Role of trabecular morphology in the etiology of age-related vertebral fractures

Sex-Specific Association Patterns of Bone Microstructure and Lower Leg Arterial Calcification

In conversations about bone loss and the importance of calcium homeostasis, patients frequently inquire about the association with arterial calcifications. Although a relationship between bone loss and the occurrence of vascular calcifications is suspected, it is not yet fully investigated and understood. This study aims to analyze associations between bone mineralization, structure, and vascular calcification at the lower leg in patients with low bone mineral density in HR-pQCT. We retrospectively analyzed 774 high-resolution quantitative computed tomography (HR-pQCT) scans of the distal tibia for the presence of vascular calcifications. After sex-specific propensity score matching for age and BMI to account for confounders, 132 patients remained for quantification of bone microstructure, bone density, lower leg arterial calcification (LLAC), and laboratory parameters of bone turnover. The interactions between bone parameters and vascular calcification were quantified by regression analyses. The calcium metabolism was not different between individuals with and without LLAC, nor oral calcium supplementation. Female patients with LLAC had a higher cortical perimeter (p = 0.016) compared to female patients without LLAC, whereas male patients with LLAC had lower cortical pore diameter than male patients without LLAC (p = 0.027). The appearance of LLAC was sex specifically associated with bone parameters. In female patients, only plaque density was associated with HR-pQCT bone parameters and age, whereas in male patients, plaque volume was associated with HR-pQCT parameters of the distal tibia. Female patients exhibit an increasing plaque density depended on age and trabecular thinning. Decreasing cortical pore diameter and trabecular number along with increasing bone mineralization are linked to increasing plaque volume in male patients.

High-resolution local trabecular strain within trabecular structure under cyclic loading

Trabecular bone structure is a complex microstructure consisting of rods and plates, which poses challenges for its mechanical characterization. Digital image correlation (DIC) offers the possibility to characterize the strain response on the surface of trabecular bone. This study employed DIC equipped with a telecentric lens to investigate the strain state of individual trabeculae within their trabecular structure by assessing the longitudinal strain of the trabeculae at both the middle and near the edges of the trabeculae. Due to the high-resolution of the used DIC system, local surface strain of trabeculae was analyzed too. Lastly, the correlation between longitudinal trabecular strain and the orientation and slenderness of the trabeculae was investigated. The results showed that the strain magnification close to the edge of the trabeculae was higher and reached up to 8-folds the strain along the middle of the trabeculae. On the contrary, no strain magnification was found for most of the trabeculae between the longitudinal trabecular strain along the middle of the trabeculae and the globally applied strain. High-resolution full-field strain maps were obtained on the surface of trabeculae showing heterogeneous strain distribution with increasing load. No significant correlation was found between longitudinal trabecular strain and its orientation or slenderness. These findings and the applied methodology can be used to broaden our understanding of the deformation mechanisms of trabeculae within the trabecular network.

Micro-computed tomography assessment of bone structure in aging mice

High-resolution computed tomography (CT) is widely used to assess bone structure under physiological and pathological conditions. Although the analytic protocols and parameters for micro-CT (μCT) analyses in mice are standardized for long bones, vertebrae, and the palms in aging mice, they have not yet been established for craniofacial bones. In this study, we conducted a morphometric assessment of craniofacial bones, in comparison with long bones, in aging mice. Although age-related changes were observed in the microarchitecture of the femur, tibia, vertebra, and basisphenoid bone, and were more pronounced in females than in males, the microarchitecture of both the interparietal bone and body of the mandible, which develop by intramembranous ossification, was less affected by age and sex. By contrast, the condyle of the mandible was more affected by aging in males compared to females. Taken together, our results indicate that mouse craniofacial bones are uniquely affected by age and sex.

Structure-function relationships of the human vertebral endplate

BACKGROUND

Although deformation and fracture of the vertebral endplate have been implicated in spinal conditions such as vertebral fracture and disc degeneration, few biomechanical studies of this structure are available. The goal of this study was to quantify the mechanical behavior of the vertebral endplate.

METHODS

Eight-five rectangular specimens were dissected from the superior and/or inferior central endplates of human lumbar spine segments L1 to L4. Micro-computed tomography (μCT) imaging, four-point-bend testing, and ashing were performed to quantify the apparent elastic modulus and yield stress (modulus and yield stress, respectively, of the porous vertebral endplate), tissue yield stress (yield stress of the tissue of the vertebral endplate, excluding pores), ultimate strain, fracture strain, bone volume fraction (BV/TV), bone mineral density (BMD), and various measures of tissue density and composition (tissue mineral density, ash fraction, and ash density). Regression was used to assess the dependence of mechanical properties on density and composition.

RESULTS

Wide variations in elastic and failure properties, and in density and tissue composition, were observed. BMD and BV/TV were good predictors of many of the apparent-level mechanical properties, including modulus, yield stress, and in the case of the inferior vertebral endplate, failure strains. Similar values of the mechanical properties were noted between superior and inferior vertebral endplates. In contrast to the dependence of apparent stiffness and strength on BMD and BV/TV, none of the mechanical properties depended on any of the tissue-level density measurements.

CONCLUSION

The dependence of many of the mechanical properties of the vertebral endplate on BV/TV and BMD suggests possibilities for noninvasive assessment of how this region of the spine behaves during habitual and injurious loading. Further study of the nonmineral components of the endplate tissue is required to understand how the composition of this tissue may influence the overall mechanical behavior of the vertebral endplate.

Misalignment Error in Cancellous Bone Apparent Elastic Modulus Depends on Bone Volume Fraction and Degree of Anisotropy

Cancellous bone is an anisotropic structure with architectural and mechanical properties that vary due to both skeletal site and disease state. This anisotropy means that, in order to accurately and consistently measure the mechanical properties of cancellous bone, experiments should be performed along the primary mechanical axis (PMA), that is, the orientation in which the mechanical properties are at their maximum value. Unfortunately, some degree of misalignment will always be present, and the magnitude of the resulting error is expected to be architecture dependent. The goal of this work is to quantify the dependence of the misalignment error, expressed in terms of change in apparent elastic modulus (ΔE), on both the bone volume fraction (BV/TV) and the degree of anisotropy (DA). Finite element method (FEM) models of bovine cancellous bone from five different skeletal sites were created at 5 deg and 20 deg from the PMA determined for each region. An additional set of models was created using image dilation/erosion steps in order to control for BV/TV and better isolate the effect of DA. Misalignment error was found to increase with increasing DA and decreasing BV/TV. At 5 deg misaligned from the PMA, error is relatively low (<5%) in all cases but increases to 8-24% error at 20 deg. These results suggest that great care is needed to avoid introducing misalignment error into experimental studies, particularly when studying regions with high anisotropy and/or low bone volume fraction, such as vertebral or osteoporotic bone.

The phytoestrogen glabrene prevents osteoporosis in ovariectomized rats through upregulation of the canonical Wnt/β-catenin signaling pathway

This study systematically investigated the effects of phytoestrogen glabrene on postmenopausal osteoporosis in an ovariectomy (OVX) rat model. Glabrene administration (25, 50, and 100 mg/kg) for 13 weeks can significantly slow down the body weight gain and slightly increase the uterus weight of OVX rats. The increased levels of U-Ca, U-P levels, urine DPD/creatinine, serum ALP, OCN, triglycerides, and total cholesterol induced by OVX were dramatically inhibited in rats, whereas no difference occurred for S-Ca and S-P in all groups. Furthermore, glabrene can enhance bone mineral density of the right femur, fourth-lumbar vertebra and tibia and improve biomechanical parameters, such as femoral neck loading force, three-point bending of the tibia, and vertebral compression in OVX rats. Moreover, glabrene greatly suppressed the expression of TRAP protein but increased OPG and BGP protein expression in tibia tissue of OVX rats. In addition, OVX-induced reduction of Lrp-5, β-catenin, Runx2, and Osx protein expression was all restored by glabrene treatment. The present study indicated that glabrene might be a potential alternative medicine for the prevention and treatment of postmenopausal osteoporosis via activation of the Wnt/β-catenin signaling pathway.

Relationships Among Bone Morphological Parameters and Mechanical Properties of Cadaveric Human Vertebral Cancellous Bone

Mechanical properties and morphological features of the vertebral cancellous bone are related to resistance to fracture and capability of withstanding surgical treatments. In particular, vertebral strength is related to its elastic properties, whereas the ease of fluid motion, related to the success of incorporation orthopedic materials (eg, bone cement), is regulated by the hydraulic permeability (K). It has been shown that both elastic modulus and permeability of a material are affected by its morphology. The objective of this study was to establish relations between local values of K and the aggregate modulus (H), and parameters descriptive of the bone morphology. We hypothesized that multivariate statistical models, by including the contribution of several morphology parameters at once, would provide a strong correlation with K and H of the vertebral cancellous bone. Hence, μCT scans of human lumbar vertebra were used to determine a set of bone morphology descriptors. Subsequently, indentation tests on the bone samples were conducted to determine local values of K and H. Finally, a multivariate approach supported by principal component analysis was adopted to develop predictive statistical models of bone permeability and aggregate modulus as a function of bone morphology descriptors. It was found that linear combinations of bone volume fraction, trabecular thickness, trabecular spacing, structure model index, connectivity density, and degree of anisotropy provide a strong correlation (R 2 ~ 76%) with K and a weaker correlation (R 2 ~ 47%) with H. The results of this study can be exploited in computational mechanics frameworks for investigating the potential mechanical behavior of human vertebra and to develop strategies to treat or prevent pathological conditions such as osteoporosis, age-related bone loss, and vertebral compression fractures. © 2020 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Locked Plating and Advanced Augmentation Techniques in Osteoporotic Fractures

"The incidence of osteoporotic fracture is increasing with the aging US population. Because osteoporosis leads to a decrease in bone mineral density with a decrease in both trabecular and cortical bones, osteoporotic fracture presents fixation challenges with standard plate and screw constructs. Locked plating has been developed to create a fixed-angle plate-screw construct that is more resistant to failure in osteoporotic bone. Endosteal replacement, additional plates, and cement augmentation have all been demonstrated to further supplement osteoporotic fracture fixation. Technologies on the horizon to treat osteoporotic fracture include SMV screws, hydroxyapatite-coated implants, and far cortical locking screws."

Global sagittal alignment in elderly patients with osteoporosis and its relationship with severity of vertebral fracture and quality of life

We compared global sagittal alignment and quality of life in osteoporotic patients with and without vertebral compression fracture (VCF) and determined its relationship with VCF severity. The findings revealed osteoporotic patients with VCF showed decreased quality of life and worse global sagittal alignment, which was significantly associated with VCF severity.

INTRODUCTION

The aim of this study was to compare the global sagittal alignment and quality of life in elderly osteoporotic patients with and without vertebral compression fracture (VCF), and to investigate the relationship between global sagittal alignment and severity of VCF.

METHODS

A consecutive series of 72 female patients with osteoporosis aged over 60 years and 31 age-matched females without osteoporosis were prospectively enrolled. The patients were divided into VCF and non-VCF group. Patient's clinical demography, nature of VCF, and bone mineral density (BMD) were also recorded. Spinal deformity index was used to evaluate severity of VCF. EOS® biplanar imaging system was then used to evaluate global sagittal parameters: T1 pelvic angle (TPA) and global sagittal angle (GSA). In addition, quality of life was assessed with self-reported questionnaires: the Oswestry Disability Index (ODI) and Short-form 12 (SF-12).

RESULTS

Osteoporotic patients and controls were found to be significantly different in terms of TPA, GSA, and BMD. And in patients with VCF, they were found to have significantly higher TPA and GSA. TPA and GSA were significantly correlated with SF-12 and ODI. The number of VCF and SDI significantly correlated with global sagittal alignment. Using regression analysis, parameters significantly associated with abnormal global alignment were the number of VCF (OR = 1.13) and SDI (OR = 1.84).

CONCLUSION

Osteoporotic patients with VCF showed worse global sagittal alignment and decreased quality of life. The number and severity of VCF had a negative influence on global sagittal balance, which indicates that poorer sagittal global alignment may imply worse quality of life and more severe VCF.

From Tension to Compression: Asymmetric Mechanical Behaviour of Trabecular Bone's Organic Phase

Trabecular bone is a cellular composite material comprising primarily of mineral and organic phases with their content ratio known to change with age. Therefore, the contribution of bone constituents on bone's mechanical behaviour, in tension and compression, at varying load levels and with changing porosity (which increases with age) is of great interest, but remains unknown. We investigated the mechanical response of demineralised bone by subjecting a set of bone samples to fully reversed cyclic tension-compression loads with varying magnitudes. We show that the tension to compression response of the organic phase of trabecular bone is asymmetric; it stiffens in tension and undergoes stiffness reduction in compression. Our results indicate that demineralised trabecular bone struts experience inelastic buckling under compression which causes irreversible damage, while irreversible strains due to microcracking are less visible in tension. We also identified that the values of this asymmetric mechanical response is associated to the original bone volume ratio (BV/TV).

Biomechanical effects of metastasis in the osteoporotic lumbar spine: A Finite Element Analysis

BACKGROUND

Cancer patients are likely to undergo osteoporosis as consequence of hormone manipulation and/or chemotherapy. Little is known about possible increased risk of fracture in this population. The aim of this study was to describe the biomechanical effect of a metastatic lesion in an osteoporotic lumbar spine model.

METHODS

A finite element model of two spinal motion segments (L3-L5) was extracted from a previously developed L3-Sacrum model and used to analyze the effect of metastasis size and bone mineral density (BMD) on Vertebral bulge (VB) and Vertebral height (VH). VB and VH represent respectively radial and axial displacement and they have been correlated to burst fracture. A total of 6 scenarios were evaluated combining three metastasis sizes (no metastasis, 15% and 30% of the vertebral body) and two BMD conditions (normal BMD and osteoporosis).

RESULTS

15% metastasis increased VB and VH by 178% and 248%, respectively in normal BMD model; while VB and VH increased by 134% and 174% in osteoporotic model. 30% metastasis increased VB and VH by 88% and 109%, respectively, when compared to 15% metastasis in normal BMD model; while VB and VH increased by 59% and 74% in osteoporotic model.

CONCLUSION

A metastasis in the osteoporotic lumbar spine always leads to a higher risk of vertebral fracture. This risk increases with the size of the metastasis. Unexpectedly, an increment in metastasis size in the normal BMD spine produces a greater impact on vertebral stability compared to the osteoporotic spine.

A novel use of 3D printing model demonstrates the effects of deteriorated trabecular bone structure on bone stiffness and strength

Trabecular bone structure is crucial to normal mechanical behavior of bones. Studies have shown that osteoporosis negatively affects trabecular bone structure, mainly by reducing bone volume fraction (BV/TV) and thus increasing fracture risk. One major limitation in assessing and quantifying the effect of this structural deterioration is that no two trabecular structures are identical. Thus, when we compare a group of healthy bones against a different group of bones that experienced resorption (i.e. decreased BV/TV) we only discover an "average" mechanical effect. It is impossible to quantify the mechanical effect of individual structural deterioration for each sample, simply because we never have the same sample in both states (intact and deteriorated structure). 3D printing is a new technology that can assist in overcoming this issue. Here we report a preliminary study that compares a healthy 3D printed trabecular bone model with the same model after bone resorption was simulated. Since the deteriorated structural bone model is derived from the healthy one, it is possible to directly estimate (percentage wise) the decrease of tissue stiffness and strength as a result of bone resorption for this specific structure. Our results demonstrate that a relatively small decrease in BV/TV (about 8%) leads to a dramatic decrease in structural strength (24%) and structural stiffness (17%), (P < 0.01). Structural strength decreased from an average of 9.14 ± 2.85MPa to 6.97 ± 2.44MPa, while structural stiffness decreased from an average of 282.5 ± 63.4N/mm to 233.8 ± 51.2N/mm. This study demonstrates that 3D printing is a novel and valuable tool for quantifying the effect of structural deterioration on the mechanical properties of trabecular bone. In the future, this approach may help us attain better personal fracture risk assessments by CT scanning, 3D printing and mechanically testing individual bone replicas from patients suffering excessive bone resorption.

Vertebral cross-sectional area: an orphan phenotype with potential implications for female spinal health

A high priority in imaging-based research is the identification of the structural basis that confers greater risk for spinal disorders. New evidence indicates that factors related to sex influence the fetal development of the axial skeleton. Girls are born with smaller vertebral cross-sectional area compared to boys-a sexual dimorphism that is present throughout life and independent of body size. The smaller female vertebra is associated with greater flexibility of the spine that could represent the human adaptation to fetal load. It also likely contributes to the higher prevalence of spinal deformities, such as exaggerated lordosis and progressive scoliosis in adolescent girls when compared to boys, and to the greater susceptibility for spinal osteoporosis and vertebral fractures in elderly women than men.

Antiosteoporotic activity of Du-Zhong-Wan water extract in ovariectomized rats

Context Eucommiae Cortex and Radix Dipsaci, occurring in a ratio of 1:1 in Du-Zhong-Wan (DZW), a Chinese herbal medicine, is available as a water extract followed by ethanol precipitation for the treatment of osteoporosis, fractures and menopausal syndrome. Objective This study investigates the protective effects of DZW in ovariectomy (OVX)-induced bone loss in a rat osteopenia model. Materials and methods Sixty Sprague-Dawley rats were randomly divided into the sham-operated group (SHAM) and five OVX subgroups: OVX with vehicle (OVX), 17β-estradiol (E2) and with three graded doses of DZW. Daily oral administration of the different samples started on the fifth week and lasted for 12 weeks, respectively. The body weight, uterus wet weight, serum biochemical parameters, bone mineral density (BMD), bone biomechanical properties, bone microarchitecture and immunohistochemistry were examined. Results Compared with the SHAM group, the DZW treatment significantly reversed the osteoporotic changes in OVX rats. The DZW-H group showed that serum tartrate-resistant acid phosphatase 5b (TRACP-5b) levels reduced by 152.25% (p < 0.01) and osteocalein (OCN) levels dose dependently increased by 118.43% (p < 0.01) as compared with the OVX group. Compared with the OVX group, the DZW at different three dosages of DZW evidently increased the right femur BMD by 112.43, 114.56 and 116.45%, and dramatically promoted bone quality and bone strength (p < 0.05). Further, immunohistochemical evaluation also showed that DZW administration increased ER expression in uteri (p < 0.01). Conclusions DZW exhibits an anti-osteoporotic effect, probably mediated via phyto-estrogenic effects. It might be a potential herbal alternative for the management of postmenopausal osteoporosis.

Vertical Trabeculae are Thinned More Than Horizontal Trabeculae in Skeletal-Unloaded Rats

Skeletal unloading results in a rapid thinning of the trabecular bone network, but it is unknown whether vertical and horizontal trabeculae are equally affected. Therefore, the purpose of the present study was to investigate whether horizontal and vertical trabeculae were thinned similarly during skeletal unloading in rats. Fifty-seven 16-week-old female Wistar rats were randomized into six groups: baseline; control 4 weeks; botulinum toxin A (BTX) 4 weeks; control 8 weeks; BTX 8 weeks; and two BTX injections 8 weeks (BTX + BTX8). The BTX animals were injected in the right hind limb with 4 IU BTX at the start of the study, while the BTX + BTX8 were also injected with 2 IU BTX after 4 weeks. The animals were killed after 0, 4, or 8 weeks. The distal femoral metaphyses were μCT scanned, and the strengths of the femoral necks, mid-diaphyses, and distal femoral metaphyses were ascertained. Disuse resulted in a significant loss of BV/TV, thinning of the trabeculae, and decrease in the degree of anisotropy, and in a significant reduced bone strength after both 4 and 8 weeks. The ratio of horizontal to vertical trabecular thickness (Tb.Th.horz/Tb.Th.vert) and the ratio of horizontal to vertical bone volume (BV.horz/BV.vert) were significantly higher in BTX animals than in control animals. In addition, the horizontal and vertical trabecular thickness probability density functions were more similar in BTX animals than in control animals. In conclusion, skeletal unloading decreased BV/TV, Tb.Th, the degree of anisotropy, and mechanical strength, while BV.horz/BV.vert and Tb.Th.horz/Tb.Th.vert were increased. This indicates that the more loaded vertical trabeculae are pronouncedly more thinned than the less loaded supporting horizontal trabeculae during unloading.

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

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

•

first time ever study to relate microarchitecture to the fracture toughness of cancellous bone from the femoral head of FNF victims

•

reduction in bone mass relates to a reduction in the number of trabeculae and trabecular thickness and an increase in trabeculae spacing

•

bone loss observed appears to be a consequence of thinning of the trabeculae in males and perforation of the trabeculae in females

•

study hints that TbTh, TbSp, SMI and TbN may provide a proxy or surrogate for BV/TV

•

fracture models can be improved by including microarchitecture, BMD and the bone mineral quality of osteoporotic cancellous bone

Laser-wakefield accelerators as hard x-ray sources for 3D medical imaging of human bone

A bright μm-sized source of hard synchrotron x-rays (critical energy Ecrit > 30 keV) based on the betatron oscillations of laser wakefield accelerated electrons has been developed. The potential of this source for medical imaging was demonstrated by performing micro-computed tomography of a human femoral trabecular bone sample, allowing full 3D reconstruction to a resolution below 50 μm. The use of a 1 cm long wakefield accelerator means that the length of the beamline (excluding the laser) is dominated by the x-ray imaging distances rather than the electron acceleration distances. The source possesses high peak brightness, which allows each image to be recorded with a single exposure and reduces the time required for a full tomographic scan. These properties make this an interesting laboratory source for many tomographic imaging applications.

Kefir improves bone mass and microarchitecture in an ovariectomized rat model of postmenopausal osteoporosis

SUMMARY

Kefir treatment in ovariectomized (OVX) rats could significantly decrease the levels of bone turnover markers and prevent OVX-induced bone loss, deterioration of trabecular microarchitecture, and biomechanical dysfunction that may be due to increase intracellular calcium uptake through the TRPV6 calcium channel.

INTRODUCTION

Osteoporosis is a disease characterized by low bone mass and structural deterioration of bone tissue, leading to an increased fracture risk. The incidence of osteoporosis increases with age and occurs most frequently in postmenopausal women due to estrogen deficiency, as the balance between bone resorption and bone formation shifts towards increased levels of bone resorption. Among various methods of prevention and treatment for osteoporosis, an increase in calcium intake is the most commonly recommended preventive measure. Kefir is a fermented milk product made with kefir grains that degrade milk proteins into various peptides with health-promoting effects, including immunomodulating-, antithrombotic-, antimicrobial-, and calcium-absorption-enhancing bioactivities.

METHODS

The aim of this study is to investigate the effect of kefir on osteoporosis prophylaxis in an ovariectomized rat model. A total of 56 16-week-old female Sprague-Dawley (SD) rats were divided into 7 experimental groups: sham (normal), OVX/Mock, OVX/1X kefir (164 mg/kg BW/day), OVX/2X kefir (328 mg/kg BW/day), OVX/4X kefir (656 mg/kg BW/day), OVX/ALN (2.5 mg/kg BW/day), and OVX/REBONE (800 mg/kg BW/day). After 12-week treatment with kefir, the bone physiology in the OVX rat model was investigated. Accordingly, the aim of this study was to investigate the possible transport mechanism involved in calcium absorption using the Caco-2 human cell line.

RESULTS

A 12-week treatment with kefir on the OVX-induced osteoporosis model reduced the levels of C-terminal telopeptides of type I collagen (CTx), bone turnover markers, and trabecular separation (Tb. Sp.). Additionally, treatment with kefir increased trabecular bone mineral density (BMD), bone volume (BV/TV), trabecular thickness (Tb. Th), trabecular number (Tb. N), and the biomechanical properties (hardness and modulus) of the distal femur with a dose-dependent efficacy. In addition, in in vitro assay, we found that kefir increased intracellular calcium uptake in Caco-2 cell through TRPV6 calcium channels and not through L-type voltage-operated calcium channels.

CONCLUSION

The protective effect of kefir in the OVX rat model may occur through increasing intracellular calcium uptake through the TRPV6 calcium channel.

Mechanical loading causes detectable changes in morphometric measures of trabecular structure in human cancellous bone

The relationships between mechanical loads and bone microstructure are of interest to those who seek to predict bone mechanical properties from microstructure or to predict how organization of bone microstructure is driven by mechanical loads. While strains and displacements in the material are inherently responsible for mechanically caused changes in the appearance of the microstructure, it is the morphometric measures of microstructural organization that are often available for assessment of bone quality. Therefore, an understanding of how strain history is reflected in morphometric measures of bone microstructure has practical implications in that it may provide clinically measurable indices of mechanical history in bone and improve interpretation of bone mechanical properties from microstructural information. The objective of the current study was to examine changes in morphometric measures of cancellous bone microstructure in response to varying levels of continuum level strains. The experimental approach included stereologic analysis of microcomputed tomography (μCT) images of human cancellous bone samples obtained at sequentially increasing levels of strain in a custom-made loading apparatus mounted in a μCT scanner. We found that the degree of anisotropy (DA) decreased from baseline to failure and from failure to postfailure. DA partially recovered from postfailure levels upon unloading; however, the final DA was less than at failure and less than at baseline. We also found that average trabecular thickness (Tb.Th.Av) increased with displacements at postfailure and did not recover when unloaded. Average trabecular number decreased when the specimens were unloaded. In addition, the heterogeneity of Tb.Th as measured by intra-specimen standard deviation (Tb.Th.SD) increased and that of trabecular number (Tb.N.SD) decreased with displacements at postfailure. Furthermore, the intraspecimen coefficient of variation of trabecular number decreased at postfailure displacements but did not recover upon unloading. Finally, the coefficient of variation of trabecular separation at unload was less than that at baseline. These measures can be developed into image-based indices to estimate strain history, damage, and residual mechanical properties where direct analysis of stresses and strains, such as through finite element modeling, may not be feasible. It remains to be determined how wide a time interval can be used to estimate strain history before remodeling becomes an overriding effect on the trabecular architecture.

The micro-structure of bone trabecular fracture: an inter-site study

Trabecular bone fracture represents a major health problem, therefore the improvement of its assessment is mandatory for the reduction of the economic and social burden. The micro-structure of the trabecular bone was found to have an important effect on trabecular mechanical behavior. Nonetheless, the high variability of the trabecular micro-structure suggests a search for the local characteristics leading to the fracture. This work concerns the study of the local trabecular fracture zone and its morphometrical characterization, aiming to prediction of the probable fracture zone. Ninety micro-CT datasets acquired before and after the mechanical compression of 45 trabecular specimens were analyzed. Specimens were extracted from the lower limbs of two donors: 4 femora and 4 tibiae. A previously validated tool for the identification of the 3D fracture zone was applied and the local fracture zone was identified and analyzed in all the specimens. Fifteen morphometrical parameters were extracted for each local fracture zone. Standard statistical non-parametric analysis was performed to compare fractured and un-fractured zones together with a classification analysis for the prediction of the fracture zone. The statistical analysis showed strong statistical difference in the micro-structure of the trabecular fractured zone compared to the un-fractured one. Ten out of 15 measured parameters, like SMI, Tb.Th, BV/TV, off-axis angle, BS/BV and others, showed a statistical difference between full 3D fractured and un-fractured zones. Nonetheless, a satisfactory classification of the fractured zone was possible with none of the identified parameters. On the other hand, a total classification accuracy of 95.5% was presented by the application of a linear classifier based on a combination of the most representative parameters, like BS/BV and the off-axis angle. The study points out the local essence and peculiar characteristics of the fracture zone, it highlights the weakness of some parameters in discriminate between fractured and un-fractured zones and encourage focussing the future studies over the local fracture zone itself with the aim to identify objective differences that could one day lead to the improvement of clinical assessment of fracture risk.

Fast trabecular bone strength predictions of HR-pQCT and individual trabeculae segmentation-based plate and rod finite element model discriminate postmenopausal vertebral fractures

Although high-resolution peripheral quantitative computed tomography (HR-pQCT) has advanced clinical assessment of trabecular bone microstructure, nonlinear microstructural finite element (µFE) prediction of yield strength using a HR-pQCT voxel model is impractical for clinical use due to its prohibitively high computational costs. The goal of this study was to develop an efficient HR-pQCT-based plate and rod (PR) modeling technique to fill the unmet clinical need for fast bone strength estimation. By using an individual trabecula segmentation (ITS) technique to segment the trabecular structure into individual plates and rods, a patient-specific PR model was implemented by modeling each trabecular plate with multiple shell elements and each rod with a beam element. To validate this modeling technique, predictions by HR-pQCT PR model were compared with those of the registered high-resolution micro-computed tomography (HR-µCT) voxel model of 19 trabecular subvolumes from human cadaveric tibia samples. Both the Young's modulus and yield strength of HR-pQCT PR models strongly correlated with those of µCT voxel models (r²  = 0.91 and 0.86). Notably, the HR-pQCT PR models achieved major reductions in element number (>40-fold) and computer central processing unit (CPU) time (>1200-fold). Then, we applied PR model µFE analysis to HR-pQCT images of 60 postmenopausal women with (n = 30) and without (n = 30) a history of vertebral fracture. HR-pQCT PR model revealed significantly lower Young's modulus and yield strength at the radius and tibia in fracture subjects compared to controls. Moreover, these mechanical measurements remained significantly lower in fracture subjects at both sites after adjustment for areal bone mineral density (aBMD) T-score at the ultradistal radius or total hip. In conclusion, we validated a novel HR-pQCT PR model of human trabecular bone against µCT voxel models and demonstrated its ability to discriminate vertebral fracture status in postmenopausal women. This accurate nonlinear µFE prediction of the HR-pQCT PR model, which requires only seconds of desktop computer time, has tremendous promise for clinical assessment of bone strength.

Antiosteoporotic activity of echinacoside in ovariectomized rats

PURPOSE

Echinacoside (ECH), isolated from Cistanche tubulosa (Schrenk) R. Wight stems, has been reported to enhance bone regeneration in MC3T3-E1 cells in vitro. The objectives of this study were to investigate the antiosteoporotic effect of ECH on bone metabolism in the ovariectomized (OVX) rat model of osteoporosis in vivo.

METHODS

Fifty-six aged 6 months female Sprague-Dawley rats were randomly assigned into sham-operated group (SHAM) and six OVX subgroups (n=8 each). The OVX rats were then subdivided into six groups treated with vehicle (OVX), Xian-ling-gu-bao (XLGB, 0.5 g/kg body weight/day, orally), 17β-estradiol (E2, 50 μg/kg body weight/day, orally) or ECH (30, 90, and 270 mg/kg body weight, daily, orally) for 12 weeks respectively. We evaluated the pharmacological effects of E2, XLGB and ECH against osteoporosis by evaluating the body weight, uterus wet weight, serum and urine biochemical parameters, bone mineral density (BMD), bone biomechanical properties, bone microarchitecture, bone histomorphology and uterus immunohistochemistry.

RESULTS

In OVX rats, the increases of body weight, serum hydroxyproline (HOP) levels, and the decreases of uterus wet weight and BMD were significantly reversed by ECH treatment. Moreover, three dosages of ECH completely corrected the increased urine concentration of calcium (Ca), inorganic phosphorus (P), and HOP observed in OVX rats. Furthermore, Micro-CT analysis results of distal femur showed that all ECH-treated groups notably enhanced bone quality compared to OVX group (p<0.05). Consistent with this finding, total femur BMD and biomechanical strength of tibia were significantly improved (p<0.05) after 12 weeks ECH administration. Histological results also showed the protective activity of ECH through promotion of bone formation and suppression of bone resorption. In addition, the ECH administration also significantly enhanced the expression of ER in the uteri according to immunohistochemical evaluation (p<0.05). Those findings, based on the serum and urine biochemical, BMD, Micro-CT, biomechanical test, histopathological and immunohistochemical parameters, showed that ECH has a notable antiosteoporotic effect, similar to estrogen, especially effective for prevention osteoporosis induced by estrogen deficiency.

CONCLUSION

These results suggest that ECH, as a new class of phytoestrogen, has a remarkable antiosteoporotic activity, and may be a promising candidate for treatment of postmenopausal osteoporosis induced by estrogen deficiency in a natural way through herbal resources.

Vertebral fragility and structural redundancy

The mechanisms of age-related vertebral fragility remain unclear, but may be related to the degree of "structural redundancy" of the vertebra; ie, its ability to safely redistribute stress internally after local trabecular failure from an isolated mechanical overload. To better understand this issue, we performed biomechanical testing and nonlinear micro-CT-based finite element analysis on 12 elderly human thoracic ninth vertebral bodies (age 76.9 ± 10.8 years). After experimentally overloading the vertebrae to measure strength, we used nonlinear finite element analysis to estimate the amount of failed tissue and understand the failure mechanisms. We found that the amount of failed tissue per unit bone mass decreased with decreasing bone volume fraction (r(2)  = 0.66, p < 0.01). Thus, for the weak vertebrae with low bone volume fraction, overall failure of the vertebra occurred after failure of just a tiny proportion of the bone tissue (<5%). This small proportion of failed tissue had two sources: the existence of fewer vertically oriented load paths to which load could be redistributed from failed trabeculae; and the vulnerability of the trabeculae in these few load paths to undergo bending-type failure mechanisms, which further weaken the bone. Taken together, these characteristics suggest that diminished structural redundancy may be an important aspect of age-related vertebral fragility: vertebrae with low bone volume fraction are highly susceptible to collapse because so few trabeculae are available for load redistribution if the external loads cause any trabeculae to fail.

Trabecular architecture and vertebral fragility in osteoporosis

Osteoporosis heightens vertebral fragility owing to the biomechanical effects of diminished bone structure and composition. These biomechanical effects are only partially explained by loss in bone mass, so additional factors that are independent of bone mass are also thought to play an important role in vertebral fragility. Recent advances in imaging equipment, imaging-processing methods, and computational capacity allow researchers to quantify trabecular architecture in the vertebra at the level of the individual trabecular elements and to derive biomechanics-based measures of architecture that are independent of bone mass and density. These advances have shed light on the role of architecture in vertebral fragility. In addition to the adverse biomechanical consequences associated with trabecular thinning and loss of connectivity, a reduction in the number of vertical trabecular plates appears to be particularly harmful to vertebral strength. In the clinic, detailed architecture analysis is primarily applied to peripheral sites such as the distal radius and tibia. Analysis of trabecular architecture at these peripheral sites has shown mixed results for discriminating between patients with and without a vertebral fracture independent of bone mass, but has the potential to provide unique insight into the effects of therapeutic treatments. Overall, it does appear that trabecular architecture has an independent role on vertebral strength. Additional research is required to determine how and where architecture should be measured in vivo and whether assessment of trabecular architecture in a clinical setting improves prospective fracture risk assessment for the vertebra.

Local analysis of trabecular bone fracture

Assessment of bone fracture risk is the first step in the prevention of traumatic events. In several previous study the use of bone mineral density and bone volume fraction was suggested for the identification of the failure zone, nonetheless the limits of this approach were also investigated, underling the need of other information to fully describe the failure event. In the present study, a comparison between fracture and non-fracture zones of trabecular bone is proposed with the aim of analyze the local structural differences attempting to identify the morphometrical parameters who best can describe the trabecular fracture zone. Eighteen trabecular specimens were extracted from the lower limb of two donors without skeletal disorders. All the specimens were scanned by means of a micro-CT and mechanically tested. After the mechanical compression every specimen was scanned again obtaining for every specimen two datasets: pre- and post-failure. An automatic registration scheme, comprising of a three-dimensional automatic registration method to define the differences between the two datasets, and the application of a criterion for defining "broken" or "unbroken" trabeculae, was applied for the identification of the full 3D fracture zone. The morphometrical analysis of fracture and non-fracture zone was performed by the study of several morphometrical parameters, such as bone volume fraction, off-axis angle, structural model index, connectivity density, etc. The results of the two different structures were compared by means of a Wilcoxon non-parametric test. Ten out of 12 morphometrical parameters were found statistically significantly different between fracture and non-fracture zones, underlining the strong structural difference between the two areas. Nonetheless, only three of them have shown differences superior to 30%, with a reduce overlapping of their distributions: off-axis angle, structural model index and connectivity density. On the other hand, bone volume fraction showed a smaller, even if significant, difference with great overlap of the distributions, in agreement with the limits already pointed out in the literature.

Segmental variations in trabecular bone density and microstructure of the spine in senescence-accelerated mouse (SAMP6): a murine model for senile osteoporosis

The senescence-accelerated mouse strain P6 (SAMP6) is a model of senile osteoporosis, which possesses many features of senile osteoporosis in humans. So far, little is known about the systemic bone microstructural changes that occur at the cervical, thoracic, and lumbar vertebrae. In this study, we therefore investigated segmental variations of vertebral trabecular bone mineral density (BMD) and three-dimensional microstructure in SAMP6 and the normal control mouse (SAMR1) at 12 months of age using quantitative micro computed tomography (micro-CT) and image analysis software. The vertebral height and vertebral cross-sectional area (CSA) increased, while vertebral trabecular BMD and trabecular bone volume fraction (BV/TV) decreased from the cervical to lumbar spine both in SAMR1 and SAMP6. As compared with SAMR1, the thoracic vertebral CSA had a tendency to be low and the lumbar vertebral CSA was significantly declined in SAMP6. The vertebral trabecular BMD, BV/TV, trabecular thickness (Tb.Th), and trabecular number (Tb.N) significantly decreased in cervical, thoracic and lumbar spine of SAMP6. Trabecular bone pattern factor (TBPf) was higher at the lumbar spine and the structure model index (SMI) of the lower thoracic and lumbar spine was higher in SAMP6. These results indicate that vertebral trabecular bone microstructures are remarkably heterogeneous throughout the spine in both SAMR1 and SAMP6. The decrease of vertebral trabecular bone density in SAMP6 advanced faster caudally than cranially within the spine, similar phenomena were observed in humans. These findings highlight the relevance of SAMP6 for studies of vertebral fragility associated with senile osteoporosis.

A traditional Chinese herbal preparation, Er-Zhi-Wan, prevent ovariectomy-induced osteoporosis in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Er-Zhi-Wan (EZW), a classic Chinese formulation, which contains Fructus Ligustri Lucidi (FLL) and Herba Ecliptae (HE). EZW is widely used to prevent and treat various kidney diseases for its actions of nourishing the kidney and strengthening tendon and bone. Although recent reports indicate that EZW restrains osteoclastic bone resorption, its effects on the protection against define OVX-induced bone loss in mature rats have not been systematically investigated.

MATERIALS AND METHODS

Sixty 3-month-old female Sprague-Dawley rats were randomly assigned into sham-operated group (Sham) and five OVX subgroups, OVX with vehicle (OVX); OVX with Estradiol Valerate (EV, 0.4 mg/kg body weight/day); OVX with EZW of graded doses (9.0, 4.5, or 2.25 g/kg/day). Daily oral administration of EV and EZW on 5th week for 26 weeks. Bone turnover markers (Serum alkaline phosphatase (ALP), bone-specific alkaline phosphatase (BALP), osteocalcin (OCN), deoxypyridinoline (DPD)), other parameters, including serum calcium (S-Ca), serum phosphorus (S-P), urine calcium (U-Ca), phosphorus (U-P), and bone mineral density (BMD) of the femur, 4th lumbar vertebra and tibia, bone biomechanical properties and trabecular microarchitecture parameters were measured.

RESULTS

Administration of EZW could significantly prevent ovariectomy-induced bone loss, biomechanical reduction, deterioration of trabecular microarchitecture and the body weight gain without affecting the weight of the uterus, and increased S-Ca, S-P levels, decreased level of bone turnover markers and U-Ca, U-P levels in ovariectomized rats.

CONCLUSION

The present study indicated that EZW had a definite antiosteoporotic effect without hyperplastic effect on uterus, and it might be a potential alternative medicine for treatment of postmenopausal osteoporosis.

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.

Exercise prescription after fragility fracture in older adults: a scoping review

The purpose of this study is to identify and chart research literature on safety, efficacy, or effectiveness of exercise prescription following fracture in older adults. We conducted a systematic, research-user-informed, scoping review. The population of interest was adults aged ≥45 years with any fracture. "Exercise prescription" included post-fracture therapeutic exercise, physical activity, or rehabilitation interventions. Eligible designs included knowledge synthesis studies, primary interventional studies, and observational studies. Trained reviewers independently evaluated citations for inclusion. A total of 9,415 citations were reviewed with 134 citations (119 unique studies) identified: 13 knowledge syntheses, 95 randomized or controlled clinical trials, and 11 "other" designs, representing 74 articles on lower extremity fractures, 34 on upper extremity, eight on vertebral, and three on mixed body region fractures. Exercise prescription characteristics were often missing or poorly described. Six general categories emerged describing exercise prescription characteristics: timing post-fracture, person prescribing, program design, functional focus, exercise script parameters, and co-interventions. Upper extremity and ankle fracture studies focused on fracture healing or structural impairment outcomes, whereas hip fracture studies focused more on activity limitation outcomes. The variety of different outcome measures used made pooling or comparison of outcomes difficult. There was insufficient information to identify evidence-informed parameters for safe and effective exercise prescription for older adults following fracture. Key gaps in the literature include limited numbers of studies on exercise prescription following vertebral fracture, poor delineation of effectiveness of different strategies for early post-fracture mobilization following upper extremity fracture, and inconsistent details of exercise prescription characteristics after lower extremity fracture.

Influence of vertical trabeculae on the compressive strength of the human vertebra

Vertebral strength, a key etiologic factor of osteoporotic fracture, may be affected by the relative amount of vertically oriented trabeculae. To better understand this issue, we performed experimental compression testing, high-resolution micro-computed tomography (µCT), and micro-finite-element analysis on 16 elderly human thoracic ninth (T(9)) whole vertebral bodies (ages 77.5 ± 10.1 years). Individual trabeculae segmentation of the µCT images was used to classify the trabeculae by their orientation. We found that the bone volume fraction (BV/TV) of just the vertical trabeculae accounted for substantially more of the observed variation in measured vertebral strength than did the bone volume fraction of all trabeculae (r(2) = 0.83 versus 0.59, p < .005). The bone volume fraction of the oblique or horizontal trabeculae was not associated with vertebral strength. Finite-element analysis indicated that removal of the cortical shell did not appreciably alter these trends; it also revealed that the major load paths occur through parallel columns of vertically oriented bone. Taken together, these findings suggest that variation in vertebral strength across individuals is due primarily to variations in the bone volume fraction of vertical trabeculae. The vertical tissue fraction, a new bone quality parameter that we introduced to reflect these findings, was both a significant predictor of vertebral strength alone (r(2) = 0.81) and after accounting for variations in total bone volume fraction in multiple regression (total R(2) = 0.93). We conclude that the vertical tissue fraction is a potentially powerful microarchitectural determinant of vertebral strength.

Anabolic and antiresorptive drugs improve trabecular microarchitecture and reduce fracture risk following radiation therapy

Many patients with symptomatic bone metastases receive radiation therapy, even though radiation is known to have potential adverse effects on bone. We hypothesized that the concurrent use of a bisphosphonate drug (zoledronic acid, ZA) or a combination of ZA plus an anabolic agent (parathyroid hormone, PTH) would lead to improvements in the microarchitecture and mechanical properties of irradiated bone. Human breast cancer cells were injected into the distal femur of 56 female nude mice, which were then divided into four groups: no treatment (0 Gy), radiation administered 4 weeks postinjection (20 Gy), radiation plus ZA (12.5 microg/kg weekly from weeks 4 to 12) (20 Gy + ZA), and radiation followed by ZA (25 microg/kg weekly from weeks 4 to 8) and PTH(1-34) (100 microg microg/kg daily from weeks 8 to 12) (20 Gy + ZA + PTH). Left limbs served as normal control bones. Bone loss over the 12-week study was tracked with serial radiography and bone densitometry. At the end of the study, micro-computed tomography and mechanical testing were used to quantify bone microarchitecture and bone strength. Radiation alone failed to prevent tumor-induced decreases in bone mineral density (BMD), trabecular bone volume, and bone strength. Treatment with 20 Gy + ZA or 20 Gy + ZA + PTH as adjuncts to radiation was effective at preserving trabecular bone architecture and bone strength at normal levels. ZA reduced the risk of mechanical fragility following irradiation of a lytic bone lesion. Supplemental use of PTH did not result in further increases in bone strength but was associated with significant increases in BMD and bone mass, suggesting that it may be beneficial in enhancing bone architecture following radiation therapy.

Multiscale modelling and nonlinear finite element analysis as clinical tools for the assessment of fracture risk

The risk of osteoporotic fractures is currently estimated based on an assessment of bone mass as measured by dual-energy X-ray absorptiometry. However, patient-specific finite element (FE) simulations that include information from multiple scales have the potential to allow more accurate prognosis. In the past, FE models of bone were limited either in resolution or to the linearization of the mechanical behaviour. Now, nonlinear, high-resolution simulations including the bone microstructure have been made possible by recent advances in simulation methods, computer infrastructure and imaging, allowing the implementation of multiscale modelling schemes. For example, the mechanical loads generated in the musculoskeletal system define the boundary conditions for organ-level, continuum-based FE models, whose nonlinear material properties are derived from microstructural information. Similarly microstructure models include tissue-level information such as the dynamic behaviour of collagen by modifying the model's constitutive law. This multiscale approach to modelling the mechanics of bone allows a more accurate characterization of bone fracture behaviour. Furthermore, such models could also include the effects of ageing, osteoporosis and drug treatment. Here we present the current state of the art for multiscale modelling and assess its potential to better predict an individual's risk of fracture in a clinical setting.

Correlation of mechanical properties within the equine third metacarpal with trabecular bending and multi-density micro-computed tomography data

Computed tomography (CT) data can be employed with respect to determining mechanical properties and has been used to predict parameters such as elastic modulus, yield strength, and ultimate strength of intact bone. Micro-computed tomography (muCT) possesses the resolution capable of detecting apparent bone density in extremely local regions and can characterize the trabecular structure. It has been asserted that this micro-structure is susceptible to micro-buckling and bending, which has a controversial role in predicting the global mechanical properties of bone. The current study measured the mechanical properties of relatively high apparent density bone from the equine distal third metacarpal. The mechanical properties were correlated with trabecular morphology parameters and apparent densities of localized regions obtained with muCT. These data were used to test two hypotheses: (1) accounting for trabecular bending using trabecular morphology parameters would provide better global mechanical property predictions than using only apparent density, and (2) regions of low apparent density dominate the overall mechanical behavior and provide greater correlation to the measured mechanical properties than regions of high apparent density. The data indicated that accounting for trabecular bending with morphological parameters resulted in stronger correlations to mechanical properties than correlations that relied only on apparent density (r2= 0.91 versus r2= 0.81). Low apparent density regions were more strongly correlated with mechanical properties than high apparent density regions (r2= 0.85 versus r2= 0.77), demonstrating the importance of selecting appropriate regions when attempting to predict mechanical properties from CT data.

Anisotropy and inhomogeneity of the trabecular structure can describe the mechanical strength of osteoarthritic cancellous bone

Osteoarthritic cancellous bone was studied to investigate the development of this pathology, and the functional changes it induces in the bone. In order to predict how the morphological alterations of the tissue induced by the pathology can change the mechanical properties of the structure, two different strategies have been used in the literature: (1) emphasising the influence of structural anisotropy; (2) stressing the highly inhomogeneous characteristics of cancellous bone. The aim of the present study was to verify the theory that mechanical strength of osteoarthritic cancellous bone depends both on tissue anisotropy and inhomogeneity. Twenty-five specimens were extracted from osteoarthritic femoral heads, along selected directions, and analysed by means of a microtomograph. The same specimens were mechanically tested in compression to determine the mechanical strength. The most representative structural parameters, confirmed by a stepwise analysis, were used to define four models to describe the measured mechanical strength. The models were applied neglecting (global analysis) or considering (local analysis) tissue inhomogeneities to verify whether the correlation with ultimate stress could be improved. The coefficient of determination increased from 0.53, considering only bone volume fraction, up to 0.88, combining it with off-axis angle and normalised eigenvalue. A further improvement was found performing a local analysis (R(2)=0.90), which corresponded to a decrease of 17% in the residual error. The proposed approach of considering both tissue anisotropy and inhomogeneity improved the accuracy in predicting the mechanical behaviour of cancellous bone tissue and should be suitable for more general loading conditions.

Simulation of vertebral trabecular bone loss using voxel finite element analysis

Trabecular bone loss in human vertebral bone is characterised by thinning and eventual perforation of the horizontal trabeculae. Concurrently, vertical trabeculae are completely lost with no histological evidence of significant thinning. Such bone loss results in deterioration in apparent modulus and strength of the trabecular core. In this study, a voxel-based finite element program was used to model bone loss in three specimens of human vertebral trabecular bone. Three sets of analyses were completed. In Set 1, strain adaptive resorption was modelled, whereby elements which were subject to the lowest mechanical stimulus (principal strain) were removed. In Set 2, both strain adaptive and microdamage mechanisms of bone resorption were included. Perforation of vertical trabeculae occurred due to microdamage resorption of elements with strains that exceeded a damage threshold. This resulted in collapse of the trabecular network under compression loading for two of the specimens tested. In Set 3, the damage threshold strain was gradually increased as bone loss progressed, resulting in reduced levels of microdamage resorption. This mechanism resulted in trabecular architectures in which vertical trabeculae had been perforated and which exhibited similar apparent modulus properties compared to experimental values reported in the literature. Our results indicate that strain adaptive remodelling alone does not explain the deterioration in mechanical properties that have been observed experimentally. Our results also support the hypothesis that horizontal trabeculae are lost principally by strain adaptive resorption, while vertical trabeculae may be lost due to perforation from microdamage resorption followed by rapid strain adaptive resorption of the remaining unloaded trabeculae.

Role of trabecular microarchitecture in whole-vertebral body biomechanical behavior

The role of trabecular microarchitecture in whole-vertebral biomechanical behavior remains unclear, and its influence may be obscured by such factors as overall bone mass, bone geometry, and the presence of the cortical shell. To address this issue, 22 human T(9) vertebral bodies (11 female; 11 male; age range: 53-97 yr, 81.5 +/- 9.6 yr) were scanned with microCT and analyzed for measures of trabecular microarchitecture, BMC, cross-sectional area, and cortical thickness. Sixteen of the vertebrae were biomechanically tested to measure compressive strength. To estimate vertebral compressive stiffness with and without the cortical shell for all 22 vertebrae, two high-resolution finite element models per specimen-one intact model and one with the shell removed-were created from the microCT scans and virtually compressed. Results indicated that BMC and the structural model index (SMI) were the individual parameters most highly associated with strength (R(2) = 0.57 each). Adding microarchitecture variables to BMC in a stepwise multiple regression model improved this association (R(2) = 0.85). However, the microarchitecture variables in that regression model (degree of anisotropy, bone volume fraction) differed from those when BMC was not included in the model (SMI, mean trabecular thickness), and the association was slightly weaker for the latter (R(2) = 0.76). The finite element results indicated that the physical presence of the cortical shell did not alter the relationships between microarchitecture and vertebral stiffness. We conclude that trabecular microarchitecture is associated with whole-vertebral biomechanical behavior and that the role of microarchitecture is mediated by BMC but not by the cortical shell.

Contributions of trabecular rods of various orientations in determining the elastic properties of human vertebral trabecular bone

Trabecular bone networks consist of two basic microstructural types: plates and rods. Although trabecular rods represent only a small fraction of total bone volume, their existence has important roles in failure initiation and progression. The goal of this study was to quantitatively examine the contributions of trabecular rods in various orientations to the anisotropic elastic moduli of human vertebral trabecular bone. Twenty-one human vertebral trabecular bone specimens were scanned by microcomputed tomography (microCT). A coordinate system of orthotropic axes representing the best elastic orthotropic symmetry was determined for each sample. Individual trabeculae segmentation (ITS), a 3D image analysis technique, was performed to identify each individual trabecular rod and determine its orientation in the orthotropic coordinate system. Next, three rod-removed images were created where longitudinal, oblique, or transverse trabecular rods were removed, respectively, from the original microCT images. The original and three categories of rod-removed images were then converted to finite element (FE) models for evaluation of their elastic moduli and anisotropy. Both the transverse and oblique rod-removal caused significant decreases in all six elastic moduli. However, the removal of longitudinal rods only caused significant changes in E(33), G(23), and G(31) but not in any transverse/in-plane elastic properties (E(11), E(22), and G(12)). The analysis of covariance (ANCOVA) with repeated measures was applied to detect the moduli change in the different models caused by the effects beyond just bone volume loss. The results suggested that the loss of transverse rods induced a significant decrease in in-plane mechanical competence, which was greater than what could be explained only by the associated bone volume loss. In contrast, the reduction in the axial Young's modulus caused by the loss of transverse rods was proportional to the bone volume decrease. Furthermore, the loss of longitudinal rods affected the axial Young's modulus through both bone volume loss and architectural change. With aging, the reduction in in-plane mechanical competence would be magnified by the preferential loss of transverse rods. The predictive ability of bone mineral density, a surrogate of BV/TV in clinical measurements, may reduce more quickly for transverse mechanical properties than for the axial mechanical properties.

Predictive value of femoral head heterogeneity for fracture risk

Osteoporosis (OP) is characterized by low bone mass and weak bone structure, which results in increased fracture risk. It has been suggested that osteoporotic bone is strongly adapted to the main loading direction and less adapted to the other directions. In this study, we hypothesized that osteoporotic femoral heads have 1) an increased anisotropy; 2) a more heterogenic distribution of bone volume fraction (BV/TV) throughout the femoral head; and, 3) a more heterogenic distribution of the trabecular thickness (Tb.Th.) throughout the femoral head, as compared to non-osteoporotic bone. To test these hypotheses, we used 7 osteoporotic femoral heads from patients who fractured their femoral neck and 7 non-fractured femoral heads from patients with osteoarthrosis (OA). Bone structural parameters from the entire trabecular region were analyzed using microCT. We found that the degree of anisotropy was higher in the fractured femoral heads, i.e. 1.72, compared to a value of 1.61 in the non-fractured femoral heads. The BV/TV and Tb.Th. and their variations throughout the femoral head, however, were all significantly lower in the fractured group. Hence, the first hypothesis was confirmed, whereas the other two were rejected. Interestingly, the variation of Tb.Th. throughout the femoral head provided a 100% discrimination between the OP and OA groups, i.e. for the same BV/TV, all fractured cases had a less heterogenic distribution. In conclusion, our results suggest that bone loss in OP takes place uniformly throughout the femoral head, leading to an overall decrease in bone mass and trabecular thickness. Furthermore, the variation of Tb.Th. in the femoral head could be an interesting parameter to improve the prediction of fracture risk in the proximal femur.

Bone volume fraction explains the variation in strength and stiffness of cancellous bone affected by metastatic cancer and osteoporosis

Preventing nontraumatic fractures in millions of patients with osteoporosis or metastatic cancer may significantly reduce the associated morbidity and reduce health-care expenditures incurred by these fractures. Predicting fracture occurrence requires an accurate understanding of the relationship between bone structure and the mechanical properties governing bone fracture that can be readily measured. The aim of this study was to test the hypothesis that a single analytic relationship with either bone tissue mineral density or bone volume fraction (BV/TV) as independent variables could predict the strength and stiffness of normal and pathologic cancellous bone affected by osteoporosis or metastatic cancer. After obtaining institutional review board approval and informed consent, 15 patients underwent excisional biopsy of metastatic prostate, breast, lung, ovarian, or colon cancer from the spine and/or femur to obtain 41 metastatic cancer specimens. In addition, 96 noncancer specimens were excised from 43 age- and site-matched cadavers. All specimens were imaged using micro-computed tomography (micro-CT) and backscatter emission imaging and tested mechanically by uniaxial compression and nanoindentation. The minimum BV/TV, measured using quantitative micro-CT, accounted for 84% of the variation in bone stiffness and strength for all cancellous bone specimens. While relationships relating bone density to strength and stiffness have been derived empirically for normal and osteoporotic bone, these relationships have not been applied to skeletal metastases. This simple analytic relationship will facilitate large-scale screening and prediction of fracture risk for normal and pathologic cancellous bone using clinical CT systems to determine the load capacity of bones altered by metastatic cancer, osteoporosis, or both.

Microarchitecture influences microdamage accumulation in human vertebral trabecular bone

It has been suggested that accumulation of microdamage with age contributes to skeletal fragility. However, data on the age-related increase in microdamage and the association between microdamage and trabecular microarchitecture in human vertebral cancellous bone are limited. We quantified microdamage in cancellous bone from human lumbar (L(2)) vertebral bodies obtained from 23 donors 54-93 yr of age (8 men and 15 women). Damage was measured using histologic techniques of sequential labeling with chelating agents and was related to 3D microarchitecture, as assessed by high-resolution microCT. There were no significant differences between sexes, although women tended to have a higher microcrack density (Cr.Dn) than men. Cr.Dn increased exponentially with age (r = 0.65, p < 0.001) and was correlated with bone volume fraction (BV/TV; r = -0.55; p < 0.01), trabecular number (Tb.N; r = -0.56 p = 0.008), structure model index (SMI; r = 0.59; p = 0.005), and trabecular separation (Tb.Sp; r = 0.59; p < 0.009). All architecture parameters were strongly correlated with each other and with BV/TV. Stepwise regression showed that SMI was the best predictor of microdamage, explaining 35% of the variance in Cr.Dn and 20% of the variance in diffuse damage accumulation. In addition, microcrack length was significantly greater in the highest versus lowest tertiles of SMI. In conclusion, in human vertebral cancellous bone, microdamage increases with age and is associated with low BV/TV and a rod-like trabecular architecture.

Variation in Bone Quality during Regenerative Process

Since preferential orientation of c-axis of biological apatite (BAp) crystallites depends strongly on the shape of hard tissue, closely relating to the in vivo stress distribution, it is a useful parameter to judge the bone quality. In this study, preferential alignment of BAp crystallites in original and regenerated hard tissues were analyzed by the micro-beam X-ray diffractometer (μ-XRD) with a beam spot of 50 or 100 μm in diameter. Regenerating processes of bone defects introduced artificially in the rabbit ulna or skull were healed by inserting a biodegradable gelatin hydrogel incorporating basic fibroblast growth factor-2 (FGF-2). Recovery of BAp orientation alignment depends strongly on the regenerated portion and period, which is insufficient to recover the original level, while bone mineral density (BMD) is almost improved to the original level. This means that BMD recovers prior to improvement of the BAp orientation and the related mechanical function in the regenerated tissues. Thus, reloading on the regenerated portion caused by BMD restoration is suggested to accelerate to produce the appropriate BAp preferential alignment due to the remodeling process. The BAp orientation was finally concluded to be one of the most important indices to check the regenerative degree and process in the regenerated bone under the tissue engineering technique.

Polarization-modulated second harmonic generation imaging: method for quantitative assessment of disorganization in anulus

An experimental method for quantifying disorder within the anulus fibrosus is described based on polarization-modulated second harmonic generation imaging (PM-SHG-I). This method is demonstrated by imaging the anular lamellar architecture of a mouse model of compressive loading. Results were consistent with those obtained in an earlier study where organization was quantified directed secants image analysis on photomicrographs. In this study the orientation within individual lamellia is quantified by average orientation of the collagen molecules within a defined volume of a single lamellar as measured by the PM-SHG-I. Lamellar boundaries can be identified through the SHG intensity images, and confirmed through co-registration with photomicrographs of the same region. The orientation within the lamellar is quantified by the polarization angle of the maximum second harmonic intensity. PM-SHG-I offers several advantages as compared with the method of directed secants: first, it is nondestructive, allowing repeated measurements of the same tissue; second, images are captured on the order of seconds and capable of obtaining information up to a depth of 200-300 microns, thus allowing for real-time assessment of load damage; third, organization is measured at a much higher resolution, as it is based on disorder within the molecular arrays of a single lamella.