Variability in tibia-fibular geometry is associated with increased tibial strain from running loads.

Variation in tibial geometry may alter strain magnitude and distribution during locomotion. We investigated the effect of tibia-fibula geometric variations on tibial strain with running loads applied at various speeds. Participant-specific three-dimensional models of the tibia-fibula were created using lower limb computed tomography scans from 30 cadavers. Finite-element models were developed in FEBio, and running loads from 3, 4 and 5 m s were applied to extract effective strain from the tibial shaft. Linear regression models evaluated the relationship between geometric characteristics and effective strain along the tibial shaft. We found a statistically significant positive relationship between: (i) increased thickness of the midshaft to upper tibia with increased condyle prominence and effective strain at points along the distal anterolateral and proximal posterior regions of the tibial shaft; and (ii) increased midshaft cortical thickness and effective strain at points along the medial aspect of the distal tibial shaft. It is possible that increased thickness in the more proximal region of the tibia causes strain to redistribute to areas that are more susceptible to the applied loads. A thickness imbalance between the upper and distal portions of the tibial shaft could have a negative impact on tibial stress injury risk.