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Impression of foot taken weightbearing

Discussion in 'Biomechanics, Sports and Foot orthoses' started by tarik amir, Jun 8, 2007.

  1. tarik amir

    tarik amir Active Member

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    Hi All,

    A rep from 'sidas', came to my practice some time ago to demonstrate the use of their equipment that can capture the weightbearing impression of the foot from which an orthotic is then directly moulded to. The subjects foot was placed into the neutral position and the bladder underneath the foot was pushed up into the medial arch. The patient was a severe pronator and once the mould was taken, the foot was perfectly in neutral.

    My question is, if the foots neutral position is taken weightbearing and an orthotic fabricated directly to this mould, would there be any reason to use modifications such as medial skives, heel posts, forefoot posts and so on?? The arch of the orthotic appears to be holding up the foot where it should be without these modifications.

    I have never fabricated an orthotic from a weightbearing mould and would like any feedback from practitioners that have. The subject never returned so I could not evaluate the orthoses.

  2. Admin2

    Admin2 Administrator Staff Member

  3. You only need medial heel skives, rearfoot posts and other such orthosis modifications to exert sufficient STJ supination moments in a patient with a maximally pronated foot if the patient will be standing, walking, running or participating in weightbearing sports on your foot orthoses. However, if your patients will be standing in an orthosis casting machine the rest of their lives, then these modifications won't be necessary. :rolleyes:
  4. tarik amir

    tarik amir Active Member

    Hi Kevin,
    We couldn't find footwear that would take the casting machine :)

    The observation was that the orthotic moulded very well to all areas of the foot, which is something I don't see often from orthoses manufactured from orthotic labs (there always seems to be space between the foot and the orthotic, especially anteriorly). My assumption was that once in the shoe, it would generate sufficient supinatory force (as was seen when on the machine). You can't add a medial heel skive using this machine, so I am wanting to know if the arch height is optimal can the mentioned modifactions not be required.
  5. Tarik:

    Good comeback....now I'll talk more.... :eek:

    It is not until the late midstance phase of gait that the STJ pronation moments acting on the foot are at their maximum. Late midstance phase is a dynamic phase of gait that the orthosis casting machine can not duplicate. The angular velocities, internal and external moments, internal and external forces, and muscle contractile forces of static bipedal stance are very different from the dynamic kinematics and kinetics of walking and/or running gait. Therefore, an "orthosis casting machine" will produce orthoses that will work identically to the type of foot orthoses I have been making for my patients for the past quarter century, it's just that the orthosis casting machine orthoses may have a slightly different shape and be made of a different material than my orthoses.

    Also, even though a patient may feel initially very comfortable while standing on foot orthoses made to a higher medial longitudinal arch height, once this same patient starts walking on the orthoses, and especially starts walking and standing on the orthoses all day-every day, those high-arched, blister-causing orthoses sometimes become aerial assault weapons aimed at the clinician's head at the first orthosis followup visit. ;)

    By the way, a "medial heel skive" could be added to the orthosis by placing multiple layers of moleskin to the medial heel cup of the resultant orthosis as I described in the original paper (Kirby KA: The medial heel skive technique: improving pronation control in foot orthoses. JAPMA, 82: 177-188, 1992).
    Last edited: Jun 8, 2007
  6. tarik amir

    tarik amir Active Member

    Thanks Kevin for your response.
    To date, has any other system of capturing an impression of the foot come close for you to consider adopting (ie to change from using POP)?
  7. No. Why mess with something that works so well? :confused:
  8. Kevin,

    Do you ever take weightbearing/ semi weightbearing casts? If you do, I think it may be educational for us all if you could explain your protocol. Even if you don't, it may be helpful for us if you provide a rationale as to why not? I have been splitting the atom (with an axe) with you for nearly ten years now, in all of our discussions I can't recall us ever talking about this. Nor can I recollect this being included in one of your newsletters. :confused:
  9. Not currently in the traditional fashion. However, I do commonly modify the neutral suspension casting technique to also place a dorsiflexion loading force on the plantar first metatarsal head and plantar hallux in those patients in whom I want to elongate the arch and preload the medial bands of the plantar aponeurosis in.
    I don't like foam beds or casting in foam in a semi-weightbearing fashion since I prefer to be able to visualize the plantar, medial and lateral aspects of the negative cast and dorsal aspect of the foot at all times during the casting procedure. I feel I have better overall control of the foot position being able to see the foot shape from all sides while using plaster casting. I do use the modified casting technique described above (i.e. place a dorsiflexion loading force on the plantar first metatarsal head and plantar hallux) in most patients with cavus feet and laterally deviated STJ axes in order to lower the longitudinal arch height and, therefore, decrease the STJ supination moment from the orthosis. In addition, I use this modified casting technique in some older patients with pes planus deformities that have more plantarflexion range of motion of their medial forefoot when comparing their non-weightbearing position to their weightbearing position (i.e. in a NWB position they have a very high medial arch and in their WB position they have a very low medial arch). In these patients, I use the modified casting technique to lower the longitudinal arch height so that they will be better able to tolerate the arch height of the orthosis. Of course this is also dependent on the fact that I don't make very flexible foot orthoses and have found the need to modify the standard casting technique taught to me by Mert Root, John Weed, Ron Valmassy and others in order to optimize patient comfort and function.
    So that's the problem, Simon.........we should have been using a cyclotron all along..... :rolleyes:
  10. I've observed this with outsourced orthotics as well. The impression i get is that many labs do a lot of "cast correction" which you will obviously not get from sidas. I guess if you are using a rigid material many prescribers baulk from making the insole exactly the shape of the foot for fear of limiting movement too much and creating the kind of problems Kevin mentioned.

    I've seen a lot of Sidas devices (second hand). The material used for the shells appears to be a good deal more flexible than polyprop or Carbon fibre so i guess this is less of a concern.


    This is why i use softer materials with any patients who look like they can throw well. Less bruises! :D

    This has always been my concern with the Sidas type system. If the patient needs an "arch support" we're cool. If the patient needs to have some of the supination moments generated from anywhere else there is a problem.

    I would say that getting this is akin to saying "if a saucepan can boil water do i need a kettle?"
    I think whilst in some cases getting the optimal MLA is all that is required the modifications can often do the job more comfortably, with more flexibility and better.

    Has anyone got any experiance actually useing SIDAS?


    *sounds like MASS to me!
  11. This is not specifically aimed at you Robeer, just got me interested as I'm currently doing some research into orthoses geometry and it's effects. What is optimal medial longitudinal arch height and how is it determined?
  12. A good question. I should have used speech marks!

    I would guess that optimum would be enough to generate sufficient supination moments to aceive the desired theraputic effect but not so high as to cause volumes of ORF in the MLA area which will cause soft tissue damage.

    But then i suppose we should also consider triplanar factors such as sagittal plane alteration, lines of force etc!

    As usual Simon you ask hard questions. Probably a thread all by it'self. I'll need to think about that one. I feel another migraine coming on! :mad:

    I need a Robeer :(

  13. Here's fun.

    In feb 2006 Kevin wrote

    If an orthotic is in close contact with the foot in a neutral position and if that orthotic is made of rigid material how much contact phase Pronation is available?

    I know Simon has tweaked me before about this when i neglected to consider the possibility of movement over the insole in another thread. Not sure how much of this can go on with a tight fitting insole in a firmly laced shoe but hey, what do i know?

    What say you?



    "drink Robeer"
  14. Try this: Lets say we are walkin' with our tight fitting shoes and orthotics lookin' sharp and dandy, but not fopish. We heel strike posterior lateral shoe; lateral to the STJ axis, so we have pronation moment from GRF; if we have a net pronation moment, we have pronation motion. At this point in time the only point of contact between the system and the ground is the posterior lateral border of the shoe, so where is the external supination moment coming from? In other words, how does the orthotic control pronation at this time? Until we get a reasonable proportion of the shoe + orthotic + foot into contact with the ground I'm not sure that the orthotic can do a great deal to counter pronation. When does contact phase begin and when does it end? Need to be careful on terminology here. I prefer "Ranchos" terminology to describe the phases of gait.
  15. A smart response Robeer, since "that's the real trick"- Han Solo. But how do we determine this without manufacturing a dozen or so devices to find our optimum? "That's the real question"- Simon Spooner
  16. "Ooooooohhhh its a scythe!" Edmund Blackadder (the second) I see what you mean now. We can control the foot - shoe interface (To a degree) how do we measure / analyse / control the shoe - ground interface?

    Well that makes everything more complex by a factor of 2 does'nt it. Cheers.

  17. Here is something even more frightening check out the STJ kinematic graph.
    Follow the link:http://www.latrobe.edu.au/podiatry/pod12pbmdesc.html
    Go to week 6: The subtalar joint and look at the kinematic graph on the third page.

    The top line is Wright's data, the bottom one is McPoils. By the time that forefoot loading starts, pronation is stopping / has stopped and is reversing- in these subjects at least (without pathology? Can't remember)

    I guess If you can show me a graph where pronation continues longer then the orthoses stand a chance, but it seems to me that all our clever worked out angles can't do very much early on during stance. Or really until the whole of the rearfoot post is in ground contact. Didn't Root design his orthoses to work at midstance? I'm sure Prof. Kirby will tell me ;)
    Last edited: Jun 12, 2007
  18. The rearfoot post was designed by Root and coworkers (I think Tom Sgarlato was the first to apply a dental acrylic rearfoot post to Rohadur....got the idea from one of his dentist friends) to allow more smooth pronation during contact phase with its 4 degree grind laterally. I don't think Root and coworkers figured that the foot orthosis would do much in contact phase to the STJ other than start to decelerate pronation early in midstance phase. Contact phase is very short compared to midstance so we do have a significant ability to control early stance phase pronation with an orthosis, especially if the orthosis has a medial heel skive to hopefully exert increased GRF medial to the STJ axsi at initial heel contact.
  19. efuller

    efuller MVP

    The line for FFL looks off in that graph. As I recall looking at EMED rollover processes the lateral forefoot would often contact in about the 4th frame out of 50. The medial forefoot would contact usually by frame 7. This would be about 1/7th of the stance phase where the graph has FFL around 1/3 of stance phase. 1/7th of the step would be about the time that pronation stops and this would make sense. Once the pronation starts, something has to stop it. The medial forefoot is probably going to be part of the something that stops pronation.

    On the effect of skives and timing and effectiveness of orthoses. All you have to do is look at the center of pressure path of an in shoe sensor. There usually is a very rapid progression of the center of pressure path in the first few frames. Usually the first frame has the posterior lateral contact point that you describe. However, the second, 3rd and 4th frames usually have the center of pressure closer to the center of the heel. At this time a medial heel skive should be able to influence the pronation moment from shoe reactive force. It should also be noted that what makes the STJ move is shoe versus foot force and not ground versus shoe force. Looking at these forces there will be a force couple that would produce eversion of the shoe relative to the foot.

    If there is tight coupling of foot motion to shoe motion, I would agree that point of application of force from the ground to the shoe will be very important in determining pronation moment from ground reaction force. I've seen a pretty significant shift in location of center of pressure in comparing a dual density midsole shoe with a non dual density midsole shoe. Also there is Nigg's classic article showing an increase in pronation velocity with increase in lateral flare at the heel of the shoe. A lateral flare will place the center of pressure more laterally, assuming that the shoe hits the ground inverted.

    Yet, I do believe that a skive has influence before forefoot loading because it can change location of center of pressure under the heel before the forefoot loads. I have made orthoses for myself with varying amounts of skive and have felt my peroneus brevis muscle become fatigued with high amounts of skive. This was especially noticeable at heel contact. After removing the rearfoot post, under the orthotic, the fatigue went away. Yes, I know, N =1.


    Eric Fuller
  20. efuller

    efuller MVP

    Some thoughts:

    Weight bearing casts: I have made for my self devices from a fully weight bearing foam box impression (RCSP) a semi weight bearing foam box impression (RCSP), A foam box impression in the MASS position. and Neutral suspension casts with varying amounts of arch fill. The fully weight bearing cast was not as comfortable because it did not have as much force in the arch as the semi weight bearing casted device. I could have supinated the STJ slightly in the full weight bearing cast and raised the arch some. The MASS position devices had the highest arch and were extremely painful. (After 4 hours of wearing I would wake up in the middle of the night because my feet hurt.) Additionally, you can add a medial heel skive to a device made foam box impression. There are many ways to get to the optimal height, whatever that is.

    I think that adding rearfoot correction or forefoot correction is what makes a device custom. This is where we earn our money as prescribers. Knowing when to add or not add a wedge is an important decision.

    The correct arch height:
    I've come up with a measurement where I place my finger under the medial arch of a relaxed standing patient and push up with a comfortable amount of force and then measure the height of the top of my finger off of the ground in millimeters. (This not neutral position, but Relaxed standing position.) In patients in which I want pronation control I make the arch height of the orthosis that high. I agree with Kevin, when a patient has supination related problems I will make the arch height of the orthosis a little lower than the measured arch height. Interestingly, I have had some patients who found this arch height uncomfortable. In some of those, I rechecked arch height and what they thought was relaxed, there posterior tibial muscle was contracting and when asked to stand more pronated there posterior tibial muscle was not obviously tense and there arch was noticeably lower. I'm still working on this measure, but have been pretty happy with it. I'd be willing to bet that some patients will prefer a lot more push in their arch than others with exactly the same arch height. There are more facters involved, but you have to start somewhere.

    Kevin mentioned pushing up on the first ray when casting to lower the arch height. You can also add more arch fill in the cast to lower arch height.


  21. Yeah, Eric, but how does tensegrity make your orthoses better for your patients??...... :rolleyes: :eek: :p
  22. efuller

    efuller MVP

    The arch height triangulation gives the holistic tensegrity arch system tension and compression elements that manipulate and stabilize the locking mechanism of the midtarsal joint which gives the billboard mechanism a contraption to wagerize the construct. It is really too complicated to understand. :)


  23. Sorry, i'd switched off when i read "holistic". :) For some reason that always reminds of sitting through a presentation on how applying marigold reduces IM angles in HAV. I get flashbacks. You could hear the spirit of Science screaming. Sometimes, late at night, i still hear that screaming!

    I'd still like to know what people think about this

  24. We looked at a few rearfoot post designs here:
    Paton J.S., Spooner S.K.:Effect of extrinsic rearfoot post design on the lateral-to-medial position and velocity of the centre of pressure. JAPMA 96;5: 383-392

    Basically we used a single subject design study, made 4 pairs of orthoses with identical shells but with varying rearfoot post designs: no rearfoot post- shell only; standard; internal oblique; external oblique.

    Data collected with F-scan and then broken down according to Ranchos Los Amigos definitions so loading response = 0-10% of stance.

    In all trials the maximum medial position of the COP occured within the first 10% of stance phase, i.e. during loading response. As we stated in the paper: "It is reasonable to assume that the maximal medial position of the COP will correspond to the point during the stance phase of gait at which maximal pronation is reached."

    During the loading response phase of gait, significant differences were observed in the lateral to medial position of the COP in the left foot between two of the rearfoot posting techniques tested against the same foot with the orthotic shell only (P < 0.0125). The effect of the rearfoot posts was to move the COP in a medial direction. It should be noted that while these differences were statistically significant, they were small in real terms: differences in means were 0.093 inches and 0.104 inches.

    During the loading response, the lateral to medial COP position in the right foot failed to show any significant differences, indicating that the addition of a rearfoot post had no predictable effect on the COP position in the right foot of this subject.

    At initial contact (the moment the foot touches the floor) in both feet the rearfoot posts increased the COP velocity compared with the same foot functioning with the orthotic shell alone. During the loading response phase of gait, no significant difference was identified between any of the comparisons tested in either foot, except for the left foot external oblique post which increased the velocity of the COP.

    Here's another confounding problem that we discussed in the paper: lets say we see a medial shift in the COP with an orthotic. Little certainty can be given to the the position of the axis relative to the COP at this time or to the magnitude of the force. It is possible that the shift in the COP position was also accompanied by a shift in the axial position, which may have either enhanced the effect or negated it. The magnitude of the force may also have changed, again either enhancing or negating the effect of the shift in COP in terms of the moments produced about the subtalar joint axis. Furthermore, a more medial positioned COP may just mean that the subject is striking the ground more medially.

    And remember "It is reasonable to assume that the maximal medial position of the COP will correspond to the point during the stance phase of gait at which maximal pronation is reached." In other words, a more medially positioned COP can be due to more pronation.

    Beware! Pressure plate data viewed in isolation can be a somewhat blunt instrument.
  25. I know that biotensegrity works and is the holistic essence of everything that allows the body to function since I am best friends with some of the only people that know anything about biotensegrity and they allow me to talk to them at any time of day about how they are right and everyone else with any standard scientific training is wrong.

    And I know that the Spinal Engine works as it does, because it it has never, I mean, I really-really-really mean never has it been shown to be false. Of course, if it was shown to be false, I would ignore that information anyway.

    I have research, that will eventually be published, that will prove that everything I say is right and everything that anyone else says who disagrees with me is wrong. It was going to be published years ago, but my attorney who is managing my multiple patents on things I can't divulge, says I can't give out too much free information, especially to the non-believers.

    And finally if I write with very big letters I know that someone will eventually listen to me.

    Does anyone know....who I am??:confused:
  26. Kevin,You fogot to includ lot of typo'd with t bige leters.
  27. efuller

    efuller MVP

    Stand on the device and try and pronate your foot.

    To alter motion you have to alter the moments applied to the foot. Moments can come from the ground, the orthotic, muscles among other things. The orthotic cannot apply enough moment to stop all motion. It can make motion uncomfortable though. Someone may be less likely to exhibit late stance phase pronation if it is uncomfortable to pronate into a rigid piece of plastic. The souce of the moment to prevent this further motion can be directly from the orthotic or it can be from supinatory muscles. I've seen people walk with resupination after taking their orthoses out, so I'm sure that this happens at least some of the time.

    On shock absorption:
    The joint with the most capability to absorb shock is the knee. There was a thought that STJ pronation was necessary to allow knee flexion. This idea has been discredited. It can be proven with the simple test of pronating your foot maximally and then attempting to flex your knee. You can still flex your knee no matter what motions are going on at your STJ.

    Eric Fuller
  28. efuller

    efuller MVP

    Sorry Simon, I had forgotton you had written that paper. I really appreciate the fact tha someone else is paying attention to center of pressure relative to the STJ axis.

    I haven't calculated moments about the STJ, but 0.1" x body weight could be a significant change in moment.

    So, if you saw that the maximum medial excursion occured by 10% then don't you agree that there is some problem with the timing of Forefoot Loading described in the graphs alluded to at the top of the thread. I was guessing from memory and thought full forefoot loading occured around 10% but was not sure.

    I'm trying to remember if your oblique posts were what I would consider a half post. For example you could have the post on the medial side only. The post on the lateral side, even if beveled 4 degrees upward will still help give a more solid connection from ground to lateral heel.

    I agree, it is really hard to do perfect research. Ideally you would have axis position, emg data, center of pressure, and absolute foot segment position data to be able make any solid conclusions.


    Eric Fuller
  29. Eric and Simon:

    During walking, lets say that the average magnitude of ground reaction force (GRF) is 1.0x body weight at the center of pressure (CoP). For each mm of medial movement of the CoP away from the subtalar joint (STJ) axis, then the percentage change in STJ supination moment decreases for each mm the CoP moves medially.

    For example, if the CoP moves from being 1 mm medial to the STJ axis to 2 mm medial to the STJ axis, and the subject weighs 750 N (168 lbs), then the STJ supination moment will approximately change from 0.75 Nm to 1.5 Nm, or a 100% change in STJ supination moment. However, if the CoP moves from being 20 mm medial to the STJ axis to being 21 mm medial to the STJ axis, then the STJ supination moment will approximately change from 15.0 Nm to 15.75 Nm or only a 5% change in STJ supination moment.

    Of course, the absolute change in STJ supination moment is the same for each mm medial CoP movement, but the relative change does decrease as the CoP moves further medial to the STJ axis. This fact may explain why it takes so little change in medial CoP movement or STJ movement laterally in some patients to effect a change in their pronation-related symptoms. For the past two decades, it is for these reasons that during my lectures on these subjects I have stated that I believed that changes in STJ axis location relative to GRF of as little as 1 mm are significant enough to either cause symptoms or relieve symptoms in a patient.

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