Welcome to the Podiatry Arena forums

You are currently viewing our podiatry forum as a guest which gives you limited access to view all podiatry discussions and access our other features. By joining our free global community of Podiatrists and other interested foot health care professionals you will have access to post podiatry topics (answer and ask questions), communicate privately with other members, upload content, view attachments, receive a weekly email update of new discussions, access other special features. Registered users do not get displayed the advertisements in posted messages. Registration is fast, simple and absolutely free so please, join our global Podiatry community today!

  1. Everything that you are ever going to want to know about running shoes: Running Shoes Boot Camp Online, for taking it to the next level? See here for more.
    Dismiss Notice
  2. Have you considered the Critical Thinking and Skeptical Boot Camp, for taking it to the next level? See here for more.
    Dismiss Notice
  3. Have you considered the Clinical Biomechanics Boot Camp Online, for taking it to the next level? See here for more.
    Dismiss Notice
Dismiss Notice
Have you considered the Clinical Biomechanics Boot Camp Online, for taking it to the next level? See here for more.
Dismiss Notice
Have you liked us on Facebook to get our updates? Please do. Click here for our Facebook page.
Dismiss Notice
Do you get the weekly newsletter that Podiatry Arena sends out to update everybody? If not, click here to organise this.

The greater your biomechancial knowledge the less you know about how foot orthotics work?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by mike weber, Sep 21, 2009.

  1. Members do not see these Ads. Sign Up.
    I´m having abit a crisis of sorts at the moment.

    As I´ve increased my knowledge of different biomechanical theories I´m comming the realisiation that we know next to nothing about how the device that we issue to patients works.

    The free fall began about 2 weeks ago after reading Niggs paper on leg stiffness in the orthoses thread and is getting worse with every article I read.

    Alot of the articles are flawed from the beginning using Subtalar neutral and the really interesting ones come to the conclusion that this needs to be researched in more detail.

    Is there light at the end of the tunnel or if a patient asks how do this orthotic work we should answer "I´m not sure".
  2. Re: the greater your biomechancial knowledge the less you know about how orthotics work

    Michael, foot orthoses do seem to consistently reduce the internal inversion moment (see this thread: http://www.podiatry-arena.com/podiatry-forum/showthread.php?t=37252) what we don't necessarily know yet are the details of why. We're working on it.
  3. Craig Payne

    Craig Payne Moderator

    Re: the greater your biomechancial knowledge the less you know about how orthotics work

    Reminds me of the best bit of feedback I have ever had from a Boot Camp: "...in which you leave knowing less than when you arrived. . ."

    We do know how foot orthotics work. They have to lower the load in the tissues. How else can they work?
  4. pgcarter

    pgcarter Well-Known Member

    Shaking your faith in our sphere of practice does not actually make for confident willing young pods. I used to tell my young students that it is clear that orthoses help in a variety of ways for a range of conditions but knowing the precise mechanism and magnitude of each specific effect was still beyond us. Leaving them feeling like we know nothing and that what we teach them is all "made up" creates a fair bit of stress for them. It is clear that we can alter the focus/foci of plantar pressures. It is clear we can alter basic things like stopping (decelaration)time and stopping distance, and we know that when you change those things peak forces are altered, but just exactly how and why ????? I'm a believer in the "new wear patch theory". Change the line of transmission of the peak forces through joints and instead of wearing the same old patch out even more they are putting the peak forces through a less worn patch, which feels better. We have not actually "fixed" anything but given them a fresh (or fresher)patch of cartilage to wear out. And if this works until they fall of their perch then we have improved mobility and quality of life.
    regards Phill
  5. Michael:

    Actually, what you describe here, Michael, is a fairly normal occurrence among podiatrists who are exposed to new theories regarding foot orthoses, after being taught rather dogmatic older theories regarding foot orthoses in podiatry school.

    If it makes you feel any better, I had a similar crisis during my Biomechanics Fellowship, during late 1984 (i.e. 25 years ago), when I started to note a lack of correlation of traditional "Root" biomechanical measurements to foot function, started seeing a good correlation of subtalar joint (STJ) axis location to foot function and foot pathologies and found that the STJ axis did not change directions at the midtarsal joint when using the palpation method, which I fully had believed would occur. You may want to read Thomas Kuhn's masterpiece, The Structure of Scientific Revolutions, in order to better understand the processes of change in scientific theory that has occurred within the scientific community for at least the last thousand years. (Thanks to Eric Fuller for first introducing me to this must-read book.)

    Just be thankful that you hopefully won't have to spend the next 25 years of your life convincing your profession that your ideas are mechanically sound and make good sense.;)
  6. 25 years.

    So you think you're done then kevin ;)

    I doubt it!

  7. Thanks Simon, thats my point they seem to be and the details why are what I´m after as it seems you are too.

    I agree Craig but how is it changed In the electric frequency of muscle as discussed by Nigg or does affecting the position of the Stj axis reduce Tissue load ?

    Thanks Phil but I´m not a young Pod Ive been treating patients for the last 15 years I teach Biomechancial Theory to the 2nd year Pod here in Sweden I beleive understand the different theories I can tell the many different orthotic mods I make when Ive finished with a patient assessment. But what exactly are these mods doing I can also explain the theory behand the mods and even give you a % chance that these mods will work and the patient will get reduced symptoms but I really want to know what is the device doing in the body.

    The new wear path theory fits perfect with tissue stress theory, but if you look at the new study done by Javier and Kevin ( and I need to read it again) the

    So the results support the idea about varus wedge reducing ankle inversion moments, but the thing I find most intersting is that there was There were no significant changes in peak internal tibial rotation among the three conditions tested.

    So if this is the case how do we control Tibial Position?
  8. LuckyLisfranc

    LuckyLisfranc Well-Known Member

    We shouldn't stress about this. Half of the common drugs used in society are equally mysterious in their mode of action. We shouldnt view orthotics any differently. If we focussed less on the *how* and more on *how well* we would be a far more productive and useful profession to society.

    The precise mechanisms by which the antidepressant drugs exert their therapeutic effects remain unknown...
    Handbook of psychiatric drug therapy

    Mechanism of general anaesthesia remains unclear...
    Sevoflurane monograph - Anaesthesia UK http://www.frca.co.uk/article.aspx?articleid=280

    The precise mechanism of the action of glucocorticoids in asthma is unknown...
    http://druginformation.com/RxDrugs/T/triamcinolone acetonide (AZMACORT).html

    Like organised medicine, let's move ahead with looking at how well these things do their job, and accept (at least for now) that the "exact mechanism of action for foot orthoses in foot pain remains unclear".

  9. Ok I agree the how well is important but I without stressing would like to know how. If I know the how then the how well ,will follow .

    here is a made up example. What if new research comes out as finds definate proof that EVA shore 60 does reduced the effective nature of muscle and will infact cause a increase in muscle stress. It will not matter how nice you are, how well you explain to the patient your finding from their assessment, it will not matter how well finished your device is, it will be causing stress on the patient that you though you were reducing might be important to understand the how.
  10. We don't need to know the aetiology of a pathology or the mode of action of the treatment, but when we do know these, the efficacy of the care should surely improve.
  11. LuckyLisfranc

    LuckyLisfranc Well-Known Member

    Not sure I follow you.

    After years of reading conflicting posts on this website (perhaps the definitive source of debate on orthoses anywhere), I think we can safely say there are only some basic concepts that some people and the research agree on.

    What is also clear to me, is that for decades thousands of podiatrists, physio's and orthotists etc use have used foot orthoses daily with reasonable levels of clinical success. Some evidence supports this, some is lacking, some conflicts with this.

    There are various hypotheses, various theories but no exact single mechanism of action that is agreed upon.

    We can keep going in circles, on we can start moving on and accept there are some limitations in our understanding. This needn't be a barrier to not start producing lots more meaningful outcomes studies, or indeed treating foot conditions at the coal face with incompletely understood non-surgical methods such as foot orthoses.

    If the pharmaceutical industry worked in this way people would still be dying of AIDS rather than living productive lives, and the 5 year survival rate for most cancers would still be appalling.

  12. Lucky,

    I take your point.

    Bunion surgery has been performed for a long time, do you think our improved understanding of foot function and the biomechanical effects of the various surgical procedures performed has improved the efficacy of hallux valgus surgery over the years?
  13. LuckyLisfranc

    LuckyLisfranc Well-Known Member

    I think it is broader than just foot function. Good outcomes in surgery are equally attributable to understanding and compensating for medical, physiological and pharmacological issues. More attention is paid to this than the functional issues - which are often distilled down into bullet points on position, degree of 1st MT head degeneration, length, and passive mobility of the sesamoids and main articulation.

    Our understanding of patient selection (or who shouldn't have surgery at all), medical factors, predicting those likely to suffer complications, the role of adjunctive pharmacotherapy (eg DVT prophylaxis), and outcomes research on the benefits of differing surgical approaches has improved outcomes. Don't ask me for a reference though...however, the 'disasters' that I use to see as a new graduate are a lot less common these days as orthopaedics and podiatry develop more refined (yet simple!) guidelines and accepted practice for these procedures.

    Such that now, there are rarely more than 3 different types of bunion correction procedures used for the vast majority of all patients. Scarf +/- Akin (UK podiatry and orthopaedic circles), Chevron/Austin (US and Australian podiatry), and proximal osteotomies for large IM angles (not so common).

    I feel surgical research and outcomes in foot surgery are more commonly accepted in the craft despite the same innumerable functional variations. Most procedures (arthrodesis, arthroplasty, osteotomy and translation) are reasonably reliable and predictable, with accepted and small rates of failure or complications.

    In my view, clinical guidelines and acceptable standards of peer review and practice (distilled from the research) are more palatable to foot surgeons than orthotic practitioners. It is more a case of 'get on with the job' according to the best available evidence, rather than worrying why one form of bunion fixation should be used over another.

    However, like orthoses, they are equal measure of art and science - and some of the exact science remains unclear.

    Just my humble opine.

  14. No change is peak internal tibial rotation was found in our study probably because we were just using simple rearfoot wedges, not well-shaped, anti-pronation custom foot orthoses.
  15. Yes and no.

    If we know that an intervention works, but not how, we are limited to that intervention. Learning other interventions becomes little more than trial and error. If we (or at least some of us) know HOW they work then we can modify, refine, improve and redesign.

    Acupuncture is a good example. There is some pretty compelling evidence that it can be effective for certain things, but also huge rafts of studies in which it performs no better than a placebo. Because we do not understand how it works it is very hard to work out why some studies show one thing and others something different, and also to tell the things it can treat effectively from those it can't.

  16. Lucky:

    I have a different perspective. The abundance of discussion on biomechanical theory that exists here on Podiatry Arena is in no way related to how much this type of discussion occurs in podiatry offices, between podiatrists or at podiatry seminars. In addition, just because a few of us choose to spend a large amount of our free time discussing theory, does not mean we are somehow withholding treatment from our patients with foot orthoses. I, for one, prefer to have an idea of how my treatments work so I can be more effective at designing better treatments for my subsequent patients.

    It is because of this general lack of discussion on biomechanical theory among podiatrists within the international podiatry community, and because there is virtually no other place to discuss high-level biomechanical theory with the leaders in the profession that we do have so much discussion here on Podiatry Arena on these subjects. Where else can I have intelligent discussions on tissue stress theory, subtalar joint axis rotational equilibrium theory, the neuromotor effects of foot orthoses and preferred motion pathway theory with multiple podiatrists other than on Podiatry Arena? Considering the time constraints of my very busy practice, I don't have the hours in the day to publicly have these types of discussions, largely because the average podiatrist wouldn't have a clue of what I am talking about. I believe that this is why so much biomechanical theoretical discussion takes place on Podiatry Arena.

    Podiatry Arena is the international mecca for discussion of foot and lower extremity biomechanical theory on the Internet.

    And Craig, you can quote me on that!!
  17. joejared

    joejared Active Member

    You'll be alright. Just live and study with the assumption that learning never stops, until you become fertilizer for flowers. This past year for me involves not only growth because of my newer products, but also learning because of new demands. Personally, I'm loving the challenge.
  18. I will keep that in mind when I re read the paper again this weekend
  19. pommypod

    pommypod Member

    I have read all these comments with interest and you lot seem to be the bio genius brigade. I on the otherhand didnt get it first time round in the 80's when it was rushed in 3rd year in the UK. I would like to ask your opinion on a number of things

    !. Root et al is now out the window? so what about all those orthoses made with that theory in mind, did any really work?
    2. Whats with all these gaitplate, Amfit, the strippey sock one, the computer does it all for you type set ups. Are some people in a circle of it cost me a fortune so therfore I must get my money back or are they superior assessment devices. Some I have seen in operation recently I thought had also gone out of fashion. Do you just need to know how to push the buttons?
    3. Why does everyone get casted in neutral no matter what, car smashes, athletes?
    4. Why do some quite eminent bio people sell orthotics for high heels. Is that not the ultimate rubbish?
    5. I have been out of the bio exam for a number of years and am currently wading through Valmassey, after a period of serious headaches I took to reading a lot on here and looking at material from different companies. But everyone disagrees on everything
    6. Will I ever get it?

    Apart from that I'm signing up for Craigs Boot camp next year in Auckland, did want to do it this year but when i'm in Uk its on in OZ and visa versa.

    7. How did you recruit that squirrell?
  20. Yep. Lots of evidence.

    The toys are great, but they are just toys. They don't provide a "superior assessment". Amfit can capture a nice 3d image. So can laser scanner, so can a foam box or plaster of paris. They're all just means to an end.

    My patients don't all get cast in neutral. I don't think there is anything special about a neutral position.

    Depends on the condition and the orthotic.

    Broadly true. Perhaps there is some truth in the "wisdom of crowds" idea.

    There are loads of areas to disagree on but also a few core elements which very few people would dispute. Perhaps the thing to do is to focus on the "canon". Sort of a biomechanics creed of central truths which we agree on. Good thread there.

    6. Will I ever get it?
    Depends what you want to "get";). If you wonder if you will ever get to the point of full enlightenment then... no. The more you understand the more you will see to learn!

    Enjoy the journey.

  21. efuller

    efuller MVP

    There is still some truth in Root. The partially compensated varus still exists. However, the STJ can't tell the difference between rearfoot and forefoot varus.
    My orthotics work. Just because they work does not mean that the explanation of how they work is true. How exactly was casting the foot in neutral position supposed to help the foot that stands on the orthosis? Voodoo?

    If you change things under the foot, the stress on the foot will change. Your job is to figure out which changes will make things better and which will make them worse.

    Give someone a hammer and everything looks like a nail. Some people never questioned or experimented on different techniques. You can add wedging to device made from a weightbearing impression of the foot.

    If the patients are going to wear the shoes, then you can change the forces applied to the foot in those shoes. It's more difficult to make it work, but it can improve the patients comfort.

    Just like with Root, you have to take what works and makes sense and discard what does not. Partially compensated rearfoot varus exists. The definition of neutral position is garbage. Measurement of forefoot to rearfoot relationship cannot be done accurately.

    Keep thinking about it.


  22. pommypod

    pommypod Member

    Thankyou :)
  23. pommypod

    pommypod Member

    I bow to the greater experience :)
  24. Peter1234

    Peter1234 Active Member

    hi, just wanted to say that there should be a counsellor at each podiatry degree currently running. I have just completed a degree in podiatry and can totally identify with this mans crisis. The crisis started for me in the first year of my degree and has not stopped.

    For me (and my humble opinion!!) Hylton Menz latest article 'Foot orthoses: how much customisation is necessary?' helped me in this respect. He uses physiotherapy and their current understanding of lower back pain, where they divide their clinicians into 'lumpers' and 'splitters'. The former is a categorization of clinician who believes there is a generic or standard approach to treatment, and the latter the more detailed and analytical clinician.

    Furthermore he goes on to say that we currently simply don't know the details ie. what conditions that orthoses work for. 'WE HAVE NO CLINICAL GUIDELINES' which is why it is so confusing for students and teachers alike.

    The fact that some clinicians are pointing out the tissue stress model gets my blood boiling - is there actually ANY OTHER plausible model? when you cut yourself it hurts, when you overuse an area of the body it hurts- simple.

    If we are to find a way forward we have to stop postulating and either get more specific, meaning treat each condition/pain with an orthoses as it occurs and note the prescription that works best (longitudinal study that has a central 'data bank' where all the data is stored and that is added to by each clinician every time they see a patient).
    OR maybe we just have to accept that the outcome variables are too great at present - feet are just too different - some feet respond like so, others like so. In other words get real- and accept that orthoses have limitations. And if that is the case maybe we are going to have to consider and adopt many of the other treatment modalities (excuse my french!) that are available.
  25. Peter1234

    Peter1234 Active Member

    ps. I think Pierrinowski (hope I spelt that right) and Nigg also have some literature on subtalar axis height and coupling movement of foot/ankle/tibial complex.
  26. I feel so fortunate to be studying Podiatry for the same reason I find it difficult at times. :)

    More on RF wedges: Murley and Bird (2006) “The effect of three levels of foot orthotic wedging on the surface electromyographic activity of selected lower limb muscles during gait”.

    "4. Why do some quite eminent bio people sell orthotics for high heels. Is that not the ultimate rubbish?"

    This is a really interesting question. One for which many un-verifiable opinions will exist. Perhaps the neuromotor theory may have more of an application for such a device? Who knows really? Exciting stuff. For some reason - for people in professional circles who feel compelled to wear unsuitable footwear - a cobra style orthotic may be providing just enough sensory feedback for the body so that there is minimal improvement in comfort levels. Has anyone done a qualitative study to see that there is such minimal improvements as a benchmark? Not that I can find. Probably not the Holy Grail of BMX.

    The Australian Podiatry Council published a 1998 article “Clinical guidelines for orthotic therapy provided by podiatrists”. Furthermore, the American College of Foot & Ankle Orthopedics & Medicine (2004) set out: “Prescription custom foot orthoses practice guidelines”.

    Nicolopoulos, Scott and Giannoudis (2000) did a good overview “Biomechanical basis of foot orthotic prescription”. Hume, Hopkins, Rome, Maulder, Coyle and Nigg (2008) reviewed some aspects: “Effectiveness of foot orthoses for treatment and prevention of lower limb injuries: a review”. As you will see guidelines are not as sophisticated as they will be with all the new research that will come out in the next 10 yrs. It is just the tip of the iceberg! My lecturer took a very detached approach to all this othosis stuff and as a consequently it really is evident how little evidence there is to guide our Tx. out there! Good man!
  27. Peter1234

    Peter1234 Active Member

    I hope i didnt sound unappreciative...not at all. I feel very privileged to be studying podiatry (d), of course. But maybe we should also appreciate that as we are specialists in the lower limb we should know to adopt the BEST possible treatments regardless of whether they come from trad chinese medicine, physio or osteopathy. Should we be so proud of our profession that we become blinded by other treatments that may work as well or better??!! I have heard people say that; 'that is for the physio to do!!' or 'we don't do those treatments'.. well we treat the lower limb, why can't we do it too? Especially considering the fact that we study three years of the lower limbs and should surely embrace all the best treatments.

    With regards to the biomech lit; the problem i have sometimes is that so much of the literature is VERY analytical and does not have a direct application to practice. Much of the lit is directed toward how orthoses change
    -Force (ie magnitude and time)
    -kinetics (ie direction of force)
    -kinematics (movement)

    it speaks to me sometimes almost like justifying as opposed to directly testing orthoses on pathologies. I must surely be wrong. I dont believe technology will ever be a replacement for a good work up, but an adjunct maybe?

    just a whinging pom maybe??:boohoo:

    PS: thanks very much for those papers!!
  28. You didn't sound unappreciative at all! Me... I just rant a lot... bad habit! :) Glad you liked the articles :)
  29. pgcarter

    pgcarter Well-Known Member

    You'd have to think that amount of tibial rotation caused by a rear foot wedge will vary a great deal with the specific nature of the anatomy of the individual, ligamentous tone etc and joint axis angles are going to influence these results a lot....were these issues dealt with in any of these studies? or is it another lesson in how many variables there are rendering the results not worth much?
    regards Phill Carter
  30. Ben

    Ben Member

    I really like your last comment. I think this gets missed with research and not being specific with the foot structure and anatomy of individuals. Certainly with the nigg stuff, they went to the extent of putting pins in tibia's but then decided to use a bit of padding in the arch area of a shoe insole to act like an orthotic. This hardly represents what most Podiatrists would do. I think when we had the article ? Menz on orthotic therapy for cavus feet, it gave us good evidence to use them. I feel same should be done with examining specific foot types for each study rather than a collective group of all sorts.
  31. After a week of reading and help from a wise wise man the crisis has reduced we can probably be safe in saying the we understand 70 % or so of how an orthotic works.

    Things that we know a device can adjust and change movement and axis position.

    Things that would be good to know which research maybe looking at.
    1.Ways to determine the position of the STJ axis at various stages on the gait cycle so can look at the point at which muscle work is the most so we can determine how to create the most affective lever arm with our device when required in the gait cycle .

    2 greater knowledge of the MTJ axis using the functional axis of nester et al As a profession it important that clincially we can determine motion of the x,y,z, axis but also have orthotic tools to address some of these biomechanical issues of the MTJ axis ( think skrive tech for STJ axis but specific device for MTJ axis)

    3 consider the functional axis of the MTJ which means that the cuboid and navicular move in the same direction at the same time. We may also need to condsider that there is some movement of navicular on cuboid. There is about 5 degrees in all 3 body plans is this important ?

    4 also think about the internal axis of individual bone especially the bone that have insertion point of muscle ie navicular.

    5 think about internal moments of the major axis STJ and MTJ ( see the debate after the article on 7 degree wedge effects on walking)

    So all these are looking at bone position and axis position

    What we need to research more involves muscle as well.

    So heres where Im at. With our device we are attempting to create equilibium at which muscle can function.

    How can we do this.
    1 adjust the axis position to adjust the lever arm of muscle.

    what we need to determine is how important is the neuromotor effects to help the muscle function better.

    it seems we can do this by adjusting the stiffness of our device and thinking about how much on the surface area of the foot comes in contact with the device.

    So heres where I´m at
    the greater the contact with device and foot the greater neuro feed back provided the more messages to the muscles which means the muscles function better.

    The muscle work can be measured and with nigg et al and other papers there is a point which muscle works best. This can changed through what materials the foot is standing on.

    It appears that the stiffer the device the better the muscle affectiviness.

    what we need to detect is what is the best stiffiness for each patient. This will also adjust from what shoes they wear and what activities they use the device for and what surface is under the shoe.

    So what we are attempting to do is find equilibium of muscle function. Through adjusting lever arm length, neurofeedback from the device and adjusting leg stiffness through the use of materials.

    We will also ned to consider the knee much much more especially when thinking about shock absorption.

    So lots of info and words hope that makes sense and If I´m wrong with my thought some wise people can help.

    thanks for reading
  32. Peter1234

    Peter1234 Active Member

    WOW, that is way above my head. I am sure you are right though. There seems to be a newer school of thought...that believes in finding the foots' most effective pathway for centre of pressure - as opposed to STJ neutral-meaning that less energy is expended for each step. What do you think of that idea? And how would you find that?
  33. Cameron

    Cameron Well-Known Member


    I taught foot orthotics and prosthetics (theory and practice for over 10 years) and have to agree the more I learned about bioengineering and biomechanics the less confident I became in tying to understand the function of foot orthoses. In the end I settled for selecting orthoses by material, then at least you had some hard data about material testing. (Finer feelings aside) as an academic podiatric biomechanics based upon subtalar neutral theory is just an anathema (to me) full of no science and hence a complete nonsense.

  34. efuller

    efuller MVP

    I'm not sure we know that we can change axis position or change movement.

    I'm not sure that we need to determine position of STJ axis in various stages of gait for everyone. I think we should look and see if someone has a medially deviated STJ axis in the position that they are in, in stance, then is their axis more medially deviated than someone who has an average axis in every position of gait. Once we establish that someone who is a 95th percentile in medial deviation in stance is still a 95th percentile throughout gait then we don't really need to know where the axis is in gait. We can be pretty sure that they need increased supination moments from our treatment no matter what time in gait it is.

    An aixs is an imaginary line that describes motion at a joint. We don't need to be studying imaginary lines, we need to be studying joint surfaces and ligaments.

    Probably not. See Van Langaalan.

    What is an internal axis of a bone and why do you think it is important? The tendon that attaches to a bone will apply a force to the bone in the direction of the tendon.

    How do you adjust an axis position? I can see how the axis position changes relative to the ground, when you supinate the STJ. This occurs because the position of the axis is determined by the shape of the facets of the bone and as you externally rotate the talus the STJ axis position will also externally rotate. However, if you can achieve a change in position of the STJ comfortably, you may not need to wory about the position of the axis anymore.

    Neruomotor effects are important and stiffness of the device may be related to those neuromotor effectts. We need to be careful in our terminology. For example we need to know what muscular changes are better before we try and make those changes.

    Some basic neuro anatomy. With the exception of some reflex arcs, sensory input is processed in the brain and then you get altered muscle activity because of altered brain output. Are you proposing a new orthotic reflex?

    Orthotic stiffnes probably does matter. It would be good to identify feet that do better with a stiffer device. It would also be good to figure out why a stiffer device helps those people. Two separate questions.


  35. hi Eric Thanks for your reply. A few questions

    If we cause the foot to supinate with a medial skrive we change the patients movement and due to the change in talus we also cause the axis to deviate laterally


    An internal axis I would describe as the point at which bone move around in relationship to the 3 body planes. I think that in some respects we forget the Joints are made up of bones that will move in relationship to each other. ie if the MTJ inverts and the navicular inverts on the cuboid is that important ? I do take your point about the amount of movement between navicular and cuboid may not be important.

    I also beleive that it would have an effect on the lever arm of the tendon as well.

    No But there maybe its worth considering be very intersting if there was

    I will continue to read thanks for your thoughts Eric
  36. It would, of course, be ideal, for research purposes, to know where the subtalar joint (STJ) is at all times during gait. However, as Eric said, this is not necessary when we are assigned the task to simply reduce the tissue stresses sufficiently to heal the patient's injury or make them feel more comfortable during their weightbearing activities. You should know which direction you need to push the foot to get them better (i.e. push them toward supination if their STJ axis is medial, push them toward pronation if their STJ axis is lateral) but really don't need to know exactly where the STJ is at all times.

    Foot orthoses are much more efficient at controlling abnormal moments across the midtarsal joint (MTJ) than controlling abnormal moments across the STJ simply due to the fact that foot orthoses do not cross the STJ axis in their direct application of external forces to the body. We have a great potential to alter MTJ motion with foot orthoses but, as of yet, do not have the bone-pin studies that will show the large changes in MTJ motion that can occur with foot orthoses. Once these bone pin studies are done, I believe that we will no longer be saying that foot orthoses only change moments, and not motion of the foot joints.

    I don't think that this is really too important clinically, but is an interesting question from an academic standpoint and as to how we should model the MTJ axis, as having one or two joint axes.

    I don't know either what an "internal axis of individual bone" is.

    I don't think the term "equilibrium of muscle function" is a good term to use. It would be more appropriate and meaningful to say that we are designing foot orthoses to optimize muscle function since many muscle forces are non-equilibrium situations of accelerating and decelerating joint motions. For example, in the patient with posterior tibial tendinitis, we are using inverted, medial heel skive orthoses to increase the external rearfoot inversion moment so that the posterior tibial muscle forces are decreased and the magnitude of tensile stress in the posterior tibial tendon is decreased. In other words, we are optimizing the stresses on the posterior tibial tendon with the inverted, medial heel skive orthosis so that the tensile stresses acting within the tendon are lower on the stress-strain curve, toward the elastic range, and away from its plastic range that is causing the tissue damage within the tendon.

    Hope this helps.
  37. Thanks Kevin definently food for thought from both you and Eric

    Perhaps I should and say individual bone axis Ie the talus will have a individual axis but we discuss the STJ axis. They of course maybe following the same direction.

    Looking forward to reading about that

    I agree now that It´s clearly stated.

    Thanks again Kevin of to think and read some more
  38. I agree with Eric and Kevin.
    Reading between your lines, I think what you are trying to describe here Michael, is that if we were to consider a bone of the foot in isolation then the movement of this bone, i.e. the navicular could be observed to occur about an instantaneous centre of rotation and translation- right?
  39. Right and much better said so now a few more understand what I was trying to say. Is it important ? I would think yes especially for the bone who have insertion points.
  40. adavies

    adavies Active Member

    I think we tending to move away from the orginal state. Crisis Bollrick Crisis!!!

    Being able to indentify chinks in our armour - i.e. our knowledge base, I believe we tend to become better at what we do.
    Straightening those chinks makes our 'armour' better able to cope which tricky situations.

    After all we are ALL still learning

    Kiwi AD

Share This Page