Analyses of bone structure in living and extinct primates typically assume a direct relationship between bone form and function even though the mechanisms of bone's adaptive response to loads is not fully understood. The primary objective of this project is collecting comparative age-related data on the development of bone from a number of locations in the postcranial skeleton of humans, chimpanzees, and macaques to test an explanatory model for the patterns of change associated with locomotor development in these species. This project quantifies the changes in trabecular bone microstructure and elastic properties during ontogeny in humans, chimpanzees, and macaques using high-resolution computed tomography (CT) scan data in the postcranial skeleton. The relative contributions of locomotor loading, body mass, sex, and age on the development of trabecular and cortical bone structure are examined, as are kinematic and kinetic analyses of locomotor ontogeny in a sample of juvenile modern humans to relate structural changes to changes in locomotion in humans. By quantifying the ontogenetic changes in bone structure across three different primates with divergent locomotor behaviors and developmental trajectories, the role of general developmental processes, genetic patterning, and the mechanical loading environment on bone structure are more clearly defined. The simultaneous analysis of locomotor development, bone structural and mechanical adaptations, and within and between species variation is unique and produces a more concrete understanding of bone functional morphology. Ultimately, this study will provide insight into the adaptive response of trabecular bone to mechanical loads and will provide important information regarding the functional utility of trabecular bone structure in the mammalian skeleton.
This study contributes to the training of undergraduate and graduate students at three universities, result in the production of a large comparative dataset of high-resolution CT and kinematic data for use by other researchers and for incorporation into the biological anthropology curriculum, has direct relevance for understanding the normal and pathological locomotor system in children and adults and will be of broad interest in orthopedics, internal medicine, bone metabolism, and biomechanics, and, finally, the results of this study will also contribute relevant data to the understanding of the prevalent health conditions of osteoporosis and osteoarthritis.
The ontogeny of bipedal walking is considered uniquely challenging, due in part to the balance requirements of single limb support. Thus, locomotor development in humans and our bipedal ancestors may track developmental milestones including the maturation of the neuromuscular control system. In this project, we examined the ontogeny of locomotor mechanics in children aged 1-8, and bone growth and development in an age-matched skeletal sample to identify bony markers of neuromuscular control. Intellectual merit: We show that step-to-step variation in locomotor kinematics decreases significantly with age, an indication that older children increase stability as their neuromuscular control system matures. Analyses of trabecular bone architecture in the distal tibia of an age-matched skeletal sample (the Norris Farms #36 archaeological skeletal collection) show a bony signal of this shift in locomotor stability. Using a grid of eleven cubic volumes of interest (VOIs) in the distal metaphysis of each tibia, we show that the degree of anisotropy (DA) of trabecular struts changes with age. DA is a measure of the degree of orientation of trabecular struts, with more oriented struts better able to resist more predictable loads. Intra-individual variation in DA across these VOIs is generally high at young ages, likely reflecting variation in loading due to kinematic instability. With increasing age, mean DA converges on higher values and becomes less variable across the distal tibia. We believe the ontogeny of distal tibia trabecular architecture reflects the development of locomotor stability in bipeds. It is possible that this novel bony marker of development may be used to assess the relationship between locomotor development and other life history milestones in fossil hominins. Broader impacts: The proposed research enhanced the infrastructure of research in biological anthropology by incorporating recent technological and methodological advances in trabecular bone analysis into understanding skeletal adaptation, ontogeny, and paleontological and bioarchaeological behavioral reconstructions. This project represented the initiation of collaboration among researchers at three universities in the U.S. to direct expertise and resources toward answering questions of interest across biological anthropology. The study contributed to the training of undergraduate and graduate students at three universities and resulted in the production of a large comparative ontogenetic dataset of HRCT and kinematic data for use by other researchers and for incorporation into the biological anthropology curriculum. It is anticipated that the data and results from this study will help in understanding the normal as well as the pathological locomotor system in children and adults and will be of broad interest in orthopedics, internal medicine, bone metabolism, and biomechanics. As an investigation of bone development and structure, the results of this study will also have society-wide and possibly global implications contributing relevant data to the understanding of the prevalent health conditions of osteoporosis and osteoarthritis.
