The myths of foot orthoses… A guest article by Ian Griffiths

So I am absolutely chuffed to bits that I have managed to convince and lure another guest writer at 'The Sports Physio'. I'm even more chuffed that I have been able to convince one as well-respected and recognised as Ian Griffiths a highly specialised Sports Podiatist. Ian has a wealth of knowledge and experience in all things foot, ankle and lower limb injury wise, his full bio can be found here, he also has an excellent blog that's well worth reading here and he is an absolute must follow on Twitter where he regularly gives out free advice and tips. So Ian has kindly written a fantastic piece on dispelling the myths of what foot orthoses (not 'orthotics' as I've been incorrectly calling them) do and don't do… take it away Ian

Adam has very kindly asked me to write a piece for his blog and whilst I can’t necessarily promise the usual levels of controversy, I certainly feel I have picked a topic here in which some commonly held ‘myths’ can be dispelled and hopefully some healthy debate is generated off of the back of this. I also hope that we can give some coverage to answering some of the common things you may see or be asked regarding foot orthoses in your clinic. It is worth just noting two things before we get stuck in to the meaty stuff. Firstly, despite its length this is not intending to be an all encompassing piece which will answer all questions (the topic is just too large, and as you will see shortly not all questions have answers yet). Secondly, I need to make clear that in expressing my understanding of this topic here I am very much standing on the shoulders of giants – in particular my friend and mentor Dr Simon Spooner. I am going to try and keep this piece much closer to a blog than an academic article in format purely for ease of reading, so very few references present and instead just some suggested reading at the end. If anyone reading this is desperate for any formal references based on any comments I’ve made then I can make these available on request of course.

“Unlearning comes before learning”

Before taking on new ideas and concepts we often have to be willing to re-evaluate what we think we already know or were once taught. In the context of foot orthoses this is usually with regard to how they ‘work’, or what we are actually aiming to achieve by issuing them. Many of us were taught that orthoses are biomechanical devices (how can they be when they are not living tissue?) which will ‘correct’ foot posture by realigning the skeleton and/or holding the foot in its neutral position. Essentially, all the focus has historically been very firmly fixed on controlling the position and motion of the foot (kinematics). What I hope to give people a cursory introduction to in this blog is that this may not be as appropriate as was once thought.

So, let’s look at these points individually. Do they ‘correct’ foot posture? Well in order to do so it suggests we have a solid understanding of what is incorrect. This is far from the case, with no consensus on what a ‘normal’ foot is and no clear agreement on the foot level characteristics that will consistently predict or even correlate with lower extremity overuse injury. I don’t want to go off on a tangent on this one, and those that know me will already know my thoughts on this subject (with respect to “overpronation” etc) but it is an important question to ask. If we don’t know what position the human foot should be in then what is our goal when introducing orthoses? The idea that a foot should function in its neutral (STJ) position has hopefully long been put to bed, with not one single study ever performed (be it static or dynamic) showing this to be true of any sample of the population taken.

Even if we knew for sure that ‘STJ neutral’ was king, would foot orthoses hold the foot in this position? Well, no. They cannot physically hold the foot (they are inert materials) and again not a single shred of evidence exists showing that this is what orthoses do. The research performed on the kinematic responses to orthoses give us some very interesting data. We will talk about the limitations of foot orthoses research later, but for know all you need to know is that there are just as many studies available which show that rearfoot kinematics do not significantly change as there are that show they do. (NB Therefore easy to cherry pick references which support your beliefs on this topic should you be inclined to do so!). The best explanation of this based on our current understanding is that the kinematic response to foot orthoses (i.e. if someone shows any angular changes at all, and if so how much of a change) is subject specific/different for everyone. We do not really know why.

Orthoses STJ Neutral

Image 1: Depicting the classic 'before and after' shot associated with orthoses introduction. this is a fake. i know as it is my wife's left foot and I took the pictures 30 seconds apart on a demo orthosis that wasn't even hers.


So do foot orthoses ‘work’? Well this will depend on how you define ‘work’. If you define it as eliciting a visual change at foot level then the answer is that they will not work in this way for everyone, and it will be difficult/impossible to predict those individuals that they will work for. If you define ‘work’ as improving pain levels and reducing musculoskeletal symptoms then this is also difficult to predict and will vary from person to person, so they could be deemed to sometimes not ‘work’ in this regard. However the bit to get your head round is that they do not need to change position or alignment to reduce pain levels. Why? We’ll come to that… And how else could we define ‘work’? We’ll come to that too…

Confused? I hope so. We all should be. Preferred the old ways we were all taught at undergraduate level with respect to foot orthoses because they were simpler/easier? Yeah, me too. (That’s why a lot of clinicians still stick with it!) A summary of the salient points so far:

  • Orthoses are mechanical devices, not biomechanical devices
  • We don’t know what the best/ideal/normal/correct foot posture is for everyone
  • Even if we did, orthoses don’t hold the foot in this (or any) position
  • Kinematic responses to orthoses are subject specific
  • Orthoses do not need to change kinematics to reduce pain

So how do orthoses really ‘work’ then?

We know that they change alignment in some of the people some of the time. We know that they reduce pain and improve symptoms in some of the people some of the time. But what do they do in all of the people all of the time? They change kinetics. If you define ‘work’ as altering kinetic variables, then all devices are deemed to ‘work’ (Remember this won’t necessarily correlate with clinical success!) Kinetics are forces – all too easy to ignore (particularly clinically) by virtue of being invisible. Forces are what drive motion. They start it and they stop it [Newtons’ 1st]. It is force which will be the key contributor to tissue damage. NB Although obvious it is worth briefly noting that they w
ill of course be a close relationship between kinetics and kinematics, but we will discuss them completely separately here to try and simplify things.

There are now many papers which have looked at the kinetic responses to foot orthoses. Most research will report on the kinetic and kinematic data separately. The first paper I read which really allowed the penny to drop for me regarding this entire concept was in 2003 [Williams et al]. To summarise, they measured both kinematics (angular changes) and kinetics (using inverse dynamics to calculate work loads in tissues) in three different environments (no orthoses, and two different orthoses environments of different levels of inversion) in runners. Interestingly there were no significant kinematic differences between all groups, but the demands placed on the tissues they measured significantly decreased as the level of inversion of the orthoses increased. Therefore these orthoses worked (i.e had a mechanical effect) without appearing to work (change alignment). Worth reiterating that whether or not this equates to clinical success is of course a different story and again brings us back to subject specificity.

Traditionally, if a patient returned and reported no improvements and on review it was deemed there was “not enough correction” then orthoses would often be adjusted and possibly have more wedging applied to them until such time as the patient reported improvement. We thought we were shooting for a situation where the foot was in a better position – could it be we may have been measuring and trying to change one thing, unknowingly altering another thing, and clinically succeeding by accident? Food for thought. Anecdotally, in my own clinical practice I often see patients getting great clinical outcomes from devices with seemingly little positional change observed. Anyone who has given out enough devices will have seen this too I’m sure. Just to further muddy the waters it is certainly the current belief that kinetic responses to an intervention will also be subject specific, and difficult to predict. (As well as being invisible). Nightmare.

So where does this leave the clinician?

Anyone issuing foot orthoses needs to have a sound clinical rationale for doing so, which should include an understanding of what they are trying to achieve and how best they feel it can be achieved. In light of the discussion so far you can see this is a far more complex set of considerations than simply looking at a foot and deciding it needs some ‘support’ merely based on its position either statically or dynamically. Anyone who tells you otherwise has unfortunately fallen prey of the Dunning-Kruger effect. Another summary before we go on:

  • Foot orthoses will always change kinetic parameters
  • Kinetic responses to orthoses will be subject specific
  • The inability to measure/observe kinetics clinically is probably why disproportionate attention is given to kinematics

When we introduce foot orthoses we are essentially making an alteration of the foot level environment. It is key that we have some understanding of how the choices we make here may influence the kinetic parameters, and try to use our understanding of this to achieve our treatment goals. I’m sure most readers are familiar with the concept of equal and opposite reactions [Newtons 3rd]. The fundamental mechanical function of foot orthoses is their influence of reaction forces at the foot-orthosis interface. Dr Spooner has postulated that they do this in one of three ways, and we can manipulate these to our advantage by virtue of three key design variables in our orthoses. This makes such mechanical/scientific sense to me that it has changed the way I practice and prescribe devices. It also has implications for picking off the shelf/prefabricated devices which we will talk a bit about later on. To try and give this some clinical context I will also need to take a slight detour away from orthoses briefly and talk about tissue loading and damage.

Kinetics at the ‘foot-orthosis interface’…

The meeting point of the foot and the orthosis shell is what we refer to as the foot-orthosis interface. When the foot applies a force onto an orthosis, the orthosis will apply a force back (the orthoses reaction force or ORF). It is our understanding of the reaction forces here and how decisions we make will affect them, which is important. Decisions we make will only modify these reaction forces in three possible ways (irrespective of what type of orthoses we are issuing):

  1. Altering the magnitude of the reaction forces
  2. Altering the vector of the reaction forces
  3. Altering the temporal patterns of the reaction forces

Orthoses foot interface

Image 2: The foot-orthosis interface


So basically, all we can look to change at the foot-orthosis interface is how high the forces are, the direction they push in, and the time they spend there. That’s it. These factors may of course have subsequent effects (both desirable or undesirable) such as changing joint moments or changing tissue loads, and as we have already touched on they may or may not be accompanied by a kinematic response, but the only ways in which orthoses are thought to exert their mechanical (kinetic) effects at foot level are via one or more of points 1,2 and 3.

It is thought that we can only achieve alterations in one or more of the above three key kinetic variables by virtue of the following design options in our orthoses:

A. The surface geometry of the orthoses (shape/contour)

B. The load-deformation characteristics of the orthoses (stiffness)

C. The frictional characteristics of the orthoses (think top cover selection)

So when writing a prescription for a custom made device, or when picking from the hundreds of different prefabricated devices available on the market, these are the three key decisions the clinician has to make. How stiff does it need to be? What shape does it need to be? What top cover do I want (if any)? That’s it. There is nothing else in the clinicians’ control. Every single modification or design feature that exists and can be incorporated into an orthosis will change one or more of A, B, C and in turn will more than likely alter kinetics at the foot-orthosis interface via one (or more) of 1, 2, 3. It is making these decisions in the context of a real person with a real pathology that should be the goal of anyone implementing orthoses therapy as part of a rehabilitation strategy.

I have just realised that this probably needs a whole separate blog of its own, where we discuss joint axes, lever arms, external and internal moments etc but hopefully the main introductory message is clear – things are complex and not as simple as we once thought.

Still with me? It’s a bit intense I know, and further illustrates why some (lazy?) clinicians still just dish out ‘arch supports’ with the same prescription or from the same off the shelf company for all their patients. It’s easier. Lots.

So when do we give orthoses?

Let’s take a step back from the physics behind things for a while and get onto tissue damage. I make no excuses for grossly oversimplifying things here, but generally speaking you can summarise that with respect to musculoskeletal overuse injuries, ti
ssue dysfunction could be said to occur when a healthy tissue is loaded in an ‘abnormal’ way, when an unhealthy tissue is loaded in a ‘normal’ way or (and perhaps worst of all) an unhealthy tissue is loaded in an ‘abnormal’ way. It has been postulated that each of the body’s tissues has a zone of optimal stress and the tissue must be loaded within this zone to remain healthy. [This zone will of course will be different for each of the body’s tissues].

Thus, for a given individual with a given pathology, the aim of orthoses therapy should be that it helps facilitate the loading of the ‘target tissue’ to fall back within its zone of optimal stress (if it can).

The difficulty here of course (nothing in this game is ever easy) is that we do not necessarily know exactly what that zone is for a given tissue, and furthermore that it is likely to be a dynamic variable which itself is dependant on tissue health (e.g dysfunctional tissue = narrower zone). Worth noting here however, that for a given individual with a given pathology it is highly unlikely that there is one type or style of orthotic device which will result in a good outcome, meaning that one highly specific prescription for each patient and each dysfunctional tissue is unlikely. Dr Spooner refers to the concept of there being a range of ‘positive solution sets’ and I tend to describe it as an ‘envelope of success’. This is the reason that a lot of individuals will report at least some improvement in symptoms when given a device of any description for the first time (thus potentially perpetuating the aforementioned lazy clinicians’ beliefs that this is a simple game and they are on the right track) – if it puts the target tissue back within its zone of optimal stress then a good outcome will be achieved (even if the clinician did it by accident!)

It brings up a few more questions. If we are using this tissue stress approach to management of lower extremity overuse injury then how do we treat asymptomatic individuals? That’s a toughie. With the old adage ‘if it ain’t broke then don’t fix it’ ringing in your ears you still sometimes just see movement patterns that your clinical experience tells you may increase the risk of a tissue being loaded outside of its zone of optimal stress (even if the research doesn’t support you). You have to judge it on an athlete by athlete basis and make the call based on that individual, their level of conditioning, their training regime, their goals etc etc. Assessing/screening uninjured athletes is actually my least favourite thing to do. It is a very bold shout to claim with authority that you need to change something as it increases risk of injury (particularly in light of our current understanding of injury risk being poorer than we like to admit) in an asymptomatic individual.

Next question – do orthoses have to be worn for life? Another good one that gets asked a lot. Answer = it depends. For some individuals you may just want devices in situ to allow a tissue to be more appropriately loaded whilst rehabilitation and/or healing takes place. For others it is certainly the case that they may need those devices in place for the tissue to not be loaded outside of its physiological window and removing them may result in recurrence of injury. There is no one answer for all on this. Again you have to make the call based on the information you have in front of you at the time and your clinical experience. Remember despite what you may read from those with a financial motivation – there has never been a single piece of work published which has shown that orthoses ‘brace’ the foot or result in muscle weakness.

Last common question – custom made orthoses or off the shelf orthoses? The discussion about comparison of costs and durability aside, what is the main difference between these devices and when would you use one over the other? Well as already mentioned you have three main things to make decisions on (shell stiffness, shape and frictional characteristics) and you need to manipulate these to alter kinetic at the foot-orthosis interface in a way that will achieve your treatment goal. If there is a prefabricated device which ticks all the boxes then is it technically any worse than a custom made device? No. However it has to be pointed out that there are distinct advantages to designing the device yourself; mainly the far greater control you have over the prescription variables of interest. In my opinion the able clinician has both a very clear idea of the design features that may best achieve their goals and a good enough knowledge of the prefabricated orthoses market that they can identify one which is a reasonable off the shelf solution in delivering those design features (if there is one). Certainly beware the clinician who only recommends custom made devices exclusively, but also beware those that only recommend one type of prefabricated device.

Orthoses cogs

Image 3: The main considerations with foot orthoses


Research Limitations…

I’ve alluded to the research several times, and in this day and age we are quite rightly trying to all implement more evidence based practice. Should we continue to do things just because we always have and they have always worked? Probably not. I’m not suggesting we stop them (for example the clinician giving out generic orthoses and getting good feedback) as we mustn’t forget the most important thing in all of this is the patient, but I do feel we should at least be constantly striving to understand the underlying mechanisms.

The problem with foot orthoses research is it is undeniably difficult to design. Individuals will often know if they are in the control group or not. It is not possible to have a ‘sham’ device in these studies as even this will alter kinetics at the foot-orthosis interface and therefore potentially have a mechanical effect. Quite often the orthoses given to pathological sample groups in a study do not appear to resemble the sort of orthoses that clinicians would give for that pathology in the ‘real world’. The list goes on. These difficulties may be why there is such disparity in the conclusions reached in orthoses research to date. All I urge people to do when they see a study incorporating foot orthoses is to look at the methodology rather than just the one line conclusion in the abstract.

Finally, and most crucially, you may remember me saying that kinetic responses to foot orthoses are variable and subject specific, just like kinematic responses. How many articles have you seen that have standardised for this? None. (can it even be done?) What they often do instead is give the subjects a device and monitor the kinematic responses or pain reductions and perhaps compare to a ‘control’ group. It is therefore highly likely that all individuals in these sort of trials are receiving a different kinetic ‘dose’ from the orthoses. This could be likened to a pharmaceutical company performing a trial on a drug and giving every subject a different (and unknown!) dose of the drug – how on earth would they learn anything about that drug?!


For those still reading – if I haven’t managed to articulate things well enough that any of the above made sense I hope that at least I’ve managed to get across that the practice of issuing foot orthoses is complex, and our understanding of the subject (whilst not where we would like it to be) has certainly developed over recent years.
No doubt it will continue to develop, and I hope research looking at how orthoses prescription variables alter kinetic parameters, and in turn how these changes correlate with clinical success for a given pathology will be at the forefront. It seems to be the case that all the current research is looking at how good orthoses are for pathology X, or if they prevent pathology Y, or how do they compare to Physiotherapy in the treatment of pathology Z, when actually it’s pretty clear we need to take things back a few steps and actually investigate how they ‘work’ much more, and look to try and improve our study designs and methodologies.

So a last two bullet points for all:

  • Significant consideration should be given to the subject specific responses to foot orthoses [will this change what you ‘promise’ your patients?]
  • Orthoses goals may more appropriate to consider in reference to the zone of optimal stress rather than aiming for a kinematic ‘norm’

And to close out, a paragraph from that man Dr Spooner again which sums things up beautifully:

“The skilled clinician is capable of identifying the dysfunctional tissue (and the severity of injury to it); they understand the biomechanical function of the tissue during given activities; and they comprehend the manner in which each of the 3 orthoses design variables interact with one another, and ultimately their kinetic influence on the foot.”

Suggested Reading…

McPoil TG, Hunt GC: Evaluation and management of foot and ankle disorders: present problems and future directions. Journal of Orthopaedic and Sports Physical Therapy 21: 381, 1995.

Nester CJ: Lessons from dynamic cadaver and invasive bone pin studies: do we know how the foot really moves during gait? Journal of Foot and Ankle Research 2: 18, 2009.

Kirby KA, Spooner SK, Scherer PR, Schuberth JM: Foot Orthoses. Foot & Ankle Specialist 5: 334, 2012.

Williams DS, McClay I, Baitch SP: Effect of inverted orthoses on lower-extremity mechanics in runners. Medicine and Science in Sport and Exercise 35: 2060, 2003.




  1. Great article Ian, highly indformative as expected.
    How is the above applicable, if at all, to the success some individuals have from using Footbalance “custom” insoles (as sold in Sweatshop stores). An example of any change in load (kinetics) helping some people initially?
    Sweatshop are careful to stress on their website that their insoles are not to be seen as orthotics saying that they simply serve to provide added comfort, but in certain contexts is comfort not another way of saying optimum distribution of load? They may be a stab in the dark way of trying to relieve pain but do you believe such “custom” insoles can be useful for rehab, if you’re lucky?

    • Hey Matt
      Thanks for reading the blog. Yours is a sensible question, as the up-sell of foot orthoses by running stores is on the increase. I guess the debate over what constitutes an orthotic device (i.e. when does an ‘insole’ become an ‘orthosis’?) is almost a separate discussion. Nomenclature notwithstanding, the fact is that ANYTHING you put into the shoe (even an odour eater) will alter kinetics at the foot-orthosis interface. Therefore it has the potential to result in the user experiencing changes (either positive or negative). Our challenge as professionals is to try and use our understanding of this to achieve a clinical outcome. Even then we do not always get it right. In the running stores it may be the case that they are issuing them based on similar reasoning, but I suspect this would be rare. Fair to say they’ll help some and they’ll hinder others.

  2. We also need to remind orthotic uses to check the integrity of the orthotic through it’s life. Orthotic failure is more common the public and clinicians think. The footwear that is used with orthotic is also important.

    • Hi Bruce,
      Your point about device integrity can (in my opinion) be viewed in the context of the points I made in the blog. If an orthosis undergoes material change (e.g. creep) or failure this will immediately alter one or more of the three variables I refer to (load-deformation characteristics, geometry and frictional characteristics). In turn this will change the kinetics at the foot-orthosis interface. Therefore if a device was ‘working’ clinically, then a change in its properties may result in it failing to continue to ‘work. (Of course it may not – as there is an envelope of success and it still may maintain loading of the target tissue within its zone of optimal stress). You are absolutely right though – this should be at least monitored.
      As far as footwear – suffice to say I do not subscribe to the school of thought that ‘thou must have a neutral shoe if you wear orthoses’ and I believe it is more of a case of considering the net effect of the entire foot level environment (footwear + orthoses) in the context of what you are trying to achieve. But let’s leave it there for now as that may form part of a follow up blog in time….

  3. Great article, Ian. I think you covered the main points of foot orthosis therapy quite nicely. Keep up the good work.

  4. Ian:
    After reading your article a second time, I wanted to make a few small points.
    You listed the functions of foot orthoses as being the following:
    1. Altering the magnitude of the reaction forces
    2. Altering the vector of the reaction forces
    3. Altering the temporal patterns of the reaction forces
    In addition, another important function of foot orthoses is that they alter the plantar locations of the ground reaction forces acting on the foot during weightbearing activities. This is especially important when one considers how we can pick and choose the specific plantar areas of the foot we either want to load or unload to accomplish our goals of foot orthosis therapy for the patient.
    Secondly, in addition to your fine review of the problems with foot orthosis research, I believe it is worth mentioning also that when we see a kinetic or kinematic effect from foot orthoses, we really have no way of know whether this kinetic or kinematic change is caused by the direct mechanical effect of the foot orthosis (i.e. caused by the change in the location, magnitude and temporal patterns of ground reaction forces that result from direct mechanical contact of the orthosis with the plantar foot) or is caused by the neuromotor effect of the foot orthosis (i.e. caused by changes in sensory input to the CNS from the mechanical effects of the orthosis on the plantar foot that results from alterations in the magnitudes and temporal patterns of motor stimuli from the CNS to the muscles of the foot and lower extremity). Certainly, much of the variation we see in kinetic and kinematic response to foot orthoses may be explained by the different neuromotor responses from CNS to different orthosis designs.
    Greatly enjoyed your article, Ian. I believe it is your finest one yet.

    • Hi Kevin/Ian
      Great article. I like the thinking Kevin and mirrors my own, especially with what we know about pain and tissue damage not always having an isomorphic relationship.
      I think we can assign a pain output from the brain to an impending event via a bayesian probability or to a the interpretation of a specific set of sensory information from the body. Moseley/Butler discuss this as a neurotag. Melzack as a neurosignature.
      Does the orthosis alter the specific somatosensory feedback that has a pain association? It maybe that huge kinematic change is not required in some cases to alter the output of pain from the brain. Just a subtle change. This could be by changes in plantar surface pressure or even frictional changes with a top covering. It would depend on the need of the individual and their issue.

    • Thanks for your comments Kevin – as you know I have always valued your opinion (particularly as your shoulders are another of the pairs I have stood on for most of my career). I think you are absolutely right that other mechanisms of action are likely to be at play here with respect to the CNS. I tried to keep this blog as simple (and short) as I could and therefore focused purely on the mechanical effects of foot orthoses. I perhaps should’ve at least mentioned the psychological effects that devices may also ‘work’ via, but left this out also. As I said in the intro – I wasn’t expecting it to answer all the questions or be all encompassing! I may actually hunt out the old thread on Podiatry Arena that discussed mechanical Vs neuromotor effects of orthoses and post here for those interested.
      Hope to catch up soon

      • To elaborate a little further on this subject, the neuromotor effects of foot orthoses would be described as either the conscious or subconscious change in efferent output to the muscles from the central nervous system (CNS) in response to a change in afferent input into the CNS which is caused by changes in mechanical pressure on the plantar foot from the orthosis.
        For example, an orthosis that is slightly inverted with a medial heel skive may reduce the pronation of the subtalar joint (STJ) during the early stance phase of gait by the external STJ supination moment it creates on the plantar foot by its direct mechanical effect. However, an orthosis that is highly inverted with a high medial arch and a large medial heel skive may actually cause more STJ pronation motion, especially during the late midstance phase of gait, due to its effect to cause the CNS to increase the internal STJ pronation moment from the peroneal muscles in late midstance in order to avoid a lateral ankle injury. This late midstance pronation that is commonly seen with the highly inverted orthosis would be properly classified as a neuromotor effect of the orthosis, since the STJ pronation motion is directly opposite to the way the orthosis is “pushing on” the plantar foot.
        Here is the thread from over four years ago on Podiatry Arena on this subject
        Direct Mechanical vs Neuromotor Effects of Foot Orthoses-
        The problem is that regardless of how we design the orthosis, unless we know how the patient’s CNS will respond to the orthosis beforehand, then the clinician should always evaluate the gait and symptomatic response to every orthosis dispensed to a patient and then fine-tune the orthoses depending on the direct mechanical and neuromotor effects the orthoses cause within the kinetics and kinematics of the patient’s gait.
        Interesting discussion.

  5. I’ve been reading some of the comments on twitter regarding this blog. I don’t tweet, so I’ll pick up on one of the twitter comments here if I may.
    Trevor Prior asked: “How do you determine the kinetic effect required / provided for your patients?”.
    It is important to understand that the kinetic effect of a given foot orthosis is not a constant. To understand this we must realise that foot orthoses can only provide reaction to the loading forces applied to them. Orthoses transmit loads from the body through their structure to the shoe and so to the ground. To produce static equilibrium, an orthosis must provide an equal and opposite reaction (Newton’s 3rd Law of Motion). When loads are applied to an orthosis, the orthosis tries to absorb its effects by developing internal forces that vary from one point to another. The intensity of these internal forces is the mechanical stress. When subjected to external loads, orthoses change their shape; though sometimes imperceptibly. This change in shape is termed displacement or deformation and is measured by the mechanical strain. The necessary orthosis reaction force is generated by the stress caused by the action of the loads within the orthosis material, and by the ensuing strain in the elements of the orthosis structure. The pattern and distribution of stresses and strains within an orthoses are chiefly determined by the shape of the orthoses; the exact magnitude of the stresses and strains within an orthoses are determined chiefly by the material it is constructed from (Young’s modulus of the material).
    Since during activities of daily living there are step to step variabilities in the loading patterns that the body applies to the foot orthosis, there must also be variability in the stress and strain developed within the orthoses in response to the variation in loading patterns. Viz. the orthosis reaction forces will be dependent upon the loading forces applied. But this does not really tell us how to determine the kinetic effect required.
    To answer this we must think (at this time) in a qualitative manner. That is, if we can accurately identify the tissue which is dysfunctional, i.e. being over (or under) loaded and is the source of the patients pain, and we can understand the biomechanical role of that tissue (what are the internal moments created by that tissue when loaded in specific ways) then we can attempt to design our orthoses to create an enhanced external moment from our orthosis to assist that tissue in its biomechanical role- hence providing “rest” to that tissue in order to fascilite healing and repair. The indicators of whether or not we have been successful in this will be things like reduction in pain and improvements in indicators of tissue health observed using modern imaging techniques.
    I’m currently in Spain lecturing on “how foot orthoses work” and finite element analyses of foot orthoses design characteristics, so time is a little short but I hope this helps to clarify a couple of points for the readers of Ian’s blog about my work.

    • I should have said here that UNDER UNIFORM LOADING- The pattern and distribution of stresses and strains within an orthoses are chiefly determined by the shape of the orthoses; the exact magnitude of the stresses and strains within an orthoses are determined chiefly by the material it is constructed from (Young’s modulus of the material).

    • Thanks for your input here Simon. You’ve taught me more about foot orthoses than anyone and I only hope I didn’t butcher things too much in my interpretation of your work for Adams readers here on the blog!
      See you in Zaragoza…

      • No worries, I was just out for dinner with some of our Spanish colleagues and I was recommending you as a potential visiting lecturer for the future.

  6. Another point which occurs to me, perhaps for the first time, is that low levels of physical stress can result in tissue harm just as much as excessively high levels of tissue loading (this is not new to me, the implications which follow are). This being the case, sometimes it might be necessary to design foot orthoses which increase the loading on the dysfunctional tissue- now that is a new thought- right Griff?

    • Designing an orthosis to increase load on the target tissue… Perhaps the most controversial thing since someone first suggested increasing external pronation moments with orthoses?? The forefathers of podiatric biomechanics will be turning in their graves 😉

  7. This article is of great relevance to me as a sports biomechanist and a store manager of a footwear store where we create custom insoles using the Sidas Comformable system. I carry many of the same beliefs as what has been written in the article and believe that custom insoles/orthotics have a part to play in improving comfort and alleviating injury symptoms. I follow many of these articles/threads/forums and find that I have learnt possibly more from this research than I ever did in my university degrees. Similarly my experiences dealing with customers over the past 5 years have influenced my opinions with regards to custom insoles and running shoes.
    The argument about whether running shops should be selling custom insoles is very subjective in my opinion. The success of these insoles does depend on many factors and for me the most critical factor is the clinican. Yes I use the term clinician and not store assistant as I do believe that to understand the patients requirements, one must be adequately trained and educated on lower limb biomechancis and understand the purpose of the insole design. This article has put to paper many of my beliefs, insoles are not about STJ neutral rather about load redistribution. Similarly, my belief is that adequate footwear plays a critical factor, contrary to many other’s beliefs.
    In short I appreciate this article as a thought provoking insight into the benefits of custom orthotics and footwear. I am always open to changing my views, as Craig Payne would say “I go where the reseach takes me” lol. I hope this thread helps to question those who believe that not all running shops are attempting to throw orthotics/insoles at every poor sole whom walks in the shop. Many of us are just as interested in optimising strength and conditioning, flexibilty, altering running technique as we are about making a sale. It is unfair to generalise all such stores into one.
    Many thanks and look forward to learning more from you guys,

    • Hi Thomas
      Many thanks for your comments, you make some excellent points and your right we shouldn’t tar all running shops and their employees with the same brush, a trait I am probably guilty of!
      It is unfortunate however that there are many running shops that just haven’t employed the right staff with the right knowledge and skills to give advise on footwear, many have poor in house training and are ‘salemen’ rather than ‘clinicians’ and all to often do I regularly hear stories from my patients of sketchy poor advice and guidance given on running shoe and orthoses
      However its great to hear that not all shops are like this and your comments has restored my faith in some running shoe shops having the customers interests at heart rather than a sale, good job!

      • I agree Adam that not enough running specialty stores have sufficient health science backgrounds to enable them to provide adequate education and service to their customers outside of just selling shoes. In fact I have relocated to Melbourne from Cork to pursue such employment with Footpro where I have had the opportunity to expand my learning in a very progressive work environment. Footpro is very similar to it’s northern hemisphere big brother Profeet in London to give you an idea of what we do.
        I understand that you have heard from customers whom receive poor advice from “salesmen” but unfortunately bad advice is not localised to retail. I have recently experienced an upsurge in the amount of customers referred to us by their health practitioners whom have recommended minimal footwear as it will change their running technique. If you refer to research by Joe Hamill this has been concluded as false and footwear plays little roll in adapting foot strike patterns. Others whom maintain the old school belief of running is bad and recommend taking up cycling etc. Evidently I am cherry picking examples and the majority of health pracs are very well educated and keep up to date with research, I am simply making my argument for some decent running stores out there.
        Articles like these ones are very informative for health pracs and footwear stores alike and are making relevant information available to wide audiences, I can only thank you for an excellent service. I will be attempting my own articles in future as part of staff training and educating our customer database, I hope you won’t mind if I reference some of your work.

  8. In the words of Peter Higgs ” “how can scientists be sure that the observations they make are real?” (Maxwell Society speech May 1950).. Beautifully written Griff.. seems to have put the cat amongst the pigeons! Just to throw a curve ball here..Displacement, velocity and acceleration are all vector measurements in other words they have both magnitude AND direction, and I reckon I could make a reasonable case that orthoses always change at least one of these all the time and therefore they do change kinematics all the time, it is just that most people are looking at it in completely the wrong way and trying to titrate gross angular or rotational changes that do not exist to orthotic function. Thoughts?

    • I agree, Simon. It is the variation in the displacement at the foot-orthosis interface which links to variation in the reaction forces at each point at the foot-orthosis interface via Hookes Law (F=-k X where: F is the restoring force, k = spring stiffness and X = displacement). We have probably been looking in the wrong place for our kinematic changes.

  9. Griff, the article is well written and stimulated the debate nicely. Being grey and getting on, I recall the days before Podiatric biomechanics took off in the UK and the subsequent introduction by Ray Anthony. Most will know he founded RX labs, now a subsidiary of Langer with very purist Rootian orthoses.
    Simon, an eloquent response as always and the point of my question was to come at orthoses from the opposite direction. I have read over the years, the various theories and concepts and do not regularly contribute to the debate as I feel I have nothing new to add. However, when I am in clinic, I still have to prescribe devices.
    Whilst the way they may or may not work is important and we should strive to get as close to the answer as we can, in the interim, patients still need treatment.
    My thoughts are much with Simon B, orthoses exert an effect as he describes BUT, how do we write a prescription? I, like most, have my own beliefs and have constantly striven to make this as reproducible as possible.
    The kinetics are important if not key and, accepting the limitations of a curved object and force sensors, you will be aware that I am a fan of plantar pressure analysis as this gives feedback as to the immediate effects. In an ideal world, all patients would then be reviewed once they have adapted and neuromotor changes have occurred. We should then look to how function varies during the day, with activity and on the uneven pavements of London or where ever – the point being there are only so many variables we can control. The inshoe analysis constantly shows me how aspects of control I thought would work do not and make be re-evaluate.
    Taking up the tissue stress model Simon refers to, contrary to belief (I have not always articulated my thoughts well) the broad principles are fundamental to my practice. I am still firmly of the opinion that there is an optimal range of function for all, within which, the relative stresses / strains on the locomotor system are minimised – this is affected by a whole variety of factors, too long for this post. Our goal, should be to determine what that range is and then move / direct to that range with all the interventions available which includes orthoses. In some instances, a device that off loads a structure will not direct to the optimum position of function and what the patient requires is something that increases load (as Simon S alludes to) but works because it now allows the structure to function more normally – the peroneals are a great example as a device with a lateral forefoot post could reduce stress, whereas a device with medial control facilitating 1st ray plantarflexion, will improve peroneus longus function and provide dynamic ankle stability.
    I recently saw a patient who received a pair of these from me over 20 years ago – still using them and happy but they were knackered. He wanted a new set. Being a pragmatist, no point changing what had worked but, would I have provided the same device / prescription to-day – no. Do I feel I would have got the same result – most probably. This is a good example of the ‘window’ of control that exists for each individual and referred to be Griff.
    When I have students / colleagues etc. visit and I lecture, I am asked how I assess and more importantly how I decide how to manage. The latter has evolved with experience, evidence and the thoughts of my esteemed colleagues who do post regularly. I do not have all the answers but I am still looking for them. I think the use of objective assessment tools has to be the way forward with an open and broad mind.
    Recently had a case of fibula stress reaction – very rare with a foot type that does pronate (by the way, in my opinion which I believe Griff referred to, pronation is a symptom – people pronate for a reason, find the cause and you have one factor to manage) but had reduced internal tibial rotation. I could provide an orthotic to modify the pronation and it would work as it will reduce the stress. However, it does not address the cause which is the lack of internal tibial rotation which should accompany the pronation. Address the former initially, then look to orthoses if necessary.
    So, let’s have two strands of debate; one that discusses the potential effects of orthoses and the other that provides a realistic and practical way to determine orthotic prescription.
    Trevor Prior

  10. Hi Ian
    I regularly think of orthoses shape and stiffness (design features as well as material properties) in my prescription, but I haven’t considered friction as the third brother of those two beyond ‘dont slip off me’ and ‘is that topcover durable?’ Is there more to it than that?
    PS I dont think you can keep repeating the ‘kinetic’ story enough- it is a big paradigm shift.

  11. In reference to Ian’s excellent point statement about altering kinetics (i.e. forces and moments) being a key in understanding how foot orthoses work, it is very important to understand that there may be quite significant changes in the kinetics of the foot and lower extremity with foot orthoses with very little change in kinematics (i.e. position and motion).
    When a foot orthosis alters the external forces acting on the plantar foot which, in turn, alter the external moments acting about the foot and lower extremity joints, there will also need to be an alteration in the internal forces and moments acting within the foot and lower extremity joints in order to maintain translational and rotational equilibrium at any joint within the foot and lower extremity.
    In other words, every change in foot orthosis morphology and foot orthosis stiffness will produce a change in external forces and external moments acting on the plantar foot which will also always produce a change in the internal forces and internal moments within the structural components of the foot and lower extremity. However, this change in foot orthosis morphology and stiffness does not necessarily need to lead to a change in joint position or joint motion (i.e. kinematics) if some other internal force or internal moment is resisting that change in joint position or joint motion.
    Understanding these concepts very neatly explains much of the “mystery” of how foot orthoses can produce such impressive therapeutic results with only a minimum change within the kinematics of the foot and lower extremity during weightbearing activities and will help the foot-health clinician better comprehend how foot orthoses can be more effectively designed to decrease the pathological internal loading forces and moments which create the majority of pathology seen in our clinical practices.

    • Great post. My thoughts are aligned with yours on this Kevin, and I really felt that a good explanation of internal and internal moments would help give the tissue stress approach further context, but was concerned I was trying to cram too much into one piece. I did refer to the need to go into this further in the middle of the blog, and I feel it would go nicely alongside your concepts of STJ axis deviation and rotational equilibrium. I did not include it in the end, instead leaving it for a follow up blog should Adam feel it has sufficient mileage for his blog.
      Just to make clear to anyone reading these comments who isn’t a Podiatrist… It is a genuine privilege to have some of the greatest minds in the world with respect to Podiatric biomechanics (Simon Spooner & Trevor Prior, UK / Kevin Kirby, USA / Simon Bartold, AUS) commenting on and debating this topic. Drink this in!

  12. I cannot add to the brilliant of this article. Informative and stimulating with a healthy does of inspiration and a realisation that – By God! Do I need to learn more physic’s – And to most that may sound like a negative, but I can assure it is only a positive. It also to good to see I was on the right track even when I was studying my degree, but still have much more to learn.
    To all who have contributed; Thank-you greatly you have aided me greatly in my professional understanding. With Thanks and my deepest gratitude.

  13. Fantastic Blog, and productive debate guys. I’m a PT new to custom orthosis fitting, and have just audit-ed my first 50 pairs of customs purely based on relief of symptoms and improved MSK dysfunctions ( as described by the patients) and adding your insights to this makes awesome reading. I have always believed that we are getting good results due to the ‘relative control ‘ of applied ground reaction forces, and but never been made to think about them quite as much as the last 20 minutes of reading.
    Look forward to the next chapter.

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