Textural characteristics of the iliac-femoral trabecular pattern in a bipedally trained Japanese macaque

Trabecular architecture of the distal femur in extant hominids

Extant great apes are characterized by a wide range of locomotor, postural and manipulative behaviours that each require the limbs to be used in different ways. In addition to external bone morphology, comparative investigation of trabecular bone, which (re-)models to reflect loads incurred during life, can provide novel insights into bone functional adaptation. Here, we use canonical holistic morphometric analysis (cHMA) to analyse the trabecular morphology in the distal femoral epiphysis of Homo sapiens (n = 26), Gorilla gorilla (n = 14), Pan troglodytes (n = 15) and Pongo sp. (n = 9). We test two predictions: (1) that differing locomotor behaviours will be reflected in differing trabecular architecture of the distal femur across Homo, Pan, Gorilla and Pongo; (2) that trabecular architecture will significantly differ between male and female Gorilla due to their different levels of arboreality but not between male and female Pan or Homo based on previous studies of locomotor behaviours. Results indicate that trabecular architecture differs among extant great apes based on their locomotor repertoires. The relative bone volume and degree of anisotropy patterns found reflect habitual use of extended knee postures during bipedalism in Homo, and habitual use of flexed knee posture during terrestrial and arboreal locomotion in Pan and Gorilla. Trabecular architecture in Pongo is consistent with a highly mobile knee joint that may vary in posture from extension to full flexion. Within Gorilla, trabecular architecture suggests a different loading of knee in extension/flexion between females and males, but no sex differences were found in Pan or Homo, supporting our predictions. Inter- and intra-specific variation in trabecular architecture of distal femur provides a comparative context to interpret knee postures and, in turn, locomotor behaviours in fossil hominins.

Cortical and Trabecular Bone Modeling and Implications for Bone Functional Adaptation in the Mammalian Tibia

Bone modeling involves the addition of bone material through osteoblast-mediated deposition or the removal of bone material via osteoclast-mediated resorption in response to perceived changes in loads by osteocytes. This process is characterized by the independent occurrence of deposition and resorption, which can take place simultaneously at different locations within the bone due to variations in stress levels across its different regions. The principle of bone functional adaptation states that cortical and trabecular bone tissues will respond to mechanical stimuli by adjusting (i.e., bone modeling) their morphology and architecture to mechanically improve their mechanical function in line with the habitual in vivo loading direction. This principle is relevant to various research areas, such as the development of improved orthopedic implants, preventative medicine for osteopenic elderly patients, and the investigation of locomotion behavior in extinct species. In the present review, the mammalian tibia is used as an example to explore cortical and trabecular bone modeling and to examine its implications for the functional adaptation of bones. Following a short introduction and an exposition on characteristics of mechanical stimuli that influence bone modeling, a detailed critical appraisal of the literature on cortical and trabecular bone modeling and bone functional adaptation is given. By synthesizing key findings from studies involving small mammals (rodents), large mammals, and humans, it is shown that examining both cortical and trabecular bone structures is essential for understanding bone functional adaptation. A combined approach can provide a more comprehensive understanding of this significant physiological phenomenon, as each structure contributes uniquely to the phenomenon.

Sesamoid bones also show functional adaptation in their microanatomy-The example of the patella in Perissodactyla

The patella is the largest sesamoid bone of the skeleton. It is strongly involved in the knee, improving output force and velocity of the knee extensors, and thus plays a major role in locomotion and limb stability. However, the relationships between its structure and functional constraints, that would enable a better understanding of limb bone functional adaptations, are poorly known. This contribution proposes a comparative analysis, both qualitative and quantitative, of the microanatomy of the whole patella in perissodactyls, which show a wide range of morphologies, masses, and locomotor abilities, in order to investigate how the microanatomy of the patella adapts to evolutionary constraints. The inner structure of the patella consists of a spongiosa surrounded by a compact cortex. Contrary to our expectations, there is no increase in compactness with bone size, and thus body size and weight, but only an increase in the tightness of the spongiosa. No particular thickening of the cortex associated with muscle insertions is noticed but a strong thickening is observed anteriorly at about mid-length, where the strong intermediate patellar ligament inserts. The trabeculae are mainly oriented perpendicularly to the posterior articular surface, which highlights that the main stress is anteroposteriorly directed, maintaining the patella against the femoral trochlea. Conversely, anteriorly, trabeculae are rather circumferentially oriented, following the insertion of the patellar ligament and, possibly also, of the quadriceps tendon. A strong variation is observed among perissodactyl families but also intraspecifically, which is in accordance with previous studies suggesting a higher variability in sesamoid bones. Clear trends are nevertheless observed between the three families. Equids have a much thinner cortex than ceratomorphs. Rhinos and equids, both characterized by a development of the medial border, show an increase in trabecular density laterally suggesting stronger stresses laterally. The inner structure in tapirs is more homogeneous despite the absence of medial development of the medial border with no "compensation" of the inner structure, which suggests different stresses on their knees associated with a different morphology of their patellofemoral joint.

The Functional and Allometric Implications of Hipbone Trabecular Microarchitecture in a Sample of Eutherian and Metatherian Mammals

The pelvis plays an active role in weight bearing and countering the ground reaction forces incurred by the hindlimbs thus making it a critical component of the locomotor skeleton. Accordingly, this anatomical region is theoretically ideal for inferring locomotor behavior from both external skeletal morphology and trabecular microarchitecture, with the latter possibly offering nuanced insights into the mechanical loading environment given its increased plasticity and higher turnover rate. However, trabecular microarchitecture is also known to be influenced by a variety of factors including body size, sex, age, genetic regulation, diet and activity level, that collectively hinder the ability to generate consistent functional inferences. In this study, a comparative sample of mammals (42 species spanning four orders) of varying sizes, yet comparable locomotor repertoires, were evaluated to determine the effects of body size, phylogeny and locomotion on hipbone trabecular microarchitecture. This study found a weak functional signal detected in differences in bone volume fraction and the degree of anisotropy across certain pre-assigned locomotor categories, while confirming previously recognized allometric scaling trends reported for other mammalian samples based on the femur. Within primates, a more anisotropic pattern was observed for quadrupedal species attributed to their repetitive loading regimes and stereotypical limb excursions, while isotropic values were revealed for taxa utilizing more varied arboreal repertoires. Humans, despite a frequent and predictable loading environment associated with their use of bipedalism, showed relatively isotropic values. This study highlights the confounding factors that influence trabecular microarchitecture and consequently limit its utility as a method for investigating locomotor adaptation.

Trabecular architecture in the humeral metaphyses of non-avian reptiles (Crocodylia, Squamata and Testudines): Lifestyle, allometry and phylogeny

The lifestyle of extinct tetrapods is often difficult to assess when clear morphological adaptations such as swimming paddles are absent. According to the hypothesis of bone functional adaptation, the architecture of trabecular bone adapts sensitively to physiological loadings. Previous studies have already shown a clear relation between trabecular architecture and locomotor behavior, mainly in mammals and birds. However, a link between trabecular architecture and lifestyle has rarely been examined. Here, we analyzed trabecular architecture of different clades of reptiles characterized by a wide range of lifestyles (aquatic, amphibious, generalist terrestrial, fossorial, and climbing). Humeri of squamates, turtles, and crocodylians have been scanned with microcomputed tomography. We selected spherical volumes of interest centered in the proximal metaphyses and measured trabecular spacing, thickness and number, degree of anisotropy, average branch length, bone volume fraction, bone surface density, and connectivity density. Only bone volume fraction showed a significant phylogenetic signal and its significant difference between squamates and other reptiles could be linked to their physiologies. We found negative allometric relationships for trabecular thickness and spacing, positive allometries for connectivity density and trabecular number and no dependence with size for degree of anisotropy and bone volume fraction. The different lifestyles are well separated in the morphological space using linear discriminant analyses, but a cross-validation procedure indicated a limited predictive ability of the model. The trabecular bone anisotropy has shown a gradient in turtles and in squamates: higher values in amphibious than terrestrial taxa. These allometric scalings, previously emphasized in mammals and birds, seem to be valid for all amniotes. Discriminant analysis has offered, to some extent, a distinction of lifestyles, which however remains difficult to strictly discriminate. Trabecular architecture seems to be a promising tool to infer lifestyle of extinct tetrapods, especially those involved in the terrestrialization.

Trabecular architecture of the great ape and human femoral head

Studies of femoral trabecular structure have shown that the orientation and volume of bone are associated with variation in loading and could be informative about individual joint positioning during locomotion. In this study, we analyse for the first time trabecular bone patterns throughout the femoral head using a whole-epiphysis approach to investigate how potential trabecular variation in humans and great apes relates to differences in locomotor modes. Trabecular architecture was analysed using microCT scans of Pan troglodytes (n = 20), Gorilla gorilla (n = 14), Pongo sp. (n = 5) and Homo sapiens (n = 12) in medtool 4.1. Our results revealed differences in bone volume fraction (BV/TV) distribution patterns, as well as overall trabecular parameters of the femoral head between great apes and humans. Pan and Gorilla showed two regions of high BV/TV in the femoral head, consistent with hip posture and loading during two discrete locomotor modes: knuckle-walking and climbing. Most Pongo specimens also displayed two regions of high BV/TV, but these regions were less discrete and there was more variability across the sample. In contrast, Homo showed only one main region of high BV/TV in the femoral head and had the lowest BV/TV, as well as the most anisotropic trabeculae. The Homo trabecular structure is consistent with stereotypical loading with a more extended hip compared with great apes, which is characteristic of modern human bipedalism. Our results suggest that holistic evaluations of femoral head trabecular architecture can reveal previously undetected patterns linked to locomotor behaviour in extant apes and can provide further insight into hip joint loading in fossil hominins and other primates.

Cancellous bone and theropod dinosaur locomotion. Part II-a new approach to inferring posture and locomotor biomechanics in extinct tetrapod vertebrates

This paper is the second of a three-part series that investigates the architecture of cancellous bone in the main hindlimb bones of theropod dinosaurs, and uses cancellous bone architectural patterns to infer locomotor biomechanics in extinct non-avian species. Cancellous bone is widely known to be highly sensitive to its mechanical environment, and therefore has the potential to provide insight into locomotor biomechanics in extinct tetrapod vertebrates such as dinosaurs. Here in Part II, a new biomechanical modelling approach is outlined, one which mechanistically links cancellous bone architectural patterns with three-dimensional musculoskeletal and finite element modelling of the hindlimb. In particular, the architecture of cancellous bone is used to derive a single 'characteristic posture' for a given species-one in which bone continuum-level principal stresses best align with cancellous bone fabric-and thereby clarify hindlimb locomotor biomechanics. The quasi-static approach was validated for an extant theropod, the chicken, and is shown to provide a good estimate of limb posture at around mid-stance. It also provides reasonable predictions of bone loading mechanics, especially for the proximal hindlimb, and also provides a broadly accurate assessment of muscle recruitment insofar as limb stabilization is concerned. In addition to being useful for better understanding locomotor biomechanics in extant species, the approach hence provides a new avenue by which to analyse, test and refine palaeobiomechanical hypotheses, not just for extinct theropods, but potentially many other extinct tetrapod groups as well.

Trabecular bone patterning in the hominoid distal femur

BACKGROUND

In addition to external bone shape and cortical bone thickness and distribution, the distribution and orientation of internal trabecular bone across individuals and species has yielded important functional information on how bone adapts in response to load. In particular, trabecular bone analysis has played a key role in studies of human and nonhuman primate locomotion and has shown that species with different locomotor repertoires display distinct trabecular architecture in various regions of the skeleton. In this study, we analyse trabecular structure throughout the distal femur of extant hominoids and test for differences due to locomotor loading regime.

METHODS

Micro-computed tomography scans of Homo sapiens (n = 11), Pan troglodytes (n = 18), Gorilla gorilla (n = 14) and Pongo sp. (n = 7) were used to investigate trabecular structure throughout the distal epiphysis of the femur. We predicted that bone volume fraction (BV/TV) in the medial and lateral condyles in Homo would be distally concentrated and more anisotropic due to a habitual extended knee posture at the point of peak ground reaction force during bipedal locomotion, whereas great apes would show more posteriorly concentrated BV/TV and greater isotropy due to a flexed knee posture and more variable hindlimb use during locomotion.

RESULTS

Results indicate some significant differences between taxa, with the most prominent being higher BV/TV in the posterosuperior region of the condyles in Pan and higher BV/TV and anisotropy in the posteroinferior region in Homo. Furthermore, trabecular number, spacing and thickness differ significantly, mainly separating Gorilla from the other apes.

DISCUSSION

The trabecular architecture of the distal femur holds a functional signal linked to habitual behaviour; however, there was more similarity across taxa and greater intraspecific variability than expected. Specifically, there was a large degree of overlap in trabecular structure across the sample, and Homo was not as distinct as predicted. Nonetheless, this study offers a comparative sample of trabecular structure in the hominoid distal femur and can contribute to future studies of locomotion in extinct taxa.

The effects of cracks on the quantification of the cancellous bone fabric tensor in fossil and archaeological specimens: a simulation study

Cancellous bone is very sensitive to its prevailing mechanical environment, and study of its architecture has previously aided interpretations of locomotor biomechanics in extinct animals or archaeological populations. However, quantification of architectural features may be compromised by poor preservation in fossil and archaeological specimens, such as post mortem cracking or fracturing. In this study, the effects of post mortem cracks on the quantification of cancellous bone fabric were investigated through the simulation of cracks in otherwise undamaged modern bone samples. The effect on both scalar (degree of fabric anisotropy, fabric elongation index) and vector (principal fabric directions) variables was assessed through comparing the results of architectural analyses of cracked vs. non-cracked samples. Error was found to decrease as the relative size of the crack decreased, and as the orientation of the crack approached the orientation of the primary fabric direction. However, even in the best-case scenario simulated, error remained substantial, with at least 18% of simulations showing a > 10% error when scalar variables were considered, and at least 6.7% of simulations showing a > 10° error when vector variables were considered. As a 10% (scalar) or 10° (vector) difference is probably too large for reliable interpretation of a fossil or archaeological specimen, these results suggest that cracks should be avoided if possible when analysing cancellous bone architecture in such specimens.

The developing juvenile ischium: macro-radiographic insights

Despite the importance of the human pelvis as a weight-bearing structure, there is a paucity of literature that discusses the development of the juvenile innominate from a biomechanical perspective. This study aims to add to the limited body of literature pertaining to this topic through the qualitative analysis of the gross architecture of the human ischium during the juvenile period. Macro-radiographs of 55 human ischia ranging from 28 intra-uterine weeks to 14 years of age were examined using intensity-gradient color mapping to highlight changes in gross structural morphology with increasing age. A clear pattern of maturation was observed in the juvenile ischium with increasing age. The acetabular component and ramus of the ischium consistently displayed low bone intensity in the postnatal skeletal material. Conversely the posterior body of the ischium, and in particular the ischial spine and lesser sciatic notch, exhibited increasing bone intensity which first arose at 1-2 years of age and became more expansive in older cohorts. The intensity patterns observed within the developing juvenile ischium are indicative of the potential factors influencing the maturation of this skeletal element. While the low intensity acetabular fossa indicates a lack of significant biomechanical interactions, the posterior increase in bone intensity may be related to the load-bearing nature of the posterior ischium.

Trabecular evidence for a human-like gait in Australopithecus africanus

Although the earliest known hominins were apparently upright bipeds, there has been mixed evidence whether particular species of hominins including those in the genus Australopithecus walked with relatively extended hips, knees and ankles like modern humans, or with more flexed lower limb joints like apes when bipedal. Here we demonstrate in chimpanzees and humans a highly predictable and sensitive relationship between the orientation of the ankle joint during loading and the principal orientation of trabecular bone struts in the distal tibia that function to withstand compressive forces within the joint. Analyses of the orientation of these struts using microCT scans in a sample of fossil tibiae from the site of Sterkfontein, of which two are assigned to Australopithecus africanus, indicate that these hominins primarily loaded their ankles in a relatively extended posture like modern humans and unlike chimpanzees. In other respects, however, trabecular properties in Au africanus are distinctive, with values that mostly fall between those of chimpanzees and humans. These results indicate that Au. africanus, like Homo, walked with an efficient, extended lower limb.

A comparative study of the trabecular bony architecture of the talus in humans, non-human primates, and Australopithecus

This study tested the hypothesis that talar trabecular microarchitecture reflects the loading patterns in the primate ankle joint, to determine whether talar trabecular morphology might be useful for inferring locomotor behavior in fossil hominins. Trabecular microarchitecture was quantified in the anteromedial, anterolateral, posteromedial, and posterolateral quadrants of the talar body in humans and non-human primates using micro-computed tomography. Trabecular bone parameters, including bone volume fraction, trabecular number and thickness, and degree of anisotropy differed between primates, but not in a manner entirely consistent with hypotheses derived from locomotor kinematics. Humans have highly organized trabecular struts across the entirety of the talus, consistent with the compressive loads incurred during bipedal walking. Chimpanzees possess a high bone volume fraction, consisting of plate-like trabecular struts. Orangutan tali are filled with a high number of thin, connected trabeculae, particularly in the anterior portion of the talus. Gorillas and baboons have strikingly similar internal architecture of the talus. Intraspecific analyses revealed no regional differences in trabecular architecture unique to bipedal humans. Of the 22 statistically significant regional differences in the human talus, all can also be found in other primates. Trabecular thickness, number, spacing, and connectivity density had the same regional relationship in the talus of humans, chimpanzees, gorillas, and baboons, suggesting a deeply conserved architecture in the primate talus. Australopithecus tali are human-like in most respects, differing most notably in having more oriented struts in the posteromedial quadrant of the body compared with the posterolateral quadrant. Though this result could mean that australopiths loaded their ankles in a unique manner during bipedal gait, the regional variation in degree of anisotropy was similar in humans, chimpanzees, and gorillas. These results collectively suggest that the microarchitecture of the talus does not simply reflect the loading environment, limiting its utility in reconstructing locomotion in fossil primates.

More than just a bump: cam-type femoroacetabular impingement and the evolution of the femoral neck

Recent orthopaedic literature has implicated femoroacetabular impingement, the pathologic abutment of structural aberrancies in the proximal femur and acetabular rim, as an important cause of groin pain in young individuals and a potential factor in early idiopathic osteoarthritis. The etiology and risk factors for developing cam-type morphology are still unknown. The osseous anatomy of the proximal femur in humans is the culmination of nearly 400 million years of evolution. Coxa recta and coxa rotunda are the two predominant morphologies in modern animals. While the former, characterized by a straight head-neck junction, is often present in cursorial creatures, the latter, [corrected] distinguished by high offset at this junction, is exemplified in most humans. Based on the ontology and phylogeny of the proximal femur, coxa rotunda probably developed from a more primitive coxa recta. We believe that cam-type morphology is neither a redevelopment of coxa recta nor a malformation such as slipped capital epiphysis. The aspherical osteocartilaginous bump is associated with an extended physis and has been noted to appear during mid-adolescence. While this protuberance may contribute to future pathology, the authors feel that increased loading of the hip, not impingement activities, during late childhood and early adolescence predispose patients to develop this morphology.

Study of femoral torsion during prenatal growth: interpretations associated with the effects of intrauterine pressure

The developing fetus is protected from external environmental influences by maternal tissues. However, these structures have a limited elasticity, such that the fetus must grow in a confined space, constraining its size at the end of pregnancy. Can these constraints modify the morphology of the fetal skeleton? The intensity of these constraints increases between 5 months and birth, making it the most appropriate period to address this question. A sample of 89 fetal femora was analyzed, and results provide evidence that during this period, the torsion of the femoral shaft (quantified by means of a new three-dimensional method) increases gradually. Two explanations were considered: this increase could signal effects of constraints induced by the intrauterine cavity, developmental patterning, or some combination of these two. Different arguments tend to support the biomechanical explanation, rather than a programming pattern formation. Indeed, the identification of the femur as a first degree lever, created by the hyperflexion of the fetal lower limbs on the pelvis, could explain the increase in femoral shaft torsion during prenatal life. A comparison with femora of infants is in accordance with this mechanical interpretation, which is possible through bone modeling/remodeling. Although genetic and epigenetic mechanisms may regulate timing of fetal development, our data suggest that at birth, the fetal skeleton also has an intrauterine mechanical history through adaptive bone plasticity.