Correlation of bone mineral density with strength and microstructural parameters of cortical bone in vitro

Mineral and cross-linking in collagen fibrils: The mechanical behavior of bone tissue at the nano-scale

The mineralized collagen fibril is the main building block of hard tissues and it directly affects the macroscopic mechanics of biological tissues such as bone. The mechanical behavior of the fibril itself is determined by its structure: the content of collagen molecules, minerals, and cross-links, and the mechanical interactions and properties of these components. Advanced glycation end products (AGEs) form cross-links between tropocollagen molecules within the collagen fibril and are one important factor that is believed to have a major influence on the tissue. For instance, it has been shown that brittleness in bone correlates with increased AGEs densities. However, the underlying nano-scale mechanisms within the mineralized collagen fibril remain unknown. Here, we study the effect of mineral and AGEs cross-linking on fibril deformation and fracture behavior by performing destructive tensile tests using coarse-grained molecular dynamics simulations. Our results demonstrate that after exceeding a critical content of mineral, it induces stiffening of the collagen fibril at high strain levels. We show that mineral morphology and location affect collagen fibril mechanics: The mineral content at which this stiffening occurs depends on the mineral's location and morphology. Further, both, increasing AGEs density and mineral content lead to stiffening and increased peak stresses. At low mineral contents, the mechanical response of the fibril is dominated by the AGEs, while at high mineral contents, the mineral itself determines fibril mechanics.

Effect of the Material Properties and Knee Position to the Bone Bruise Pattern in Skeletally Mature and Immature Subjects

A bone bruise is generated by a bony collision that could occur when the anterior cruciate ligament (ACL) is injured, and its pattern reflects the injury mechanism and skeletal maturity. Thus, the bone bruise pattern is useful to predict a subject-specific injury mechanism, although the sensitivity and/or effect of the material property and the knee position at injury is still unclear. The objective of the present study was to determine the effect of the material property and knee position on the bone bruise pattern in skeletally mature and immature subjects using finite element analysis. Finite element models were created from a magnetic resonance (MR) image in the sagittal plane of a skeletally mature (25 y. o.) and immature (9 y. o.) male subject. The femur and tibia were collided at 2 m/s to simulate the impact trauma and determine the maximum principal stress. The analysis was performed at 15, 30, and 45 deg of knee flexion, and neutral, 10 mm anterior and posterior translated position at each knee flexion angle. Although high stress was distributed toward the metaphysis area in the mature model, the stress did not cross the growth plate in the immature model. The size of the stress area was larger in the mature model than those in the immature model. The location of the stress area changed depending on the joint position. Young's modulus of cartilage and trabecular bone also affected the location of the stress area. The Young's modulus for the cartilage affected peak stress during impact, while the size of the stress area had almost no change. These results indicate that the bone bruise pattern is strongly associated with subject-specific parameters. In addition, the bone bruise pattern was affected not only by knee position but also by tissue qualities. In conclusion, although the bone bruise distribution was generally called footprint of the injury, the combined evaluation of the quality of the structure and the bone bruise distribution is necessary for properly diagnosing tissue injury based on the MR imaging.

The Biomechanics of Musculoskeletal Tissues during Activities of Daily Living: Dynamic Assessment Using Quantitative Transmission-Mode Ultrasound Techniques

The measurement of musculoskeletal tissue properties and loading patterns during physical activity is important for understanding the adaptation mechanisms of tissues such as bone, tendon, and muscle tissues, particularly with injury and repair. Although the properties and loading of these connective tissues have been quantified using direct measurement techniques, these methods are highly invasive and often prevent or interfere with normal activity patterns. Indirect biomechanical methods, such as estimates based on electromyography, ultrasound, and inverse dynamics, are used more widely but are known to yield different parameter values than direct measurements. Through a series of literature searches of electronic databases, including Pubmed, Embase, Web of Science, and IEEE Explore, this paper reviews current methods used for the in vivo measurement of human musculoskeletal tissue and describes the operating principals, application, and emerging research findings gained from the use of quantitative transmission-mode ultrasound measurement techniques to non-invasively characterize human bone, tendon, and muscle properties at rest and during activities of daily living. In contrast to standard ultrasound imaging approaches, these techniques assess the interaction between ultrasound compression waves and connective tissues to provide quantifiable parameters associated with the structure, instantaneous elastic modulus, and density of tissues. By taking advantage of the physical relationship between the axial velocity of ultrasound compression waves and the instantaneous modulus of the propagation material, these techniques can also be used to estimate the in vivo loading environment of relatively superficial soft connective tissues during sports and activities of daily living. This paper highlights key findings from clinical studies in which quantitative transmission-mode ultrasound has been used to measure the properties and loading of bone, tendon, and muscle tissue during common physical activities in healthy and pathological populations.

Method for Evaluating Cortical Bone Young's Modulus: Numerical Twin Reconstruction, Finite Element Calculation, and Microstructure Analysis

The determination of bone mechanical properties remains crucial, especially to feed up numerical models. An original methodology of inverse analysis has been developed to determine the longitudinal elastic modulus of femoral cortical bone. The method is based on a numerical twin of a specific three-point bending test. It has been designed to be reproducible on each test result. In addition, the biofidelity of the geometric acquisition method has been quantified. As the assessment is performed at the scale of a bone shaft segment, the Young's modulus values obtained (between 9518.29 MPa and 14181.15 MPa) are considered average values for the whole tissue, highlighting some intersubject variability. The material microstructure has also been studied through histological analysis, and bone-to-bone comparisons highlighted discrepancies in quadrants microstructures. Furthermore, significant intrasubject variability exists since differences between the bone's medial-lateral and anterior-posterior quadrants have been observed. Thus, the study of microstructures can largely explain the differences between the elastic modulus values obtained. However, a more in-depth study of bone mineral density would also be necessary and would provide some additional information. This study is currently being setup, alongside an investigation of the local variations of the elastic modulus.

Finite element analysis of bone mechanical properties using MRI-derived bound and pore water concentration maps

Ultrashort echo time (UTE) MRI techniques can be used to image the concentration of water in bones. Particularly, quantitative MRI imaging of collagen-bound water concentration (Cbw) and pore water concentration (Cpw) in cortical bone have been shown as potential biomarkers for bone fracture risk. To investigate the effect of Cbw and Cpw on the evaluation of bone mechanical properties, MRI-based finite element models of cadaver radii were generated with tissue material properties derived from 3 D maps of Cbw and Cpw measurements. Three-point bending tests were simulated by means of the finite element method to predict bending properties of the bone and the results were compared with those from direct mechanical testing. The study results demonstrate that these MRI-derived measures of Cbw and Cpw improve the prediction of bone mechanical properties in cadaver radii and have the potential to be useful in assessing patient-specific bone fragility risk.

Twelve Months of Denosumab and/or Alendronate Is Associated With Improved Bone Fatigue Life, Microarchitecture, and Density in Ovariectomized Cynomolgus Monkeys

Prolonged use of antiresorptives such as the bisphosphonate alendronate (ALN) and the RANKL inhibitor denosumab (DMAb) are associated with rare cases of atypical femoral fracture (AFF). The etiology of AFF is unclear, but it has been hypothesized that potent osteoclast inhibitors may reduce bone fatigue resistance. The purpose of this study was to quantify the relationship between antiresorptive treatment and fatigue life (cycles to failure) in bone from ovariectomized cynomolgus monkeys. We analyzed humeral bone from 30 animals across five treatment groups. Animals were treated for 12 months with subcutaneous (sc) vehicle (VEH), sc DMAb (25 mg/kg/month), or intravenous (iv) ALN (50 μg/kg/month). Another group received 6 months VEH followed by 6 months DMAb (VEH-DMAb), and the final group received 6 months ALN followed by 6 months DMAb (ALN-DMAb). A total of 240 cortical beam samples were cyclically tested in four-point bending at 80, 100, 120, or 140 MPa peak stress. High-resolution imaging and density measurements were performed to evaluate bone microstructure and composition. Samples from the ALN (p = 0.014), ALN-DMAb (p = 0.008), and DMAb (p < 0.001) groups illustrated higher fatigue-life measurements than VEH. For example, at 140 MPa the VEH group demonstrated a median ± interquartile range (IQR) fatigue life of 1987 ± 10593 cycles, while animals in the ALN, ALN-DMAb, and DMAb groups survived 9850 ± 13648 (+395% versus VEH), 10493 ± 16796 (+428%), and 14495 ± 49299 (+629%) cycles, respectively. All antiresorptive treatment groups demonstrated lower porosity, smaller pore size, greater pore spacing, and lower number of canals versus VEH (p < 0.001). Antiresorptive treatment was also associated with greater apparent density, dry density, and ash density (p ≤ 0.03). We did not detect detrimental changes following antiresorptive treatments that would explain their association with AFF. In contrast, 12 months of treatment may have a protective effect against fatigue fractures. © 2022 American Society for Bone and Mineral Research (ASBMR).

Tracking changes of individual cortical pores over 1 year via HR-pQCT in a small cohort of 60-year-old females

Introduction

High-resolution peripheral quantitative computed tomography (HR-pQCT) is a powerful tool that has revolutionized 3D longitudinal assessment of bone microarchitecture. However, cortical porosity, a common characteristic of cortical bone loss, is still often determined by static evaluation of overall porosity at one timepoint. Therefore, we sought to 1) describe a technique to evaluate individual cortical pore dynamics in aging females over one year using HR-pQCT imaging and 2) determine whether formation and expansion of pores would exceed contraction and infilling of pores.

Methods

HR-pQCT (60.7 μm resolution) images were acquired one year apart at the distal tibia and distal radius in seven female volunteers (60-72 years of age). Baseline and one-year images were registered at each bone site and a custom software was used to quantify dynamic activity of individual cortical pores using the following categories: developed, infilled, expanded, contracted, and static.

Results

Over the one-year period, cortical pores actively developed, contracted, expanded, and infilled. More pores expanded and developed vs. infilled or contracted leading to increased pore area in both tibial and radial sites (p = 0.0034 and p = 0.0474, respectively). Closed pores in the tibia, those that were not connected to the endosteal or periosteal surfaces, were the most dynamic of any pores type (open/closed) at either bone site.

Conclusion

This study demonstrates an approach to longitudinally track individual cortical pore activity in tibial and radial sites. These data expand conventional parameters for assessing cortical porosity and show increased porosity in one year of aging is caused by newly developed pores and expansion of existing pores.

HR-pQCT parameters of the distal radius correlate with the bending strength of the radial diaphysis

High resolution, peripheral quantitative computed tomography (HR-pQCT) scanners can now characterize an individual's trabecular architecture, cortical structure, and volumetric bone mineral density at a nominal resolution of 61 μm. While predictions of failure load of the distal radius and tibial diaphysis in compression by finite element analysis (FEA) of HR-pQCT scans have been validated against mechanical tests of cadaveric bones in compression, namely for images with nominal resolutions of 82 μm and 165 μm, the HR-pQCT parameters that best predict bending strength of cortical bone remain unknown. Therefore, we scanned cadaveric forearms from 31 elderly donors (Female: 72.8 ± 8.8 years and Male: 72.1 ± 6.3 years), and then loaded the radial diaphysis to failure in three-point bending after denuding each bone (38 in total). The cortical parameters had stronger correlations with ultimate moment than the trabecular parameters such that cortical area and estimated failure load of the distal radius had the highest Spearman correlation coefficients (r = 0.89 and r = 0.81, respectively, p < 0.0001). Despite being a known determinant of bone strength, cortical porosity of the distal radius did not correlate with ultimate moment (p = 0.8537). In multivariate linear regressions with section modulus (SM) of the radial diaphysis as one of two predictors of bending strength, cortical area and cortical thickness were each significant contributors to the prediction of ultimate moment. Their contribution was one-half and one-third, respectively, of the contribution from SM. None of the HR-pQCT parameters were strongly correlated with post-yield displacement, an indicator of bone brittleness. In support of HR-pQCT imaging of the distal radius to identify individuals with osteoporosis, the present study found that parameters of the cortex and failure load predictions by linear FEA are strongly related to the bending strength of cortical bone.

Spatial assessment of femoral neck bone density and microstructure in hip osteoarthritis

Osteoarthritis (OA) is known to involve profound changes in bone density and microstructure near to, and even distal to, the joint. Critically, however, a full, spatial picture of these abnormalities has not been well documented in a quantitative fashion in hip OA. Here, micro-computed tomography (44.8 μm/voxel) and data-driven computational anatomy were used to generate 3-D maps of the distribution of bone density and microstructure in human femoral neck samples with early (6F/4M, mean age = 51.3 years), moderate (14F/8M, mean age = 60 years), and severe (16F/6M, mean age = 63.3 years) radiographic OA. With increasing severity of radiographic OA, there was decreased cortical bone mineral density (BMD) (p=0.003), increased cortical thickness (p=0.001), increased cortical porosity (p=0.0028), and increased cortical cross-sectional area (p=0.0012, due to an increase in periosteal radius (p=0.018)), with no differences detected in the total femoral neck or trabecular compartment measures. No OA-related region-specific differences were detected through Statistical Parametric Mapping, but there were trends towards decreased tissue mineral density (TMD) in the inferior femoral neck with increasing OA severity (0.050 < p ≤ 0.091), possibly due to osteophytes. Overall, the lack of differences in cortical TMD among radiographic OA groups indicated that the decrease in cortical BMD with increasing OA severity was largely due to the increased cortical porosity rather than decreased tissue mineralization. As porosity is inversely associated with stiffness and strength in cortical bone, increased porosity may offset the effect that increased cortical cross-sectional area would be expected to have on reducing stresses within the femoral neck. The use of high-resolution imaging and quantitative spatial assessment in this study provide insight into the heterogeneous and multi-faceted changes in density and microstructure in hip OA, which have implications for OA progression and fracture risk.

A review on properties of magnesium-based alloys for biomedical applications

With changing lifestyles, the demand for bone implantation has been increasing day by day. The deficiency of nutritious elements within the human body results in certain diseases like osteoporosis, rickets, and other skeletal disorders; lack of physical activities; and the increasing number of accidents are the primary reasons for bone damage/fracture. Metallic implants made up of chrome steel, cobalt-based alloys, and titanium-based alloys are being majorly used worldwide owing to their high strength and high corrosion resistance which makes them permanent orthopedic bioimplant materials, however, they display a stress-shielding effect and it also requires an implant removal surgery. Thus, these problems can be addressed through the employment of biodegradable materials. Among the available biodegradable metallic materials, Mg alloys have been identified as a prospective orthopedic implant material. These alloys are biodegradable as well as biocompatible, however, they experience a relatively higher rate of degradation limiting their usability as implant material. This study attempts to comprehensively assess the effects of various alloying elements such as Ca, Zn, Sn, Mn, Sr and Rare earth elements (REEs) on the mechanical and degradation behavior (bothin vivoandin vitro) of Mg alloys. Since the microstructure, mechanical properties and degradation response of the Mg alloys are dependent on the processing route, hence detailed processing- property database of different Mg alloys is provided in this paper.

Bone Stress Evaluation with and without Cortical Bone Using Several Dental Restorative Materials Subjected to Impact Load: A Fully 3D Transient Finite-Element Study

Statement of problem. Previous peri-implantitis, peri-implant bone regeneration, or immediate implant placement postextraction may be responsible for the absence of cortical bone. Single crown materials are then relevant when dynamic forces are transferred into bone tissue and, therefore, the presence (or absence) of cortical bone can affect the long-term survival of the implant. Purpose: the purpose of this study is to assess the biomechanical response of dental rehabilitation when selecting different crown materials in models with and without cortical bone. Methods: several crown materials were considered for modeling six types of crown rehabilitation: full metal (MET), metal-ceramic (MCER), metal-composite (MCOM), peek-composite (PKCOM), carbon fiber-composite (FCOM), and carbon fiber-ceramic (FCCER). An impact-load dynamic finite-element analysis was carried out on all the 3D models of crowns mentioned above to assess their mechanical behavior against dynamic excitation. Implant-crown rehabilitation models with and without cortical bone were analyzed to compare how the load-impact actions affect both type of models. Results: numerical simulation results showed important differences in bone tissue stresses. The results show that flexible restorative materials reduce the stress on the bone and would be especially recommendable in the absence of cortical bone. Conclusions: this study demonstrated that more stress is transferred to the bone when stiffer materials (metal and/or ceramic) are used in implant supported rehabilitations; conversely, more flexible materials transfer less stress to the implant connection. Also, in implant-supported rehabilitations, more stress is transferred to the bone by dynamic forces when cortical bone is absent.

An examination of histomorphometric relationships in the anterior and posterior human femoral cortex

INTRODUCTION

Static cortical bone histomorphometry utilised in forensic age-at-death estimation generally examines only the anterior femoral mid-shaft, as biomechanical strain at the posterior femur is thought to result in increased bone remodelling, osteon density and adversely affect age-at-death estimates. As osteon density increases there is a corresponding decrease in geometric variables, such as osteon area and Haversian canal diameter. The present study tests whether the inverse relationship between osteon density and osteon geometry is reflected in a modern documented Australian sample, and if this relationship differs between the anterior and posterior femoral mid-shaft.

MATERIALS AND METHODS

The study sample comprises 215 femoral microradiographs (117♂ 98♀) of recorded age (18‒97 years) from the Melbourne Femur Reference Collection (MFRC). The following variables were measured in Image J across six 1 mm² regions of interest (ROIs) from the anterior and posterior; mean intact and fragmentary secondary osteon count, osteon population density, osteon and Haversian canal area, perimeter, and diameter.

RESULTS

Osteon area was positively correlated with Haversian canal size and shape metrics, and negatively correlated with osteon density. Chronological age was significantly correlated with most variables. There were significant between-group effects between the youngest (18‒34 years) and all other age groups (35‒49, 50-74 and 75 + years) for both regions.

CONCLUSION

Our findings support an increased rate of remodelling associated with decreases in osteon geometry in the anterior and posterior femur. Future studies should examine static osteon histomorphometry using anterior and posterior measurements in larger samples of documented age and sex.

A comparison of rib cortical bone compressive and tensile material properties: Trends with age, sex, and loading rate

The objectives of this study were to develop novel methods for quantifying human rib cortical bone material properties in compression and to compare the compressive material property data to existing tensile data for matched subjects. Cylindrical coupons were obtained from the rib cortical bone of 30 subjects (M = 19, F = 11) ranging from 18 to 95 years of age (Avg. = 48.5 ± 24.3). Two coupons were obtained from each subject. One coupon was tested in compression at 0.005 strain/s, while the other coupon was tested in compression at 0.5 strain/s. Load and displacement data were recorded so that the elastic modulus, yield stress, yield strain, ultimate stress, ultimate strain, elastic strain energy density (SED), plastic SED, and total SED could be calculated. All compressive material properties were significantly different between the two loading rates. An ANOVA revealed that sex alone had no significant effect on the compressive material properties. The interaction between sex and age was significant for some material properties, but this may have been a consequence of the lack of older females in the subject pool. None of the compressive material properties were significantly correlated with age, but were more correlated with sample density. This finding differed for the tensile material properties, which showed stronger correlations with age. When comparing between tension and compression, significant differences were observed for all material properties except for the total SED, once the effects of loading rate and age had been accounted for. This was the first study to quantify the material properties of human rib cortical bone in compression. The results of this study demonstrated that rib and thorax finite element models should consider the effects of loading rate, loading mode, and age when incorporating material properties published in the literature.

Estimation of Cortical Bone Microstructure From Ultrasound Backscatter

Multichannel pulse-echo ultrasound using linear arrays and single-channel data acquisition systems opens new perspectives for the evaluation of cortical bone. In combination with spectral backscatter analysis, it can provide quantitative information about cortical microstructural properties. We present a numerical study, based on the finite-difference time-domain method, to estimate the backscatter cross section of randomly distributed circular pores in a bone matrix. A model that predicts the backscatter coefficient using arbitrary pore diameter distributions was derived. In an ex vivo study on 19 human tibia bones (six males, 13 females, 83.7 ± 8.4 years), multidirectional ultrasound backscatter measurements were performed using an ultrasound scanner equipped with a 6-MHz 128-element linear array with sweep motor control. A normalized depth-dependent spectral analysis was performed to derive backscatter and attenuation coefficients. Site-matched reference values of tissue acoustic impedance Z , cortical thickness (Ct.Th), pore density (Ct.Po.Dn), porosity (Ct.Po), and characteristic parameters of the pore diameter (Ct.Po.Dm) distribution were obtained from 100-MHz scanning-acoustic microscopy images. Proximal femur areal bone mineral density (aBMD), stiffness S , and ultimate force Fu from the same donors were available from a previous study. All pore structure and material properties could be predicted using linear combinations of backscatter parameters with a median to high accuracy (0.28 ≤ adjusted R² ≤ 0.59). The combination of cortical thickness and backscatter parameter provided similar or better prediction accuracies than aBMD. For the first time, a method for the noninvasive assessment of the pore diameter distribution in cortical bone by ultrasound is proposed. The combined assessment of cortical thickness, sound velocity, and pore size distribution in a mobile, nonionizing measurement system could have a major impact on preventing osteoporotic fractures.

Longitudinal Evolution of Bone Microarchitecture and Bone Strength in Type 2 Diabetic Postmenopausal Women With and Without History of Fragility Fractures-A 5-Year Follow-Up Study Using High Resolution Peripheral Quantitative Computed Tomography

Introduction

Diabetic bone disease is characterized by an increased fracture risk which may be partly attributed to deficits in cortical bone quality such as higher cortical porosity. However, the temporal evolution of bone microarchitecture, strength, and particularly of cortical porosity in diabetic bone disease is still unknown. Here, we aimed to prospectively characterize the 5-year changes in bone microarchitecture, strength, and cortical porosity in type 2 diabetic (T2D) postmenopausal women with (DMFx) and without history of fragility fractures (DM) and to compare those to nondiabetic fracture free controls (Co) using high resolution peripheral quantitative computed tomography (HR-pQCT).

Methods

Thirty-two women underwent baseline HR-pQCT scanning of the ultradistal tibia and radius and a FU-scan 5 years later. Bone microarchitectural parameters, including cortical porosity, and bone strength estimates via µFEA were calculated for each timepoint and annualized. Linear regression models (adjusted for race and change in BMI) were used to compare the annualized percent changes in microarchitectural parameters between groups.

Results

At baseline at the tibia, DMFx subjects exhibited the highest porosity of the three groups (66.3% greater Ct.Po, 71.9% higher Ct.Po.Volume than DM subjects, p < 0.022). Longitudinally, porosity increased significantly over time in all three groups and at similar annual rates, while DMFx exhibited the greatest annual decreases in bone strength indices (compared to DM 4.7× and 6.7× greater decreases in failure load [F] and stiffness [K], p < 0.025; compared to Co 14.1× and 22.2× greater decreases in F and K, p < 0.020).

Conclusion

Our data suggest that despite different baseline levels in cortical porosity, T2D women with and without fractures experienced long-term porosity increases at a rate similar to non-diabetics. However, the annual loss in bone strength was greatest in T2D women with a history of a fragility fractures. This suggests a potentially non-linear course of cortical porosity development in T2D bone disease: major porosity may develop early in the course of disease, followed by a smaller steady annual increase in porosity which in turn can still have a detrimental effect on bone strength-depending on the amount of early cortical pre-damage.

Prediction of cross section fracture path of cortical bone through nanoindentation array

Although great progresses in the fracture mechanisms and deformation behaviors of cortical bones have been achieved, the effective methods to predict the surface fracture path of cortical bones are still difficult. By using depth-sensing nanoindentation measurement technique, the hardness distribution map of cortical bones was obtained through nanoindentation array. Combined with the compressive tests under approximate in vivo environment and micro computed tomography (CT) analysis, the correlation between hardness distribution map and compressive fracture path on the cross section of cortical bone was established. Through extracting the high hardness regions from the hardness distribution map and connecting the high hardness regions combined with the minimum directional derivative principle, the fracture path on cross section under compressive stress was accurately predicted. The feasibility of the prediction method was verified through the comparison between the fitted and actual fracture paths of specimens with sampling orientations of 90° and 45°. The relation between the regions where the fracture propagation path passed through and distribution of Haversian canals were also analyzed.

Effect of geometrical structure variations on the viscoelastic and anisotropic behaviour of cortical bone using multi-scale finite element modelling

Multi-scale finite element analysis is performed to ascertain the effect of geometrical changes at multiple structural scales on the mechanical properties of cortical bone. Finite element models are developed, with reference to experimental data from existing literature, to account for bone's viscoelastic behaviour and anisotropic structure from the most fundamental level of bone consisting of mineralised collagen fibrils, up to the macroscopic level consisting of osteons and the Haversian canals. A statistical approach is incorporated to perform sensitivity analyses on the effects of different geometrical parameters on the effective material properties of cortical bone at each length scale. Numerical results indicate that there is an exponential correlation between the mineral volume fraction and the effective stiffness constants at each length scale. This contributes to the exponential behaviour of the instantaneous moduli describing cortical bone's two-phase stress relaxation process: a fast and slow response relaxation behaviour. Results indicate that the fast response relaxation time is independent of bone's structural anisotropy, whilst being dependent on variations in the global mineral volume fraction between length scales. However, the slow response relaxation time is independent of the changes in mineral volume fraction. It is also observed that the slow response relaxation time varies with bone's anisotropic structure, and therefore, contributes to the anisotropic properties of bone.

Calcium Deficiency in Diet Decreases the Magnesium Content in Bone and Affects Femur Physicochemical Properties in Growing Rats

This study evaluates the effect of three calcium levels in the diet (normal, moderate, and severe calcium depletion) on bone metabolism of male Wistar rats during their growth period. Bone mineral density (BMD) and femur length were determined in vivo during the growth stage using a single X-ray transmission system. The apparent calcium absorption was calculated in the rat adolescent and adulthood stages. At the end of the experiment, calcium concentrations in serum and urine were analyzed. The bones were evaluated postmortem to corroborate in vivo analyses. Microstructural properties of cortical and trabecular tissues of femurs bones were assessed using scanning electron microscopy. Bone mineral contents (Mg, Ca, P, and K) were quantified by inductively coupled plasma. Severe calcium depletion in the diets in the development stage affects the bone quality parameters such as bone mineral density and mineral content. Moreover, it was found thinner cortical and trabecular bone areas. Additionally, it was found that severe calcium depletion increased the apparent absorption of calcium as a defense mechanism, but with the decrease of the BMD peak, and the thickness of cortical bone as well as trabecular bone porosity. The severe calcium depletion increased the efficiency of apparent absorption calcium as a defense mechanism, but, even so, decreases the BMD peak as well as the thickness of cortical bone and trabecular bone porosity.

Assessment of bone healing using (Ti,Mg)N thin film coated plates and screws: Rabbit femur model

Magnesium (Mg) based implants such as plates and screws are often preferred to treat bone defects because of the positive effects of magnesium in bone growth and healing. Their low corrosion resistance, however, leads to fast degradation and consequently failure before healing was completed. Previously, we developed Mg doped titanium nitrate (TiN) thin film coatings to address these limitations and demonstrated that <10 at% Mg doping led to enhanced mineralization in vitro. In the present study, in vivo performance of (Ti,Mg)N coated Ti6Al4V based plates and screws were studied in the rabbit model. Bone fractures were formed on femurs of 16 rabbits and then fixed with either (Ti,Mg)N coated (n = 8) or standard TiN coated (n = 8) plates and screws. X-ray imaging and μCT analyses showed enhanced bone regeneration on fracture sites fixed with (Ti,Mg)N coated plates in comparison with the Mg free ones. Bone mineral density, bone volume, and callus volume were also found to be 11.4, 23.4, and 42.8% higher, respectively, in accordance with μCT results. Furthermore, while TiN coatings promoted only primary bone regeneration, (Ti,Mg)N led to secondary bone regeneration in 6 weeks. These results indicated that Mg presence in the coatings accelerated bone regeneration in the fracture site. (Ti,Mg)N coating can be used as a practical method to increase the efficiency of existing bone fixation devices of varying geometry.

Determination of basal bone mineral density in the femur bones of male and female Wistar rats

Changes in bone mineral content of calcium (Ca), phosphorous (P), magnesium and potassium for male and female Wistar rats during their development from 3 weeks old to adulthood (27 weeks old) were measured. Bone mineral content was related to areal bone mineral density (BMD) which was measured in vivo at the femoral neck using a calibrated X-ray transmission system to obtain basal curves as a function of the age of the specimen. Diagnostic curves were built to determine low BMD (osteopaenia) and osteoporosis in female rats fed a Ca-depleted diet (50%) based on the obtained data and the criteria established by the World Health Organization. Bone mineral content is directly related to sex and age, but P did not change throughout the experimental period. P content did not exhibit significant changes with growing, while Ca was greatest in male rats, producing significant differences in the Ca:P ratio. Male rats reach the Ca:P ratio peak before female rats. However, areal BMD does not follow the same trend. On the other hand, osteoporosis produced a 45% decrease in this parameter for young and mature adults. These results make Z-score values available to diagnose bone-mass losses and hence the possibility of improving the conditions of non-contact measurement of BMD in vivo. This technique can be used for future experiments with Wistar rats.

Elastic Modulus of Woven Bone: Correlation with Evolution of Porosity and X-ray Greyscale

The woven bone created during the healing of bone regeneration processes is characterized as being extremely inhomogeneous and having a variable stiffness that increases with time. Therefore, it is important to study how the mechanical properties of woven bone are dependent on its microarchitecture and especially on its porosity and mineral content. The porosity and the x-ray greyscale of specimens taken from bone transport studies in sheep were assessed by means of ex vivo imaging. Our study demonstrates that the porosity of the woven bone in the distraction area diminishes during the healing process from 73.3% 35 days after surgery to 31.9% 525 days after surgery. In addition, the woven bone's porosity is negatively correlated with its Young's modulus. The x-ray greyscale, was measured as an indicator of the level of mineralization of the woven bone. Greyscale index has been demonstrated to be inversely proportional to porosity and to increase to up to 60-80% of the level in cortical bone. The results of this study may contribute to the development of micromechanical models of woven bone and improvements in in silico modelling.

Association between intracortical microarchitecture and the compressive fatigue life of human bone: A pilot study

Many mechanical properties of cortical bone are largely governed by the underlying microarchitecture; however, the influence of microarchitecture on the fatigue life of bone is poorly understood. Furthermore, imaging-based studies investigating intracortical microarchitecture may expose bone samples to large doses of radiation that may compromise fatigue resistance. The purpose of this pilot study was to 1) investigate the relationship between intracortical microarchitecture and the fatigue life of human bone in compression and 2) examine the effects of synchrotron irradiation on fatigue life measurements. Cortical samples were prepared from the femoral and tibial shafts of three cadaveric donors. A subset of samples was imaged using synchrotron X-ray microCT to quantify microarchitecture, including porosity, canal diameter, lacunar density, lacunar volume, and lacunar orientation. A second group of control samples was not imaged and used only for mechanical testing. Fatigue life was quantified by cyclically loading both groups in zero-compression until failure. Increased porosity and larger canal diameter were both logarithmically related to a shorter fatigue life, whereas lacunar density demonstrated a positive linear relationship with fatigue life (r² = 45–73%, depending on measure). Irradiation from microCT scanning reduced fatigue life measurements by 91%, but relationships with microarchitecture measurements remained. Additional research is needed to support the findings of this pilot study and fully establish the relationship between intracortical microarchitecture and the compressive fatigue life of bone.

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Increased porosity and larger canal diameters were associated with a shorter compressive fatigue life.

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A higher lacunar density was related to a longer compressive fatigue life.

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Irradiation from synchrotron X-ray microCT scanning reduced fatigue life by 91%.

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The influence of microarchitecture on fatigue life exhibited similar trends for both irradiated and non-irradiated bone.

What is the influence of two strain rates on the relationship between human cortical bone toughness and micro-structure?

Cortical bone fracture mechanisms are well studied under quasi-static loading. The influence of strain rate on crack propagation mechanisms needs to be better understood, however. We have previously shown that several aspects of the bone micro-structure are involved in crack propagation, such as the complete porosity network, including the Haversian system and the lacunar network, as well as biochemical aspects, such as the maturity of collagen cross-links. The aim of this study is to investigate the influence of strain rate on the toughness of human cortical bone with respect to its microstructure and organic non-collagenous composition. Two strain rates will be considered: quasi-static loading (10−4 s−1), a standard condition, and a higher loading rate (10−1 s−1), representative of a fall. Cortical bone samples were extracted from eight female donors (age 50–91 years). Three-point bending tests were performed until failure. Synchrotron radiation micro-computed tomography imaging was performed to assess bone microstructure including the Haversian system and the lacunar system. Collagen enzymatic cross-link maturation was measured using a high performance liquid chromatography column. Results showed that that under quasi-static loading, the elastic contribution of the fracture process is correlated to both the collagen cross-links maturation and the microstructure, while the plastic contribution is correlated only to the porosity network. Under fall-like loading, bone organization appears to be less linked to crack propagation.

Ivory vs. osseous ivory substitutes-Non-invasive diffractometric discrimination

A new discrimination method for the bioapatite materials bone, antler and ivory was developed using X-ray diffractometry and comprises non-invasive measurements in order to take valuable objects into account. Our approach deals with the analysis of peak intensity ratios resulting from several measurements on each object. For instance, the intensity ratio of the apatite reflections 002 and 310 has been described in the literature as representing the degree of apatite crystal orientation and varies depending on the sample orientation. The decisive factor for the material identification is the value dispersion of intensity ratios resulting from the total of all measurements on one object. This pattern of data points, visualised via kernel density estimation (KDE), is characteristic for ivory, bone and antler, respectively, and enables the discrimination of these materials. The observation is justifiable since apatite crystal orientation adapts to the collagen fibre arrangement which shows major differences between different sorts of bioapatite materials. The patterns of data points were received via analysis of 88 objects made of bone (n = 30), antler (n = 27) and ivory (n = 31). In order to verify several identifications X-ray computer tomography was supplemented. The presented method usefully supplements already existing approaches concerning microscopic, elementary and biochemical analyses.

An In Silico Model for the Prediction of Changes in Mineral Density in Cortical Bone Remodeling

An in silico model for the estimation of volumetric bone mineral density (vBMD) changes at a cortical bone site subjected to mechanobiological bone remodeling is proposed in this manuscript. Mechanisms of cell differentiation, receptor-ligand binding, mechanical signaling, and resorption or deposition of bone matrix were considered, therefore providing a comprehensive description of mechanobiological bone remodeling in the bone microenvironment and enabling the analysis of temporal evolution of disease or therapy scenarios. The proposed model is composed by five modules, namely, bone cells populations, mechanobiology, volume fractions and porosity, mineral density, and structural stiffness. The model is an extension of other models found in the literature because equations for the obtaining of cortical vBMD and the binding of parathyroid hormone (PTH) to parathyroid hormone 1 receptor are included. The proposed model showed a satisfactory agreement with the solutions of other in silico models found in the literature. Simulations of walking and running exercise routines were performed for the evaluation of model capability regarding the control of the numerical error and prediction of vBMD. The computational method used to solve the case study controlled the relative numerical error by less than 1 × 10-7 for approximately 1.7 × 106 time steps. The predicted values correlate with the concept of increasing BMD by vigorous physical activity; however, they contrast with the specific effect of physical activities on cortical vBMD.

Relation between cross-sectional bone geometry and double zonal osteon frequency and morphology

OBJECTIVES

While double-zonal osteons (DZ) are characterized by a hyper-mineralized ring inside their lamellae, recent findings suggest that this ring is also defined by a change in the collagen fibers' orientation. Collagen and minerals are essential components to the maintenance of adequate bone strength and their alteration can modify the mechanical properties of the bone tissue. Consequently, the aim of this study is to explore the effect of past loads, as estimated from cross-sectional geometric properties, on the formation of DZ osteons compared to type I (common) osteons.

MATERIALS AND METHODS

The sample consists of paired humerus and femur midshaft sections (n = 23) of Eurocanadian settlers from the historical St. Matthew cemetery, Quebec City (1771-1860). Histomorphometric variables included in this study are osteon density for DZ and type I osteons (DZD; OPD), osteon area (DZOn.Ar; On. Ar), Haversian canal area (DZH.Ar; H.Ar), and the area within the hypermineralized ring (HR. Ar). Loading history is estimated from cross-sectional properties including the following variable: cortical and total area (CA, TA), maximum and minimum second moment of area (I_max , I_min ) and polar moment of area (J).

RESULTS

When the humerus and femur of the same individuals are compared, the femur has a higher OPD, DZD, and relative DZD (DZD/OPD). DZ osteons have a smaller area and Haversian canal area compared to type I osteons. The area within the hypermineralized ring in DZ is higher than the Haversian canal area of the type I osteons. Correlations between the residual scores of the regression of histomorphometric variables and cross-sectional properties of the humerus on the femur were not significant.

DISCUSSION

Based on the analysis of the entire cross-section, the lack of correlation between variations in cross-sectional properties and remodeling combined with the significant differences between humeri and femura suggests that the creation of DZ or type I osteons in the bone tissue might be due to a bone specific response, possibly related to differences in bone tissue age that needs to be further investigated. Definitive conclusion regarding biomechanical loads still seem to be premature as regional variations associated with mechanical properties remain to be explored.

Clinical application of 3D printing technology to the surgical treatment of atlantoaxial subluxation in small breed dogs

Atlantoaxial instability (AAI)/subluxation commonly occurs in small breed dogs. Ventral stabilization techniques using screws and/or pins and a plate or, more commonly, polymethylmethacrylate are considered to provide the most favorable outcome. However, the implantation of screws of sufficient sizes for long-term stability becomes challenging in toy breed dogs (e.g. <2 kg). We herein report the application of 3D printing technology to implant trajectory planning and implant designing for the surgical management of AAI in 18 dogs. The use of our patient-specific drill guide templates resulted in overall mean screw corridor deviations of less than 1 mm in the atlas and axis, which contributed to avoiding iatrogenic injury to the surrounding structures. The patient-specific titanium plate was effective for stabilizing the AA joint and provided clinical benefits to 83.3% of cases (15/18). Implant failure requiring revision surgery occurred in only one case, and the cause appeared to be related to the suboptimal screw-plate interface. Although further modifications are needed, our study demonstrated the potential of 3D printing technology to be effectively applied to spinal stabilization surgeries for small breed dogs, allowing for the accurate placement of screws and minimizing peri- and postoperative complications, particularly at anatomical locations at which screw corridors are narrow and technically demanding.

Single injection of PTH improves osteoclastic parameters of remodeling at a stress fracture site in rats

Stress fractures (SFx) result from repetitive cyclical loading of bone. They are frequent athletic injuries and underlie atypical femoral fractures following long-term bisphosphonate (BP) therapy. We investigated the effect of a single PTH injection on the healing of SFx in the rat ulna. SFx was induced in 120 female Wistar rats (300 ± 15 g) during a single loading session. A single PTH (8 µg.100g^-1 ) or vehicle (VEH) saline injection was administered 24 h after loading. Rats were divided into four groups (n = 15) and ulnae were examined 1, 2, 6, or 10 weeks following SFx. Two Toluidine Blue and TRAP-stained sections of the SFx were examined for histomorphometric analysis using Osteomeasure™ software. An increase in osteoclast number (N.Oc) and perimeter (Oc.Pm) was observed two weeks following PTH treatment (p < 0.01). At 6 weeks, bone formation was the main activity in BMUs. At 10 weeks, the proportion of healing along the SFx line remained 50% greater in PTH groups (p = 0.839), leading to a 43% reduction in the porosity area of BMU (p = 0.703). The main effect of time was a significant variable along the entire SFx remodeling cycle, with significant interactions between time and treatment type affecting (N.Oc) (p = 0.047) and (Oc.Pm) (p = 0.002). We conclude that a single PTH injection increases osteoclastogenesis by the second week of the remodeling cycle in a SFx in vivo. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Is bone loss a physiological cost of reproduction in the Great fruit-eating bat Artibeus lituratus?

During mammalian pregnancy and lactation, the maternal demand for calcium is increased to satisfy fetus and newborn skeletal growth. In addition to the dietary intake, females use the calcium contained in their bones to supply this increased demand, leading to a decrease in maternal bone mineral content. In reproductive insectivorous female bats, bone loss has been described as a physiological cost of reproduction, due to the reported increased risk of bone fracture. This physiological cost may be the mechanism underlying the conflict between increasing litter size and maintaining wing skeletal integrity, which would help to explain the small litter size of most bat species. If bone loss is a linking cost between reproduction and survival in bats, and most bat species have small litter sizes, one would expect to find a loss of bone and an increasing probability of bone fracture during pregnancy and lactation in other non-insectivorous bats. In this study, we tested for the existence of this cost in the Great-fruit eating bat, Artibeus lituratus. We analyzed trabecular structure, bone strength and bone mineral content for the humerus bone, hypothesizing that bone loss during reproduction in females would increase the risk of fracture. Our results showed a decrease of 22-31% in bone trabecular area in lactating females, rapidly compensated following weaning. Bone strength did not differ among reproductive and non-reproductive groups and seems to be more influenced by bone organic components rather than mineral contents. Since we observed bone loss during reproduction yet the humerus strength seems to be unaffected, we suggest that bone loss may not represent a physiological cost during reproduction for this frugivorous bat.

Phosphorylation of Extracellular Bone Matrix Proteins and Its Contribution to Bone Fragility

Phosphorylation of bone matrix proteins is of fundamental importance to all vertebrates including humans. However, it is currently unknown whether increase or decline of total protein phosphorylation levels, particularly in hypophosphatemia-related osteoporosis, osteomalacia, and rickets, contribute to bone fracture. To address this gap, we combined biochemical measurements with mechanical evaluation of bone to discern fracture characteristics associated with age-related development of skeletal fragility in relation to total phosphorylation levels of bone matrix proteins and one of the key representatives of bone matrix phosphoproteins, osteopontin (OPN). Here for the first time, we report that as people age the total phosphorylation level declines by approximately 20% for bone matrix proteins and approximately 30% for OPN in the ninth decade of human life. Moreover, our results suggest that the decline of total protein phosphorylation of extracellular matrix (ECM) contributes to bone fragility, but less pronouncedly than glycation. We theorize that the separation of two sources of OPN negative charges, acidic backbone amino acids and phosphorylation, would be nature's means of assuring that OPN functions in both energy dissipation and biomineralization. We propose that total phosphorylation decline could be an important contributor to the development of osteoporosis, increased fracture risk and skeletal fragility. Targeting the enzymes kinase FamC20 and bone alkaline phosphatase involved in the regulation of matrix proteins' phosphorylation could be a means for the development of suitable therapeutic treatments. © 2018 American Society for Bone and Mineral Research.

Effect of water glass coating of tricalcium phosphate granules on in vivo bone formation

BACKGROUND

Recently, some authors introduced a water glass (WG, sodium-silicate glass; Na2O·SiO2·nH2O) coating over tricalcium phosphate (TCP) bioceramic to modulate its resorption rate and enhance the bone cell behaviors. In this study, four different types of granular samples were prepared to evaluate the ability of new bone formation in vivo using micro-computed tomography and histology.

METHODS

Four types sample groups: group A (pure HA as a negative resorption control); group B (pure TCP as a positive resorption control); group C (WG-coated TCP as an early resorption model); and group D (same as group C but heat-treated at 500°C as a delayed resorption model). Cylindrical tube-type carriers with holes were fabricated with HA by extrusion and sintering. Each carrier was filled densely with each granular sample. Four types of tubes were implanted into the medial femoral condyle and medial tibial condyle of New Zealand White rabbits.

RESULTS

The HA group (A) showed the lowest amount of new bone formation. All the TCP sample groups (B, C, and D) showed more new bone formation. On the other hand, among the TCP groups, group C (early resorption model) showed slightly more bone formation. The amount of residual bioceramics was most abundant in the HA group (A). All the TCP sample groups showed less residual bioceramics than group A. Among the TCP groups, group C showed slightly more residual bioceramics. Group B showed the lowest amount of residual bioceramics.

CONCLUSIONS

The WG-coated TCP sample (group C) is the best bone substitute candidate because of its proper biodegradation rate and the Si ions release because the WG-coated layer reduces the material resorption and enhances the new bone formation. That is, the WG-coated TCP is believed to be the best material for the application of an artificial bone substitute material.

Standardizing compression testing for measuring the stiffness of human bone

Objectives

The ability to determine human bone stiffness is of clinical relevance in many fields, including bone quality assessment and orthopaedic prosthesis design. Stiffness can be measured using compression testing, an experimental technique commonly used to test bone specimens in vitro. This systematic review aims to determine how best to perform compression testing of human bone.

Methods

A keyword search of all English language articles up until December 2017 of compression testing of bone was undertaken in Medline, Embase, PubMed, and Scopus databases. Studies using bulk tissue, animal tissue, whole bone, or testing techniques other than compression testing were excluded.

Results

A total of 4712 abstracts were retrieved, with 177 papers included in the analysis; 20 studies directly analyzed the compression testing technique to improve the accuracy of testing. Several influencing factors should be considered when testing bone samples in compression. These include the method of data analysis, specimen storage, specimen preparation, testing configuration, and loading protocol.

Conclusion

Compression testing is a widely used technique for measuring the stiffness of bone but there is a great deal of inter-study variation in experimental techniques across the literature. Based on best evidence from the literature, suggestions for bone compression testing are made in this review, although further studies are needed to establish standardized bone testing techniques in order to increase the comparability and reliability of bone stiffness studies.

Cite this article: S. Zhao, M. Arnold, S. Ma, R. L. Abel, J. P. Cobb, U. Hansen, O. Boughton. Standardizing compression testing for measuring the stiffness of human bone. Bone Joint Res 2018;7:524–538. DOI: 10.1302/2046-3758.78.BJR-2018-0025.R1.

Secondary osteons scale allometrically in mammalian humerus and femur

Intra-cortical bone remodelling is a cell-driven process that replaces existing bone tissue with new bone tissue in the bone cortex, leaving behind histological features called secondary osteons. While the scaling of bone dimensions on a macroscopic scale is well known, less is known about how the spatial dimensions of secondary osteons vary in relation to the adult body size of the species. We measured the cross-sectional area of individual intact secondary osteons and their central Haversian canals in transverse sections from 40 stylopodal bones of 39 mammalian species (body mass 0.3-21 000 kg). Scaling analysis of our data shows that mean osteonal resorption area (negative allometry, exponent 0.23,R² 0.54,p<0.005) and Haversian canal area (negative allometry, exponent 0.31,R² 0.45,p<0.005) are significantly related to body mass, independent of phylogeny. This study is the most comprehensive of its kind to date, and allows us to describe overall trends in the scaling behaviour of secondary osteon dimensions, supporting the inference that the osteonal resorption area may be limited by the need to avoid fracture in smaller mammalian species, but the need to maintain osteocyte viability in larger mammalian species.

Elevated Levels of Peripheral Kynurenine Decrease Bone Strength in Rats with Chronic Kidney Disease

The diagnosis and treatment of bone disorders in patients with chronic kidney disease (CKD) represent a clinical challenge. CKD leads to mineral and bone complications starting early in the course of renal failure. Recently, we have observed the positive relationship between intensified central kynurenine turnover and bone strength in rats with subtotal 5/6 nephrectomy (5/6 Nx)-induced CKD. The aim of the present study was to determine the association between peripheral kynurenine pathway metabolites and bone strength in rats with 5/6 Nx-induced CKD. The animals were sacrificed 1 and 3 months after 5/6 Nx or sham operation. Nephrectomized rats presented higher concentrations of serum creatinine, urea nitrogen, and parathyroid hormone both 1 and 3 months after nephrectomy. These animals revealed higher concentrations of kynurenine and 3-hydroxykynurenine in the serum and higher gene expression of aryl hydrocarbon receptor (AhR) as a physiological receptor for kynurenine and AhR-dependent cytochrome in the bone tissue. Furthermore, nephrectomy significantly increased the number of osteoclasts in the bone without affecting their resorptive activity measured in serum. These changes were particularly evident in rats 1 month after 5/6 Nx. The main bone biomechanical parameters of the tibia were unchanged between nephrectomized and sham-operated rats but were significantly increased in older compared to younger animals. A similar trend was observed for geometrical parameters measured with calipers, bone mineral density based on Archimedes' method and image of bone microarchitecture obtained from micro-computed tomography analyses of tibial cortical bone. In nephrectomized animals, peripheral kynurenine levels correlated negatively with the main parameters of bone biomechanics, bone geometry, and bone mineral density values. In conclusion, our data suggest that CKD-induced elevated levels of peripheral kynurenine cause pathological changes in bone structure via AhR pathway. This finding opens new opportunities for the treatment/prevention of osteoporosis in CKD.

Understanding Bone Strength Is Not Enough

Increases in fracture risk beyond what are expected from bone mineral density (BMD) are often attributed to poor "bone quality," such as impaired bone tissue strength. Recent studies, however, have highlighted the importance of tissue material properties other than strength, such as fracture toughness. Here we review the concepts behind failure properties other than strength and the physical mechanisms through which they cause mechanical failure: strength describes failure from a single overload; fracture toughness describes failure from a modest load combined with a preexisting flaw or damage; and fatigue strength describes failure from thousands to millions of cycles of small loads. In bone, these distinct failure mechanisms appear to be more common in some clinical fractures than others. For example, wrist fractures are usually the result of a single overload, the failure mechanism dominated by bone strength, whereas spinal fractures are rarely the result of a single overload, implicating multiple loading cycles and increased importance of fatigue strength. The combination of tissue material properties and failure mechanisms that lead to fracture represent distinct mechanistic pathways, analogous to molecular pathways used to describe cell signaling. Understanding these distinct mechanistic pathways is necessary because some characteristics of bone tissue can increase fracture risk by impairing fracture toughness or fatigue strength without impairing bone tissue strength. Additionally, mechanistic pathways to failure associated with fracture toughness and fatigue involve multiple loading events over time, raising the possibility that a developing fracture could be detected and interrupted before overt failure of a bone. Over the past two decades there have been substantial advancements in fracture prevention by understanding bone strength and fractures caused by a single load, but if we are to improve fracture risk prevention beyond what is possible now, we must consider material properties other than strength. © 2017 American Society for Bone and Mineral Research.

Characterization of a new ultrasound device designed for measuring cortical porosity at the human tibia: A phantom study

Quantitative ultrasound (QUS) measurements of trabecular bone are a useful tool for the assessment of osteoporotic fracture risk. However, cortical bone properties (e.g. porosity) have an impact on bone strength as well and thus current research is focused on QUS assessment of cortical bone properties. Simulation studies of ultrasound propagation through cortical bone indicate that anisotropy, calculated from the ratio of the velocities in axial and tangential directions, is correlated with porosity. However, this relationship is affected by error sources, specifically bone surface curvature and variability of probe positioning. With the aim of in vivo estimation of cortical porosity a new ultrasound device was developed, which sequentially measures velocities in 3 different directions (axial=0° and ±37.5°) using the axial transmission method. Measurements on planar porosity phantoms (0-25%) were performed to confirm the results of the afore mentioned simulation studies. Additionally, measurements on cylindrical phantoms without pores (min. radius=34mm for strongest curvature) were performed to estimate the influence of surface curvature on velocity measurements (the tibia bone surface is fairly flat but may show surface curvature in some patients). The velocities in the axial and ±37.5° directions were used to calculate an anisotropy index. The velocities measured on the porosity phantoms showed a decrease by -6.3±0.2m/s and -10.1±0.2m/s per percent increase in porosity in axial and ±37.5° directions, respectively. Surface curvature had an effect on the velocities measured in ±37.5° directions which could be minimized by a correction algorithm resulting in an error of 5m/s. The anisotropy index could be used to estimate porosity with an accuracy error of 1.5%. These results indicate that an estimation of porosity using velocity measurements in different directions might be feasible, even in bones with curved surface. These results obtained on phantom material indicate that the approach tested may be suited for porosity measurements on human tibia bone.

Electrical Stimulation of Denervated Rat Skeletal Muscle Ameliorates Bone Fragility and Muscle Loss in Early-Stage Disuse Musculoskeletal Atrophy

We tested whether daily muscle electrical stimulation (ES) can ameliorate the decrease in cortical bone strength as well as muscle and bone geometric and material properties in the early stages of disuse musculoskeletal atrophy. 7-week-old male F344 rats were randomly divided into three groups: age-matched control group (Cont); a sciatic denervation group (DN); and a DN + direct electrical stimulation group (DN + ES). Denervated tibialis anterior (TA) muscle in the DN + ES group received ES with 16 mA at 10 Hz for 30 min/day, 6 days/week. Micro CT, the three-point bending test, and immunohistochemistry were used to characterize cortical bone mechanical, structural, and material properties of tibiae. TA muscle in the DN + ES group showed significant improvement in muscle mass and myofiber cross-sectional area relative to the DN group. Maximal load and stiffness of tibiae, bone mineral density estimated by micro CT, and immunoreactivity of DMP1 in the cortical bone tissue were also significantly greater in the DN + ES group than in the DN group. These results suggest that daily ES-induced muscle contraction treatment reduced the decrease in muscle mass and cortical bone strength in early-stage disuse musculoskeletal atrophy and is associated with a beneficial effect on material properties such as mineralization of cortical bone tissue.

The effects of sclerostin antibody plus parathyroid hormone (1-34) on bone formation in ovariectomized rats

Previous studies have demonstrated the effects of sclerostin antibody (Scl-Ab) and parathyroid hormone (1-34, PTH) on healing in osteoporosis; however, reports about the combined effects of Scl-Ab plus PTH on osteoporosis are limited. This study was designed to investigate the impact of combined treatment with Scl-Ab and PTH on osteoporosis healing in ovariectomized (OVX) rats. After bilateral ovariectomy, 12 weeks were allowed to pass for the establishment of standard conditions for osteoporosis in animal models. The rats then randomly received a vehicle (control), Scl-Ab (25 mg/kg body weight, twice weekly), PTH (60 μg/kg, three times per week) or PTH plus Scl-Ab until death at 12 weeks. The blood and distal femurs of the rats were harvested for evaluation. The results of treatment for osteoporosis were evaluated by serum analysis, histology, microcomputed tomography (micro-CT) and biomechanical tests. Results from this study indicated that PTH + Scl-Ab had stronger effects on the prevention and treatment of osteoporosis than either of the monotherapies in OVX rats. The PTH + Scl-Ab produced the strongest effects on bone volume fraction (BV/TV), bone trabecular thickness (Tb.Th), trabecular number (Tb.N) and trabecular spacing (Tb.Sp), bone mineral density (BMD) and strength of distal femurs and increased the levels of procollagen type I N‑terminal propeptide (PINP) and osteocalcin. In contrast, monotherapy with PTH or Scl-Ab showed no differences between treated groups in the assessment of the metaphysis of contralateral femurs by histology, serum, biomechanical tests and micro-CT. These results seem to indicate that Scl-Ab plus PTH has an additive effect on osteoporosis in OVX rats.

Horticultural activity predicts later localized limb status in a contemporary pre-industrial population

OBJECTIVES

Modern humans may have gracile skeletons due to low physical activity levels and mechanical loading. Tests using pre-historic skeletons are limited by the inability to assess behavior directly, while modern industrialized societies possess few socio-ecological features typical of human evolutionary history. Among Tsimane forager-horticulturalists, we test whether greater activity levels and, thus, increased loading earlier in life are associated with greater later-life bone status and diminished age-related bone loss.

MATERIALS AND METHODS

We used quantitative ultrasonography to assess radial and tibial status among adults aged 20+ years (mean ± SD age = 49 ± 15; 52% female). We conducted systematic behavioral observations to assess earlier-life activity patterns (mean time lag between behavioural observation and ultrasound = 12 years). For a subset of participants, physical activity was again measured later in life, via accelerometry, to determine whether earlier-life time use is associated with later-life activity levels. Anthropometric and demographic data were collected during medical exams.

RESULTS

Structural decline with age is reduced for the tibia (female: -0.25 SDs/decade; male: 0.05 SDs/decade) versus radius (female: -0.56 SDs/decade; male: -0.20 SDs/decade), which is expected if greater loading mitigates bone loss. Time allocation to horticulture, but not hunting, positively predicts later-life radial status (β_Horticulture  = 0.48, p = 0.01), whereas tibial status is not significantly predicted by subsistence or sedentary leisure participation.

DISCUSSION

Patterns of activity- and age-related change in bone status indicate localized osteogenic responses to loading, and are generally consistent with the logic of bone functional adaptation. Nonmechanical factors related to subsistence lifestyle moderate the association between activity patterns and bone structure.

Effects of losartan treatment on the physicochemical properties of diabetic rat bone

Inhibitors of the renin-angiotensin system used to treat several diseases have also been shown to be effective on bone tissue, suggesting that angiotensin-converting enzyme inhibitors and angiotensin receptor blockers may reduce fracture risk. The present study investigated the effects of losartan on the physicochemical and biomechanical properties of diabetic rat bone. Losartan (5 mg/kg/day) was administered via oral gavage for 12 weeks. Bone mineral density (BMD) was measured using dual-energy X-ray absorptiometry. Whole femurs were tested under tension to evaluate the biomechanical properties of bone. The physicochemical properties of bone were analyzed by Fourier transform infrared spectroscopy. Although losartan did not recover decreases in the BMD of diabetic bone, it recovered the physicochemical (mineral and collagen matrix) properties of diabetic rat bone. Furthermore, losartan also recovered ultimate tensile strength of diabetic rat femurs. Losartan, an angiotensin II type 1 receptor blocker, has a therapeutic effect on the physicochemical properties of diabetic bone resulting in improvement of bone strength at the material level. Therefore, specific inhibition of this pathway at the receptor level shows potential as a therapeutic target for diabetic patients suffering from bone diseases such as osteopenia.

Bone Mineral Density, Mechanical, Microstructural Properties and Mineral Content of the Femur in Growing Rats Fed with Cactus Opuntia ficus indica (L.) Mill. (Cactaceae) Cladodes as Calcium Source in Diet

Mechanical, microstructural properties, mineral content and bone mineral density (BMD) of the femur were evaluated in growing rats fed with Opuntia ficus indica (L.) Mill. (Cactaceae) cladodes at different maturity stages as calcium source. Male weanling rats were fed with cladodes at early maturity stage (25 and 60 days of age, belonging to groups N-60 and N-200, respectively) and cladodes at late maturity stage (100 and 135 days of age, belonging to groups N-400 and N-600, respectively) for 6 weeks. Additionally, a control group fed with calcium carbonate as calcium source was included for comparative purposes. All diets were fitted to the same calcium content (5 g/kg diet). The failure load of femurs was significantly lower (p ≤ 0.05) in groups N-60 and N-200 in comparison to N-400, N-600 and control groups. The cortical width (Ct.Wi) and trabecular thickness (Tb.Th) of the femurs in control and N-600 groups were significantly higher (p ≤ 0.05) than Ct.Wi and Tb.Th of femurs in groups N-60 and N-200. Trabecular separation of the femurs in N-60 and N-200 groups showed the highest values compared with all experimental groups. The highest calcium content in the femurs were observed in control, N-600 and N-400 groups; whereas the lowest phosphorus content in the bones were detected in N-200, N-600 and N-400 groups. Finally, the BMD in all experimental groups increased with age; nevertheless, the highest values were observed in N-600 and control groups during pubertal and adolescence stages. The results derived from this research demonstrate, for the first time, that the calcium found in Opuntia ficus indica cladodes is actually bioavailable and capable of improving mineral density and mechanical and microstructural properties of the bones. These findings suggest that the consumption of cladodes at late maturity stage within the diet might have a beneficial impact on bone health.

Risk of vertebral compression fractures in multiple myeloma patients: A finite-element study

The purpose of this study was to develop and validate a finite element (FE) model to predict vertebral bone strength in vitro using multidetector computed tomography (MDCT) images in multiple myeloma (MM) patients, to serve as a complementing tool to assess fracture risk. In addition, it also aims to differentiate MM patients with and without vertebral compression fractures (VCFs) by performing FE analysis on vertebra segments (T1-L5) obtained from in vivo routine MDCT imaging scans. MDCT-based FE models were developed from the in vitro vertebrae samples and were then applied to the in vivo vertebrae segments of MM patients (n = 4) after validation. Predicted fracture load using FE models correlated significantly with experimentally measured failure load (r = 0.85, P < 0.001). Interestingly, an erratic behavior was observed in patients with fractures (n = 2) and a more gradual change in FE-predicted strength values in patients without fractures (n = 2). Severe geometric deformations were also observed in models that have already attained fractures. Since BMD is not a reliable parameter for fracture risk prediction in MM subjects, it is necessary to use advanced tools such as FE analysis to predict individual fracture risk. If peaks are observed between adjacent segments in an MM patient, it can be safe to conclude that the spine is experiencing regions of structural instability. Such an FE visualization may have therapeutic consequences to prevent MM associated vertebral fractures.

Mechanical properties of cortical bone and their relationships with age, gender, composition and microindentation properties in the elderly

The growing incidence of skeletal fractures poses a significant challenge to ageing societies. Since a major part of physiological loading in the lower limbs is carried by cortical bone, it would be desirable to better understand the structure-mechanical property relationships and scale effects in this tissue. This study aimed at assessing whether microindentation properties combined with chemical and morphological information are usable to predict macroscopic elastic and strength properties in a donor- and site-matched manner. Specimens for quasi-static macroscopic tests in tension, compression, and torsion and microindentation were prepared from a cohort of 19 male and 20 female donors (46 to 99 years). All tests were performed under fully hydrated conditions. The chemical composition of the extra-cellular matrix was investigated with Raman spectroscopy. The results of the micro-mechanical tests were combined with morphological and compositional properties using a power law relationship to predict the macro-mechanical results. Microindentation properties were not gender dependent, remarkably constant over age, and showed an overall small variation with standard deviations of approximately 10 %. Similar results were obtained for chemical tissue composition. Macro-mechanical stiffness and strength were significantly related to porosity for all load cases (p<0.05). In case of macroscopic yield strain and work-to-failure this was only true in torsion and compression, respectively. The correlations of macro-mechanical with micro-mechanical, morphological, and chemical properties showed no significance for cement line density, mineralisation, or variations in the microindentation results and were dominated by porosity with a moderate explanatory power of predominately less than 50 %. The results confirm that age, with minor exceptions gender, and small variations in average mineralisation have negligible effect on the tissue microindentation properties of human lamellar bone in the elderly. Furthermore, our findings suggest that microindentation experiments are suitable to predict macroscopic mechanical properties in the elderly only on average and not on a one to one basis. The presented data may help to form a better understanding of the mechanisms of ageing in bone tissue and of the length scale at which they are active. This may be used for future prediction of fracture risk in the elderly.