Bone quality: a determinant for certain risk factors for bone fragility

Transmenopausal changes in cortical bone quality

Bone's resistance to fracture depends on its amount and quality, the latter including its structural and material/compositional properties. Bone material properties are dependent on bone turnover rates, which are significantly elevated immediately following menopause. Previously published data reported that following menopause, the amount of organic matrix synthesized at actively forming surfaces is significantly decreased, while glycosaminoglycan content was also modulated at resorbing surfaces, in the cancellous compartment. In the present study, we used Raman microspectroscopic analysis of paired iliac crest biopsies obtained before and shortly after menopause (1 year after cessation of menses) in healthy females to investigate changes in material/compositional properties due to menopause, in the cortical compartment. Specifically, the mineral/matrix ratio, the relative proteoglycan content, the mineral maturity/crystallinity, and the relative pyridinoline collagen cross-link content were determined at actively forming intracortical surfaces (osteons) as a function of tissue age, as well as in interstitial bone. Results indicated that it is the freshly synthesized organic matrix content that significantly declines following menopause, in agreement with what was previously reported for the cancellous compartment. This decline was not evident in the freshly deposited mineral content. None of the compositional/quality properties were altered following menopause either. Finally, no differences in any of the monitored parameters were evident in cortical interstitial bone.

Living near greenness is associated with higher bone strength: A large cross-sectional epidemiological study in China

BACKGROUND

Living near green spaces may benefit various health outcomes. However, no studies have investigated the greenness-bone linkage in the general population. Moreover, to which extent ambient air pollution (AAP), physical activity (PA), and body mass index (BMI) mediate this relationship remains unclear. We aimed to explore the association between greenness and bone strength and the potential mediating roles of AAP, PA, and BMI in Chinese adults.

METHODS

This cross-sectional analysis enrolled 66,053 adults from the China Multi-Ethnic Cohort in 2018-2019. The normalized difference vegetation index (NDVI) and enhanced vegetation index (EVI) were employed to define residential greenness. The calcaneus quantitative ultrasound index (QUI) was used to indicate bone strength. Multiple linear regression models and mediation analyses were used to estimate the residential greenness-bone strength association and potential pathways operating through AAP (represented by PM_2.5 [particulate matter <2.5 μm in diameter]), PA, and BMI. Stratification analyses were performed to identify susceptible populations.

RESULTS

Higher residential exposure to greenness was significantly associated with an increase in QUI, with changes (95% confidence interval) of 3.28 (3.05, 3.50), 3.57 (3.34, 3.80), 2.68 (2.46, 2.90), and 2.93 (2.71, 3.15) for every interquartile range increase in NDVI_500m, NDVI_1000m, EVI_500m, and EVI_1000m, respectively. Sex, urbanicity, annual family income, smoking, and drinking significantly modified the association of greenness-bone strength, with more remarkable associations in males, urban residents, subjects from wealthier families, smokers, and drinkers. For the NDVI_500m/EVI_500m-QUI relationship, the positive mediating roles of PM_2.5 and PA were 6.70%/8.50 and 2.43%/2.69%, respectively, whereas those negative for BMI and PA-BMI were 0.88%/1.06% and 0.05%/0.05%, respectively.

CONCLUSION

Living in a greener area may predict higher bone strength, particularly among males, urban residents, wealthier people, smokers, and drinkers. AAP, PA, BMI, and other factors may partially mediate the positive association. Our findings underscore the importance of optimizing greenness planning and management policies.

3D Interrelationship between Osteocyte Network and Forming Mineral during Human Bone Remodeling

During bone remodeling, osteoblasts are known to deposit unmineralized collagenous tissue (osteoid), which mineralizes after some time lag. Some of the osteoblasts differentiate into osteocytes, forming a cell network within the lacunocanalicular network (LCN) of bone. To get more insight into the potential role of osteocytes in the mineralization process of osteoid, sites of bone formation are three-dimensionally imaged in nine forming human osteons using focused ion beam-scanning electron microscopy (FIB-SEM). In agreement with previous observations, the mineral concentration is found to gradually increase from the central Haversian canal toward pre-existing mineralized bone. Most interestingly, a similar feature is discovered on a length scale more than 100-times smaller, whereby mineral concentration increases from the LCN, leaving around the canaliculi a zone virtually free of mineral, the size of which decreases with progressing mineralization. This suggests that the LCN controls mineral formation but not just by diffusion of mineralization precursors, which would lead to a continuous decrease of mineral concentration from the LCN. The observation is, however, compatible with the codiffusion and reaction of precursors and inhibitors from the LCN into the bone matrix.

Mineral and organic matrix composition at bone forming surfaces in postmenopausal women with osteoporosis treated with either teriparatide or zoledronic acid

The ability of bone to resist fracture is dependent on the composite nature of its mineral and organic matrix content. Teriparatide (TPTD) and zoledronic acid (ZOL) are approved anabolic and antiresorptive therapies, respectively, to reduce fracture risk in women with postmenopausal osteoporosis. In the SHOTZ study, postmenopausal women with osteoporosis were treated with TPTD (20 μg daily, subcutaneous) or ZOL (5 mg/year, intravenous infusion) for 24 months. Iliac crest biopsies were obtained at 6 months and again at 24 months from approximately one third of the original study cohort. To investigate the early effects of these two drugs on the quality of newly formed bone, we used vibrational spectroscopic techniques to analyze tetracycline-labelled transiliac biopsies obtained from participants at the 6-month time point. Raman spectra were acquired at forming trabecular and intra-cortical surfaces (identified by fluorescent double labels), to determine mineral, organic matrix, glycosaminoglycan, and tissue water content, as well as mineral maturity/crystallinity at three specific tissue ages (1-5, 15, and ≥25 days). Fourier transformed infrared microspectroscopy was used to determine pyridinoline/divalent collagen cross-link ratios. At 6 months, treatment with TPTD versus ZOL resulted in lower mineral and higher organic matrix content, increased tissue water content, and lower mineral/matrix, mineral maturity/crystallinity, glycosaminoglycan content, and pyridinoline/divalent enzymatic collagen cross-link ratio. Our results suggest that TPTD and ZOL have differential effects on material properties of newly formed bone at individual remodeling sites, highlighting their different mechanisms of action.

Rib histomorphometry: A reliability and validation study with a critical review of histological techniques for forensic age estimation

Fragmented human remains present a challenge for forensic experts as they attempt to identify individuals using standard forensic methods. Several histological age estimation techniques have been developed during the last fifty years to aid in this process. However, very few validation studies have been conducted in order to test their accuracy and bias, and thus, validation assessment is required as we employ them while testifying in court. Histological variables are assessed from rib thin sections from two Mediterranean samples; Cretans (N = 41) and Greek-Cypriots (N = 47). Intra and inter-observer errors are assessed through TEM analysis and Intra-class Correlation Coefficient by testing observers with different levels of experience as they collected data on osteon counts and area measurements. The relation between the variables and age is determined using correlation coefficients. Histomorphometric data are applied to four widely used age estimation formulas assessing the performance of the methods for the entire sample. Inaccuracy and bias are calculated with age estimations and known age tested for significance and proportional bias assessed. Overall, histological parameters presented acceptable intra- and inter-observer errors. All variables exhibited statistically significant correlation with age (P < 0.01). For three of the techniques, data showed a systematic underestimation of age with an increase in inaccuracy in older individuals. One of the age estimation formulas produced overestimation of young individuals yet, it more accurately estimated the age of older individuals. This validation study explores inter-population variation in bone remodeling dynamics and presents a critical evaluation on methodological issues that can affect the performance of existing histological techniques.

In vivo Labeling of Bone Microdamage in an Animal Model of Type 1 Diabetes Mellitus

Type 1 diabetes mellitus (DM1) is linked to a decrease in bone strength. Bone strength entails both bone mineral density and bone quality. Limited data are available regarding diabetes-induced microdamage, which can severely influence bone quality. This study has investigated bone microdamage as a measure of bone quality in an animal model of DM1. Microdamage in the neck of the femur was labelled in vivo using multiple fluorochromes at 4, 12 and 24 weeks after the onset of DM1. Microcracks were quantified and their morphology analyzed using microscopy techniques. The mean length of microcracks at 24 weeks, and crack numerical and surface densities were significantly higher (p < 0.05) 4 weeks after the onset of DM1 when compared with control. Diffuse damage density was highest at 12 weeks after the onset of DM1. The arrangement of the collagen fibrils became progressively more irregular from 4 to 24 weeks of DM. This is the first study to analyze microdamage in vivo at different time points of DM1. DM1is associated with microcracks from the early stage, however bone microstructure shows toughening mechanisms that arrest their growth but disease progression further deteriorates bone quality resulting in longer microcracks which may increase fracture risk.

Organic matrix quality discriminates between age- and BMD-matched fracturing versus non-fracturing post-menopausal women: A pilot study

Women with similar areal Bone Mineral Densities (BMD) may show divergent fracture incidence due to differences in bone quality. The hypothesis tested in the present pilot study is that postmenopausal (PM) women who have sustained osteoporotic fractures have altered organic matrix quality compared to those who have not. We used Raman microspectroscopy to analyze transiliac biopsies collected from fracturing (n = 6, mean age 62.5 ± 7.4 yrs; Cases) and non-fracturing PM women (n = 6, age- and BMD-matched; mean age 62.2 ± 7.3 yrs; Controls). Previous results show differences in intrinsic material properties by nanoindentation that are more homogenously distributed and could facilitate microcrack propagation in Cases, along with lower mineral carbonate/phosphate ratio by Fourier transform infrared spectroscopic imaging, and no differences in bone tissue mineralization by digitized microradiography. No differences between groups were seen by conventional histomorphometry. Spectra were acquired 2 μm away from previously performed nanoindents, in cortical and cancellous compartments. The determined parameters were: mineral to matrix ratio (MM), and nanoporosity (a surrogate for tissue water (TW)), glycosaminoglycan (GAG), pyridinoline (Pyd; trivalent enzymatic collagen cross-link), N(6)-carboxymethyllysine (CML; advanced glycation endproduct), and pentosidine (PEN; advanced glycation endproduct) content. ANCOVA indicated no differences in any of the spectroscopic outcomes between cancellous and cortical compartments. On the other hand, Cases had lower nanoporosity (TW) and GAG, and elevated Pyd, and CML content compared to Controls. In conclusion, the results of the present study indicate significant differences in organic matrix quality in PM women that sustain fragility fractures versus age- and BMD-matched controls, highlighting its importance as a potential independent determinant of fracture incidence.

Material properties and osteoporosis

The main clinical tool for the diagnosis and treatment of skeletal diseases such as osteoporosis is the determination of bone mineral density by dual x-ray absorptiometry. Although this outcome contributes to the determination of bone strength, the clinical evidence to date suggests that it does not correlate strongly with fracture incidence. The main reason for this discrepancy is the fact that several other bone properties, such as material properties, are not taken into account. This short review summarizes the reasons why material properties are important in the determination of bone strength and briefly discusses some of them as well as their influence on bone’s mechanical performance.

Type 2 Diabetes Mellitus Increases the Risk to Hip Fracture in Postmenopausal Osteoporosis by Deteriorating the Trabecular Bone Microarchitecture and Bone Mass

T2DM is linked to an increase in the fracture rate as compared to the nondiabetic population even with normal or raised bone mineral density (BMD). Hence, bone quality plays an important role in the pathogenesis of skeletal fragility due to T2DM. This study analyzed the changes in the trabecular bone microstructure due to T2DM at various time points in ovariectomized and nonovariectomized rats. Animals were divided into four groups: (I) control (sham), (II) diabetic (sham), (III) ovariectomized, and (IV) ovariectomized with diabetes. The trabecular microarchitecture of the femoral head was characterized using a micro-CT. The differences between the groups were analyzed at 8, 10, and 14 weeks of the onset of T2DM using a two-way analysis of variance and by post hoc multiple comparisons. The diabetic group with and without ovariectomies demonstrated a significant increase in trabecular separation and a decrease in bone volume fraction, trabecular number, and thickness. BMD decreased in ovariectomized diabetic animals at 14 weeks of the onset of T2DM. No significant change was found in connectivity density and degree of anisotropy among groups. The structural model index suggested a change towards a weaker rod-like microstructure in diabetic animals. The data obtained suggested that T2DM affects the trabecular structure within a rat's femoral heads negatively and changes are most significant at a longer duration of T2DM, increasing the risk to hip fractures.

Vibrational spectroscopic techniques to assess bone quality

Although musculoskeletal diseases such as osteoporosis are diagnosed and treatment outcome is evaluated based mainly on routine clinical outcomes of bone mineral density (BMD) by DXA and biochemical markers, it is recognized that these two indicators, as valuable as they have proven to be in the everyday clinical practice, do not fully account for manifested bone strength. Thus, the term bone quality was introduced, to complement considerations based on bone turnover rates and BMD. Bone quality is an "umbrella" term that incorporates the structural and material/compositional characteristics of bone tissue. Vibrational spectroscopic techniques such as Fourier transform infrared microspectroscopy (FTIRM) and imaging (FTIRI), and Raman spectroscopy, are suitable analytical tools for the determination of bone quality as they provide simultaneous, quantitative, and qualitative information on all main bone tissue components (mineral, organic matrix, tissue water), in a spatially resolved manner. Moreover, the results of such analyses may be readily combined with the outcomes of other techniques such as histology/histomorphometry, small angle X-ray scattering, quantitative backscattered electron imaging, and nanoindentation.

Chronic kidney disease and fragility fracture

Osteoporosis is defined simply as "a skeletal disorder characterized by compromised bone strength predisposing to an increased risk of fracture. Thus, any bone lesion that causes fragility fracture is osteoporosis, which has quite heterogeneous backgrounds. Chronic kidney disease-related bone and mineral disease (CKD-MBD) is defined as "a systemic disorder of mineral and bone metabolism due to CKD, which is manifested by abnormalities in bone and mineral metabolism and/or extra-skeletal calcification". Although CKD-MBD is one of the possible causes of osteoporosis, we do not have evidences that CKD-MBD is the only or crucial determinant of bone mechanical strength in CKD patients. The risk of hip fracture is considerably high in CKD patients. Drugs that intervene in systemic mineral metabolism, indeed, lead to the improvement on bone histology in CKD patients. However, it remains unclear whether the intervention in systemic mineral metabolism also improves bone strength, today. Thus, the use of drugs that directly act on bone and the introduction of fracture liaison concept are promising strategies for fragility fracture prevention among CKD patients, as well as treatment for CKD-MBD.

Ethnic differences in urinary calcium and phosphate excretion between Gambian and British older adults

Ethnic differences in renal calcium and phosphate excretion exist, which may depend on differences in their dietary intakes and regulatory factors. We report highly significant differences in urinary calcium and phosphate excretion between white British and Gambian adults after statistical adjustment for mineral intakes, indicating an independent effect of ethnicity.

INTRODUCTION

Populations vary in their risk of age-related osteoporosis. There are racial or ethnic differences in the metabolism of the bone-forming minerals calcium (Ca) and phosphate (P), with a lower renal Ca and P excretion in African-Americans compared to white counterparts, even at similar intakes and rates of absorption. Also, Africans in The Gambia have a lower Ca excretion compared to white British subjects, groups known to differ in their dietary Ca intake. Here, we report on differences in urinary Ca and P excretion between Gambian and white British adults while allowing for known predictors, including dietary intakes.

METHODS

Participants were healthy white British (n = 60) and Gambian (n = 61) men and women aged 60-75 years. Fasting blood and 2-h urine samples were collected. Markers of Ca and P metabolism were analysed. Dietary intake was assessed with country-specific methods.

RESULTS

White British older adults had higher creatinine-corrected urinary Ca and P excretion (uCa/uCr, uP/uCr) and lower tubular maximum of Ca and P compared to Gambian counterparts. The predictors of urinary Ca and P differed between groups. Multiple regression analysis showed that dietary Ca and Ca/P were predictors of uCa/uCr and uP/uCr, respectively. Ethnicity remained a significant predictor of uCa/uCr and uP/uCr after adjustment for diet and other factors.

CONCLUSIONS

Gambian older adults have higher renal Ca conservation than British counterparts. Dietary mineral intakes were predictors of the differences in urinary Ca and P excretion, but ethnicity remained a highly significant predictor after statistical adjustment. This suggests that ethnicity has an independent effect on renal Ca and P handling.

Biomineralized matrices dominate soluble cues to direct osteogenic differentiation of human mesenchymal stem cells through adenosine signaling

Stem cell differentiation is determined by a repertoire of signals from its microenvironment, which includes the extracellular matrix (ECM) and soluble cues. The ability of mesenchymal stem cells (MSCs), a common precursor for the skeletal system, to differentiate into osteoblasts and adipocytes in response to their local cues plays an important role in skeletal tissue regeneration and homeostasis. In this study, we investigated whether a bone-specific calcium phosphate (CaP) mineral environment could induce osteogenic differentiation of human MSCs, while inhibiting their adipogenic differentiation, in the presence of adipogenic-inducing medium. We also examined the mechanism through which the mineralized matrix suppresses adipogenesis of hMSCs to promote their osteogenic differentiation. Our results show that hMSCs cultured on mineralized matrices underwent osteogenic differentiation despite being cultured in the presence of adipogenic medium, which indicates the dominance of matrix-based cues of the mineralized matrix in directing osteogenic commitment of stem cells. Furthermore, the mineralized matrix-driven attenuation of adipogenesis was reversed with the inhibition of A2b adenosine receptor (A2bR), implicating a role of adenosine signaling in mineralized environment-mediated inhibition of adipogenesis. Such synthetic matrices with an intrinsic ability to direct differentiation of multipotent adult stem cells toward a targeted phenotype while inhibiting their differentiation into other lineages not only will be a powerful tool in delineating the role of complex microenvironmental cues on stem cell commitment but also will contribute to functional tissue engineering and their translational applications.

Lower bone mineral density in Somali women living in Sweden compared with African-Americans

Vitamin D deficiency can lead to osteomalacia. Bone mineral density was lower in Somali women, living in Sweden, in relation to both the American and the African-American reference populations. The majority, 73 %, had vitamin D deficiency, and supplementation should be considered to prevent from osteomalacia, osteoporosis and future fractures.

PURPOSE

Low vitamin D can lead to osteomalacia. The hypothesis was that bone mineral density (BMD) in Somali women living in Sweden was lower in comparison with different ethnic reference populations.

METHODS

Women from Somalia, n = 67, median age 35.8 years (range 18 to 56), latitude 0-10° North living in Gothenburg, Sweden, latitude 57° North, >2 years were studied. All wore traditional Islamic clothing and had skin photo type V. BMD was recorded as the Z-score and compared with white American and African-American women, respectively, using standard data from the dual energy X-ray absorptiometry (DXA) manufacturer (Lunar Prodigy enCORETM, GE Healthcare, LU44663). A fasting blood test was drawn for analysis of serum 25(OH)D.

RESULTS

The median Z-score compared with the American white population was -0.9 SD of the lumbar spine (p < 0.00001), 0.1 SD of the left hip and 0.0 SD of the right hip (ns). The median Z-score compared with the African-American population was -1.6 SD of the lumbar spine (p < 0.00001), -0.9 SD of the left hip and -0.9 SD of the right hip (p < 0.001). The majority, 73 %, had vitamin D deficiency, serum 25(OH)D <25 nmol/l (<10 ng/ml). BMD did not correlate to vitamin D levels or to the number of years in Sweden. One wrist fracture was reported.

CONCLUSIONS

BMD was lower in these fairly young immigrant women from Somalia, living in Sweden, in relation to both the American and the African-American reference populations. Vitamin D supplementation should be considered to prevent from osteomalacia, osteoporosis and future fractures.

Vibrational spectroscopic imaging for the evaluation of matrix and mineral chemistry

Metabolic bone diseases manifesting fragility fractures (such as osteoporosis) are routinely diagnosed based on bone mineral density (BMD) measurements, and the effect of various therapies also evaluated based on the same outcome. Although useful, it is well recognized that this metric does not fully account for either fracture incidence or the effect of various therapies on fracture incidence, thus, the emergence of bone quality as a contributing factor in the determination of bone strength. Infrared and Raman vibrational spectroscopic techniques are particularly well-suited for the determination of bone quality as they provide quantitative and qualitative information of the mineral and organic matrix bone components, simultaneously. Through the use of microspectroscopic techniques, this information is available in a spatially resolved manner, thus, the outcomes may be easily correlated with outcomes from techniques such as histology, histomorphometry, and nanoindentation, linking metabolic status with material properties.

Ethnic differences in calcium, phosphate and bone metabolism

The prevalence of osteoporosis and the incidence of age-related fragility fracture vary by ethnicity. There is greater than 10-fold variation in fracture probabilities between countries across the world. Mineral and bone metabolism are intimately interlinked, and both are known to exhibit patterns of daily variation, known as the diurnal rhythm (DR). Ethnic differences are described for Ca and P metabolism. The importance of these differences is described in detail between select ethnic groups, within the USA between African-Americans and White-Americans, between the Gambia and the UK and between China and the UK. Dietary Ca intake is higher in White-Americans compared with African-Americans, and is higher in White-British compared with Gambian and Chinese adults. Differences are observed also for plasma 25-hydroxy vitamin D, related to lifestyle differences, skin pigmentation and skin exposure to UVB-containing sunshine. Higher plasma 1,25-dihydroxy vitamin D and parathyroid hormone are observed in African-American compared with White-American adults. Plasma parathyroid hormone is also higher in Gambian adults and, in winter, in Chinese compared with White-British adults. There may be ethnic differences in the bone resorptive effects of parathyroid hormone, with a relative skeletal resistance to parathyroid hormone observed in some, but not all ethnic groups. Renal mineral excretion is also influenced by ethnicity; urinary Ca (uCa) and urinary P (uP) excretions are lower in African-Americans compared with White-Americans, and in Gambians compared with their White-British counterparts. Little is known about ethnic differences in the DR of Ca and P metabolism, but differences may be expected due to known differences in lifestyle factors, such as dietary intake and sleep/wake pattern. The ethnic-specific DR of Ca and P metabolism may influence the net balance of Ca and P conservation and bone remodelling. These ethnic differences in Ca, P and the bone metabolism may be important factors in the variation in skeletal health.

Transmenopausal changes in trabecular bone quality

Bone strength depends on its amount and quality. Bone quality includes its structural and material properties. Bone material properties are dependent on bone turnover rates. Remodeling rates are significantly increased immediately after menopause. In the present study, we used Raman microspectroscopic analysis of double iliac crest biopsies with a spatial resolution of 1 µm obtained before and immediately after menopause (1 year after cessation of menses) in healthy females to investigate changes in material properties attributable to menopause. In particular, the mineral/matrix ratio, the relative proteoglycan and lipid content, the mineral maturity/crystallinity, and the relative pyridinoline collagen cross-link content were determined in trabecular bone as a function of surface metabolic activity and tissue age. The results indicate that significant changes (specifically in mineral/matrix ratio) were evident at active bone forming surfaces, whereas the relative proteoglycan content was altered at resorbing surfaces. These changes were not accompanied by altered mineral content or quality as monitored by Raman microspectroscopic analysis.

Trps1 differentially modulates the bone mineral density between male and female mice and its polymorphism associates with BMD differently between women and men

The objective of our study was to identify genetic factors that regulate bone mineral density (BMD) in mice using well defined recombinant inbred strains. For this purpose we chose the BXD recombinant inbred (RI) strains derived from progeny of the C57BL/6J (B6) and DBA/2J (D2) progenitor strains. We sampled both male and female mice (∼4 each) of 46 strains at 3 months-of-age, measured their BMD, and conducted QTL mapping. The data were analyzed to identify candidates genes contained within the most significant quantitative trait locus (QTL). Evaluation of candidate genes included functional assessment, single nucleotide polymorphism (SNP) genotyping and direct sequencing. We established that there was a QTL for BMD in males on chromosome 15 that has the impact larger than QTLs on all other chromosomes. The QTL on chromosome 15 was narrowed to a genomic region between 38 Mbp and 52 Mbp. By examining transcripts within this region, we found an important candidate gene: trichorhinophalangeal syndrome, type I (Trps1). SNP analysis identified a nonsynonymous SNP (rs32398060) in Trps1 that co-segregated with bone mineral density. Analysis of association between this SNP within TRPS1 and BMD in a human population confirmed its significance.

In situ mechanical behavior of mineral crystals in human cortical bone under compressive load using synchrotron X-ray scattering techniques

It is of great interest to delineate the effect of orientation distribution of mineral crystals on the bulk mechanical behavior of bone. Using a unique synergistic approach combining a progressive loading scheme and synchrotron X-ray scattering techniques, human cortical bone specimens were tested in compression to examine the in situ mechanical behavior of mineral crystals aligned in different orientations. The orientation distribution was quantitatively estimated by measuring the X-ray diffraction intensity from the (002) plane in mineral crystals. In addition, the average longitudinal (c-axis), transverse (a-axis), and shear strains of the subset of mineral crystals aligned in each orientation were determined by measuring the lattice deformation normal to three distinct crystallographic planes (i.e. 002, 310, and 213) in the crystals. The experimental results indicated that the in situ strain and stress of mineral crystals varied with orientations. The normal strain and stress in the longitudinally aligned mineral crystals were markedly greater than those in the transversely oriented crystals, whereas the shear stress reached a maximum for the crystals aligned in ±30° with respect to the loading direction. The maximum principal strain and stress were observed in the mineral crystals oriented along the loading axis, with a similar trend observed in the maximum shear strain and stress. By examining the in situ behavior, the contribution of mineral crystals to load bearing and the bulk behavior of bone are discussed.

Role of trabecular microarchitecture in the formation, accumulation, and morphology of microdamage in human cancellous bone

Alterations in microdamage morphology and accumulation are typically attributed to impaired remodeling, but may also result from changes in microdamage initiation and propagation. Such alterations are relevant for cancellous bone with high metabolic activity and numerous bone quality changes. This study investigates the role of trabecular microarchitecture on morphology and accumulation of microdamage in human cancellous bone. Trabecular bone cores from donors of varying ages and bone volume fraction (BV/TV) were separated into high and low BV/TV groups. Samples were subjected to no load or uniaxial compression to 0.6% (pre-yield) or 1.1% (post-yield) strain. Microdamage was stained with lead uranyl acetate and specimens were imaged via microcomputed tomography to quantify microdamage and determine its morphology in three-dimensions (3D). Donors with high BV/TV had greater post-yield strain and were tougher than low BV/TV donors. High BV/TV bone had less microdamage than low BV/TV bone under post- but not pre-yield loading. Microdamage under both loading conditions showed significant correlations with microarchitecture and BV/TV, but the key predictor was structure model index (SMI). As SMI increased (more trabecular rods), microdamage morphology became crack-like. Thus, low BV/TV and increased SMI have strong influences on microdamage accumulation in bone through altered initiation. 

Measuring differences in compositional properties of bone tissue by confocal Raman spectroscopy

The full range of fracture risk determinants arise from each hierarchical level comprising the organization of bone. Raman spectroscopy is one tool capable of characterizing the collagen and mineral phases at a near submicron-length scale, but the ability of Raman spectra to distinguish compositional differences of bone is not well defined. Therefore, we analyzed multiple Raman peak intensities and peak ratios to characterize their ability to distinguish between the typically less mineralized osteonal tissue and the more mineralized interstitial tissue in intracortical human bone. To further assess origins of variance, we collected Raman spectra from embedded specimens and for two orientations of cut. Per specimen, Raman peak intensities or ratios were averaged among multiple sites within five osteons and five neighboring interstitial tissue. The peak ratios of ν(1) phosphate (PO(4)) to proline or amide III detected the highest increases of 15.4 or 12.5%, respectively, in composition from osteonal to interstitial tissue. The coefficient of variance was less than 5% for each as opposed to a value of ~8% for the traditional ν(1)PO(4)/amide I, a peak ratio that varied the most between transverse and longitudinal cuts for each tissue type. Although embedding affected Raman peaks, it did not obscure differences in most peak ratios related to mineralization between the two tissue types. In studies with limited sample size but sufficient number of Raman spectra per specimen for spatial averaging, ν(1)PO(4)/amide III or ν(1)PO(4)/proline is the Raman property that is most likely to detect a compositional difference between experimental groups.

Bone matrix quality and plasma homocysteine levels

It has recently been reported in the clinical literature that blood homocysteine levels correlate well with fracture risk, although a couple of reports exist to the opposite. Bone strength depends on both bone quantity and quality. The purpose of the present study was to investigate possible correlations between plasma homocysteine levels and bone material properties (Bone Mineral Density Distribution; BMDD, and collagen cross-link ratio). In the present study, femoral heads from subjects (N=19, females, age range 70-95 years old) with known homocysteine plasma levels were investigated. The bone material was collected during hemiarthroplasty surgery. We have determined collagen cross-link ratio and bone mineralization density distribution (BMDD) in bone tissue from patients with acute femoral neck fractures, by Fourier Transform Infrared Imaging (FTIRI) and quantitative Backscattered Electron Imaging (qBEI), respectively. The collagen cross-link ratio that was spectroscopically determined was pyridinoline/divalent cross-links (pyr/divalent). The BMDD variables quantified were: CaMean: the weighted mean calcium concentration; CaPeak: the most frequent Ca concentration; CaWidth: the width of the distribution, a measure of the mineralization homogeneity; CaLow: the percentage of bone area that is mineralized below the 5th percentile in the reference range; CaHigh: the percentage of bone area that is mineralized above the 95th percentile in the reference range. There was a significant correlation between plasma homocysteine levels and collagen cross-link ratio in areas of primary mineralized bone (p<0.0001), unlike the case of trabecular bone surfaces undergoing resorption (p>0.05). On the other hand there was no correlation in any of the BMDD parameters and plasma homocysteine levels (p>0.05). The results are consistent with the known effect of homocysteine on collagen post-translational modifications. These changes were independent of bone mineral characteristics. The results of the present study offer a mechanism by which homocysteine affects bone quality, but caution should be exercised since all patients examined had sustained fracture.

Bone morphometry strongly predicts cortical bone stiffness and strength, but not toughness, in inbred mouse models of high and low bone mass

Inbred strains of mice make useful models to study bone properties. Our aim was to compare bone competence and cortical morphometric parameters of two inbred strains to better determine the role of bone structure and geometry in the process of bone failure. Morphometric analysis was performed on 20 murine femora with a low bone mass (C57BL/6J; B6) and 20 murine femora with a high bone mass (C3H/HeJ; C3H) using desktop microCT. The bones were tested under three-point bending to measure their mechanical properties. Results showed that the C3H strain is a more reproducible model regarding bone morphometric and mechanical phenotypes than the B6 strain. Bone strength, stiffness, yield force, yield displacement, and toughness, as well as morphometric traits, were all significantly different between the two strains, whereas postyield displacement was not. It was found that bone volume, cortical thickness, and cross-sectional area predicted almost 80% (p < 0.05) of bone stiffness, strength, and yield force. Nevertheless, cortical bone postyield properties such as bone toughness could not be explained by morphometry, but postyield whitening was observed in that phase. In conclusion, we found that morphometric parameters are strong predictors of preyield but not postyield properties. The lack of morphometric influence on bone competence in the postyield phase in combination with the observed postyield whitening confirmed the important contribution of ultrastructure and microdamage in the process of overall bone failure behavior, especially in the postyield phase.

Differential effects of bone structural and material properties on bone competence in C57BL/6 and C3H/He inbred strains of mice

The femoral neck is a relevant and sensitive site for studying the degree of osteopenia. Engineering principles predict that bone structural parameters, like cross-sectional geometry, are important determinants of bone mechanical parameters. Mechanical parameters are also directly affected by the material properties of the bone tissue. However, the relative importance of structural and material properties is still unknown. The aim of this study was to compare bone competence and structural parameters between a murine strain showing a low bone mass phenotype, C57BL/6 (B6), and another one showing a high bone mass phenotype, C3H/He (C3H), in order to better determine the role of bone structure and geometry in bone failure behavior. Murine femora of 12- and 16-week-old B6 and 12- and 16-week-old C3H inbred strains were mechanically tested under axial loading of the femoral head. In order to assess the structural properties, we performed three-dimensional morphometric analyses in five different compartments of the mouse femur using micro-computed tomography. The mechanical tests revealed that B6 femora became stiffer, stronger, and tougher at 12-16 weeks, while bone brittleness stayed constant. C3H bone stiffness increased, but strength remained constant, work to failure decreased, and bone became more brittle. These age effects indicated that B6 did not reach peak bone properties at 16 weeks of age and C3H did reach maximal skeletal biomechanical properties before 16 weeks of age. Our investigations showed that 83% of the strength of the femoral neck in the B6 strain was explained by cortical thickness at this location; in contrast, in C3H none of the mechanical properties of the femoral neck was explained by bone structural parameters. The relative contributions of bone structural and material properties on bone strength are different in B6 and C3H. We hypothesize that these different contributions are related to differences at the ultrastructural level of bone that affect bone failure.

Osteoporosis in children with cancer

As increasing numbers of childhood cancer patients are surviving, the long-term complications of the disease and its treatment have become ever more increasingly important. Reduced bone mineral density and increased fracture risk have been reported during and after treatment of children with cancer. The causes of osteoporosis are multifactorial. Among others, the disease itself, chemotherapy, irradiation and genetic susceptibility play a role. Bone mineral density in later life depends largely on the peak bone mass achieved in adolescence or young adulthood. Therefore, optimizing peak bone mass is of clinical importance. Preventive and therapeutic strategies, such as calcium and vitamin D supplementation, physical activity and bisphosphonates, are considered.

Age-related factors affecting the postyield energy dissipation of human cortical bone

The risk of bone fracture depends in part on tissue quality, not just the size and mass. This study assessed the postyield energy dissipation of cortical bone in tension as a function of age and composition. Specimens were prepared from tibiae of human cadavers in which male and female donors were divided into two age groups: middle aged (51 to 56 years, n = 9) and elderly (72 to 90 years, n = 8). By loading, unloading, and reloading a specimen with rest periods inserted in between, tensile properties at incremental strain levels were assessed. In addition, postyield toughness was estimated and partitioned as plastic strain energy related to permanent deformation, released elastic strain energy related to stiffness loss, and hysteresis energy related to viscous behavior. Porosity, mineral and collagen content, and collagen crosslinks of each specimen were also measured to determine the micro- and ultrastructural properties of the tissue. Age affected all the energy terms plus strength but not elastic stiffness. The postyield energy terms were correlated with porosity, pentosidine (a marker of nonenzymatic crosslinks), and collagen content, all of which varied significantly with age. General linear models suggested that pentosidine concentration and collagen content provided the best explanation of the age-related decrease in the postyield energy dissipation. Among them, pentosidine concentration had the greatest contribution to plastic strain energy and was the best explanatory variable of damage accumulation.

Quantitative trait loci modulate vertebral morphology and mechanical properties in a population of 18-month-old genetically heterogeneous mice

The aim of this study was to examine effects of polymorphic genes on vertebral bone morphology and mechanical properties. Genotypes from 525 18-month-old female mice were compared to geometric traits obtained from micro-computed tomography and mechanical properties from compression testing. Genetic markers were associated with traits on at least 13 different chromosomes, demonstrating the complexity of genetic control over vertebral form, function and aging.

Cortical bone remodeling rates in a sample of African American and European American descent groups from the American Midwest: comparisons of age and sex in ribs

This study employs regression analysis to explore population and sex differences in the pattern of age-associated bone loss, as reflected by histomorphometric variables that are measures of intracortical and endocortical bone remodeling. A comparison of an African American sample from the Washington Park Cemetery in St. Louis, Missouri, and a European American rib sample composed of cadavers, autopsies, and forensic cases from Missouri reveals the existence of complex age-associated patterns for differences in measures of intracortical remodeling and cortical area. Females from the two samples express similar bone dimensions and dynamics. The African American females appear to lose more bone than their male counterparts, but this difference is absent in the European American sample. When age-associated patterns are considered, it is in the younger cohorts that African Americans exhibit greater relative cortical area than European Americans, but this is reversed in the older ages, when the latter group manifests greater bone mass. The European American males consistently differ in the slopes and intercepts for the variables compared to the other groups, and differences are highly significant with African American females, with the former group maintaining bone mass while the latter exhibit a more rapid bone loss. Achieving larger relative cortical area due to smaller endosteal area, coupled with better bone quality due to lower intracortical porosity early in life, may be a mechanism by which African Americans, especially females, maintain adequate bone mass in older ages, which buffers them from bone loss and related fragility fractures despite higher rates of intracortical remodeling and endosteal expansion later in life. These results suggest that both genetic and environmental factors are responsible for the differences in bone remodeling and bone mass observed between these samples.

Characteristics of calcaneus quantitative ultrasound normative data in Chinese mainland men and women

INTRODUCTION

Quantitative ultrasound (QUS) assessment at the calcaneus, as a safe and reliable method for evaluating skeletal status, is rapidly gaining in popularity. Assessment by QUS provides three parameters of skeletal status: broadband ultrasound attenuation (BUA), speed of sound (SOS) and derived data-stiffness index (STI). The objective of the present study was firstly to determine the normative QUS data on healthy Chinese mainland men and women and secondly to investigate the effects of sex, age and body size on these three QUS parameters.

METHODS

A study cohort consisting of 725 healthy Chinese women and 568 men aged 10-83 years participated in this investigation. The three QUS parameters all exhibited a characteristic mild rise-then-fall pattern with increasing age in both sexes. Younger men and women had similar QUS values, while older women had lower values than older men. Age-related differences were more pronounced among females. Pearson's correlation and regression analysis showed that weight was a major determinant of QUS in both sexes, along with age.

RESULTS

There were some discrepancies between our data and results from other populations, even when the same type of QUS instrument was used, probably as a result of various factors, including ethnic, life-style environment and diet, among others.

CONCLUSIONS

These normative data will be useful for comparing the results of individual studies, predicting fracture risk of Chinese men and women and determining diagnostic criteria of osteoporosis by QUS.

Parathyroid hormone and rates of bone formation are raised in perimenopausal rural Gambian women

To investigate rates of bone turnover and calcium homeostasis in Gambian women, we recruited 103 peri- and postmenopausal women, aged 45 to 80+ years and 11 women of reproductive age. Fasting blood was analyzed for plasma osteocalcin, PTH, 25-hydroxyvitamin D [25(OH)D], 1,25-dihydroxyvitamin D [1,25(OH)(2)D], total- and bone-specific alkaline phosphatase. Plasma and urinary calcium, inorganic phosphate, sodium, potassium, creatinine, and albumin and urine free deoxypyridinoline (Dpd) was also measured. Samples from 20 premenopausal and 31 postmenopausal women from Cambridge, UK were analyzed, using the same methodology for comparison. For the Gambian women, peak calcium excretion occurred at around 50 years of age. For women aged > or =45 years, calcium excretion decreased by 3.0% per year of age (SE 1%; P < 0.005). In this age group, 25(OH)D also decreased with age (P < 0.005). Urinary sodium output, pH, and titratable acid output decreased (all P < 0.05) and total alkaline phosphatase (P < 0.005), osteocalcin (P < 0.005), and PTH (P < 0.05) increased with age. Comparisons were made between the following groups of Gambian and British women: premenopausal, early (age 55-64 years)- and late (age 65+ years)-postmenopausal. Gambian women of all ages were lighter (P < 0.001), shorter (P < 0.01), and had higher plasma bone-specific alkaline phosphatase activity (P < 0.05) and higher concentrations of osteocalcin (P < 0.05), PTH (P < 0.001), 1,25(OH)(2)D (P < 0.001), and 25(OH)D (P < 0.001). There were no consistent differences in calcitonin, while urinary free Dpd outputs were lower in the Gambians (P < 0.001). Plasma calcium, phosphate, and albumin (P < 0.01) were significantly lower. Urinary calcium, phosphate, sodium, and potassium excretion were lower, particularly in the postmenopausal group (P < 0.001). Although Gambian urine pH was more acidic, titratable acid output was lower (P < 0.01). These data show that Gambian women with low dietary calcium intakes and good vitamin D status have low urinary calcium excretion and that menopausal changes in calcium and bone metabolism among Gambian women are similar to those seen in other populations. In addition, they demonstrate that Gambian women of all ages have raised plasma PTH and 1,25(OH)(2)D concentrations and raised markers of osteoblast activity. We postulate that high endogenous PTH concentrations may be beneficial to bone health in Gambian women, removing fatigue damage and improving bone quality.

Intrapopulation variability in mineralization density at the human femoral mid-shaft

One of several microstructural variables known to affect the mechanical properties of bone is the degree of mineralization of bone matrix. The aim of this study was to examine mineralization density, and its variability with age and sex, from a biomechanical perspective. Histological sections, prepared from mid-shaft femora obtained at autopsy from 40 individuals, were imaged using quantitative backscattered electron microscopy. Each cross-section montage was divided into 48 segments according to anatomical position. Mean grey-level values were quantified for each segment. One-way ANOVA with Tukey HSD post hoc tests were used to test for differences in mineralization between segments, age groups and sexes. Results showed a decrease in overall degree of mineralization density with adult age, but an increase in its coefficient of variation. Degree of mineralization was significantly lower in the periosteal third of the cortex, particularly in the antero-lateral aspect. This pattern was most prevalent amongst the youngest individuals in the sample. Whereas males between ages 45-64 years had a higher average degree of mineralization than females, the opposite was true of the older age group. Mineralization significantly decreased between middle and older age groups in males, but not in females. Despite limited consistencies in the location of high and low average mineralization bone through the cortex, the degree of interindividual variation, even within a single age and sex group, overwhelmed population level trends. The patterns of variability identified in this study are consistent with results of an analysis of collagen fibre orientation using the same sample material.

Aging of microstructural compartments in human compact bone

Composition of microstructural compartments in compact bone of aging male subjects was assessed using Raman microscopy. Secondary mineralization of unremodeled fragments persisted for two decades. Replacement of these tissue fragments with secondary osteons kept mean composition constant over age, but at a fully mineralized limit. Slowing of remodeling may increase fracture susceptibility through an increase in proportion of highly mineralized tissue. In this study, the aging process in the microstructural compartments of human femoral cortical bone was investigated and related to changes in the overall tissue composition within the age range of 17-73 years. Raman microprobe analysis was used to assess the mineral content, mineral crystallinity, and carbonate substitution in fragments of primary lamellar bone that survived remodeling for decades. Tissue composition of the secondary osteonal population was investigated to determine the composition of turned over tissue volume. Finally, Raman spectral analysis of homogenized tissue was performed to evaluate the effects of unremodeled and newly formed tissue on the overall tissue composition. The chemical composition of the primary lamellar bone exhibited two chronological stages. Organic matrix became more mineralized and the crystallinity of the mineral improved during the first stage, which lasted for two decades. The mineral content and the mineral crystallinity did not vary during the second stage. The results for the primary lamellar bone demonstrated that physiological mineralization, as evidenced by crystal growth and maturation, is a continuous process that may persist as long as two decades, and the growth and maturation process stops after the organic matrix becomes "fully mineralized." The average mineral content and the average mineral crystallinity of the homogenized tissue did not change with age. It was also observed that the mineral content of the homogenized tissue was consistently greater than the osteons and similar to the "fully mineralized" stage of primary bone. The results of this study demonstrated that unremodeled compartments of bone grow older through maturation and growth of mineral crystals in a protracted fashion. However, the secondary osteonal remodeling impedes this aging process and maintains the mean tissue age fairly constant over decades. Therefore, slowing of remodeling may lead to brittle bone tissue through accumulation of fully mineralized tissue fragments.

Bone brittleness varies with genetic background in A/J and C57BL/6J inbred mice

The contribution of genetic and environmental factors to variations in bone quality are understood poorly. We tested whether bone brittleness varies with genetic background using the A/J and C57BL/6J inbred mouse strains. Whole bone four-point bending tests revealed a 70% decrease in postyield deflection of A/J femurs compared with C57BL/6J, indicating that A/J femurs failed in a significantly more brittle manner. Cyclic loading studies indicated that A/J femurs accumulated damage differently than C57BL/6J femurs, consistent with their increased brittleness. Differences in matrix composition also were observed between the two mouse strains. A/J femurs had a 4.5% increase in ash content and an 11.8% decrease in collagen content. Interestingly, a reciprocal relationship was observed between femoral geometry and material stiffness; this relationship may have contributed to the brittle phenotype of A/J femurs. A/J femurs are more slender than those of C57BL/6J femurs; however, their 47% smaller moment of inertia appeared to be compensated by an increased tissue stiffness at the expense of altered tissue damageability. Importantly, these differences in whole bone mechanical properties between A/J and C57BL/6J femurs could not have been predicted from bone mass or density measures alone. The results indicated that bone brittleness is a genetically influenced trait and that it is associated with genetically determined differences in whole bone architecture, bone matrix composition, and mechanisms of cyclical damage accumulation.

The influence of growth hormone deficiency, growth hormone replacement therapy, and other aspects of hypopituitarism on fracture rate and bone mineral density

To assess the influence of factors affecting fracture risk and bone density in adult hypopituitary patients with growth hormone deficiency (GHD), data from a large-scale pharmacoepidemiological survey (the Pharmacia & Upjohn International Metabolic Database [KIMS]) were analyzed and compared with data from a control population (the European Vertebral Osteoporosis Study [EVOS]). The KIMS group consisted of 2084 patients (1112 men and 972 women) with various types of pituitary disease and EVOS consisted of 1176 individuals (581 men and 595 women). Fracture and bone mineral density (BMD) data were available from 2024 patients from the KIMS group and 392 patients from EVOS. The prevalence of fractures in patients with hypopituitarism was 2.66 times that in the non-GH-deficient EVOS population. Adult-onset hypopituitarism with GHD was associated with a higher fracture risk than childhood-onset disease, and patients with isolated GHD had a similar prevalence of fractures to those with multiple pituitary hormone deficiencies. Hormonal replacement therapy with L-thyroxine, glucocorticoids, and sex steroids did not affect the risk of fracture in KIMS patients. In addition, fracture rates in KIMS were independent of body mass index (BMI) and the country of origin. However, smoking was associated with a higher fracture rate in this group. In summary, this is the first large-scale analysis to support the hypothesis of an increased fracture risk in adult patients with hypopituitarism and GHD. This increased risk appears to be attributable to GHD alone, rather than to other pituitary hormone deficiencies or to their replacement therapy.

In vivo diffuse damage in human vertebral trabecular bone

Accumulation of microdamage in vivo may lead to loss of bone quality. Until recently, linear microcracks were the only known form of in vivo microdamage, but through the use of confocal microscopy an additional level of damage (diffuse damage) has been identified. In this study, in vivo diffuse damage was characterized and quantified in human vertebral trabecular bone as a function of tissue morphology, age, race, gender, and previously quantified in vivo linear microcracks. Presence of diffuse damage in human vertebral tissue was confirmed and validated by simultaneous use of polarized, ultraviolet, and laser confocal microscopy. Diffuse damage was found to occur preferentially within trabecular packets rather than in interstitial bone (p < 0.05). It was consistently higher in men compared with women (p < 0.05), but was not different by race or age group. Diffuse damage did not correlate with linear microcracks, but both exhibited the same probability distribution in which the percentage of individuals having a particular amount of damage decreased exponentially as damage content increased. These findings suggest that diffuse damage accumulation and repair are governed by the same biological phenomena as microcracks, but diffuse damage contributes independently to the microdamage content of bone.

Dependence of trabecular damage on mechanical strain

Trabecular damage may play a role in hip fracture, bone remodeling, and prosthesis loosening. We hypothesized that when trabecular bone is loaded beyond its elastic range, both the type and the amount of damage depend on the applied strains. Thirty specimens of trabecular bone from the bovine tibia underwent compression tests to one of three levels of strain (0.4. 1.0. and 2.5%) (n = 10 per group). The 0.4% level was a mechanically nondestructive control group that accounted for any systematic errors. Optical microscopy at magnifications as high as x200 was then used to quantify the trabecular damage for each group. The amount of damage in the yield group (1.0% strain) did not differ from that in the control group (p = 0.66), whereas damage in the post-ultimate strain group (2.5% strain) increased more than 3-fold (p < 0.0008). Four types of damage were observed: transverse cracks, shear bands, parallel cracks, and complete fractures, of which the first two were dominant. These findings therefore indicate that damage occurs within trabeculae at yield. By comparison with our previous work, it can also be concluded that substantial modulus reductions in trabecular bone (as much as 60%) are caused by damage primarily within trabeculae. The ability to detect such damage clinically may improve in vivo estimates of whole-bone strength by identifying regions of densitometrically normal but mechanically compromised trabecular bone.

Decrease in canine proximal femoral ultimate strength and stiffness due to fatigue damage

Fractures of the proximal femur represent a significant health concern especially in the elderly. Fatigue damage and microfractures have been implicated in the etiology of hip fractures; however, the extent to which these factors are sufficient to bring about significant reductions in proximal femur strength and stiffness is unknown. This study examined the hypothesis that fatigue loading of the proximal femur results in highly correlated decreases in bone stiffness and strength through the accumulation of bone microdamage. One canine femur from each of 10 pairs was monotonically loaded to failure to determine the ultimate strength. The contralateral femur was then cyclically loaded at 50% of the ultimate load value for either 3600 cycles or until a 40% reduction in stiffness was achieved. This femur was then monotonically loaded to failure. For two additional femur pairs, the fatigued femur was histologically processed to reveal bone microdamage. In support of the hypothesis, the data demonstrated a linear relationship between strength loss and stiffness loss (Adj. R2 = 0.79, p < 0.0004) with significant decreases in residual whole bone strength (p < 0.004) following cyclic loading. In addition, damage (microcracks) in the cortical bone and broken trabeculae were observed in the neck and head region of the femur fatigued until its stiffness was reduced by 40% but not fractured subsequent to cyclic loading.

Differences in mineral homeostasis, volumetric bone mass and femoral neck axis length in black and white South African women

In South Africa, appendicular and lumbar spine bone mineral density (BMD) have been found to be similar in black and white women. However, femoral BMD has been found to be higher in black than in white women. Two different techniques were used to recalculate BMD to eliminate the possible confounding influence of ethnic differences in height on areal BMD measurements. Volumetric bone mineral apparent density (BMAD) values were calculated and bone mineral content (BMC) was corrected for body and bone size. This report analyses differences in BMD (corrected for height and weight), BMAD, BMC (corrected for body and bone size), femoral neck axis length (FNAL), mineral homeostasis and bone turnover (BT) in a group of 20 to 49-year-old premenopausal (105 whites and 74 blacks) and 45 to 64-year-old postmenopausal (50 whites and 65 blacks) female South African nurses. The corrected BMD and BMC findings were congruous, showing that both pre- and postmenopausal blacks and whites have similar distal radius and lumbar spine bone mass but that whites have lower femoral neck bone mass than blacks. In contrast, BMAD findings suggest that pre- and postmenopausal whites have lower bone mass at the lumbar spine and femoral neck than blacks but similar bone mass at the distal radius to blacks. There is a greater rate of decline in BMD in postmenopausal whites than in blacks. BMD at the femoral neck was 12.1% lower in premenopausal whites and 16.5% lower in postmenopausal whites than in blacks. There was a positive association between femoral neck BMD and weight in premenopausal blacks (R2 = 0.5, p = 0.0001) but not in whites. Blacks had shorter FNAL than whites in both the pre- and post-menopausal groups. Blacks had lower serum 25-hydroxyvitamin D (25-(OH)D) and higher 1,25-dihydroxyvitamin D (1,25-(OH)2D) levels than whites. There were no ethnic differences in biochemical markers of bone formation (serum alkaline phosphatase and osteocalcin) or bone resorption (urine hydroxyproline and pyridinoline), or in dietary calcium intake in either the pre- or postmenopausal groups. In the postmenopausal group, whites had higher ionized serum calcium (p = 0.003), similar serum albumin, lower serum parathyroid hormone (p = 0.003) and higher urinary calcium excretion (p = 0.0001) than blacks. These results suggest that the higher peak femoral neck BMD in South African blacks than in whites might be determined by greater weight-bearing in blacks and that the significantly lower femoral neck BMD in postmenopausal whites than in blacks is determined by lower peak femoral neck BMD and a faster postmenopausal decline in BMD in whites. The higher incidence of femoral neck fractures in South African whites than in blacks is probably determined by the lower femoral neck BMD and longer FNAL in whites. The greater rate of decline in BMD in postmenopausal whites than in blacks is associated with an increase in urinary calcium excretion in whites. Measurement of biochemical markers of BT has not contributed to the understanding of ethnic differences in BMD and skeletal metabolism in our subjects.

Bone quantity and quality in past populations

BACKGROUND

The study of osteoporosis in past populations offers valuable insight into the patterns and prevalence of the disease in both the past and in the present.

METHODS AND RESULTS

A review is made of different paleopathological studies better to understand bone loss in past populations and to examine the contribution such studies can make to our knowledge of osteoporosis in modern populations. The review includes studies of bone mass in past populations from different geographic regions. Nutritionally based hypotheses, traditionally used to explain bone loss in past populations, are reviewed and assessed against the current clinical and epidemiological findings. In general, the various studies have revealed different degrees of low bone mass in past populations; however, the pattern of bone loss and fragility seen in age-related and postmenopausal osteoporosis today is not evident in the past. Bone loss in earlier populations is often found in both sexes, whereas significant bone loss in females occurs often among the young-age categories. In addition, a prevalence of osteoporotic fracture is absent.

CONCLUSIONS

We suggest that, despite influences that may have reduced bone mass in past populations, a protection of bone quality may have occurred, reducing the likelihood of bone fragility and fracture typically seen in modern osteoporotics. It seems evident that, although reduced bone mass may be prevalent in past history, clinically recognized osteoporosis is not.

Determinants of vertebral fracture prevalence among native Japanese women and women of Japanese descent living in Hawaii

Age-adjusted prevalence of vertebral fracture has been reported to be higher among native Japanese women than among women of Japanese descent living in Hawaii. In this cross-sectional population-based study, we examined a variety of potential risk factors for associations with prevalent vertebral fractures and investigated whether these factors could explain the difference in vertebral fracture prevalence between native Japanese and Japanese-American women. Spine radiographs and data on spine bone mineral density (BMD) and other potential risk factors were collected among 802 Japanese women aged 50-88 years living in Hiroshima and 840 Japanese-American women aged 52-88 years living in Hawaii. In logistic regression analysis, BMD was a major predictor of prevalent vertebral fracture. In linear regression models, weight, age, and menstrual history (age at menopause or years between menarche and menopause) were significantly associated with BMD and thus might contribute to fracture risk indirectly through their effects on BMD. However, age and menstrual history provided additional and complementary information about fracture prevalence after adjusting for BMD. These variables together explained much of the difference in vertebral fracture prevalence between the two study populations. We conclude that the observed difference in age-adjusted prevalence of spine fracture between native Japanese and Japanese-American women was accounted for primarily by the differences in BMD, duration of estrogen exposure, and/or duration of estrogen deficiency. Thus, current BMD is a major but not the sole risk factor for vertebral fractures. Age-related and menopause-related mechanisms may also play an important role in spine fracture independent of BMD.

Quantitative ultrasound bone measurements: normal values and comparison with bone mineral density by dual X-ray absorptiometry

Normative data for qualitative ultrasound (QUS) measurements: speed of sound (SOS), broadband ultrasound attenuation (BUA), and stiffness were established in 118 healthy women aged 20-86 years and in 42 healthy men aged 22-76 years. The relations between age, weight, height, and QUS were studied. QUS measurements were negatively correlated with age in both sexes. In women, age was accepted as first factor (R2 = 0.39 for SOS, 0.35 for BUA, and 0.45 for stiffness, P < 0.001); weight was accepted as second factor for BUA (R2 = 0.44, P < 0.001). In men, age was the only significant parameter (R2 = 0.41 for SOS, 0.39 for BUA, 0.43 for stiffness, P < 0.001). QUS measurements of the right and left feet were highly correlated unless unilateral foot pathology such as algodystrophy was present. Significant correlations were found between QUS of the calcaneus and dual X-ray absorptiometry (DXA) of the lumbar spine (R = 0.67, P < 0.01 for SOS; R = 0.57, P < 0.02 for BUA; R = 0.65, P < 0.01 for stiffness).

Mineral density quantitation of the human cortical iliac crest by backscattered electron image analysis: variations with age, sex, and degree of osteoarthritis

Bone samples from the rim of the iliac crest were obtained at autopsy from 59 patients aged 23 to 75 years, of whom 10 men and 10 women aged 50-75 years had osteoarthritis diagnosed by hand X-rays. An equal number in the same age group and 10 men and 9 women aged less than 50 years were without osteoarthritis. After embedding the bone in PMMA, the blocks were cut, polished, and coated with carbon. The fractions of bone falling within four consecutive bands of signal level were derived from digital backscattered electron imaging. Normal males had more low and medium density bone and normal females more very high density phase tissue proportionately. In both male and female osteoarthritis cases, low and medium fractions were low. The very high density fraction was mainly calcified fibrocartilage; when it was excluded from the calculations, the low, medium, and high phases occurred equally in normal males but increased stepwise in normal females and in osteoarthritis cases of both sexes. The results suggest a lower rate of bone renewal in females than males, and in male osteoarthritis subjects than normal males. An increased proportion of bone of high density would reduce the quality of the bone by increasing its stiffness.

Ethnic differences in bone density in female South African nurses

In the United States, the higher prevalence of osteoporosis and the higher incidence of fractures in whites than in blacks may be attributed to the finding of lower bone density (BD) in both white children and adults. In South Africa, osteoporosis and fractures also occur more frequently in whites than in blacks. Appendicular BD has been found to be similar in black and white children in South Africa, but there is little information available on BD of adults in South Africa. This cross-sectional study aimed to assess changes in BD with age in adult females in South Africa and to assess possible differences in peak BD and in the rate of postmenopausal bone loss between blacks and whites. Data for 180 black and 184 white female nurses aged 20-64 years were analyzed. The distal radius bone density (RBD) was measured by single photon absorptiometry. The lumbar spine bone density (SBD) and the femur bone density (FBD) were measured by dual-energy X-ray absorptiometry. Blacks were shorter than whites (p = 0.0001), and blacks' weight, body mass index, and skinfold thickness increased with age. Peak SBD and RBD were similar in blacks and whites, but peak FBD was higher in blacks (p = 0.0001). This ethnic difference in peak FBD became apparent in the fourth decade. Peak FBD was similar in black and white subjects with normal body mass indices (p = 0.09), but in overweight subjects peak FBD was higher in blacks than in whites (p = 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Stress distributions within the proximal femur during gait and falls: implications for osteoporotic fracture

The rates of fracture at sites with different relative amounts of cortical and trabecular bone (hip, spine, distal radius) have been used to make inferences about the pathomechanics of bone loss and the existence of type I and type II osteoporosis. However, fracture risk is directly related to the ratio of tissue stress to tissue strength, which in turn is dependent not only on tissue composition but also tissue geometry and the direction and magnitude of loading. These three elements determine how the load is distributed within the tissue. As a result, assumptions on the relative structural importance of cortical and trabecular bone, and how these tissues are affected by bone loss, can be inaccurate if based on regional tissue composition and bone density alone. To investigate the structural significance of cortical and trabecular bone in the proximal femur, and how it is affected by bone loss, we determined the stress distributions in a normal and osteoporotic femur resulting from loadings representing: (1) gait; and (2) a fall to the side with impact onto the greater trochanter. A three-dimensional finite element model was generated based on a representative femur selected from a large database of femoral geometries. Stresses were analyzed throughout the femoral neck and intertrochanteric regions. We found that the percentage of total load supported by cortical and trabecular bone was approximately constant for all load cases but differed depending on location. Cortical bone carried 30% of the load at the subcapital region, 50% at the mid-neck, 96% at the base of the neck and 80% at the intertrochanteric region. These values differ from the widely held assumption that cortical bone carries 75% of the load in the femoral neck and 50% of the load at the intertrochanteric region. During gait, the principal stresses were concentrated within the primary compressive system of trabeculae and in the cortical bone of the intertrochanteric region. In contrast, during a fall, the trabecular stresses were concentrated within the primary tensile system of trabeculae with a peak magnitude 4.3 times that present during gait. While the distribution of stress for the osteoporotic femur was similar to the normal, the magnitude of peak stress was increased by between 33% and 45%. These data call into question several assumptions which serve as the basis for theories on the pathomechanics of osteoporosis. In addition, we expect that the insight provided by this analysis will result in the improved development and interpretation of non-invasive techniques for the quantification of in vivo hip fracture risk.