Risk factors for achilles tendon pain in runners

Last week I reported on a study that found a correlation between timing of events of the gluteal muscles and achilles tendinopathy. This was a correlation study and the achilles pain could have easily altered the gait to give the findings in the gluteal muscles or it could be that the gluteal muscles timing issue was involved in the pathogenesis of achilles tendon pathology. It is impossible to draw either conclusion from this type of cross sectional study as to if it was the chicken or egg. A number of other places also reported on this study and I read with alarm some of the comments now being made following that study. A number were talking about now working on the gluteal muscles in those with achilles tendon problems and even worse were going to start doing gluteal strengthening in those with achilles tendinopathy, when the study did not even identify a weakness! Its like the story on running shoes causing osteoarthritis (they don’t) that I followed. It goes to show how dangerous it is when people not experienced in the reading, critical appraisal and application of research read, appraise and try to apply research. ‘Gullible’ is one word that comes to mind. Back to the achilles tendon issue: Cross-sectional studies are one thing to identify correlations that can generate hypotheses for testing in prospective studies; the factors that are identified from that can then be used in clinical trials. The publication of this prospective study gives me the opportunity to get the above off my chest! Now to the new study:

Prospective analysis of intrinsic and extrinsic risk factors on the development of Achilles tendon pain in runners
T. Hein, P. Janssen, U. Wagner-Fritz, G. Haupt, S. Grau
Scandinavian Journal of Medicine & Science in Sports; Early View
There are currently no generally accepted, consistent results that clearly characterize factors causing Achilles tendon pain (AT) in runners. Therefore, we carried out a prospective study to evaluate the multifactorial influence of clinical, biomechanical (isometric strength measurements and three-dimensional kinematics) and training-related risk factors on the development of AT. Two hundred sixty-nine uninjured runners were recruited and underwent an initial examination. One hundred forty-two subjects completed their participation by submitting training information on a weekly basis over a maximal period of 1 year. Forty-five subjects developed an overuse injury, with 10 runners suffering from AT. In an uninjured state, AT runners already demonstrated decreased knee flexor strength and abnormal lower leg kinematics (sagittal knee and ankle joint) compared with a matched control group. A relationship between years of running experience or previous overuse injuries and the development of new symptoms could not be established. The interrelationship of biomechanical and training-specific variables on the generation of AT is evident. A combination of alterations in lower leg kinematics and higher impacts caused by fast training sessions might lead to excessive stress on the Achilles tendon during weight bearing and thus to AT in recreational runners.

This is one of those cases where the abstract is very misleading.

At baseline the runners had a questionnaire about their running history, a clinical assessment, isometric muscle strength testing and a 3D biomechanical assessment and were followed for 12 months. Of the 269 runners that started the study, 127 (47%) had dropped out or were excluded (not good). No information was provided on the characteristics of the dropouts compared to those that completed the study to see if this introduced any potential bias.

Of those that completed the study, 32% developed an overuse injury in the 12 months (which is more than half of the 70% figure that all the propaganda and rhetoric tells us happen).

What the authors presented in the results was an analysis of the 10 runners who got achilles tendon pain. They selected 10 age, sex and weight matched control subjects from their non-injured group. I am not comfortable with them not providing any information on how that group was selected (eg was it random?) and would also preferred matching to be 1:2 or more. They had all the 3D and other data from the initial assessment from all subjects, so why not include all that data for the non-achilles tendon pain group. It would have substantially strengthened the study. The selection of control groups in these matched type study designs is crucial.

The authors reported:

  • no differences based on the clinical assessment of range of motion
  • those who developed achilles tendon pain had decreased knee flexor strength
  • no differences in 3D hip movement
  • the achilles tendon pain group had lower ankle dorsiflexion; greater rearfoot maximum eversion; reduced maximum knee flexion
  • no differences in training, no training errors; except for a shift from slow to fast training sessions prior to onset of achilles tendon pain

The authors did no statistical tests to compare these between the two groups and when I look at the graphs in the paper, all the confidence intervals overlap and I see no difference in the variables that they claim there is a difference (anyone else want to have a look and see if you can see the differences?).

I counted 36 different parameters that they measured. Given that there were only 10 subjects in each group, this is not good! Just by random chance there is probably going to be some differences when you measure this many variables in this small number of subjects.

As always, I go where the evidence takes me until convinced otherwise, and this study really doesn’t provide  much of any value and shows how you have to be careful not to fall for what is in the abstract.

T. Hein, P. Janssen, U. Wagner-Fritz, G. Haupt, S. Grau (2013). Prospective analysis of intrinsic and extrinsic risk factors on the development of Achilles tendon pain in runners Scandinavian Journal of Medicine & Science in Sports DOI: 10.1111/sms.12137

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