Dairy Food Intake Is Not Associated with Measures of Bone Microarchitecture in Men and Women: The Framingham Osteoporosis Study.

Previous studies reported that dairy foods are associated with higher areal bone mineral density (BMD) in older adults. However, data on bone strength and bone microarchitecture are lacking. We determined the association of dairy food intake (milk, yogurt, cheese, milk + yogurt, and milk + yogurt + cheese, servings/week) with high resolution peripheral quantitative computed tomography (HR-pQCT) measures of bone (failure load, cortical BMD, cortical thickness, trabecular BMD, and trabecular number). This cross-sectional study included participants with diet from a food frequency questionnaire (in 2005-2008 and/or 1998-2001) and measurements of cortical and trabecular BMD and microarchitecture at the distal tibia and radius (from HR-pQCT in 2012-2015). Sex-specific multivariable linear regression estimated the association of dairy food intake (energy adjusted) with each bone measure adjusting for covariates. Mean age was 64 (SD 8) years and total milk + yogurt + cheese intake was 10.0 (SD 6.6) and 10.6 (6.4) servings/week in men and women, respectively. No significant associations were observed for any of the dairy foods and bone microarchitecture measures except for cheese intake, which was inversely associated with cortical BMD at the radius (p = 0.001) and tibia (p = 0.002) in women alone. In this cohort of primarily healthy older men and women, dairy intake was not associated with bone microarchitecture. The findings related to cheese intake and bone microarchitecture in women warrant further investigation.

Is There an Association Between Bone Microarchitecture and Fracture in Patients who were Treated for High-grade Osteosarcoma? A Controlled Study at Long-term Follow-up Using High-resolution Peripheral Quantitative CT.

BACKGROUND: Neoadjuvant chemotherapy in patients with primary osteosarcoma improves survival rates, but it also causes side effects in various organs including bone. Low bone mineral density (BMD) can occur owing partly to chemotherapy or limited mobility. This can cause a higher risk of fractures compared with those who do not receive such treatment. Changes in BMD alone cannot explain the propensity of fractures. Studying microarchitectural changes of bone might help to understand the effect. QUESTIONS/PURPOSES: (1) Do patients who were treated for osteosarcoma (more than 20 years previously) have low BMD? (2) Do these patients experience more fractures than controls who do not have osteosarcoma? (3) What differences in bone microarchitecture are present between patients treated for high-grade osteosarcoma and individuals who have never had osteosarcoma? METHODS: We contacted 48 patients who were treated for osteosarcoma and who participated in an earlier study. These patients underwent multimodal treatment including chemotherapy more than 20 years ago. Of the original patient group, 60% (29 of 48) were missing, leaving 40% (19 of 48) available for inclusion in this study; all 19 agreed to participate. There were nine men and 10 women with a mean age of 46 ± 4 years and a mean time from surgery to examination of 28 ± 3 years. BMD was measured by dual-energy x-ray absorptiometry, and any fracture history was assessed using a questionnaire. Additionally, high-resolution peripheral quantitative CT was performed to compare the groups in terms of microarchitectural changes, such as cortical and trabecular area, cortical and trabecular thickness, cortical porosity, and endocortical perimeter. Participants in the control group were selected from a cohort consisting of a population-based random sample of 499 healthy adult women and men. Osteoporosis or low BMD was not an exclusion criterion for entering this study; however, the patients in the control group were selected based on a normal BMD (that is, T score > -1.0 at both the spine and hip). Also, the participants were matched based on age and sex. Differences between patients and controls were assessed using the Wilcoxon rank sum test for continuous variables and a chi-square test for categorical variables. A multiple regression analysis was performed. Model assumptions were checked using histograms and quantile-quantile plots of residuals. RESULTS: Twelve of 19 patients who were treated for osteosarcoma had either osteopenia (eight patients) or osteoporosis (four patients). More patients with osteosarcoma reported sustaining fractures (11 of 19 patients) than did control patients (2 of 19 controls; p < 0.001). Among all microarchitectural parameters, only the endocortical perimeter was increased in patients compared with the control group (75 ± 15 mm versus 62 ± 18 mm; p = 0.04); we found no differences between the groups in terms of cortical and trabecular area, cortical and trabecular thickness, or cortical porosity. CONCLUSION: Although patients who were treated for osteosarcoma had osteopenic or osteoporotic BMD and a higher proportion of patients experienced fractures than did patients in the control group, we could not confirm differences in microarchitectural parameters using high-resolution peripheral quantitative CT. Therefore, it seems that bone geometry and microstructural parameters are not likely the cause of the increased proportion of fractures observed in our patients who were treated for osteosarcoma. Until we learn more about the bone changes associated with chemotherapy in patients with osteosarcoma, we recommend that patients undergo regular BMD testing, and we recommend that physicians consider osteoporosis treatment in patients with low BMD. These data might provide the impetus for future multicenter prospective studies examining the association between chemotherapy and bone microarchitecture. LEVEL OF EVIDENCE: Level III, therapeutic study.

Liquid-phase ASEM imaging of cellular and structural details in cartilage and bone formed during endochondral ossification: Keap1-deficient osteomalacia.

Chondrogenesis and angiogenesis drive endochondral ossification. Using the atmospheric scanning electron microscopy (ASEM) without decalcification and dehydration, we directly imaged angiogenesis-driven ossification at different developmental stages shortly after aldehyde fixation, using aqueous radical scavenger glucose solution to preserve water-rich structures. An embryonic day 15.5 mouse femur was fixed and stained with phosphotungstic acid (PTA), and blood vessel penetration into the hypertrophic chondrocyte zone was visualised. We observed a novel envelope between the perichondrium and proliferating chondrocytes, which was lined with spindle-shaped cells that could be borderline chondrocytes. At postnatal day (P)1, trabecular and cortical bone mineralisation was imaged without staining. Additional PTA staining visualised surrounding soft tissues; filamentous connections between osteoblast-like cells and osteocytes in cortical bone were interpreted as the osteocytic lacunar-canalicular system. By P10, resorption pits had formed on the tibial trabecular bone surface. The applicability of ASEM for pathological analysis was addressed using knockout mice of Keap1, an oxidative-stress sensor. In Keap1-/- femurs, we observed impaired calcification and angiogenesis of epiphyseal cartilage, suggesting impaired bone development. Overall, the quick ASEM method we developed revealed mineralisation and new structures in wet bone tissue at EM resolution and can be used to study mineralisation-associated phenomena of any hydrated tissue.

Effect of Drilling Techniques on Microcracks and Pull-Out Strength of Cortical Screw Fixed in Human Tibia: An In-Vitro Study.

The strength between the cortical screw and bone following an orthopaedic implant surgery is an important determinant for the success of osteosynthesis. An excessive axial cutting force during drilling produces microcracks in the bone surface, resulting in reduced strength between the screw and bone, resulting in loosening of implant. The present work, investigates the influence of drilling parameters on microcracks generated in the drilled surface and pull-out strength of screw fixed in cortical bone of human tibia. The holes were drilled by two different techniques: conventional surgical bone drilling (CSBD) and rotary ultrasonic bone drilling (RUBD), by a recently developed operation theatre (OT) compatible machine. Cutting force generated in drilling of human tibia using RUBD was 30-40% lesser than that of CSBD. Scanning electron microscopy (SEM) also revealed that RUBD produced significantly lesser and thinner microcracks than that of CSBD in human bones. Biomechanical pull-out test results showed that, the pull-out strength of screws inserted into drilled holes by RUBD was much higher (100-150%) than that of CSBD. A significant difference in pull-out strength (p < 0.05) between RUBD and CSBD was revealed by statistical analysis at 95% confidence interval.

Osteon circularity and longitudinal morphology: Quantitative and qualitative three-dimensional perspectives on human Haversian systems.

OBJECTIVES: Haversian systems result from bone remodeling, and show variation in size and shape among differing ages, body weights, mechanical environments, and species. While variables such as osteon circularity (On.Cr.) are generally studied in single transverse cross-sections, little is known about On.Cr. variation along an osteon's length, investigated here, in order to strengthen our understanding of bone microstructure. MATERIALS AND METHODS: Up to 875 measurements of On.Cr. were generated for 41 osteonal segments from the proximal anterior diaphysis of femoral human cortical bone of three adult male samples (ages 46, 62, 74). We employed four hypotheses to investigate On.Cr. variability, in cross-section and longitudinally. H1: There is no difference in On.Cr. among osteons comprising single cross-sections, H2: There is no difference in On.Cr. among individuals when single cross-sections are compared, H3: There is no difference in On.Cr. among measurements taken from an osteon along the longitudinal axis, and H4: There is no discernable pattern in an osteon's deviation from circularity. RESULTS: Quantitative analysis of single cross-sections revealed relatively consistent On.Cr. measurements within individual cross-sections and among individuals, supporting both, H1 and H2. Along individual osteonal segments, substantial degrees of dispersion from central tendencies were observed in 27 out of 41 analyzed osteons (despite relatively low overall standard deviations and interquartile ranges), leading to a rejection of H3. Qualitative characterization of morphological deviation from a "typical" circularity suggests a patterned deviation, leading also to a rejection of H4. DISCUSSION: On.Cr. variation is discussed in the context of both, phenomena intrinsic to a given osteon (including repetitive, small perturbations at roughly 45 µm intervals), and extrinsic (including shared reversal sheaths, osteonal branching, transverse connections, and osteonal repathing). Interesting associations between On.Cr. and other characteristics of the local Haversian network emphasize the role of Haversian systems as integrated parts of a greater morphological complex.

Detection and imaging of gadolinium accumulation in human bone tissue by micro- and submicro-XRF.

Gadolinium-based contrast agents (GBCAs) are frequently used in patients undergoing magnetic resonance imaging. In GBCAs gadolinium (Gd) is present in a bound chelated form. Gadolinium is a rare-earth element, which is normally not present in human body. Though the blood elimination half-life of contrast agents is about 90 minutes, recent studies demonstrated that some tissues retain gadolinium, which might further pose a health threat due to toxic effects of free gadolinium. It is known that the bone tissue can serve as a gadolinium depot, but so far only bulk measurements were performed. Here we present a summary of experiments in which for the first time we mapped gadolinium in bone biopsy from a male patient with idiopathic osteoporosis (without indication of renal impairment), who received MRI 8 months prior to biopsy. In our studies performed by means of synchrotron radiation induced micro- and submicro-X-ray fluorescence spectroscopy (SR-XRF), gadolinium was detected in human cortical bone tissue. The distribution of gadolinium displays a specific accumulation pattern. Correlation of elemental maps obtained at ANKA synchrotron with qBEI images (quantitative backscattered electron imaging) allowed assignment of Gd structures to the histological bone structures. Follow-up beamtimes at ESRF and Diamond Light Source using submicro-SR-XRF allowed resolving thin Gd structures in cortical bone, as well as correlating them with calcium and zinc.

The structure of cortical bone as revealed by the application of methods for the calcified matrix study.

Calcination and decalcification are basic procedures useful to a morphological approach of a biological, composite material like cortical bone. The study was carried out on a whole human femur conserved in liquid (from an educational collection). Cortical fracturing and SEM observation of vascular canals surface collagen texture was used to study bone deproteination at scalar temperatures (400-1,200°C) and acid bone decalcification at crescent time intervals. Heating burned and vaporized the organic matrix with shrinkage of the bone specimens as documented by the weight loss and transverse surface morphometry. SEM showed a pattern of aligned spherulites at 400°C which maintained the collagen fibrils layout (like a mineral cast), followed by a spherulites fusion progression with the temperature increments. At 1200°C a crystalline-like structure of tightly-packed trapezohendron units. XRD analysis supported the SEM morphology displaying the complete Debey rings of hydroxyapatite and spotted Debey rings of withlockite. Surface Ca and P elution was documented after 12 hr of exposition to the acid solution by dissolution of spherulites and the whole canal surface decalcified in depth after 15 days by SEM-EDAX analysis. The periodic pattern of collagen fibrils was still evident up to 15 days of decalcification together with fine granular deposits of a not-collagenic proteic material, while after 30 days no period was observed in the decalcified fibrils. Collagen mineral cast at 400°C calcination. Complete crystalline transformation at 1200°C. Up to 15 days of decalcification fibrils period maintained.

Material properties of the skull layers of the primate parietal bone: A single-subject study.

The outer cortical table of the parietal bone has been commonly used as a calvarial bone graft site for the craniofacial reconstruction. However, little is known about how removing the outer table may affect the function and structure of the inner table, and how the knowledge of the biomechanics and material properties of cortical bones will help the calvarial graft to better integrate into the biological and mechanical functions of its surrounding native tissues. In this study, it was hypothesized that there were significant differences in both density and material properties between inner and outer cortical plates in cranial bones. Twelve cylindrical specimens, including inner-outer layers, of cortical parietal bone of a female baboon were collected. Cortical thicknesses and densities were measured, and elastic properties were assessed using an ultrasonic technique. Results demonstrated remarkable difference in both thickness (t = 8.248, p ≤0.05) and density (t = 4.926, p≤0.05) between inner and outer cortical paired samples. Orthotropic characteristics of the cortical plates were detected as well, these findings suggest that there are differences in biomechanical properties between two surfaces of cranial bones at both tissue and organ levels. How these differences are linked to the stress environments of the inner and outer cranial cortical layers awaits further studies. Further study will greatly enhance our ability to address questions derived from both morphological and craniofacial medicine fields about the development and biomechanics of craniofacial skeletons.

Long-term peroral administration of bitter apricot seeds influences cortical bone microstructure of rabbits.

Apricot seeds due to the presence of cyanogenic glycoside amygdalin belong to the popular "alternative cancer cures", although anticancer effect of amygdalin remains controversial. This in vivo study points to the effect of long-term peroral administration of bitter apricot seeds on bone microstructure of rabbits since chronic amygdalin toxicity in relation to bone parameters has not been investigated yet. Rabbits (n = 16) were randomly divided into four experimental groups of 4 animals each. Three experimental groups S1, S2 and S3 received commercial feed for rabbits mixed with crushed bitter apricot seeds at doses 60, 300 and 420 mg/kg bw during five months, respectively. The control (C) group received no apricot seeds. The long-term consumption of apricot seeds had no impact on total body weight, femoral weight and femoral length of rabbits. Also, microcomputed tomography (3D analysis) of cortical and trabecular bone tissues did not reveal any significant impact of amygdalin toxicity on relative bone volume, BMD, cortical bone thickness, bone surface, trabecular number, thickness, and their separation. On the other hand, histological (2D) analysis demonstrated evident changes in cortical bone microstructure consistent with a decreased density of secondary osteons in the middle part of substantia compacta due to a replacement of Haversian bone tissue by plexiform bone tissue, vasoconstriction in the primary osteons' vascular canals, Haversian canals, and decreased sizes of secondary osteons in rabbits from S1, S2 and S3 groups. These negative changes are associated with different vascularization and biomechanical properties of cortical bones.

Femtosecond lasers for high-precision orthopedic surgery.

Laser micromachining with ultrashort pulses has shown great promise for clean, safe surgical treatment of bone tissue. However, comparisons of performance and development of "best practice" have been hampered by the difficulty of comparing results across a wide variety of experimental approaches and under surgically irrelevant conditions (e.g., dried, dead bone). Using a femtosecond (fs) pulsed laser system (τ = 140 fs, repetition rate = 1 kHz, λ = 800 nm), a comprehensive study of femtosecond laser microsurgery using the standard metrics of laser micromachining (ablation threshold, incubation effects, ablation rates, effect of focal point depth within the material and heat affected zone (HAZ)) was conducted on live, freshly harvested bovine and ovine cortical bone. Three important points of optimism for future implementation in the surgical theatre were identified: (1) the removal of material is relatively insensitive to the focal point depth within the material, removing the need for extreme depth precision for excellent performance; (2) femtosecond laser ablation of fresh bone demonstrates very little incubation effect, such that multiple passes of the laser over the same region of bone removes the same amount of material; and (3) the complete absence of collateral damage, heat- or shock-induced, on both the macro- and microscopic scales can be achieved readily, within a broad parameter range. Taken together, these results indicate a handheld or robotic deployed fiber laser platform for femtosecond laser microsurgery is a very viable prospect.

Compositional and mechanical properties of growing cortical bone tissue: a study of the human fibula.

Human cortical bone contains two types of tissue: osteonal and interstitial tissue. Growing bone is not well-known in terms of its intrinsic material properties. To date, distinctions between the mechanical properties of osteonal and interstitial regions have not been investigated in juvenile bone and compared to adult bone in a combined dataset. In this work, cortical bone samples obtained from fibulae of 13 juveniles patients (4 to 18 years old) during corrective surgery and from 17 adult donors (50 to 95 years old) were analyzed. Microindentation was used to assess the mechanical properties of the extracellular matrix, quantitative microradiography was used to measure the degree of bone mineralization (DMB), and Fourier transform infrared microspectroscopy was used to evaluate the physicochemical modifications of bone composition (organic versus mineral matrix). Juvenile and adult osteonal and interstitial regions were analyzed for DMB, crystallinity, mineral to organic matrix ratio, mineral maturity, collagen maturity, carbonation, indentation modulus, indicators of yield strain and tissue ductility using a mixed model. We found that the intrinsic properties of the juvenile bone were not all inferior to those of the adult bone. Mechanical properties were also differently explained in juvenile and adult groups. The study shows that different intrinsic properties should be used in case of juvenile bone investigation.

Acoustic diffusion constant of cortical bone: Numerical simulation study of the effect of pore size and pore density on multiple scattering.

While osteoporosis assessment has long focused on the characterization of trabecular bone, the cortical bone micro-structure also provides relevant information on bone strength. This numerical study takes advantage of ultrasound multiple scattering in cortical bone to investigate the effect of pore size and pore density on the acoustic diffusion constant. Finite-difference time-domain simulations were conducted in cortical microstructures that were derived from acoustic microscopy images of human proximal femur cross sections and modified by controlling the density (Ct.Po.Dn) ∈[5-25] pore/mm2 and size (Ct.Po.Dm) ∈[30-100] µm of the pores. Gaussian pulses were transmitted through the medium and the backscattered signals were recorded to obtain the backscattered intensity. The incoherent contribution of the backscattered intensity was extracted to give access to the diffusion constant D. At 8 MHz, significant differences in the diffusion constant were observed in media with different porous micro-architectures. The diffusion constant was monotonously influenced by either pore diameter or pore density. An increase in pore size and pore density resulted in a decrease in the diffusion constant (D =285.9Ct.Po.Dm-1.49, R2=0.989 , p=4.96×10-5,RMSE=0.06; D=6.91Ct.Po.Dn-1.01, R2=0.94, p=2.8×10-3 , RMSE=0.09), suggesting the potential of the proposed technique for the characterization of the cortical microarchitecture.

PYY is a negative regulator of bone mass and strength.

OBJECTIVE: Bone loss in anorexia nervosa and following bariatric surgery is associated with an elevated circulating concentration of the gastrointestinal, anorexigenic hormone, peptide YY (PYY). Selective deletion of the PYY receptor Y1R in osteoblasts or Y2R in the hypothalamus results in high bone mass, but deletion of PYY in mice has resulted in conflicting skeletal phenotypes leading to uncertainty regarding its role in the regulation of bone mass. As PYY analogs are under development for treatment of obesity, we aimed to clarify the relationship between PYY and bone mass. METHODS: The skeletal phenotype of Pyy knockout (KO) mice was investigated during growth (postnatal day P14) and adulthood (P70 and P186) using X-ray microradiography, micro-CT, back-scattered electron scanning electron microscopy (BSE-SEM), histomorphometry and biomechanical testing. RESULTS: Bones from juvenile and Pyy KO mice were longer (P < 0.001), with decreased bone mineral content (P < 0.001). Whereas, bones from adult Pyy KO mice had increased bone mineral content (P < 0.05) with increased mineralisation of both cortical (P < 0.001) and trabecular (P < 0.001) compartments. Long bones from adult Pyy KO mice were stronger (maximum load P < 0.001), with increased stiffness (P < 0.01) and toughness (P < 0.05) compared to wild-type (WT) control mice despite increased cortical vascularity and porosity (P < 0.001). The increased bone mass and strength in Pyy KO mice resulted from increases in trabecular (P < 0.01) and cortical bone formation (P < 0.05). CONCLUSIONS: These findings demonstrate that PYY acts as a negative regulator of osteoblastic bone formation, implicating increased PYY levels in the pathogenesis of bone loss during anorexia or following bariatric surgery.

Identification of collagen fibrils in cross sections of bone by electron energy loss spectroscopy (EELS).

Transmission electron microscopic (TEM) images of ion-milled bovid cortical bone cut approximately normal to the axes of fibrils show that mineral occurs in the form of plates surrounding and laying between circular or elliptical features about 50 nm in diameter. The classification of these features as either pores or collagen fibrils is highly debated. Electron energy loss spectroscopy (EELS) mapping of these features in ion milled sections shows that they are lacking significant amounts of mineral or collagen, although their appearance suggests that they are cross sections of collagen fibrils. However, analogous sections prepared using an ultramicrotome show that, while these circular features show reduced concentrations of calcium and phosphorus, some of them contain quantities of carbon and nitrogen in bonding states comparable to the composition of collagen. This work demonstrates that the observed circular features are sections of collagen fibrils, but that bombardment by argon ions during broad beam ion milling destroys the collagen and associated gap-zone mineral.

No Signature of Osteocytic Osteolysis in Cortical Bone from Lactating NMRI Mice.

The roles of osteocytes in bone homeostasis have garnered increasing attention since it has been realized that osteocytes communicate with other organs. It has long been debated whether and/or to which degree osteocytes can break down the bone matrix surrounding them in a process called osteocytic osteolysis. Osteocytic osteolysis has been indicated to be induced by a number of skeletal challenges including lactation in CD1 and C57BL/6 mice, whereas immobilization-induced osteocytic osteolysis is still a matter of controversy. Motivated by the wish to understand this process better, we studied osteocyte lacunae in lactating NMRI mice, which is a widely used outbred mouse strain. Surprisingly, no trace of osteocytic osteolysis could be detected in tibial or femoral cortical bone either by 3D investigation by synchrotron nanotomography, by studies of lacunar cross-sectional areas using scanning electron microscopy, or by light microscopy. These results lead us to conclude that osteocytic osteolysis does not occur in NMRI mice as a response to lactation, in turn suggesting that osteocytic osteolysis may not play a generic role in mobilizing calcium during lactation.

Surface characterization of the raw and cooked bovine cortical metatarsal bone.

PURPOSE: The purpose of this study was to quantify the elastic properties and evaluate microscopical features of raw and boiled metatarsal bovine bone. METHODS: The elastic modulus, hardness and microscopic surface of raw and cooked bovine metatarsal bone have been investigated using nanoindentation, SEM/EDX and Panasis microscope. RESULTS: Regarding raw bovine bone, the average elastic modulus was 30.515 ± 6,769 GPa, while the average hardness was 0.5683 ± 0.211 GPa. When it comes to boiled bone corresponding values were 22.298 ± 7.0303 GPa and 0.408 ± 0.199 GPa, respectively. The values for investigated parameters were significantly higher (p < 0.05) in raw bone specimens. Elastic modulus significantly correlated with hardness (p < 0.05). EDX analysis revealed significant decrease in wt% of oxygen in boiled samples (p < 0.05) No significant differences could be observed in SEM images particularly when analysing in smaller magnifications. Using higher magnification, additional branching of the existing voids as well as discrete reorganization and smoother edges of nutrient canals could be observed. The surface of boiled specimens was without the presence of crusts and layering, and no microscopical evidence of structural damage could be observed. CONCLUSIONS: This study provides detailed analysis of hardness, elastic modulus of raw and cooked bovine bone and their relation and changes during exposure to temperature. These results of elastic moduli and hardness could be comparable to similar studies of bovine and human bone tissue, but the careful analysis of experimental design, type of the bone as well as limitations of the employed techniques must be carried out before interpolation of the results to other theoretical, clinical, biomaterial and archeological studies.

Computed tomography porosity and spherical indentation for determining cortical bone millimetre-scale mechanical properties.

The cortex of the femoral neck is a key structural element of the human body, yet there is not a reliable metric for predicting the mechanical properties of the bone in this critical region. This study explored the use of a range of non-destructive metrics to measure femoral neck cortical bone stiffness at the millimetre length scale. A range of testing methods and imaging techniques were assessed for their ability to measure or predict the mechanical properties of cortical bone samples obtained from the femoral neck of hip replacement patients. Techniques that can potentially be applied in vivo to measure bone stiffness, including computed tomography (CT), bulk wave ultrasound (BWUS) and indentation, were compared against in vitro techniques, including compression testing, density measurements and resonant ultrasound spectroscopy. Porosity, as measured by micro-CT, correlated with femoral neck cortical bone's elastic modulus and ultimate compressive strength at the millimetre length scale. Large-tip spherical indentation also correlated with bone mechanical properties at this length scale but to a lesser extent. As the elastic mechanical properties of cortical bone correlated with porosity, we would recommend further development of technologies that can safely measure cortical porosity in vivo.

Homogenization of cortical bone reveals that the organization and shape of pores marginally affect elasticity.

With ageing and various diseases, the vascular pore volume fraction (porosity) in cortical bone increases, and the morphology of the pore network is altered. Cortical bone elasticity is known to decrease with increasing porosity, but the effect of the microstructure is largely unknown, while it has been thoroughly studied for trabecular bone. Also, popular micromechanical models have disregarded several micro-architectural features, idealizing pores as cylinders aligned with the axis of the diaphysis. The aim of this paper is to quantify the relative effects on cortical bone anisotropic elasticity of porosity and other descriptors of the pore network micro-architecture associated with pore number, size and shape. The five stiffness constants of bone assumed to be a transversely isotropic material were measured with resonant ultrasound spectroscopy in 55 specimens from the femoral diaphysis of 29 donors. The pore network, imaged with synchrotron radiation X-ray micro-computed tomography, was used to derive the pore descriptors and to build a homogenization model using the fast Fourier transform (FFT) method. The model was calibrated using experimental elasticity. A detailed analysis of the computed effective elasticity revealed in particular that porosity explains most of the variations of the five stiffness constants and that the effects of other micro-architectural features are small compared to usual experimental errors. We also have evidence that modelling the pore network as an ensemble of cylinders yields biased elasticity values compared to predictions based on the real micro-architecture. The FFT homogenization method is shown to be particularly efficient to model cortical bone.

Investigation of strontium transport and strontium quantification in cortical rat bone by time-of-flight secondary ion mass spectrometry.

Next-generation bone implants will be functionalized with drugs for stimulating bone growth. Modelling of drug release by such functionalized biomaterials and drug dispersion into bone can be used as predicting tool for biomaterials testing in future. Therefore, the determination of experimental parameters to describe and simulate drug release in bone is essential. Here, we focus on Sr2+ transport and quantification in cortical rat bone. Sr2+ dose-dependently stimulates bone-building osteoblasts and inhibits bone-resorbing osteoclasts. It should be preferentially applied in the case of bone fracture in the context of osteoporotic bone status. Transport properties of cortical rat bone were investigated by dipping experiments of bone sections in aqueous Sr2+ solution followed by time-of-flight secondary ion mass spectrometry (ToF-SIMS) depth profiling. Data evaluation was carried out by fitting a suitable mathematical diffusion equation to the experimental data. An average diffusion coefficient of D = (1.68 ± 0.57) · 10-13 cm2 s-1 for healthy cortical bone was obtained. This value differed only slightly from the value of D = (4.30 ± 1.43) · 10-13 cm2 s-1 for osteoporotic cortical bone. Transmission electron microscopy investigations revealed a comparable nano- and ultrastructure for both types of bone status. Additionally, Sr2+-enriched mineralized collagen standards were prepared for ToF-SIMS quantification of Sr2+ content. The obtained calibration curve was used for Sr2+ quantification in cortical and trabecular bone in real bone sections. The results allow important insights regarding the Sr2+ transport properties in healthy and osteoporotic bone and can ultimately be used to perform a simulation of drug release and mobility in bone.

The Influence of Cortical Porosity on the Strength of Bone During Growth and Advancing Age.

PURPOSE OF REVIEW: Bone densitometry provides a two-dimensional projected areal apparent bone mineral density that fails to capture the heterogeneity of bone's material composition and macro-, micro-, and nano-structures critical to its material and structural strength. Assessment of the structural basis of bone fragility has focused largely on trabecular bone based on the common occurrence of fragility fractures at sites with substantial amounts of trabecular bone. This review focuses on the contribution of cortical bone to bone fragility throughout life. RECENT FINDINGS: Accurately differentiating cortical and trabecular bone loss has important implications in quantifying bone fragility as these compartments have differing effects on bone strength. Recent advances in imaging methodology have improved distinction of these two compartments by (i) recognition of a cortico-trabecular transitional zone and (ii) quantifying bone microstructure in a region of interest that is a percentage of bone length rather than a fixed point. Additionally, non-invasive three-dimensional imaging methods allow more accurate quantification of changes in the cortical, trabecular, and cortico-trabecular compartments during growth, aging, disease, and treatment. Over 75% of the skeleton is assembled as cortical bone. Of all fragility fractures, ~ 80% are appendicular and involve regions rich in cortical bone and ~ 70% of all age-related appendicular bone loss is cortical and is mainly due to unbalanced intracortical remodeling which increases cortical porosity. The failure to achieve the optimal peak bone microstructure during growth due to disease and the deterioration in cortical and trabecular bone produced by bone loss compromise bone strength. The loss of strength produced by microstructural deterioration is disproportionate to the bone loss producing this deterioration. The reason for this is that the loss of strength increases as a 7th power function of the rise in cortical porosity and a 3rd power function of the fall in trabecular density (Schaffler and Burr in J Biomech. 21(1):13-6, 1988), hence the need to quantify bone microstructure.