Growth and development of trabecular structure in the calcaneus of Japanese macaques (Macaca fuscata) reflects locomotor behavior, life history, and neuromuscular development

The relationship between primate distal fibula trabecular architecture and arboreality, phylogeny and size

The fibula, despite being traditionally overlooked compared to the femur and the tibia, has recently received attention in primate functional morphology due to its correlation with the degree of arboreality (DOA). Highlighting further fibular features that are associated with arboreal habits would be key to improving palaeobiological inferences in fossil specimens. Here we present the first investigation on the trabecular bone structure of the primate fibula, focusing on the distal epiphysis, across a vast array of species. We collected μCT data on the distal fibula for 21 species of primates, with representatives from most of the orders, and we employed a recently developed approach implemented in the R package 'indianaBones' to isolate the entire trabecular bone underlying an epiphysis or articular facet. After extracting both traditional trabecular parameters and novel topological indices, we tested for the posited relationship between trabecular bone and DOA. To disentangle this effect from others related to body size and phylogenetic relationship, we included a body mass proxy as covariate and employed phylogenetic comparative methods. We ran univariate/multivariate and exploratory/inferential statistical analyses. The trabecular structure of the fibular distal epiphysis in primates does not appear to be associated with the DOA. Instead, it is strongly affected by body mass and phylogenetic relationships. Although we identified some minor trends related to human bipedalism, our findings overall discourage, at this stage, the study of distal fibula trabecular bone to infer arboreal behaviors in extinct primates. We further found that body size distribution is strongly related to phylogeny, an issue preventing us from unravelling the influence of the two factors and that we believe can potentially affect future comparative analyses of primates. Overall, our results add to previous evidence of how trabecular traits show variable correlation with locomotor aspects, size and phylogenetic history across the primate skeleton, thus outlining a complex scenario in which a network of interconnected factors affects the morphological evolution of primates. This work may represent a starting point for future studies, for example, focusing on the effect of human bipedalism on distal fibula trabecular bone, or aiming to better understand the effects of body size and phylogenetic history on primate morphological evolution.

The Ontogeny of the Human Calcaneus: Insights From Morphological and Trabecular Changes During Postnatal Growth

OBJECTIVES

To investigate the developmental changes in the human calcaneal internal and external morphology linked to the acquisition of mature bipedal locomotion.

METHODS

Seventy seven micro-CT scans of modern juvenile calcanei (from perinates to 15 years old) are employed. The chronological period spans from the Middle/Late Neolithic (4800-4500 BCE) to the 20th century. Through a comprehensive approach that comprises geometric morphometric methods and whole-bone trabecular analysis, the calcaneal growing morphology has been explored.

RESULTS

Morphological changes reflect the development of bipedal locomotion, showing its potential when tracking the major locomotor milestones. The calcaneal shape is immature and almost featureless during the first year of life. The internal architecture is dense and isotropic with numerous thin trabeculae closely packed together. The internal architecture changes to better adapt to variations in load stimulated by a more mature gait by increasing bone mass and alignment, with fewer and thicker struts. The external morphology shows its plasticity by increasing the surface area where greater strain is expected and changing the orientation of the articular facets.

CONCLUSIONS

Analysis of morphological changes in the growing calcaneus highlights the importance of an integrative methodology when exploring developmental bone plasticity. The changes in calcaneal internal and external morphologies reflect the different loading patterns experienced during growth, gradually shifting from a more generalized morphology to a more adult-like one, reflecting major locomotor achievement. Our research shows that although initially genetically driven, calcaneal plasticity may display mechanical influences and provide precious information on tracking the main locomotor milestones.

Trabecular Bone Ontogeny of the Human Distal Tibia

OBJECTIVES

There is an increasing understanding of how trabecular bone adapts to biomechanical changes during ontogeny. However, limited research exists regarding the distal tibia, which is important in weight-bearing locomotion as part of the ankle joint. This study aims to document the ontogenetic trabecular patterns of the distal tibia, in addition to changes in its structural heterogeneity.

MATERIALS AND METHODS

Thirty-eight distal tibiae, ranging in age from 28 intrauterine weeks to 8 postnatal years, from the Scheuer juvenile skeletal collection were examined. Trabecular bone was analyzed using a quantitative volume of interest approach and qualitative whole bone mapping following microcomputed tomography.

RESULTS

Fetal and perinatal tibia lack mature organization and are associated with high bone volume fraction. During the first year of life, there is a decrease in bone volume fraction and an indication of early re-organization of trabecular struts in the distal tibia. After one year of age, the distal tibia exhibits increased trabecular structural heterogeneity.

DISCUSSION

The trabecular architecture of the fetal and perinatal distal tibia lacks mature organization and instead reflects ossification patterns. At these stages, there is a rapid accumulation of bone mass associated with gestational overproduction, hypothesized to be in preparation for subsequent postnatal changes. During the first year of life there is a decrease in volume fraction, associated with constructive regression. It is postulated this is related to changing biomechanical forces associated with the bipedal gait, in addition to growth demands. After one year of age, the distal tibia exhibits structural heterogeneity with trabecular adaption to accommodate specific bipedal stresses.

Restructuring of Femoral Cortical Bone During Growth and Locomotor Development of Wild Chimpanzees (Pan troglodytes verus)

OBJECTIVE

Chimpanzees are altricial in terms of their locomotor development and transition from being carried to engaging in suspensory and arboreal locomotor behaviors to eventually relying on terrestrial quadrupedalism as their main form of locomotion. Here, we consider the mechanical implications of femoral cortical bone restructuring during growth and locomotor development in wild chimpanzees.

MATERIALS AND METHODS

Cortical bone structure was examined in an ontogenetic sample of wild chimpanzees from a single subspecies (P. t. verus) spanning in age from 2 weeks to 12.6 years. Diaphyseal cross-sections were extracted from micro-CT scans of the femur at 35%, 50%, and 65% of total intermetaphyseal length and variation in cortical bone structure was assessed based on bending rigidity (Imax/Imin, Ix/Iy), relative medullary area, and cortical bone porosity.

RESULTS

Diaphyseal shape is relatively circular with a high amount of cortical bone porosity and a large relative medullary area during early infancy. Distinct shifts in cortical bone structure occurred for each studied parameter with the biggest changes occurring within the first 5 years. Values appear to stabilize as quadrupedal walking increases in frequency and is established as the main form of locomotion.

DISCUSSION

Collectively, the results suggest a degree of integration in which cortical bone restructures in response to rapid changes in locomotion in addition to nonmechanical influences such as hormonal, and growth factors, without compromising function and structural integrity. The extent of influence of each factor varies throughout growth and highlights the need for caution in functional interpretations of cortical bone geometry.

Raccoons Reveal Hidden Diversity in Trabecular Bone Development

Trabecular bone, and its ability to rapidly modify its structure in response to strain exerted on skeletal elements, has garnered increased attention from researchers with the advancement of CT technology that allows for the analysis of its complex lattice-like framework. Much of this research has focused on adults of select taxa, but analysis into trabecular development across ontogeny remains limited. In this paper, we explore the shift in several trabecular characteristics in the articular head of the humerus and femur in Procyon lotor across the entirely of the species' lifespan. Our results show that while body mass plays a role in determining trabecular structure, other elements such as bone growth, increased activity, and puberty result in trends not observed in the interspecific analysis of adults. Furthermore, differences in the trabeculae of the humerus and femur suggest combining distinct boney elements in meta-analysis may obfuscate the variety in the structures. Finally, rates at which fore and hindlimb trabeculae orient themselves early in life differ enough to warrant further exploration to identify the currently unknown causes for their variation.

The developing juvenile talus: Radiographic identification of distinct ontogenetic phases and structural trajectories

Trabecular bone architecture in the developing skeleton is a widely researched area of bone biomechanics; however, despite its significance in weight-bearing locomotion, the developing talus has received limited examination. This study investigates the talus with the purpose of identifying ontogenetic phases and developmental patterns that contribute to the growing understanding of the developing juvenile skeleton. Colour gradient mapping and radiographic absorptiometry were utilised to investigate 62 human tali from 38 individuals, ranging in age-at-death from 28 weeks intrauterine to 20 years of age. The perinatal talus exhibited a rudimentary pattern comparable to the structural organisation observed within the late adolescent talus. This early internal organisation is hypothesised to be related to the vascular pattern of the talus. After 2 years of age, the talus demonstrated refinement, where radiographic trajectories progressively developed into patterns consistent with adult trabecular organisation, which are linked to the forces associated with the bipedal gait, suggesting a strong influence of biomechanical forces on the development of the talus.

Trabecular bone ontogeny tracks neural development and life history among humans and non-human primates

Trabecular bone-the spongy bone inside marrow cavities-adapts to its mechanical environment during growth and development. Trabecular structure can therefore be interpreted as a functional record of locomotor behavior in extinct vertebrates. In this paper, we expand upon traditional links between form and function by situating ontogenetic trajectories of trabecular bone in four primate species into the broader developmental context of neural development, locomotor control, and ultimately life history. Our aim is to show that trabecular bone structure provides insights into ontogenetic variation in locomotor loading conditions as the product of interactions between increases in body mass and neuromuscular maturation. Our results demonstrate that age-related changes in trabecular bone volume fraction (BV/TV) are strongly and linearly associated with ontogenetic changes in locomotor kinetics. Age-related variation in locomotor kinetics and BV/TV is in turn strongly associated with brain and body size growth in all species. These results imply that age-related variation in BV/TV is a strong proxy for both locomotor kinetics and neuromuscular maturation. Finally, we show that distinct changes in the slope of age-related variation in bone volume fraction correspond to the age of the onset of locomotion and the age of locomotor maturity. Our findings compliment previous studies linking bone development to locomotor mechanics by providing a fundamental link to brain development and life history. This implies that trabecular structure of fossil subadults can be a proxy for the rate of neuromuscular maturation and major life history events like locomotor onset and the achievement of adult-like locomotor repertoires.

The developing juvenile distal tibia: Radiographic identification of distinct ontogenetic phases and structural trajectories

A novel combination of radiographic colour gradient mapping and radiographic absorptiometry was utilised to examine 96 human distal tibiae from 54 individuals ranging in age-at-death from the foetal to 23 years. The purpose of this was to identify previously undocumented changes in the internal organisation during the development of the distal tibia and determine whether these changes could be described as distinct phases. Previous studies have demonstrated a rudimentary structural organisation in other skeletal elements that mirror more mature patterns of bone organisation. Results showed that the perinatal tibia did not exhibit a rudimentary structural pattern similar to the architecture observed within the late adolescent tibia. This lack of early internal organisation is hypothesised to be related to the rudimentary ossification process that is being laid down around a pre-existing vascular template which will be subsequently modified by locomotive forces. Between birth and 2 years of age, the tibia exhibited a period of regression where radiodensity decreased in comparison to the perinatal tibia. This period of regression was postulated to be due to a combination of factors including changing locomotive forces, weaning and growth resulting in a stage of development which is extremely demanding on calcium liberation from the skeleton. After 2 years of age, the distal tibia demonstrated refinement where radiographic trajectories progressively developed into patterns consistent with adult trabecular organisation. These trajectories are linked to the forces associated with the bipedal gait, suggesting a strong influence of biomechanical forces on the development of the distal tibia.