From cadaver to computer: Incorporating computers into the topographical anatomy laboratory

Traditionally, students have studied human anatomy through dissection and prosection. This requires considerable input from demonstrators, with students working mainly in large groups. Increasing student numbers, decreasing funds for staff, and a need to encourage students to develop independent learning skills that will be of value throughout their professional lives, have meant that the nature of their learning in the Topographical Anatomy Laboratory has had to change. The situation in which groups of students are guided by demonstrators has moved towards a more self‐directed learning environment. Several innovations have been introduced at University College London, including a multimedia laboratory which is the focus of this paper. The results of the evaluation and the lessons learned from the early stages of setting up a self‐directed learning environment are presented

Virtual reconstruction of cranial remains : the H. Heidelbergensis, Kabwe 1 fossil

Human skeletal remains and fossils are often fragmented and distorted, limiting further research. Thus, reconstruction has long been used to restore the original morphology of specimens and enable subsequent research. With advances in computing and imaging, virtual reconstruction approaches are increasingly being applied to this task. Thus, models of fragmentary remains are increasingly being reconstructed from medical images, using visualization software and geometric morphometric techniques to repair defects and restore symmetry. In this chapter we review some virtual reconstruction techniques and provide a description of CT based virtual reconstruction applied to a fossil hominin, the Kabwe 1 cranium. This specimen is dated from 150 - 250 thousand years ago and was reconstructed to enable further biomechanical research, however the approaches and tools used to make the reconstruction are directly applicable to more recent skeletal remains

Seeing distinct groups where there are none : spurious patterns from between-group PCA

Using sampling experiments, we found that, when there are fewer groups than variables, between-groups PCA (bgPCA) may suggest surprisingly distinct differences among groups for data in which none exist. While apparently not noticed before, the reasons for this problem are easy to understand. A bgPCA captures the g-1 dimensions of variation among the g group means, but only a fraction of the∑ni-g  dimensions of within-group variation ( are the sample sizes), when the number of variables, p, is greater than g-1. This introduces a distortion in the appearance of the bgPCA plots because the within-group variation will be underrepresented, unless the variables are sufficiently correlated so that the total variation can be accounted for with just g-1 dimensions. The effect is most obvious when sample sizes are small relative to the number of variables, because smaller samples spread out less, but the distortion is present even for large samples. Strong covariance among variables largely reduces the magnitude of the problem, because it effectively reduces the dimensionality of the data and thus enables a larger proportion of the within-group variation to be accounted for within the g-1-dimensional space of a bgPCA. The distortion will still be relevant though its strength will vary from case to case depending on the structure of the data (p, g, covariances etc.). These are important problems for a method mainly designed for the analysis of variation among groups when there are very large numbers of variables and relatively small samples. In such cases, users are likely to conclude that the groups they are comparing are much more distinct than they really are.  Having many variables but just small sample sizes is a common problem in fields ranging from morphometrics (as in our examples) to molecular analyses

Middle Cranial Fossa Anatomy and the Origin of Modern Humans

Anatomically, modern humans differ from archaic forms in possessing a globular neurocranium and a retracted face and in cognitive functions, many of which are associated with the temporal lobes. The middle cranial fossa (MCF) interacts during growth and development with the temporal lobes, the midface, and the mandible. It has been proposed that evolutionary transformations of the MCF (perhaps from modification of the temporal lobes) can have substantial influences on craniofacial morphology. Here, we use three-dimensional (3D) geometric morphometrics and computer reconstructions of computed tomography-scanned fossil hominids, fossil and recent modern humans and chimpanzees to address this issue further. Mean comparisons and permutation analyses of scaled 3D basicranial landmarks confirm that the MCF of Homo sapiens is highly significantly different (P < 0.001) from H. neanderthalensis, H. heidelbergensis, and Pan troglodytes. Modern humans have a unique configuration with relatively more anterolateral projection of the MCF pole relative to the optic chiasm and the foramen rotundum. These findings are discussed in the context of evolutionary changes in craniofacial morphology and the origins of modern human autapomorphies. In particular, the findings of this study point to variations in the temporal lobe, which, through effects on the MCF and face, are central to the evolution of modern human facial form.Anthropolog

morphomap : An R package for long bone landmarking, cortical thickness, and cross-sectional geometry mapping

OBJECTIVES: This study describes and demonstrates the functionalities and application of a new R package, morphomap, designed to extract shape information as semilandmarks in multiple sections, build cortical thickness maps, and calculate biomechanical parameters on long bones. METHODS: morphomap creates, from a single input (an oriented 3D mesh representing the long bone surface), multiple evenly spaced virtual sections. morphomap then directly and rapidly computes morphometric and biomechanical parameters on each of these sections. The R package comprises three modules: (a) to place semilandmarks on the inner and outer outlines of each section, (b) to extract cortical thicknesses for 2D and 3D morphometric mapping, and (c) to compute cross-sectional geometry. RESULTS: In this article, we apply morphomap to femora from Homo sapiens and Pan troglodytes to demonstrate its utility and show its typical outputs. morphomap greatly facilitates rapid analysis and functional interpretation of long bone form and should prove a valuable addition to the osteoarcheological analysis software toolkit. CONCLUSIONS: Long bone loading history is commonly retrodicted by calculating biomechanical parameters such as area moments of inertia, analyzing external shape and measuring cortical thickness. morphomap is a software written in the open source R environment, it integrates the main methodological approaches (geometric morphometrics, cortical morphometric maps, and cross-sectional geometry) used to parametrize long bones

The biomechanical significance of the frontal sinus in Kabwe 1 (Homo heidelbergensis)

Paranasal sinuses are highly variable among living and fossil hominins and their function(s) are poorly understood. It has been argued they serve no particular function and are biological 'spandrels’ arising as a structural consequence of changes in associated bones and/or soft tissue structures. In contrast, others have suggested that sinuses have one or more functions, in olfaction, respiration, thermoregulation, nitric oxide production, voice resonance, reduction of skull weight, and craniofacial biomechanics. Here we assess the extent to which the very large frontal sinus of Kabwe 1 impacts on the mechanical performance of the craniofacial skeleton during biting. It may be that the browridge is large and the sinus has large trabecular struts traversing it to compensate for the effect of a large sinus on the ability of the face to resist forces arising from biting. Alternatively, the large sinus may have no impact and be sited where strains that arise from biting would be very low. If the former is true, then infilling of the sinus would be expected to increase the ability of the skeleton to resist biting loads, while removing the struts might have the opposite effect. To these ends, finite element models with hollowed and infilled variants of the original sinus were created and loaded to simulate different bites. The deformations arising due to loading were then compared among different models and bites by contrasting the strain vectors arising during identical biting tasks. It was found that the frontal bone experiences very low strains and that infilling or hollowing of the sinus has little effect on strains over the cranial surface, with small effects over the frontal bone. The material used to infill the sinus experienced very low strains. This is consistent with the idea that frontal sinus morphogenesis is influenced by the strain field experienced by this region such that it comes to lie entirely within a region of the cranium that would otherwise experience low strains. This has implications for understanding why sinuses vary among hominin fossils

Finite element analysis of the cranium : Validity, sensitivity and future directions

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

Middle Pliocene hominin diversity : Australopithecus deyiremeda and Kenyanthropus platyops

Geometric morphometric shape analyses are used to compare the maxillae of the Kenyanthropus platyops holotype KNM-WT 40000, the Australopithecus deyiremeda holotype BRT-VP-3/1 and other australopiths. The main aim is to explore the relationship between these two specimens and contemporary Australopithecus afarensis. Five landmarks placed on lateral views of the maxillae quantify key aspects of the morphology. Generalized Procrustes analyses and principal component analyses of the resulting shape coordinates were performed. The magnitudes of differences in shape and their significances were assessed using Procrustes and Mahalanobis’ distances, respectively. Both KNM-WT 40000 and BRT-VP-3/1 show statistically significant differences in maxillary shape from A. afarensis, but do so in dissimilar ways. Moreover, the former differs more from A. afarensis than the latter. KNM-WT 40000 has a more anteriorly positioned zygomatic process with a transversely flat, and more orthognathic subnasal clivus. BRT-VP-3/1 has a more inferiorly positioned zygomatic process, a slightly retracted dental arcade, but without shortening of the anterior maxilla. These findings are consistent with previous conclusions that the two fossils should be attributed to separate species, rather than to A. afarensis, and with the presence of three contemporary hominin species in the Middle Pliocene of eastern Africa

The Mechanical Significance of the Temporal Fasciae in Macaca fascicularis: An Investigation Using Finite Element Analysis

Computational finite element analyses (FEAs) of the skull predict structural deformations under user specified loads and constraints, with results normally presented as stress and strain distributions over the skull's surface. The applied loads are generally a representation of the major adductor musculature, with the skull constrained at bite positions and at the articulating joints. However, virtually all analyses ignore potentially important anatomical structures, such as the fasciae that cover the temporalis muscle and attach onto the zygomatic arch. In vivo experimental studies have shown that removal of the temporal fasciae attachment onto the zygomatic arch in Cebus monkeys results in significant bone adaptation and remodeling in this region, suggesting the fasciae play an important role in stabilising the arch during biting. Here we investigate this potential stabilising role by carrying out FEAs of a macaque skull with and without temporal fasciae included. We explore the extent to which the zygomatic arch might be stabilized during biting by a synchronized tensioning of the temporal fasciae, acting to oppose masseteric contraction forces. According to our models, during temporalis muscle bulging the forces generated within the tensioned temporal fasciae are large enough to oppose the pull of the masseter. Further, a near bending-free state of equilibrium within the arch can be reached, even under forceful biting. We show that it is possible to eliminate the high strain gradients in and around the zygomatic arch that are present in past computational studies, with strains being more uniform in magnitude than previously thought. © 2011 Wiley-Liss, Inc