Fracture risk and height: an association partly accounted for by cortical porosity of relatively thinner cortices

Combined Effect of Dietary Acid Load and Cardiometabolic Syndrome on Bone Resorption Marker among Post-Menopausal Women in Malaysia

Background

This study aimed to investigate factors associated with bone resorption status and determine the independent and interactive effects of dietary acid load (DAL) and cardiometabolic syndrome (CMS) on bone resorption in post-menopausal women.

Methods

Overall, 211 community-dwelling post-menopausal women were recruited from the National Council of Senior Citizens Organization, Malaysia. DAL was estimated using the potential renal acid load from the food frequency questionnaire. Sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI) and smoking behaviour was assessed using the Global Adult Tobacco Survey 2011. Serum 25(OH) vitamin D levels were determined using the ADVIA Centaur vitamin D assay and serum C-terminal telopeptides of type I collagen (CTX1) were used as surrogate markers to assess bone resorption. CMS was determined based on the harmonised criteria.

Results

Age (β = -0.145, t = -2.002, P < 0.05) was negatively associated while DAL (β = 0.142, t = 2.096, P < 0.05) and sleep quality (β = 0.147, t = 2.162, P < 0.05) were positively associated with CTX1. Height was positively correlated with CTX1 (r = 0.136, P <0.05). Conversely, other variables (CMS traits, CMS, serum 25(OH) vitamin D level, years of menopause, years of education and physical activity) were not significantly associated with CTX1 levels. There was no significant interaction between DAL and CMS on bone resorption.

Conclusion

Our findings propose that high DAL, but not CMS, is a potential risk factor for bone resorption. The analysis did not demonstrate the combined effects of DAL and CMS on bone resorption.

Am I big boned? Bone length scaled reference data for HRpQCT measures of the radial and tibial diaphysis in White adults

Cross-sectional size of a long bone shaft influences its mechanical properties. We recently used high-resolution peripheral quantitative computed tomography (HRpQCT) to create reference data for size measures of the radial and tibial diaphyses. However, data did not take into account the impact of bone length. Human bone exhibits relatively isometric allometry whereby cross-sectional area increases proportionally with bone length. The consequence is that taller than average individuals will generally have larger z-scores for bone size outcomes when length is not considered. The goal of the current work was to develop a means of determining whether an individual's cross-sectional bone size is suitable for their bone length. HRpQCT scans performed at 30 % of bone length proximal from the distal end of the radius and tibia were acquired from 1034 White females (age = 18.0 to 85.3 y) and 392 White males (age = 18.4 to 83.6 y). Positive relationships were confirmed between bone length and cross-sectional areas and estimated mechanical properties. Scaling factors were calculated and used to scale HRpQCT outcomes to bone length. Centile curves were generated for both raw and bone length scaled HRpQCT data using the LMS approach. Excel-based calculators are provided to facilitate calculation of z-scores for both raw and bone length scaled HRpQCT outcomes. The raw z-scores indicate the magnitude that an individual's HRpQCT outcomes differ relative to expected sex- and age-specific values, with the scaled z-scores also considering bone length. The latter enables it to be determined whether an individual or population of interest has normal sized bones for their length, which may have implications for injury risk. In addition to providing a means of expressing HRpQCT bone size outcomes relative to bone length, the current study also provides centile curves for outcomes previously without reference data, including tissue mineral density and moments of inertia.

Does mandibular bone structure predict subsequent height loss? A longitudinal cohort study of women in Gothenburg, Sweden

BACKGROUND

Several risk factors for loss of height with increasing age have been identified.

OBJECTIVE

To investigate if mandibular bone structure predicts future height loss in middle-aged and elderly Swedish women.

DESIGN

Prospective cohort study with longitudinally measured heights, radiographical assessments of the cortical bone using Klemetti's Index (normal, moderate or severely eroded cortex) and classification of the trabecular bone using an index proposed by Lindh et al (sparse, mixed or dense trabeculation). No intervention was performed.

SETTING

Gothenburg, Sweden.

PARTICIPANTS

A population-based sample of 937 Swedish women born in 1914, 1922 and 1930 was recruited. At the baseline examination, the ages were 38, 46 and 54 years. All had undergone a dental examination with panoramic radiographs of the mandible, and a general examination including height measurements on at least two occasions.

MAIN OUTCOME MEASURE

Height loss was calculated over three periods 12-13 years (1968-1980, 1980-1992, 1992-2005).

MAIN RESULTS

Mean annual height loss measures were 0.075 cm/year, 0.08 cm/year and 0.18 cm/year over the three observation intervals, corresponding to absolute decreases of 0.9 cm, 1.0 cm and 2.4 cm. Cortical erosion in 1968, 1980 and 1992 significantly predicted height loss 12 years later. Sparse trabeculation in 1968, 1980 and 1992 also predicted significant shrinkage over 12 or 13 years. Multivariable regression analyses adjusting for baseline covariates such as height, birth year, physical activity, smoking, body mass index and education yielded consistent findings except for cortical erosion 1968-1980.

CONCLUSION

Mandibular bone structure characteristics such as severe cortical erosion and sparse trabeculation may serve as early risk factors for height loss. Since most individuals visit their dentist at least every 2 years and radiographs are taken, a collaboration between dentists and physicians may open opportunities for predicting future risk of height loss.

Is There a Causal Relationship between Physical Activity and Bone Microarchitecture? A Study of Adult Female Twin Pairs

The reasons for the association between physical activity (PA) and bone microarchitecture traits are unclear. We examined whether these associations were consistent with causation and/or with shared familial factors using a cross-sectional study of 47 dizygotic and 93 monozygotic female twin pairs aged 31-77 years. Images of the nondominant distal tibia were obtained using high-resolutionperipheral quantitative computed tomography. The bone microarchitecture was assessed using StrAx1.0 software. Based on a self-completed questionnaire, a PA index was calculated as a weighted sum of weekly hours of light (walking, light gardening), moderate (social tennis, golf, hiking), and vigorous activity (competitive active sports) = light + 2 * moderate + 3 * vigorous. We applied Inference about Causation through Examination of FAmiliaL CONfounding (ICE FALCON) to test whether cross-pair cross-trait associations changed after adjustment for within-individual associations. Within-individual distal tibia cortical cross-sectional area (CSA) and cortical thickness were positively associated with PA (regression coefficients [β] = 0.20 and 0.22), while the porosity of the inner transitional zone was negatively associated with PA (β = -0.17), all p < 0.05. Trabecular volumetric bone mineral density (vBMD) and trabecular thickness were positively associated with PA (β = 0.13 and 0.14), and medullary CSA was negatively associated with PA (β = -0.22), all p ≤ 0.01. Cross-pair cross-trait associations of cortical thickness, cortical CSA, and medullary CSA with PA attenuated after adjustment for the within-individual association (p = 0.048, p = 0.062, and p = 0.028 for changes). In conclusion, increasing PA was associated with thicker cortices, larger cortical area, lower porosity of the inner transitional zone, thicker trabeculae, and smaller medullary cavities. The attenuation of cross-pair cross-trait associations after accounting for the within-individual associations was consistent with PA having a causal effect on the improved cortical and trabecular microarchitecture of adult females, in addition to shared familial factors. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Automated, calibration-free quantification of cortical bone porosity and geometry in postmenopausal osteoporosis from ultrashort echo time MRI and deep learning

BACKGROUND

Assessment of cortical bone porosity and geometry by imaging in vivo can provide useful information about bone quality that is independent of bone mineral density (BMD). Ultrashort echo time (UTE) MRI techniques of measuring cortical bone porosity and geometry have been extensively validated in preclinical studies and have recently been shown to detect impaired bone quality in vivo in patients with osteoporosis. However, these techniques rely on laborious image segmentation, which is clinically impractical. Additionally, UTE MRI porosity techniques typically require long scan times or external calibration samples and elaborate physics processing, which limit their translatability. To this end, the UTE MRI-derived Suppression Ratio has been proposed as a simple-to-calculate, reference-free biomarker of porosity which can be acquired in clinically feasible acquisition times.

PURPOSE

To explore whether a deep learning method can automate cortical bone segmentation and the corresponding analysis of cortical bone imaging biomarkers, and to investigate the Suppression Ratio as a fast, simple, and reference-free biomarker of cortical bone porosity.

METHODS

In this retrospective study, a deep learning 2D U-Net was trained to segment the tibial cortex from 48 individual image sets comprised of 46 slices each, corresponding to 2208 training slices. Network performance was validated through an external test dataset comprised of 28 scans from 3 groups: (1) 10 healthy, young participants, (2) 9 postmenopausal, non-osteoporotic women, and (3) 9 postmenopausal, osteoporotic women. The accuracy of automated porosity and geometry quantifications were assessed with the coefficient of determination and the intraclass correlation coefficient (ICC). Furthermore, automated MRI biomarkers were compared between groups and to dual energy X-ray absorptiometry (DXA)- and peripheral quantitative CT (pQCT)-derived BMD. Additionally, the Suppression Ratio was compared to UTE porosity techniques based on calibration samples.

RESULTS

The deep learning model provided accurate labeling (Dice score 0.93, intersection-over-union 0.88) and similar results to manual segmentation in quantifying cortical porosity (R2 ≥ 0.97, ICC ≥ 0.98) and geometry (R2 ≥ 0.82, ICC ≥ 0.75) parameters in vivo. Furthermore, the Suppression Ratio was validated compared to established porosity protocols (R2 ≥ 0.78). Automated parameters detected age- and osteoporosis-related impairments in cortical bone porosity (P ≤ .002) and geometry (P values ranging from <0.001 to 0.08). Finally, automated porosity markers showed strong, inverse Pearson's correlations with BMD measured by pQCT (|R| ≥ 0.88) and DXA (|R| ≥ 0.76) in postmenopausal women, confirming that lower mineral density corresponds to greater porosity.

CONCLUSION

This study demonstrated feasibility of a simple, automated, and ionizing-radiation-free protocol for quantifying cortical bone porosity and geometry in vivo from UTE MRI and deep learning.

Pathology or expected morphology? Investigating patterns of cortical porosity and trabecularization during infancy and early childhood

Increased cortical porosity is associated with a heightened risk of skeletal fragility due to bone loss and structural decay in adults. However, few studies have examined the etiology of cortical porosity in infants and children. This study examines whether age-related changes in femoral growth and locomotor development influence femoral midshaft cortical porosity in a sample of 48 individuals (fetal to 3.99 years) from the 10th-13th century cemetery of St. Étienne de Toulouse, France. Histological sections were prepared and imaged using light microscopy. Midshaft geometric variables such as total area, cortical area, and pore area were calculated using BoneJ. Increased porosity and cortical trabecularization were found to be significantly associated with age, being almost exclusively present in individuals aged 0.5-1.99 years. At approximately 6 months of age infants typically begin engaging in regular femoral loading and experience an acceleration in growth. The observed increase in midshaft porosity and trabecularization, therefore, likely results from the reorganization and redistribution of cortical bone, stimulated by increased growth velocity and the onset of weight-bearing activities. The reduction in cortical porosity and trabecularization in individuals aged 2.0-3.99 years indicates that children are approaching some sort of homeostasis as growth velocity slows and their femora adapt to consistent loading. Understanding what expected skeletal development looks like is necessary when conducting bioarcheological studies and this study provides evidence for a pattern of transient midshaft porosity during infancy and early childhood.

Estimation of Thickness and Speed of Sound for Transverse Cortical Bone Imaging Using Phase Aberration Correction Methods: An In Silico and Ex Vivo Validation Study

Delay-and-sum (DAS) beamforming of backscattered echoes is used for conventional ultrasound imaging. Although DAS beamforming is well suited for imaging in soft tissues, refraction, scattering, and absorption, porous mineralized tissues cause phase aberrations of reflected echoes and subsequent image degradation. The recently developed refraction corrected multi-focus technique uses subsequent focusing of waves at variable depths, the tracking of travel times of waves reflected from outer and inner cortical bone interfaces, the estimation of the shift needed to focus from one interface to another to determine cortical thickness (Ct.Th), and the speed of sound propagating in a radial bone direction (Ct.ν11). The method was validated previously in silico and ex vivo on plate shaped samples. The aim of this study was to correct phase aberration caused by bone geometry (i.e., curvature and tilt with respect to the transducer array) and intracortical pores for the multi-focus approach. The phase aberration correction methods are based on time delay estimation via bone geometry differences to flat bone plates and via the autocorrelation and cross correlation of the reflected ultrasound waves from the endosteal bone interface. We evaluate the multi-focus approach by incorporating the phase aberration correction methods by numerical simulation and one experiment on a human tibia bone, and analyze the precision and accuracy of measuring Ct.Th and Ct.ν11. Site-matched reference values of the cortical thickness of the human tibia bone were obtained from high-resolution peripheral computed tomography. The phase aberration correction methods resulted in a more precise (coefficient of variation of 5.7%) and accurate (root mean square error of 6.3%) estimation of Ct.Th, and a more precise (9.8%) and accurate (3.4%) Ct.ν11 estimation, than without any phase aberration correction. The developed multi-focus method including phase aberration corrections provides local estimations of both cortical thickness and sound velocity and is proposed as a biomarker of cortical bone quality with high clinical potential for the prevention of osteoporotic fractures.

Cortical bone structure of the proximal femur and incident fractures

PURPOSE

Fracture risk is most frequently assessed using Dual X-ray absorptiometry to measure areal bone mineral density (aBMD) and using the Fracture Risk Assessment Tool (FRAX). However, these approaches have limitations and additional bone measurements may enhance the predictive ability of these existing tools. Increased cortical porosity has been associated with incident fracture in some studies, but not in others. In this prospective study, we examined whether cortical bone structure of the proximal femur predicts incident fractures independent of aBMD and FRAX score.

METHODS

We pooled 211 postmenopausal women with fractures aged 54-94 years at baseline and 232 fracture-free age-matched controls based on a prior nested case-control study from the Tromsø Study in Norway. We assessed baseline femoral neck (FN) aBMD, calculated FRAX 10-year probability of major osteoporotic fracture (MOF), and quantified femoral subtrochanteric cortical parameters: porosity, area, thickness, and volumetric BMD (vBMD) from CT images using the StrAx1.0 software. Associations between bone parameters and any incident fracture, MOF and hip fracture were determined using Cox's proportional hazard models to calculate hazard ratio (HR) with 95% confidence interval.

RESULTS

During a median follow-up of 7.2 years, 114 (25.7%) of 443 women suffered one or more incident fracture. Cortical bone structure did not predict any incident fracture or MOF after adjustment for age, BMI, and previous fracture. Each SD higher total cortical porosity, thinner cortices, and lower cortical vBMD predicted hip fracture with increased risk of 46-62% (HRs ranging from 1.46 (1.01-2.11) to 1.62 (1.02-2.57)). After adjustment for FN aBMD or FRAX score no association remained significant. Both lower FN aBMD and higher FRAX score predicted any incident fracture, MOF and hip fractures with HRs ranging from 1.45-2.56.

CONCLUSIONS

This study showed that cortical bone measurements using clinical CT did not add substantial insight into fracture risk beyond FN aBMD and FRAX. We infer from these results that fracture risk related to the deteriorated bone structure seems to be largely captured by a measurement of FN aBMD and the FRAX tool.

Pore-Size Distribution and Frequency-Dependent Attenuation in Human Cortical Tibia Bone Discriminate Fragility Fractures in Postmenopausal Women With Low Bone Mineral Density

Osteoporosis is a disorder of bone remodeling leading to reduced bone mass, structural deterioration, and increased bone fragility. The established diagnosis is based on the measurement of areal bone mineral density by dual‐energy X‐ray absorptiometry (DXA), which poorly captures individual bone loss and structural decay. Enlarged cortical pores in the tibia have been proposed to indicate structural deterioration and reduced bone strength in the hip. Here, we report for the first time the in vivo assessment of the cortical pore‐size distribution together with frequency‐dependent attenuation at the anteromedial tibia midshaft by means of a novel ultrasonic cortical backscatter (CortBS) technology. We hypothesized that the CortBS parameters are associated with the occurrence of fragility fractures in postmenopausal women (n = 55). The discrimination performance was compared with those of DXA and high‐resolution peripheral computed tomography (HR‐pQCT). The results suggest a superior discrimination performance of CortBS (area under the receiver operating characteristic curve [AUC]: 0.69 ≤ AUC ≤ 0.75) compared with DXA (0.54 ≤ AUC ≤ 0.55) and a similar performance compared with HR‐pQCT (0.66 ≤ AUC ≤ 0.73). CortBS is the first quantitative bone imaging modality that can quantify microstructural tissue deteriorations in cortical bone, which occur during normal aging and the development of osteoporosis. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Causal Associations of Anthropometric Measurements With Fracture Risk and Bone Mineral Density: A Mendelian Randomization Study

Uncovering additional causal clinical traits and exposure variables is important when studying osteoporosis mechanisms and for the prevention of osteoporosis. Until recently, the causal relationship between anthropometric measurements and osteoporosis had not been fully revealed. In the present study, we utilized several state-of-the-art Mendelian randomization (MR) methods to investigate whether height, body mass index (BMI), waist-to-hip ratio (WHR), hip circumference (HC), and waist circumference (WC) are causally associated with two major characteristics of osteoporosis, bone mineral density (BMD) and fractures. Genomewide significant (p  ≤ 5 × 10^-8 ) single-nucleotide polymorphisms (SNPs) associated with the five anthropometric variables were obtained from previous large-scale genomewide association studies (GWAS) and were utilized as instrumental variables. Summary-level data of estimated bone mineral density (eBMD) and fractures were obtained from a large-scale UK Biobank GWAS. Of the MR methods utilized, the inverse-variance weighted method was the primary method used for analysis, and the weighted-median, MR-Egger, mode-based estimate, and MR pleiotropy residual sum and outlier methods were utilized for sensitivity analyses. The results of the present study indicated that each increase in height equal to a single standard deviation (SD) was associated with a 9.9% increase in risk of fracture (odds ratio [OR] = 1.099; 95% confidence interval [CI] 1.067-1.133; p = 8.793 × 10^-10 ) and a 0.080 SD decrease of estimated bone mineral density (95% CI -0.106-(-0.054); p = 2.322 × 10^-9 ). We also found that BMI was causally associated with eBMD (beta = 0.129, 95% CI 0.065-0.194; p = 8.113 × 10^-5 ) but not associated with fracture. The WHR adjusted for BMI, HC adjusted for BMI, and WC adjusted for BMI were not found to be related to fracture occurrence or eBMD. In conclusion, the present study provided genetic evidence for certain causal relationships between anthropometric measurements and bone mineral density or fracture risk. © 2021 American Society for Bone and Mineral Research (ASBMR).

High Cortico-Trabecular Transitional Zone Porosity and Reduced Trabecular Density in Men and Women with Stress Fractures

To determine whether stress fractures are associated with bone microstructural deterioration we quantified distal radial and the unfractured distal tibia using high resolution peripheral quantitative computed tomography in 26 cases with lower limb stress fractures (15 males, 11 females; mean age 37.1 ± 3.1 years) and 62 age-matched healthy controls (24 males, 38 females; mean age 35.0 ± 1.6 years). Relative to controls, in men, at the distal radius, cases had smaller cortical cross sectional area (CSA) (p = 0.012), higher porosity of the outer transitional zone (OTZ) (p = 0.006), inner transitional zone (ITZ) (p = 0.043) and the compact-appearing cortex (CC) (p = 0.023) while trabecular vBMD was lower (p = 0.002). At the distal tibia, cases also had a smaller cortical CSA (p = 0.008). Cortical porosity was not higher, but trabecular vBMD was lower (p = 0.001). Relative to controls, in women, cases had higher distal radial porosity of the OTZ (p = 0.028), ITZ (p = 0.030) not CC (p = 0.054). Trabecular vBMD was lower (p = 0.041). Distal tibial porosity was higher in the OTZ (p = 0.035), ITZ (p = 0.009), not CC. Stress fractures are associated with compromised cortical and trabecular microstructure.

Bone microstructure of adult patients with non-surgical hypoparathyroidism assessed by high-resolution peripheral quantitative computed tomography

There is limited evidence regarding changes in bone microstructure in patients with hypoparathyroidism. In the current study, we used a non-invasive technique to assess bone structure in hypoparathyroidism patients and discovered site-specific changes which were mainly influenced by age and menstrual status. Such changes were more prominent in the trabeculae as well as in non-surgical as opposed to post-surgical patients.

INTRODUCTION

Hypoparathyroidism (hypoPT) is a rare disease characterized by the lack of parathyroid hormone. There is limited evidence regarding changes in bone microstructure in patients with non-surgical hypoPT. We investigated bone microstructure of patients with non-surgical hypoPT using a non-invasive technique.

METHODS

Patients with hypoPT were assessed using high-resolution peripheral quantitative computed tomography (HR-pQCT) and compared to age- and sex-matched healthy controls randomly selected from a pre-existing HR-pQCT database in a cross-sectional study. Preliminary comparison between patients with different etiologies of hypoPT was performed. Associations between bone microstructure and clinical parameters were investigated using correlation and regression analyses.

RESULTS

A total of 94 patients with non-surgical hypoPT were recruited. Patients displayed an increase in trabecular volumetric BMD of the tibia (170.57 ± 34.32 vs. 156.48 ± 40.55 mg HA/cm³, p = 0.011) and increase in trabecular number of both the radius (1.48 ± 0.29 vs. 1.36 ± 0.22 mm^-1, p = 0.003) and tibia (1.42 ± 0.23 vs. 1.24 ± 0.22 mm^-1, p < 0.001) compared to healthy controls. Trabecular number was higher for non-surgical hypoPT compared to post-surgical hypoPT (1.37 ± 0.25 and 1.17 ± 0.13 mm^-1, p = 0.022). Trends towards increase in cortical volumetric BMD were only present for post-menopausal female and male patients above the age of 50. For female patients, cortical volumetric BMD and area increased with age and decreased after menopause. For males, age had little influence on bone microstructure, but cortical porosity increased with longer treatment durations.

CONCLUSIONS

Results from this pilot study suggested that both cortical and trabecular bone were altered in this group of patients with hypoPT. Etiology for hypoPT might influence bone microstructure, mainly on trabeculae. Age, menstrual status, and treatment duration were likely to influence bone microstructure in hypoPT.

Are the Relationships of Lean Mass and Fat Mass With Bone Microarchitecture Causal or Due to Familial Confounders? A Novel Study of Adult Female Twin Pairs

It is not known whether the relationships of lean mass (LM) and fat mass (FM) with bone microarchitecture and geometry are causal and/or are because of confounders, including familial confounders arising from genetic and environment effects shared by relatives. We tested the hypotheses that: (i) LM is associated with cortical bone traits, (ii) FM is associated with trabecular bone traits, and (iii) these relationships of LM and FM with bone microarchitecture and geometry have a causal component. Total body composition was quantified for 98 monozygotic (MZ) and 54 dizygotic (DZ) white female twin pairs aged 31 to 77 years. Microarchitecture at the distal tibia and distal radius was quantified using HRpQCT and StrAx software. We applied the Inference about Causation through Examination of FAmiliaL CONfounding (ICE FALCON) method. Within‐individuals, distal tibia total bone area, cortical area, cortical thickness, and trabecular number were positively associated with LM (standardized regression coefficient (β) = 0.13 to 0.43; all p < 0.05); porosity of the inner transitional zone (ITZ) was negatively associated with LM (β = −0.22; p < 0.01). Trabecular number was positively associated with FM (β = 0.40; p < 0.001), and trabecular thickness was negatively associated with FM (β = −0.27; p < 0.001). For porosity of ITZ and trabecular number, the cross‐pair cross‐trait association with LM was significant before and after adjustment for the within‐individual association with LM (all ps < 0.05). For trabecular number, the cross‐pair cross‐trait association with FM was significant before and after adjustment for the within‐individual association with FM (p < 0.01). There were no significant changes in these cross‐pair cross‐trait associations after adjustment for the within‐individual association (p = 0.06 to 0.99). Similar results were found for distal radius measures. We conclude that there was no evidence that the relationships of LM and FM with bone microarchitecture and geometry are causal; they must in part due to by familial confounders affecting both bone architecture and body composition. © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

CT based quantitative measures of the stability of fractured metastatically involved vertebrae treated with spine stereotactic body radiotherapy

Mechanical instability secondary to vertebral metastases can lead to pathologic vertebral compression fracture (VCF) mechanical pain, neurological compromise, and the need for surgical stabilization. Stereotactic body radiation therapy (SBRT) as a treatment for spinal metastases is effective for pain and local tumor control, it has been associated with an increased risk of VCF. This study quantified computed tomography (CT) based stability measures in metastatic vertebrae with VCF treated with spine SBRT. It was hypothesized that semi-automated quantification of VCF based on CT metrics would be related to clinical outcomes. 128 SBRT treated spinal metastases patients were identified from a prospective database. Of these, 18 vertebral segments were identified with a VCF post-SBRT. A semi-automated system for quantifying VCF was developed based on CT imaging before and after SBRT. The system identified and segmented SBRT treated vertebral bodies, calculated stability metrics at single time points and changes over time. In the vertebrae that developed a new (n = 7) or progressive (n = 11) VCF following SBRT, the median time to VCF/VCF progression was 1.74 months (range 0.53-7.79 months). Fractured thoracolumbar vertebrae that went on to be stabilized (cemented and/or instrumented), had greater fractured vertebral body volume progression over time (12%) compared to those not stabilized (0.4%, p < 0.05). Neither the spinal instability neoplastic score (SINS) or any single timepoint stability metrics in post-hoc analyses correlated with future stabilization. This pilot study presents a quantitative semi-automated method assessing fractured thoracolumbar vertebrae based on CT. Increased fractured vertebral body volume progression post-SBRT was shown to predict those patients who were subsequently stabilized, motivating study of methods that assess temporal radiological changes toward augmenting existing clinical management in the metastatic spine.

Normative Data for Impact Microindentation for Australian Men: Cross-Sectional Data From the Geelong Osteoporosis Study

Impact microindentation (IMI) is a novel technique for assessing the bone material strength index (BMSi) in vivo. However, no studies have presented normative data for BMSi. The aim of this study was to develop such normative data using a population-based sample of men, randomly selected from electoral rolls for the Barwon Statistical Division in southeastern Australia to participate in the Geelong Osteoporosis Study. BMSi was measured on the tibial plateau using an OsteoProbe in 405 men (ages 33 to 96 years) during the period 2016 to 2019. Associations between BMSi, age, and anthropometry were examined using linear regression models. BMSi values ranged from 49.0 to 100.5. BMSi was negatively correlated with age (r = -0.152, p = 0.002), weight (r = -0.103, p = 0.039), and BMI (r = -0.187, p < 0.001), and positively correlated with height (r = +0.107, p = 0.032). Mean ± SD BMSi was 82.6 ± 7.0 for the whole group, and ranged from 85.6 ± 6.0 for ages 30 to 39 years to 79.8 ± 6.6 for ages 80+ years. This study provides normative data that can be used to calculate T- and Z-scores for BMSi. These data will be useful for identifying men with low BMSi. Further research is warranted to derive optimal cut points for BMSi that discriminate fracture risk. © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

Changes in Skeletal Microstructure Through Four Continuous Years of rhPTH(1-84) Therapy in Hypoparathyroidism

Bone remodeling is reduced in hypoparathyroidism, resulting in increased areal bone mineral density (BMD) by dual-energy X-ray absorptiometry (DXA) and abnormal skeletal indices by transiliac bone biopsy. We have now studied skeletal microstructure by high-resolution peripheral quantitative computed tomography (HR-pQCT) through 4 years of treatment with recombinant human PTH(1-84) (rhPTH[1-84]) in 33 patients with hypoparathyroidism (19 with postsurgical disease, 14 idiopathic). We calculated Z-scores for our cohort compared with previously published normative values. We report results at baseline and 1, 2, and 4 years of continuous therapy with rhPTH(1-84). The majority of patients (62%) took rhPTH(1-84) 100 μg every other day for the majority of the 4 years. At 48 months, areal bone density increased at the lumbar spine (+4.9% ± 0.9%) and femoral neck (+2.4% ± 0.9%), with declines at the total hip (-2.3% ± 0.8%) and ultradistal radius (-2.1% ± 0.7%) (p < .05 for all). By HR-pQCT, at the radius site, very similar to the ultradistal DXA site, total volumetric BMD declined from baseline but remained above normative values at 48 months (Z-score + 0.56). Cortical volumetric BMD was lower than normative controls at baseline at the radius and tibia (Z-scores -1.28 and - 1.69, respectively) and further declined at 48 months (-2.13 and - 2.56, respectively). Cortical porosity was higher than normative controls at baseline at the tibia (Z-score + 0.72) and increased through 48 months of therapy at both sites (Z-scores +1.80 and + 1.40, respectively). Failure load declined from baseline at both the radius and tibia, although remained higher than normative controls at 48 months (Z-scores +1.71 and + 1.17, respectively). This is the first report of noninvasive high-resolution imaging in a cohort of hypoparathyroid patients treated with any PTH therapy for this length of time. The results give insights into the effects of long-term rhPTH(1-84) in hypoparathyroidism. © 2020 American Society for Bone and Mineral Research.

Associations Between Breastfeeding History and Early Postmenopausal Bone Loss

This study aimed to evaluate associations of parity and breastfeeding history with postmenopausal bone loss. Early postmenopausal women from the Canadian Multicentre Osteoporosis Study were divided into three groups based on their reproductive histories: nulliparous (NP, n = 10), parous with < 6 months breastfeeding (P-NBF, n = 14), and parous with > 6 months breastfeeding (P-BF, n = 21). Women underwent dual X-ray absorptiometry and high-resolution peripheral quantitative computed tomography imaging at baseline and after 6 years to evaluate bone mineral density (BMD), bone microstructure, and finite element-estimated failure load. Average age at baseline was 57 years. Baseline density, microstructure, and failure load were not different among groups. In all women, total and cortical BMD decreased significantly at the tibia and radius. P-BF women only experienced a significant decline in tibial trabecular BMD, with a greater magnitude of change for P-BF than NP women (p = 0.002). Overall, results suggest that early postmenopausal bone health did not differ based on parity or breastfeeding history. Over the 6-year follow-up period, postmenopausal bone loss was evident in all women, with subtle differences in the rate of postmenopausal change among women with varying breastfeeding histories. Parous women who had breastfed for at least 6 months showed an elevated rate of trabecular BMD loss at the tibia. Meanwhile, correlation analyses suggest that longer durations of breastfeeding may be associated with reduced cortical bone loss at the radius. The lack of differences among groups in FE-derived failure load suggests that parity and breastfeeding history is unlikely to significantly affect postmenopausal risk of fracture.

HR-pQCT Measures of Bone Microarchitecture Predict Fracture: Systematic Review and Meta-Analysis

High-resolution peripheral quantitative computed tomography (HR-pQCT) is a noninvasive imaging modality for assessing volumetric bone mineral density (vBMD) and microarchitecture of cancellous and cortical bone. The objective was to (1) assess fracture-associated differences in HR-pQCT bone parameters; and (2) to determine if HR-pQCT is sufficiently precise to reliably detect these differences in individuals. We systematically identified 40 studies that used HR-pQCT (39/40 used XtremeCT scanners) to assess 1291 to 3253 and 3389 to 10,687 individuals with and without fractures, respectively, ranging in age from 10.9 to 84.7 years with no comorbid conditions. Parameters describing radial and tibial bone density, microarchitecture, and strength were extracted and percentage differences between fracture and control subjects were estimated using a random effects meta-analysis. An additional meta-analysis of short-term in vivo reproducibility of bone parameters assessed by XtremeCT was conducted to determine whether fracture-associated differences exceeded the least significant change (LSC) required to discern measured differences from precision error. Radial and tibial HR-pQCT parameters, including failure load, were significantly altered in fracture subjects, with differences ranging from -2.6% (95% confidence interval [CI] -3.4 to -1.9) in radial cortical vBMD to -12.6% (95% CI -15.0 to -10.3) in radial trabecular vBMD. Fracture-associated differences reported by prospective studies were consistent with those from retrospective studies, indicating that HR-pQCT can predict incident fracture. Assessment of study quality, heterogeneity, and publication biases verified the validity of these findings. Finally, we demonstrated that fracture-associated deficits in total and trabecular vBMD and certain tibial cortical parameters can be reliably discerned from HR-pQCT-related precision error and can be used to detect fracture-associated differences in individual patients. Although differences in other HR-pQCT measures, including failure load, were significantly associated with fracture, improved reproducibility is needed to ensure reliable individual cross-sectional screening and longitudinal monitoring. In conclusion, our study supports the use of HR-pQCT in clinical fracture prediction. © 2019 American Society for Bone and Mineral Research.

Trabecular bone score: a useful clinical tool for the evaluation of skeletal health in women of short stature

PURPOSE

Areal bone mineral density (aBMD) by DXA is underestimated in those with smaller bones and overestimated in those with larger bones. Trabecular bone score (TBS) predicts fracture risk, and is not influenced by bone size. The aim of this study was to evaluate TBS and BMD in women with short stature.

METHODS

We retrospectively analyzed DXA scans of all women aged 50-90 years with short stature (<144 cm) obtained in a single center, from 2006 to 2016. The comparison group comprised women >161 cm in height, matched for age and LS BMD, selected from the same database.

RESULTS

The study population included 342 women. The two groups were similar in age, and aBMD at the LS and total hip. Femoral neck aBMD was lower in cases than in taller women. In contrast, TBS was higher in women with short stature than in their taller counterparts (1.347 ± 0.102 vs. 1.250 ± 0.110; p < 0.001). Bone mineral apparent density (BMAD) and the LS TBS-adjusted BMD T-score were also significantly higher in shorter than in taller women. From the entire cohort, 121 women (67 cases) were osteoporotic by aBMD determinations. Among these subjects, TBS was also greater in cases (1.303 ± 0.103) than in women with standard height (1.190 ± 0.099; p < 0.001). Despite being considered osteoporotic, 36% of short women, but none of the taller ones, had a normal TBS.

CONCLUSIONS

TBS can be a useful adjunct to aBMD for assessing bone quality in short women, in whom aBMD measurement tends to read lower, and, thus could overestimate fracture risk.

Adding Marrow Adiposity and Cortical Porosity to Femoral Neck Areal Bone Mineral Density Improves the Discrimination of Women With Nonvertebral Fractures From Controls

Advancing age is accompanied by a reduction in bone formation and remodeling imbalance, which produces microstructural deterioration. This may be partly caused by a diversion of mesenchymal cells towards adipocytes rather than osteoblast lineage cells. We hypothesized that microstructural deterioration would be associated with an increased marrow adiposity, and each of these traits would be independently associated with nonvertebral fractures and improve discrimination of women with fractures from controls over that achieved by femoral neck (FN) areal bone mineral density (aBMD) alone. The marrow adiposity and bone microstructure were quantified from HR-pQCT images of the distal tibia and distal radius in 77 women aged 40 to 70 years with a recent nonvertebral fracture and 226 controls in Melbourne, Australia. Marrow fat measurement from HR-pQCT images was validated using direct histologic measurement as the gold standard, at the distal radius of 15 sheep, with an agreement (R² = 0.86, p < 0.0001). Each SD higher distal tibia marrow adiposity was associated with 0.33 SD higher cortical porosity, and 0.60 SD fewer, 0.24 SD thinner, and 0.72 SD more-separated trabeculae (all p < 0.05). Adjusted for age and FN aBMD, odds ratios (ORs) (95% CI) for fracture per SD higher marrow adiposity and cortical porosity were OR, 3.39 (95% CI, 2.14 to 5.38) and OR, 1.79 (95% CI, 1.14 to 2.80), respectively. Discrimination of women with fracture from controls improved when cortical porosity was added to FN aBMD and age (area under the receiver-operating characteristic curve [AUC] 0.778 versus 0.751, p = 0.006) or marrow adiposity was added to FN aBMD and age (AUC 0.825 versus 0.751, p = 0.002). The model including FN aBMD, age, cortical porosity, trabecular thickness, and marrow adiposity had an AUC = 0.888. Results were similar for the distal radius. Whether marrow adiposity and cortical porosity indices improve the identification of women at risk for fractures requires validation in prospective studies. © 2019 American Society for Bone and Mineral Research.

Time course of rapid bone loss and cortical porosity formation observed by longitudinal μCT in a rat model of CKD

BACKGROUND

Rodent studies of bone in chronic kidney disease have primarily relied on end-point examinations of bone microarchitecture. This study used longitudinal in vivo microcomputed tomography (in vivo μCT) to characterize the onset and progression of bone loss, specifically cortical porosity, in the Cy/+ rat of model of CKD.

METHODS

Male CKD rats and normal littermates were studied. In vivo μCT scans of the right distal tibia repeated at 25, 30, and 35 weeks were analyzed for longitudinal changes in cortical and trabecular bone morphometry. In vitro μCT scans of the tibia and femur identified spatial patterns of bone loss across distal, midshaft and proximal sites.

RESULTS

CKD animals had reduced BV/TV and cortical BV at all time points but developed cortical porosity and thinning between 30 and 35 weeks. Cortical pore formation was localized near the endosteal surface. The severity of bone loss was variable across bone sites, but the distal tibia was representative of both cortical and trabecular changes.

CONCLUSIONS

The distal tibia was found to be a sensitive suitable site for longitudinal imaging of both cortical and trabecular bone changes in the CKD rat. CKD trabecular bone loss progressed through ~30 weeks followed by a sudden acceleration in cortical bone catabolism. These changes varied in timing and severity across individuals, and cortical bone loss and porosity progressed rapidly once initiated. The inclusion of longitudinal μCT in future studies will be important for both reducing the number of required animals and to track individual responses to treatment.

Interaction of body fat percentage and height with appendicular functional muscle-bone unit

The interaction of body fat percentage and height with appendicular BMC for LBM was analyzed. Only body fat had significant negative correlation with the appendicular BMC for LBM.

PURPOSE/INTRODUCTION

For the clinical evaluation of the functional muscle-bone unit, it was proposed to evaluate the adaptation of the bone to the acting forces. A frequently used parameter for this is the total body less head bone mineral content (TBLH-BMC) determined by dual-energy X-ray absorptiometry (DXA) in relation to the total body lean body mass (LBM). Body fat percentage seemed to correlate negatively and height positively with TBLH-BMC for LBM. It was supposed that appendicular BMC for LBM is a more accurate surrogate for the functional muscle-bone unit since appendicular LBM does not incorporate the mass of internal organs. The aim of this study was to analyze the interaction of body fat percentage and height with appendicular BMC for LBM.

METHODS

As part of the National Health and Nutrition Examination Survey (NHANES) study, between the years 1999 and 2004, whole-body DXA scans on randomly selected Americans from 8 years of age were carried out. From all eligible DXA scans, three major US ethnic groups were evaluated (non-Hispanic Whites, non-Hispanic Blacks, and Mexican Americans) for further statistical analysis.

RESULTS

For the statistical analysis, the DXA scans of 8190 non-Hispanic White children and adults (3903 female), of 4931 non-Hispanic Black children and adults (2250 female), and 5421 of Mexican American children and adults (2424 female) were eligible. Only body fat had a significant negative correlation with the appendicular BMC for LBM.

CONCLUSIONS

Only body fat had significant negative correlation with appendicular BMC for LBM, and thus, should be addressed when evaluating functional muscle-bone unit.

Scaling of adult human bone and skeletal muscle mass to height in the US population

OBJECTIVES

The scaling of structural components to body size is well studied in mammals, although comparable human observations in a large and diverse sample are lacking. The current study aimed to fill this gap by examining the scaling relationships between total body (TB) and regional bone and skeletal muscle (SM) mass with body size, as defined by stature, in a nationally representative sample of the US population.

METHODS

Subjects were 17,126 non-Hispanic (NH) white, NH black, and Mexican American men and women, aged ≥18 years, evaluated in the National Health and Nutrition Examination Survey who had TB and regional bone mineral (BMin) and lean soft tissue (LST) mass measured by dual-energy X-ray absorptiometry. BMin and appendicular LST served as surrogate bone and SM mass measures, respectively. The allometric model, BMin or LST = α(height)^β , in a logarithmic form was used to generate scaling exponents.

RESULTS

The findings were similar across all gender and race groups: body mass scaled to height with powers of ~2.0 (mean β ± SE, 1.94 ± 0.08-2.29 ± 0.09) while TB and appendicular BMin and appendicular LST scaled to height with consistently larger powers than those for body mass (eg, all P < .05 in NH white men and women); the largest BMin and LST scaling powers to height were observed in the lower extremities.

CONCLUSIONS

Bone and SM mass, notably those of the lower extremities, increase as proportions of body mass with greater adult height. Metabolic and biomechanical implications emerge from these observations, the first of their kind in a representative adult US population sample.

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.

Metacarpal Indices and Their Association with Fracture in South African Children and Adolescents

This prospective study assessed whether metacarpal indices predict fracture risk in children and adolescents. Radiogrammetry was performed at the second metacarpal midshaft on annual hand-wrist radiographs of 359 South African (SA) children aged 10-17 years. Bone length, bone width, and medullary width were measured, and the following proxies for bone strength calculated: metacarpal index (MCI), bone mineral density (BMD), section modulus (SM), stress-strain index (SSI), and slenderness index (SLI). Height and weight were measured annually. Self-reported physical activity (PA) and fracture history were obtained at ages 15 years (for the preceding 12 months) and 17 years, respectively. At 17 years, 82 (23%) participants (black, 16%; white, 42%; p < 0.001) reported a previous fracture. None of the bone measures or indices were associated with fracture in black participants. In white females, after adjusting for PA, a 1 standard deviation (SD) greater SLI doubled the fracture risk [odds ratio (OR) 2.08; 95% confidence interval (CI) 1.08, 3.98]. In white males, a 1 SD greater BMD was associated with a 2.62-fold increase in fracture risk (OR 3.62; 95% CI 1.22, 10.75), whilst a 1 SD greater SM (OR 2.29; 95% CI 1.07, 4.89) and SSI (OR 2.23; 95% CI 1.11, 4.47) were associated with a more than twofold increase in fracture risk, after height, and PA adjustment. No single index consistently predicted fracture across the four groups possibly due to ethnic and sex differences in bone geometry, muscle mass, and skeletal loading. Metacarpal radiogrammetry did not reliably predict fracture in SA children.

Recent Advances in the Genetics of Fractures in Osteoporosis

Genetic susceptibility, together with old age, female sex, and low bone mineral density (BMD) are amongst the strongest determinants of fracture risk. Tmost recent large-scale genome-wide association study (GWAS) meta-analysis has yielded fifteen loci. This review focuses on the advances in the research of genetic determinants of fracture risk. We first discuss the genetic architecture of fracture risk, touching upon different methods and overall findings. We then discuss in a second paragraph the most recent advances in the field and focus on the genetics of fracture risk and also of other endophenotypes closely related to fracture risk such as bone mineral density (BMD). Application of state-of-the-art methodology such as Mendelian randzation in fracture GWAS are reviewed. The final part of this review touches upon potential future directions in genetic research of osteoporotic fractures.

Bone biopsy in nephrology practice

Renal osteodystrophy (ROD), a group of metabolic bone diseases secondary to chronic kidney disease (CKD), still represents a great challenge to nephrologists. Its management is tailored by the type of bone lesion - of high or low turnover - that cannot be accurately predicted by serum biomarkers of bone remodeling available in daily clinical practice, mainly parathyroid hormone (PTH) and alkaline phosphatase (AP). In view of this limitation, bone biopsy followed by bone quantitative histomorphometry, the gold-standard method for the diagnosis of ROD, is still considered of paramount importance. Bone biopsy has also been recommended for evaluation of osteoporosis in the CKD setting to help physicians choose the best anti-osteoporotic drug. Importantly, bone biopsy is the sole diagnostic method capable of providing dynamic information on bone metabolism. Trabecular and cortical bones may be analyzed separately by evaluating their structural and dynamic parameters, thickness and porosity, respectively. Deposition of metals, such as aluminum and iron, on bone may also be detected. Despite of these unique characteristics, the interest on bone biopsy has declined over the last years and there are currently few centers around the world specialized on bone histomorphometry. In this review, we will discuss the bone biopsy technique, its indications, and the main information it can provide. The interest on bone biopsy should be renewed and nephrologists should be capacitated to perform it as part of their training during medical residency.

Women with fracture, unidentified by FRAX, but identified by cortical porosity, have a set of characteristics that contribute to their increased fracture risk beyond high FRAX score and high cortical porosity

The Fracture Risk Assessment Tool (FRAX) is widely used to identify individuals at increased risk for fracture. However, cortical porosity is associated with risk for fracture independent of FRAX and is reported to improve the net reclassification of fracture cases. We wanted to test the hypothesis that women with fracture who are unidentified by high FRAX score, but identified by high cortical porosity, have a set of characteristics that contribute to their fracture risk beyond high FRAX score and high cortical porosity. We quantified FRAX score with femoral neck areal bone mineral density (FN aBMD), and femoral subtrochanteric architecture, in 211 postmenopausal women aged 54-94 years with non-vertebral fractures, and 232 fracture-free controls in Tromsø, Norway, using StrAx software. Of 211 fracture cases, FRAX score > 20% identified 53 women (sensitivity 25.1% and specificity 93.5%), while cortical porosity cut-off > 80th percentile identified 61 women (sensitivity 28.9% and specificity 87.9%). The 43 (20.4%) additional fracture cases identified by high cortical porosity alone, had lower FRAX score (12.3 vs. 26.2%) than those identified by FRAX alone, they were younger, had higher FN aBMD (806 vs. 738 mg/cm²), and fewer had a prior fracture (23.3 vs. 62.9%), all p < 0.05. They had higher cortical porosity (48.7 vs. 42.1%), thinner cortices (3.75 vs. 4.12 mm), lower cortical and total volumetric BMD (942 vs. 1053 and 586 vs. 699 mg HA/cm³), larger medullary and total cross-sectional areas (245 vs. 190 and 669 vs. 593 mm²), and higher cross-sectional moment of inertia (2619 vs. 2388 cm⁴) all p < 0.001. When the fracture cases and controls with high cortical porosity were compared, cases had higher cortical porosity, lower cortical vBMD, lower total vBMD, smaller cortical CSA/Total CSA, larger medullary CSA and larger total CSA than controls (all p ≤ 0.05). Thus, fracture cases, unidentified by FRAX, but identified by cortical porosity, had an architecture where the positive impact of larger bone size did not offset the negative effect of thinner cortices with increased porosity. A measurement of cortical porosity may be a marker of other characteristics that capture additional fracture risk components, not captured by FRAX.

Sexual Dimorphism in Cortical and Trabecular Bone Microstructure Appears During Puberty in Chinese Children

Distal forearm fractures during growth are more common in males than females. Because metaphyseal cortical bone is formed by coalescence of trabeculae emerging from the periphery of the growth plate, we hypothesized that the later onset of puberty in males produces a longer delay in trabecular bone formation and coalescence, which leaves a transient phase of high cortical porosity, low matrix mineral density, and high trabecular density relative to females. We quantified the nondominant distal radial microstructure using high-resolution peripheral quantitative computed tomography in 214 healthy Chinese boys and 219 Chinese girls aged between 7 and 17 years living in Hong Kong. Measurements of 110 slices (9.02 mm) were acquired 5 mm proximal to the growth plate of the nondominant distal radius. Porosity was measured using StrAx1.0 (Straxcorp, Melbourne, VIC, Australia) and trabecular plate and rod structure were measured using individual trabecula segmentation (ITS). Mechanical properties were estimated using finite element analysis (FEA). Results were adjusted for age, total bone cross-sectional area (CSA), dietary calcium intake, and physical activity. In boys, total bone CSA was 17.2% to 22.9% larger throughout puberty, cortical/total bone CSA was 5.1% smaller in Tanner stage 2 only, cortical porosity was 9.4% to 17.5% higher, and matrix mineral density was 1.0% to 2.5% lower in Tanner stage 2 to 5, than girls. Boys had higher trabecular rod BV/TV in Tanner stage 3 and 4, but higher trabecular plate BV/TV and plate to rod ratio in Tanner stage 5, than girls. Boys had 17.0% lower apparent modulus than girls in Tanner stage 2. A transient phase of higher porosity due to dissociation between bone mineral accrual and linear growth may contribute to higher distal radial bone fragility in Chinese boys compared to girls. © 2018 American Society for Bone and Mineral Research.

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

PURPOSE OF REVIEW

Bone densitometry provides a two-dimensional projected areal apparent bone mineral density that fails to capture the heterogeneity of bone's material composition and macro-, micro-, and nano-structures critical to its material and structural strength. Assessment of the structural basis of bone fragility has focused largely on trabecular bone based on the common occurrence of fragility fractures at sites with substantial amounts of trabecular bone. This review focuses on the contribution of cortical bone to bone fragility throughout life.

RECENT FINDINGS

Accurately differentiating cortical and trabecular bone loss has important implications in quantifying bone fragility as these compartments have differing effects on bone strength. Recent advances in imaging methodology have improved distinction of these two compartments by (i) recognition of a cortico-trabecular transitional zone and (ii) quantifying bone microstructure in a region of interest that is a percentage of bone length rather than a fixed point. Additionally, non-invasive three-dimensional imaging methods allow more accurate quantification of changes in the cortical, trabecular, and cortico-trabecular compartments during growth, aging, disease, and treatment. Over 75% of the skeleton is assembled as cortical bone. Of all fragility fractures, ~ 80% are appendicular and involve regions rich in cortical bone and ~ 70% of all age-related appendicular bone loss is cortical and is mainly due to unbalanced intracortical remodeling which increases cortical porosity. The failure to achieve the optimal peak bone microstructure during growth due to disease and the deterioration in cortical and trabecular bone produced by bone loss compromise bone strength. The loss of strength produced by microstructural deterioration is disproportionate to the bone loss producing this deterioration. The reason for this is that the loss of strength increases as a 7th power function of the rise in cortical porosity and a 3rd power function of the fall in trabecular density (Schaffler and Burr in J Biomech. 21(1):13-6, 1988), hence the need to quantify bone microstructure.

Association of High-resolution Peripheral Quantitative Computed Tomography (HR-pQCT) bone microarchitectural parameters with previous clinical fracture in older men: The Osteoporotic Fractures in Men (MrOS) study

High-resolution peripheral quantitative computed tomography (HR-pQCT) assesses both volumetric bone mineral density (vBMD) and trabecular and cortical microarchitecture. However, studies of the association of HR-pQCT parameters with fracture history have been small, predominantly limited to postmenopausal women, often performed limited adjustment for potential confounders including for BMD, and infrequently assessed strength or failure measures. We used data from the Osteoporotic Fractures in Men (MrOS) study, a prospective cohort study of community-dwelling men aged ≥65 years, to evaluate the association of distal radius, proximal (diaphyseal) tibia and distal tibia HR-pQCT parameters measured at the Year 14 (Y14) study visit with prior clinical fracture. The primary HR-pQCT exposure variables were finite element analysis estimated failure loads (EFL) for each skeletal site; secondary exposure variables were total vBMD, total bone area, trabecular vBMD, trabecular bone area, trabecular thickness, trabecular number, cortical vBMD, cortical bone area, cortical thickness, and cortical porosity. Clinical fractures were ascertained from questionnaires administered every 4 months between MrOS study baseline and the Y14 visit and centrally adjudicated by masked review of radiographic reports. We used multivariate-adjusted logistic regression to estimate the odds of prior clinical fracture per 1 SD decrement for each Y14 HR-pQCT parameter. Three hundred forty-four (19.2%) of the 1794 men with available HR-pQCT measures had a confirmed clinical fracture between baseline and Y14. After multivariable adjustment, including for total hip areal BMD, decreased HR-pQCT finite element analysis EFL for each site was associated with significantly greater odds of prior confirmed clinical fracture and major osteoporotic fracture. Among other HR-pQCT parameters, decreased cortical area appeared to have the strongest independent association with prior clinical fracture. Future studies should explore associations of HR-pQCT parameters with specific fracture types and risk of incident fractures and the impact of age and sex on these relationships.

Prediction of Fractures in Men Using Bone Microarchitectural Parameters Assessed by High-Resolution Peripheral Quantitative Computed Tomography-The Prospective STRAMBO Study

Areal bone mineral density (aBMD) poorly identifies men at high fracture risk. Our aim was to assess prediction of fractures in men by bone microarchitectural measures. At baseline, 825 men aged 60 to 87 years had the assessment of bone microarchitecture at distal radius and distal tibia by high-resolution peripheral QCT (HR-pQCT; XtremeCT-I, Scanco Medical, Brüttisellen, Switzerland). Bone strength was estimated by micro-finite element analysis. During the prospective 8-year follow-up, 105 men sustained fractures (59 vertebral fractures in 49 men and 70 nonvertebral fractures in 68 men). After adjustment for age, body mass index (BMI), prior falls, and fractures, most HR-pQCT measures at both skeletal sites predicted fractures. After further adjustment for aBMD, low distal radius trabecular number (Tb.N) was most strongly associated with higher fracture risk (hazard ratio [HR] = 1.63 per SD, 95% confidence interval [CI] 1.31-2.03, p < 0.001). In similar models, low Tb.N was associated with higher risk of major osteoporotic fracture (HR = 1.80 per SD, p < 0.001), vertebral fracture (HR = 1.78 per SD, p < 0.01) and nonvertebral fracture (HR = 1.46 per SD, p < 0.01). In comparison with the reference model (age, BMI, falls, fractures, aBMD), the adjustment for distal radius Tb.N increased the estimated fracture probability in men who sustained fractures versus those who did not have ones (difference = 4.1%, 95% CI 1.9-6.3%, p < 0.001). However, the adjustment for distal radius Tb.N did not increase the area under the curve (AUC, p = 0.37). Similar results were found for distal radius trabecular separation (Tb.Sp) and connectivity density (Conn. D). They were predictive of all fracture types and increased the estimated fracture risk, but not AUC, in men who had incident fractures. Thus, poor distal radius trabecular microarchitecture is predictive of fracture after adjustment for age, BMI, falls, fractures, and aBMD. Although distal radius Tb.N, Conn. D, and Tb.Sp improve the discrimination between men who will or who will not have fracture, they do not provide clinically relevant improvement of fracture prediction in older men. © 2018 American Society for Bone and Mineral Research.

The challenges of diagnosing osteoporosis and the limitations of currently available tools

Dual-energy X-ray absorptiometry (DXA) was the first imaging tool widely utilized by clinicians to assess fracture risk, especially in postmenopausal women. The development of DXA nearly coincided with the availability of effective osteoporosis medications. Although osteoporosis in adults is diagnosed based on a T-score equal to or below − 2.5 SD, most individuals who sustain fragility fractures are above this arbitrary cutoff. This incongruity poses a challenge to clinicians to identify patients who may benefit from osteoporosis treatments. DXA scanners generate 2 dimensional images of complex 3 dimensional structures, and report bone density as the quotient of the bone mineral content divided by the bone area. An obvious pitfall of this method is that a larger bone will convey superior strength, but may in fact have the same bone density as a smaller bone. Other imaging modalities are available such as peripheral quantitative CT, but are largely research tools. Current osteoporosis medications increase bone density and reduce fracture risk but the mechanisms of these actions vary. Anti-resorptive medications (bisphosphonates and denosumab) primarily increase endocortical bone by bolstering mineralization of endosteal resorption pits and thereby increase cortical thickness and reduce cortical porosity. Anabolic medications (teriparatide and abaloparatide) increase the periosteal and endosteal perimeters without large changes in cortical thickness resulting in a larger more structurally sound bone. Because of the differences in the mechanisms of the various drugs, there are likely benefits of selecting a treatment based on a patient’s unique bone structure and pattern of bone loss. This review retreats to basic principles in order to advance clinical management of fragility fractures by examining how skeletal biomechanics, size, shape, and ultra-structural properties are the ultimate predictors of bone strength. Accurate measurement of these skeletal parameters through the development of better imaging scanners is critical to advancing fracture risk assessment and informing clinicians on the best treatment strategy. With this information, a “treat to target” approach could be employed to tailor current and future therapies to each patient’s unique skeletal characteristics.

Are there effects of age, gender, height, and body fat on the functional muscle-bone unit in children and adults?

The aim was to describe the effect of age, gender, height, different stages of human life, and body fat on the functional muscle-bone unit. All these factors had a significant effect on the functional muscle-bone unit and should be addressed when assessing functional muscle-bone unit in children and adults.

INTRODUCTION

For the clinical evaluation of the functional muscle-bone unit, it was proposed to evaluate the adaptation of the bone to the acting forces. A frequently used parameter for this is the total body less head bone mineral content (TBLH-BMC) determined by dual-energy X-ray absorptiometry (DXA) in relation to the lean body mass (LBM by DXA). LBM correlates highly with muscle mass. Therefore, LBM is a surrogate parameter for the muscular forces acting in everyday life. The aim of the study was to describe the effect of age and gender on the TBLH-BMC for LBM and to evaluate the impact of other factors, such as height, different stages of human life, and of body fat.

METHODS

As part of the National Health and Nutrition Examination Survey (NHANES) study, between the years 1999-2006 whole-body DXA scans on randomly selected Americans from 8 years of age were carried out. From all eligible DXA scans (1999-2004), three major US ethnic groups were evaluated (non-Hispanic Whites, non-Hispanic Blacks, and Mexican Americans) for further statistical analysis.

RESULTS

For the statistical analysis, the DXA scans of 8190 non-Hispanic White children and adults (3903 female), of 4931 non-Hispanic Black children and adults (2250 female) and 5421 of Mexican-American children and adults (2424 female) were eligible. Age, gender, body height, and especially body fat had a significant effect on the functional muscle-bone unit.

CONCLUSIONS

When assessing TBLH-BMC for LBM in children and adults, the effects of age, gender, body fat, and body height should be addressed. These effects were analyzed for the first time in such a large cohort.

Menopause-Related Appendicular Bone Loss is Mainly Cortical and Results in Increased Cortical Porosity

After menopause, remodeling becomes unbalanced and rapid. Each of the many remodeling transactions deposits less bone than it resorbed, producing microstructural deterioration. Trabecular bone is said to be lost more rapidly than cortical bone. However, because 80% of the skeleton is cortical, we hypothesized that most menopause-related bone loss and changes in bone microstructure are cortical, not trabecular in origin, and are the result of intracortical remodeling. Distal tibial and distal radial microstructure were quantified during 3.1 years (range, 1.5 to 4.5 years) of follow-up using high-resolution peripheral quantitative computed tomography and StrAx software in 199 monozygotic and 125 dizygotic twin pairs aged 25 to 75 years in Melbourne, Australia. The annual increases in tibial cortical porosity accelerated, being 0.44%, 0.80%, and 1.40% in women remaining premenopausal, transitioning to perimenopause, and from perimenopausal to postmenopause, respectively. Porosity increased in the compact-appearing, outer, and inner transitional zones of the cortex (all p < 0.001). The annual decrease in trabecular bone volume/tissue volume (BV/TV) also accelerated, being 0.17%, 0.26%, and 0.31%, respectively. Little bone loss was observed before menopause. The reduction in BV/TV was due to a decrease in trabecular number (p < 0.001). The greatest bone loss, 7.7 mg hydroxyapatite (HA) annually, occurred in women transitioning from perimenopausal to postmenopause and of this, 6.1 mg HA (80%) was cortical. Results were similar for the distal radius. Despite microarchitectural changes, no significant bone loss was observed before menopause. Over 90% of appendicular bone loss occurs during and after menopause, over 80% is cortical, and this may explain why 80% of fractures are appendicular. © 2017 American Society for Bone and Mineral Research.

Bone Strength Estimated by Micro-Finite Element Analysis (µFEA) Is Heritable and Shares Genetic Predisposition With Areal BMD: The Framingham Study

Genetic factors contribute to the risk of bone fractures, partly because of effects on bone strength. High-resolution peripheral quantitative computed tomography (HR-pQCT) estimates bone strength using micro-finite element analysis (µFEA). The goal of this study was to investigate if the bone failure load estimated by HR-pQCT-based µFEA is heritable and to what extent it shares genetic regulation with areal bone mineral density (aBMD). Bone microarchitecture was measured by HR-pQCT at the ultradistal tibia and ultradistal radius in adults from the Framingham Heart Study (n = 1087, mean age 72 years; 57% women). Radial and tibial failure load in compression were estimated by µFEA. Femoral neck (FN) and ultradistal forearm (UD) aBMD were measured by dual-energy X-ray absorptiometry (DXA). Heritability (h2 ) of failure load and aBMD and genetic correlations between them was estimated adjusting for covariates (age and sex). Failure load values at the non-weight-bearing ultradistal radius and at the weight-bearing ultradistal tibia were highly correlated (r = 0.906; p < 0.001). Estimates of h2 adjusted for covariates were 0.522 for the radius and 0.497 for the tibia. Additional adjustment for height did not impact on the h2 results, but adjustment for aBMD at the UD and FN somewhat decreased h2 point estimates: 0.222 and 0.380 for radius and tibia, respectively. In bivariate analysis, there was a high phenotypic and genetic correlation between covariate-adjusted failure load at the radius and UD aBMD (ρP  = 0.826, ρG  = 0.954, respectively), whereas environmental correlations were lower (ρE  = 0.696), all highly significant (p < 0.001). Similar correlations were observed between tibial failure load and femoral neck aBMD (ρP  = 0.577, ρG  = 0.703, both p < 0.001; ρE  = 0.432, p < 0.05). These data from adult members of families from a population-based cohort suggest that bone strength of distal extremities estimated by micro-finite element analysis is heritable and shares some genetic composition with areal BMD, regardless of the skeletal site. © 2017 American Society for Bone and Mineral Research.

Cortical and trabecular morphology is altered in the limb bones of mice artificially selected for faster skeletal growth

Bone strength is influenced by mineral density and macro- and microstructure. Research into factors that contribute to bone morphology and strength has focused on genetic, environmental and morphological factors (e.g., body mass index), but little is known regarding the impact of rates of skeletal elongation on adult skeletal morphology and strength. Using micro-CT, we examined the impact of rates of skeletal elongation on bone cortical and trabecular morphology, and on rates of estrogen-dependent bone loss in the tibia in CD-1 mice, and in mice with accelerated skeletal growth (Longshanks). Groups of adult mice (n = 7/group) were subjected to ovariectomy or sham surgeries, scanned for 6 weeks, and indices of bone morphology were collected. Results show that Longshanks mice had significantly less trabecular bone at skeletal maturity, characterized by fewer, thinner trabeculae, and furthermore lost trabecular bone more slowly in response to ovariectomy. Artificial selection for rapid skeletal growth relative to somatic growth thus had a significant impact on trabecular bone morphology in Longshanks. Our data do not unequivocally demonstrate a causal relationship between rapid bone growth and reduced trabecular bone quality, but suggest that rapid linear bone growth may influence the risk of cancellous bone fragility.

Quantifying sex, race, and age specific differences in bone microstructure requires measurement of anatomically equivalent regions

INTRODUCTION

Individuals differ in forearm length. As microstructure differs along the radius, we hypothesized that errors may occur when sexual and racial dimorphisms are quantified at a fixed distance from the radio-carpal joint.

METHODS

Microstructure was quantified ex vivo in 18 cadaveric radii using high resolution peripheral quantitative computed tomography and in vivo in 158 Asian and Caucasian women and men at a fixed region of interest (ROI), a corrected ROI positioned at 4.5-6% of forearm length and using the fixed ROI adjusted for cross sectional area (CSA), forearm length or height. Secular effects of age were assessed by comparing 38 younger and 33 older women.

RESULTS

Ex vivo, similar amounts of bone mass fashioned adjacent cross sections. Larger distal cross sections had thinner porous cortices of lower matrix mineral density (MMD), a larger medullary CSA and higher trabecular density. Smaller proximal cross-sections had thicker less porous cortices of higher MMD, a small medullary canal with little trabecular bone. Taller persons had more distally positioned fixed ROIs which moved proximally when corrected. Shorter persons had more proximally positioned fixed ROIs which moved distally when corrected, so dimorphisms lessened. In the corrected ROIs, in Caucasians, women had 0.6 SD higher porosity and 0.6 SD lower trabecular density than men (p<0.01). In Asians, women had 0.25 SD higher porosity (NS) and 0.5 SD lower trabecular density than men (p<0.05). In women, Asians had 0.8 SD lower porosity and 0.3 SD higher trabecular density than Caucasians (p<0.01). In men, Asians and Caucasians had similar porosity and trabecular density. Results were similar using an adjusted fixed ROI. Adjusting for secular effects of age on forearm length resulted in the age-related increment in porosity increasing from 2.08 SD to 2.48 SD (p<0.05).

CONCLUSION

Assessment of sex, race and age related differences in microstructure requires measurement of anatomically equivalent regions.

Targeted Disruption of NF1 in Osteocytes Increases FGF23 and Osteoid With Osteomalacia-like Bone Phenotype

Neurofibromatosis type 1 (NF1, OMIM 162200), caused by NF1 gene mutations, exhibits multi-system abnormalities, including skeletal deformities in humans. Osteocytes play critical roles in controlling bone modeling and remodeling. However, the role of neurofibromin, the protein product of the NF1 gene, in osteocytes is largely unknown. This study investigated the role of neurofibromin in osteocytes by disrupting Nf1 under the Dmp1-promoter. The conditional knockout (Nf1 cKO) mice displayed serum profile of a metabolic bone disorder with an osteomalacia-like bone phenotype. Serum FGF23 levels were 4 times increased in cKO mice compared with age-matched controls. In addition, calcium-phosphorus metabolism was significantly altered (calcium reduced; phosphorus reduced; parathyroid hormone [PTH] increased; 1,25(OH)₂ D decreased). Bone histomorphometry showed dramatically increased osteoid parameters, including osteoid volume, surface, and thickness. Dynamic bone histomorphometry revealed reduced bone formation rate and mineral apposition rate in the cKO mice. TRAP staining showed a reduced osteoclast number. Micro-CT demonstrated thinner and porous cortical bones in the cKO mice, in which osteocyte dendrites were disorganized as assessed by electron microscopy. Interestingly, the cKO mice exhibited spontaneous fractures in long bones, as found in NF1 patients. Mechanical testing of femora revealed significantly reduced maximum force and stiffness. Immunohistochemistry showed significantly increased FGF23 protein in the cKO bones. Moreover, primary osteocytes from cKO femora showed about eightfold increase in FGF23 mRNA levels compared with control cells. The upregulation of FGF23 was specifically and significantly inhibited by PI3K inhibitor Ly294002, indicating upregulation of FGF23 through PI3K in Nf1-deficient osteocytes. Taken together, these results indicate that Nf1 deficiency in osteocytes dramatically increases FGF23 production and causes a mineralization defect (ie, hyperosteoidosis) via the alteration of calcium-phosphorus metabolism. This study demonstrates critical roles of neurofibromin in osteocytes for osteoid mineralization. © 2017 American Society for Bone and Mineral Research.

Bone Microarchitecture Assessed by HR-pQCT as Predictor of Fracture Risk in Postmenopausal Women: The OFELY Study

Several cross-sectional studies have shown that impairment of bone microarchitecture contributes to skeletal fragility. The aim of this study was to prospectively investigate the prediction of fracture (Fx) by bone microarchitecture assessed by high-resolution peripheral computed tomography (HR- pQCT) in postmenopausal women. We measured microarchitecture at the distal radius and tibia with HR-pQCT in the OFELY study, in addition to areal BMD with dual-energy X-ray absorptiometry (DXA) in 589 women, mean ± SD age 68 ± 9 years. During a median [IQ] 9.4 [1.0] years of follow-up, 135 women sustained an incident fragility Fx, including 81 women with a major osteoporotic Fx (MOP Fx). After adjustment for age, women who sustained Fx had significantly lower total and trabecular volumetric densities (vBMD) at both sites, cortical parameters (area and thickness at the radius, vBMD at the tibia), trabecular number (Tb.N), connectivity density (Conn.D), stiffness, and estimated failure load at both sites, compared with control women. After adjustment for age, current smoking, falls, prior Fx, use of osteoporosis-related drugs, and total hip BMD, each quartile decrease of several baseline values of bone microarchitecture at the radius was associated with significant change of the risk of Fx (HR of 1.39 for Tb.BMD [p = 0.001], 1.32 for Tb.N [p = 0.01], 0.76 for Tb.Sp.SD [p = 0.01], 1.49 [p = 0.01] for Conn.D, and 1.27 for stiffness [p = 0.02]). At the tibia, the association remained significant for stiffness and failure load in the multivariate model for all fragility Fx and for Tt.BMD, stiffness, and failure load for MOP Fx. We conclude that impairment of bone microarchitecture-essentially in the trabecular compartment of the radius-predict the occurrence of incident fracture in postmenopausal women. This assessment may play an important role in identifying women at high risk of fracture who could not be adequately detected by BMD measurement alone, to benefit from a therapeutic intervention. © 2017 American Society for Bone and Mineral Research.

Women with type 2 diabetes mellitus have lower cortical porosity of the proximal femoral shaft using low-resolution CT than nondiabetic women, and increasing glucose is associated with reduced cortical porosity

Increased cortical porosity has been suggested as a possible factor increasing fracture propensity in patients with type 2 diabetes mellitus (T2DM). This is a paradox because cortical porosity is generally associated with high bone turnover, while bone turnover is reduced in patients with T2DM. We therefore wanted to test the hypothesis that women with T2DM have lower bone turnover markers (BTM) and lower cortical porosity than those without diabetes, and that higher serum glucose and body mass index (BMI) are associated with lower BTM, and with lower cortical porosity. This cross-sectional study is based on a prior nested case-control study including 443 postmenopausal women aged 54-94years from the Tromsø Study, 211 with non-vertebral fracture and 232 fracture-free controls. Of those 443 participants, 22 women exhibited T2DM and 421 women did not have diabetes. All had fasting blood samples assayed for procollagen type I N-terminal propeptide (PINP), C-terminal cross-linking telopeptide of type I collagen (CTX) and glucose, and femoral subtrochanteric architecture was quantified using low-resolution clinical CT and StrAx1.0 software. Women with T2DM had higher serum glucose (7.2 vs. 5.3mmol/L), BMI (29.0 vs. 26.4kg/m²), and higher femoral subtrochanteric total volumetric bone mineral density (vBMD) (783 vs. 715mgHA/cm³), but lower cortical porosity (40.9 vs. 42.8%) than nondiabetic women (all p<0.05). Each standard deviation (SD) increment in glucose was associated with 0.10-0.12 SD lower PINP and CTX, and 0.13 SD lower cortical porosity (all p<0.05). Each SD increment in BMI was associated with 0.10-0.18 SD lower serum PINP and CTX, and 0.19 SD thicker cortices (all p<0.05). Increasing glucose and BMI were associated with lower bone turnover suggesting that reduced intracortical and endocortical remodeling leads to reduced porosity and thicker cortices. Using low-resolution clinical CT, cortical porosity was lower in women with T2DM compared to women without diabetes. This indicates that other changes in bone qualities, not increased cortical porosity, are likely to explain the increased fracture propensity in patients with T2DM.

Heritability and Genetic Correlations for Bone Microarchitecture: The Framingham Study Families

High-resolution peripheral quantitative computed tomography (HR-pQCT) measures bone microarchitecture and volumetric bone mineral density (vBMD), important risk factors for osteoporotic fractures. We estimated the heritability (h² ) of bone microstructure indices and vBMD, measured by HR-pQCT, and genetic correlations (ρ_G ) among them and between them and regional aBMD measured by dual-energy X-ray absorptiometry (DXA), in adult relatives from the Framingham Heart Study. Cortical (Ct) and trabecular (Tb) traits were measured at the distal radius and tibia in up to 1047 participants, and ultradistal radius (UD) aBMD was obtained by DXA. Heritability estimates, adjusted for age, sex, and estrogenic status (in women), ranged from 19.3% (trabecular number) to 82.8% (p < 0.01, Ct.vBMD) in the radius and from 51.9% (trabecular thickness) to 98.3% (cortical cross-sectional area fraction) in the tibia. Additional adjustments for height, weight, and radial aBMD had no major effect on h² estimates. In bivariate analyses, moderate to high genetic correlations were found between radial total vBMD and microarchitecture traits (ρ_G from 0.227 to 0.913), except for cortical porosity. At the tibia, a similar pattern of genetic correlations was observed (ρ_G from 0.274 to 0.948), except for cortical porosity. Environmental correlations between the microarchitecture traits were also substantial. There were high genetic correlations between UD aBMD and multivariable-adjusted total and trabecular vBMD at the radius (ρ_G  = 0.811 and 0.917, respectively). In summary, in related men and women from a population-based cohort, cortical and trabecular microarchitecture and vBMD at the radius and tibia were heritable and shared some h² with regional aBMD measured by DXA. These findings of high heritability of HR-pQCT traits, with a slight attenuation when adjusting for aBMD, supports further work to identify the specific variants underlying volumetric bone density and fine structure of long bones. Knowledge that some of these traits are genetically correlated can serve to reduce the number of traits for genetic association studies. © 2016 American Society for Bone and Mineral Research.

Estrogens and Androgens in Skeletal Physiology and Pathophysiology

Estrogens and androgens influence the growth and maintenance of the mammalian skeleton and are responsible for its sexual dimorphism. Estrogen deficiency at menopause or loss of both estrogens and androgens in elderly men contribute to the development of osteoporosis, one of the most common and impactful metabolic diseases of old age. In the last 20 years, basic and clinical research advances, genetic insights from humans and rodents, and newer imaging technologies have changed considerably the landscape of our understanding of bone biology as well as the relationship between sex steroids and the physiology and pathophysiology of bone metabolism. Together with the appreciation of the side effects of estrogen-related therapies on breast cancer and cardiovascular diseases, these advances have also drastically altered the treatment of osteoporosis. In this article, we provide a comprehensive review of the molecular and cellular mechanisms of action of estrogens and androgens on bone, their influences on skeletal homeostasis during growth and adulthood, the pathogenetic mechanisms of the adverse effects of their deficiency on the female and male skeleton, as well as the role of natural and synthetic estrogenic or androgenic compounds in the pharmacotherapy of osteoporosis. We highlight latest advances on the crosstalk between hormonal and mechanical signals, the relevance of the antioxidant properties of estrogens and androgens, the difference of their cellular targets in different bone envelopes, the role of estrogen deficiency in male osteoporosis, and the contribution of estrogen or androgen deficiency to the monomorphic effects of aging on skeletal involution.

A Comparison of Peripheral Imaging Technologies for Bone and Muscle Quantification: a Mixed Methods Clinical Review

PURPOSE OF REVIEW

Bone and muscle peripheral imaging technologies are reviewed for their association with fractures and frailty. A narrative systematized review was conducted for bone and muscle parameters from each imaging technique. In addition, meta-analyses were performed across all bone quality parameters.

RECENT FINDINGS

The current body of evidence for bone quality's association with fractures is strong for (high-resolution) peripheral quantitative computed tomography (pQCT), with trabecular separation (Tb.Sp) and integral volumetric bone mineral density (vBMD) reporting consistently large associations with various fracture types across studies. Muscle has recently been linked to fractures and frailty, but the quality of evidence remains weaker from studies of small sample sizes. It is increasingly apparent that musculoskeletal tissues have a complex relationship with interrelated clinical endpoints such as fractures and frailty. Future studies must concurrently address these relationships in order to decipher the relative importance of one causal pathway from another.

The clinical contribution of cortical porosity to fragility fractures

Cortical bone is not compact; rather it is penetrated by many Haversian and Volkmann canals for blood supply. The lining of these canals are the intracortical bone surfaces available for bone remodeling. Increasing intracortical bone remodeling increases cortical porosity. However, cortical bone loss occurs more slowly than trabecular loss due to the fact that less surface per unit of bone matrix volume is available for bone remodeling. Nevertheless, most of the bone loss over time is cortical because cortical bone constitutes 80% of the skeleton, and the relative proportion of trabecular bone diminishes with advancing age. Higher serum levels of bone turnover markers are associated with higher cortical porosity of the distal tibia and the proximal femur. Greater porosity of the distal radius is associated with higher odds for forearm fracture, and greater porosity of the proximal femur is associated with higher odds for non-vertebral fracture in postmenopausal women. Measurement of cortical porosity contributes to fracture risk independent of areal bone mineral density and Fracture Risk Assessment Tool. On the other hand, antiresorptive treatment reduces porosity at the distal radius and at the proximal femoral shaft. Thus, porosity is a substantial determinant of the bone fragility that underlies the risk of fractures and may be a target for fracture prevention.