Mechanics of Ankle Sprain Prone Runners

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Research shows that individuals who do and do not develop chronic ankle instability after an initial ankle sprain have different running kinematics.

Ankle sprains are a common injury for runners. Generally, ankle problems persist after an individual sprains their ankle. Ankle instability following an initial sprain is called chronic ankle instability (CAI). Two types of chronic ankle instability are possible: mechanical instability and functional instability. Both types of chronic ankle instability are characterized by complaints by individuals of their ankles giving way, but individuals with mechanical instability display lax lateral ankle ligaments. A study published in the August 2011 issue of the Journal of Sports Medicine looked at the mechanics of individuals who suffered from chronic ankle instability, both functional instability and mechanical instability, as well as individuals who suffered  from an ankle strain, but were lucky enough not to develop chronic ankle instability. Individuals who managed to avoid developing chronic ankle instability after an ankle sprain were appropriately labeled "copers" (Foot clearance in walking and running in individuals with ankle instability, 2011, Cathleen Brown).

The study found that individuals with chronic ankle instability had a lower minimum metatarsal height during the terminal swing. A graph comparing the metatarsal heights of copers, individuals with mechanical ankle instability and individuals with functional ankle instability as a function of time can be seen below.  

Metatarsal height of copers compared to individuals with functional ankle instability and mechanical ankle instability during running.

Individuals with a lower foot height while running should see more ankle strains due to inadvertent toe strikes that would result. The individuals suffering from mechanical ankle instability had a significantly higher external foot rotation than the functional instability and coper groups. The mechanical instability group was found to be less plantar flexed during foot contact and were less everted.  Differences in gait were also found. The copers had far less frontal gait, possibly a sign of more control in their stride.

Similarly, differences were seen in the mechanics of the copers and chronic ankle instability suffering individuals while walking. The copers had less external foot rotation than the individuals suffering from chronic ankle instability. However, no significant difference was found in dorsiflexion while walking.

The results here are preliminary, only 11 male individuals were in each cohort.  Thus, the study did not have much statistical power. However, the results do suggest that rehabilitation for individuals suffering from ankle strains can focus on the kinematics of their running or walking.

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