Welcome to blog 45 (subscribe here).
In Sydney, this weekend for first sold out Mastering Lower Limb Tendinopathy Course of the year – other dates around Australia can be found here.
Also, Erics Meira’s Hip and Knee course in Melbourne in August is filling fast – limited spots left.
This week I focus on a study investigating a potential mechanism that may explain the link between foot pronation and Achilles tendinopathy. A sound study with interesting findings, but we also need to ask; 1) how strong is the link between foot pronation and Achilles tendinopathy; and 2) what do we know about the use of orthotic devices for prevention? 3) what do we know about the use of orthotic devices for treatment? Some interesting clinical questions to ponder.
Background: Although the Achilles tendon is the strongest and largest in the body, it is commonly injured. Most likely because it undergoes high and repetitive loading. Achilles tendinopathy is a common running injury, but it is also very common among people who do not run, as walking is a relatively high loading activity for the Achilles tendon. The authors argue in their intro that foot pronation is thought to be ‘strongly associated with Achilles tendon injuries’ (more on that later). Possibly the whipping or torsion of the tendon described by Clement way back in 1984 explains this. The authors aim was to test this hypothesis by measuring blood flow in the tendon pre and post running.
What they did: Healthy participants were asked to run barefoot for 10 minutes and then with neutral running shoes for 10 minutes. Three Achilles tendon blood flow measurements were taken, baseline, post barefoot and post shod running. Participants were asked to self-select running speed and this was monitored to ensure consistent through both trials. Blood flow was measured with an oxygen-to-see device which measures the perfusion and oxygenation of the subcutaneous tissue up to a depth of 8 mm using an optical fiber probe. To do this it used both white light spectroscopy (wavelengths of 500-800 nm) and the laser Doppler technique (830 nm and 30 mW). They used 4 synchronised high speed cameras to measure 2D kinematics (sagittal and frontal planes) during running on a 45-meter track. Kinematic variables related to ankle dorsiflexion and one of the components of pronation ie foot eversion (eversion excursion, dorsiflexion excursion, average and maximal velocities, and initial foot strike pattern). They investigated whether kinematic variables influenced Achilles blood flow after each running condition.
What they found: There was a significant increase in blood flow after both running conditions, more so after the shod condition (62% vs 43%), but this may have been because the shod condition followed the barefoot (ie they did not randomize or counterbalance order of tasks). The main finding was that people who displayed greater eversion excursion had a lower increase in blood flow following the shod condition (eversion excursion explained 11% of within participant change in blood flow following this task). The figure below shoes the potential differences between participants in eversion excursion. Dorsiflexion excursion or foot strike did not influence blood flow.
Clinical interpretation: This is an interesting study in that the authors have identified a potential mechanism between foot eversion and Achilles tendon pain. The authors suggest antipronation measures such as taping, orthoses or foot intrinsic muscle exercises may reduce the risk of Achilles tendon pain onset. A strength of the study is they controlled for speed and considered the influence of foot strike.
Some clinical questions may help to provide some context in applying these findings…
1. How strong is the relationship between foot eversion and onset of Achilles pain? My current PhD student (Igor Sancho) is just completing a systematic review that includes this, and he found that there is conflicting evidence for a link between foot eversion and Achilles tendon pain. Listen out for more on that soon (I don’t want to steel Igor’s thunder).
Given the at best weak relationship, the issue with intervening with a blanket strategy for people who may display increased foot eversion and giving them foot orthotics is that you will be treating lot’s of people who although have this risk factor, may never develop the injury. You may run the risk of causing them harm or impairing performance. The other problem clinically is identifying excessive pronationor eversion accurately.
2. How strong is the association the authors have found in this study? Similar to the association between foot eversion and injury, the association with change in blood flow and pronation in this study is weak – see figure below.
3. Further, can we prevent injury with shoe inserts? There are only very few studies that I am aware of that investigate the influence of shoe inserts on Achilles tendon pain onset. House et al. 2013 found that shock absorbing insoles reduced the incidence of Achilles tendinopathy during marine training. However, Larsen et al. 2002 found no effect of custom made shoe orthoses, again in a military population.
4. Lastly, what do we know about treating Achilles tendon pain with foot orthotics. The state of the art randomized controlled trial from Shannon Munteanu at La Trobe Uni from 2014 showed no benefit at 1, 3, 6, and 12 months for custom orthotics compared to sham orthotics when added to exercise in managing Achilles tendon pain.
Although I may not agree with the clinical implications of the study, there is not doubt this study is novel and very interesting, and gives a snapshot of load profile on the tendon with a specific kinematic pattern. The authors should be congratulated for this. Follow up prospective work (rare as Hens teeth in the tendinopathy aetiology literature) would be lovely to see!
See you next time
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