Lacunar-canalicular network in femoral cortical bone is reduced in aged women and is predominantly due to a loss of canalicular porosity.

The lacunar-canalicular network (LCN) of bone contains osteocytes and their dendritic extensions, which allow for intercellular communication, and are believed to serve as the mechanosensors that coordinate the processes of bone modeling and remodeling. Imbalances in remodeling, for example, are linked to bone disease, including fragility associated with aging. We have reported that there is a reduction in scale for one component of the LCN, osteocyte lacunar volume, across the human lifespan in females. In the present study, we explore the hypothesis that canalicular porosity also declines with age. To visualize the LCN and to determine how its components are altered with aging, we examined samples from young (age: 20-23 y; n = 5) and aged (age: 70-86 y; n = 6) healthy women donors utilizing a fluorescent labelling technique in combination with confocal laser scanning microscopy. A large cross-sectional area of cortical bone spanning the endosteal to periosteal surfaces from the anterior proximal femoral shaft was examined in order to account for potential trans-cortical variation in the LCN. Overall, we found that LCN areal fraction was reduced by 40.6% in the samples from aged women. This reduction was due, in part, to a reduction in lacunar density (21.4% decline in lacunae number per given area of bone), but much more so due to a 44.6% decline in canalicular areal fraction. While the areal fraction of larger vascular canals was higher in endosteal vs. periosteal regions for both age groups, no regional differences were observed in the areal fractions of the LCN and its components for either age group. Our data indicate that the LCN is diminished in aged women, and is largely due to a decline in the canalicular areal fraction, and that, unlike vascular canal porosity, this diminished LCN is uniform across the cortex.

Classification of fracture and non-fracture groups by analysis of coherent X-ray scatter.

Osteoporotic fractures present a significant social and economic burden, which is set to rise commensurately with the aging population. Greater understanding of the physicochemical differences between osteoporotic and normal conditions will facilitate the development of diagnostic technologies with increased performance and treatments with increased efficacy. Using coherent X-ray scattering we have evaluated a population of 108 ex vivo human bone samples comprised of non-fracture and fracture groups. Principal component fed linear discriminant analysis was used to develop a classification model to discern each condition resulting in a sensitivity and specificity of 93% and 91%, respectively. Evaluating the coherent X-ray scatter differences from each condition supports the hypothesis that a causal physicochemical change has occurred in the fracture group. This work is a critical step along the path towards developing an in vivo diagnostic tool for fracture risk prediction.

A mechanostatistical approach to cortical bone remodelling: an equine model.

In this study, the development of a mechanostatistical model of three-dimensional cortical bone remodelling informed with in vivo equine data is presented. The equine model was chosen as it is highly translational to the human condition due to similar Haversian systems, availability of in vivo bone strain and biomarker data, and furthermore, equine models are recommended by the US Federal Drugs Administration for comparative joint research. The model was derived from micro-computed tomography imaged specimens taken from the equine third metacarpal bone, and the Frost-based 'mechanostat' was informed from both in vivo strain gauges and biomarkers to estimate bone growth rates. The model also described the well-known 'cutting cone' phenomena where Haversian canals tunnel and replace bone. In order to make this model useful in practice, a partial least squares regression (PLSR) surrogate model was derived based on training data from finite element simulations with different loads. The PLSR model was able to predict microstructure and homogenised Young's modulus with errors less than 2.2% and 0.6%, respectively.

X-ray diffraction from bone employing annular and semi-annular beams.

There is a compelling need for accurate, low cost diagnostics to identify osteo-tissues that are associated with a high risk of fracture within an individual. To satisfy this requirement the quantification of bone characteristics such as 'bone quality' need to exceed that provided currently by densitometry. Bone mineral chemistry and microstructure can be determined from coherent x-ray scatter signatures of bone specimens. Therefore, if these signatures can be measured, in vivo, to an appropriate accuracy it should be possible by extending terms within a fracture risk model to improve fracture risk prediction.In this preliminary study we present an examination of a new x-ray diffraction technique that employs hollow annular and semi-annular beams to measure aspects of 'bone quality'. We present diffractograms obtained with our approach from ex vivo bone specimens at Mo Kα and W Kα energies. Primary data is parameterized to provide estimates of bone characteristics and to indicate the precision with which these can be determined.

Energy-dispersive X-ray diffraction using an annular beam.

We demonstrate material phase identification by measuring polychromatic diffraction spots from samples at least 20 mm in diameter and up to 10 mm thick with an energy resolving point detector. Within our method an annular X-ray beam in the form of a conical shell is incident with its symmetry axis normal to an extended polycrystalline sample. The detector is configured to receive diffracted flux transmitted through the sample and is positioned on the symmetry axis of the annular beam. We present the experiment data from a range of different materials and demonstrate the acquisition of useful data with sub-second collection times of 0.5 s; equating to 0.15 mAs. Our technique should be highly relevant in fields that demand rapid analytical methods such as medicine, security screening and non-destructive testing.

The micro-architecture of human cancellous bone from fracture neck of femur patients in relation to the structural integrity and fracture toughness of the tissue.

Osteoporosis is clinically assessed from bone mineral density measurements using dual energy X-ray absorption (DXA). However, these measurements do not always provide an accurate fracture prediction, arguably because DXA does not grapple with 'bone quality', which is a combined result of microarchitecture, texture, bone tissue properties, past loading history, material chemistry and bone physiology in reaction to disease. Studies addressing bone quality are comparatively few if one considers the potential importance of this factor. They suffer due to low number of human osteoporotic specimens, use of animal proxies and/or the lack of differentiation between confounding parameters such as gender and state of diseased bone. The present study considers bone samples donated from patients (n = 37) who suffered a femoral neck fracture and in this very well defined cohort we have produced in previous work fracture toughness measurements (FT) which quantify its ability to resist crack growth which reflects directly the structural integrity of the cancellous bone tissue. We investigated correlations between BV/TV and other microarchitectural parameters; we examined effects that may suggest differences in bone remodelling between males and females and compared the relationships with the FT properties. The data crucially has shown that TbTh, TbSp, SMI and TbN may provide a proxy or surrogate for BV/TV. Correlations between FT critical stress intensity values and microarchitecture parameters (BV/TV, BS/TV, TbN, BS/BV and SMI) for osteoporotic cancellous tissue were observed and are for the first time reported in this study. Overall, this study has not only highlighted that the fracture model based upon BMD could potentially be improved with inclusion of other microarchitecture parameters, but has also given us clear clues as to which of them are more influential in this role.

The relationship between porosity and specific surface in human cortical bone is subject specific.

A characteristic relationship for bone between bone volume fraction (BV/TV) and specific surface (BS/TV) has previously been proposed based on 2D histological measurements. This relationship has been suggested to be bone intrinsic, i.e., to not depend on bone type, bone site and health state. In these studies, only limited data comes from cortical bone. The aim of this paper was to investigate the relationship between BV/TV and BS/TV in human cortical bone using high-resolution micro-CT imaging and the correlations with subject-specific biometric data such as height, weight, age and sex. Images from femoral cortical bone samples of the Melbourne Femur Collection were obtained using synchrotron radiation micro-CT (SPring8, Japan). Sixteen bone samples from thirteen individuals were analysed in order to find bone volume fraction values ranging from 0.20 to 1. Finally, morphological models of the tissue microstructure were developed to help explain the relationship between BV/TV and BS/TV. Our experimental findings indicate that the BV/TV vs BS/TV relationship is subject specific rather than intrinsic. Sex and pore density were statistically correlated with the individual curves. However no correlation was found with body height, weight or age. Experimental cortical data points deviate from interpolating curves previously proposed in the literature. However, these curves are largely based on data points from trabecular bone samples. This finding challenges the universality of the curve: highly porous cortical bone is significantly different to trabecular bone of the same porosity. Finally, our morphological models suggest that changes in BV/TV within the same sample can be explained by an increase in pore area rather than in pore density. This is consistent with the proposed mechanisms of age-related endocortical bone loss. In addition, these morphological models highlight that the relationship between BV/TV and BS/TV is not linear at high BV/TV as suggested in the literature but is closer to a square root function.

The normal-equivalent: a patient-specific assessment of facial harmony.

Evidence-based practice in oral and maxillofacial surgery would greatly benefit from an objective assessment of facial harmony or gestalt. Normal reference faces have previously been introduced, but they describe harmony in facial form as an average only and fail to report on harmonic variations found between non-dysmorphic faces. In this work, facial harmony, in all its complexity, is defined using a face-space, which describes all possible variations within a non-dysmorphic population; this was sampled here, based on 400 healthy subjects. Subsequently, dysmorphometrics, which involves the measurement of morphological abnormalities, is employed to construct the normal-equivalent within the given face-space of a presented dysmorphic face. The normal-equivalent can be seen as a synthetic identical but unaffected twin that is a patient-specific and population-based normal. It is used to extract objective scores of facial discordancy. This technique, along with a comparing approach, was used on healthy subjects to establish ranges of discordancy that are accepted to be normal, as well as on two patient examples before and after surgical intervention. The specificity of the presented normal-equivalent approach was confirmed by correctly attributing abnormality and providing regional depictions of the known dysmorphologies. Furthermore, it proved to be superior to the comparing approach.

Using smooth particle hydrodynamics to investigate femoral cortical bone remodelling at the Haversian level.

In the neck of the femur, about 70% of the strength is contributed by the cortical bone, which is the most highly stressed part of the structure and is the site where failure is almost certainly initiated. A better understanding of cortical bone remodelling mechanisms can help discern changes at this anatomical site, which are essential if an understanding of the mechanisms by which hips weaken and become vulnerable to fracture is to be gained. The aims of this study were to (i) examine a hypothesis that low strain fields arise because of subject-specific Haversian canal distributions causing bone resorption and reduced bone integrity and (ii) introduce the use of a meshless particle-based computational modelling approach SPH to capture bone remodelling features at the level of the Haversian canals. We show that bone remodelling initiated by strain at the Haversian level is highly influenced by the subject-specific pore distribution, bone density, loading and osteocyte density. SPH is shown to be effective at capturing the intricate bone pore shapes that evolved over time.

Robust and regional 3D facial asymmetry assessment in hemimandibular hyperplasia and hemimandibular elongation anomalies.

Hemimandibular hyperplasia (HH) and hemimandibular elongation (HE) anomalies present with facial asymmetry and deranged occlusion. Currently, diagnosis and assessment of the facial dysmorphology is based on subjective clinical evaluation, supported by radiological scans. Advancements in objective assessments of facial asymmetry from three-dimensional (3D) facial scans facilitate a re-evaluation of the patterns of facial dysmorphology. Automated, robust and localised asymmetry assessments were obtained by comparing a 3D facial scan with its reflected image using a weighted least-squares superimposition. This robust superimposition is insensitive to severe asymmetries. This provides an estimation of the anatomical midline and a spatially dense vector map visualising localised directional differences between the left and right hemifaces. Analysis was conducted on three condylar hyperplasia phenotypes confirmed by clinical and CT evaluation: HH; HE; and hybrid phenotype. The midline extraction revealed chin point displacements in all cases. The upper lip philtrum and nose tip deviation to the affected side and a marked asymmetry of the mid face was noted in cases involving HE. Downward and medial rotation of the mandible with minor involvement of the midface was seen in the HH associated deformity. The hybrid phenotype case exhibited asymmetry features of both HH and HE cases.

Relating age and micro-architecture with apparent-level elastic constants: a micro-finite element study of female cortical bone from the anterior femoral midshaft.

Homogenized elastic properties are often assumed for macro-finite element (FE) models used in orthopaedic biomechanics. The accuracy of material property assignments may have a strong effect on the ability of these models to make accurate predictions. For cortical bone, most macro-scale FE models assume isotropic elastic material behaviour and do not include variation of material properties due to bone micro-architecture. The first aim of the present study was to evaluate the variation of apparent-level (homogenized) orthotropic elastic constants of cortical bone with age and indices of bone micro-architecture. Considerable age-dependent differences in porosity were noted across the cortical thickness in previous research. The second aim of the study was to quantify the resulting differences in elastic constants between the periosteum and endosteum. Specimens were taken from the anterior femoral midshaft of 27 female donors (age 53.4 +/- 23.6 years) and micro-FE (gFE) analysis was used to derive orthotropic elastic constants. The variation of orthotropic elastic constants (Young's moduli, shear moduli, and Poisson's ratios) with various cortical bone micro-architectural indices was investigated. The ratio of canal volume to tissue volume, Ca.V/TV, analogous to porosity, was found to be the strongest predictor (r2(ave) = 0.958) of the elastic constants. Age was less predictive (r2(ave) = 0.385) than Ca.V/TV. Elastic anisotropy increased with increasing Ca.V/TV, leading to lower elastic moduli in the transverse, typically less frequently loaded, directions. Increased Ca.V/TV led to a more substantial reduction in elastic constants at the endosteal aspect than at the periosteal aspect. The results are expected to be most applicable in similar midshaft locations of long bones; specific analysis of other sites would be necessary to evaluate elastic properties elsewhere. It was concluded that Ca.V/TV was the most predictive of cortical bone elastic constants and that considerable periosteal-endosteal variations in these constants can develop with bone loss.

Imaging the 3D structure of secondary osteons in human cortical bone using phase-retrieval tomography.

By applying a phase-retrieval step before carrying out standard filtered back-projection reconstructions in tomographic imaging, we were able to resolve structures with small differences in density within a densely absorbing sample. This phase-retrieval tomography is particularly suited for the three-dimensional segmentation of secondary osteons (roughly cylindrical structures) which are superimposed upon an existing cortical bone structure through the process of turnover known as remodelling. The resulting images make possible the analysis of the secondary osteon structure and the relationship between an osteon and the surrounding tissue. Our observations have revealed many different and complex 3D structures of osteons that could not be studied using previous methods. This work was carried out using a laboratory-based x-ray source, which makes obtaining these sorts of images readily accessible.

Augmentation of linear facial anthropometrics through modern morphometrics: a facial convexity example.

BACKGROUND: The facial region has traditionally been quantified using linear anthropometrics. These are well established in dentistry, but require expertise to be used effectively. The aim of this study was to augment the utility of linear anthropometrics by applying them in conjunction with modern 3-D morphometrics. METHODS: Facial images of 75 males and 94 females aged 18-25 years with self-reported Caucasian ancestry were used. An anthropometric mask was applied to establish corresponding quasi-landmarks on the images in the dataset. A statistical face-space, encoding shape covariation, was established. The facial median plane was extracted facilitating both manual and automated indication of commonly used midline landmarks. From both indications, facial convexity angles were calculated and compared. The angles were related to the face-space using a regression based pathway enabling the visualization of facial form associated with convexity variation. RESULTS: Good agreement between the manual and automated angles was found (Pearson correlation: 0.9478-0.9474, Dahlberg root mean squared error: 1.15°-1.24°). The population mean angle was 166.59°-166.29° (SD 5.09°-5.2°) for males-females. The angle-pathway provided valuable feedback. CONCLUSIONS: Linear facial anthropometrics can be extended when used in combination with a face-space derived from 3-D scans and the exploration of property pathways inferred in a statistically verifiable way.

Visualization of 3D osteon morphology by synchrotron radiation micro-CT.

Cortical bone histology has been the subject of scientific inquiry since the advent of the earliest microscopes. Histology - literally the study of tissue - is a field nearly synonymous with 2D thin sections. That said, progressive developments in high-resolution X-ray imaging are enabling 3D visualization to reach ever smaller structures. Micro-computed tomography (micro-CT), employing conventional X-ray sources, has become the gold standard for 3D analysis of trabecular bone and is capable of detecting the structure of vascular (osteonal) porosity in cortical bone. To date, however, direct 3D visualization of secondary osteons has eluded micro-CT based upon absorption-derived contrast. Synchrotron radiation micro-CT, through greater image quality, resolution and alternative contrast mechanisms (e.g. phase contrast), holds great potential for non-destructive 3D visualization of secondary osteons. Our objective was to demonstrate this potential and to discuss areas of bone research that can be advanced through the application of this approach. We imaged human mid-femoral cortical bone specimens derived from a 20-year-old male (Melbourne Femur Collection) at the Advanced Photon Source synchrotron (Chicago, IL, USA) using the 2BM beam line. A 60-mm distance between the target and the detector was employed to enhance visualization of internal structures through propagation phase contrast. Scan times were 1 h and images were acquired with 1.4-µm nominal isotropic resolution. Computer-aided manual segmentation and volumetric 3D rendering were employed to visualize secondary osteons and porous structures, respectively. Osteonal borders were evident via two contrast mechanisms. First, relatively new (hypomineralized) osteons were evident due to differences in X-ray attenuation relative to the surrounding bone. Second, osteon boundaries (cement lines) were delineated by phase contrast. Phase contrast also enabled the detection of soft tissue remnants within the vascular pores. The ability to discern osteon boundaries in conjunction with vascular and cellular porosity revealed a number of secondary osteon morphologies and provided a unique 3D perspective of the superimposition of secondary osteons on existing structures. Improvements in resolution and optimization of the propagation phase contrast promise to provide further improvements in structural detail in the future.

Bimodal distribution of osteocyte lacunar size in the human femoral cortex as revealed by micro-CT.

Tomographic reconstructions of sections of human femoral bone were created from x-ray data sets taken using synchrotron radiation of 26.4 keV and with isotropic voxels 1.47 µm on a side. We demonstrate that it is possible to segment the data to isolate both the osteocyte lacunae and the Haversian canals in the bone as well as identifying osteon boundaries. From this information a wealth of data relating to bone structure becomes available. The data were used to map the spatial positions of the osteocyte lacunae, relative to the Haversian canals and of the osteon boundaries. The dimensions and volume of the imaged osteocyte lacunae were measured for close to 10,000 lacunae. When averaged over the 11 osteons measured, osteocyte densities varied from 4×10(4)per mm(3) close to the Haversian canals to about 9×10(4)per mm(3) at 80% of osteon radius. The nearest-neighbour distances varied from 10 µm to 40 µm with a peak at 23 µm and an approximately normal distribution. The distribution of lacunar long-axis length was also approximately normal with a small positive skew and the peak value was 8 µm with a range from 3 µm to 20 µm. The most significant finding from this study was that the distribution of the measured volumes of osteocyte lacunae had two distinct peaks, one at 200 µm(3) and a second at 330 µm(3).

Is current bite mark analysis a misnomer?

Four human-to-human bite mark cases in which forensic odontological opinion was found to be in error, or at best deeply divided between experts, are described. These are used to illustrate that there is a growing awareness on the part of the legal profession that bite mark opinions by experts may often be little more than that and that these opinions often cannot be substantiated given the paucity of rigorous scientific evaluation, and will therefore be increasingly challenged. This may not best serve justice and so it is argued that forensic odontology needs to bring more scientific rigour to the evaluation of bite marks. This may threaten to disenfranchise some of the current practitioners and there may be some resistance to change. Forensic odontology is not the only identification science facing such problems, but nevertheless a paradigm shift is predicted in the way bite mark evidence will have to be gathered and evaluated in the future. Some new scientific approaches are described that strive to unravel some of the most basic problems confronting our profession when we attempt to make morphometric comparisons between injuries and the dentition of the biter. A need to capture the actions and consequences of biting in 3D dimensions and simultaneously in real-time is proposed as a path of investigation highly likely to bring some clarity to a confused situation. There is also an urgent need for the ongoing controversy between some of our eminent peers relating to the assumed uniqueness, or otherwise, of the human anterior dentition to be resolved.

A comparison of cortical bone thickness in the femoral midshaft of humans and two non-human mammals.

Fragments of bone shafts that lack diagnostic features can be difficult to identify as human or non-human-an important task in forensic science and archaeology. Some workers have found the thickness of cortical bone in the shaft to be a useful distinction, although the sparse literature in the field is contradictory in how this may be applied. The aim of the present study was to determine whether any difference is discernible between humans, kangaroos and sheep (mammals whose remains are commonly confused with those of humans in Australia) at the femoral midshaft, with a view to a larger-scale analysis if differences were discovered. Cross-sections at the midpoint of the shaft were measured to determine the diameter of the whole shaft and the medullary cavity on each bone; an index describing cortical thickness relative to shaft diameter was calculated. Statistically significant differences were found between all three groups, with humans showing the thickest cortical bone, and sheep the thinnest. These differences may be linked to a higher load on the human femur, due to a larger body mass carried on two legs, as opposed to the sheep's four. Further work now needs to be carried out to determine if differences are present when comparing multiple sites on the skeleton, and between non-human mammals of different sizes.

Ontogenetic patterning of cortical bone microstructure and geometry at the human mid-shaft femur.

The bone growth process has long-lasting effects on adult bone structure and mechanical adaptation, yet the tissue level dynamics of growth are poorly studied. The specific aims of this study were to (1) quantify changes in bone size and shape through ontogeny, (2) describe the distribution of tissue types and patterns of cortical drift and expansion through ontogeny, and (3) explore relationships between cortical drift and ontogenetic variation geometric size and shape. The study utilized 14 juvenile (ages 2-19) mid-shaft femur blocks removed at autopsy from individuals who died suddenly. Eighty-mum-thick sections were imaged using polarized and brightfield microscopy. For descriptive purposes the sample was divided into five age groups. Features of collagen fiber matrix orientation, vascularity (e.g., pore orientation and density), and osteocyte lacunar density and shape were used to classify primary and secondary tissue types in LM images. This information, combined with evaluation of resorptive versus depositional bone surfaces, was used to identify cortical drift direction. A pattern of posterior and medial drift was identified at the mid-shaft femur in the toddler years. The drift pattern shifts antero-laterally in late childhood, predating the appearance of a more adult-like geometry. On the basis of the presence of transitional fibrolamellar bone complex, growth is more rapid during the toddler years and peri-puberty, and slower in early to late childhood and in later adolescence. Extensive variability in histological and geometric organization typifies the sample, particularly beginning in late childhood. The potential implications of this variability for adult fracture risk warrant further study. Anat Rec, 2009. (c) 2008 Wiley-Liss, Inc.

Evaluation of two dental identification computer systems: DAVID and WinID3.

Human identification, by comparing dental characteristics, is considered to be one of the most reliable, accurate and rapid methods of resolving the identity of visually un-identifiable deceased persons. In recent decades computer programs have evolved to aid odontologists by suggesting records that have similar dental features. The aim of the present study was to compare two of those programs; Disaster And Victim IDentification (DAVID) and WinID3 in terms of effectiveness, accuracy and speed of data entry and to further compare them with the efficiency of the classical method of manually matching postmortem and antemortem dental records. An open disaster was simulated whereby 52 fragmented remains made of acrylic replicas and 77 provisional victims were represented on Interpol F2 postmortem and antemortem forms. The results assessed were the first seven possible matches made by each program. Manual matching of dental characteristics performed better than both programs (P<0.001) yielding 29 identifications. Eleven and six positive matches were the result of the DAVID and the WinID3 programs respectively (P=0.185). Data entry was quicker for WinID3. It was concluded that both programs are still not as accurate as the time-consuming manual matching method. The difference in performance between the DAVID and the WinID3 programs was attributed to the inclusion of more comparable dental characteristics, the inclusion of the type of dentition (deciduous or permanent) and the weighting of those characteristics by the DAVID program.

3-D imaging and quantitative comparison of human dentitions and simulated bite marks.

This study presents a technique developed for 3-D imaging and quantitative comparison of human dentitions and simulated bite marks. A sample of 42 study models and the corresponding bites, made by the same subjects in acrylic dental wax, were digitised by laser scanning. This technique allows image comparison of a 3-D dentition with a 3-D bite mark, eliminating distortion due to perspective as experienced in conventional photography. Cartesian co-ordinates of a series of landmarks were used to describe the dentitions and bite marks, and a matrix was created to compare all possible combinations of matches and non-matches using cross-validation techniques. An algorithm, which estimated the probability of a dentition matching its corresponding bite mark, was developed. A receiver operating characteristic graph illustrated the relationship between values for specificity and sensitivity. This graph also showed for this sample that 15% of non-matches could not be distinguished from the true match, translating to a 15% probability of falsely convicting an innocent person.