Those who have done one of my Clinical Biomechanics Boot Camps know the dilemma I have of about the pathomechanical link between foot biomechanics and load in the Achilles tendon, and the speculation that it’s potentially a joint moment issue at the subtalar joint and not the ankle joint. Having said that, this new study just turned up that puts a totally different perspective on that:
The effect of foot overpronation on Achilles tendon blood supply in healthy male subjects
K. Karzs, M. Kalogeris, D. Mandalidis, N. Geladas, K. Karteroliotis and S. Athanasopoulos
Scandinavian Journal of Medicine & Science in Sports; Early View
The purpose of this study was to investigate Achilles tendon blood flow in individuals with overpronated feet during non-weight- and weight-bearing positions. Achilles tendon blood flow was measured by means of the pulsatility index (PI) and the resistance index (RI) in 15 male individuals with overpronated feet and 15 counterparts with normal feet, using power Doppler ultrasonography (PDI). Achilles tendon ultrasonographic (US) assessment was performed at its musculo-tendinous junction (MTJ), mid-tendon (MT), and osseotendinous junction (OTJ) at a non-weight-bearing relaxed position (RP) and during two-leg stance (TLS) and one-leg upright stance (OLS). PI and RI indices were significantly greater in individuals with overpronated feet compared to individuals with normal feet at the OTJ in OLS position (P < 0.01), and at MT in both TLS (P < 0.001) and OLS positions (P < 0.001). All individuals demonstrated also greater PI and RI indices at MT followed by the OTJ and MTJ in all positions (P < 0.001), and in OLS compared to TLS and the RP at the OTJ (P < 0.01) as well as at MT and MTJ (P < 0.001). The findings of the present study suggest that foot overpronation may affect Achilles tendon blood flow, particularly at mid-tendon, thus enhancing the possibility for injury.
I won’t get into the nonsensical issue of ‘overpronation’ and the use of that term (been there done that, unfortunately many times), except to say I am surprised given the issues around the term, that it was even used in a scientific publication.
The study compared 15 ‘overpronated’ to 15 normal individuals. They determined ‘overpronated’ by three measurements: the calf to calcaneus angle (>5 degrees was overpronated), navicular drop (>10mm was considered overpronated) and the navicular angle (<120 degrees was considered overpronated). I won't quibble too much about that except to say that the measurements used only measured the frontal and sagittal place components of 'overpronation' and did not include a transverse plane measure (eg navicular drift). This is important as a foot could be 'overpronated' in one plane, but not another, which just confirms the questionable use of the term 'overpronation'. This could be crucial to the results of the study as it could be that one, two or all of the components of 'overpronation' that correlate to the findings and they left out the transverse plane component (The transverse plane component is that medial midfoot bulging and forefoot abduction you get in an 'overpronated' foot). Enough of that. They then used Doppler ultrasound to determine the Achilles tendon blood flow between the two groups (overpronated and normal). The statistics look fine in showing that the overpronated group had a reduced blood flow in the Achilles tendon compared to the normal group.
It gets interesting when you start to speculate the reasons. Does the ‘overpronation’ and the resultant excessive torsional forces results in an ischaemic ‘wringing out’ effect of the tendon causing a hypoxia and degeneration? I recall this being speculated in the 1980’s and was somewhat dismissive of it at the time! Now there is some data supporting it.
All this is, is a correlation. A very interesting correlation. A prospective study is needed to determine if this is a risk factor. If it is, it does contribute to our understanding of the relationship between ‘overpronation’ and the risk for Achilles tendinopathy.
As always, I go where the evidence takes me until convinced otherwise …. and this is interesting and at this stage, that is all it is.
Karzis, K., Kalogeris, M., Mandalidis, D., Geladas, N., Karteroliotis, K., & Athanasopoulos, S. (2016). The effect of foot overpronation on Achilles tendon blood supply in healthy male subjects Scandinavian Journal of Medicine & Science in Sports DOI: 10.1111/sms.12722