The generally accepted role of foot orthotics in those with plantar fasciitis is to reduce the load in the plantar fascia so it can get better. To achieve that, the foot orthotic needs to have the right design features that reduce the load in the foot type of the individual. The role is not to treat “overpronation“! Initially, I was quite excited to see this study turn up:
The Effects of Orthotic Intervention on Multi-Segment Foot Kinematics and Plantar Fascia Strain in Recreational Runners
Jonathan Sinclair, Josh Isherwood, and Paul J. Taylor
Journal of Applied Biomechanics; in press
Chronic injuries are a common complaint in recreational runners. Foot orthoses have been shown to be effective for the treatment of running injuries but their mechanical effects are still not well understood. This study aims to examine the influence of orthotic intervention on multi-segment foot kinematics and plantar fascia strain during running. Fifteen male participants ran at 4.0 m.s-1 with and without orthotics. Multi-segment foot kinematics and plantar fascia strain were obtained during the stance phase and contrasted using paired t-tests. Relative coronal plane range of motion of the midfoot relative to the rearfoot was significantly reduced with orthotics (1.0°) compared to without (2.2°). Similarly relative transverse plane range of motion was significantly lower with orthotics (1.1°) compared to without (1.8°). Plantar fascia strain did not differ significantly between orthotic (7.1) and no-orthotic (7.1) conditions. This study shows that although orthotics did not serve to reduce plantar fascia strain, they are able to mediate reductions in coronal and transverse plane rotations of the midfoot.
That initial excitement did not last long …
The study used 15 healthy runners with unknown foot types and a foot orthotic that no expert clinician would use for plantar fasciitis and found that there was no change in the “strain” in the plantar fascia, but some very small changes in kinematics of the midfoot. While this study is not close to being the triple face palm of this loon, it still deserves a face palm:
Let me explain:
Firstly, with all foot orthotic studies I ask: “are the foot orthotics that are used in the study typically and commonly used by expert clinicians in clinical practice?“. They weren’t. The “foot orthotics” used in this study were the same as used by the authors in a previous study: Sorbothane Shock stopper – Sorbo Pro (these). Like the previous study the authors gave no reason or rationale for using these. On the website of the manufacturer the foot orthotics are described as having “Pronation control“, but that “control” is so weak I can flatten it with my finger, so guess what a few times body weight is going to do to it when running? No expert clinician would use these to treat plantar fasciitis and they certainly have no design features that would be expected to reduce the load in the plantar fascia. I just do not understand why you would want to investigate the effect of a foot orthotic that is not designed to reduce load in the plantar fascia on loads in the plantar fascia! Kogler et al way back in 1999 showed what design features are needed to reduce the load (I discussed that here). Curiously the above authors did not reference Koglers work. A study like the one above would have been a perfect opportunity to further develop Kolger’s work from in vitro to in vivo and test what clinicians actually use rather than a not very effective generic device without the appropriate design features. This study probably will now unfortunately and wrongly get extrapolated to foot orthotics in general.
Secondly, we know nothing about the foot types in the healthy asymptomatic group of runners used in the study. We have no idea if they even had foot types that foot orthotics would probably have been used clinically if they had symptoms. More and more studies are using metrics like the Foot Posture Index as an inclusion criteria, so we can judge if the subjects used may or may not have had foot orthotics in clinical practice. The above study did not provide us with that information, so all the feet may be ‘normal’ and not even had high loads in the plantar fascia. The assumption is that those with plantar fascsitis have high loads in the plantar fascia (which is why they got it), so there might be a greater scope for a reduction in those feet compared to the feet used in the above study.
Thirdly, I am not totally convinced that they are were even measuring strain or load in the plantar fascia. What they were measuring was the distance between the marker on the calcaneus and the marker on the first metatarsal head, with the assumption that if this distance decreased, then strain in the plantar fascia was reduced. This may or may not be the case, but based on my understanding of windlass mechanics and the huge body of literature on that, I am not totally convinced. I would like to be convinced as it would be awesome if it did, as this will then give the opportunity of a methodology to test the actual design features that could reduce the load in foot types that need the load reduced.
On a positive note:
Firstly, as I just stated, if the method they used to determine plantar facscia strain did actually measure plantar fascia strain, then this will then give the opportunity of a methodology to test the actual design features that could and could not reduce the load in foot types that need the load reduced. This means that Kogler’s cadaver work could be tested and the design features assumed to reduce the load can be tested and other design features can be assessed.
Secondly, despite what I said above about the actual design features of the foot orthotic that the authors used, there were some kinematic changes in the midfoot, but were very small, yet still statistically significant. The changes could easily be attributed to the ‘mass’ in the arch area of the foot orthotics used. However, I am just not convinced of the clinical significance of these kinematic changes.
As always, I go where the evidence takes me until convinced otherwise ….and the conclusion of this study:
This study shows that although orthotics did not serve to reduce plantar fascia strain, they are able to mediate reductions in coronal and transverse plane rotations of the midfoot.
Needs to be restated as:
This study shows that foot orthotics without the design features that would be expected to reduce strain in the plantar fascia did not reduce plantar fascia strain
Sinclair J, Isherwood J, & Taylor PJ (2014). The Effects of Orthotic Intervention on Multi-Segment Foot Kinematics and Plantar Fascia Strain in Recreational Runners. Journal of applied biomechanics PMID: 25268399