The effect of ankle posture on the load pathway through the hindfoot.

The foot-ankle complex is frequently injured in a wide array of debilitating events such as car crashes. Numerical models and experimental tests have been used to assess injury risk, but most do not account for the variations in ankle posture that frequently occur during these events. In this study, the positions of the bones of the foot-ankle complex (particularly, the hindfoot) were quantified over a range of postures. Computed tomography scans were taken of a male cadaveric leg under axial loading with the ankle in five postures in which fractures are commonly reported. The difference in the location of the talus and calcaneus between the neutral and each repositioned posture was quantified, and substantial rotations and displacements were observed for all postures tested (talus: 3°-21.5°, 1.5-10.5 mm; calcaneus: 10°-20°, 1.5-24.5 mm). Strains were also recorded at six locations on bones of the ankle during testing and were found to be highest in the calcaneus during inversion-external rotation and highest in the talus during eversion-external rotation. Postural changes likely affect the load pathway of the foot-ankle complex, potentially altering the stress and strain fields from that of the neutral case and changing the location of fracture. This highlights the need for injury-predicting studies examining the effect of these positional changes and to develop revised injury criteria accounting for the most vulnerable conditions.