Why tibial stress fractures occur posteromedially... usually!

Tibial stress fracture can be the scurge of the endurance athlete, and they are a sports medicine curiosity, because they nearly always present in the same location, the posterior aspect of the tibia.

The reason for this is most likely down to the sagittal plane bending moment, in other words, the way the tibia is bent when load is applied.

stress fracture final.jpg

During running, the orientation of the GRF  predominantly bends the lower leg convex posteriorly.
The plantarflexor line-of-action is offset and predominantly bends it concave posteriorly.
The ‘resultant’ bending moment is the summation of the reaction and muscle moments, and this will largely determine whether there will be failure of bone.

This 'ying and yang" effect of the tendency of bone to bend becasue of the applied GRF, and the ability of muscle (particularly the triceps surae) to resist or "balance' this bending, again underlines the importance of strength for runners.

This concept, and the basis for this infographic, is described eloquently in one of my favorte papers of all time,

Sagittal plane bending moments acting on the lower leg during running, Phuak et al, 2010, Gait & Posture 31  218–222.

Included on this paper are Kay Crossley, Mark Creaby and Anthony Schache, so it is not wonder this paper is excellent.

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Simon Bartold
Director of Bartold Clinical

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