The Relationship Between Joint Size and Trabecular Bone Density in Human and Nonhuman Primates

Abstract

Biomechanically, a relationship is expected between loading and joint size, i.e., an organism with greater mechanical loading may have a large joint surface in order to mitigate greater joint stresses. However, among primates, hominoids have large long bone joint surfaces relative to diaphyseal strength, and also demonstrate generally greater joint mobility. Consequently, it has been proposed that relative joint size may also be related to greater joint excursion. Subchondral trabecular bone mass may be more directly influenced by mechanical loading of a joint. Thus, since subchondral trabecular bone density is a function of both joint size (volume) and trabecular bone mass, both mechanical loading and joint excursion could influence it. Although there has been some research investigating the relationship between trabecular bone mass and joint volume, the potential impact of joint size on trabecular bone has not been fully tested across many species in multiple limb elements. This study investigates trabecular bone density (trabecular bone fraction, TBF) in multiple proximal epiphyses in primates with varying modes of locomotion. We used a peripheral Quantitative Computed Tomography (pQCT) scanner to estimate TBF in the femur, humerus, 3rd metatarsal and 3rd metacarpal. This was done in modern humans, chimpanzees, orangutans, vervet monkeys, olive baboons, gelada baboons and patas monkeys. Pearson's correlations were used to test relationships between joint size and trabecular density in each species. The results show that TBF has broadly similar values across a large range of joint sizes. There is no strong correlation between the variables; modern humans, despite having larger joint sizes than the other primates, display low trabecular density, while orangutans and chimpanzees with intermediate joint sizes have relatively low trabecular density compared to the cercopithecines. Olive baboons with larger joints among the cercopithecines have trabecular densities that are most similar to that of vervets and patas monkeys, whose joints are relatively smaller. These results support the proposal that increased joint size is likely correlated with greater joint mobility to increase joint excursion, and is not necessarily a function of increased mechanical loading. Therefore, relationships between subchondral bone density and mechanical loading are not straightforward when compared across taxa with differences in joint excursion.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.