Foot posture as a risk of lower limb overuse injury: a systematic review and meta-analysis
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When reading a study, especially a high-quality randomized controlled trial or systematic review, I always question myself on the usefulness of updating my own practice based on reported conclusions, some of which challenge my beliefs. A systematic review on a famous topic by Bradley S Neal and colleagues entitled Foot posture as a risk factor for lower limb overuse injury: a systematic review and meta-analysiswas just published in the Journal of Foot and Ankle Research. The research question was quite simple: is static foot posture a risk factor for musculoskeletal injuries ? And the conclusions was as follows: This systematic review identified strong and very limited evidence of small effect that a pronated foot posture is a risk factor for medial tibial stress syndrome (MTSS) and patellofemoral pain, respectively.
What does it mean? Do I need to start believing that pronating feet cause musculoskeletal pathologies? Do I need to start measuring the "navicular dop"? Do I need to equip my patients with plantar orthoses to correct these "flaws"?
In general, this review was very well conducted with a high quality methodology. My critique is more on analysis and conclusions suggesting associations that don’t exist (see below: critique for scientists). However, I must credit the authors for mentioning the limits in interpreting their results: "… the meta-analysis did not encompass all potentially available data, reducing confidence in its results." Some questions remain: why did the authors did not mention the absence of link between the majority of reviewed pathologies and static foot measurements? Is it always necessary to find links (as small as they can be) to support our own convictions?
In this review, there is a gathering of medium quality studies reporting non-statistically significant findings. However, when combined in a certain manner, they tend to show borderline statistical significance with a small effect size... This study will definitely not change my clinical practice because of my extremely low confidence level in its results. I will not start measuring "navicular drops" nor telling my patients that their ever established pronating feet have anything to do with the recent injury (including medial tibial stress syndrome) for which they seek medical attention! It's just too bad that the included studies weren't performed in Africa where the majority of people have flat feet ;)
My critique for scientists, clinicians and the authors of the systematic review:
- All 5 high-quality studies included show NO statistically significant effect of foot posture on pathologies... when considering all pathologies.
- In the meta-analysis, the only pathologies that could be associated with static foot measurements are MTSS (medial tibial stress syndrome) and PFPS (patellofemoral pain syndrome). All other pathologies (foot/ankle injuries, bone stress reactions, non-specific lower limb overuse injury) DID NOT show any significant link with such measurements.
- In order to find a bigger effect of static foot measurements on MTSS, the authors had to combine 3 measurements (Navicular drop, FPI-8, Resting calcaneum position) that are not correlated (e.g. a rigid flat foot or rigid cavus foot will show minimal navicular drop but inverse FPI).
- Therefore, the only valid meta-analysis is the one linking MTSS to Navicular drop through 6 studies. However, note that those results are at the very limit of statistical significance as shown by the 0.01 inferior limit of the confidence interval (results with a confidence interval including 0.00 are considered non-significant). Moreover, since every single study did not show any significant results, we can certainly take results with a grain of salt... Even if the goal of a meta-analysis is to optimize statistical power by combining studies.
- Although results were significant, it must be noted that the effect size is very small (0.19 for MTSS) and that higher quality studies are responsible for attenuation of that effect.
- Thus, results are not so convincing and quite unstable. In fact, only one study would be needed to redirect results to non-significant links between anatomy and MTSS! Studies like those from Hestroni-2006 (or Burne-2004 for PFPS), for instance, which showed opposite results but were excluded from the meta-analysis secondary to "absence of adequate data".
- Interestingly, the between-group mean difference (injured vs. uninjured) in Navicular drop for all the package of included studies was inferior to 1.5mm... (according to 2012-Sabino: Reliability analysis of the clinical application of the navicular drop test, measurement error was 2.26mm).
- Authors had to isolate the Navicular drop from other measurements (FPI-8 and Resting calcaneum position) in order to find significant results between foot posture and PFPS... or else it wouldn't have been statistically significant. Note that only one study is included within this forest plot, which makes it a pseudo-meta-analysis! Why did the authors combine measurements when looking at MTSS but not for PFPS? To report significant results? :)
- Since only one study reaches this conclusion (2009-Boling), it would be necessary to review it thoroughly to ensure the adequacy of its quality and results. In that study, the difference between navicular drop measurements of injured vs. uninjured was less that 1mm...
* The same research group has published another similar paper, reviewing links between dynamic measurements and injuries, which concluded the following: That other systematic review identified very limited evidence that dynamic foot function during walking and running is a risk factor for patellofemoral pain, Achilles tendinopathy, and non- specific lower limb overuse injuries.