The effects of femoral metaphyseal morphology on growth plate biomechanics in juvenile chimpanzees and humans

The distal femoral metaphyseal surface presents dramatically different morphologies in juvenile extant hominoids—humans have relatively flat metaphyseal surfaces when compared with the more complex metaphyseal surfaces of apes. It has long been speculated that these different morphologies reflect different biomechanical demands placed on the growth plate during locomotor behaviour, with the more complex metaphyseal surfaces of apes acting to protect the growth plate during flexed-knee behaviours like squatting and climbing. To test this hypothesis, we built subject-specific parametric finite-element models from the surface scans of the femora of five Pan and six Homo juveniles. We then simulated the loading conditions of either a straight-leg or flexed-knee gait and measured the resulting stresses at the growth plate. When subjected to the simulated flexed-knee loading conditions, both the maximum and mean von Mises stresses were significantly lower in the Pan models than in the Homo models. Further, during these loading conditions, von Mises stresses were strongly negatively correlated with ariaDNE, a measure of complexity of the metaphyseal surface. These results indicate that metaphyseal surface morphology has a robust effect on growth plate mechanics.