Trabecular Orientation Research Articles

Trabecular orientation in the human femur and tibia and the relationship with lower-limb alignment for patients with osteoarthritis of the knee

Wolff׳s Law suggests that the orientation of trabeculae in human bone changes in response to altered loading patterns. The aim of this study was to investigate trabecular orientation in both the femur and tibia and to compare this with the mechanical axis of the leg. The study involved analysis of radiographs from patients with osteoarthritis of the knee (n=91). For each patient, the trabecular orientation in both the distal femur and proximal tibia was measured from a standard anteroposterior radiograph of the knee and the mechanical axis of the leg was calculated from a long leg view taken while weight bearing. There was a significant correlation between the mechanical axis and the trabecular orientation in each of the regions considered in the femur (r=−0.41, −0.30, 0.52, and 0.23) and tibia (r=−0.27 and 0.31). Multiple regression analysis, with mechanical axis as the dependent variable, produced an R2 of 0.62. Greater trabecular anisotropy (i.e. greater alignment) was observed in the medial femur and tibia compared to the lateral side (p<0.01). The results give an insight into the trabecular changes that may take place during development of osteoarthritis and following surgery. In particular, we propose that the orientation of the trabeculae in both the distal femur and proximal tibia will reflect the angle of mechanical loading through the knee.

G0200205 Micro Cantilever Bendingによる海綿骨骨梁単体の弾性率計測

Cancellous bone has a three-dimensional network of single trabecula. It has been reported that the apparent elastic modulus of cancellous bone is much smaller than that of cortical bone and that the elastic modulus depends on the trabecular network. However, the mechanical properties of single trabecula are still unclear, because mechanical tests of single trabecula are challenging. This study aimed to develop an experimental method to measure the elastic properties of single trabecula that was 1 mm in length by micro cantilever bending. In the experiments, 10 single-trabecula specimens taken from the proximal epiphysis of a 2-year-old bovine femur were used. The tests were conducted using a small testing device that consisted of an acrylic plate for applying load to the specimen, a linear stage, and a load cell. The specimen was in contact with the edge of a taper bore drilled in the acrylic plate and was deformed by applying the displacement with the stage. The deflection of the specimen was observed by optical microscopy. A finite element model of the specimen was constructed from a micro-CT observation. The elastic modulus of the specimen was calculated from the force-deflection relation by finite element analysis. As a result, elastic modulus of single trabecula was 8.2 ± 3.3 GPa. There was no correlation between the elastic modulus and trabecular orientation in the femur. The study showed that the elastic modulus of single trabecula was much smaller than that of the cortical bone in bovine femoral diaphyses by proposed method.

Pore cross-section area on predicting elastic properties of trabecular bovine bone for human implants

A clear understanding of the dependence of mechanical properties of bone remains a task not fully achieved. In order to estimate the mechanical properties in bones for implants, pore cross-section area, calcium content, and apparent density were measured in trabecular bone samples for human implants. Samples of fresh and defatted bone tissue, extracted from one year old bovines, were cut in longitudinal and transversal orientation of the trabeculae. Pore cross-section area was measured with an image analyzer. Compression tests were conducted into rectangular prisms. Elastic modulus presents a linear tendency as a function of pore cross-section area, calcium content and apparent density regardless of the trabecular orientation. The best variable to estimate elastic modulus of trabecular bone for implants was pore cross-section area, and affirmations to consider Nukbone process appropriated for marrow extraction in trabecular bone for implantation purposes are proposed, according to bone mechanical properties. Considering stress-strain curves, defatted bone is stiffer than fresh bone. Number of pores against pore cross-section area present an exponential decay, consistent for all the samples. These graphs also are useful to predict elastic properties of trabecular samples of young bovines for implants.

Correlation between 3D microstructural and 2D histomorphometric properties of subchondral bone with healthy and degenerative cartilage of the knee joint.

Cartilage degeneration of the knee joint is considered to be a largely mechanically driven process. We conducted a microstructural and histomorphometric analysis of subchondral bone samples of intact cartilage and in samples with early and higher- grade arthritic degeneration to compare the different states and correlate the findings with the condition of hyaline cartilage. These findings will enable us to evaluate changes in biomechanical properties of subchondral bone during the evolution of arthritic degeneration, for which bone density alone is an insufficient parameter. From a continuous series of 80 patients undergoing implantation of total knee endoprosthesis 30 osteochondral samples with lesions macroscopically classified as ICRS grade 1b (group A) and 30 samples with ICRS grade 3a or 3b lesions (group B) were taken. The bone samples were assessed by 2D histomorphometry (semiautomatic image analysis system) and 3D microstructural analysis (high-resolution micro-CT system). The cartilage was examined using the semiquantitative real-time PCR gene expression of collagen type I and II and aggrecan. Both histomorphometry and microstructural and biomechanical analysis of subchondral bone in groups A and B consistently revealed progressive changes of both bone and cartilage compared with healthy controls. The severity of cartilage degeneration as assessed by RT PCR was significantly correlated with BV/TV (Bone Volume Fraction), Tb.Th (Trabecular Thickness) showed a slight increase. Tb.N (Trabecular Number), Tb.Sp (Trabecular separation) SMI (Structure Model Index), Conn.D (Connectivity Density) and DA (Degree of Anisotropy) were inversely correlated. We saw sclerotic transformation and phagocytic reticulum cells. Bone volume fraction decreased with an increasing distance from the cartilage with the differences compared with healthy controls becoming greater in more advanced cartilage damage. The density of subchondral bone alone is considered an unreliable parameter for classifying changes evolving over time. The progressive damage of subchondral bone seen in the present study correlates well with cartilage changes. Trabecular orientation is also impaired, which explains the changes in biomechanical parameters and the inadequate load transfer and excessive loading of cartilage. Besides subchondral bone density, which in turn correlates with cartilage thickness, other parameters such as structure model index and grade of anisotropy best reflect mechanical properties such as Young modulus, compressive strength, tensile stress, and failure energy. However, it remains unclear whether the mechanical interaction of the mineralized subchondral tissues with articular cartilage works vice versa. The possibility of a biochemical signalling from the degenerating cartilage via the synovial fluid and bone- cartilage crosstalks via subchondral pores may indeed explain a certain depth-dependency of subchondral bone changes.

Quantification of trabecular spatial orientation from low-resolution images

No accepted methodology exists to assess trabecular bone orientation from clinical CT scans. The aim of this study was to test the hypothesis that the distribution of grey values in clinical CT images is related to the underlying trabecular architecture and that this distribution can be used to identify the principal directions and local anisotropy of trabecular bone. Fourteen trabecular bone samples were extracted from high-resolution (30 μm) micro-CT scans of seven human femoral heads. Trabecular orientations and local anisotropy were calculated using grey-level deviation (GLD), a novel method providing a measure of the three-dimensional distribution of image grey values. This was repeated for different image resolutions down to 300 μm and for volumes of interest (VOIs) ranging from 1 to 7 mm. Outcomes were compared with the principal mechanical directions and with mean intercept length (MIL) as calculated for the segmented 30-μm images. For the 30-μm images, GLD predicted the mechanical principal directions equally well as MIL. For the 300-μm images, which are resolutions that can be obtained in vivo using clinical CT, only a small increase (3°–6°) in the deviation from the mechanical orientations was found. VOIs of 5 mm resulted in a robust quantification of the orientation. We conclude that GLD can quantify structural bone parameters from low-resolution CT images.

Morphometry and fabric orientation of trabecular bone in human craniofacial regions (918.17)

Variation in primate craniofacial form has been attributed to orofacial function. Strain gage experiments show that during orofacial function the zygoma is subjected to high strain relative to the browridge. Trabecular bone morphometry and orientation are reflective of function, but trabecular bone in these regions has been unexplored. This study uses µCT to quantify the morphometric properties of trabecular bone, anisotropy, and fabric orientation in the human browridge and zygoma. We hypothesize that zygomatic trabecular bone will have significantly greater bone volume fraction and anisotropy relative to the browridge as an adaption to larger, more unidirectional loads. Primary orientations of trabecular bone will differ by region consistent with their function.No significant differences were found between the browridge and zygoma in BVF (0.38 vs. 0.31), and DA (1.65 vs. 1.85), but SMI was significantly lower in the browridge (0.075; honeycomb‐like vs. SMI=1.0752; ideal plate‐like, p&lt;0.034). Orientation was highly significantly different between regions. The zygoma is made up of mediolaterally oriented plates with a slight inferosuperior tilt, while trabecular bone in the browridge is made of denser sagittally oriented plates.Both regions may be more similar in overall elasticity than predicted, but further analysis needs to test the combined effects of differences in individual features. Orientation of trabeculae in the zygoma appears to be consistent with what would be predicted based on orofacial strain patterns.Grant Funding Source: NSF BCS 0725141

Effects of freeze–thaw and micro-computed tomography irradiation on structure–property relations of porcine trabecular bone

We study the effects of freeze–thaw and irradiation on structure–property relations of trabecular bone. We measure the porosity, apparent density, mineral content, trabecular orientation, trabecular thickness, fractal dimension, surface area, and connectivity of trabecular bone using micro-computed tomography (micro-CT) and relate them to Young׳s modulus and ultimate strength measured by uniaxial compression testing. The analysis is done on six-month porcine trabecular bone from femoral heads. The effects of freeze–thaw are studied by using bones from three different groups: fresh bone and bones frozen for one and five years. We find that the porosity and apparent density have most dominant influence on the elastic modulus and strength of fresh bone. Also, five years of freezing lowers both Young׳s modulus and ultimate strength of trabecular bone. Additionally, the effects of radiation are investigated by comparing Young׳s modulus before and after micro-CT exposure. We find that the micro-CT irradiation has a negligible effect on the Young׳s modulus of trabecular bone. These findings provide insights on the effects of tissue preservation and imaging on properties of trabecular bone.

Assessment of Transverse Isotropy in Clinical-Level CT Images of Trabecular Bone Using the Gradient Structure Tensor

The aim of this study was to develop a GST-based methodology for accurately measuring the degree of transverse isotropy in trabecular bone. Using femoral sub-regions scanned in high-resolution peripheral QCT (HR-pQCT) and clinical-level-resolution QCT, trabecular orientation was evaluated using the mean intercept length (MIL) and the gradient structure tensor (GST) on the HR-pQCT and QCT data, respectively. The influence of local degree of transverse isotropy (DTI) and bone mineral density (BMD) was incorporated into the investigation. In addition, a power based model was derived, rendering a 1:1 relationship between GST and MIL eigenvalues. A specific DTI threshold (DTI thres) was found for each investigated size of region of interest (ROI), above which the estimate of major trabecular direction of the GST deviated no more than 30° from the gold standard MIL in 95% of the remaining ROIs (mean error: 16°). An inverse relationship between ROI size and DTI thres was found for discrete ranges of BMD. A novel methodology has been developed, where transversal isotropic measures of trabecular bone can be obtained from clinical QCT images for a given ROI size, DTI thres and power coefficient. Including DTI may improve future clinical QCT finite-element predictions of bone strength and diagnoses of bone disease.

Orthotropic HR-pQCT-based FE models improve strength predictions for stance but not for side-way fall loading compared to isotropic QCT-based FE models of human femurs

Quantitative computed tomography (QCT) based nonlinear homogenized finite element (hFE) models of the human femur do not take bone׳s microstructure into account due to the low resolution of the QCT images. Models based on high-resolution peripheral quantitative computed tomography (HR-pQCT) are able to include trabecular orientation and allow the modeling of a cortical shell. Such a model showed improvements compared to QCT-based models when studying human vertebral bodies. The goal of this study was to compare the femoral strength prediction ability of subject specific nonlinear homogenized FE (hFE) models based on HR-pQCT and QCT images.Thirty-six pairs of femurs were scanned with QCT as well as HR-pQCT, and tested in one-legged stance (STANCE) and side-ways fall (SIDE) configurations up to failure. Non-linear hFE models were generated from HR-pQCT images (smooth meshes) and compared to recently published QCT based models (voxel meshes) as well as experiments with respect to ultimate force.HR-pQCT-based hFE models improved ultimate force (R2=0.87 vs 0.80, p=0.02) predictions only in STANCE configuration but not in SIDE (R2=0.86 vs 0.84, p=0.6). Damage locations were similar for both types of models.In conclusion, it was shown for the first time on a large femur dataset that a more accurate representation of trabecular orientation and cortex only improve FE predictions in STANCE configuration, where the main trabecular orientation is aligned with the load direction. In the clinically more relevant SIDE configuration, the improvements were not significant.

A CT-image-based framework for the holistic analysis of cortical and trabecular bone morphology

This study introduces a standardized framework for the holistic analysis of cortical and trabecular bone structure. This method, although applicable to all bones of the skeleton, is particularly useful for irregular-shaped or small bones for which the application of traditional methods has been especially challenging. Traditional analyses have quantified cortical or trabecular structure in only selected regions of a bone, such as single cross-sections of cortical bone or volumes of interest of trabecular structure in epiphyses. The proposed method improves on these traditional methods by visualizing and quantifying the internal bony structure throughout the entire bone and in user-defined anatomical subregions. Here, we describe and demonstrate the method using high-resolution microtomographic scans of a first metacarpal of an orangutan, gorilla, chimpanzee and human. Using automated morphological filters, the cortical bone is defined and extracted from the underlying trabecular structure to create two 3D models, one of the cortex and one of the trabecular bone that can be analysed separately. We test the sensitivity of the morphological parameters used to create these 3D models, demonstrating that the parameters defined here are robust and can provide accurate measures of cortical thickness, relative bone density, trabecular orientation, trabecular thickness and degree of anisotropy. This new, holistic method is able to reveal morphological and functional information about bone loading that is obscured or ignored using traditional methods, thus providing more informed interpretations of behaviour in extant and fossil taxa.

Effects of glucosamine and risedronate alone or in combination in an experimental rabbit model of osteoarthritis.

BackgroundThe osteoarthritis (OA) treatment in humans and in animals is a major orthopaedic challenge because there is not an ideal drug for preserving the joint structure and function. The aim of this study was to assess the effects of the treatment with oral glucosamine and risedronate alone or in combination on articular cartilage, synovial membrane and subchondral bone in an experimental rabbit model of OA. Osteoarthritis was surgically induced on one knee of 32 New Zealand White rabbits using the contralateral as healthy controls. Three weeks later treatments were started and lasted 8 weeks. Animal were divided in four groups of oral treatment: the first group received only saline, the second 21.5 mg/kg/day of glucosamine sulfate, the third 0.07 mg/kg/day of risedronate; and the fourth group both drugs simultaneously at the same dosages. Following sacrifice femurs were removed and osteochondral cylinders and synovial membrane were obtained for its histological and micro-CT evaluation.ResultsSample analysis revealed that the model induced osteoarthritic changes in operated knees. OA placebo group showed a significant increase in cartilage thickness respect to the control and inflammatory changes in synovial membrane; whereas subchondral bone structure and volumetric bone mineral density remained unchanged. All the treated animals showed an improvement of the cartilage swelling independent of the drug used. Treatment with glucosamine alone seemed to have no effect in the progression of cartilage pathology while risedronate treatment had better results in superficial fibrillation and in resolving the inflammatory changes of the tissues, as well as modifying the orientation of trabecular lattice. The combination of both compounds seemed to have additive effects showing better results than those treated with only one drug.ConclusionsThe results of this animal study suggested that glucosamine sulfate and risedronate treatment alone or in combination may be able to stop cartilage swelling. The risedronate treatment could partially stop the fibrillation and the inflammation of synovial membrane as well as modify the orientation of trabeculae in healthy and in osteoarthritic knees.

A novel approach to estimate trabecular bone anisotropy using a database approach

Continuum finite element (FE) models of bones have become a standard pre-clinical tool to estimate bone strength. These models are usually based on clinical CT scans and material properties assigned are chosen as isotropic based only on the density distribution. It has been shown, however, that trabecular bone elastic behavior is best described as orthotropic. Unfortunately, the use of orthotropic models in FE analysis derived from CT scans is hampered by the fact that the measurement of a trabecular orientation (fabric) is not possible from clinical CT images due to the low resolution of such images. In this study, we explore the concept of using a database (DB) of high-resolution bone models to derive the fabric information that is missing in clinical images. The goal of this study was to investigate if models with fabric derived from a relatively small database can already produce more accurate results than isotropic models.A DB of 33 human proximal femurs was generated from micro-CT scans with a nominal isotropic resolution of 82µm. Continuum FE models were generated from the images using a pre-defined mesh template in combination with an iso-anatomic mesh morphing tool. Each element within the mesh template is at a specific anatomical location. For each element within the cancellous bone, a spherical region around the element centroid with a radius of 2mm was defined. Bone volume fraction and the mean-intercept-length fabric tensor were analyzed for that region. Ten femurs were used as test cases. For each test femur, four different models were generated: (1) an orthotropic model based on micro-CT fabric measurements (gold standard), (2) an orthotropic model based on the fabric derived from the best-matched database model, (3) an isotropic-I model in which the fabric tensor was set to the identity tensor, and (4) a second isotropic-II model with its total bone stiffness fitted to the gold standard. An elastic-plastic damage model was used to simulate failure and post failure behavior during a fall to the side.The results show that all models produce a similar stress distribution. However, compared to the gold standard, both isotropic-I and II models underestimated the stress/damage distributions significantly. We found no significant difference between DB-derived and gold standard models. Compared to the gold standard, the isotropic-I models further underestimated whole bone stiffness by 26.3% and ultimate load by 14.5%, while these differences for the DB-derived orthotropic models were only 4.9% and 3.1% respectively.The results indicate that the concept of using a DB to estimate patient-specific anisotropic material properties can considerably improve the results. We expect that this approach can lead to more accurate results in particular for cases where bone anisotropy plays an important role, such as in osteoporotic patients and around implants.

The Effect of the Achilles Tendon on Trabecular Structure in the Primate Calcaneus

Humans possess the longest Achilles tendon relative to total muscle length of any primate, an anatomy that is beneficial for bipedal locomotion. Reconstructing the evolutionary history of the Achilles tendon has been challenging, in part because soft tissue does not fossilize. The only skeletal evidence for Achilles tendon anatomy in extinct taxa is the insertion site on the calcaneal tuber, which is rarely preserved in the fossil record and, when present, is equivocal for reconstructing tendon morphology. In this study, we used high-resolution three-dimensional microcomputed tomography (micro-CT) to quantify the microstructure of the trabecular bone underlying the Achilles tendon insertion site in baboons, gibbons, chimpanzees, and humans to test the hypothesis that trabecular orientation differs among primates with different tendon morphologies. Surprisingly, despite their very different Achilles tendon lengths, we were unable to find differences between the trabecular properties of chimpanzee and human calcanei in this specific region. There were regional differences within the calcaneus in the degree of anisotropy (DA) in both chimpanzees and humans, though the patterns were similar between the two species (higher DA inferiorly in the calcaneal tuber). Our results suggest that while trabecular bone within the calcaneus varies, it does not respond to the variation of Achilles tendon morphology across taxa in the way we hypothesized. These results imply that internal bone architecture may not be informative for reconstructing Achilles tendon anatomy in early hominins.

Trabecular Pattern of the Proximal Ulna: A Morphological Study

Background The trabecular architecture of the olecranon and proximal ulna has not been studied in detail. We undertook a primarily cadaveric study aiming to link with the theory of biomechanics. Methods Eight pairs of ulnae were obtained from cadavers. Half of the ulnae were sliced longitudinally, each slice 2 mm to 3 mm thick (Group I), and the remaining half were sliced vertically (Group II) and radiographed to study the trabecular orientation of the olecranon and proximal ulna. Computerized tomography (CT) scans of eight patients (Group III) were studied to determine the real-life trabecular pattern. Results In Group I, two main sets of trabeculae were observed. The first set of trabeculae consists of three bundles, which arise from the anterior cortex. Anterior and middle bundles support the subarticular subchondral area. The posterior bundle curves and spreads to posterior cortex. The second set arises from posterior cortex and terminates under subchondral area. In Group II, trabeculae subtend a 90° angle to the articular surface. CT (Group III) confirmed the cadaveric observations. Conclusions Trabeculae of the olecranon and proximal ulna comprise a cluster that resists compressive loading and a further cluster that resists tensile stresses, which should be taken into consideration in the prosthetic design of elbow replacement to facilitate stress absorption.

Trabecular bone anisotropy and orientation in an Early Pleistocene hominin talus from East Turkana, Kenya

Among the structural properties of trabecular bone, the degree of anisotropy is most often found to separate taxa with different habitual locomotor modes. This study examined the degree of anisotropy, the elongation, and primary orientation of trabecular bone in the KNM-ER 1464 Early Pleistocene hominin talus as compared with extant hominoid taxa. Modern human tali were found to have a pattern of relatively anisotropic and elongated trabeculae on the lateral aspect, which was not found in Pan, Gorilla, Pongo, or KNM-ER 1464. Trabecular anisotropy in the fossil talus most closely resembled that of the African apes except for a region of high anisotropy in the posteromedial talus. The primary orientation of trabeculae in the anteromedial region of KNM-ER 1464 was strikingly different from that of the great apes and very similar to that of modern humans in being directed parallel to the talar neck. These results suggest that, relative to that of modern humans, the anteromedial region of the KNM-ER 1464 talus may have transmitted body weight to the midfoot in a similar manner while the lateral aspect may have been subjected to more variable loading conditions.

Stochastic multi-scale prediction on the apparent elastic moduli of trabecular bone considering uncertainties of biological apatite (BAp) crystallite orientation and image-based modelling

An assessment of the mechanical properties of trabecular bone is important in determining the fracture risk of human bones. Many uncertainty factors contribute to the dispersion of the estimated mechanical properties of trabecular bone. This study was undertaken in order to propose a computational scheme that will be able to predict the effective apparent elastic moduli of trabecular bone considering the uncertainties that are primarily caused by image-based modelling and trabecular stiffness orientation. The effect of image-based modelling which focused on the connectivity was also investigated. A stochastic multi-scale method using a first-order perturbation-based and asymptotic homogenisation theory was applied to formulate the stochastically apparent elastic properties of trabecular bone. The effective apparent elastic modulus was predicted with the introduction of a coefficient factor to represent the variation of bone characteristics due to inter-individual differences. The mean value of the predicted effective apparent Young's modulus in principal axis was found at approximately 460 MPa for respective 15.24% of bone volume fraction, and this is in good agreement with other experimental results. The proposed method may provide a reference for the reliable evaluation of the prediction of the apparent elastic properties of trabecular bone.

Internal Bone Structure and Orientation in the Browridge of Homo, Pan, Gorilla, Papio, and Cebus

Assessing the variation of the internal bone structure, anisotropy and orientation in the browridge across regions and species can aid in our understanding of craniofacial adaptation. Also, quantifying species and region specific variation may serve to improve the accuracy of finite element models. In this study, μCT was used to determine the structural properties, degree of anisotropy (DA) and primary trabecular orientation in 3 equally divided browridge regions of 8 Homo, 5 Pan, 7 Cebus, 4 Papio, and 1 Gorilla. Both bone volume fraction (BVF) and degree of anisotropy (DA) differed significantly by species (Kruskal‐Wallis Test, p&lt;0.001 and p&lt;0.015, respectively). Most regions across species showed orthotropy. In all species and regions, trabeculae tend to show less variability in orientation across transverse and coronal planes. Orientations in the sagittal plane instead show higher variability across individuals. The results suggest that BVF, DA and orientation of trabecular‐like bone within the supraorbital region may be reflective of feeding strategies and that characterization of subcortical structure in craniofacial regions may improve finite element models. Additional study of trabecular bone orientation within zygomatic regions is ongoing to examine how trabecular bone orientation and DA differ across the entire craniofacial region in these species.Grant Funding Source: Science Foundation Physical Anthropology HOMINID program (NSF BCS 0725141)

Inner architecture of vertebral centra in terrestrial and aquatic mammals: A two‐dimensional comparative study

Inner vertebral architecture is poorly known, except in human and laboratory animals. In order to document this topic at a broad comparative level, a 2D-histomorphometric study of vertebral centra was conducted in a sample of 98 therian mammal species, spanning most of the size range and representing the main locomotor adaptations known in therian taxa. Eleven variables relative to the development and geometry of trabecular networks were extracted from CT scan mid-sagittal sections. Phylogeny-informed statistical tests were used to reveal the respective influences of phylogeny, size, and locomotion adaptations on mammalian vertebral structure. The use of random taxon reshuffling and squared change parsimony reveals that 9 of the 11 characteristics (the two exceptions are total sectional area and structural polarization) contain a phylogenetic signal. Linear discriminant analyses suggest that the sampled taxa can be arranged into three categories with respect to locomotion mode: a) terrestrial + flying + digging + amphibious forms, b) coastal oscillatory aquatic taxa, and c) pelagic oscillatory aquatic forms represented by oceanic cetaceans. Pairwise comparison tests and linear regressions show that, when specific size increases, the length of trabecular network (Tt.Tb.Le), as well as trabecular proliferation in total sections (Pr.Tb.Tt), increase with positive allometry. This process occurs in all locomotion categories but is particularly pronounced in pelagic oscillators. Conversely, mean trabecular width has a lesser increase with size in pelagic oscillators. Trabecular orientation is not influenced by size. All tests were corrected for multiple testing. By using six structural variables or indices, locomotion mode can be predicted with a 97.4% success rate for terrestrial forms, 66.7% for coastal oscillatory, and 81.3% for pelagic oscillatory. The possible functional meaning of these results and their potential use for paleobiological inference of locomotion in extinct taxa are discussed.

Shear strength behavior of human trabecular bone

The shear strength of human trabecular bone may influence overall bone strength under fall loading conditions and failure at bone-implant interfaces. Here, we sought to compare shear and compressive yield strengths of human trabecular bone and elucidate the underlying failure mechanisms. We analyzed 54 specimens (5-mm cubes), all aligned with the main trabecular orientation and spanning four anatomic sites, 44 different cadavers, and a wide range of bone volume fraction (0.06–0.38). Micro-CT-based non-linear finite element analysis was used to assess the compressive and shear strengths and the spatial distribution of yielded tissue; the tissue-level constitutive model allowed for kinematic non-linearity and yielding with strength asymmetry. We found that the computed values of both the shear and compressive strengths depended on bone volume fraction via power law relations having an exponent of 1.7 (R2=0.95 shear; R2=0.97 compression). The ratio of shear to compressive strengths (mean±SD, 0.44±0.16) did not depend on bone volume fraction (p=0.24) but did depend on microarchitecture, most notably the intra-trabecular standard deviation in trabecular spacing (R2=0.23, p<0.005). For shear, the main tissue-level failure mode was tensile yield of the obliquely oriented trabeculae. By contrast, for compression, specimens having low bone volume fraction failed primarily by large-deformation-related tensile yield of horizontal trabeculae and those having high bone volume failed primarily by compressive yield of vertical trabeculae. We conclude that human trabecular bone is generally much weaker in shear than compression at the apparent level, reflecting different failure mechanisms at the tissue level.

Effect of Cortical Bone Layer on Fast and Slow Waves in Cancellous Bone: Investigations Using Stratified Models

Fast and slow longitudinal waves can propagate through cancellous bone in the direction of the strong trabecular orientation. In in vivo experiments, the cortical bone layer surrounding cancellous bone is considered to affect the fast and slow wave propagations. In this study, the effects of the cortical bone layer were investigated using the stratified models of cancellous bone. In the experimental and simulated results, it was shown that the boundary condition between the cancellous and cortical bone regions affected both the fast and slow waves, particularly the slow wave. The slow wave could be clearly observed for the stratified bone model with a distinct boundary, but the slow wave amplitude decreased as the boundary became less distinct. This was because the generation of the slow wave was interrupted by the gradually varying pore spaces. Moreover, it was shown that the reflected waves within the cortical bone layer could affect the observation of the fast and slow waves. Despite the effects of the cortical bone layer, both the fast and slow waves could be observed for all stratified bone models.