Mitigating Stress: Exploring how our feet change shape with size

Abstract

If human skeletal shape increases proportionally with size (isometric scaling) this can produce exponential increases in joint contact stresses. However, if skeletal shape changes as a function of size (allometric scaling) this can mitigate increases in joint contact stress by changing the surface area to volume ratio. Here we explored whether human foot bones scale with allometry and, if so, to identify the shape features that are associated with bone size. Computed tomography scans of the two largest foot bones (talus, calcaneus) were obtained from 36 healthy individuals. We implemented a scaling analysis for each joint surface area and bone. We performed a Procrustes ANOVA to establish the shape features associated with bone size. In line with our hypothesis, articular surfaces on the talus and the posterior facet of the calcaneus all scaled with positive allometry. Interestingly, the calcaneus scaled with negative allometry, appearing more cube-like with increasing size. This may be important for mitigation of internal bone stresses with increasing skeletal size. Our findings suggest distinct, but varied scaling strategies within the foot. This may reflect the requirement to maintain healthy joint contact and internal bone stresses with increasing size.