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Many studies have noted that the bones of the human upper limb display bilateral asymmetry, commonly linking this asymmetry in external and internal morphology to handedness and lateralization. Few studies, however, have attempted to track asymmetry throughout ontogeny. This study assesses the ontogenetic development of cortical and trabecular bone asymmetry in the humerus. We predict that directional asymmetry in structural properties will emerge in concert with hand preference and increased activity levels during the juvenile period. Paired humeri from 57 individuals from the Norris Farms #36 archaeological skeletal collection ranging in age from neonate to adult were used in the current study. Cortical bone cross-sectional properties and three-dimensional trabecular bone structure were quantified from microcomputed tomography data. The results indicate significant absolute asymmetry in all measured cortical and trabecular bone variables across all ages. Trabecular bone displays significantly higher absolute asymmetry than cortical bone. Contrary to expectations, however, this study found very little evidence for significant directional asymmetry in humeral length and cortical or trabecular bone variables, except in adults. The presence of significant absolute asymmetry in all age groups, and the lack of significant directional asymmetry in almost all variables at all ages, suggests that structural differences due to higher levels of habitual loading in the dominant arm are overlain on a template of potentially significant existing asymmetry. Anat Rec, 301:1012-1025, 2018. © 2017 Wiley Periodicals, Inc., (© 2017 Wiley Periodicals, Inc.)

Most analyses of trabecular microarchitecture in mammals have focused on the functional significance of interspecific variation, but they have not effectively considered the influence of body size or phylogeny on bone architecture. The goals of this study were to determine the relationship between trabecular bone and body size in the humeral and femoral heads of extant primates, and to assess the influence of phylogeny on bone microstructure. Using a sample of 235 individuals from 34 primate species, ranging in body size from 0.06 to 130 kg, the relationships between trabecular bone structure and body size were assessed by using conventional and phylogenetic regression analyses. Bone volume fraction, trabecular thickness and trabecular spacing increase with body size, whereas bone surface-area-to-volume ratio decreases. Shape variables such as trabecular number, connectivity density and degree of anisotropy scale inversely with size. Most of these variables scale with significant negative allometry, except bone surface-area-to-volume ratio, which scales with slight positive allometry. Phylogenetic regressions indicate a relatively weak phylogenetic signal in some trabecular bone variables. These data demonstrate that, relative to body size, large primates have thinner and more tightly packed trabeculae than small primates. The relatively thin trabeculae in large primates and other mammals, coupled with constraints on trabecular thickness related to osteocyte function, suggest that increased skeletal loads in the postcranial joints of large mammals are probably mitigated not only through alterations in trabecular microarchitecture, but also through other mechanisms such as changes in cortical bone distribution, limb posture and gait speed.

Although the correspondence between habitual activity and diaphyseal cortical bone morphology has been demonstrated for the fore- and hind-limb long bones of primates, the relationship between trabecular bone architecture and locomotor behavior is less certain. If sub-articular trabecular and diaphyseal cortical bone morphology reflects locomotor patterns, this correspondence would be a valuable tool with which to interpret morphological variation in the skeletal and fossil record. To assess this relationship, high-resolution computed tomography images from both the humeral and femoral head and midshaft of 112 individuals from eight anthropoid genera (Alouatta, Homo, Macaca, Pan, Papio, Pongo, Trachypithecus, and Symphalangus) were analyzed. Within-bone (sub-articular trabeculae vs. mid-diaphysis), between-bone (forelimb vs. hind limb), and among-taxa relative distributions (femoral:humeral) were compared. Three conclusions are evident: (1) Correlations exists between humeral head sub-articular trabecular bone architecture and mid-humerus diaphyseal bone properties; this was not the case in the femur. (2) In contrast to comparisons of inter-limb diaphyseal bone robusticity, among all species femoral head trabecular bone architecture is significantly more substantial (i.e., higher values for mechanically relevant trabecular bone architectural features) than humeral head trabecular bone architecture. (3) Interspecific comparisons of femoral morphology relative to humeral morphology reveal an osteological "locomotor signal" indicative of differential use of the forelimb and hind limb within mid-diaphysis cortical bone geometry, but not within sub-articular trabecular bone architecture., (Copyright © 2011 Wiley Periodicals, Inc.)