of the foot to the orthoses shape matter?

    I venture not.
     
  8. Re: POP casting vs Impression box casting

    You venture correctly.... probably.:drinks The topography partially determines the load/ deformation.
     
  9. Re: POP casting vs Impression box casting

    To an extent. The sum of the load/ deformations across the interface will determine the net reaction force. Think about the calculation of the net ground reaction force vector. Gets v. complex.

    I'm all over energy transfer right now. In the counter-intuitive spring wedge problem, there will be greater energy transfer at the thick end of the the wedge from the foot to the orthosis, and moreover, greater potential for energy return (to potentially re-supinate the foot) from the thick end of the orthosis wedge to the foot. Haven't given it enough thought yet. But it's "excitin"

    It's all about energy...

    Prediction: "energy appears to be the new black this season"- Spooner 2011

    Too much energy in a tissue = pathology.
     
  10. RobinP

    RobinP Well-Known Member

    Re: POP casting vs Impression box casting

    Yes, sorry,I added "one element" in after I had written the post and put it in the incorrect place.

    Did we reach any conclusion on the thermal conductive properties "thang"?

    I couldn't find a definitive answer as to whether heat altered the Young's Modulus of a material. I think it does but only if it changes the microstructure of the material. Is this likely in any of the material we use?I wouldn't have thought so.

    If a material has a given thermal conductive rating then its ability to conduct heat by comparison to another material with a different rating will represent a difference in transfer of energy.

    Not sure if this means that it can alter the load deformation charcteristics. It will transfer energy created by friction differently depending on its rating so will indirectly have a kinetic effect?

    Robin
     
  11. Re: POP casting vs Impression box casting

    Comes down to the working temperature and the material. Temperature will change the material properties without a doubt; think toffee cold and hot. But does the thermal conductivity of the device change the operating temperature enough to significantly alter material properties? Personally, I don't think it'll make any difference. But it'll give Robeer something to do.:drinks
     
  12. Re: POP casting vs Impression box casting

    Yeah. I'm bored to tears me. :pigs:Did I tell you tomorrow is day 3 of a new job? ;)

    I'm more interested in the effects of temperature on the foot than the device. Been mulling that. I wonder if that needs approaching from a wound care perspective as well as a purely mechanical one.
     
  13. Re: POP casting vs Impression box casting

    Heres something for you - An overview of temperature monitoring devices for
    early detection of diabetic foot disorders
     
  14. RobinP

    RobinP Well-Known Member

    Re: POP casting vs Impression box casting

    WOUND CARE!...... WOUND CARE!......... Who gives a SH!T about wound care?;)

    I want biomechanics!
     
  15. Re: POP casting vs Impression box casting

    Well, its... you know. Wound care. Nothing wrong with it. I can be interested in that as well. I'm sort of Bi / curious.

    I feel a bit dirty.
     
  16. RobinP

    RobinP Well-Known Member

    Re: POP casting vs Impression box casting

    As well you should young man. Wound care indeed!
     
  17. Re: POP casting vs Impression box casting

    [​IMG]
     
  18. Re: POP casting vs Impression box casting

    Even though this thread is all over the place, I do have a few comments.

    First of all, I consider that the three-dimensional (3D) shape of the orthosis and whether it is congruous to the plantar foot or not to be one of the most critical factors in a clinician being able to achieve optimum outcomes with custom foot orthoses. If you are not concerned with orthosis shape, then why not just put a flat insole inside the patients shoe? Even though you may be quite satisfied with yourself, unfurtunately, your patients may not be very satisfied with you in doing so.

    Secondly, I consider that each foot orthosis casting/imaging method has its pros and cons. I prefer using neutral suspension casting technique with plaster since this is what I have been trained to do and have done for the last 30 years. Foam box casting will give an impression of the foot, but it can not be readily compared visually to the plantar contours of the foot as can a plaster negative cast. In addition, foam box casting will not allow the practitioner to vary the dorsiflexion load on the medial and lateral columns of the forefoot with as much variety and accuracy as can a clinician using neutral suspension casting. However, other than being less messy, less time consuming and less costly, there may be some other benefits to foam box casting that I am not aware of.

    Third, casting/imaging is only one link of the chain that will produce optimum custom foot orthoses for our patients. It will do the clinician little good if they use the best casting method and use best casting technique only to fail with their orthosis therapy for their patient by not understanding the type of mechanical stress which is affecting the patients injured body part, not understanding the biomechanical function of their patient's foot and lower extremity, not order the correct type of custom foot orthosis, not order the best modifications on that foot orthosis, not fit the orthosis properly into the proper shoe, and not follow up with the patient to assess for potential problems being caused by the orthoses.

    Personally, I think that sometimes we tend to lose sight of the forest for the trees. Putting our discussions in perspective in regard to their relative importance helps improve the worth of our discussions for all those involved.
     
  19. RobinP

    RobinP Well-Known Member

    Re: POP casting vs Impression box casting

    Thanks for that summarisation Kevin. Better this thread stays on track. I plead guilty to going well off thread.

    With regards to the above quote; I couldn't agree more, the shape of the orthosis is vital to the outcome. What I am questioning, in my own practice, is how vital is it that the shape reflects the topography of the foot?

    Increasingly, I think the answer is that it is not vital.

    Medial heel skives, cuboid pads, reverse mortons extensions and metatarsal domes are all used frequently as orthosis design features. They do not reflect the surface topography. Admittedely, they are all additions to a cast that has potentially mirrored the surface topography beautifully. But they are not a reflection of the foot. They are desgned to alter the orthosis reaction force(ORF) and they will do so.

    If I were to add each one of those additions to an orthosis(potentially quite unlikely admittedely), how much contact would there be of the foot on the original shape as taken by the cast? Perhaps not much. What is the value of having a cast that accurately depicts the foot when potentially so little may remains of the original shape.



    So apart from having a desire to create a calcaneal bisection to act as a baseline for prescribing, I can't see any benefit to having the extra mess and time involved in casting. If I feel that high medial and lateral column control is required eg orthosis to treat DMICS, I may take a POP cast.

    I am sure I am in the minority here.

    I have been trying to imagine what I would think had I not had my original grounding in sub talar neutral theory but still a knowledge of biomechanics/pathology/anatomy.

    Why would I think that something that conforms to the foot in a non weight bearing randomly chosen position would be the most effective way of applying a given force. It vexes me so!


    Regards,

    Robin
     
  20. Re: POP casting vs Impression box casting

    Can you summarise why you believe shape and congruence are critical, Kevin?

    Is it worth cracking this off into it's own thread?
     
  21. Re: POP casting vs Impression box casting

    Yes.

    The question, so far as this thread is concerned, is congruous to the plantar foot in what position Foam and POP both capture the surface of the plantar foot. The debate, for me, is what shape we think the plantar foot should be in when we capture it. A neutral shape? A non weight bearing shape? A weight bearing shape? A non weight bearing shape with expansions to simulate weight bearing? All of the above (it depends)?

    I believe the shape of the foot must be one of the variables we must consider when considering the shape of the orthoses we think will work best. In this, I think the non weight bearing and the weight bearing shapes are important considerations. However, like Robin, I do not believe that the "best" shape for an orthoses necessarily matches any shape one can manipulate the foot into.

    I consider it much like the root wedge / skive argument. Once I thought I had to measure the rearfoot varus to match the rearfoot wedge to that rearfoot varus. Now I'm happy enough to add a socking great heel skive which does not correlate to any measurement of the rearfoot. Once I thought I had to measure the foot to match the amount of Arch heigh to the neutral arch height. Now I'm happy enough to make the amount of arch match to how hard I want the insole to push in the arch. As Simon said, I think we are trying to manipulate forces, not shapes.
     
  22. Re: orthotic device and plantar topography of the foot discussion

    But by changing shapes will manipulate forces - the greater the change in shape the greater manipulation of force.
     
  23. Re: orthotic device and plantar topography of the foot discussion

    Absolutely. The point being that we have the freedom to change the shape however we want to change the force however we want. We are not bounden to change the shape only as much as the position of the foot.
     
  24. Re: orthotic device and plantar topography of the foot discussion

    So, you need to go back a step and define the effects of curvature, which is why I asked Kevin to summarise his thoughts.

    Think on this:

    Lets say we know foot orthoses work by altering the magnitude, timing and distribution of forces at the foots interface with the device.

    Let us take two insoles of the same material: one is completely flat, the other we construct from a fully weightbearing cast of the foot. The two devices will have the same Young's moduli, yet the device will have different geometry. What differences occur in the magnitude, timing and distribution of the reaction forces as a function of geometry and how?
     
  25. Re: orthotic device and plantar topography of the foot discussion

    Timing is easy - the one which comes in contact with the 1st will begin altering the GRF´s earlier.

    Distribution - the device which contact the foot further from the Joint axis of the foot will have the greater effect due to greater positional changes in the CoP in relation to joint axis

    Magnitude - Not sure if this would be different if they have the same Youngs moduli - I would have said the device with the arch however small would have a change an increase stiffness of the device - increase in stiffness greater reaction force.
     
  26. cpoc103

    cpoc103 Active Member

    Re: orthotic device and plantar topography of the foot discussion

    Once again I have to go with Robert and Robin on this one.
    Kevin would agree orthoses shape is of the utmost importance, and an understanding of both kinematic and kinetic forces and manipulations is very important if clinicians are to prescribe the best devices for the best possible healing outcomes.

    However, I do not think that exact plantar topography must be captured, what about the modifications we make to the positive cast such as arch fill, skives, blakes inverted devices and so on, this is no longer representative of the topography of what we have captured, and all this before we add forefoot mods.

    Also while taking casts today(using foam box) I thought I would pay extra attention to matching what I captured and the foot, and yes while I did not have a pop cast to exactly measure height of arch contour etc, I got a pretty good view of what I was trying to capture. I was able to see the plantarflexed 1st, and also a navic drift.

    There is no doubt that a pop is best in order to manipulate medial and lateral borders, but I can also do this with box, albeit a little more difficult but it can be manipulated, just need to shave off any extra material from my fingers going into the box.
    On a side note maybe this is a little naive of me, but im not understanding why clinicians are still trying to achieve a bisection for a root device, I havent prescribed a root device for many years nor has my colleagues??

    col.
     
  27. Re: orthotic device and plantar topography of the foot discussion

    If I was feeling cynical, I would say it was to place a patina of pseudoscience over what is at best a SWAG. And because no matter what we believe on an intellectual level, the picture of the before and after with the calc line inclined then straight, has burned its way deep into our subconcious where it subtley and covertly moulds our thinking.

    If I was feeling cynical ;)
     
  28. Re: orthotic device and plantar topography of the foot discussion

    I find this really odd - there is nothing wrong with a Root device - the Chinese whisper of what Root may or may not have written has got people thinking that a Root device is wrong.

    Taking the Spooner approach with the added bonus of my crap spelling and English ( if Im allowed )- How does an orthotic work ? - by altering the magnitude, timing and distribution of forces at the foots interface with the device.

    Will a Root device do this ? Of course it will but you have to know when it is appropriate and not that the Key.
     
  29. Re: orthotic device and plantar topography of the foot discussion

    I consider a pure, canonical root device to be a little like a very old receipe for cake.

    It made a good cake then. It'll still be a good cake now.

    But we now have new ingrediants available. Better ovens. Better equipment. More variety. An understanding of how the ingrediants interact. So now If I want to bake a cake I will avail myself of those things and hopefully make a BETTER cake. And even if I want to make a similar cake, I might use margerine instead of butter.

    In the same way, whilst there is nothing wrong with a root device there have been developments since then. All the myriad extra modifications. And not least the realisation that we are altering forces not holding positions. That frees us to work outside of the root protocol.

    So although what we might end up with may look a lot like a root device, it may not be made the same way or for the same reasons.
     
  30. cpoc103

    cpoc103 Active Member

    Re: orthotic device and plantar topography of the foot discussion

    Not saying Root is wrong, however given all the research suggesting we do not know the foot functions optimally with a STJ in neutral with a vertical heel and tibial position, is'nt a modified root device or another style of device say SALRE or blakes not a better option for altering timing magnitude and distribution of forces??

    col.
     
  31. cpoc103

    cpoc103 Active Member

    Re: orthotic device and plantar topography of the foot discussion

    Sorry getting back to Simons Q,
    would timing not be the same for both flat device and casted since GRF is going to happen at the same time, it is magnitude and distribution that will change or have I gone mad??

    col.
     
  32. Re: orthotic device and plantar topography of the foot discussion

    Different. Not neccessarily better.
     
  33. cpoc103

    cpoc103 Active Member

    Re: orthotic device and plantar topography of the foot discussion

    Yes sorry true thats kinda what I meant..
     
  34. Re: orthotic device and plantar topography of the foot discussion

    I would we don´t know yet - research needs to catch up
     
  35. Re: orthotic device and plantar topography of the foot discussion

    Not sure research could tell us this. Hinges on "is more always better". The answer, unless your name is Ed, is no.

    I'd say that what patients pay us for is to match the prescription to what is required. The more choices we have in prescription, the better we should be able to do this. Dragging back to the debate, although the topography of the foot is of course of vital importance, the ability to move outside of it (for eg with a heel skive) allows us a broader choice.
     
  36. Athol Thomson

    Athol Thomson Active Member

    Re: orthotic device and plantar topography of the foot discussion

    Like most things in our profession I think it might be subject specific.

    For some people having plantar topography closely match the orthoses shape may be important for them to achieve that all important comfort variable. For others it may not matter at all.

    I think we will be trying to quantify or understand 'tolerance' of devices/covers etc long after kinetic variables are quantified.

    Athol
     
    Last edited: Jun 29, 2011
  37. RobinP

    RobinP Well-Known Member

    Re: orthotic device and plantar topography of the foot discussion

    It depends.....;)

    I think that is the point of this discussion. It might be, but for a given foot, a pure Root device may well be the best option for altering timing, magnitude and distribution.



    What I am interested in is using material thickness and surface topography to mirror the change in forces caused by additions. Clearly there will always be a need for additions on some devices but, hyothetically, if the change in kinetics can be measured for a given addition and other modifications to material stiffness and topography obtain the same result then what would be the benefit of having the addition.

    Obviously I am not going to be doing any research into it as I am too busy browsing through podiatry arena.

    Robin
     
  38. Re: orthotic device and plantar topography of the foot discussion

    Classic
     
  39. RobinP

    RobinP Well-Known Member

    Re: orthotic device and plantar topography of the foot discussion

    Good point.
     
  40. Re: orthotic device and plantar topography of the foot discussion

    Robin, thanks for making yourself available for selection and joining our research team. I'll put a methodology to you shortly.
     
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