Inter-sex differences in structural properties of aging femora: implications on differential bone fragility: a cadaver study

Improved femoral micro-architecture in adult male individuals with overweight: fracture resistance due to regional specificities

BACKGROUND

It is still unclear whether femoral fracture risk is positively or negatively altered in individuals with overweight. Considering the lack of studies including men with overweight, this study aimed to analyze regional specificities in mechano-structural femoral properties (femoral neck and intertrochanteric region) in adult male cadavers with overweight compared to their normal-weight age-matched counterparts.

METHODS

Ex-vivo osteodensitometry, micro-computed tomography, and Vickers micro-indentation testing were performed on femoral samples taken from 30 adult male cadavers, divided into the group with overweight (BMI between 25 and 30 kg/m2; n = 14; age:55 ± 16 years) and control group (BMI between 18.5 and 25 kg/m2; n = 16; age:51 ± 18 years).

RESULTS

Better quality of trabecular and cortical microstructure in the inferomedial (higher trabecular bone volume fraction, trabecular thickness, and cortical thickness, coupled with reduced cortical pore diameter, p < 0.05) and superolateral femoral neck (higher trabecular number and tendency to lower cortical porosity, p = 0.043, p = 0.053, respectively) was noted in men with overweight compared to controls. Additionally, the intertrochanteric region of men with overweight had more numerous and denser trabeculae, coupled with a thicker and less porous cortex (p < 0.05). Still, substantial overweight-induced change in femoral osteodensitometry parameters and Vickers micro-hardness was not demonstrated in assessed femoral subregions (p > 0.05).

CONCLUSIONS

Despite the absence of significant changes in femoral osteodensitometry, individuals with overweight had better trabecular and cortical femoral micro-architecture implying higher femoral fracture resistance. However, the microhardness was not significantly favorable in the individuals who were overweight, indicating the necessity for further research.

Bone loss in chronic liver diseases: Could healthy liver be a requirement for good bone health?

Given that the liver is involved in many metabolic mechanisms, it is not surprising that chronic liver disease (CLD) could have numerous complications. Secondary osteoporosis and increased bone fragility are frequently overlooked complications in CLD patients. Previous studies implied that up to one-third of these individuals meet diagnostic criteria for osteopenia or osteoporosis. Recent publications indicated that CLD-induced bone fragility depends on the etiology, duration, and stage of liver disease. Therefore, the increased fracture risk in CLD patients puts a severe socioeconomic burden on the health system and urgently requires more effective prevention, diagnosis, and treatment measures. The pathogenesis of CLD-induced bone loss is multifactorial and still insufficiently understood, especially considering the relative impact of increased bone resorption and reduced bone formation in these individuals. It is essential to note that inconsistent findings regarding bone mineral density measurement were previously reported in these individuals. Bone mineral density is widely used as the "golden standard" in the clinical assessment of bone fragility although it is not adequate to predict individual fracture risk. Therefore, microscale bone alterations (bone microstructure, mechanical properties, and cellular indices) were analyzed in CLD individuals. These studies further support the thesis that bone strength could be compromised in CLD individuals, implying that an individualized approach to fracture risk assessment and subsequent therapy is necessary for CLD patients. However, more well-designed studies are required to solve the bone fragility puzzle in CLD patients.

Automatic analysis of skull thickness, scalp-to-cortex distance and association with age and sex in cognitively normal elderly

Personalized neurostimulation has been a potential treatment for many brain diseases, which requires insights into brain/skull geometry. Here, we developed an open source efficient pipeline BrainCalculator for automatically computing the skull thickness map, scalp-to-cortex distance (SCD), and brain volume based on T 1 -weighted magnetic resonance imaging (MRI) data. We examined the influence of age and sex cross-sectionally in 407 cognitively normal older adults (71.9±8.0 years, 60.2% female) from the ADNI. We demonstrated the compatibility of our pipeline with commonly used preprocessing packages and found that BrainSuite Skullfinder was better suited for such automatic analysis compared to FSL Brain Extraction Tool 2 and SPM12- based unified segmentation using ground truth. We found that the sphenoid bone and temporal bone were thinnest among the skull regions in both females and males. There was no increase in regional minimum skull thickness with age except in the female sphenoid bone. No sex difference in minimum skull thickness or SCD was observed. Positive correlations between age and SCD were observed, faster in females (0.307%/y) than males (0.216%/y) in temporal SCD. A negative correlation was observed between age and whole brain volume computed based on brain surface (females -1.031%/y, males -0.998%/y). In conclusion, we developed an automatic pipeline for MR-based skull thickness map, SCD, and brain volume analysis and demonstrated the sex-dependent association between minimum regional skull thickness, SCD and brain volume with age. This pipeline might be useful for personalized neurostimulation planning.

Hip structure analysis and femoral osteodensitometry in aged postmenopausal women with hip osteoarthritis and femoral neck fracture

PURPOSE

Osteoarthritis (OA), osteoporosis, and bone fractures are frequent aging-related conditions. Regardless of the growing research interest in the effects of hip OA on femoral fracture risk, data about the region specificity of osteodensitometric and hip structure analysis (HSA) parameters of the proximal femora are lacking in aged postmenopausal women with hip OA compared to individuals with femoral neck fragility fracture.

METHODS

This study included 76 postmenopausal women admitted for total hip arthroplasty due to non-traumatic femoral neck fracture (FN_Fx group, n = 39) and hip osteoarthritis (OA group, n = 37).

RESULTS

Osteodensitometric parameters differed significantly between the OA and FN_Fx groups, depicting lower bone mineral density in the FN_Fx group (p < 0.05). The most significant increase in these parameters was registered in the intertrochanteric region of the OA group. Moreover, the OA-induced changes in HSA-derived parameters displayed significant regional heterogeneity, with the intertrochanteric region showing the most notable difference between OA and FN_Fx group.

CONCLUSION

Our data may indicate that OA displayed the most prominent positive effect on the intertrochanteric femoral region, revealing the regional heterogeneity in structural geometry and biomechanical indices of proximal femora in OA individuals. Since we did not observe significant differences in the femoral neck region, we may speculate that OA does not have a substantial protective effect on the femoral neck fracture risk in aged postmenopausal women.

Mechano-structural alteration in proximal femora of individuals with alcoholic liver disease: Implications for increased bone fragility

Although increased hip fracture risk is noted in patients with alcoholic liver disease (ALD), their femoral microstructural and mechanical properties were not investigated previously. The present study aimed to analyze the associations between subregional deteriorations in femoral mechano-structural properties and clinical imaging findings to explain increased femoral fracture risk among ALD patients. This study analyzed proximal femora of 33 male cadaveric donors, divided into ALD (n = 13, 57 ± 13 years) and age-matched control group (n = 20, 54 ± 13 years). After pathohistological verification of ALD stage, DXA and HSA measurements of the proximal femora were performed, followed by micro-CT and Vickers microindentation of the superolateral neck, inferomedial neck, and intertrochanteric region. Bone mineral density and cross sectional area of the femoral neck were deteriorated in ALD donors, compared with healthy controls (p < 0.05). Significant ALD-induced degradation of trabecular and cortical microstructure and Vickers microhardness reduction were noted in the analyzed femoral regions (p < 0.05). Still, the most prominent ALD-induced mechano-structural deterioration was noted in intertrochanteric region. Additionally, more severe bone alterations were observed in individuals with an irreversible stage of ALD, alcoholic liver cirrhosis (ALC), than in those with an initial ALD stage, fatty liver disease. Observed osteodensitometric and mechano-structural changes illuminate the basis for increased femoral fracture risk in ALD patients. Additionally, our data suggest bone strength reduction that may result in increased susceptibility to intertrochanteric femoral fracture in men with ALD. Thus, femoral fracture risk assessment should be advised for all ALD patients, especially in those with ALC.

The comparison of age- and sex-specific alteration in pubic bone microstructure: A cross-sectional cadaveric study

BACKGROUND

The burden of age-associated fragility fracture of the pelvis has gradually amplified over the years. Commonly used clinical tools cannot fully explain age-associated fracture risk increase, and microstructural analysis could be required to elucidate pubic bone strength decline in elderly.

MATERIAL AND METHODS

The study sample encompassed 46 pubic bones obtained from cadaveric donors divided into a young women (<45 years, n = 11), aged women (>60 years, n = 11), young men (<45 years, n = 12) and aged men group (>60 years, n = 12). Micro-computed tomography was used to evaluate the cortical and trabecular microstructure of pubic bone samples.

RESULTS

Apart from age-associated loss in quantitative trabecular parameters, significant alteration of micro-CT parameters that more closely reflect internal trabecular microarchitectural complexity may contribute to pubic bone strength decline in men and women of advanced age (p < 0.05). Additionally, decreased cortical thickness and increased Ct.Po, Po.Dm and Po.N were found in the anterior and posterior cortical surface of pubic bone samples from the aged individuals (p < 0.05). The more pronounced alteration was noted in aged female donors, illustrated in a significant deterioration trend of the Tb.N, Tb.Sp, and thinner posterior cortical surface with decreased pore spacing (p < 0.05).

CONCLUSION

Our data suggest that age-associated deterioration in trabecular and cortical pubic bone micro-architecture could unravel a morphological basis for decreased pubic bone strength and increased pubic bone fragility, which leads to fracture predilection in the elderly women. Thus, the individual fracture risk assessment should be advised in the elderly, with a particular accent on aged women.

The severity of hepatic disorder is related to vertebral microstructure deterioration in cadaveric donors with liver cirrhosis

Patients with liver cirrhosis (LC) commonly suffer from osteoporosis and vertebral fracture, but data about their vertebral micro-architectural changes are still limited. This study aimed to evaluate the potential differences in trabecular micro-architecture of lumbar vertebrae between male LC patients and healthy controls, in relation to etiology and pathohistological scoring of the liver disorder. After pathohistological examination of liver tissue, micro-computed tomography was performed on the vertebral samples included into: alcoholic liver cirrhosis group (ALC; n = 16; age: 59 ± 8 years), non-alcoholic liver cirrhosis group (non-ALC; n = 15; age: 69 ± 10 years) and control group (n = 16; age: 58 ± 6 years). Our data showed significant impairment of the trabecular microstructure in the lumbar vertebrae from LC donors, regardless of the alcoholic/non-alcoholic origin of liver disorder, as illustrated by lower BV/TV, Tb.Th, and Tb.N compared with controls (p < .05). Moreover, depredation in trabecular micro-architecture was inversely associated with pathohistological scores (p < .05), indicating that severity of liver disorder could be an important predictor of reduced vertebral strength in LC. We noticed significant micro-architectural deterioration in the trabecular compartment of the lumbar vertebrae of male individuals with alcoholic and non-alcoholic LC, which was associated with the severity of the liver disease. Thus, clinical assessment of fracture risk should be advised for all LC patients, regardless of the alcoholic origin of liver cirrhosis. Additionally, adequate and timely treatment of liver disorder may decelerate the progression of bone impairment in LC patients.

External bone size identifies different strength-decline trajectories for the male human femora

Understanding skeletal aging and predicting fracture risk is increasingly important with a growing elderly population. We hypothesized that when categorized by external bone size, the male femoral diaphysis would show different strength-age trajectories which can be explained by changes in morphology, composition and collagen cross-linking. Cadaveric male femora were sorted into narrow (n = 15, 26-89 years) and wide (n = 15, 29-82 years) groups based upon total cross-sectional area of the mid-shaft normalized to bone length (Tt.Ar/Le) and tested for whole bone strength, tissue-level strength, and tissue-level post-yield strain. Morphology, cortical TMD (Ct.TMD), porosity, direct measurements of enzymatic collagen cross-links, and pentosidine were obtained. The wide group alone showed significant negative correlations with age for tissue-level strength (R² = 0.50, p = 0.002), tissue-level post-yield strain (R² = 0.75, p < 0.001) and borderline significance for whole bone strength (R² = 0.14, p = 0.108). Ct.TMD correlated with whole bone and tissue-level strength for both groups, but pentosidine normalized to enzymatic cross-links correlated negatively with all mechanical properties for the wide group only. The multivariate analysis showed that just three traits for each mechanical property explained the majority of the variance for whole bone strength (Ct.Area, Ct.TMD, Log(PEN/Mature; R² = 0.75), tissue-level strength (Age, Ct.TMD, Log(DHLNL/HLNL); R² = 0.56), and post-yield strain (Age, Log(Pyrrole), Ct.Area; R² = 0.51). Overall, this highlights how inter-individual differences in bone structure, composition, and strength change with aging and that a one-size fits all understanding of skeletal aging is insufficient.

Inter-site Variability of the Human Osteocyte Lacunar Network: Implications for Bone Quality

PURPOSE OF REVIEW

This article provides a review on the variability of the osteocyte lacunar network in the human skeleton. It highlights characteristics of the osteocyte lacunar network in relation to different skeletal sites and fracture susceptibility.

RECENT FINDINGS

Application of 2D analyses (quantitative backscattered electron microscopy, histology, confocal laser scanning microscopy) and 3D reconstructions (microcomputed tomography and synchrotron radiation microcomputed tomography) provides extended high-resolution information on osteocyte lacunar properties in individuals of various age (fetal, children's growth, elderly), sex, and disease states with increased fracture risk. Recent findings on the distribution of osteocytes in the human skeleton are reviewed. Quantitative data highlighting the variability of the osteocyte lacunar network is presented with special emphasis on site specificity and maintenance of bone health. The causes and consequences of heterogeneous distribution of osteocyte lacunae both within specific regions of interest and on the skeletal level are reviewed and linked to differential bone quality factors and fracture susceptibility.

External Bone Size Is a Key Determinant of Strength-Decline Trajectories of Aging Male Radii

Given prior work showing associations between remodeling and external bone size, we tested the hypothesis that wide bones would show a greater negative correlation between whole-bone strength and age compared with narrow bones. Cadaveric male radii (n = 37 pairs, 18 to 89 years old) were evaluated biomechanically, and samples were sorted into narrow and wide subgroups using height-adjusted robustness (total area/bone length). Strength was 54% greater (p < 0.0001) in wide compared with narrow radii for young adults (<40 years old). However, the greater strength of young-adult wide radii was not observed for older wide radii, as the wide (R² = 0.565, p = 0.001), but not narrow (R² = 0.0004, p = 0.944) subgroup showed a significant negative correlation between strength and age. Significant positive correlations between age and robustness (R² = 0.269, p = 0.048), cortical area (Ct.Ar; R² = 0.356, p = 0.019), and the mineral/matrix ratio (MMR; R² = 0.293, p = 0.037) were observed for narrow, but not wide radii (robustness: R² = 0.015, p = 0.217; Ct.Ar: R² = 0.095, p = 0.245; MMR: R² = 0.086, p = 0.271). Porosity increased with age for the narrow (R² = 0.556, p = 0.001) and wide (R² = 0.321, p = 0.022) subgroups. The wide subgroup (p < 0.0001) showed a significantly greater elevation of a new measure called the Cortical Pore Score, which quantifies the cumulative effect of pore size and location, indicating that porosity had a more deleterious effect on strength for wide compared with narrow radii. Thus, the divergent strength-age regressions implied that narrow radii maintained a low strength with aging by increasing external size and mineral content to mechanically offset increases in porosity. In contrast, the significant negative strength-age correlation for wide radii implied that the deleterious effect of greater porosity further from the centroid was not offset by changes in outer bone size or mineral content. Thus, the low strength of elderly male radii arose through different biomechanical mechanisms. Consideration of different strength-age regressions (trajectories) may inform clinical decisions on how best to treat individuals to reduce fracture risk. © 2019 American Society for Bone and Mineral Research.

Region-dependent patterns of trabecular bone growth in the human proximal femur: A study of 3D bone microarchitecture from early postnatal to late childhood period

OBJECTIVES

Parallel with body growth and development, bone structure in non-adults is reorganized to achieve the particular design observed in mature individuals. We traced the changes in three-dimensional trabecular microarchitectural design during the phases of locomotor maturation to clarify how human bone adapts to mechanical demands.

MATERIALS AND METHODS

Micro-CT was performed on biomechanically-relevant subregions of the proximal femur (medial, intermediate and lateral neck regions, intertrochanteric region, metaphyseal region) from early postnatal period to late childhood.

RESULTS

Developmental patterns of trabecular microarchitecture showed that gestationally overproduced bone present at birth underwent the most dramatic reduction during the first year, followed by a reversing trend in some of the quantitative parameters (e.g., bone volume fraction, trabecular anisotropy). Certain regional anisotropy already present at birth is further accentuated into the childhood suggesting an adaptation to differential loading environments. Trabecular eccentricity in the femoral neck was particularly accentuated during childhood, giving the medial neck-the site mostly loaded in walking-superior microarchitectural design (high bone volume fraction and anisotropy, the earliest appearance and predominance of plate- and honeycomb-shaped trabeculae).

DISCUSSION

While providing quantitative data on how bone microarchitecture adapts to increasing mechanical demands occurring during the phases of locomotor maturation, the study reveals how regional anisotropy develops in the proximal femur to ensure a functional and competent bone structure. Decomposing the region-specific patterns of bone mass accrual is important in understanding skeletal adaptations to bipedalism, as well for understanding why fractures often occur location-dependent, both in pediatric and elderly individuals.

Hyperostosis frontalis interna in postmenopausal women-Possible relation to osteoporosis

To improve our understanding of hyperostosis frontalis interna (HFI), we investigated whether HFI was accompanied by changes in the postcranial skeleton. Based on head CT scan analyses, 103 postmenopausal women were divided into controls without HFI and those with HFI, in whom we measured the thickness of frontal, occipital, and parietal bones. Women in the study underwent dual energy x-ray absorptiometry to analyze the bone density of the hip and vertebral region and external geometry of the proximal femora. Additionally, all of the women completed a questionnaire about symptoms and conditions that could be related to HFI. Women with HFI had a significantly higher prevalence of headaches, neurological and psychiatric disorders, and a significantly lower prevalence of having given birth. Increased bone thickness and altered bone structure in women with HFI was localized only on the skull, particularly on the frontal bone, probably due to specific properties of its underlying dura. Bone loss in the postcranial skeleton showed the same pattern in postmenopausal women with HFI as in those without HFI. Recording of HFI in medical records can be helpful in distinguishing whether reported disorders occur as a consequence of HFI or are related to other diseases, but does not appear helpful in identifying women at risk of bone loss.

Difference in the trajectory of change in bone geometry as measured by hip structural analysis in the narrow neck, intertrochanteric region, and femoral shaft between men and women following hip fracture

Prior studies have shown that women have declines in bone structure and strength after hip fracture, but it is unclear whether men sustain similar changes. Therefore, the objective was to examine sex differences in proximal femur geometry following hip fracture. Hip structural analysis was used to derive metrics of bone structure and strength: aerial bone mineral density, cross-sectional bone area (CSA), cortical outer diameter, section modulus (SM), and buckling ratio (BR) from dual-energy x-ray absorptiometry scans performed at baseline (within 22days of hospital admission), two, six, or twelve months after hip fracture in men and women (n=282) enrolled in the Baltimore Hip Studies 7th cohort. Weighted estimating equations were used to evaluate sex differences at the narrow neck (NN), intertrochanteric (IT), and femoral shaft (FS). Men had significantly different one year NN changes compared to women in CSA: -6.33% (-12.47, -0.20) vs. 1.37% (-3.31, 6.43), P=0.049; SM: -4.98% (-11.08, 1.10) vs. 3.94% (-2.51, 10.42), P=0.042; and BR: 7.50% (0.65, 14.36) vs. -1.20% (-6.41, 4.00), P=0.044. One year IT changes displayed similar patterns, but the sex differences were not statistically significant for CSA: -4.07% (-10.83, 2.67) vs. 0.41% (-3.41, 4.24), P=0.252; SM: -4.78% (-12.10, 5.53) vs. -0.31 (-4.74, 4.11), P=0.287; and BR: 4.59% (-0.65, 9.84) vs. 1.52% (-4.23, 7.28), P=0.425. Differences in FS geometric parameters were even smaller in magnitude and not significantly different by sex. Women generally experienced non-significant increases in bone tissue and strength following hip fracture, while men had structural declines that were statistically greater at the NN region. Reductions in the mechanical strength of the proximal femur after hip fracture could put men at higher risk for subsequent fractures of the contralateral hip.

Modeling the Mechanical Consequences of Age-Related Trabecular Bone Loss by XFEM Simulation

The elderly are more likely to suffer from fracture because of age-related trabecular bone loss. Different bone loss locations and patterns have different effects on bone mechanical properties. Extended finite element method (XFEM) can simulate fracture process and was suited to investigate the effects of bone loss on trabecular bone. Age-related bone loss is indicated by trabecular thinning and loss and may occur at low-strain locations or other random sites. Accordingly, several ideal normal and aged trabecular bone models were created based on different bone loss locations and patterns; then, fracture processes from crack initiation to complete failure of these models were observed by XFEM; finally, the effects of different locations and patterns on trabecular bone were compared. Results indicated that bone loss occurring at low-strain locations was more detrimental to trabecular bone than that occurring at other random sites; meanwhile, the decrease in bone strength caused by trabecular loss was higher than that caused by trabecular thinning, and the effects of vertical trabecular loss on mechanical properties were more severe than horizontal trabecular loss. This study provided a numerical method to simulate trabecular bone fracture and distinguished different effects of the possible occurrence of bone loss locations and patterns on trabecular bone.

Quantification of Age-Related Tissue-Level Failure Strains of Rat Femoral Cortical Bones Using an Approach Combining Macrocompressive Test and Microfinite Element Analysis

Bone mechanical properties vary with age; meanwhile, a close relationship exists among bone mechanical properties at different levels. Therefore, conducting multilevel analyses for bone structures with different ages are necessary to elucidate the effects of aging on bone mechanical properties at different levels. In this study, an approach that combined microfinite element (micro-FE) analysis and macrocompressive test was established to simulate the failure of male rat femoral cortical bone. Micro-FE analyses were primarily performed for rat cortical bones with different ages to simulate their failure processes under compressive load. Tissue-level failure strains in tension and compression of these cortical bones were then back-calculated by fitting the experimental stress–strain curves. Thus, tissue-level failure strains of rat femoral cortical bones with different ages were quantified. The tissue-level failure strain exhibited a biphasic behavior with age: in the period of skeletal maturity (1–7 months of age), the failure strain gradually increased; when the rat exceeded 7 months of age, the failure strain sharply decreased. In the period of skeletal maturity, both the macro- and tissue-levels mechanical properties showed a large promotion. In the period of skeletal aging (9–15 months of age), the tissue-level mechanical properties sharply deteriorated; however, the macromechanical properties only slightly deteriorated. The age-related changes in tissue-level failure strain were revealed through the analysis of male rat femoral cortical bones with different ages, which provided a theoretical basis to understand the relationship between rat cortical bone mechanical properties at macro- and tissue-levels and decrease of bone strength with age.

Multi-level femoral morphology and mechanical properties of rats of different ages

A macro-micro-nano-multi-level study was conducted to explore age-related structural and mechanical properties of bone, as well as the effects of aging on bone properties. A total of 70 male Wistar rats were used, ranging in the ages of 1, 3, 5, 7, 9, 11, 14, 15, 16, and 17 months (n = 7/age group). After micro-computed tomography (CT) scanning, longitudinal cortical bone specimens with a length of 5mm were cut along the femoral shaft axis from left femur shafts for mechanical testing, and the cross-sectional areas were measured. The macro-mechanical properties obtained in mechanical testing and microarchitecture parameters measured by micro-CT were significantly correlated with the animal age (r(2) = 0.96, p < 0.001). Scanning electron microscopy was used for detecting the microarchitecture features of the fractured surfaces, which exhibited age-related plate-fibrous-mixed fibrous-plate texture, resulting in changes in macro-mechanical properties (r(2) > 0.90, p < 0.001). The mineral phase of the left femoral shaft and head was analyzed by atomic force microscopy. Longitudinal and transverse trabecular bone tissues, as well as longitudinal cortical bone tissue, were used for nanoindentation test, and the chemical composition was evaluated by quantitative chemical analyses. The correlations between mineral content and bone material properties (i.e., elastic properties of the bone tissue and size and roughness of bone mineral grains) were highly significant (r > 0.95, p < 0.001). Multi-level femur morphology, mechanical property, and mineral content were significantly correlated with the animal age. The correlations between bone mineral content and bone material morphological and mechanical properties may partly explain the increase in bone fragility with aging, which will provide a theoretical basis for the investigation of age-related bone properties in clinics.

Quantification of Alterations in Cortical Bone Geometry Using Site Specificity Software in Mouse models of Aging and the Responses to Ovariectomy and Altered Loading

Investigations into the effect of (re)modeling stimuli on cortical bone in rodents normally rely on analysis of changes in bone mass and architecture at a narrow cross-sectional site. However, it is well established that the effects of axial loading produce site-specific changes throughout bones' structure. Non-mechanical influences (e.g., hormones) can be additional to or oppose locally controlled adaptive responses and may have more generalized effects. Tools currently available to study site-specific cortical bone adaptation are limited. Here, we applied novel site specificity software to measure bone mass and architecture at each 1% site along the length of the mouse tibia from standard micro-computed tomography (μCT) images. Resulting measures are directly comparable to those obtained through μCT analysis (R (2) > 0.96). Site Specificity analysis was used to compare a number of parameters in tibiae from young adult (19-week-old) versus aged (19-month-old) mice; ovariectomized and entire mice; limbs subjected to short periods of axial loading or disuse induced by sciatic neurectomy. Age was associated with uniformly reduced cortical thickness and site-specific decreases in cortical area most apparent in the proximal tibia. Mechanical loading site-specifically increased cortical area and thickness in the proximal tibia. Disuse uniformly decreased cortical thickness and decreased cortical area in the proximal tibia. Ovariectomy uniformly reduced cortical area without altering cortical thickness. Differences in polar moment of inertia between experimental groups were only observed in the proximal tibia. Aging and ovariectomy also altered eccentricity in the distal tibia. In summary, site specificity analysis provides a valuable tool for measuring changes in cortical bone mass and architecture along the entire length of a bone. Changes in the (re)modeling response determined at a single site may not reflect the response at different locations within the same bone.

Evidence of degraded BMD and geometry at the proximal femora in male patients with alcoholic liver cirrhosis

We examined the association of alcoholic cirrhosis in 33 patients with areal bone mineral density (BMD) and the assessed bone geometric strength of their proximal femora. Lower areal BMD, cross-sectional area and section modulus, thinner cortex, and higher buckling ratio suggest that the alcoholic liver cirrhosis is associated with lower measures of bone strength.

INTRODUCTION

Hepatic bone disease is an important complication of chronic liver disease and is associated with significant morbidity through fractures resulting in pain, deformity, and immobility. In this study, we examined the association of alcoholic cirrhosis and liver insufficiency stage with areal bone mineral density (aBMD) and additionally employed hip structure analysis (HSA) as an advanced method to assess bone geometric strength of the proximal femur in men with alcoholic liver cirrhosis.

METHODS

The study included 33 male patients with alcoholic liver cirrhosis and a control group of 36 healthy patients. Laboratory testing included the following biochemical markers of bone turnover: serum levels of osteocalcin and C-telopeptide of type 1 collagen. Areal BMD was measured by dual x-ray absorptiometry on the proximal femora. Structural parameters were then derived from these scans using hip structure analysis software.

RESULTS

After adjusting for age, body height, and weight, we found lower cross-sectional area (p = 0.005) and section modulus (p = 0.005), thinner cortex (p = 0.012), and higher buckling ratio (p = 0.043) in the neck region among patients with cirrhosis. The findings suggest that alcoholic liver cirrhosis is associated with lower measures of bone strength. These findings were consistent with decreased osteocalcin values and increased C-telopeptide of type 1 collagen in patients with cirrhosis, indicating reduction in bone formation and increased bone resorption.

CONCLUSION

Our results emphasize that HSA-derived structural indices of proximal femoral structure may be an important index of greater fragility in patients with alcoholic cirrhosis.

Are we taking full advantage of the growing number of pharmacological treatment options for osteoporosis?

We are becoming increasingly aware that the manner in which our skeleton ages is not uniform within and between populations. Pharmacological treatment options with the potential to combat age-related reductions in skeletal strength continue to become available on the market, notwithstanding our current inability to fully utilize these treatments by accounting for an individual's unique biomechanical needs. Revealing new molecular mechanisms that improve the targeted delivery of pharmaceuticals is important; however, this only addresses one part of the solution for differential age-related bone loss. To improve current treatment regimes, we must also consider specific biomechanical mechanisms that define how these molecular pathways ultimately impact whole bone fracture resistance. By improving our understanding of the relationship between molecular and biomechanical mechanisms, clinicians will be better equipped to take full advantage of the mounting pharmacological treatments available. Ultimately this will enable us to reduce fracture risk among the elderly more strategically, more effectively, and more economically. In this interest, the following review summarizes the biomechanical basis of current treatment strategies while defining how different biomechanical mechanisms lead to reduced fracture resistance. It is hoped that this may serve as a template for the identification of new targets for pharmacological treatments that will enable clinicians to personalize care so that fracture incidence may be globally reduced.

Atomic force microscopy characterization of the external cortical bone surface in young and elderly women: potential nanostructural traces of periosteal bone apposition during aging

On the basis of the suggestion that bone nanostructure bears “tissue age” information and may reflect surface deposition/modification processes, we performed nanoscale characterization of the external cortical bone surface at the femoral neck in women using atomic force microscopy (AFM). The specific aims were to assess age-related differences in bone nanostructure and explore the existence of nanostructural traces of potential bone apposition at this surface. Our findings revealed that the external cortical surface represents a continuous phase composed of densely packed mineral grains. Although the grains varied in size and shape, there was a domination of small grains indicative of freshly deposited bone (mean grain size: young, 35 nm; old, 37 nm; p > 0.05). Advanced quantitative analysis of surface morphological patterns revealed comparable roughness and complexity of the surface, suggesting a similar rate of mineral particle deposition at the surface in both groups. Calcium/phosphorus ratio, a measure of bone tissue age, was within the same range in both groups. In summary, our AFM analyses showed consistent nanostructural and compositional bone features, suggesting existence of new bone at the periosteal bone surface in both young and elderly women. Considering observed age-related increase in the neck diameter, AFM findings may support the theory of continuous bone apposition at the periosteal surface.

Enhanced trabecular micro-architecture of the femoral neck in hip osteoarthritis vs. healthy controls: a micro-computer tomography study in postmenopausal women

PURPOSE

A controversial relationship between osteoarthritis (OA) and bone fragility has been attracting considerable attention. However, despite interest in the effects of OA on femoral neck fracture risk and numerous studies analysing the changes in the arthritic femoral head, there is insufficient data about femoral neck 3D bone micro-architecture in individuals with hip osteoarthritis. We compared trabecular micro-architecture of the femoral neck between postmenopausal women with coxarthrosis and controls to explore whether coxarthrosis may indicate reduced bone fragility from the trabecular micro-architectural perspective.

METHODS

The study sample included nine women with hip osteoarthritis and 13 age-matched controls. The femoral neck sections were scanned using micro-computed tomography, evaluating the cancellous bone from the superolateral and inferomedial neck subregions.

RESULTS

Osteoarthritic subjects demonstrated a general trend of improved trabecular micro-architecture in both analysed subregions when compared with age-matched controls. In particular, several architectural properties that are important predictors of cancellous bone strength showed significantly better values in the OA group, even after adjusting for bone volume fraction. Namely, the OA group expressed higher trabecular connectivity (p = 0.008), lower SMI indicating more plate-like structure (p = 0.005), and reduced anisotropy (p = 0.006) particularly in the inferomedial neck. Osteoarthritic cases also trended towards higher BV/TV, particularly in the superolateral neck. All micro-architectural parameters displayed significant regional heterogeneity (p ≤ 0.01), with the inferomedial neck region showing more favourable values than the superolateral region.

CONCLUSIONS

Enhanced trabecular micro-architecture of the femoral neck in postmenopausal osteoarthritic subjects suggests reduced cancellous bone fragility in comparison with their age-matched healthy controls.

Age-related deterioration in trabecular bone mechanical properties at material level: nanoindentation study of the femoral neck in women by using AFM

Despite general belief that the mechanical properties of bone material contribute to whole bone strength, it is still obscure what the age effects are on mechanical behavior of the bone material, particularly in the case of the femoral neck trabeculae. In this study, atomic force microscopy was used for imaging and measuring the size of mineral grains, as well as nano-scale mechanical characterization (nanoindentation) of the bone mineralized matrix of trabeculae, with the aim to explore the age effects on bone elasticity and give new insight into age-related bone fragility. The bone samples in this study comprised trabecular bone specimens of the femoral neck region, collected from eight skeletal healthy women (five young adults: 27-38yrs., three elderly: 83-94yrs.) at autopsy. Bone trabeculae in the elderly displayed a higher modulus and nanohardness, signifying a decreased amount of energy that can be accommodated by the bone tissue during loading. Regression analysis revealed that nearly 65% of variability in the bone matrix elastic modulus can be statistically explained by the changes in size of the matrix mineral grains. This study revealed that the bone trabeculae of elderly women express less elastic behavior at the material level, which makes them more vulnerable to unusual impact loads originating from a fall. The observed age-related structural and mechanical alteration at the bone material level adds new evidence for understanding why hip fractures are more frequent in elderly women.

Micro-structural basis for particular vulnerability of the superolateral neck trabecular bone in the postmenopausal women with hip fractures

In this study we analyzed the trabecular bone micro-architecture in the inferomedial and superolateral subregions of the femoral neck in a group with hip fractures and a control group of elderly women, with aim to clarify the micro-structural basis of bone fragility. Proximal femora from 29 Caucasian female cadavers were collected at Institute of Forensic Medicine in Belgrade (15 women with hip fracture: age 79.5±8.5 yrs.; and 14 women without hip fractures: age 74.1±9.3 yrs.). The femoral neck section was scanned in dry conditions using a micro-computed tomography (Scanco μCT 40), at 70 kV, 114 μA, 300 ms integration time, 36 μm resolution, isotropic, 1024×1024 pixels per slice, automatically evaluating trabecular micro-architecture using the built-in program of the micro-CT with direct 3D morphometry. The samples were foam padded to avoid any movement artifacts during scanning. Analysis of the neck section in the fracture group compared to the control cases demonstrated significantly lower bone volume fraction (mean: 6.3% vs. 11.2%, p=0.002), lower connectivity density (0.33/mm(3) vs. 0.74/mm(3), p=0.019) and higher trabecular separation (0.87 mm vs. 0.83 mm, p=0.030). Division into the superolateral and inferomedial regions of interest revealed that the superolateral neck displayed even more differences in micro-architectural properties between the fracture and non-fracture groups. Namely, while in the inferomedial neck only bone volume fraction and degree of anisotropy displayed significant inter-group variability (lower BV/TV with higher degree of anisotropy in the fracture group), in the superolateral neck almost all parameters were different between the fracture cases and the controls, where the fracture group showed a lower trabecular bone volume fraction (3.6% vs. 8.2%, p=0.001), lower connectivity (0.21 vs. 0.63/mm(3), p=0.008), more rod like trabecular structure (SMI: 2.94 vs. 2.62, p=0.049), higher separation and the thinned trabeculae (Tb.Sp: 0.89 vs. 0.85 mm, p=0.013; Tb.Th: 0.17 vs. 0.20 mm, p=0.05). In addition, after adjusting for the effects of BV/TV, the majority of differences disappeared, demonstrating that the bone loss manifests itself via the changes in micro-architectural parameters: trabecular thinning, rising the spacing between individual trabeculae, reducing trabecular connectivity and accentuating trabecular perforations leading to predominance of rod-like trabecular elements. Preferential impairment of the superolateral neck trabecular structure and organization in women with hip fracture reveals the region-dependent micro-structural basis of bone fragility in elderly women.

Nanostructure and mineral composition of trabecular bone in the lateral femoral neck: implications for bone fragility in elderly women

Despite interest in investigating age-related hip fractures, the determinants of decreased bone strength in advanced age are not clear enough. Hitherto it has been obscure how the aging process affects the femoral neck nanostructure and composition, particularly in the lateral subregion of the femoral neck, which is considered as a fracture-initiating site. The femoral bone samples used in this study were obtained at autopsy in 10 women without skeletal disease (five younger: aged 20-40 years, and five elderly: aged 73-94 years). Atomic force microscopy (AFM) was applied to explore the mineral grain size in situ in young vs. old trabecular bone samples from the lateral femoral neck. The chemical compositions of the samples were determined using inductively coupled plasma optical emission spectroscopy and direct current argon arc plasma optical emission spectrometry. Our AFM study revealed differences in trabecular bone nanostructure between young and elderly women. The mineral grain size in the trabeculae of the old women was larger than that in the young (median: 95 vs. 59nm), with a particular bimodal distribution: 45% were small grains (similar to the young) and the rest were larger. Since chemical analyses showed that levels of calcium and phosphorus were unchanged with age, our study suggests that during aging the existing bone mineral is reorganized and forms larger aggregates. Given the mechanical disadvantage of large-grained structures (decreased material strength), the observed nanostructural differences contribute to our understanding of the increased fragility of the lateral femoral neck in aged females. Moreover, increasing data on mineral grains in natural bone is essential for advancing calcium-phosphate ceramics for bone tissue replacement.