Normal human craniofacial growth and development from 0 to 4 years

Knowledge of human craniofacial growth (increase in size) and development (change in shape) is important in the clinical treatment of a range of conditions that afects it. This study uses an extensive collection of clinical CT scans to investigate craniofacial growth and development over the frst 48 months of life, detail how the cranium changes in form (size and shape) in each sex and how these changes are associated with the growth and development of various soft tissues such as the brain, eyes and tongue and the expansion of the nasal cavity. This is achieved through multivariate analyses of cranial form based on 3D landmarks and semi-landmarks and by analyses of linear dimensions, and cranial volumes. The results highlight accelerations and decelerations in cranial form changes throughout early childhood. They show that from 0 to 12 months, the cranium undergoes greater changes in form than from 12 to 48 months. However, in terms of the development of overall cranial shape, there is no signifcant sexual dimorphism in the age range considered in this study. In consequence a single model of human craniofacial growth and development is presented for future studies to examine the physio-mechanical interactions of the craniofacial growth

Morphometric maps of bilateral asymmetry in the human humerus : An implementation in the R package morphomap

In biological anthropology, parameters relating to cross-sectional geometry are calculated in paired long bones to evaluate the degree of lateralization of anatomy and, by inference, function. Here, we describe a novel approach, newly added to the morphomap R package, to assess the lateralization of the distribution of cortical bone along the entire diaphysis. The sample comprises paired long bones belonging to 51 individuals (10 females and 41 males) from The New Mexico Decedent Image Database with known biological profile, occupational and loading histories. Both males and females show a pattern of right lateralization. In addition, males are more lateralized than females, whereas there is not a significant association between lateralization with occupation and loading history. Body weight, height and long-bone length are the major factors driving the emergence of asymmetry in the humerus, while interestingly, the degree of lateralization decreases in the oldest individuals

A Comparison of Semilandmarking Approaches in the Analysis of Size and Shape

Often, few landmarks can be reliably identified in analyses of form variation and covariation. Thus, ‘semilandmarking’ algorithms have increasingly been applied to surfaces and curves. However, the locations of semilandmarks depend on the investigator’s choice of algorithm and their density. In consequence, to the extent that different semilandmarking approaches and densities result in different locations of semilandmarks, they can be expected to yield different results concerning patterns of variation and co-variation. The extent of such differences due to methodology is, as yet, unclear and often ignored. In this study, the performance of three landmark-driven semilandmarking approaches is assessed, using two different surface mesh datasets (ape crania and human heads) with different degrees of variation and complexity, by comparing the results of morphometric analyses. These approaches produce different semilandmark locations, which, in turn, lead to differences in statistical results, although the non-rigid semilandmarking approaches are consistent. Morphometric analyses using semilandmarks must be interpreted with due caution, recognising that error is inevitable and that results are approximations. Further work is needed to investigate the effects of using different landmark and semilandmark templates and to understand the limitations and advantages of different semilandmarking approaches

morphomap: an R package for analysis of diaphyseal cortical thickness, shape and cross-sectional geometry

The cross-sectional geometry of long bones is commonly used to infer their biomechanical properties in investigations of past and present primate locomotion as well as to assess intensity and repetitiveness of physical activities, and to estimate body mass. While cross-sectional geometry has proved to be very useful for reconstructing bone loading patterns, a limitation of the technique has been that only a few cross sections along the diaphysis can be analyzed. The advent of virtual imaging and image processing offers the prospect of semi automating the sectioning and calculation of geometric properties at high resolution. We present the morphomap package, developed in the R environment, to extract cross sections from long bone meshes at specified intervals along the diaphysis and to calculate two and three dimensional morphometric maps, cross-sectional geometric parameters, and semilandmarks on the periosteal and endosteal contours of each cross section. We demonstrate the validity of this computational tool by showing that it obtains the same results as those from manual and other computational approaches. We then demonstrate the functionality of morphomap in a comparison of human and chimpanzee femora. The tool produces 61 cross sections along each diaphysis, at increments of 1% between 20% and 80% of their biomechanical length, automatically draws morphometric maps and calculates the parameters described above. The results illustrate the potential of morphomap in identifying differences in diaphyses that can be related to differences in locomotion and lifestyle in living and fossil primates

Analyse par éléments finis du crâne : validité, sensibilité et directions futures

La méthode des éléments finis (FEA) est de plus en plus appliquée en recherche biomécanique du squelette en général, et dans les études de fossiles en particulier. Ces études sont fondées sur le principe selon lequel les FEA fournissent des résultats qui se rapprochent de la réalité. Cet article fournit une meilleure compréhension de la fiabilité de la méthode des FEA, en présentant une étude de validité dans laquelle les déformations subies par un vrai crâne de cadavre humain sont comparées à celles d’un modèle par éléments finis de ce crâne sous une charge simulée équivalente. En outre, la sensibilité du modèle vis-à-vis de simplifications dans la segmentation et des propriétés des matériaux est également évaluée. Nos résultats montrent que les déformations absolues ne sont pas prédites avec précision, mais que la répartition des régions de relativement hautes et basses contraintes, et par conséquent les modes de déformation globale, sont raisonnablement estimés.Finite element analysis (FEA) is increasingly applied in skeletal biomechanical research in general, and in fossil studies in particular. Underlying such studies is the principle that FEA provides results that approximate reality. This paper provides further understanding of the reliability of FEA by presenting a validation study in which the deformations experienced by a real cadaveric human cranium are compared to those of an FE model of that cranium under equivalent simulated loading. Furthermore, model sensitivity to simplifications in segmentation and material properties is also assessed. Our results show that absolute deformations are not accurately predicted, but the distribution of the regions of relatively high and low strains, and so the modes of global deformation, are reasonably approximated.</p

Measuring the asymmetry in long bone morphometric maps of cortical thickness: occupation-related differences in the modern human humerus

Reconstructing the loading history in human species is crucial to understand lifestyle strategies and mobility pattern in past populations. A fundamental approach to the reconstruction of physical behaviour relies on the comparison of the differences in cortical thickness distributions among antimeres. The comparison of antimeric bones from the same individual offers the prospect of identifying asymmetry of loading and so, of activity, because genetic, systemic and environmental factors affecting bone form are the same for both sides [1]. In the present study we have tested the new morphomapAsymmetry function, an implementation of morphomap R package [2], to calculate and map asymmetry of the cortical thickness. We selected 41 male individuals and 10 female individuals from The New Mexico Decedent Image Database (NMDID) [3]. We chose only individuals ranging in age from 20 to 50 who have worked in the army, in building companies or at a desk. We tested the hypothesis that diaphyseal cortical thickness asymmetry is unrelated to occupation and sex. On each humerus we extracted 61 cross-sections along the diaphysis from 20% to 80% of the total biomechanical length. On each cross-section we calculated 48 equiangular semilandmarks: 24 on the periosteal and 24 on the endosteal contour, centred at the centre of gravity of the cross-section. The right humeri have been mirrored by using the function morphomapMirror. We measured the thickness between paired semilandmarks (periosteal and endosteal), and we built morphometric maps of cortical thickness for each individual. Eventually, we computed the difference between right and left sides and mapped the differences in morphometric maps. In this way, the diaphysis is unrolled and the differences in thickness along the direction (anterior-lateral-medial-posterior) and the longitudinal axis are reported respectively on the x and y axis. We analysed asymmetry by performing a principal component analysis on the matrices of cortical thickness of the left and right humerus. Each individual is represented by left and right morphometric maps of cortical thickness after subtracting the mean morphometric maps between sides. We calculated the pattern and magnitude of asymmetry pooled by occupation and sex. Additionally, we decomposed the total asymmetry into the “directional” and “fluctuant” components of asymmetry [4,5]. The first two PC scores account for the 33.91% of the total variance (PC1=41.05%; PC2=7.47%). PC1 is related to directional asymmetry showing a shared pattern of right-hand lateralization (except one individual left-hand lateralized). The pattern and magnitude of asymmetry among the three occupation groups are not statistically different from each other. However, the magnitude of total asymmetry is higher in army and building than desk group. The decomposition of the asymmetry into directional and fluctuant components reveals as 9.60% of the total variance is associated with directional asymmetry and 90.4% with fluctuant asymmetry. Lastly, the comparison between female and male individuals show as the pattern of asymmetry is indistinguishable. On the contrary, the magnitude of asymmetry is higher in the male subsample. The analysis of asymmetry of the cortical thickness presented here confirmed a general trend of right lateralization among the individuals belonging to the different groups of occupation. Males show a higher degree of asymmetry than females. In conclusion, these results do not falsify the hypothesis that pattern and magnitude of asymmetry differ among the occupation groups considered in this study. In perspective, recent developments in statistical analysis methods applied to the study of skeletal material show the potentiality of this approach to study the pattern of lateralization in relation to physical activity in past populations including extinct human species

Measuring the asymmetry in long bone morphometric maps of cortical thickness: occupationrelated differences in the modern human humerus

Reconstructing the loading history in human species is crucial to understand lifestyle strategies and mobility pattern in past populations. A fundamental approach to the reconstruction of physical behaviour relies on the comparison of the differences in cortical thickness distributions among antimeres. The comparison of antimeric bones from the same individual offers the prospect of identifying asymmetry of loading and so, of activity, because genetic, systemic and environmental factors affecting bone form are the same for both sides [1]. In the present study we have tested the new morphomapAsymmetry function, an implementation of morphomap R package [2], to calculate and map asymmetry of the cortical thickness. We selected 41 male individuals and 10 female individuals from The New Mexico Decedent Image Database (NMDID) [3]. We chose only individuals ranging in age from 20 to 50 who have worked in the army, in building companies or at a desk. We tested the hypothesis that diaphyseal cortical thickness asymmetry is unrelated to occupation and sex. On each humerus we extracted 61 cross-sections along the diaphysis from 20% to 80% of the total biomechanical length. On each cross-section we calculated 48 equiangular semilandmarks: 24 on the periosteal and 24 on the endosteal contour, centred at the centre of gravity of the cross-section. The right humeri have been mirrored by using the function morphomapMirror. We measured the thickness between paired semilandmarks (periosteal and endosteal), and we built morphometric maps of cortical thickness for each individual. Eventually, we computed the difference between right and left sides and mapped the differences in morphometric maps. In this way, the diaphysis is unrolled and the differences in thickness along the direction (anterior-lateral-medial-posterior) and the longitudinal axis are reported respectively on the x and y axis. We analysed asymmetry by performing a principal component analysis on the matrices of cortical thickness of the left and right humerus. Each individual is represented by left and right morphometric maps of cortical thickness after subtracting the mean morphometric maps between sides. We calculated the pattern and magnitude of asymmetry pooled by occupation and sex. Additionally, we decomposed the total asymmetry into the “directional” and “fluctuant” components of asymmetry [4,5]. The first two PC scores account for the 33.91% of the total variance (PC1=41.05%; PC2=7.47%). PC1 is related to directional asymmetry showing a shared pattern of right-hand lateralization (except one individual left-hand lateralized). The pattern and magnitude of asymmetry among the three occupation groups are not statistically different from each other. However, the magnitude of total asymmetry is higher in army and building than desk group. The decomposition of the asymmetry into directional and fluctuant components reveals as 9.60% of the total variance is associated with directional asymmetry and 90.4% with fluctuant asymmetry. Lastly, the comparison between female and male individuals show as the pattern of asymmetry is indistinguishable. On the contrary, the magnitude of asymmetry is higher in the male subsample. The analysis of asymmetry of the cortical thickness presented here confirmed a general trend of right lateralization among the individuals belonging to the different groups of occupation. Males show a higher degree of asymmetry than females. In conclusion, these results do not falsify the hypothesis that pattern and magnitude of asymmetry differ among the occupation groups considered in this study. In perspective, recent developments in statistical analysis methods applied to the study of skeletal material show the potentiality of this approach to study the pattern of lateralization in relation to physical activity in past populations including extinct human species

The application of muscle wrapping to voxel-based finite element models of skeletal structures

Finite elements analysis (FEA) is now used routinely to interpret skeletal form in terms of function in both medical and biological applications. To produce accurate predictions from FEA models, it is essential that the loading due to muscle action is applied in a physiologically reasonable manner. However, it is common for muscle forces to be represented as simple force vectors applied at a few nodes on the model's surface. It is certainly rare for any wrapping of the muscles to be considered, and yet wrapping not only alters the directions of muscle forces but also applies an additional compressive load from the muscle belly directly to the underlying bone surface. This paper presents a method of applying muscle wrapping to high-resolution voxel-based finite element (FE) models. Such voxel-based models have a number of advantages over standard (geometry-based) FE models, but the increased resolution with which the load can be distributed over a model's surface is particularly advantageous, reflecting more closely how muscle fibre attachments are distributed. In this paper, the development, application and validation of a muscle wrapping method is illustrated using a simple cylinder. The algorithm: (1) calculates the shortest path over the surface of a bone given the points of origin and ultimate attachment of the muscle fibres; (2) fits a Non-Uniform Rational B-Spline (NURBS) curve from the shortest path and calculates its tangent, normal vectors and curvatures so that normal and tangential components of the muscle force can be calculated and applied along the fibre; and (3) automatically distributes the loads between adjacent fibres to cover the bone surface with a fully distributed muscle force, as is observed in vivo. Finally, we present a practical application of this approach to the wrapping of the temporalis muscle around the cranium of a macaque skull

Estimation of sex from sternal measurements in a Western Australian population

In Australia, particularly Western Australia, there is a relative paucity of contemporary population-specific morphometric standards for the estimation of sex from unknown skeletal remains. This is largely a historical artefact from lacking, or poorly documented, repositories of human skeletons available for study. However, medical scans, e.g. MSCT (multislice spiral computed tomography) are an ingenious and practical alternative source for contemporary data. To that end, this study is a comprehensive analysis of sternal sexual dimorphism in a sample of modern Western Australian (WA) individuals with a main purpose to develop a series of statistically robust standards for the estimation of sex. The sample comprises thoracic MSCT scans, with a mean of 0.9 millimeter (mm) slice thickness, on 187 non-pathological sterna. Following 3D volume rendering, 10 anatomical landmarks were acquired using OsiriX® (version 3.9) and a total of 8 inter landmark linear measurements were calculated using Morph Db (an in-house developed database application). Measurements were analyzed using basic descriptive statistics and discriminant function analyses, with statistical analyses performed using SPSS 19.0. All measurements are sexually dimorphic and sex differences explain 9.8–47.4% of sample variance. The combined length of the manubrium and body, sternal body length, manubrium width, and corpus sterni width at first sternebra contribute significantly to sex discrimination and yield the smallest sex-biases. Cross-validated classification accuracies, i.e., univariate, stepwise and direct function, are 72.2–84.5%, with a sex bias of less than 5%. We conclude that the sternum is a reliable element for sex estimation among Western Australians

Combining geometric morphometrics and functional simulation: an emerging toolkit for virtual functional analyses

The development of virtual methods for anatomical reconstruction and functional simulation of skeletal structures offers great promise in evolutionary and ontogenetic investigations of form-function relationships. Key developments reviewed here include geometric morphometric methods for the analysis and visualization of variations in form (size and shape), finite element methods for the prediction of mechanical performance of skeletal structures under load and multibody dynamics methods for the simulation and prediction of musculoskeletal function. These techniques are all used in studies of form and function in biology, but only recently have they been combined in novel ways to facilitate biomechanical modelling that takes account of variations in form, can statistically compare performance, and relate performance to form and its covariates. Here we provide several examples that illustrate how these approaches can be combined and we highlight areas that require further investigation and development before we can claim a mature theory and toolkit for a statistical biomechanical framework that unites these methods