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