Three-dimensional methods for quantification of cancellous bone architecture

Structural and molecular analyses of bone bridge formation within the growth plate injury site and cartilage degeneration at the adjacent uninjured area

Injury to the growth plate is common and yet the injured cartilage is often repaired with undesirable bony tissue, leading to bone growth defects in children. Using a rat tibial growth plate injury model, our previous studies have shown sequential inflammatory, fibrogenic, osteogenic and bone maturation responses involved in the bony repair. However, it remains unclear whether there is progressive accumulation of bone within the injury site and any potential degenerative changes at the adjacent non-injured area of the growth plate. This study examined effects of growth plate injury on the structure, composition and some cellular and molecular changes at the injury site and adjacent uninjured area. Micro-CT analysis revealed that while the bone volume within the injury site at day 14 was small, the bone bridge was considerably larger at the injury site by 60 days post-injury. Interestingly, formation of bone bridges in the adjacent uninjured area was detected in 60% of injured animals at day 60. Immunohistochemical analyses revealed reduced chondrocyte proliferation (PCNA labelling) but increased apoptosis (nick translation labelling) in the adjacent uninjured area. RT-PCR analysis on adjacent uninjured growth plate tissue found increased expression of osteocalcin at day 60, differential expression of apoptosis-regulatory genes and alterations in genes associated with chondrocyte proliferation/differentiation, including Sox9 and IGF-I. Therefore, this study has demonstrated progressive changes in the structure/composition of the injury site and adjacent uninjured area and identified cellular and molecular alterations or degeneration in adjacent uninjured growth plate in response to injury.

Mechanical and microarchitectural analyses of cancellous bone through experiment and computer simulation

The relationship between microarchitecture to the failure mechanism and mechanical properties can be assessed through experimental and computational methods. In this study, both methods were utilised using bovine cadavers. Twenty four samples of cancellous bone were extracted from fresh bovine and the samples were cleaned from excessive marrow. Uniaxial compression testing was performed with displacement control. After mechanical testing, each specimen was ashed in a furnace. Four of the samples were exemplarily scanned using micro-computed tomography (μCT) and three dimensional models of the cancellous bones were reconstructed for finite element simulation. The mechanical properties and the failure modes obtained from numerical simulations were then compared to the experiments. Correlations between microarchitectural parameters to the mechanical properties and failure modes were then made. The Young's modulus correlates well with the bone volume fraction with R² = 0.615 and P value 0.013. Three different types of failure modes of cancellous bone were observed: oblique fracture (21.7%), perpendicular global fracture (47.8%), and scattered localised fracture (30.4%). However, no correlations were found between the failure modes to the morphological parameters. The percentage of error between computer predictions and the actual experimental test was from 6 to 12%. These mechanical properties and information on failure modes can be used for the development of synthetic cancellous bone.

The bone architecture is enhanced with combined PTH and alendronate treatment compared to monotherapy while maintaining the state of surface mineralization in the OVX rat

This study examined the effect of PTH and alendronate alone and in combination on the bone architecture, mineralization, and estimated mechanics in the OVX rat. Female Wistar rats aged 7-9months were assigned to one of five groups: (1) sham+vehicle, (2) OVX+vehicle, (3) OVX+PTH, (4) OVX+alendronate, and (5) OVX+PTH and alendronate. Surgery was performed at baseline (week 0), and biweekly treatment (15μg/kg of alendronate and/or daily (5days/week) 40μg/kg hPTH(1-34)) was administered from week 6 to week 14. Micro-CT scans of the right proximal tibial metaphysis were made in vivo at weeks 0, 6, 8, 10, 12 and 14 and measurements of bone microarchitecture and estimated mechanical parameters (finite element analysis) were made from the images. Synchrotron radiation micro-CT scans of the proximal tibia and fourth lumbar vertebrae were conducted ex vivo at the study endpoint to determine the degree and spatial distribution of the bone mineralization. Alendronate preserved the microarchitecture after OVX, and increased cortical (9%, p<0.05) and trabecular thickness (5%, p<0.05). PTH mono- and combined therapy induced increases in cortical (25-35%, p<0.05) and trabecular thicknesses (46-48%, p<0.05), resulting in a full restoration of bone volume in the PTH group, and an increase beyond baseline in the combined group. Improvements in estimated mechanical outcomes were observed in all treatment groups by the end of the study, with the combined group experiencing the greatest increase in predicted stiffness (63%, p<0.05). Alendronate treatment increased the peak mineral content above the other treatment groups at the trabecular (tibia: 6% above PTH, 6% above combined, L4: 4% above PTH, 4% above combined) and endocortical (tibia: 4% above PTH, 3% above combined, L4: 1% above PTH, 2% above combined) surfaces, while no differences in mineralization between the PTH and combined groups were observed. Combined treatment resulted in more pronounced improvements of the bone architecture than PTH monotherapy, while maintaining the state of mineralization observed with PTH treatment.

Episcopic 3D Imaging Methods: Tools for Researching Gene Function

This work aims at describing episcopic 3D imaging methods and at discussing how these methods can contribute to researching the genetic mechanisms driving embryogenesis and tissue remodelling, and the genesis of pathologies. Several episcopic 3D imaging methods exist. The most advanced are capable of generating high-resolution volume data (voxel sizes from 0.5x0.5x1 µm upwards) of small to large embryos of model organisms and tissue samples. Beside anatomy and tissue architecture, gene expression and gene product patterns can be three dimensionally analyzed in their precise anatomical and histological context with the aid of whole mount in situ hybridization or whole mount immunohistochemical staining techniques. Episcopic 3D imaging techniques were and are employed for analyzing the precise morphological phenotype of experimentally malformed, randomly produced, or genetically engineered embryos of biomedical model organisms. It has been shown that episcopic 3D imaging also fits for describing the spatial distribution of genes and gene products during embryogenesis, and that it can be used for analyzing tissue samples of adult model animals and humans. The latter offers the possibility to use episcopic 3D imaging techniques for researching the causality and treatment of pathologies or for staging cancer. Such applications, however, are not yet routine and currently only preliminary results are available. We conclude that, although episcopic 3D imaging is in its very beginnings, it represents an upcoming methodology, which in short terms will become an indispensable tool for researching the genetic regulation of embryo development as well as the genesis of malformations and diseases.

Dependence of trabecular structure on bone quantity: a comparison between osteoarthritic and non-pathological bone

BACKGROUND

The mechanical characterization of trabecular bone is related to its structure. In order to describe the trabecular structure and to study the mechanical behavior of the trabecular tissue, several parameters are presented in the literature. Some studies suggest a possible dependence of the structure on bone volume fraction; this dependence could bias the validity of previous studies. The problem increases its complexity when pathological bone such as osteoarthritic tissue is studied, where the organization of the trabecular structure could be different if compared to the non-pathological tissue. The primary aim of this study was to evaluate the dependence between trabecular structure and bone volume fraction. The secondary aim was to compare osteoarthritic and non-pathological bone considering the correlation between structure and bone volume fraction.

METHODS

Sixty trabecular bone specimens were extracted from femoral heads of two groups of 30 Caucasian donors; an osteoarthritic group and a non-pathological group. Several structural parameters, such as bone volume fraction, direct trabecular thickness, fabric tensor eigenvalues and their normalizations, were calculated from micro-CT analysis. A statistical analysis was carried out to identify the dependences between structural parameters and bone volume fraction. The comparison between osteoarthritic bone and non-pathological bone was also performed.

FINDINGS

Only the normalized eigenvalues of the fabric tensor were not correlated to bone volume fraction (R<0.5). The first and second normalized eigenvalues were significantly different between osteoarthritic bone and non-pathological bone (respectively P<0.05 and P<0.001).

INTERPRETATION

In conclusion, orientation and anisotropy of the trabecular structure do not depend on bone volume fraction. Moreover, differences in the first and second normalized fabric tensor eigenvalues suggest in the osteoarthritic group a structure more oriented along the main trabecular direction.

Minkowski tensor shape analysis of cellular, granular and porous structures

Predicting physical properties of materials with spatially complex structures is one of the most challenging problems in material science. One key to a better understanding of such materials is the geometric characterization of their spatial structure. Minkowski tensors are tensorial shape indices that allow quantitative characterization of the anisotropy of complex materials and are particularly well suited for developing structure-property relationships for tensor-valued or orientation-dependent physical properties. They are fundamental shape indices, in some sense being the simplest generalization of the concepts of volume, surface and integral curvatures to tensor-valued quantities. Minkowski tensors are based on a solid mathematical foundation provided by integral and stochastic geometry, and are endowed with strong robustness and completeness theorems. The versatile definition of Minkowski tensors applies widely to different types of morphologies, including ordered and disordered structures. Fast linear-time algorithms are available for their computation. This article provides a practical overview of the different uses of Minkowski tensors to extract quantitative physically-relevant spatial structure information from experimental and simulated data, both in 2D and 3D. Applications are presented that quantify (a) alignment of co-polymer films by an electric field imaged by surface force microscopy; (b) local cell anisotropy of spherical bead pack models for granular matter and of closed-cell liquid foam models; (c) surface orientation in open-cell solid foams studied by X-ray tomography; and (d) defect densities and locations in molecular dynamics simulations of crystalline copper.

Patient-Specific Finite-Element Analyses of the Proximal Femur with Orthotropic Material Properties Validated by Experiments

Patient-specific high order finite-element (FE) models of human femurs based on quantitative computer tomography (QCT) with inhomogeneous orthotropic and isotropic material properties are addressed. The point-wise orthotropic properties are determined by a micromechanics (MM) based approach in conjunction with experimental observations at the osteon level, and two methods for determining the material trajectories are proposed (along organs outer surface, or along principal strains). QCT scans on four fresh-frozen human femurs were performed and high-order FE models were generated with either inhomogeneous MM-based orthotropic or empirically determined isotropic properties. In vitro experiments were conducted on the femurs by applying a simple stance position load on their head, recording strains on femurs’ surface and head’s displacements. After verifying the FE linear elastic analyses that mimic the experimental setting for numerical accuracy, we compared the FE results to the experimental observations to identify the influence of material properties on models’ predictions. The strains and displacements computed by FE models having MM-based inhomogeneous orthotropic properties match the FE-results having empirically based isotropic properties well, and both are in close agreement with the experimental results. When only the strains in the femoral neck are being compared a more pronounced difference is noticed between the isotropic and orthotropic FE result. These results lay the foundation for applying more realistic inhomogeneous orthotropic material properties in FEA of femurs.

Scaling VOI size in 3D μCT studies of trabecular bone: a test of the over-sampling hypothesis

For comparative 3D microCT studies of trabecular bone, the use of a volume of interest (VOI) scaled to body size may avoid over-sampling the trabecular mass in smaller versus larger-bodied taxa and comparison of regions that are not functionally homologous (Fajardo and Müller: Am J Phys Anthropol 115 (2001) 327-336), though the influence on quantitative analyses using scaled versus nonscaled VOIs remains poorly characterized. We compare trabecular architectural properties reflecting mass, organization, and orientation from three volumes of interest (large, scaled, and small) obtained from the distal first metacarpal in a sample of Homo (n = 10) and Pan (n = 12). We test the null hypotheses that neither absolute VOI size, nor scaling of the VOI to metacarpal size as a proxy for body size, biases intraspecific analyses nor impacts the detection of interspecific differences. These hypotheses were only partially supported. While certain properties (e.g., bone volume fraction or trabecular thickness) were not affected by varying VOI size within taxa, others were significantly impacted (e.g., intersection surface, connectivity, and structure). In comparing large versus scaled VOIs, we found that the large VOI inflated the number and/or magnitude of significant differences between Homo and Pan. In summary, our results support the use of scaled VOIs in studies of trabecular architecture.

Calcitropic hormones and IGF-I are influenced by dietary protein

Elderly men and women with protein deficiencies have low levels of circulating IGF-I, and it is likely this contributes to reduced bone formation and increased bone resorption. We hypothesized that calcitropic hormones are involved in this effect and are affected by dietary protein. We therefore investigated the influence of a low-protein diet on the PTH-1,25-dihydroxyvitamin D3 [1,25(OH)₂D₃] axis and IGF-I in rats, using pamidronate to block resorption that normally contributes to mineral homeostasis. We fed 6-month-old Sprague Dawley female rats isocaloric diets containing 2.5% or 15% casein for 2 wk. Pamidronate was then administered sc (0.6 mg/kg/) for 5 d. Blood samples were collected at different time points. Serum 1,25(OH)₂D₃, IGF-I, PTH, calcium, and phosphorus were determined in all rats; vertebral bone strength and histomorphometric analysis were performed in rats subject to the longest low-protein diets. We found 2 wk of low protein increased PTH levels, decreased 1,25(OH)₂D₃, calcium, and IGF-I, suggesting that increased PTH compensates for low-protein-induced decreases in 1,25(OH)₂D₃. Pamidronate augmented the increased PTH after 8 wk of low protein and prevented the 1,25(OH)₂D₃ decrease. IGF-I remained low. Protein malnutrition induced decreases in relative bone volume and trabecular thickness, which was prevented by pamidronate. Maximal load was reduced by protein restriction, but rescued by pamidronate. In summary, the low protein diet resulted in hyperparathyroidism, a reduction in circulating levels of IGF-I, and reduced 1,25(OH)₂D₃ despite hyperparathyroidism. Blocking resorption resulted in further increases in PTH and improved microarchitecture and biomechanical properties, irrespective of vitamin D status or protein intake.

Fabric dependence of quasi-waves in anisotropic porous media

Assessment of bone loss and osteoporosis by ultrasound systems is based on the speed of sound and broadband ultrasound attenuation of a single wave. However, the existence of a second wave in cancellous bone has been reported and its existence is an unequivocal signature of poroelastic media. To account for the fact that ultrasound is sensitive to microarchitecture as well as bone mineral density (BMD), a fabric-dependent anisotropic poroelastic wave propagation theory was recently developed for pure wave modes propagating along a plane of symmetry in an anisotropic medium. Key to this development was the inclusion of the fabric tensor--a quantitative stereological measure of the degree of structural anisotropy of bone--into the linear poroelasticity theory. In the present study, this framework is extended to the propagation of mixed wave modes along an arbitrary direction in anisotropic porous media called quasi-waves. It was found that differences between phase and group velocities are due to the anisotropy of the bone microarchitecture, and that the experimental wave velocities are more accurately predicted by the poroelastic model when the fabric tensor variable is taken into account. This poroelastic wave propagation theory represents an alternative for bone quality assessment beyond BMD.

In vivo CT quantification of trabecular bone dynamics in mice after sciatic neurectomy using monochromatic synchrotron radiation

We demonstrated the capability of in vivo synchrotron radiation CT (SRCT) in analyzing short-term changes in trabecular bone architecture (TBA) and the degree of bone mineralization (DBM) in small animals. Mice underwent unilateral sciatic neurectomy (SN) and sham operation on the contralateral side (SO) at 13 weeks of age. In vivo SRCT scans (11.7-μm cubic voxel) were made of both knees 7 and 17 days (group 1, n = 7) or only 17 days (group 2, n = 6) after surgery. In three mice in group 2, one knee was scanned twice on the same day in different orientations for reproducibility testing. Two scan data sets of the tibial proximal metaphysis acquired at different time points (group 1) or at the same time point (group 2) were registered for detecting differences in volume fraction (BV/TV), trabecular thickness (Tb.Th), trabecular number (Tb.N), connectivity density (Conn.D), and mean DBM (mDBM). The reproducibility test showed small errors of <2.5% in the TBA indexes and <3.0% in mDBM, while mismatched bone regions amounted to >25%. In group 1, Tb.Th increased but Tb.N and Conn.D decreased in both SN and SO; BV/TV and mDBM increased only in SO; accordingly, BV/TV, Tb.Th, and mDBM became lower in SN than in SO. No significant interaction between SN and irradiation was found; the SN effects on TBA and DBM were similar between groups 1 and 2, although synchrotron irradiation led to higher Tb.Th and lower Tb.N in group 1. In conclusion, in vivo SRCT has potential use for detecting short-term bone dynamics of small animals.

Trabecular bone scales allometrically in mammals and birds

Many bones are supported internally by a latticework of trabeculae. Scaling of whole bone length and diameter has been extensively investigated, but scaling of the trabecular network is not well characterized. We analysed trabecular geometry in the femora of 90 terrestrial mammalian and avian species with body masses ranging from 3 g to 3400 kg. We found that bone volume fraction does not scale substantially with animal size, while trabeculae in larger animals' femora are thicker, further apart and fewer per unit volume than in smaller animals. Finite element modelling indicates that trabecular scaling does not alter the bulk stiffness of trabecular bone, but does alter strain within trabeculae under equal applied loads. Allometry of bone's trabecular tissue may contribute to the skeleton's ability to withstand load, without incurring the physiological or mechanical costs of increasing bone mass.

Multiscale FE method for analysis of bone micro-structures

Bones are composed of hierarchical bio-composite materials characterized by complex multiscale structural geometry and behavior. The architecture and the mechanical properties of bone tissue differ at each level of hierarchy. Thus, a multiscale approach for mechanical analysis of bone is imperative. This paper proposes a new approach for 3D multiscale finite element analysis of trabecular bone that can offer physicians a "digital magnifying glass" to facilitate continuous transition between macro- and micro-scales. The approach imitates the human ability to perceive details. That is, zooming-out from an object causes fewer details to be visible. As a result, the material appears to be smoother and more homogeneous. Zooming-in, in contrast, reveals additional details and material heterogeneity. Realization of the proposed approach requires synergy between a hierarchical geometric model for representing intermediate scales and a mechanical model for local material properties of bone tissue for each scale. The geometric model facilitates seamless and continuous bi-directional transition between macro- and micro-scales, while the mechanical model preserves the effective material properties. A 2D model of a simplified trabecular structure was implemented and analyzed in order to assess the feasibility of the proposed multiscale approach. The successful results of this model led to extending the method into 3D and analyzing real trabecular structures.

Ontogenetic changes in the internal and external morphology of the ilium in modern humans

Trabecular architecture forms an important structural component of bone and, depending on the loading conditions encountered during life, is organised in a systematic, bone- and species-specific manner. However, recent studies suggested that gross trabecular arrangement (e.g. density distribution), like overall bone shape, is predetermined and/or affected by factors other than loading and perhaps less plastic than commonly assumed. To explore this issue further, the present cross-sectional ontogenetic study investigated morphological changes in external bone shape in relation to changes in trabecular bundle orientation and anisotropy. Radiographs of 73 modern human ilia were assessed using radiographic and Geometric Morphometric techniques. The study confirmed the apparently strong predetermination of trabecular bundle development, i.e. prior to external loading, although loading clearly also had an effect on overall morphology. For example, the sacro-pubic bundle, which follows the path of load transmission from the auricular surface to the acetabulum, is well defined and shows relatively high levels of anisotropy from early stages of development; the situation for the ischio-iliac strut is similar. However, while the sacro-pubic strut retains a constant relationship with the external landmarks defining the joint surfaces, the ischio-iliac bundle changes its relationship with the external landmarks and becomes aligned with the iliac tubercle only during late adolescence/early adulthood. It is tentatively proposed that the rearrangement of the ischio-iliac strut may reflect a change in locomotor pattern and/or a shift in positional behavior with increasing mass after growth of external bone dimensions has slowed/ceased.

Bone quality is partially recovered after the discontinuation of RANKL administration in rats by increased bone mass on existing trabeculae: an in vivo micro-CT study

Bone loss and recovery in a receptor activator for nuclear factor κ B ligand (RANKL)-administered rat model was assessed. Microarchitecture, mineralization and strength deteriorated faster than ovariectomy (OVX). Recovery was dependent on the loss of trabecular elements and connections. Early recovery suggests a natural mechanism in rats to overcome excess RANKL, and may have implications for long-term bone loss.

PURPOSE

To compare a model for experimental osteoporosis that induces bone loss by injecting RANKL into rats to an OVX rat model, and measure subsequent recovery of bone architecture, mineralization, and mechanics after stopping injections.

METHODS

Mature, healthy, female Wistar rats were divided into high-dose RANKL, low-dose RANKL, OVX, and vehicle control groups. The right proximal tibiae were micro-computed tomography (micro-CT) scanned in vivo every 2 weeks from week 0 to week 12 and every 4 weeks from week 12 to week 20. Bone architectural, mineralization, and mechanical changes were determined. Serum calcium, RANKL, anti-RANKL, and osteoprotegerin were measured at weeks 0, 6, and 20.

RESULTS

High-dose RANKL administration resulted in severe deterioration of the trabecular architecture (39% of baseline BV/TV), and modest decreases in tissue mineralization, bone mass, and stiffness. Bone loss occurred more rapidly than in the OVX and low-dose RANKL group, and recovery occurred prior to stopping RANKL injections. Full recovery of trabecular thickness, tissue mineralization, and cortical bone mass, partial recovery of trabecular bone volume (55% of baseline), structural model index, bone mass (69% of baseline), and stiffness (90% of baseline) but no improvement in connectivity density or trabecular number was observed.

CONCLUSION

RANKL administration resulted in rapid and dose-dependent bone loss. The recovery of trabecular bone volume and stiffness appeared to be dependent on the number of remaining trabecular elements and their interconnections. Uncontrolled recovery suggests that further investigation into the RANKL-injected rat as a model of bone loss is required.

Methodological considerations for analyzing trabecular architecture: an example from the primate hand

Micro-computed tomographic analyses of trabecular bone architecture have been used to clarify the link between positional behavior and skeletal anatomy in primates. However, there are methodological decisions associated with quantifying and comparing trabecular anatomy across taxa that vary greatly in body size and morphology that can affect characterizations of trabecular architecture, such as choice of the volume of interest (VOI) size and location. The potential effects of these decisions may be amplified in small, irregular-shaped bones of the hands and feet that have more complex external morphology and more heterogeneous trabecular structure compared to, for example, the spherical epiphysis of the femoral head. In this study we investigate the effects of changes in VOI size and location on standard trabecular parameters in two bones of the hand, the capitate and third metacarpal, in a diverse sample of nonhuman primates that vary greatly in morphology, body mass and positional behavior. Results demonstrate that changes in VOI location and, to a lesser extent, changes in VOI size had a dramatic affect on many trabecular parameters, especially trabecular connectivity and structure (rods vs. plates), degree of anisotropy, and the primary orientation of the trabeculae. Although previous research has shown that some trabecular parameters are susceptible to slight variations in methodology (e.g. VOI location, scan resolution), this study provides a quantification of these effects in hand bones of a diverse sample of primates. An a priori understanding of the inherent biases created by the choice of VOI size and particularly location is critical to robust trabecular analysis and functional interpretation, especially in small bones with complex arthroses.

Fabric dependence of wave propagation in anisotropic porous media

Current diagnosis of bone loss and osteoporosis is based on the measurement of the bone mineral density (BMD) or the apparent mass density. Unfortunately, in most clinical ultrasound densitometers: 1) measurements are often performed in a single anatomical direction, 2) only the first wave arriving to the ultrasound probe is characterized, and 3) the analysis of bone status is based on empirical relationships between measurable quantities such as speed of sound (SOS) and broadband ultrasound attenuation (BUA) and the density of the porous medium. However, the existence of a second wave in cancellous bone has been reported, which is an unequivocal signature of poroelastic media, as predicted by Biot's poroelastic wave propagation theory. In this paper, the governing equations for wave motion in the linear theory of anisotropic poroelastic materials are developed and extended to include the dependence of the constitutive relations upon fabric-a quantitative stereological measure of the degree of structural anisotropy in the pore architecture of a porous medium. This fabric-dependent anisotropic poroelastic approach is a theoretical framework to describe the microarchitectural-dependent relationship between measurable wave properties and the elastic constants of trabecular bone, and thus represents an alternative for bone quality assessment beyond BMD alone.

Preliminary radiological assessment of age-related change in the trabecular structure of the human os pubis

This preliminary study examines correlations between age-at-death and changes in the trabecular architecture of the human os pubis, utilizing continuous, quantitative data from plain film radiography, computed tomography (CT), and micro-CT scans of 65 male innominates. Radiography provides nondestructive options for assessment, digital preservation, and presentation of human skeletal remains; important for forensic and culturally sensitive archaeological materials, which must remain unmodified for opposing experts, future researchers, or repatriation and reburial. Radiographic techniques permit analysis of remains that cannot be disarticulated (e.g., religious proscription, mummies), and trabecular measures provide data where traditional surface indicators are obscured or damaged. Potentially, robust predictive models derived herein achieve R-values of 0.522, 0.447, and 0.731, respectively. Further testing of these methods may validate these techniques as further lines of evidence in age estimation, with the potential to improve on the accuracy of traditional qualitative techniques by providing quantitative, continuous variables in predicting skeletal age-at-death.

BoneJ: Free and extensible bone image analysis in ImageJ

Bone geometry is commonly measured on computed tomographic (CT) and X-ray microtomographic (μCT) images. We obtained hundreds of CT, μCT and synchrotron μCT images of bones from diverse species that needed to be analysed remote from scanning hardware, but found that available software solutions were expensive, inflexible or methodologically opaque. We implemented standard bone measurements in a novel ImageJ plugin, BoneJ, with which we analysed trabecular bone, whole bones and osteocyte lacunae. BoneJ is open source and free for anyone to download, use, modify and distribute.

Fast Tool for Evaluation of Iliac Crest Tissue Elastic Properties Using the Reduced-Basis Methods

Computationally expensive finite element (FE) methods are generally used for indirect evaluation of tissue mechanical properties of trabecular specimens, which is vital for fracture risk prediction in the elderly. This work presents the application of reduced-basis (RB) methods for rapid evaluation of simulation results. Three cylindrical transiliac crest specimens (diameter: 7.5 mm, length: 10–12 mm) were obtained from healthy subjects (20 year-old, 22 year-old, and 24 year-old females) and scanned using microcomputed tomography imaging. Cubic samples of dimensions 5×5×5 mm3 were extracted from the core of the cylindrical specimens for FE analysis. Subsequently, a FE solution library (test space) was constructed for each of the specimens by varying the material property parameters: tissue elastic modulus and Poisson’s ratio, to develop RB algorithms. The computational speed gain obtained by the RB methods and their accuracy relative to the FE analysis were evaluated. Speed gains greater than 4000 times, were obtained for all three specimens for a loss in accuracy of less than 1% in the maxima of von-Mises stress with respect to the FE-based value. The computational time decreased from more than 6 h to less than 18 s. RB algorithms can be successfully utilized for real-time reliable evaluation of trabecular bone elastic properties.

Towards quantitative 3D imaging of the osteocyte lacuno-canalicular network

Osteocytes are the most abundant cells in bone and the only cells embedded in the bone mineral matrix. They form an extended, three-dimensional (3D) network, whose processes interconnecting the cell bodies reside in thin canals, the canaliculi. Together with the osteocyte lacunae, the canaliculi form the lacuno-canalicular network (LCN). As the negative imprint of the cellular network within bone tissue, the LCN morphology is considered to play a central role for bone mechanosensation and mechanotransduction. However, the LCN has neither been visualized nor quantified in an adequate way up to now. On this account, this article summarizes the current state of knowledge of the LCN morphology and then reviews different imaging methods regarding the quantitative 3D assessment of bone tissue in general and of the LCN in particular. These imaging methods will provide new insights in the field of bone mechanosensation and mechanotransduction and thus, into processes of strain sensation and transduction, which are tightly associated with osteocyte viability and bone quality.

The neonatal ilium-metaphyseal drivers and vascular passengers

At birth the newborn is equipped with a developing locomotor apparatus, which will ultimately become involved in load transfer from the period when the child adopts a sitting posture through to the attainment of a bipedal gait. This load transfer has been considered to influence trabecular bone structural organization by setting up forces, which remodel the internal architecture into a functionally optimized form. However, during the neonatal developmental period the locomotor apparatus is nonweight bearing and instead only supports reflexive movements. Surprisingly, a structural organization has been identified within the internal trabecular architecture and external cortical morphology of the neonatal ilium, which appears to mimic the structural composition of the more mature bone. This study aims to build upon previous qualitative and quantitative investigation of this apparently precocious patterning by further examining structural data obtained from selected volumes of interest within the ilium. Analysis has revealed statistically significant differences in regional trabecular and cortical bone characteristics, which have formed the basis of a possible growth model for the ilium. Volumetric comparison has demonstrated the presence of three progressive "growth regions" and three "restricted growth regions," which appear to relate to metaphyseal and nonmetaphyseal borders of the ilium. Therefore, the structural data and statistical analysis presented in this study challenge the current concept of implied centrifugal ossification within the human ilium and present evidence of an alternative pattern of ossification that is largely dictated and controlled by vascular distribution and growth plate position.

Maternal high-fat diet: effects on offspring bone structure

Peak bone mass is believed to partly be programmed in utero. Mouse dams and offspring were given a high-fat diet and offspring studied as adults. Female offspring from high-fat dams exhibited altered trabecular structure indicative of in utero programming. In utero nutrition has consequences in later life.

INTRODUCTION

Epidemiological studies suggest that skeletal growth is programmed during intrauterine and early postnatal life. We hypothesise that development of optimal peak bone mass has, in part, a foetal origin and investigated this using a mouse model of maternal dietary fat excess.

METHODS

Offspring from mouse dams fed either standard chow (C) or lifetime high-fat diet (HF) were maintained on a HF diet to adulthood. Femur samples were taken at 30 weeks of age and bone structure, adiposity and strength analysed. Sample sizes were four to six for each sex and each diet group.

RESULTS

Offspring from HF-fed dams showed increased adiposity in the femur in comparison to offspring from C-fed dams. Female offspring from HF dams exhibited altered trabecular structure indicative of in utero programming.

CONCLUSIONS

A maternal HF diet during pregnancy increases bone marrow adiposity and alters bone structure in their offspring.

Micro-computed tomography-based highly automated 3D segmentation of the rat spine for quantitative analysis of metastatic disease

Noninvasive evaluation of metastatic disease in the spine has generally been limited to 2D qualitative or semiquantitative analysis techniques. This study aims to develop and evaluate a highly automated micro-CT-based quantitative analysis tool that can measure the architectural impact of metastatic involvement in whole vertebrae. Micro-CT analysis of rat whole vertebrae was conducted using a combination of demons deformable registration, level set curvature evolution, and intensity based thresholding techniques along with upsampling and edge enhancement techniques. The algorithm was applied to 6 lumbar vertebrae (L1-3) from 6 rnu/rnu rats (3 healthy rats and 3 with metastatic involvement). Osteolytic metastatic involvement was modeled via MT1 human breast cancer cells. Excellent volumetric concurrency was achieved in comparing the automated micro-CT-based segmentations of the whole vertebrae, trabecular centrums, and individual trabecular networks to manual segmentations (98.9%, 96.1%, and 98.3%, respectively; 6 specimens), and the automated segmentations were achieved in a fraction of the time. The algorithm successfully accounted for discontinuities in the cortical shell caused by vasculature and osteolytic destruction. As such, this work demonstrates the potential of this highly automated segmentation tool to permit rapid precise quantitative structural analysis of the spine with minimum user interaction in the analysis of both healthy and pathological (metastatically involved) vertebrae. Future optimization and the incorporation of lower-resolution imaging parameters may allow automated analysis of clinical CT-based measures in addition to preclinical micro-CT-based analyses of the structural impact and progression of pathological processes in the spine.

Trabecular bone structure in the humeral and femoral heads of anthropoid primates

The functional significance of three-dimensional trabecular bone architecture in the primate postcranial skeleton has received significant interest over the last decade. Some previous work has produced promising results, finding significant relationships between femoral head trabecular bone structure and hypothesized locomotor loading in leaping and nonleaping strepsirrhines. Conversely, most studies of anthropoid femoral head bone structure have found broad similarity across taxonomic and locomotor groups. The goal of this study is to expand on past analyses of anthropoid trabecular bone structure by assessing the effects of differential limb usage on the trabecular bone architecture of the forelimb and hindlimb across taxa characterized by diverse locomotor behaviors, including brachiation, quadrupedalism, and climbing. High-resolution x-ray computed tomography scans were collected from the proximal humerus and proximal femur of 55 individuals from five anthropoid primate species, including Symphalangus syndactylus, Papio sp., Presbytis rubicunda, Alouatta caraya, and Pan troglodytes. Trabecular bone structural features including bone volume fraction, anisotropy, trabecular thickness, and trabecular number were quantified in large volumes positioned in the center of the humeral or femoral head. Femoral head trabecular bone volume is consistently and significantly higher than trabecular bone volume in the humerus in all taxa independent of locomotor behavior. Humeral trabecular bone is more isotropic than femoral trabecular bone in all species sampled, possibly reflecting the emphasis on a mobile shoulder joint and manipulative forelimb. The results indicate broad similarity in trabecular bone structure in these bones across anthropoids.

Guidelines for assessment of bone microstructure in rodents using micro-computed tomography

Use of high-resolution micro-computed tomography (microCT) imaging to assess trabecular and cortical bone morphology has grown immensely. There are several commercially available microCT systems, each with different approaches to image acquisition, evaluation, and reporting of outcomes. This lack of consistency makes it difficult to interpret reported results and to compare findings across different studies. This article addresses this critical need for standardized terminology and consistent reporting of parameters related to image acquisition and analysis, and key outcome assessments, particularly with respect to ex vivo analysis of rodent specimens. Thus the guidelines herein provide recommendations regarding (1) standardized terminology and units, (2) information to be included in describing the methods for a given experiment, and (3) a minimal set of outcome variables that should be reported. Whereas the specific research objective will determine the experimental design, these guidelines are intended to ensure accurate and consistent reporting of microCT-derived bone morphometry and density measurements. In particular, the methods section for papers that present microCT-based outcomes must include details of the following scan aspects: (1) image acquisition, including the scanning medium, X-ray tube potential, and voxel size, as well as clear descriptions of the size and location of the volume of interest and the method used to delineate trabecular and cortical bone regions, and (2) image processing, including the algorithms used for image filtration and the approach used for image segmentation. Morphometric analyses should be based on 3D algorithms that do not rely on assumptions about the underlying structure whenever possible. When reporting microCT results, the minimal set of variables that should be used to describe trabecular bone morphometry includes bone volume fraction and trabecular number, thickness, and separation. The minimal set of variables that should be used to describe cortical bone morphometry includes total cross-sectional area, cortical bone area, cortical bone area fraction, and cortical thickness. Other variables also may be appropriate depending on the research question and technical quality of the scan. Standard nomenclature, outlined in this article, should be followed for reporting of results.

Age- and gender-dependent changes in three-dimensional microstructure of cortical and trabecular bone at the human femoral neck

We investigated age- and gender-related variation of both cortical and trabecular microstructure in human femoral neck. We found that age-related change of cortical porosity is more noticeable than that of trabecular parameter. Our data may help to gain more insight into the potential mechanism of osteoporotic femoral neck fractures.

INTRODUCTION

Variations in the microstructure of cortical and trabecular bone contribute to decreased bone strength. Age- and gender-related changes in cortical and trabecular microstructure of femoral neck is unclear. The aim of this study was to identify three-dimensional (3D) microstructural changes of both cortical and trabecular bone simultaneously in human femoral neck with age and gender, using micro-computed tomography (micro-CT). We hypothesized that there would be differences in age-related changes of cortical and trabecular bone for both women and men.

METHODS

We used 56 femoral necks of 28 women and men (57-98 years of age) from a Japanese population. The subjects were chosen to give an even age and gender distribution. Both women and men were divided into three age groups: middle (57-68 years), old (72-82 years), and elderly (87-98 years) groups. We examined cortical bone specimen from the inferior sector of femoral neck and trabecular bone specimen from the middle of femoral neck using micro-CT and 3D bone analysis software.

RESULTS

Cortical thickness (Ct.Th) decreased by 10-15%, cortical porosity (Ca.V/TV) almost doubled, and canal diameter (Ca.Dm) increased by 65-77% between the middle-aged and elderly groups for both women and men. The trabecular bone volume fraction (BV/TV) decreased by around 20%; trabecular thickness (Tb.Th), trabecular number (Tb.N), and connectivity density (Conn.D) decreased; and trabecular separation (Tb.Sp) and structure model index (SMI) increased with age for both women and men. As compared with women, men had higher Ct.Th and BV/TV and lower Ca.V/TV and Ca.Dm among three age groups. There was a significant inverse correlation between Ca.V.TV and BV/TV for both women and men.

CONCLUSION

Our findings indicate that Ct.Th and BV/TV decreased, and Ca.V/TV and Ca.Dm increased in femoral neck with age for both women and men. The most obvious age-related change is the increase of Ca.V/TV. The decrease of BV/TV with age is more noticeable than that of Ct.Th. This is the first study that has provided both cortical and trabecular microstructural data simultaneously in a Japanese sample. These data may help us to gain more insight into the potential mechanism of osteoporotic femoral neck fractures.

Reconstruction of canine mandibular bone defects using a bone transport reconstruction plate

OBJECTIVES

Reconstruction of mandibular segmental bone defects is a challenging task. This study tests a new device used for reconstructing mandibular defects based on the principle of bone transport distraction osteogenesis.

METHODS

Thirteen beagle dogs were divided into control and experimental groups. In all animals, a 3-cm defect was created on one side of the mandible. In 8 control animals, the defect was stabilized with a reconstruction plate without further reconstruction and the animals were killed 2 to 3 months after surgery. The remaining 5 animals were reconstructed with a bone transport reconstruction plate, comprising a reconstruction plate with attached intraoral transport unit, and were killed after 1 month of consolidation.

RESULTS

Clinical evaluation, cone-beam CT densitometry, three-dimensional histomorphometry, and docking site histology revealed significant new bone formation within the defect in the distracted group.

CONCLUSION

The physical dimensions and architectural parameters of the new bone were comparable to the contralateral normal bone. Bone union at the docking site remains a problem.

Micro computed tomography for vascular exploration

Vascular exploration of small animals requires imaging hardware with a very high spatial resolution, capable of differentiating large as well as small vessels, in both in vivo and ex vivo studies. Micro Computed Tomography (micro-CT) has emerged in recent years as the preferred modality for this purpose, providing high resolution 3D volumetric data suitable for analysis, quantification, validation, and visualization of results. The usefulness of micro-CT, however, can be adversely affected by a range of factors including physical animal preparation, numerical quantification, visualization of results, and quantification software with limited possibilities. Exacerbating these inherent difficulties is the lack of a unified standard for micro-CT imaging. Most micro-CT today is aimed at particular applications and the software tools needed for quantification, developed mainly by imaging hardware manufacturers, lack the level of detail needed to address more specific aims. This review highlights the capabilities of micro-CT for vascular exploration, describes the current state of imaging protocols, and offers guidelines and suggestions aimed at making micro-CT more accurate, replicable, and robust.

Hydroxyapatite whisker-reinforced polyetherketoneketone bone ingrowth scaffolds

Hydroxyapatite (HA) whisker-reinforced polyetherketoneketone (PEKK) bone ingrowth scaffolds were prepared and characterized. High levels of porosity (75-90%) and HA whisker reinforcement (0-40 vol.%) were attained using a powder processing approach to mix the HA whiskers, PEKK powder and a NaCl porogen, followed by compression molding at 350-375 degrees Celsius and particle leaching to remove the porogen. The scaffold architecture and microstructure exhibited characteristics known to be favorable for osteointegration. Scaffold porosity was interconnected with a mean pore size in the range 200-300 microm as measured by micro-computed tomography. HA whiskers were embedded within and exposed on the surface of scaffold struts, producing a microscale surface topography, shown by von Kossa staining and scanning electron microscopy. Therefore, HA whisker-reinforced PEKK bone ingrowth scaffolds may be advantageous for orthopedic implant fixation, including interbody spinal fusion.

Particle seeding enhances interconnectivity in polymeric scaffolds foamed using supercritical CO(2)

Foaming using supercritical CO(2) is a well-known process for the production of polymeric scaffolds for tissue engineering. However, this method typically leads to scaffolds with low pore interconnectivity, resulting in insufficient mass transport and a heterogeneous distribution of cells. In this study, microparticulate silica was added to the polymer during processing and the effects of this particulate seeding on the interconnectivity of the pore structure and pore size distribution were investigated. Scaffolds comprising polylactide and a range of silica contents (0-50 wt.%) were produced by foaming with supercritical CO(2). Scaffold structure, pore size distributions and interconnectivity were assessed using X-ray computed microtomography. Interconnectivity was also determined through physical measurements. It was found that incorporation of increasing quantities of silica particles increased the interconnectivity of the scaffold pore structure. The pore size distribution was also reduced through the addition of silica, while total porosity was found to be largely independent of silica content. Physical measurements and those derived from X-ray computed microtomography were comparable. The conclusion drawn was that the architecture of foamed polymeric scaffolds can be advantageously manipulated through the incorporation of silica microparticles. The findings of this study further establish supercritical fluid foaming as an important tool in scaffold production and show how a previous limitation can be overcome.

Glucocorticoid induced osteopenia in cancellous bone of sheep: validation of large animal model for spine fusion and biomaterial research

STUDY DESIGN

Glucocorticoid with low calcium and phosphorus intake induces osteopenia in cancellous bone of sheep.

OBJECTIVE

To validate a large animal model for spine fusion and biomaterial research.

SUMMARY OF BACKGROUND DATA

A variety of ovariectomized animals has been used to study osteoporosis. Most experimental spine fusions were based on normal animals, and there is a great need for suitable large animal models with adequate bone size that closely resemble osteoporosis in humans.

METHODS

Eighteen female skeletal mature sheep were randomly allocated into 3 groups, 6 each. Group 1 (GC-1) received prednisolone (GC) treatment (0.60 mg/kg/day, 5 times weekly) for 7 months. Group 2 (GC-2) received the same treatment as GC-1 for 7 months followed by 3 months without treatment. Group 3 was left untreated and served as the controls. All sheep received restricted diet with low calcium and phosphorus during experiment. After killing the animals, cancellous bone specimens from the vertebra, femurs, and tibias were micro-CT scanned and tested mechanically. Serum biomarkers were determined.

RESULTS

In lumbar vertebra, the GC treatment resulted in significant decrease of cancellous bone volume fraction and trabecular thickness, and bone strength. However, the microarchitecture and bone strength of GC-2 recovered to a similar level of the controls. A similar trend of microarchitectural changes was also observed in the distal femur and proximal tibia of both GC treated sheep. The bone formation marker serum-osteocalcin was largely reduced in GC-1 compared to the controls, but recovered with a rebound increase at month 10 in GC-2.

CONCLUSION

The current investigation demonstrates that the changes in microarchitecture and mechanical properties were comparable with those observed in humans after long-term GC treatment. A prolonged GC treatment is needed for a long-term observation to keep osteopenic bone. This model resembles long-term glucocorticoid treated osteoporotic model, and is useful in preclinical studies.

Microarchitectural adaptations in aging and osteoarthrotic subchondral bone issues

The human skeleton optimizes its microarchitecture by elaborate adaptations to mechanical loading during development and growth. The mechanisms for adaptation involve a multistep process of cellular mechanotransduction stimulating bone modelling, and remodeling resulting in either bone formation or resorption. This process causes appropriate microarchitectural changes tending to adjust and improve the bone structure to its prevailing mechanical environment. Normal individual reaches peak bone mass at age between 25 and 30 years, and thereafter bone mass declines with age in both genders. The bone loss is accompanied by microarchitectural deterioration resulting in reduced mechanical strength likely leading to fragility fractures. With aging, inevitable bone loss occurs, which is frequently the cause of osteoporosis; and inevitable bone and joint degeneration happens, which often results in osteoarthrosis. These diseases are among the major health care problems in terms of socio-economic costs. The overall goals of the current series of studies were to investigate the age-related and osteoarthrosis (OA) related changes in the 3-D microarchitectural properties, mechanical properties, collagen and mineral quality of subchondral cancellous and cortical bone tissues. The studies included mainly two parts. For human subjects: aging- (I–IV) and early OArelated (V–VI) changes in cancellous bone properties were assessed. For OA guinea pig models (VII–IX), three topics were studied: firstly, the spontaneous, age-related development of guinea pig OA; secondly, the potential effects of hyaluronan on OA subchondral bone tissues; and thirdly, the effects on OA progression of an increase in subchondral bone density by inhibition of bone remodeling with a bisphosphonate. These investigations aimed to obtain more insight into the age-related and OA-related subchondral bone adaptations.

Cancellous bone volume is an indicator for trabecular bone connectivity in dialysis patients

BACKGROUND AND OBJECTIVES

A new assessment system for bone histology, termed the turnover-mineralization-volume system, is advocated for patients with chronic kidney disease-related mineral and bone disorder. The system measures cancellous bone volume (BV/TV) as a third major evaluation axis; however, the physiologic significance of BV/TV remains unclear.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Conventional bone histomorphometry was performed in 75 iliac bone samples obtained from dialysis patients. In 47 of the 75 samples, the remaining samples were subjected to direct microfocus x-ray computed tomographic observation. Quantitative morphologic examinations, including micro-bone mineral densitometry, and marrow space star volume, Euler number, and node-strut analyses, were performed in the virtual three-dimensional space reconstructed from the microfocus x-ray computed tomographic images.

RESULTS

The levels of BV/TV were comparable in each of the conventional bone histomorphometric criteria. No significant correlations were found between BV/TV and other parameters. Two- and three-dimensional BV/TVs were significantly correlated with cancellous bone mass but not with cortical bone thickness or cortical bone mass. Two- and three-dimensional BV/TVs were significantly correlated with trabecular bone connectivity as determined by marrow space star volume, Euler number, and node-strut analyses.

CONCLUSIONS

In dialysis patients, BV/TV is not dependent on bone turnover or bone mineralization. BV/TV is unlikely to indicate the balance between bone formation and bone resorption. Instead, it reflects trabecular bone connectivity, and improved trabecular bone connectivity is physiologically beneficial in terms of bone quality. The turnover-mineralization-volume system offers an advantage over the conventional system for the assessment of bone quality.