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

Peter A Stamos,Michael A Berthaume

doi:10.1098/rsfs.2020.0092

Abstract

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.

Highlights

Locomotor biomechanics can have significant effects on skeletal morphology, during growth and development [1,2,3]
We statistically modeled how maximum and mean von Mises stress at the growth plate varied with taxon and loading condition with a generalized linear model implemented in R
We modeled the relationship between ariaDNE values and maximum and mean von Mises stresses in the walking and climbing models

Summary

Introduction

Locomotor biomechanics can have significant effects on skeletal morphology, during growth and development [1,2,3]. Thomson argued that the same physical laws govern the functional requirements of juvenile and adult bones, and morphological variation in metaphyseal and epiphyseal surfaces likely served a biomechanical function. He proposed differences in morphology reflected differences in knee joint loads engendered by locomotory kinematics. He speculated that animals that engaged in more bent-knee gaits, like sheep and wolves, experience more shear forces at the growth plate during locomotion, and require a more complex metaphyseal surface with significant metaphyseal and epiphyseal surface interdigitation to resist antero-posteriorly oriented forces and prevent the epiphysis from slipping off. Animals that engaged in more straight-legged gaits, such as humans and elephants, experience more compressive forces at the growth plate during locomotion, and there is little need for bony structures to resist antero-posteriorly oriented shear forces

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