Estimation of the forces exerted on the limb long bones of a white rhinoceros (Ceratotherium simum) using musculoskeletal modelling and simulation

Heavy animals incur large forces on their limb bones, due to the transmission of body weight and ground reaction forces, and the contractions of the various muscles of the limbs. This is particularly true for rhinoceroses, the heaviest extant animals capable of galloping. Several studies have examined their musculoskeletal system and the forces their bones incur, but no detailed quantification has ever been attempted. Such quantification could help understand better the link between form and function in giant land animals. Here we constructed three-dimensional musculoskeletal models of the forelimb and hindlimb of Ceratotherium simum, the heaviest extant rhino species, and used static optimisation (inverse) simulations to estimate the forces applied on the bones when standing at rest, including magnitudes and directions. Overall, unsurprisingly, the most active muscles were antigravity muscles, which generate moments opposing body weight (thereby incurring the ground reaction force), and thus keep the joints extended, avoiding joint collapse via flexion. Some muscles have an antigravity action around several joints, and thus were found to be highly active, likely specialised in body weight support (ulnaris lateralis; digital flexors). The humerus was subjected to the greatest amount of forces in terms of total magnitude; forces on the humerus furthermore came from a great variety of directions. The radius was mainly subject to high-magnitude compressive joint reaction forces, but to little muscular tension, whereas the opposite pattern was observed for the ulna. The femur had a pattern similar to that of the humerus, and the tibia's pattern was intermediate, being subject to great compression in its caudal side but to great tension in its cranial side (i.e. bending). The fibula was subject to by far the lowest force magnitude. Overall, the forces estimated were consistent with the documented morphofunctional adaptations of C. simum's long bones, which have larger insertion areas for several muscles and a greater robusticity overall than those of lighter rhinos, likely reflecting the intense forces we estimated here. Our estimates of muscle and bone (joint) loading regimes for this giant tetrapod improve the understanding of the links between form and function in supportive tissues and could be extended to other aspects of bone morphology, such as microanatomy.

Regional variation of the cortical and trabecular bone material properties in the rabbit skull

The material properties of some bones are known to vary with anatomical location, orientation and position within the bone (e.g., cortical and trabecular bone). Details of the heterogeneity and anisotropy of bone is an important consideration for biomechanical studies that apply techniques such as finite element analysis, as the outcomes will be influenced by the choice of material properties used. Datasets detailing the regional variation of material properties in the bones of the skull are sparse, leaving many finite element analyses of skulls no choice but to employ homogeneous, isotropic material properties, often using data from a different species to the one under investigation. Due to the growing significance of investigating the cranial biomechanics of the rabbit in basic science and clinical research, this study used nanoindentation to measure the elastic modulus of cortical and trabecular bone throughout the skull. The elastic moduli of cortical bone measured in the mediolateral and ventrodorsal direction were found to decrease posteriorly through the skull, while it was evenly distributed when measured in the anteroposterior direction. Furthermore, statistical tests showed that the variation of elastic moduli between separate regions (anterior, middle and posterior) of the skull were significantly different in cortical bone, but was not in trabecular bone. Elastic moduli measured in different orthotropic planes were also significantly different, with the moduli measured in the mediolateral direction consistently lower than that measured in either the anteroposterior or ventrodorsal direction. These findings demonstrate the significance of regional and directional variation in cortical bone elastic modulus, and therefore material properties in finite element models of the skull, particularly those of the rabbit, should consider the heterogeneous and orthotropic properties of skull bone when possible.

Airflow rates and breathlessness recovery from submaximal exercise in healthy adults: prospective, randomised, cross-over study

OBJECTIVES

Facial airflow from a hand-held fan may reduce breathlessness severity and hasten postexertion recovery. Data from randomised controlled trials are limited and the optimal airflow speed remains unknown. We aimed to determine the effect of different airflow speeds on recovery from exercise-induced breathlessness.

METHODS

A prospective, randomised, cross-over design. Ten healthy participants (seven male; mean age 29±4 years; height 175±9 cm; body mass 76.9±14.1 kg) completed six bouts of 4 min of exercise. During the first 5 min of a 20 min recovery phase, participants received one of five airflow speeds by holding a fan ~15 cm from their face, or no fan control, administered in random order. Fan A had an internal blade, and fan B had an external blade. Breathlessness was measured using a numerical rating scale (NRS) at minute intervals for the first 10 min, and facial skin temperature was recorded using a thermal imaging camera (immediately postexertion and 5 min recovery).

RESULTS

Nine participants completed the trial. A significant main effect for airflow speed (p=0.016, ηp2=0.285) and interaction effect for airflow speed over time (p=0.008, ηp2=0.167) suggest that the airflow speed modifies breathlessness during recovery from exercise. Fan speeds of 1.7 m/s or greater increased the speed of recovery from breathlessness compared with control (p<0.05) with the highest airflow speeds (2.5 m/s and 3.3 m/s) giving greatest facial cooling.

CONCLUSION

Higher airflow rates (1.7 m/s or greater) reduced self-reported recovery times from exercise-induced breathlessness and reduced facial temperature .

Form-function relationships underlie rapid dietary changes in a lizard

Macroevolutionary changes such as variation in habitat use or diet are often associated with convergent, adaptive changes in morphology. However, it is still unclear how small-scale morphological variation at the population level can drive shifts in ecology such as observed at a macroevolutionary scale. Here, we address this question by investigating how variation in cranial form and feeding mechanics relate to rapid changes in diet in an insular lizard (Podarcis siculus) after experimental introduction into a new environment. We first quantified differences in the skull shape and jaw muscle architecture between the source and introduced population using three-dimensional geometric morphometrics and dissections. Next, we tested the impact of the observed variation in morphology on the mechanical performance of the masticatory system using computer-based biomechanical simulation techniques. Our results show that small differences in shape, combined with variation in muscle architecture, can result in significant differences in performance allowing access to novel trophic resources. The confrontation of these data with the already described macroevolutionary relationships between cranial form and function in these insular lizards provides insights into how selection can, over relatively short time scales, drive major changes in ecology through its impact on mechanical performance.

Functional reorganisation of the cranial skeleton during the cynodont-mammaliaform transition

Skeletal simplification occurred in multiple vertebrate clades over the last 500 million years, including the evolution from premammalian cynodonts to mammals. This transition is characterised by the loss and reduction of cranial bones, the emergence of a novel jaw joint, and the rearrangement of the jaw musculature. These modifications have long been hypothesised to increase skull strength and efficiency during feeding. Here, we combine digital reconstruction and biomechanical modelling to show that there is no evidence for an increase in cranial strength and biomechanical performance. Our analyses demonstrate the selective functional reorganisation of the cranial skeleton, leading to reduced stresses in the braincase and the skull roof but increased stresses in the zygomatic region through this transition. This cranial functional reorganisation, reduction in mechanical advantage, and overall miniaturisation in body size are linked with a dietary specialisation to insectivory, permitting the subsequent morphological and ecological diversification of the mammalian lineage.

Assessment of the mechanical role of cranial sutures in the mammalian skull: Computational biomechanical modelling of the rat skull

Cranial sutures are fibrocellular joints between the skull bones that are progressively replaced with bone throughout ontogeny, facilitating growth and cranial shape change. This transition from soft tissue to bone is reflected in the biomechanical properties of the craniofacial complex. However, the mechanical significance of cranial sutures has only been explored at a few localised areas within the mammalian skull, and as such our understanding of suture function in overall skull biomechanics is still limited. Here, we sought to determine how the overall strain environment is affected by the complex network of cranial sutures in the mammal skull. We combined two computational biomechanical methods, multibody dynamics analysis and finite element analysis, to simulate biting in a rat skull and compared models with and without cranial sutures. Our results show that including complex sutures in the rat model does not substantially change overall strain gradients across the cranium, particularly strain magnitudes in the bones overlying the brain. However, local variations in strain magnitudes and patterns can be observed in areas close to the sutures. These results show that, during feeding, sutures may be more important in some regions than others. Sutures should therefore be included in models that require accurate local strain magnitudes and patterns of cranial strain, particularly if models are developed for analysis of specific regions, such as the temporomandibular joint or zygomatic arch. Our results suggest that, for mammalian skulls, cranial sutures might be more important for allowing brain expansion during growth than redistributing biting loads across the cranium in adults.

Biomechanical evaluation of the unilateral crossbite on the asymmetrical development of the craniofacial complex. A mechano-morphological approach

BACKGROUND AND OBJECTIVE

The occlusion effect on the craniofacial development is a controversial topic that has attracted the interest of many researchers but that remains unclear, mainly due to the difficulties on measure its mechanical response experimentally. This mechano-morphological relationship of the craniofacial growth is often explained by the periosteal and capsular matrices of the functional matrix hypothesis (FMH); however, its outcomes have not been analytically demonstrated yet. This computational study aims, therefore, to analytically demonstrate the mechano-morphological relationship in the craniofacial development of children with unilateral crossbite (UXB) using the finite element (FE) method.

METHODS

The craniofacial complex asymmetry of ten children, five of whom exhibit UXB, was 3D-analysed and compared with the biomechanical response computed from a FE analysis of each patient's occlusion. Due to the complexity of the geometry and the multitude of contacts involved, the inherent limitations of the model were evaluated by comparing computed occlusal patterns with those recorded by an occlusal analysis on 3D printed copies.

RESULTS

Comparison's outcomes proved the reliability of our models with just a deviation error below 6% between both approaches. Out of validation process, computational results showed that the significant elongation of mandibular branch in the contralateral side could be related to the mandibular shift and increase of thickness on the crossed side, and particularly of the posterior region. These morphological changes could be associated with periodontal overpressure (>4.7 kPa) and mandibular over deformation (0.002 ε) in that side, in agreement with the periosteal matrix's principles. Furthermore, the maxilla's transversal narrowing and the elevation of the maxillary and zygomatic regions on the crossed side were statistically demonstrated and seem to be related with their respective micro displacements at occlusion, as accounted by their specific capsule matrices. Our results were consistent with those reported clinically and demonstrated analytically the mechano-morphological relationship of children's craniofacial development based on the FMH's functional matrices.

CONCLUSIONS

This study is a first step in the understanding of the occlusion's effect on the craniofacial development by computational methods. Our approach could help future engineers, researchers and clinicians to understand better the aetiology of some dental malocclusions and functional disorders improve the diagnosis or even predict the craniofacial development.

A hierarchical opportunistic screening model for osteoporosis using machine learning applied to clinical data and CT images

Background

Osteoporosis is a common metabolic skeletal disease and usually lacks obvious symptoms. Many individuals are not diagnosed until osteoporotic fractures occur. Bone mineral density (BMD) measured by dual-energy X-ray absorptiometry (DXA) is the gold standard for osteoporosis detection. However, only a limited percentage of people with osteoporosis risks undergo the DXA test. As a result, it is vital to develop methods to identify individuals at-risk based on methods other than DXA.

Results

We proposed a hierarchical model with three layers to detect osteoporosis using clinical data (including demographic characteristics and routine laboratory tests data) and CT images covering lumbar vertebral bodies rather than DXA data via machine learning. 2210 individuals over age 40 were collected retrospectively, among which 246 individuals’ clinical data and CT images are both available. Irrelevant and redundant features were removed via statistical analysis. Consequently, 28 features, including 16 clinical data and 12 texture features demonstrated statistically significant differences (p < 0.05) between osteoporosis and normal groups. Six machine learning algorithms including logistic regression (LR), support vector machine with radial-basis function kernel, artificial neural network, random forests, eXtreme Gradient Boosting and Stacking that combined the above five classifiers were employed as classifiers to assess the performances of the model. Furthermore, to diminish the influence of data partitioning, the dataset was randomly split into training and test set with stratified sampling repeated five times. The results demonstrated that the hierarchical model based on LR showed better performances with an area under the receiver operating characteristic curve of 0.818, 0.838, and 0.962 for three layers, respectively in distinguishing individuals with osteoporosis and normal BMD.

Conclusions

The proposed model showed great potential in opportunistic screening for osteoporosis without additional expense. It is hoped that this model could serve to detect osteoporosis as early as possible and thereby prevent serious complications of osteoporosis, such as osteoporosis fractures.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12859-022-04596-z.

Back to the bones: do muscle area assessment techniques predict functional evolution across a macroevolutionary radiation?

Measures of attachment or accommodation area on the skeleton are a popular means of rapidly generating estimates of muscle proportions and functional performance for use in large-scale macroevolutionary studies. Herein, we provide the first evaluation of the accuracy of these muscle area assessment (MAA) techniques for estimating muscle proportions, force outputs and bone loading in a comparative macroevolutionary context using the rodent masticatory system as a case study. We find that MAA approaches perform poorly, yielding large absolute errors in muscle properties, bite force and particularly bone stress. Perhaps more fundamentally, these methods regularly fail to correctly capture many qualitative differences between rodent morphotypes, particularly in stress patterns in finite-element models. Our findings cast doubts on the validity of these approaches as means to provide input data for biomechanical models applied to understand functional transitions in the fossil record, and perhaps even in taxon-rich statistical models that examine broad-scale macroevolutionary patterns. We suggest that future work should go back to the bones to test if correlations between attachment area and muscle size within homologous muscles across a large number of species yield strong predictive relationships that could be used to deliver more accurate predictions for macroevolutionary and functional studies.

Regional Patterning in Tail Vertebral Form and Function in Chameleons (Chamaeleo calyptratus)

Previous studies have focused on documenting shape variation in the caudal vertebrae in chameleons underlying prehensile tail function. The goal of this study was to test the impact of this variation on tail function using multibody dynamic analysis (MDA). First, observations from dissections and 3D reconstructions generated from contrast-enhanced µCT scans were used to document regional variation in arrangement of the caudal muscles along the antero-posterior axis. Using MDA, we then tested the effect of vertebral shape geometry on biomechanical function. To address this question, four different MDA models were built: those with a distal vertebral shape and with either a distal or proximal musculature, and reciprocally the proximal vertebral shape with either the proximal or distal musculature. For each muscle configuration, we calculated the force required in each muscle group for the muscle force to balance an arbitrary external force applied to the model. The results showed that the models with a distal-type of musculature are the most efficient, regardless of vertebral shape. Our models also showed that the m. ilio-caudalis pars dorsalis is least efficient when combining the proximal vertebral shape and distal musculature, highlighting the importance of the length of the transverse process in combination with the lever-moment arm onto which muscle force is exerted. This initial model inevitably has a number of simplifications and assumptions, however its purpose is not to predict in vivo forces, but instead reveals the importance of vertebral shape and muscular arrangement on the total force the tail can generate, thus providing a better understanding of the biomechanical significance of the regional variations on tail grasping performance in chameleons.

Comparative cranial biomechanics in two lizard species: impact of variation in cranial design

Cranial morphology in lepidosaurs is highly disparate and characterised by the frequent loss or reduction of bony elements. In varanids and geckos, the loss of the postorbital bar is associated with changes in skull shape, but the mechanical principles underlying this variation remain poorly understood. Here, we sought to determine how the overall cranial architecture and the presence of the postorbital bar relate to the loading and deformation of the cranial bones during biting in lepidosaurs. Using computer-based simulation techniques, we compared cranial biomechanics in the varanid Varanus niloticus and the teiid Salvator merianae, two large, active foragers. The overall strain magnitude and distribution across the cranium were similar in the two species, despite lower strain gradients in V. niloticus. In S. merianae, the postorbital bar is important for resistance of the cranium to feeding loads. The postorbital ligament, which in varanids partially replaces the postorbital bar, does not affect bone strain. Our results suggest that the reduction of the postorbital bar impaired neither biting performance nor the structural resistance of the cranium to feeding loads in V. niloticus. Differences in bone strain between the two species might reflect demands imposed by feeding and non-feeding functions on cranial shape. Beyond variation in cranial bone strain related to species-specific morphological differences, our results reveal that similar mechanical behaviour is shared by lizards with distinct cranial shapes. Contrary to the situation in mammals, the morphology of the circumorbital region, calvaria and palate appears to be important for withstanding high feeding loads in these lizards.

Summary:In vivo measurements and computer-based simulations of the cranial mechanics of two large lizards indicate that similar mechanical behaviour is shared by lizards with distinct cranial architecture, and show the importance of the postorbital bar in resisting the feeding loads.

Mathematical modeling of canonical and non-canonical NF-κB pathways in TNF stimulation

BACKGROUND AND OBJECTIVE

NF-κB can be activated by the canonical and non-canonical pathways. These two pathways interplay via the TRAF1|NIK complex after stimulation by TNF. However existing mathematical models of two pathways are inadequate. In this context, an improved mathematical model is constructed to simulate these two pathways and their coupling stimulated by TNF.

METHODS

A schematic description of two NF-κB pathways and their relation after TNF stimulation is constructed at first. Then twenty-eight ordinary differential equations are utilized to build the mathematical model. Model equations are solved via the ordinary differential equation solver (ode23).

RESULTS

The proposed model firstly reconstructs the changes in concentrations of NF-κB pathway related biochemical factors with time, and further investigates the underlying mechanism of interaction between two pathways through the TRAF1|NIK complex after stimulation.

CONCLUSIONS

The model is validated through good agreement between simulation results and published experimental observations. This study helps to well understand the canonical and non-canonical pathways and their interaction. It also provides a potential tool to investigate how the dysregulated pathways act in pathological conditions.

Towards an early 3D-diagnosis of craniofacial asymmetry by computing the accurate midplane: A PCA-based method

BACKGROUND AND OBJECTIVE

Craniofacial asymmetry is a common growth disorder often caused by unilateral chewing. Although an early orthodontic treatment would avoid surgical procedures later in life, the uncertainty of defining the accurate sagittal midplane potentially leads to misdiagnosis and therefore inaccurate orthodontic treatment plans. This novel study aims to 3D-diagnose craniofacial complex malformations in children with unilateral crossbite (UXB) considering a midplane which compensates the asymmetric morphology.

METHODS

The sagittal midplane of 20 children, fifteen of whom exhibited UXB, was computed by a PCA-based method which compensates the asymmetry mirroring the 3D models obtained from cone-beam computed tomography data. Once determined, one side of the data was mirrored using the computed midplane to visualize the malformations on the hard and soft tissues by 3D-computing the distances between both halves. Additionally, 31 skull's landmarks were manually placed in each model to study the principal variation modes and the significant differences in the group of subjects with and without UXB through PCA and Mann-Whitney U test analyses respectively.

RESULTS

Morphological 3D-analysis showed pronounced deformities and aesthetic implications for patients with severe asymmetry (jaw deviation > 0.8 mm) in whole craniofacial system, while initial signs of asymmetry were found indistinctly in the mandible or maxilla. We detected significant (p < 0.05) malformations for example in mandibular ramus length (0.0086), maxillary palate width (0.0481) and condylar head width (0.0408). Craniofacial malformations increased the landmarks' variability in the group of patients with UXB over the control group requiring 8 variation modes more to define 99% of the sample' variability.

CONCLUSIONS

Our findings demonstrated the viability of early diagnosis of craniofacial asymmetry through computing the accurate sagittal midplane which compensates the individual's asymmetrical morphology. Furthermore, this study provides important computational insights into the determination of craniofacial deformities which are caused by UXB, following some empirical findings of previous clinical studies. Hence, this computational approach can be useful for the development of new software in craniofacial surgery or for its use in biomedical research and clinical practice.

The influence of musculoskeletal forces on the growth of the prenatal cortex in the ilium: a finite element study

Remodelling and adaptation of bone within the pelvis is believed to be influenced by the mechanical strains generated during locomotion. Variation in the cortical bone thickness observed in the prenatal ilium has been linked to the musculoskeletal loading associated with in utero movements; for example the development of a thicker gluteal cortex is a possible response to contractions of the gluteal muscles. This study examines if the strains generated in the prenatal iliac cortex due to musculoskeletal loading in utero are capable of initiating bone remodelling to either maintain homeostasis or form new bone. Computational modelling techniques were used firstly to predict the muscle forces and resultant joint reaction force acting on the pelvis during a range of in utero movements. Finite element analyses were subsequently performed to calculate the von Mises strains induced in the prenatal ilium. The results demonstrated that strains generated in the iliac cortex were above the thresholds suggested to regulate bone remodelling to either maintain homeostasis or form new bone. Further simulations are required to investigate the extent to which the heterogeneous cortex forms in response to these strains (i.e., remodelling) or if developmental bone modelling plays a more pivotal role.

A 3D cephalometric protocol for the accurate quantification of the craniofacial symmetry and facial growth

Background

Cephalometric analysis is used to evaluate facial growth, to study the anatomical relationships within the face. Cephalometric assessment is based on 2D radiographic images, either the sagittal or coronal planes and is an inherently inaccurate methodology. The wide availability of 3D imaging techniques, such as computed tomography and magnetic resonance imaging make routine 3D analysis of facial morphology feasible. 3D cephalometry may not only provide a more accurate quantification of the craniofacial morphology and longitudinal growth, but also the differentiation of subtle changes in occlusion. However, a reliable protocol for the computation of craniofacial symmetry and quantification of craniofacial morphology is still a topic of extensive research. Here, a protocol for 3D cephalometric analysis for both the identification of the natural head position (NHP) and the accurate quantification of facial growth and facial asymmetry is proposed and evaluated. A phantom study was conducted to assess the performance of the protocol and to quantify the ability to repeatedly and reliably align skulls with the NHP and quantify the degree of accuracy with which facial growth and facial asymmetry can be measured.

Results

The results obtained show that the protocol allows consistent alignment with the NHP, with an overall average error (and standard deviation) of just 0.17 (9.10e-6) mm, with variations of 0.21 (2.77e-17) mm in the frontonasal suture and 0.30 (5.55e-17) mm in the most prominent point in the chin. The average errors associated with simulated facial growth ranged from 1.83 to 3.75% for 2 years' growth and from - 9.57 to 14.69% for 4 years, while the error in the quantification of facial asymmetry ranged from - 11.38 to 9.31%.

Conclusions

The protocol for 3D skull alignment produces accurate and landmark free estimation of the true symmetry of the head. It allows a reliable alignment of the skull in the NHP independently of user-defined landmarks, as well as an accurate quantification of facial growth and asymmetry.

Neurocranial development of the coelacanth and the evolution of the sarcopterygian head

The neurocranium of sarcopterygian fishes was originally divided into an anterior (ethmosphenoid) and posterior (otoccipital) portion by an intracranial joint, and underwent major changes in its overall geometry before fusing into a single unit in lungfishes and early tetrapods¹. Although the pattern of these changes is well-documented, the developmental mechanisms that underpin variation in the form of the neurocranium and its associated soft tissues during the evolution of sarcopterygian fishes remain poorly understood. The coelacanth Latimeria is the only known living vertebrate that retains an intracranial joint^2,3. Despite its importance for understanding neurocranial evolution, the development of the neurocranium of this ovoviviparous fish remains unknown. Here we investigate the ontogeny of the neurocranium and brain in Latimeria chalumnae using conventional and synchrotron X-ray micro-computed tomography as well as magnetic resonance imaging, performed on an extensive growth series for this species. We describe the neurocranium at the earliest developmental stage known for Latimeria, as well as the major changes that the neurocranium undergoes during ontogeny. Changes in the neurocranium are associated with an extreme reduction in the relative size of the brain along with an enlargement of the notochord. The development of the notochord appears to have a major effect on the surrounding cranial components, and might underpin the formation of the intracranial joint. Our results shed light on the interplay between the neurocranium and its adjacent soft tissues during development in Latimeria, and provide insights into the developmental mechanisms that are likely to have underpinned the evolution of neurocranial diversity in sarcopterygian fishes.

Characterizing and Modeling Bone Formation during Mouse Calvarial Development

The newborn mammalian cranial vault consists of five flat bones that are joined together along their edges by soft fibrous tissues called sutures. Early fusion of these sutures leads to a medical condition known as craniosynostosis. The mechanobiology of normal and craniosynostotic skull growth is not well understood. In a series of previous studies, we characterized and modeled radial expansion of normal and craniosynostotic (Crouzon) mice. Here, we describe a new modeling algorithm to simulate bone formation at the sutures in normal and craniosynostotic mice. Our results demonstrate that our modeling approach is capable of predicting the observed ex vivo pattern of bone formation at the sutures in the aforementioned mice. The same approach can be used to model different calvarial reconstruction in children with craniosynostosis to assist in the management of this complex condition.

An assessment of the role of the falx cerebri and tentorium cerebelli in the cranium of the cat (Felis silvestris catus)

The falx cerebri and the tentorium cerebelli are two projections of the dura mater in the cranial cavity which ossify to varying degrees in some mammalian species. The idea that the ossification of these structures may be necessary to support the loads arising during feeding has been proposed and dismissed in the past, but never tested quantitatively. To address this, a biomechanical model of a domestic cat (Felis silvestris catus) skull was created and the material properties of the falx and tentorium were varied for a series of loading regimes incorporating the main masticatory and neck muscles during biting. Under these loading conditions, ossification of the falx cerebri does not have a significant impact on the stress in the cranial bones. In the case of the tentorium, however, a localized increase in stress was observed in the parietal and temporal bones, including the tympanic bulla, when a non-ossified tentorium was modelled. These effects were consistent across the different analyses, irrespective of loading regime. The results suggest that ossification of the tentorium cerebelli may play a minor role during feeding activities by decreasing the stress in the back of the skull.

The role of miniaturization in the evolution of the mammalian jaw and middle ear

The evolution of the mammalian jaw is one of the most important innovations in vertebrate history, and underpins the exceptional radiation and diversification of mammals over the last 220 million years^1,2. In particular, the transformation of the mandible into a single tooth-bearing bone and the emergence of a novel jaw joint-while incorporating some of the ancestral jaw bones into the mammalian middle ear-is often cited as a classic example of the repurposing of morphological structures^3,4. Although it is remarkably well-documented in the fossil record, the evolution of the mammalian jaw still poses the paradox of how the bones of the ancestral jaw joint could function both as a joint hinge for powerful load-bearing mastication and as a mandibular middle ear that was delicate enough for hearing. Here we use digital reconstructions, computational modelling and biomechanical analyses to demonstrate that the miniaturization of the early mammalian jaw was the primary driver for the transformation of the jaw joint. We show that there is no evidence for a concurrent reduction in jaw-joint stress and increase in bite force in key non-mammaliaform taxa in the cynodont-mammaliaform transition, as previously thought^5-8. Although a shift in the recruitment of the jaw musculature occurred during the evolution of modern mammals, the optimization of mandibular function to increase bite force while reducing joint loads did not occur until after the emergence of the neomorphic mammalian jaw joint. This suggests that miniaturization provided a selective regime for the evolution of the mammalian jaw joint, followed by the integration of the postdentary bones into the mammalian middle ear.

Mechanical adaptation of trabecular bone morphology in the mammalian mandible

Alveolar bone, together with the underlying trabecular bone, fulfils an important role in providing structural support against masticatory forces. Diseases such as osteoporosis or periodontitis cause alveolar bone resorption which weakens this structural support and is a major cause of tooth loss. However, the functional relationship between alveolar bone remodelling within the molar region and masticatory forces is not well understood. This study investigated this relationship by comparing mammalian species with different diets and functional loading (Felis catus, Cercocebus atys, Homo sapiens, Sus scrofa, Oryctolagus cuniculus, Ovis aries). We performed histomorphometric analyses of trabecular bone morphology (bone volume fraction, trabecular thickness and trabecular spacing) and quantified the variation of bone and tooth root volumes along the tooth row. A principal component analysis and non-parametric MANOVA showed statistically significant differences in trabecular bone morphology between species with contrasting functional loading, but these differences were not seen in sub-adult specimens. Our results support a strong, but complex link between masticatory function and trabecular bone morphology. Further understanding of a potential functional relationship could aid the diagnosis and treatment of mandibular diseases causing alveolar bone resorption, and guide the design and evaluation of dental implants.

A biomechanical analysis of prognathous and orthognathous insect head capsules: evidence for a many-to-one mapping of form to function

Insect head shapes are remarkably variable, but the influences of these changes on biomechanical performance are unclear. Among 'basal' winged insects, such as dragonflies, mayflies, earwigs and stoneflies, some of the most prominent anatomical changes are the general mouthpart orientation, eye size and the connection of the endoskeleton to the head. Here, we assess these variations as well as differing ridge and sclerite configurations using modern engineering methods including multibody dynamics modelling and finite element analysis in order to quantify and compare the influence of anatomical changes on strain in particular head regions and the whole head. We show that a range of peculiar structures such as the genal/subgenal, epistomal and circumocular areas are consistently highly loaded in all species, despite drastically differing morphologies in species with forward-projecting (prognathous) and downward-projecting (orthognathous) mouthparts. Sensitivity analyses show that the presence of eyes has a negligible influence on head capsule strain if a circumocular ridge is present. In contrast, the connection of the dorsal endoskeletal arms to the head capsule especially affects overall head loading in species with downward-projecting mouthparts. Analysis of the relative strains between species for each head region reveals that concerted changes in head substructures such as the subgenal area, the endoskeleton and the epistomal area lead to a consistent relative loading for the whole head capsule and vulnerable structures such as the eyes. It appears that biting-chewing loads are managed by a system of strengthening ridges on the head capsule irrespective of the general mouthpart and head orientation. Concerted changes in ridge and endoskeleton configuration might allow for more radical anatomical changes such as the general mouthpart orientation, which could be an explanation for the variability of this trait among insects. In an evolutionary context, many-to-one mapping of strain patterns onto a relatively similar overall head loading indeed could have fostered the dynamic diversification processes seen in insects.

Modelling human skull growth: a validated computational model

During the first year of life, the brain grows rapidly and the neurocranium increases to about 65% of its adult size. Our understanding of the relationship between the biomechanical forces, especially from the growing brain, the craniofacial soft tissue structures and the individual bone plates of the skull vault is still limited. This basic knowledge could help in the future planning of craniofacial surgical operations. The aim of this study was to develop a validated computational model of skull growth, based on the finite-element (FE) method, to help understand the biomechanics of skull growth. To do this, a two-step validation study was carried out. First, an in vitro physical three-dimensional printed model and an in silico FE model were created from the same micro-CT scan of an infant skull and loaded with forces from the growing brain from zero to two months of age. The results from the in vitro model validated the FE model before it was further developed to expand from 0 to 12 months of age. This second FE model was compared directly with in vivo clinical CT scans of infants without craniofacial conditions (n = 56). The various models were compared in terms of predicted skull width, length and circumference, while the overall shape was quantified using three-dimensional distance plots. Statistical analysis yielded no significant differences between the male skull models. All size measurements from the FE model versus the in vitro physical model were within 5%, with one exception showing a 7.6% difference. The FE model and in vivo data also correlated well, with the largest percentage difference in size being 8.3%. Overall, the FE model results matched well with both the in vitro and in vivo data. With further development and model refinement, this modelling method could be used to assist in preoperative planning of craniofacial surgery procedures and could help to reduce reoperation rates.

Predicting calvarial growth in normal and craniosynostotic mice using a computational approach

During postnatal calvarial growth the brain grows gradually and the overlying bones and sutures accommodate that growth until the later juvenile stages. The whole process is coordinated through a complex series of biological, chemical and perhaps mechanical signals between various elements of the craniofacial system. The aim of this study was to investigate to what extent a computational model can accurately predict the calvarial growth in wild-type (WT) and mutant type (MT) Fgfr2C342Y/+ mice displaying bicoronal suture fusion. A series of morphological studies were carried out to quantify the calvarial growth at P3, P10 and P20 in both mouse types. MicroCT images of a P3 specimen were used to develop a finite element model of skull growth to predict the calvarial shape of WT and MT mice at P10. Sensitivity tests were performed and the results compared with ex vivo P10 data. Although the models were sensitive to the choice of input parameters, they predicted the overall skull growth in the WT and MT mice. The models also captured the difference between the ex vivoWT and MT mice. This modelling approach has the potential to be translated to human skull growth and to enhance our understanding of the different reconstruction methods used to manage clinically the different forms of craniosynostosis, and in the long term possibly reduce the number of re-operations in children displaying this condition and thereby enhance their quality of life.

New insights into the biomechanics of Legg-Calvé-Perthes' disease: The Role of Epiphyseal Skeletal Immaturity in Vascular Obstruction

Objectives

Legg–Calvé–Perthes’ disease (LCP) is an idiopathic osteonecrosis of the femoral head that is most common in children between four and eight years old. The factors that lead to the onset of LCP are still unclear; however, it is believed that interruption of the blood supply to the developing epiphysis is an important factor in the development of the condition.

Methods

Finite element analysis modelling of the blood supply to the juvenile epiphysis was investigated to understand under which circumstances the blood vessels supplying the femoral epiphysis could become obstructed. The identification of these conditions is likely to be important in understanding the biomechanics of LCP.

Results

The results support the hypothesis that vascular obstruction to the epiphysis may arise when there is delayed ossification and when articular cartilage has reduced stiffness under compression.

Conclusion

The findings support the theory of vascular occlusion as being important in the pathophysiology of Perthes disease.

Cite this article: M. Pinheiro, C. A. Dobson, D. Perry, M. J. Fagan. New insights into the biomechanics of Legg-Calvé-Perthes’ disease: The Role of Epiphyseal Skeletal Immaturity in Vascular Obstruction. Bone Joint Res 2018;7:148–156. DOI: 10.1302/2046-3758.72.BJR-2017-0191.R1.

Bite force and cranial bone strain in four species of lizards

In vivo bone strain data provide direct evidence of strain patterns in the cranium during biting. Compared to mammals, in vivo bone strains in lizard skulls are poorly documented. This paper presents strain data from the skulls of Anolis equestris, Gekko gecko, Iguana iguana and Salvator merianae during transducer biting. Analysis of variance was used to investigate effects of bite force, bite point, diet, cranial morphology and cranial kinesis on strain magnitudes. Within individuals the most consistent determinants of variance in bone strain magnitudes are gage location and bite point, with the importance of bite force varying between individuals. Inter-site variance in strain magnitudes—strain gradient—is present in all individuals, and varies with bite point. Between individuals within species, variance in strain magnitude is driven primarily by variation in bite force, not gage location or bite point, suggesting that inter-individual variation in patterns of strain magnitude is minimal. Between species, variation in strain magnitudes is significantly impacted by bite force and species membership, as well as by interactions between gage location, species, and bite point. Independent of bite force, species differences in cranial strain magnitudes may reflect selection for different cranial morphology in relation to feeding function, but what these performance criteria are is not clear. The relatively low strain magnitudes in Iguana and Uromastyx compared to other lizards may be related to their herbivorous diet. Cranial kinesis and the presence or absence of postorbital and supratemporal bars are not important determinants of inter-specific variation in strain magnitudes.

The biomechanical role of the chondrocranium and sutures in a lizard cranium

The role of soft tissues in skull biomechanics remains poorly understood. Not least, the chondrocranium, the portion of the braincase which persists as cartilage with varying degrees of mineralization. It also remains commonplace to overlook the biomechanical role of sutures despite evidence that they alter strain distribution. Here, we examine the role of both the sutures and the chondrocranium in the South American tegu lizard Salvator merianae We use multi-body dynamics analysis (MDA) to provide realistic loading conditions for anterior and posterior unilateral biting and a detailed finite element model to examine strain magnitude and distribution. We find that strains within the chondrocranium are greatest during anterior biting and are primarily tensile; also that strain within the cranium is not greatly reduced by the presence of the chondrocranium unless it is given the same material properties as bone. This result contradicts previous suggestions that the anterior portion (the nasal septum) acts as a supporting structure. Inclusion of sutures to the cranium model not only increases overall strain magnitudes but also leads to a more complex distribution of tension and compression rather than that of a beam under sagittal bending.

Inclusion of periodontal ligament fibres in mandibular finite element models leads to an increase in alveolar bone strains

Alveolar bone remodelling is vital for the success of dental implants and orthodontic treatments. However, the underlying biomechanical mechanisms, in particular the function of the periodontal ligament (PDL) in bone loading and remodelling, are not well understood. The PDL is a soft fibrous connective tissue that joins the tooth root to the alveolar bone and plays a critical role in the transmission of loads from the tooth to the surrounding bone. However, due to its complex structure, small size and location within the tooth socket it is difficult to study in vivo. Finite element analysis (FEA) is an ideal tool with which to investigate the role of the PDL, however inclusion of the PDL in FE models is complex and time consuming, therefore consideration must be given to how it is included. The aim of this study was to investigate the effects of including the PDL and its fibrous structure in mandibular finite element models. A high-resolution model of a human molar region was created from micro-computed tomography scans. This is the first time that the fibrous structure of the PDL has been included in a model with realistic tooth and bone geometry. The results show that omission of the PDL creates a more rigid model, reducing the strains observed in the mandibular corpus which are of interest when considering mandibular functional morphology. How the PDL is modelled also affects the strains. The inclusion of PDL fibres alters the strains in the mandibular bone, increasing the strains in the tooth socket compared to PDL modelled without fibres. As strains in the alveolar bone are thought to play a key role in bone remodelling during orthodontic tooth movement, future FE analyses aimed at improving our understanding and management of orthodontic treatment should include the fibrous structure of the PDL.

Form-function relationships in dragonfly mandibles under an evolutionary perspective

Functional requirements may constrain phenotypic diversification or foster it. For insect mouthparts, the quantification of the relationship between shape and function in an evolutionary framework remained largely unexplored. Here, the question of a functional influence on phenotypic diversification for dragonfly mandibles is assessed with a large-scale biomechanical analysis covering nearly all anisopteran families, using finite element analysis in combination with geometric morphometrics. A constraining effect of phylogeny could be found for shape, the mandibular mechanical advantage (MA), and certain mechanical joint parameters, while stresses and strains, the majority of joint parameters and size are influenced by shared ancestry. Furthermore, joint mechanics are correlated with neither strain nor mandibular MA and size effects have virtually play no role for shape or mechanical variation. The presence of mandibular strengthening ridges shows no phylogenetic signal except for one ridge peculiar to Libelluloidea, and ridge presence is also not correlated with each other. The results suggest that functional traits are more variable at this taxonomic level and that they are not influenced by shared ancestry. At the same time, the results contradict the widespread idea that mandibular morphology mainly reflects functional demands at least at this taxonomic level. The varying functional factors rather lead to the same mandibular performance as expressed by the MA, which suggests a many-to-one mapping of the investigated parameters onto the same narrow mandibular performance space.

Computational biomechanics changes our view on insect head evolution

Despite large-scale molecular attempts, the relationships of the basal winged insect lineages dragonflies, mayflies and neopterans, are still unresolved. Other data sources, such as morphology, suffer from unclear functional dependencies of the structures considered, which might mislead phylogenetic inference. Here, we assess this problem by combining for the first time biomechanics with phylogenetics using two advanced engineering techniques, multibody dynamics analysis and finite-element analysis, to objectively identify functional linkages in insect head structures which have been used traditionally to argue basal winged insect relationships. With a biomechanical model of unprecedented detail, we are able to investigate the mechanics of morphological characters under biologically realistic load, i.e. biting. We show that a range of head characters, mainly ridges, endoskeletal elements and joints, are indeed mechanically linked to each other. An analysis of character state correlation in a morphological data matrix focused on head characters shows highly significant correlation of these mechanically linked structures. Phylogenetic tree reconstruction under different data exclusion schemes based on the correlation analysis unambiguously supports a sistergroup relationship of dragonflies and mayflies. The combination of biomechanics and phylogenetics as it is proposed here could be a promising approach to assess functional dependencies in many organisms to increase our understanding of phenotypic evolution.

Morphological evolution of the mammalian jaw adductor complex

The evolution of the mammalian jaw during the transition from non‐mammalian synapsids to crown mammals is a key event in vertebrate history and characterised by the gradual reduction of its individual bones into a single element and the concomitant transformation of the jaw joint and its incorporation into the middle ear complex. This osteological transformation is accompanied by a rearrangement and modification of the jaw adductor musculature, which is thought to have allowed the evolution of a more‐efficient masticatory system in comparison to the plesiomorphic synapsid condition. While osteological characters relating to this transition are well documented in the fossil record, the exact arrangement and modifications of the individual adductor muscles during the cynodont–mammaliaform transition have been debated for nearly a century.

We review the existing knowledge about the musculoskeletal evolution of the mammalian jaw adductor complex and evaluate previous hypotheses in the light of recently documented fossils that represent new specimens of existing species, which are of central importance to the mammalian origins debate. By employing computed tomography (CT) and digital reconstruction techniques to create three‐dimensional models of the jaw adductor musculature in a number of representative non‐mammalian cynodonts and mammaliaforms, we provide an updated perspective on mammalian jaw muscle evolution.

As an emerging consensus, current evidence suggests that the mammal‐like division of the jaw adductor musculature (into deep and superficial components of the m. masseter, the m. temporalis and the m. pterygoideus) was completed in Eucynodontia. The arrangement of the jaw adductor musculature in a mammalian fashion, with the m. pterygoideus group inserting on the dentary was completed in basal Mammaliaformes as suggested by the muscle reconstruction of Morganucodon oehleri. Consequently, transformation of the jaw adductor musculature from the ancestral (‘reptilian’) to the mammalian condition must have preceded the emergence of Mammalia and the full formation of the mammalian jaw joint. This suggests that the modification of the jaw adductor system played a pivotal role in the functional morphology and biomechanical stability of the jaw joint.

Application of Far Cortical Locking Technology in Periprosthetic Femoral Fracture Fixation: A Biomechanical Study

BACKGROUND

Lack of fracture movement could be a potential cause of periprosthetic femoral fracture (PFF) fixation failures. This study aimed to test whether the use of distal far cortical locking screws reduces the overall stiffness of PFF fixations and allows an increase in fracture movement compared to standard locking screws while retaining the overall strength of the PFF fixations.

METHODS

Twelve laboratory models of Vancouver type B1 PFFs were developed. In all specimens, the proximal screw fixations were similar, whereas in 6 specimens, distal locking screws were used, and in the other six specimens, far cortical locking screws. The overall stiffness, fracture movement, and pattern of strain distribution on the plate were measured in stable and unstable fractures under anatomic 1-legged stance. Specimens with unstable fracture were loaded to failure.

RESULTS

No statistical difference was found between the stiffness and fracture movement of the two groups in stable fractures. In the unstable fractures, the overall stiffness and fracture movement of the locking group was significantly higher and lower than the far cortical group, respectively. Maximum principal strain on the plate was consistently lower in the far cortical group, and there was no significant difference between the failure loads of the 2 groups.

CONCLUSION

The results indicate that far cortical locking screws can reduce the overall effective stiffness of the locking plates and increase the fracture movement while maintaining the overall strength of the PFF fixation construct. However, in unstable fractures, alternative fixation methods, for example, long stem revision might be a better option.

Skeletal immaturity, rostral sparing, and disparate hip morphologies as biomechanical causes for Legg-Calvé-Perthes' disease

Legg-Calvé-Perthes' (Perthes') disease is a developmental disease of the hip joint that may result in numerous short and long term problems. The etiology of the disease remains largely unknown, but the mechanism is believed to be vascular and/or biomechanical in nature. There are several anatomical characteristics that tend to be prevalent in children with Perthes' disease, namely: skeletal immaturity, reduced height, and rostral sparing. We present an overview of the literature, summarizing the current understanding of the pathogenesis, particularly related to how the formation of the vasculature to the femoral epiphysis places children aged 5-8 at a higher risk for Perthes' disease, how skeletal immaturity and rostral sparing could increase the probability of developing Perthes' disease, and how animal models have aided our understanding of the disease. In doing so, we also explore why Perthes' disease is correlated to latitude, with populations at higher latitudes having higher incidence rates than populations closer to the Equator. Finally, we present five hypotheses detailing how Perthes' disease could have a biomechanical cause. Clin. Anat. 29:759-772, 2016. © 2016 Wiley Periodicals, Inc.

A virtual approach to evaluate therapies for management of multiple myeloma induced bone disease

Multiple myeloma bone disease is devastating for patients and a major cause of morbidity. The disease leads to bone destruction by inhibiting osteoblast activity while stimulating osteoclast activity. Recent advances in multiple myeloma research have improved our understanding of the pathogenesis of multiple myeloma-induced bone disease and suggest several potential therapeutic strategies. However, the effectiveness of some potential therapeutic strategies still requires further investigation and optimization. In this paper, a recently developed mathematical model is extended to mimic and then evaluate three therapies of the disease, namely: bisphosphonates, bortezomib and TGF-β inhibition. The model suggests that bisphosphonates and bortezomib treatments not only inhibit bone destruction, but also reduce the viability of myeloma cells. This contributes to the current debate as to whether bisphosphonate therapy has an anti-tumour effect. On the other hand, the analyses indicate that treatments designed to inhibit TGF-β do not reduce bone destruction, although it appears that they might reduce the viability of myeloma cells, which again contributes to the current controversy regarding the efficacy of TGF-β inhibition in multiple myeloma-induced bone disease.

Masticatory biomechanics in the rabbit: a multi-body dynamics analysis

Multi-body dynamics is a powerful engineering tool which is becoming increasingly popular for the simulation and analysis of skull biomechanics. This paper presents the first application of multi-body dynamics to analyse the biomechanics of the rabbit skull. A model has been constructed through the combination of manual dissection and three-dimensional imaging techniques (magnetic resonance imaging and micro-computed tomography). Individual muscles are represented with multiple layers, thus more accurately modelling muscle fibres with complex lines of action. Model validity was sought through comparing experimentally measured maximum incisor bite forces with those predicted by the model. Simulations of molar biting highlighted the ability of the masticatory system to alter recruitment of two muscle groups, in order to generate shearing or crushing movements. Molar shearing is capable of processing a food bolus in all three orthogonal directions, whereas molar crushing and incisor biting are predominately directed vertically. Simulations also show that the masticatory system is adapted to process foods through several cycles with low muscle activations, presumably in order to prevent rapidly fatiguing fast fibres during repeated chewing cycles. Our study demonstrates the usefulness of a validated multi-body dynamics model for investigating feeding biomechanics in the rabbit, and shows the potential for complementing and eventually reducing in vivo experiments.

Validity and sensitivity of a human cranial finite element model: implications for comparative studies of biting performance

Finite element analysis (FEA) is a modelling technique increasingly used in anatomical studies investigating skeletal form and function. In the case of the cranium this approach has been applied to both living and fossil taxa to (for example) investigate how form relates to function or infer diet or behaviour. However, FE models of complex musculoskeletal structures always rely on simplified representations because it is impossible completely to image and represent every detail of skeletal morphology, variations in material properties and the complexities of loading at all spatial and temporal scales. The effects of necessary simplifications merit investigation. To this end, this study focuses on one aspect, model geometry, which is particularly pertinent to fossil material where taphonomic processes often destroy the finer details of anatomy or in models built from clinical CTs where the resolution is limited and anatomical details are lost. We manipulated the details of a finite element (FE) model of an adult human male cranium and examined the impact on model performance. First, using digital speckle interferometry, we directly measured strains from the infraorbital region and frontal process of the maxilla of the physical cranium under simplified loading conditions, simulating incisor biting. These measured strains were then compared with predicted values from FE models with simplified geometries that included modifications to model resolution, and how cancellous bone and the thin bones of the circum-nasal and maxillary regions were represented. Distributions of regions of relatively high and low principal strains and principal strain vector magnitudes and directions, predicted by the most detailed FE model, are generally similar to those achieved in vitro. Representing cancellous bone as solid cortical bone lowers strain magnitudes substantially but the mode of deformation of the FE model is relatively constant. In contrast, omitting thin plates of bone in the circum-nasal region affects both mode and magnitude of deformation. Our findings provide a useful frame of reference with regard to the effects of simplifications on the performance of FE models of the cranium and call for caution in the interpretation and comparison of FEA results.

Mechanical properties of calvarial bones in a mouse model for craniosynostosis

The mammalian cranial vault largely consists of five flat bones that are joined together along their edges by soft fibrous tissues called sutures. Premature closure of the cranial sutures, craniosynostosis, can lead to serious clinical pathology unless there is surgical intervention. Research into the genetic basis of the disease has led to the development of various animal models that display this condition, e.g. mutant type Fgfr2^C342Y/+ mice which display early fusion of the coronal suture (joining the parietal and frontal bones). However, whether the biomechanical properties of the mutant and wild type bones are affected has not been investigated before. Therefore, nanoindentation was used to compare the elastic modulus of cranial bone and sutures in wild type (WT) and Fgfr2^C342Y/+mutant type (MT) mice during their postnatal development. Further, the variations in properties with indentation position and plane were assessed. No difference was observed in the elastic modulus of parietal bone between the WT and MT mice at postnatal (P) day 10 and 20. However, the modulus of frontal bone in the MT group was lower than the WT group at both P10 (1.39±0.30 vs. 5.32±0.68 GPa; p<0.05) and P20 (5.57±0.33 vs. 7.14±0.79 GPa; p<0.05). A wide range of values was measured along the coronal sutures for both the WT and MT samples, with no significant difference between the two groups. Findings of this study suggest that the inherent mechanical properties of the frontal bone in the mutant mice were different to the wild type mice from the same genetic background. These differences may reflect variations in the degree of biomechanical adaptation during skull growth, which could have implications for the surgical management of craniosynostosis patients.

Sensitivity to model geometry in finite element analyses of reconstructed skeletal structures: experience with a juvenile pelvis

Biomechanical analysis of juvenile pelvic growth can be used in the evaluation of medical devices and investigation of hip joint disorders. This requires access to scan data of healthy juveniles, which are not always freely available. This article analyses the application of a geometric morphometric technique, which facilitates the reconstruction of the articulated juvenile pelvis from cadaveric remains, in biomechanical modelling. The sensitivity of variation in reconstructed morphologies upon predicted stress/strain distributions is of particular interest. A series of finite element analyses of a 9-year-old hemi-pelvis were performed to examine differences in predicted strain distributions between a reconstructed model and the originally fully articulated specimen. Only minor differences in the minimum principal strain distributions were observed between two varying hemi-pelvic morphologies and that of the original articulation. A Wilcoxon rank-sum test determined there was no statistical significance between the nodal strains recorded at 60 locations throughout the hemi-pelvic structures. This example suggests that finite element models created by this geometric morphometric reconstruction technique can be used with confidence, and as observed with this hemi-pelvis model, even a visual morphological difference does not significantly affect the predicted results. The validated use of this geometric morphometric reconstruction technique in biomechanical modelling reduces the dependency on clinical scan data.

Mathematical modelling of the pathogenesis of multiple myeloma-induced bone disease

Multiple myeloma (MM) is the second most common haematological malignancy and results in destructive bone lesions. The interaction between MM cells and the bone microenvironment plays an important role in the development of the tumour cells and MM-induced bone disease and forms a 'vicious cycle' of tumour development and bone destruction, intensified by suppression of osteoblast activity and promotion of osteoclast activity. In this paper, a mathematical model is proposed to simulate how the interaction between MM cells and the bone microenvironment facilitates the development of the tumour cells and the resultant bone destruction. It includes both the roles of inhibited osteoblast activity and stimulated osteoclast activity. The model is able to mimic the temporal variation of bone cell concentrations and resultant bone volume after the invasion and then removal of the tumour cells and explains why MM-induced bone lesions rarely heal even after the complete removal of MM cells. The behaviour of the model compares well with published experimental data. The model serves as a first step to understand the development of MM-induced bone disease and could be applied further to evaluate the current therapies against MM-induced bone disease and even suggests new potential therapeutic targets.

A predator-prey based mathematical model of the bone remodelling cycle: exploring the relationship between the model parameters and biochemical factors

Bone remodelling is a vital process which enables bone to repair, renew and optimize itself. Disorders in the bone remodelling process are inevitably manifested in bone-related diseases, such as hypothyroidism, primary hyperparathyroidism and osteoporosis. In our previous work, a predator-prey based mathematical model was developed to simulate bone remodelling cycles under normal and two pathological conditions, hypothyroidism and primary hyperparathyroidism, for trabecular bone at a fixed point. However, the biochemical meanings of the model parameters were not fully explored. This article first extends the previous work by proposing relationships between the model parameters and biochemical factors involved in the bone remodelling process and by examining whether those relationships do predict the behaviours observed in vivo. The model is then applied to the simulation and investigation of bone remodelling of postmenopausal osteoporosis. The proposed connections are supported by good agreement between the model simulations and published experimental observations for the normal condition and all three pathological variations in bone remodelling.

Investigating the efficacy of bisphosphonates treatment against multiple myeloma induced bone disease using a computational model

Multiple myeloma (MM)-induced bone disease is mortal for most MM patients. Bisphosphonates are first-line treatment for MM-induced bone disease, since it can inhibit osteoclast activity and the resultant bone resorption by suppressing the differentiation of osteoclast precursors into mature osteoclasts, promoting osteoclast apoptosis and disrupting osteoclast function. However, it is still unclear whether bisphosphonates have an anti-tumour effect. In our previous work, a computational model was built to simulate the pathology of MM-induced bone disease. This paper extends this proposed computational model to investigate the efficacy of bisphosphonates treatment and then clear the controversy of this therapy. The extended model is validated through the good agreement between simulation results and experimental data. The simulation results suggest that bisphosphonates indeed have an anti-tumour effect.

The effects of cervical muscle fatigue on balance - a study with elite amateur rugby league players

Neck muscle fatigue has been shown to alter an individual's balance in a similar way to that reported in subjects suffering from neck pain or subjects that have suffered a neck injury. The main purpose of the present study was to quantify the effects of neck fatigue on neck muscle electromyography (EMG) activity, balance, perceived fatigue and perceived stability. Forty four elite amateur rugby league players resisted with their neck muscles approximately 35% maximum voluntary isometric contraction (MVIC) force for 15 minutes in eight different directions. Sway velocity and surface electromyography were measured. Questionnaires were used to record perceived effort and stability. Repeated measures ANOVA showed that after 15 minutes isometric contraction, significant changes were seen in sway velocity, perceived sway and EMG median frequency. There were no differences in perceived efforts. The changes in sway velocity and median frequency were more pronounced after extension and right and left posterior oblique contractions but there was no significant difference in sway velocity after contraction in the right lateral flexion, right anterior oblique and left anterior oblique direction of contraction. All the subjects showed oriented whole-body leaning in the plane of the contraction. The experiment produced significantly altered and perceived altered balance in this group of physically fit individuals. The results may contribute to our understanding of normal functional capacities of athletes and will provide a basis for further investigation in healthy non-athletes and participants that have suffered neck injuries. This may ultimately help develop accurate and valid rehabilitation outcome measures. Key pointsUsing a percentage of MVIC permits to proportionally fatigue various neck muscle groups evenlyFatigue of different neck muscle groups will alter balance differentlyFatigue of muscles producing extension and posterior oblique will alter balance the most although subjects perceive a greater altered balance after lateral flexion.

Effects of cervical muscle fatigue on the perception of the subjective vertical and horizontal

Introduction

Cervical functional capacity outcome measures that are simple and reliable are urgently needed in order permit accurate assessment/reassessment during treatments and rehabilitation. Induced neck muscle fatigue has been shown to alter functional capacities such as balance and kinaesthetic sense in the standing posture. The Rod and Frame Test has also shown promise as a method of assessing the effects of chronic neck pain and injury, but currently only in the sitting position. The objectives of this project were therefore 1) to validate the computerised rod and frame test in the standing posture, and 2) to measure the effects that different cervical muscle fatigue protocol would have on the assessment of the subjective visual vertical and horizontal.

Method

The validation of the standing computerised rod and frame test in the standing posture was obtained by comparing results (n = 74) between the sitting and standing positions with the Spearman’s correlation coefficient. In addition, agreement between the two methods was analysed with the Bland-Altman method.

Participants (n = 56) resisted with their neck muscles approximately 35% maximum isometric voluntary contraction force for 15 minutes on a purpose built apparatus in eight different directions. Wilcoxon signed rank tests analysed changes in horizontal and vertical rod and frame test between the neutral and all different directions of contraction. The changes of recorded unsigned vertical and horizontal errors for the combined frame condition in all situations of isometric contraction were analysed with two respective one-way repeated measures analysis of variance (ANOVA).

Discussion

The Spearman’s rho and Bland-Altman plots show that the Rod and Frame Test works equally well in sitting and standing positions.

After muscle contraction, there were significant increases in error in all participants for both horizontal and vertical rod and frame tests, except after flexion. These errors were predominantly present after fatigue of muscles in the coronal plane of contraction. Proprioception alone cannot explain the difference in the rod and frame results between different muscle groups. It is suggested that an evolutionary advantage of developing improved subjective verticality awareness in the same direction as the main visual field could explain these findings.

In vivo cranial bone strain and bite force in the agamid lizard Uromastyx geyri

In vivo bone strain data are the most direct evidence of deformation and strain regimes in the vertebrate cranium during feeding and can provide important insights into skull morphology. Strain data have been collected during feeding across a wide range of mammals; in contrast, in vivo cranial bone strain data have been collected from few sauropsid taxa. Here we present bone strain data recorded from the jugal of the herbivorous agamid lizard Uromastyx geyri along with simultaneously recorded bite force. Principal and shear strain magnitudes in Uromastyx geyri were lower than cranial bone strains recorded in Alligator mississippiensis, but higher than those reported from herbivorous mammals. Our results suggest that variations in principal strain orientations in the facial skeleton are largely due to differences in feeding behavior and bite location, whereas food type has little impact on strain orientations. Furthermore, mean principal strain orientations differ between male and female Uromastyx during feeding, potentially because of sexual dimorphism in skull morphology.

Development and three-dimensional morphology of the zygomaticotemporal suture in primate skulls

Cranial sutures are an essential part of the growing skull, allowing bones to increase in size during growth, with their morphology widely believed to be dictated by the forces and displacements that they experience. The zygomaticotemporal suture in primates is located in the relatively weak zygomatic arch, and externally it appears a very simple connection. However, large forces are almost certainly transmitted across this suture, suggesting that it requires some level of stability while also allowing controlled movements under high loading. Here we examine the 2- and 3-dimensional (3D) morphology of the zygomaticotemporal suture in an ontogenetic series of Macaca fascicularis skulls. High resolution microcomputed tomography data sets were examined, and virtual and physical 3D replicas were created to assess both structure and general stability. The zygomaticotemporal suture is much more complex than its external appearance suggests, with interlocking facets between the adjacent zygomatic and temporal bones. It appears as if some movement is permitted across the suture in younger animals, but as they approach adulthood the complexity of the suture's interlocking bone facets reaches a level where these movements become minimal.

Cranial sutures work collectively to distribute strain throughout the reptile skull

The skull is composed of many bones that come together at sutures. These sutures are important sites of growth, and as growth ceases some become fused while others remain patent. Their mechanical behaviour and how they interact with changing form and loadings to ensure balanced craniofacial development is still poorly understood. Early suture fusion often leads to disfiguring syndromes, thus is it imperative that we understand the function of sutures more clearly. By applying advanced engineering modelling techniques, we reveal for the first time that patent sutures generate a more widely distributed, high level of strain throughout the reptile skull. Without patent sutures, large regions of the skull are only subjected to infrequent low-level strains that could weaken the bone and result in abnormal development. Sutures are therefore not only sites of bone growth, but could also be essential for the modulation of strains necessary for normal growth and development in reptiles.

The importance of accurate muscle modelling for biomechanical analyses: a case study with a lizard skull

Computer-based simulation techniques such as multi-body dynamics analysis are becoming increasingly popular in the field of skull mechanics. Multi-body models can be used for studying the relationships between skull architecture, muscle morphology and feeding performance. However, to be confident in the modelling results, models need to be validated against experimental data, and the effects of uncertainties or inaccuracies in the chosen model attributes need to be assessed with sensitivity analyses. Here, we compare the bite forces predicted by a multi-body model of a lizard (Tupinambis merianae) with in vivo measurements, using anatomical data collected from the same specimen. This subject-specific model predicts bite forces that are very close to the in vivo measurements and also shows a consistent increase in bite force as the bite position is moved posteriorly on the jaw. However, the model is very sensitive to changes in muscle attributes such as fibre length, intrinsic muscle strength and force orientation, with bite force predictions varying considerably when these three variables are altered. We conclude that accurate muscle measurements are crucial to building realistic multi-body models and that subject-specific data should be used whenever possible.

The head and neck anatomy of sea turtles (Cryptodira: Chelonioidea) and skull shape in Testudines

BACKGROUND

Sea turtles (Chelonoidea) are a charismatic group of marine reptiles that occupy a range of important ecological roles. However, the diversity and evolution of their feeding anatomy remain incompletely known.

METHODOLOGY/PRINCIPAL FINDINGS

Using computed tomography and classical comparative anatomy we describe the cranial anatomy in two sea turtles, the loggerhead (Caretta caretta) and Kemp's ridley (Lepidochelys kempii), for a better understanding of sea turtle functional anatomy and morphological variation. In both taxa the temporal region of the skull is enclosed by bone and the jaw joint structure and muscle arrangement indicate that palinal jaw movement is possible. The tongue is relatively small, and the hyoid apparatus is not as conspicuous as in some freshwater aquatic turtles. We find several similarities between the muscles of C. caretta and L. kempii, but comparison with other turtles suggests only one of these characters may be derived: connection of the m. adductor mandibulae internus into the Pars intramandibularis via the Zwischensehne. The large fleshy origin of the m. adductor mandibulae externus Pars superficialis from the jugal seems to be a characteristic feature of sea turtles.

CONCLUSIONS/SIGNIFICANCE

In C. caretta and L. kempii the ability to suction feed does not seem to be as well developed as that found in some freshwater aquatic turtles. Instead both have skulls suited to forceful biting. This is consistent with the observation that both taxa tend to feed on relatively slow moving but sometimes armoured prey. The broad fleshy origin of the m. adductor mandibulae externus Pars superficialis may be linked to thecheek region being almost fully enclosed in bone but the relationship is complex.