Category Archives: Biomechanics

More non-translatable foot orthotic research

I am having a bad weekend commenting on bad research. There were these two dumb studies on Homeopathy for Heel Spurs and this one on the non-existent anterior metatarsal arch. In the Clinical Biomechanics Boot Camp I really try to focus on the practical application of research, so really look for research that is translatable to clinical practice. If it’s not translatable, then what was the point of doing it? There is way too much foot orthotic research being done lately that is not translatable, wasting resources and not providing clinicians the sort of information that they need to do it better.

What brought this up for me today was this study in quite a prestigious online journal (PLoS ONE) that really tells us nothing. The only thing I get from this study is I can add it to the list of studies I use when trying to illustrate how not to do foot orthotic research.

The purpose of the study was to look at the effects of different arch heights on rearfoot and tibial motion and they found no systematic effects on eversion excursion or the range of internal tibia rotation. I have no problems with the design or analysis of this study.

What I have a problem with is the choice of foot orthotic design in the subjects used in the study:

  • all the subjects had “normal foot flexibility, ankle ROMS, normal arch height and the absence of any foot pathologies or deformities“, so are not the sort of people who would normally get foot orthotics in clinical practice. What was the point of doing that for?
  • the study focused on one design feature (arch height) and looked for generic effects of that and did not look at the effects of that design feature in the people that the design feature is designed for. What is the point of doing that for? I have no idea why. They should have tested the design feature in those who need that design feature (or subdivide the participants into those who would have that design feature indicated clinically and those that do not, so we can see if the design feature really does what we think it might do in those that do and do not need it – now that then would have been translatable research; that would have increased our understanding of the effects of different foot orthotic design features).
  • the choice of the particular design (arch height) being tested on the parameters they were looking at (rearfoot eversion and tibial rotation) is somewhat odd, as I would not have expected them to not have much effect, so why choose that to measure? A medial arch design of the types used by the authors in the study just inverts the forefoot on the rearfoot, so why would it affect the rearfoot? It probably does, but any effect of arch support design features on the rearfoot and more proximal structures has to be mediated via the midfoot joints first and how much effect they have will depend on the range of motion of those joints. The authors did not look at that or control for that. Any effect that the particular design feature has on the rearfoot or proximally will also be dependent on the location of the subtalar joint axis. Given the variability of that axis, how much of that arch support design is on the medial side of the axis? In some of the participants, the arch support would have been on the lateral side and have the opposite effect. The authors did not look at that or control for that. The windlass mechanism is an important natural way that the foot supports itself and has significant impacts on the parameters that the authors measured. If the plantar fascia was prominent in some participants, then the arch support design feature used by the authors would have interfered with the windlass mechanism. The authors did not look at that or control for that. These issues of what is the design feature for, the position of the subtalar joint axis, and the windlass mechanism would probably explain why they found no systematic effect.

The only positive I take from this study is that we need more studies that test individual design features and not just generic “foot orthotics”; those design features need to be tested on the populations that clinicians think that those design features are indicated for to see if they do what clinicians think they do. No problems testing them in populations who they are not indicated for, as long as they are compared with the populations that they are indicated for.

The above study also brings into focus about the parameter(s) that a study looks at. The above authors looked at the impact of arch support designs on rearfoot and proximal factors. What clinician with a good understanding of foot orthotics uses arch support design features to change those parameters? The study should measure the parameters that the design feature is used clinically to try and change, to see if it really does change it or not. That is translatable research.

There is no doubt that there is a divide between what researchers think is translatable foot orthotic research and what clinicians think they can use to implement into clinical practice. The clinician is the one that actually has to use it.

Wahmkow, G., Cassel, M., Mayer, F., & Baur, H. (2017). Effects of different medial arch support heights on rearfoot kinematics PLOS ONE, 12 (3) DOI: 10.1371/journal.pone.0172334

University lecturer, runner, cynic, researcher, skeptic, forum admin, woo basher, clinician, rabble-rouser, blogger, dad. Follow me on Twitter, Facebook and Google+

The models, paradigms or frameworks that underpin the clinical practice of biomechanics*

Clinical practice is always going to be underpinned by models, paradigms or frameworks. Life is underpinned by such approaches, so there is no reason to assume that clinical practice isn’t as well, despite what we might believe of the role of evidence based practice. For example, in politics there has always been and always will be the left/liberal approach compared to the right/conservative approach. Models, paradigms or frameworks are really coloured lenses that we view the world through. A scientific fact may be, for example, the unemployment rate (if we accept the shortcomings of how it is actually measured). That fact will be interpreted by a left wing liberal as something bad that needs something done about it, whereas a right wing conservative probably sees it as nothing more than the markets working efficiently. So it is with clinical practice, we all have lenses that which we view the same thing through. Members of different health professions will look at the same thing differently because of the models, paradigms or frameworks that they are viewing it from. This may be as wide as the traditional ‘medical’ model vs the ‘psychosocial’ model vs the attempt to integrate them as the ‘biopsychosocial’ model.

Science shows that you and I might think that some models, paradigms or frameworks of some professions or individuals are misguided (for example, the germ theory denialists; the subluxation model of chiropractic; the water memory of homeopathy), but they are used by different professions or individuals in those professions to underpin their approach to clinical practice.
Podiatry is no different in having different approaches to practice based on different models, paradigms or frameworks. This is never more evident than what it is in the application of biomechanics in clinical practice and its application to foot orthotic prescription. We now have a substantial body of scientific research on foot function and biomechanics and what foot orthotics do to the foot, but we also have a substantial group of models, paradigms or frameworks that can be used to interpret or view this research.

Each of these could be seen as a different coloured lens that research is viewed through and how patients are assessed and treated. Different approaches may lead to different interventions or the same intervention, but the rationale for that intervention is different. Each has its strengths and it weaknesses and it may never be the case that there is ever going to be just one (though I have my personal favourite!). Some of them have substantial overlap with others and some contradict others in places and complement them in others. Some of them are patented and some of them have commercial interests underpinning them. Some of them have their champions and some of them have their detractors.

A lot has been written and talked about these different models, paradigms or frameworks over the years and I have done my fair share of that. My approach has been to try and immerse myself in each one to try and see where it is coming from and how they explain research results, clinical findings and how they would prescribe different interventions and the rationale that they would use for that intervention. I have tried to see what they have in common (and perhaps if something is common with a lot of them, then that might be important) and to see where they differ (and perhaps those differences might point to a need for specific research projects to resolve that).

For example, when it comes to commonalities, the concept of using a foot orthotic to dorsiflex the calcaneus (as opposed to invert it) for a pronated foot is common to several of the approaches, though they may use different terminology to describe that. Maybe because it is common, it might just be an important concept (it also might not be as well). This could point to the potential for some research to investigate interventions to dorsiflex the calcaneus versus invert the calcaneus. Whatever the outcome of that research, it would still be interpreted through the lens of the different approaches. An obvious example of how the different approaches might be used to interpret different research outcomes is how a study of functional hallux limitus (assuming that it actually exists) might be viewed. Under traditional Root based theory a functional hallux limitus is secondary to what is going on proximally in the foot whereas under the Sagittal Plane model, functional hallux limitus is primary and is the cause of what is going on proximally.

At some point this has to move beyond simple academic wankery (ie an academic playing with himself) and be made useful for clinical practice. The challenge then has to be one of distilling it all down into something that is clinically useful. Models, paradigms or frameworks are fine, but they are even better if they can inform clinical practice to make better decisions. The best one for clinical practice is the one that has the most explanatory powers, the one that is most consistent with all the available evidence and the one that has the most practical applications. I very much doubt that it is possible for research to show that one model is better than another. That is not the purpose of a model, paradigm or framework. Their purpose is in there explanatory powers.

Some of the approaches listed in table one have good explanatory powers and are consistent with all or most of the evidence. Some of them are not consistent with all the evidence and some only can explain a small part of it. If they are consistent with the research, that does not prove the model, it just proves it explanatory powers. For example, Root Theory has served the profession well and continues to do so, but a number of aspects of it are not consistent with the research, but as a theoretical framework it still can explain a lot (and keep in mind that some of the so called anti-Root Theory research is not really anti-Root Theory research its actually anti-what some people have misinterpreted Root theory to be).

Another example of the explanatory powers and purpose of the models, paradigms or frameworks is Bojsen-Møller’s ‘high gear/low gear’ concept. This model perfectly explains what the research shows is the pathway of the centre of pressure as it moves through the foot. It explains why it initially has the lateral movement and later why it comes back medially. This information can be used in clinical practice to design an intervention. This is also a good illustration of how so many misinterpret the underpinning models, paradigms or frameworks and get it wrong. Bojsen-Møller’s ‘high gear/low gear’ concept might be used to explain why the centre of pressure has the path that it does. The path of the centre of pressure does not prove that Bojsen-Møller’s ‘high gear/low gear’ concept is right just because it can explain it and is consistent with the research evidence. There is plenty that this model cannot explain and plenty that it is not consistent with.

So which model, paradigm or framework has the most explanatory powers and has the most usefulness for clinical practice? In my personal opinion one of the models in Table One is more consistent with the widest body of scientific evidence and has significant explanatory powers to explain the evidence and what we see in clinical practice compared to all the others. This is not the place to get into all the reasoning behind that, and it can be done at another time and in another place, but I make no secret of being a big fan of the Tissue Stress Model. This is simply because it can explain so much more than all the others.

*The above was originally written for the College of Podiatry publication Podiatry Now, but I got shafted after putting off other deadlines to write it, only to be treated unprofessionally by them; so publishing it here.

University lecturer, runner, cynic, researcher, skeptic, forum admin, woo basher, clinician, rabble-rouser, blogger, dad. Follow me on Twitter, Facebook and Google+