Morphometric Maps of Bilateral Asymmetry in the Human Humerus: An Implementation in the R Package Morphomap

Antonio Profico,Damiano Marchi,Alessandro Mondanaro,Ileana Micarelli,Giorgio Manzi,Carlotta Zeppilli,Pasquale Raia,Paul O’Higgins

doi:10.3390/sym13091711

Abstract

In biological anthropology, parameters relating to cross-sectional geometry are calculated in paired long bones to evaluate the degree of lateralization of anatomy and, by inference, function. Here, we describe a novel approach, newly added to the morphomap R package, to assess the lateralization of the distribution of cortical bone along the entire diaphysis. The sample comprises paired long bones belonging to 51 individuals (10 females and 41 males) from The New Mexico Decedent Image Database with known biological profile, occupational and loading histories. Both males and females show a pattern of right lateralization. In addition, males are more lateralized than females, whereas there is not a significant association between lateralization with occupation and loading history. Body weight, height and long-bone length are the major factors driving the emergence of asymmetry in the humerus, while interestingly, the degree of lateralization decreases in the oldest individuals.

Highlights

In bioarchaeology and anthropology, it is of interest to infer the physical activities, occupations and behaviours of past populations from skeletal material [1,2]
The distribution of cortical bone is influenced by loading history [3,4,5], and bone remodelling seems to be significantly associated with high-frequency daily action [6]
To assess how asymmetry in the distribution of cortical thickness varies in relation to occupation, age, weight, height and biomechanical length, we performed a multiple regression with these variables as independent and maps of differences in cortical thickness between the left and right side as dependent variables

Summary

Introduction

It is of interest to infer the physical activities, occupations and behaviours of past populations from skeletal material [1,2]. Even the comparison of paired bone elements is not entirely without issues, since inflammatory processes [13] may trigger osteogenesis in distant regions [14,15], and differences in patterns of asymmetry in the upper limb have been found with ageing [16] and long-term disuse [17], in addition to loading history per se Despite these caveats, traditional methods that rely on calculations of the percentage change of cross-sectional geometric parameters (total area, cortical area, area moments of inertia) on the humerus have provided useful insights into activity patterns in modern [12] and archaeological populations [18,19,20,21,22,23,24], as well as in paleontological samples [25,26,27,28,29,30]. The hypotheses we tested have significant implications for the evaluation of asymmetry in archaeological populations and in extinct human species

Data Preparation and Processing

Description of the Function MorphomapAsymmetry

Description of the Function MorphomapMapPCA

Results