Role of cortical bone in bone fragility

Increased risk of fragility fractures in patients with primary biliary cholangitis

Large-scale studies on the risk of fragility fractures in patients with primary biliary cholangitis (PBC) are limited due to low incidence. We aimed to investigate whether PBC is associated with fragility fractures using real-world nationwide data. The Korean National Health Insurance Service claims data from 2007 to 2020 were analyzed in this population-based cohort study. Patients with PBC (n = 4951) were matched with controls (n = 19 793) using a 1:4 ratio based on age, sex, and follow-up duration. The primary outcome was fragility fracture, which comprised fractures of the vertebra, hip, distal radius, and proximal humerus. The incidence rates (IRs) and hazard ratios (HRs) were determined to assess the impact of PBC on fragility fractures. During the median follow-up period of 5.37 years, 524 patients in the PBC group had fragility fractures (IR, 18.59/1000 person-years [PYs]). After adjusting for covariates, PBC increased the risk of fragility fractures by 1.63-fold (95% confidence interval, 1.20-2.22; P = .002). The vertebra and hip were particularly susceptible to fracture in patients with PBC, with adjusted HRs of 1.77 and 2.23, respectively. In the subgroup analysis, the risk of fragility fracture was 2.53-fold higher in men and 1.59-fold higher in women with PBC than that in the respective matched control groups. Considering the morbidity and mortality related to fragility fractures, increasing awareness of fragility fracture risk and implementing appropriate preventive measures in patients with PBC are imperative.

Cortical bone thickness on preoperative CT scans as predictor of bone quality in distal femur fractures: a retrospective study in Caucasians

AIM

Distal femur fractures (DFF) are rare, but associated with high complication rates and mortality, particularly in patients with osteoporosis. To improve preoperative assessment, we analyzed if cortical bone thickness on CT and AP radiographs is associated with clinical parameters of bone quality.

METHODS

Retrospective single-center study of adult patients presenting at a level-one trauma center, with a DFF between 2011 and 2020. Clinical parameters for bone quality, such as age, sex, body mass index (BMI), energy impact level of trauma, and known history of osteoporosis, were assessed. Mean cortical bone thickness (CBTavg) on AP radiograph was determined using a previously published method. Cortical thickness on CT scan was measured at 8 and 14 cm proximal to the articular surface of the lateral condyle.

RESULTS

71 patients (46 females) between 20 and 100 years were included in the study. Cortical thickness determined by CT correlated significantly with CBTavg measurements on AP radiograph (Spearman r = 0.62 to 0.80; p < 0.001). Cortical thickness was inversely correlated with age (Spearman r = - 0.341 to - 0.466; p < 0.001) and significantly associated with trauma impact level and history of osteoporosis (p =  < 0.001). The CT-based values showed a stronger correlation with the clinical parameters than those determined by AP X-ray.

CONCLUSION

Our results showed that cortical thickness of the distal femur correlates with clinical parameters of bone quality and is therefore an excellent tool for assessing what surgical care should be provided. Interestingly, our findings indicate that cortical thickness on CT is more strongly correlated with clinical data than AP radiograph measurements.

Evaluation of cortical bone remodeling in canines treated with daily and weekly administrations of teriparatide by establishing AI-driven morphometric analyses and GIS-based spatial mapping

Larger animal models with a well-developed Haversian system, as observed in humans, are ideal to analyze cortical bone remodeling in pharmacological studies of anti-osteoporosis drugs, although they have some limitations in controlling individual variability in size, weight, age, and number. This study aimed to morphometrically analyze cortical bone remodeling focusing on Haversian canals in dogs using four regimens of TPTD with daily and weekly administrations at lower and higher weekly doses (4.9 μg/kg/week and 19.8 μg/kg/week, respectively) for 9 months. A micro-computed tomography-based analysis showed no significant differences among regimen groups. By establishing artificial intelligence (AI)-driven morphometric analyses and geographical information system (GIS)-based spatial mapping of Haversian canals that does not require confocal microscopy but is possible with more commonly used wide field microscopes, we successfully observed significant morphometric distinctions among regimens applied even in dogs. Our analytical results suggested that the daily higher regimen specifically increased the number of eroded pores creating spaces between existing canals, thus stimulating cortical bone remodeling.

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.

Progress in the application of 3D-printed sodium alginate-based hydrogel scaffolds in bone tissue repair

In recent years, hydrogels have been widely used in the biomedical field as materials with excellent bionic structures and biological properties. Among them, the excellent comprehensive properties of natural polymer hydrogels represented by sodium alginate have attracted the great attention of researchers. At the same time, by physically blending sodium alginate with other materials, the problems of poor cell adhesion and mechanical properties of sodium alginate hydrogels were directly improved without chemical modification of sodium alginate. The composite blending of multiple materials can also improve the functionality of sodium alginate hydrogels, and the prepared composite hydrogel also has a larger application field. In addition, based on the adjustable viscosity of sodium alginate-based hydrogels, sodium alginate-based hydrogels can be loaded with cells to prepare biological ink, and the scaffold can be printed out by 3D printing technology for the repair of bone defects. This paper first summarizes the improvement of the properties of sodium alginate and other materials after physical blending. Then, it summarizes the application progress of sodium alginate-based hydrogel scaffolds for bone tissue repair based on 3D printing technology in recent years. Moreover, we provide relevant opinions and comments to provide a theoretical basis for follow-up research.

The Hidden Dangers of Plant-Based Diets Affecting Bone Health: A Cross-Sectional Study with U.S. National Health and Nutrition Examination Survey (NHANES) Data from 2005-2018

The plant-based dietary pattern has been recommended for its potential health and environmental benefits, but its association with bone loss needs to be further explored. This study aimed to investigate the association between three plant-based diet indexes and bone loss in 16,085 adults, using data from the National Health and Nutrition Examination Survey. Three plant-based diet indexes (PDI, hPDI, and uPDI) were calculated from two NHANES 24-h dietary recall interviews, to characterize a plant-based diet. A multinomial logistic regression model was used to estimate the odds ratios (OR) and 95% confidence intervals (95% CI). Higher hPDI and PDI were associated with increased risk of bone loss (OR_{Q5 vs. Q1} = 1.50; 95% CI: 1.24-1.81 for hPDI; OR_{Q5 vs. Q1} = 1.22; 95% CI: 1.03-1.45 for PDI), while higher uPDI was associated with increased risk of osteoporosis (OR_{Q5 vs. Q1} = 1.48; 95% CI: 1.04-2.11). A harmful association between plant-based diet indexes (hPDI and PDI) and osteopenia was observed at the lumbar spine rather than the femoral neck. We conducted several sensitivity analyses to ensure the robustness of results, including subgroup analysis, exclusion of people taking anti-osteoporotic and estrogenic drugs, further adjustment for menopausal status, corticosteroid usage, and dietary supplements, and calculation of E-value. Our study demonstrates the deleterious effects of a plant-based diet on bone health and emphasizes the importance of a balanced diet.

Gene Therapy to Treat Osteopenia Associated With Chronic Ethanol Consumption and Aldehyde Dehydrogenase 2 Deficiency

Aldehyde dehydrogenase 2 (ALDH2) deficiency affects 35% to 45% of East Asians and 8% of the world population. ALDH2 is the second enzyme in the ethanol metabolism pathway. The common genetic variant ALDH2*2 allele has a glutamic acid-to-lysine substitution at position 487 (E487K) that reduces the enzyme activity, resulting in an accumulation of acetaldehyde after ethanol consumption. The ALDH2*2 allele is associated with increased risk of osteoporosis and hip fracture. Our prior study showed that administration of an adeno-associated virus (AAV) serotype rh.10 gene transfer vector expressing the human ALDH2 cDNA (AAVrh.10hALDH2) before initiation of ethanol consumption prevented bone loss in ALDH2-deficient homozygous knockin mice carrying the E487K mutation (Aldh2 E487K+/+). We hypothesized that AAVrh.10hALDH2 administration after establishment of osteopenia would be able to reverse bone loss due to ALDH2 deficiency and chronic ethanol consumption. To test this hypothesis, male and female Aldh2 E487K+/+ mice (n = 6) were given ethanol in the drinking water for 6 weeks to establish osteopenia and then administered AAVrh.10hALDH2 (1011 genome copies). Mice were evaluated for an additional 12 weeks. AAVrh.10hALDH2 administration after osteopenia was established corrected weight loss and locomotion phenotypes and, importantly, increased midshaft femur cortical bone thickness, the most important component of bone in the resistance to fractures, and showed a trend toward increased trabecular bone volume. AAVrh.10hALDH2 is a promising therapeutic for osteoporosis in ALDH2-deficient individuals. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Femur 3D-DXA Assessment in Female Football Players, Swimmers, and Sedentary Controls

Cortical and trabecular volumetric bone mineral density (vBMD), cortical thickness and surface BMD (sBMD, density-to-thickness ratio) were analyzed in the proximal femur of elite female football players and artistic swimmers using three-dimensional dual-energy X-ray absorptiometry (3D-DXA) software and compared to sedentary controls. Football players had significantly higher (p<0.05) vBMD (mg/cm³) in the trabecular (263±44) and cortical femur (886±69) than artistic swimmers (224±43 and 844±89) and sedentary controls (215±51 and 841±85). Football players had also higher (p<0.05) cortical thickness (2.12±0.19 mm) and sBMD (188±22 mg/cm²) compared to artistic swimmers (1.85±0.15 and 156±21) and sedentary controls (1.87±0.16 and 158±23). Artistic swimmers did not show significant differences in any parameter analyzed for 3D-DXA when compared to sedentary controls. The 3D-DXA modeling revealed statistical differences in cortical thickness and vBMD between female athletes engaged in weight-bearing (football) and non-weight bearing (swimming) sports and did not show differences between the non-weight bearing sport and the sedentary controls. 3D-DXA modeling could provide insight into bone remodeling in the sports field, allowing evaluation of femoral trabecular and cortical strength from standard DXA scans.

A multimodal 3D imaging approach of pore networks in the human femur to assess age-associated vascular expansion and Lacuno-Canalicular reduction

Cellular communication in the mechanosensory osteocyte Lacuno-Canalicular Network (LCN) regulates bone tissue remodeling throughout life. Age-associated declines in LCN size and connectivity dysregulate mechanosensitivity to localized remodeling needs of aging or damaged tissue, compromising bone quality. Synchrotron radiation-based micro-Computed Tomography (SRμCT) and Confocal Laser Scanning Microscopy (CLSM) were employed to visualize LCN and vascular canal morphometry in an age series of the anterior femur (males n = 14, females n = 11, age range = 19-101, mean age = 55). Age-associated increases in vascular porosity were driven by pore coalescence, including a significant expansion in pore diameter and a significant decline in pore density. In contrast, the LCN showed significant age-associated reductions in lacunar volume fraction, mean diameter, and density, and in canalicular volume fraction and connectivity density. Lacunar density was significantly lower in females across the lifespan, exacerbating their age-associated decline. Canalicular connectivity density was also significantly lower in females but approached comparable declining male values in older age. Our data illuminate the trajectory and potential morphometric sources of age-associated bone loss. Increased vascular porosity contributes to bone fragility with aging, while an increasingly reduced and disconnected LCN undermines the mechanosensitivity required to repair and reinforce bone. Understanding why and how this degradation occurs is essential for improving the diagnosis and treatment of age-related changes in bone quality and fragility.

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.

The influence of intra-cortical microstructure on the contrast in ultrasound images of the cortex of long bones: A 2D simulation study

Decreased thickness of the bone cortex due to bone loss in the course of ageing and osteoporosis is associated with reduced bone strength. Cortical thickness measurement from ultrasound images was recently demonstrated in young adults. This requires the identification of both the outer (periosteum) and inner (endosteum) surfaces of the bone cortex. However, with bone loss, the cortical porosity and the size of the vascular pores increase resulting in enhanced ultrasound scattering which may prevent the detection of the endosteum. The aim of this work was to study the influence of cortical bone microstructure variables, such as porosity and pore size, on the contrast of the endosteum in ultrasound images. We wanted to estimate the range of these variables for which ultrasound imaging of the endosteum is feasible. We generated synthetic data using a two-dimensional time-domain code to simulate the propagation of elastodynamic waves. A synthetic aperture imaging sequence with an array transducer operating at a center frequency of 2.5 MHz was used. The numerical simulations were conducted for 105 cortical microstructures obtained from high resolution X-ray computed tomography images of ex vivo bone samples with a porosity ranging from 2% to 24 %. Images were reconstructed using a delay-and-sum (DAS) algorithm with optimized f-number, correction of refraction at the periosteum, and sample-specific wave-speed. We observed a range variation of 18 dB of endosteum contrast in our data set depending on the bone microstructure. We found that as porosity increases, speckle intensity inside the bone cortex increases whereas the intensity of the signal from the endosteum decreases. Also, a microstructure with large pores (diameter >250 μm) was associated with poor endosteum visibility, compared with a microstructure with equal porosity but a more narrow distribution of pore sizes. These findings suggest that ultrasound imaging of the bone cortex with a probe operating at a central frequency of 2.5 MHz using refraction-corrected DAS is capable of detecting the endosteum of a cortex with moderate porosity (less than about 10%) if the largest pores remain smaller than about 200 μm.

Cortex or cancellous-which is early for the decrease of bone content for vertebral body in health?

OBJECTIVE

To obtain the cortex and cancellous parameter of the vertebral bone of healthy subjects using QCT. To explore which is earlier or faster for bone loss with age.

MATERIALS AND METHODS

733 physical examiners underwent chest low-dose CT examination were recruited, from April 1, 2021 to October 1, 2021. QCT sequence was used to obtain the bone mineral density of T12-L2 vertebral body without additional radiation. The mass and area of vertebral cortex and cancellous at the central level of L2 vertebral body were measured. The age -related characteristics of vertebral cortex and cancellous between male and female was analyzed and compared.

RESULTS

The vBMD of T12-L2 vertebral body decreased with age. Significant differences were found in volumetric bone mineral density (vBMD) of T12-L2 vertebral body. For female, significant differences were found in bone content involving cortical mass, cancellous mass, cortical area, cancellous area, cortical mass/cancellous mass and cortical area/cancellous area in different age groups, respectively. The cortical mass decreased with age in female. The cancellous mass of female increased and then decreased with peak at 31-40 y. The cortical area of female decreased gradually before 71 y. The cancellous area of female increased and then decreased with peak at 51-60 y. The values of mass ratio and area ratio in female showed a slowly downward trend with age. Significant differences of bone content between non-menopausal and menopausal women were found except the cancellous mass. For male, no significant differences were found in all parameters of bone content.

CONCLUSION

The changes of vertebral BMD, bone content of cortex and cancellous have different characteristics in different age. The change of cortex in female maybe earlier and faster than that of cancellous, especially in menopausal women.

Cortical bone material / compositional properties in growing children and young adults aged 1.5-23 years, as a function of gender, age, metabolic activity, and growth spurt

Bone material / compositional properties are significant determinants of bone quality, thus strength. Raman spectroscopic analysis provides information on the quantity and quality of all three bone tissue components (mineral, organic matrix, and tissue water). The overwhelming majority of the published reports on the subject concern adults. We have previously reported on these properties in growing children and young adults, in the cancellous compartment. The purpose of the present study was to create normative reference data of bone material / compositional properties for children and young adults, in the cortical compartment. We performed Raman (Senterra (Bruker Optik GmbH), 50× objective, with an excitation of 785 nm (100 mW) and a lateral resolution of ~0.6 μm) microspectroscopic analysis of transiliac bone samples from 54 individuals between 1.5 and 23 years of age, with no known metabolic bone disease, and which have been previously used to establish histomorphometric, bone mineralization density distribution, and cancellous bone quality reference values. The bone quality indices that were determined were: mineral/matrix ratio (MM) from the integrated areas of the v₂PO₄ (410-460 cm^-1) and the amide III (1215-1300 cm^-1) bands, tissue water in nanopores approximated by the ratio of the integrated spectral area ~ 494-509 cm^-1 to Amide III band, the glycosaminoglycan (GAG) content (ratio of integrated area 1365-1390 cm^-1 to the Amide III band, the sulfated proteoglycan (sPG) content as the ratio of the integrated peaks ~1062 cm^-1 and 1365-1390 cm^-1, the pyridinoline (Pyd) content estimated from the ratio of the absorbance height at 1660 cm^-1 / area of the amide I (1620-1700 cm^-1) band, and the mineral maturity / crystallinity (MMC) estimated from the inverse of the full width at half height of the v₁PO₄ (930-980 cm^-1) band. Analyses were performed at the three distinct cortical surfaces (endosteal, osteonal, periosteal) at specific anatomical microlocations, namely the osteoid, and the three precisely known tissue ages based on the presence of fluorescence double labels. Measurements were also taken in interstitial bone, a much older tissue that has undergone extensive secondary mineralization. Overall, significant dependencies of the measured parameters on tissue age were observed, while at any given tissue age, sex and subject age were minimal confounders. The established Raman database in the cortical compartments complements the previously published one in cancellous bone, and provides healthy baseline bone quality indices that may serve as a valuable tool to identify alterations due to pediatric disease.

Direct Assessment of Rabbit Cortical Bone Basic Multicellular Unit Longitudinal Erosion Rate: A 4D Synchrotron-Based Approach

Cortical bone remodeling is carried out by basic multicellular units (BMUs), which couple resorption to formation. Although fluorochrome labeling has facilitated study of BMU formative parameters since the 1960s, some resorptive parameters, including the longitudinal erosion rate (LER), have remained beyond reach of direct measurement. Indeed, our only insights into this spatiotemporal parameter of BMU behavior come from classical studies that indirectly inferred LER. Here, we demonstrate a 4D in vivo method to directly measure LER through in-line phase contrast synchrotron imaging. The tibias of rabbits (n = 15) dosed daily with parathyroid hormone were first imaged in vivo (synchrotron micro-CT; day 15) and then ex vivo 14 days later (conventional micro-CT; day 29). Mean LER assessed by landmarking the co-registered scans was 23.69 ± 1.73 μm/d. This novel approach holds great promise for the direct study of the spatiotemporal coordination of bone remodeling, its role in diseases such as osteoporosis, as well as related treatments. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Expansion of the osteocytic lacunar-canalicular system involved in pharmacological action of PTH revealed by AI-driven fluorescence morphometry in female rabbits

Osteoporosis is an age-related disorder that is characterized by reduced bone mass. Its prevention and treatment are important healthcare issues for maintaining social activity in aged societies. Although bone fractures mostly occur at sites of weakened cortical bone, pathophysiological and pharmacological evaluations of bone mass have tended to be predominantly assessed in trabecular bone. To statistically characterize cortical bone remodeling, we originally established multimode fluorescence imaging and artificial intelligence (AI)-driven morphometric analyses in six-month-old female rabbits with well-defined cortical remodeling, similar to that in humans. We evaluated three distinct administration frequencies of teriparatide [TPTD; human parathyroid hormone, hPTH (1–34)]: once (1/w), twice (2/w), and seven times (7/w) a week, with the same total dose (140 μg/kg/week). Our analyses revealed significant expansions of the osteocytic lacunar-canalicular system and Haversian canals accompanied by the development of cortical porosity and endosteal naïve bone formation induced by a frequent administration regimen (7/w) of TPTD; however, once-weekly (1/w) and twice-weekly (2/w) administration of TPTD showed little effect. These findings demonstrate a clear contrast between the effects of frequent and infrequent administration of TPTD on cortical bone metabolism and suggest that osteocytic bone remodeling is involved in the pharmacological action of PTH.

Na-Cl Co-transporter (NCC) gene inactivation is associated with improved bone microstructure

Gitelman syndrome (GS) is the disease model of the inactivation of thiazide-sensitive sodium chloride cotransporter (NCC), which is believed to benefit bone mass and reduce fracture risk. In this study, we found that GS patients have superior bone microarchitecture, which is associated with the disease status. Several decreased bone parameters with aging in healthy controls were reversed in GS patients to a certain extent.

PURPOSE

To evaluate the impact of the inactivation of NCC on bone turnover and microarchitecture in Gitelman syndrome patients.

METHODS

A cross-sectional study was conducted in 45 GS patients (25 males and 20 females). Serum procollagen type 1 N-terminal propeptide (P1NP), β-carboxy-terminal crosslinked telopeptide of type 1 collagen (β-CTX), and osteocalcin were measured. High-resolution peripheral quantitative computed tomography (HR-pQCT) was conducted to evaluate bone microarchitecture in GS patients and age- and sex-matched healthy controls. Areal bone mineral density (aBMD) was measured by dual-energy X-ray absorptiometry (DXA) simultaneously.

RESULTS

GS patients had a relatively lower level of β-CTX. aBMD at several skeletal sites was improved in GS patients. HR-pQCT assessment revealed that GS patients had slightly thinner but significantly more compact trabecular bone (increased trabecular number and decreased thickness), notably decreased cortical porosity, and increased volume BMD (vBMD) at both the radius and tibia compared with controls. The disease severity, represented as the relationship with the minimum level of magnesium during the course and standard base excess, was associated with bone microarchitecture parameters after adjusting for age, sex, and BMI. The decreased vBMD and Tb.BV/TV, and increased Tb.Sp and Ct.Po with aging, were reversed in GS patients to a certain extent.

CONCLUSION

GS patients have superior bone microarchitecture, which suggests that the inactivation of NCC might be beneficial for avoiding osteoporosis.

Ultrasonic Guided Waves in Bone: A Decade of Advancement in Review

The use of guided wave ultrasonography as a means to assess cortical bone quality has been a significant practice in bone quantitative ultrasound for more than 20 years. In this article, the key developments within the technology of ultrasonic guided waves (UGW) in long bones during the past decade are documented. The covered topics include data acquisition configurations available for measuring bone guided waveforms, signal processing techniques applied to bone UGW, numerical modeling of ultrasonic wave propagation in cortical long bones, formulation of inverse approaches to extract bone properties from observed ultrasonic signals, and clinical studies to establish the technology's application and efficacy. The review concludes by highlighting specific challenging problems and future research directions. In general, the primary purpose of this work is to provide a comprehensive overview of bone guided-wave ultrasound, especially for newcomers to this scientific field.

Analysis of the femoral neck from rats in the periestropause treated with oxytocin and submitted to strength training

Among the interventions used to prevent osteoporosis in female organisms, strength training (ST) and oxytocin (OT) stand out, as a promising hormone with anabolic action on bone. This study aimed to verify whether the combined action of OT and ST, compared to isolated interventions, potentiates the bone remodeling process of the femoral neck of Wistar rats during periestropause. Forty Wistar rats (18 months) with irregular estrous cycle were randomly distributed into groups: 1-Vehicle (Veh; NaCl 0.15 mol/L ip); 2-Oxytocin (Ot; 134 μg/kg/ip); 3-Strength training (St); 4-Ot + St. The animals of the 1, 2 and 4 groups received two intraperitoneal injections with an interval of 12 h every 30 days, totaling 8 injections at the end of the experimental period (18 to 21 months). The animals in the St and Ot + St groups performed ST on a ladder 3 times a week, maximal voluntary carrying capacity (MVCC) test monthly. After 120 days, the animals were euthanized; the femur was collected for analysis of biomechanical testing, densitometry, bone microtomography, Raman spectroscopy, tissue PCR, and blood for analysis of bone biomarkers, liver damage, and oxidative stress. The main effects in the Ot group were observed in the maximum load and energy in the compression testing (femoral head), and stiffness and energy in the three-points bending testing (femur diaphysis). In addition, the main effects occurred on the bone mineral density (BMD), cortical thickness (Ct.Th), number of pores (Po.N), polar moment of inertia (J), trabecular thickness (Tb.Th), and connectivity density (Conn.Dn), Bone alkaline phosphatase (Alp), Tumor necrosis factor receptor superfamily member 11b (Opg), Tumor necrosis factor ligand superfamily member 11 (Rankl) and Cathepsin K (Ctsk) expression. There was an effect in the tartrate-resistant acid phosphatase (TRAP) and alkaline phosphatase (ALP). In the St group, the main effect was observed on the energy (compression and the three-points bending), stiffness, aBMD, BMD, cortical bone area (Ct.Ar), Po.N, trabecular bone volume (BV/TV), Tb.Th and in the mineralization ratio (ѵ₁PO₄/proline), Runt-related transcription factor 2 (Runx2), Bone morphogenetic protein 2 (Bmp2), Alp, Osteopontin/secreted phosphoprotein 1 (Opn/Spp1), Opg, Tumor necrosis factor receptor superfamily member 11ª (Rank), Rankl, Ctsk expression. There was an effect in the TRAP and ALP. The interaction in the combination of therapies in the Ot + St group was verified in energy to maximum load (compression and three-points bending testing), stiffness, BMD, Ct.Th, J, Tb.Th and ѵ₁PO₄/proline. In the gene analysis there was interaction in the Runx2, Osterix/Sp7 transcription factor (Osx/Sp7), Bmp2, Alp, Osteocalcin/Bone gamma-carboxyglutamate protein (Ocn/Bglap), Opg, Rankl and Acid phosphatase 5, tartrate resistant (Trap/Acp5) expression. In addition, the combination of OT and ST resulted in a higher maximum load compared to the Veh group, with higher BV/TV than the Ot group, higher Rankl and Ctsk expression than Veh and Ot groups, and lower Po.N and lower activity of TRAP than the other groups. In oxidative stress, total antioxidant capacity (TAC) was lower. These results showed that the combination of interventions is a promising anabolic strategy for the prevention of osteoporosis in the period of periestropause, standing out from the effects of isolated interventions.

Meta-Learning Analysis of Ultrasonic Guided Waves for Coated Cortical Bone Characterization

Due to its sensitivity to geometrical and mechanical properties of waveguides, ultrasonic guided waves (UGWs) propagating in cortical bones play an important role in the early diagnosis of osteoporosis. However, as impacts of overlaid soft tissues are complex, it remains challenging to retrieve bone properties accurately. Meta-learning, i.e., learning to learn, is capable of extracting transferable features from a few data and, thus, suitable to capture potential characteristics, leading to accurate bone assessment. In this study, we investigate the feasibility to apply the multichannel identification neural network (MCINN) to estimate the thickness and bulk velocities of coated cortical bone. It minimizes the effects of soft tissue by extracting specific features of UGW, which shares the same cortical properties, while the overlaid soft tissue varies. Distinguished from most reported methods, this work moves from the hand-design inversion scheme to data-driven assessment by automatically mapping features of UGW to the space of bone properties. The MCINN was trained and validated using simulated datasets produced by the finite-difference time-domain (FDTD) method and then applied to experimental data obtained from cortical bovine bone plates overlaid with soft tissue mimics. A good match was found between experimental trajectories and theoretical dispersion curves. The results demonstrated that the proposed method was feasible to assess the thickness of coated cortical bone plates.

Spatial assessment of femoral neck bone density and microstructure in hip osteoarthritis

Osteoarthritis (OA) is known to involve profound changes in bone density and microstructure near to, and even distal to, the joint. Critically, however, a full, spatial picture of these abnormalities has not been well documented in a quantitative fashion in hip OA. Here, micro-computed tomography (44.8 μm/voxel) and data-driven computational anatomy were used to generate 3-D maps of the distribution of bone density and microstructure in human femoral neck samples with early (6F/4M, mean age = 51.3 years), moderate (14F/8M, mean age = 60 years), and severe (16F/6M, mean age = 63.3 years) radiographic OA. With increasing severity of radiographic OA, there was decreased cortical bone mineral density (BMD) (p=0.003), increased cortical thickness (p=0.001), increased cortical porosity (p=0.0028), and increased cortical cross-sectional area (p=0.0012, due to an increase in periosteal radius (p=0.018)), with no differences detected in the total femoral neck or trabecular compartment measures. No OA-related region-specific differences were detected through Statistical Parametric Mapping, but there were trends towards decreased tissue mineral density (TMD) in the inferior femoral neck with increasing OA severity (0.050 < p ≤ 0.091), possibly due to osteophytes. Overall, the lack of differences in cortical TMD among radiographic OA groups indicated that the decrease in cortical BMD with increasing OA severity was largely due to the increased cortical porosity rather than decreased tissue mineralization. As porosity is inversely associated with stiffness and strength in cortical bone, increased porosity may offset the effect that increased cortical cross-sectional area would be expected to have on reducing stresses within the femoral neck. The use of high-resolution imaging and quantitative spatial assessment in this study provide insight into the heterogeneous and multi-faceted changes in density and microstructure in hip OA, which have implications for OA progression and fracture risk.

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.

A Comparative Study on the Multiscale Mechanical Responses of Human Femoral Neck Between the Young and the Elderly Using Finite Element Method

Background: Femoral neck fracture (FNF) is the most serious bone disease in the elderly population. The multiscale mechanical response is a key to predicting the strength of the femoral neck, assessing the risk of FNF, and exploring the role of mechanosensation and mechanotransmission in bone remodeling, especially in the context of aging bone.

Methods: Multiscale finite element (FE) models of the proximal femur for both young and elderly people were developed. The models included organ scale (proximal femur), tissue scale (cortical bone), tissue element scale (osteon), and cell scale [osteocyte lacuna-canalicular network (LCN) and extracellular matrix (ECM), OLCEM]. The mechanical responses of cortical bone and osteocytes in the mid-femoral neck and the differences in mechanical responses between these two scales were investigated.

Results: The mechanical responses of cortical bone and osteocyte showed significant differences between the elderly and the young. The minimum principal strains and mean SEDs of cortical bone in the elderly were 2.067–4.708 times and 3.093–14.385 times of the values in the young, respectively; the minimum principal strains and mean SEDs of osteocyte in the elderly were 1.497–3.246 times and 3.044–12 times of the values in the young, respectively; the amplification factors of minimum principal strain in the inferior (Inf), anterior (Ant), and posterior (Post) quadrants in the young were 1.241–1.804 times of the values in the elderly, but the amplification factor of minimum principal strain in the superior (Sup) quadrant was 87.4% of the value in the elderly; the amplification factors of mean SED in the young were 1.124–9.637 times of the values in the elderly.

Conclusion: The mass and bone mineral density (BMD) of cortical bone in the femoral neck is closely related to the mechanical response of osteocytes, which provides a new idea for improving cortical bone quality. Perhaps cortical bone quality could be improved by stimulating osteocytes. Quadrantal differences of bone quality in the mid-femoral neck should be considered to improve fracture risk prediction in the future.

Decreased cortical bone density and mechanical strength with associated elevated bone turnover markers at peri-pubertal peak height velocity: a cross-sectional and longitudinal cohort study of 396 girls with adolescent idiopathic scoliosis

Decreased cortical bone density and bone strength at peak height velocity (PHV) were noted in girls with adolescent idiopathic scoliosis (AIS). These findings could provide the link to the previously reported observation that low bone mineral density (BMD) could contribute as one of the prognostic factors for curve progression that mostly occurs during PHV in AIS.

INTRODUCTION

As part of the studies related to aetiopathogenesis of AIS, we assessed bone qualities, bone mechanical strength and bone turnover markers (BTMs) focusing at the peri-pubertal period and PHV in AIS girls.

METHODS

396 AIS girls in two separate cohorts were studied. Skeletal maturity was assessed using the validated thumb ossification composite index (TOCI). Bone qualities and strength were evaluated with high-resolution peripheral quantitative computed tomography (HR-pQCT) and finite element analysis (FEA).

RESULTS

Cohort-A included 179 girls (11.95 ± 0.95 years old). Girls at TOCI-4 had numerically the highest height velocity (0.71 ± 0.24 cm/month) corresponding to the PHV. Subjects at TOCI-4 had lower cortical volumetric BMD (672.36 ± 39.07 mg/mm³), cortical thickness (0.68 ± 0.08 mm) and apparent modulus (1601.54 ± 243.75 N/mm²) than: (a) those at TOCI-1-3 (724.99 ± 32.09 mg/mm³ (p < 0.001), 0.79 ± 0.11 mm (p < 0.001) and 1910.88 ± 374.75 N/mm² (p < 0.001), respectively) and (b) those at TOCI-8 (732.28 ± 53.75 mg/mm³ (p < 0.001), 0.84 ± 0.14 mm (p < 0.001), 1889.11 ± 419.37 N/mm² (p < 0.001), respectively). Cohort-B included 217 girls (12.22 ± 0.89 years old). Subjects at TOCI-4 had higher levels of C-terminal telopeptide of type 1 collagen (1524.70 ± 271.10 pg/L) and procollagen type 1 N-terminal propeptide (941.12 ± 161.39 µg/L) than those at TOCI-8 (845.71 ± 478.55 pg/L (p < 0.001) and 370.08 ± 197.04 µg/L (p < 0.001), respectively).

CONCLUSION

AIS girls had decreased cortical bone density and bone mechanical strength with elevated BTMs at PHV. Coupling of PHV with decreased cortical and FEA parameters could provide the link to the previously reported observation that low BMD could contribute as one of the prognostic factors for curve progression that mostly occurs during PHV in AIS.

Spectrogram decomposition of ultrasonic guided waves for cortical thickness assessment using basis learning

Due to its multimode and dispersive nature, ultrasonic guided waves (UGWs) usually consist of overlapped wave packets, which challenge accurate bone characterization. To overcome this obstacle, a classic idea is to separate individual modes and to extract the corresponding dispersion curves. Reported single-channel mode separation algorithms mainly focused on offering a time-frequency representation (TFR) where the energy distributions of individual modes were apart from each other. However, such approaches are still limited to identifying the modes without significant overlapping in time-frequency domain. In this study, a spectrogram decomposition technique was developed based on a combination strategy of generalized separable nonnegative matrix factorization (GS-NMF) and adaptive basis learning, towards the automatic mode extraction under severe overlapping and low signal-to-noise ratio (SNR). The extracted modes were further used for cortical thickness estimation. The method was verified using broadband simulated and experimental datasets. Experiments were conducted on a bone-mimicking plate and bovine cortical bone plates. For simulated data, the relative errors between extracted and theoretical dispersion curves are 1.33% (SNR = ∞), 1.43% (SNR = 10 dB) and 0.88% (SNR = 5 dB). The root-mean-square errors of the estimated thickness for 3.10 mm-thick bone-mimicking plate, 3.83 mm- and 4.00 mm-thick bovine cortical bone plates are 0.039 mm, 0.049 mm, and 0.052 mm, respectively. It is demonstrated that the proposed method is capable of separating multimodal UGWs even under significantly overlapping and low SNR conditions, further facilitating the UGW-based cortical thickness assessment.

Cortical bone thickness of the distal radius predicts the local bone mineral density

AIMS

The distal radius is a major site of osteoporotic bone loss resulting in a high risk of fragility fracture. This study evaluated the capability of a cortical index (CI) at the distal radius to predict the local bone mineral density (BMD).

METHODS

A total of 54 human cadaver forearms (ten singles, 22 pairs) (19 to 90 years) were systematically assessed by clinical radiograph (XR), dual-energy X-ray absorptiometry (DXA), CT, as well as high-resolution peripheral quantitative CT (HR-pQCT). Cortical bone thickness (CBT) of the distal radius was measured on XR and CT scans, and two cortical indices mean average (CBTavg) and gauge (CBTg) were determined. These cortical indices were compared to the BMD of the distal radius determined by DXA (areal BMD (aBMD)) and HR-pQCT (volumetric BMD (vBMD)). Pearson correlation coefficient (r) and intraclass correlation coefficient (ICC) were used to compare the results and degree of reliability.

RESULTS

The CBT could accurately be determined on XRs and highly correlated to those determined on CT scans (r = 0.87 to 0.93). The CBTavg index of the XRs significantly correlated with the BMD measured by DXA (r = 0.78) and HR-pQCT (r = 0.63), as did the CBTg index with the DXA (r = 0.55) and HR-pQCT (r = 0.64) (all p < 0.001). A high correlation of the BMD and CBT was observed between paired specimens (r = 0.79 to 0.96). The intra- and inter-rater reliability was excellent (ICC 0.79 to 0.92).

CONCLUSION

The cortical index (CBTavg) at the distal radius shows a close correlation to the local BMD. It thus can serve as an initial screening tool to estimate the local bone quality if quantitative BMD measurements are unavailable, and enhance decision-making in acute settings on fracture management or further osteoporosis screening. Cite this article: Bone Joint Res 2021;10(12):820-829.

Multiscale mechanical responses of young and elderly human femurs: A finite element investigation

BACKGROUND

Bone remodeling in the elderly is no longer balanced. As a result, the morphologies and mechanical properties of bone at different scales will change. These changes would affect the mechanical responses of bone, which might exacerbate the imbalance of bone remodeling and even cause age-related bone diseases.

METHODS

Considering those changes, multiscale finite element (FE) models of bone in the young and the elderly were developed that included macroscale (proximal femur), mesoscale (cortical bone), microscale (Haversian system) and sub-microscale (osteocyte-lacuna-canaliculus-extracellular matrix system, OLCES). The stress and strain distributions at different scales and transmissions among different scales were investigated.

RESULTS

The stresses of the elderly at macroscale, mesoscale and microscale were higher than those in the young by 23.7%, 62.5% and 8.0%, respectively, and the stresses of the elderly and the young at sub-microscale were almost the same. The strain of the elderly at macroscale, mesoscale, microscale and sub-microscale were higher than those in the young by 48.6%, 56.8%, 11.9% and 25.1%, respectively. The stress and strain transmission rates (ησand ηε) from mesoscale to microscale were decreased by 1.8%, and 2.5% than those from macroscale to mesoscale in the elderly, respectively; but increased by 13.8%, and 4.7% in the young, respectively. ηε from microscale to sub-microscale in the elderly was higher than that in the young by 21.3%.

CONCLUSIONS

Degeneration of cortical bone mechanical property in the elderly causes increases in stress and strain at macroscale and mesoscale. The reduction of lacunar number in the elderly is not conducive to the mechanical transmission from mesoscale to microscale. The differences in stress and strain at microscale between the young and the elderly are smaller than those at macroscale or mesoscale. The strain stimulus sensed by osteocyte in the elderly is not weakened compared with that in the young.

Focused ultrasound simulation through cortical bone by finite element method. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2021;2021:4362-4365. [PMID: 34892186 DOI: 10.1109/embc46164.2021.9630365] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Bone tissue is constantly changed adapting to its mechanical environment and capable of repairing itself. Ultra-sound has recently been used as a diagnostic technique to assess bone conditions. To optimize the experimental model as best as possible computational simulation techniques have been focused on clinical applications in bone. This study aims to analyze by finite element method the propagation of ultrasound waves along the cortical bone. The wave propagation phenomenon is well studied and described by the Helmholtz equation. The first part of the work analytically solves the Helmholtz equation, and later the COMSOL Multiphysics software is used. It was established a cylindrical geometry as the bone sample. The software analyzes with "Pressure Acoustic, Frequency Domain" module. An extremely fine mesh is used for the solution in order not to lose information. According to the analytical solution, the results show the behavior of the acoustic pressure waves throughout the samples. In addition, attenuation coefficients are calculated for biological materials such as bone and muscle. Simulation methods allow to analyze adjustable parameters in the development of new devices. Thus, optimizing resources and allowing the researcher to better understanding the problem to be solved.

Vascularization Strategies in Bone Tissue Engineering

Bone is a highly vascularized tissue, and its development, maturation, remodeling, and regeneration are dependent on a tight regulation of blood vessel supply. This condition also has to be taken into consideration in the context of the development of artificial tissue substitutes. In classic tissue engineering, bone-forming cells such as primary osteoblasts or mesenchymal stem cells are introduced into suitable scaffolds and implanted in order to treat critical-size bone defects. However, such tissue substitutes are initially avascular. Because of the occurrence of hypoxic conditions, especially in larger tissue substitutes, this leads to the death of the implanted cells. Therefore, it is necessary to devise vascularization strategies aiming at fast and efficient vascularization of implanted artificial tissues. In this review article, we present and discuss the current vascularization strategies in bone tissue engineering. These are based on the use of angiogenic growth factors, the co-implantation of blood vessel forming cells, the ex vivo microfabrication of blood vessels by means of bioprinting, and surgical methods for creating surgically transferable composite tissues.

Bone microarchitecture in patients with autoimmune hepatitis

In patients with autoimmune hepatitis (AIH), osteoporosis represents a common extrahepatic complication, which we recently showed by an assessment of areal bone mineral density (aBMD) via dual-energy x-ray absorptiometry (DXA). However, it is well established that bone quality and fracture risk does not solely depend on aBMD, but also on bone microarchitecture. It is currently not known whether AIH patients exhibit a site-specific or compartment-specific deterioration in the skeletal microarchitecture. In order to assess potential geometric, volumetric, and microarchitectural changes, high-resolution peripheral quantitative computed tomography (HR-pQCT) measurements were performed at the distal radius and distal tibia in female patients with AIH (n = 51) and compared to age-matched female healthy controls (n = 32) as well as to female patients with AIH/primary biliary cholangitis (PBC) overlap syndrome (n = 25) and female patients with PBC alone (PBC, n = 36). DXA at the lumbar spine and hip, clinical characteristics, transient elastography (FibroScan) and laboratory analyses were also included in this analysis. AIH patients showed a predominant reduction of cortical thickness (Ct.Th) in the distal radius and tibia compared to healthy controls (p < .0001 and p = .003, respectively). In contrast, trabecular parameters such as bone volume fraction (BV/TV) did not differ significantly at the distal radius (p = .453) or tibia (p = .508). Linear regression models revealed significant negative associations between age and Ct.Th (95% confidence interval [CI], -14 to -5 μm/year, p < .0001), but not between liver stiffness, cumulative prednisolone dose (even after an adjustment for age), or disease duration with bone microarchitecture. The duration of high-dose prednisolone (≥7.5 mg) was negatively associated with trabecular thickness (Tb.Th) at the distal radius. No differences in bone microarchitecture parameters between AIH, AIH/PBC, and PBC could be detected. In conclusion, AIH patients showed a severe age-dependent deterioration of the cortical bone microarchitecture, which is most likely the major contribution to the observed increased fracture risk in these patients. © 2021 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Cortical Bone Mechanical Assessment via Free Water Relaxometry at 3 T

BACKGROUND

Investigation of cortical bone using magnetic resonance imaging is a developing field, which uses short/ultrashort echo time (TE) pulse sequences to quantify bone water content and to obtain indirect information about bone microstructure.

PURPOSE

To improve the accuracy of the previously proposed technique of free water T₁ quantification and to seek the relationship between cortical bone free water T₁ and its mechanical competence.

STUDY TYPE

Prospective.

SUBJECTS

Twenty samples of bovine tibia bone.

FIELD STRENGTH/SEQUENCES

3.0 T; ultra-fast two-dimensional gradient echo, Radio frequency-spoiled three-dimensional gradient echo.

ASSESSMENT

Cortical bone free water T₁ was quantified via three different methods: inversion recovery (IR), variable flip angle (VFA), and variable repetition time (VTR). Signal-to-noise ratio was measured by dividing the signal of each segmented sample to background noise. Segmentation was done manually. The effect of noise on T₁ quantification was evaluated. Then, the samples were subjected to mechanical compression test to measure the toughness, yield stress, ultimate stress, and Young modulus.

STATISTICAL TESTS

All the statistical analysis (Shapiro-Wilk, way analysis of variance, paired t test, Pearson correlation, and Bland-Altman plot) were done using SPSS.

RESULTS

Significant difference was found between T₁ quantification groups (P < 0.05). Average T₁ of each quantification method differed significantly after adding noise (P < 0.05). VFA-T₁ values significantly correlated with toughness (r = -0.68, P < 0.05), ultimate stress (r = -0.71, P < 0.05), and yield stress (r = -0.62, P < 0.05). No significant correlation was found between VTR-T₁ values and toughness (P = 0.07), ultimate stress (P = 0.47), yield stress (P = 0.30), and Young modulus (P = 0.39).

DATA CONCLUSION

Pore water T₁ value is associated with bone mechanical competence, and VFA method employing short-TE pulse sequence seems a superior technique to VTR method for this quantification.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY: 1.

Cortical Bone Modifications after Radiotherapy: Cortex Porosity and Osteonal Changes Evaluated Over Time

Aiming to evaluate cortical bone microarchitecture and osteonal morphology after irradiation, twelve male New Zealand rabbits were used. The animals were divided: control group (no radiation-NIr); and 3 irradiated groups, sacrificed after: 7 (Ir7d); 14 (Ir14d) and 21 (Ir21d) days. A single radiation dose of 30 Gy was used. Computed microtomography analyzed the cortical microarchitecture: cortical thickness (CtTh), bone volume (BV), total porosity (Ct.Po), intracortical porosity (CtPo-cl), channel/pore number (Po.N), fractal dimension (FD) and degree of anisotropy (Ct.DA). After scan, osteonal morphology was histologically assessed by means: area and perimeter of the osteons (O.Ar; O.p) and of the Haversian canals (C.Ar; C.p). Microtomographic analysis were performed by ANOVA, followed by Tukey and Dunnet tests. Osteon morphology analyses were performed by Kruskal-Wallis, and test Dunn's. Cortical thickness was significant difference (p<0.010) between the NIr and irradiated groups, with thicker cortex at Ir7d (1.15±0.09). The intracortical porosity revealed significant difference (p<0.001) between irradiated groups and NIr, with lower value for Ir7d (0.29±0.09). Bone volume was lower in Ir14d compared to control. Area and perimeter of the osteons were statistically different (p<0.0001) between NIr and Ir7d. Haversian canals also revealed lower values (p<0.0001) in Ir7d (80.57±9.3; 31.63±6.5) compared to NIr and irradiated groups. Cortical microarchitecture was affected by radiation, and the effects appear to be time-dependent, mostly regarding the osteons morphology at the initial days. Cortex structure in Ir21d revealed similarities to control suggesting that microarchitecture resembles normal condition after a period.

A decrease in NAD+ contributes to the loss of osteoprogenitors and bone mass with aging

Age-related osteoporosis is caused by a deficit in osteoblasts, the cells that secrete bone matrix. The number of osteoblast progenitors also declines with age associated with increased markers of cell senescence. The forkhead box O (FoxO) transcription factors attenuate Wnt/β-catenin signaling and the proliferation of osteoprogenitors, thereby decreasing bone formation. The NAD⁺-dependent Sirtuin1 (Sirt1) deacetylates FoxOs and β-catenin in osteoblast progenitors and, thereby, increases bone mass. However, it remains unknown whether the Sirt1/FoxO/β-catenin pathway is dysregulated with age in osteoblast progenitors. We found decreased levels of NAD⁺ in osteoblast progenitor cultures from old mice, associated with increased acetylation of FoxO1 and markers of cell senescence. The NAD⁺ precursor nicotinamide riboside (NR) abrogated FoxO1 and β-catenin acetylation and several marker of cellular senescence, and increased the osteoblastogenic capacity of cells from old mice. Consistent with these effects, NR administration to C57BL/6 mice counteracted the loss of bone mass with aging. Attenuation of NAD⁺ levels in osteoprogenitor cultures from young mice inhibited osteoblastogenesis in a FoxO-dependent manner. In addition, mice with decreased NAD⁺ in cells of the osteoblast lineage lost bone mass at a young age. Together, these findings suggest that the decrease in bone formation with old age is due, at least in part, to a decrease in NAD⁺ and dysregulated Sirt1/FoxO/β-catenin pathway in osteoblast progenitors. NAD⁺ repletion, therefore, represents a rational therapeutic approach to skeletal involution.

Bulk Wave Velocities in Cortical Bone Reflect Porosity and Compression Strength

The goal of this study was to evaluate whether ultrasonic velocities in cortical bone can be considered as a proxy for mechanical quality of cortical bone tissue reflected by porosity and compression strength. Micro-computed tomography, compression mechanical testing and resonant ultrasound spectroscopy were used to assess, respectively, porosity, strength and velocity of bulk waves of both shear and longitudinal polarisations propagating along and perpendicular to osteons, in 92 cortical bone specimens from tibia and femur of elderly human donors. All velocities were significantly associated with strength (r = 0.65-0.83) and porosity (r = -0.64 to -0.77). Roughly, according to linear regression models, a decrease in velocity of 100 m/s corresponded to a loss of 20 MPa in strength (which is approximately 10% of the largest strength value) and to an increase in porosity of 5%. These results provide a rationale for the in vivo measurement of one or several velocities for the diagnosis of bone fragility.

Exosome-guided bone targeted delivery of Antagomir-188 as an anabolic therapy for bone loss

The differentiation shift from osteogenesis to adipogenesis of bone marrow mesenchymal stem cells (BMSCs) characterizes many pathological bone loss conditions. Stromal cell-derived factor-1 (SDF1) is highly enriched in the bone marrow for C-X-C motif chemokine receptor 4 (CXCR4)-positive hematopoietic stem cell (HSC) homing and tumor bone metastasis. In this study, we displayed CXCR4 on the surface of exosomes derived from genetically engineered NIH-3T3 cells. CXCR4⁺ exosomes selectively accumulated in the bone marrow. Then, we fused CXCR4⁺ exosomes with liposomes carrying antagomir-188 to produce hybrid nanoparticles (NPs). The hybrid NPs specifically gathered in the bone marrow and released antagomir-188, which promoted osteogenesis and inhibited adipogenesis of BMSCs and thereby reversed age-related trabecular bone loss and decreased cortical bone porosity in mice. Taken together, this study presents a novel way to obtain bone-targeted exosomes via surface display of CXCR4 and a promising anabolic therapeutic approach for age-related bone loss.

•

Surface display of CXCR4 grants exosomes bone targeting properties.

•

Exosome-liposome hybrid nanoparticles carrying nucleic acid target bone.

•

Antagomir-188 loaded hybrid nanoparticles regulate MSC differentiation in aged mice.

Cortical bone thickness predicts the quantitative bone mineral density of the proximal humerus

Cortical thickness determined at the humerus can serve as an easy and reliable screening tool to predict the local bone status when quantitative bone mineral density (BMD) measurements are not available. It can therefore serve as a rapid screening tool in fragility fractures to identify patients requiring further diagnostic or osteoporosis treatment.

INTRODUCTION

Quantitative bone mineral density (BMD) of the humerus is difficult to determine but relevant for osteoporosis and fracture treatment. Dual-energy X-ray absorptiometry (DXA) of the femur and lumbar spine overestimates the humeral BMD and is not ubiquitously available. Therefore, this study evaluated whether the cortical bone thickness (CBT) of the humerus or DXA of the forearm is able to predict humeral BMD.

METHODS

Humeral BMD of 54 upper cadaver extremities (22 pairs, 10 single) (19-90 years) was determined by high-resolution peripheral-quantitative-computed-tomography (HR-pQCT) (volumetric BMD (vBMD)) and DXA (areal BMD (aBMD)) of the proximal humerus and distal forearm. Average and gauge cortical bone thickness (CBTavg/ CBTg) of the humeral diaphysis was determined from standard radiographs (XR) and computed-tomography (CT) and compared to the humeral BMD. Pearson (r) and intraclass-correlation-coefficients (ICC) were used to compare results and rater-reliability.

RESULTS

CBTavg from XR strongly correlated with the humeral BMD (r = 0.78 aBMD (DXA) and r = 0.64 vBMD (HR-pQCT) (p < 0.0001)). The CBTg revealed a weaker correlation (r = 0.57 aBMD and r = 0.43 vBMD). CBT derived from XR strongly correlated to those from the CT (r = 0.82-0.90) and showed an excellent intra- and inter-rater correlation (ICC 0.79-0.92). Distal forearm aBMD correlated well with the humeral aBMD (DXA) (r = 0.77) and paired specimens highly correlated to the contralateral side (humerus r = 0.89, radius r = 0.97).

CONCLUSIONS

The CBTavg can reliably be determined from standard radiographs and allows a good prediction of quantitative humeral bone mineral density (aBMD or vBMD) if measurements are not available. Furthermore, the distal forearm or the contralateral humerus can serve as a side to estimate the BMD if the ipsilateral side is impaired.

Cortical bone viscoelastic damping assessed with resonant ultrasound spectroscopy reflects porosity and mineral content

Viscoelasticity is an essential property of bone related to fragility, which is altered in aging and bone disease. Bone viscoelastic behavior is attributed to several mechanisms involving collagen and mineral properties, porosities, and bone hierarchical tissue organization. We aimed to assess the relationships between cortical bone viscoelastic damping measured with Resonant Ultrasound Spectroscopy (RUS), microstructural and compositional characteristics. We measured 52 bone specimens from the femur of 26 elderly human donors. RUS provided a shear damping coefficient at a frequency of the order of 150 kHz. The characteristics of the structure of the vascular pore network and tissue mineral density were measured using synchrotron radiation high-resolution computed tomography (SR-μCT). Fourier transformed infrared microspectroscopy (FTIRM) was used to quantify mineral-to-organic phase ratio, mineral maturity, crystallinity, and collagen maturity. Cross-links were quantified from biochemistry. Viscoelastic damping was found to increase with vascular porosity (r=0.68), to decrease with the degree of mineralization of the extravascular matrix (r=-0.68), and was marginally affected by collagen. We built a multilinear model suggesting that when porosity is controlled, the variation of mineral content explains a small additional part of the variability of damping. The work supports the consideration of viscoelasticity measurement as a potential biomarker of fragility and provides a documentation of bone viscoelastic behavior and its determinants in a frequency range rarely investigated.

Pulsed Electromagnetic Fields Ameliorate Skeletal Deterioration in Bone Mass, Microarchitecture, and Strength by Enhancing Canonical Wnt Signaling-Mediated Bone Formation in Rats with Spinal Cord Injury

Spinal cord injury (SCI) leads to extensive bone loss and high incidence of low-energy fractures. Pulsed electromagnetic fields (PEMF) treatment, as a non-invasive biophysical technique, has proven to be efficient in promoting osteogenesis. The potential osteoprotective effect and mechanism of PEMF on SCI-related bone deterioration, however, remain unknown. The spinal cord of rats was transected at vertebral level T12 to induce SCI. Thirty rats were assigned to the control, SCI, and SCI+PEMF groups (n = 10). One week after surgery, the SCI+PEMF rats were subjected to PEMF (2.0 mT, 15 Hz, 2 h/day) for eight weeks. Micro-computed tomography results showed that PEMF significantly ameliorated trabecular and cortical bone microarchitecture deterioration induced by SCI. Three-point bending and nanoindentation assays revealed that PEMF significantly improved bone mechanical properties in SCI rats. Serum biomarker and bone histomorphometric analyses demonstrated that PEMF enhanced bone formation, as evidenced by significant increase in serum osteocalcin and P1NP, mineral apposition rate, and osteoblast number on bone surface. The PEMF had no impact, however, on serum bone-resorbing cytokines (TRACP 5b and CTX-1) or osteoclast number on bone surface. The PEMF also attenuated SCI-induced negative changes in osteocyte morphology and osteocyte survival. Moreover, PEMF significantly increased skeletal expression of canonical Wnt ligands (Wnt1 and Wnt10b) and stimulated their downstream p-GSK3β and β-catenin expression in SCI rats. This study demonstrates that PEMF can mitigate the detrimental consequence of SCI on bone quantity/quality, which might be associated with canonical Wnt signaling-mediated bone formation, and reveals that PEMF may be a promising biophysical approach for resisting osteopenia/osteoporosis after SCI in clinics.

Long bone histomorphogenesis of the naked mole-rat: Histodiversity and intraspecific variation

Lacking fur, living in eusocial colonies and having the longest lifespan of any rodent, makes naked mole-rats (NMRs) rather peculiar mammals. Although they exhibit a high degree of polymorphism, skeletal plasticity and are considered a novel model to assess the effects of delayed puberty on the skeletal system, scarce information on their morphogenesis exists. Here, we examined a large ontogenetic sample (n = 76) of subordinate individuals to assess the pattern of bone growth and bone microstructure of fore- and hindlimb bones by using histomorphological techniques. Over 290 undecalcified thin cross-sections from the midshaft of the humerus, ulna, femur, and tibia from pups, juveniles and adults were analyzed with polarized light microscopy. Similar to other fossorial mammals, NMRs exhibited a systematic cortical thickening of their long bones, which clearly indicates a conserved functional adaptation to withstand the mechanical strains imposed during digging, regardless of their chisel-tooth predominance. We describe a high histodiversity of bone matrices and the formation of secondary osteons in NMRs. The bones of pups are extremely thin-walled and grow by periosteal bone formation coupled with considerable expansion of the medullary cavity, a process probably tightly regulated and adapted to optimize the amount of minerals destined for skeletal development, to thus allow the female breeder to produce a higher number of pups, as well as several litters. Subsequent cortical thickening in juveniles involves high amounts of endosteal bone apposition, which contrasts with the bone modeling of other mammals where a periosteal predominance exists. Adults have bone matrices predominantly consisting of parallel-fibered bone and lamellar bone, which indicate intermediate to slow rates of osteogenesis, as well as the development of poorly vascularized lamellar-zonal tissues separated by lines of arrested growth (LAGs) and annuli. These features reflect the low metabolism, low body temperature and slow growth rates reported for this species, as well as indicate a cyclical pattern of osteogenesis. The presence of LAGs in captive individuals was striking and indicates that postnatal osteogenesis and its consequent cortical stratification most likely represents a plesiomorphic thermometabolic strategy among endotherms which has been suggested to be regulated by endogenous rhythms. However, the generalized presence of LAGs in this and other subterranean taxa in the wild, as well as recent investigations on variability of environmental conditions in burrow systems, supports the hypothesis that underground environments experience seasonal fluctuations that may influence the postnatal osteogenesis of animals by limiting the extension of burrow systems during the unfavorable dry seasons and therefore the finding of food resources. Additionally, the intraspecific variation found in the formation of bone tissue matrices and vascularization suggested a high degree of developmental plasticity in NMRs, which may help explaining the polymorphism reported for this species. The results obtained here represent a valuable contribution to understanding the relationship of several aspects involved in the morphogenesis of the skeletal system of a mammal with extraordinary adaptations.

Reference Intervals for Bone Histomorphometric Measurements Based on Data from Healthy Premenopausal Women

This study has established the normal reference intervals for bone histomorphometric measurements derived from healthy premenopausal women, which is rarely available. We presented the static and dynamic bone histomorphometric data from trans-iliac bone biopsies in 62 healthy premenopausal women (19 blacks and 43 whites, ages 20-53 years). There were no significant differences in age and BMI between black and white women. Since there was no significant difference in bone remodeling between the two ethnic groups, we pooled data of all 62 premenopausal women to establish normal reference intervals for bone histomorphometry. The results provide normal reference intervals for both static and dynamic histomorphometric variables in cancellous and cortical bone of the ilium. None of the bone remodeling-related variables correlated with age or BMI. This study provides reference intervals for bone histomorphometric measurements in both cancellous and cortical bone of the ilium, which would be helpful in the evaluation of bone health in women.

Cortical Bone Porosity in Rabbit Models of Osteoporosis

Cortical bone porosity is intimately linked with remodeling, is of growing clinical interest, and is increasingly accessible by imaging. Thus, the potential of animal models of osteoporosis (OP) to provide a platform for studying how porosity develops and responds to interventions is tremendous. To date, rabbit models of OP have largely focused on trabecular microarchitecture or bone density; some such as ovariectomy (OVX) have uncertain efficacy and cortical porosity has not been extensively reported. Our primary objective was to characterize tibial cortical porosity in rabbit-based models of OP, including OVX, glucocorticoids (GC), and OVX + GC relative to controls (SHAM). We sought to: (i) test the hypothesis that intracortical remodeling is elevated in these models; (ii) contrast cortical remodeling and porosity in these models with that induced by parathyroid hormone (1-34; PTH); and (iii) contrast trabecular morphology in the proximal tibia across all groups. Evidence that an increase in cortical porosity occurred in all groups was observed, although this was the least robust for GC. Histomorphometric measures supported the hypothesis that remodeling rate was elevated in all groups and also revealed evidence of uncoupling of bone resorption and formation in the GC and OVX + GC groups. For trabecular bone, a pattern of loss was observed for OVX, GC, and OVX + GC groups, whereas the opposite was observed for PTH. Change in trabecular number best explained these patterns. Taken together, the findings indicated rabbit models provide a viable and varied platform for the study of OP and associated changes in cortical remodeling and porosity. Intriguingly, the evidence revealed differing effects on the cortical and trabecular envelopes for the PTH model. © 2020 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR)..

A microRNA Approach to Discriminate Cortical Low Bone Turnover in Renal Osteodystrophy

A main obstacle to diagnose and manage renal osteodystrophy (ROD) is the identification of intracortical bone turnover type (low, normal, high). The gold standard, tetracycline‐labeled transiliac crest bone biopsy, is impractical to obtain in most patients. The Kidney Disease Improving Global Outcomes Guidelines recommend PTH and bone‐specific alkaline phosphatase (BSAP) for the diagnosis of turnover type. However, PTH and BSAP have insufficient diagnostic accuracy to differentiate low from non‐low turnover and were validated for trabecular turnover. We hypothesized that four circulating microRNAs (miRNAs) that regulate osteoblast (miRNA‐30b, 30c, 125b) and osteoclast development (miRNA‐155) would provide superior discrimination of low from non‐low turnover than biomarkers in clinical use. In 23 patients with CKD 3‐5D, we obtained tetracycline‐labeled transiliac crest bone biopsy and measured circulating levels of intact PTH, BSAP, and miRNA‐30b, 30c, 125b, and 155. Spearman correlations assessed relationships between miRNAs and histomorphometry and PTH and BSAP. Diagnostic test characteristics for discriminating low from non‐low intracortical turnover were determined by receiver operator curve analysis; areas under the curve (AUC) were compared by χ² test. In CKD rat models of low and high turnover ROD, we performed histomorphometry and determined the expression of bone tissue miRNAs. Circulating miRNAs moderately correlated with bone formation rate and adjusted apposition rate at the endo‐ and intracortical envelopes (ρ = 0.43 to 0.51; p < 0.05). Discrimination of low versus non‐low turnover was 0.866, 0.813, 0.813, and 0.723 for miRNA‐30b, 30c, 125b, and 155, respectively, and 0.509 and 0.589 for PTH and BSAP, respectively. For all four miRNAs combined, the AUC was 0.929, which was superior to that of PTH and BSAP alone and together (p < 0.05). In CKD rats, bone tissue levels of the four miRNAs reflected the findings in human serum. These data suggest that a panel of circulating miRNAs provide accurate noninvasive identification of bone turnover in ROD. © 2020 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Theoretical concept of cortical to cancellous bone transformation

Microstructures of cortical and cancellous bones are altered continually by load-adaptive remodeling; in addition, their cellular mechanisms are similar despite the remarkably different porosities. The cortico-cancellous transitional zone is a site of vigorous remodeling, and intracortical remodeling cavitates the inner cortex to promote its trabecularization, which is considered the main cause of bone loss because of aging. Therefore, to prevent and treat age-related cortical bone loss effectively, it is indispensable to gain an integrated understanding of the cortical to the cancellous bone transformation via remodeling. We propose a novel theoretical concept to account for the transformation of dense cortical bone to porous cancellous bone. We develop a mathematical model of cortical and cancellous bone remodeling based on the concept that bone porosity is determined by the balance between the load-bearing function of mineralized bone and the material-transporting function of bone marrow. Remodeling simulations using this mathematical model enable the reproduction of the microstructures of cortical and cancellous bones simultaneously. Furthermore, current remodeling simulations have the potential to replicate cortical-to-cancellous bone transformation based on changes in the local balance between bone formation and resorption. We anticipate that the proposed mathematical model of cortical and cancellous bone remodeling will contribute to highlighting the essential features of cortical bone loss due to trabecularization of the cortex and help predict its spatial and temporal behavior during aging.

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A novel theoretical concept to account for cortical-to-cancellous bone transformation is proposed.

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A remodeling model to reproduce cortical and cancellous bone microstructures is developed.

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The remodeling simulation replicates cortical-to-cancellous bone transformation.

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The proposed method is valuable in clinical applications such as in predicting age-related cortical bone loss.

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

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

Distal radius bone microarchitecture: what are the differences between age 25 and old age?

This study reported that the transitional zones in older adults were enlarged at the expense of the compact-appearing cortex with a greater porosity in all cortical sub-compartments. The magnitude of differences in areal and volumetric bone mineral density (aBMD, vBMD) between older and younger groups was similar.

INTRODUCTION

Aging is strongly associated with bone loss, but little is known about magnitudes of differences in bone microarchitectures, aBMD, and vBMD from peak bone mass (PBM) to senescence. We aimed to describe differences in aBMD, vBMD, and bone microarchitecture parameters at the distal radius between older and young adults.

METHODS

We compared 201 participants, aged 62-89 years (female 47%) and 196 participants, aged 24-28 years (female 38%). Bone microarchitecture parameters at distal radius were measured using high-resolution peripheral computed tomography (HRpQCT). aBMD was measured using dual-energy X-ray absorptiometry (DXA). Unpaired t tests and chi-square tests were used to compare differences in means and proportions as appropriate.

RESULTS

Older adults had thinner compact-appearing cortices with larger (cross-sectional area: outer 30.96 mm² vs. 28.38 mm², inner 36.34 mm² vs. 32.93 mm²) and thicker (outer 0.57 mm vs. 0.54 mm, inner 0.71 mm vs. 0.65 mm) transitional zones compared with young adults (all p < 0.05). Cortical porosity was modestly higher in older adults than in young adults (54% vs. 49%, p < 0.001). The magnitude of the difference in hip aBMD between older and young adults was slightly lower than of total radial vBMD (- 0.51 SD vs. - 0.78 SD).

CONCLUSION

Compared with young adults at the time of PBM, the transitional zones in older adults were enlarged at the expense of the compact-appearing cortex with a greater porosity in all cortical sub-compartments. The similar SD differences in aBMD and vBMD between older and younger groups suggest that the differences in bone area are not leading to major artefactual change in aBMD.

Evaluation and Management of Osteoporosis and Sarcopenia in Patients with Distal Radius Fractures

Distal radius fractures (DRFs) are one of the most common fractures seen in elderly people. Patients with DRFs have a high incidence of osteoporosis and an increased risk of subsequent fractures, subtle early physical performance changes, and a high prevalence of sarcopenia. Since DRFs typically occur earlier than vertebral or hip fractures, they reflect early changes of the bone and muscle frailty and provide physicians with an opportunity to prevent progression of frailty and secondary fractures. In this review, we will discuss the concept of DRFs as a medical condition that is at the start of the fragility fracture cascade, recent advances in the diagnosis of bone fragility including emerging importance of cortical porosity, fracture healing with osteoporosis medications, and recent progress in research on sarcopenia in patients with DRFs.

Lack of the Thyroid Hormone Transporter Mct8 in Osteoblast and Osteoclast Progenitors Increases Trabecular Bone in Male Mice

Background: Bone is an important target of thyroid hormones (THs), which require transport into target cells to exert their actions. Recently, the TH-specific monocarboxylate transporter 8 (Mct8) was reported as a regulator of bone mass in male mice. However, its global deletion leads to high 3,3',5-L-triiodothyronine (T3) serum concentrations that may mask direct effects of Mct8-deficiency on bone. In this study, we assessed the bone cell intrinsic function of Mct8 ex vivo and in vivo using conditional Mct8-knockout lines specifically targeting osteoclast and osteoblast progenitors, as well as mature osteoblasts and osteocytes. Materials and Methods: Twelve-week-old male mice with a global Mct8-deficiency or a conditional Mct8-knockout in osteoclast precursors, osteoprogenitors, or mature osteoblasts/osteocytes were analyzed regarding their bone microarchitecture, turnover, and strength. Furthermore, ex vivo studies were conducted to investigate the role of Mct8 in bone cell differentiation and functionality, as well as TH uptake. Results: Global Mct8-knockout mice demonstrated 1.7-fold higher T3 serum concentrations and trabecular bone loss (-28%) likely due to an increased bone turnover as shown by increased osteoblast (+45%) and osteoclast numbers (+41%). However, cortical bone mineral density was increased. Ex vivo cultures of bone marrow-derived osteoblasts and osteoclasts revealed highest expression of Mct8 in mature bone cells. In addition, Mct8-deficiency resulted in a lower mRNA expression of osteoblast and osteoclast differentiation markers, as well as a reduced mineralization capacity and osteoclast numbers, respectively, indicating a bone cell intrinsic role of Mct8. In fact, conditional Mct8-knockout and inhibition of Mct8 in osteoblasts led to an attenuated T3 uptake ex vivo. In vivo, osteoprogenitor-specific Mct8-knockout enhanced trabecular bone volume (+16%) with osteoblast numbers being increased 3.7 fold. Interestingly, Mct8-deficiency in osteoprogenitors and late osteoblasts/osteocytes both resulted in cortical bone loss. Finally, Mct8-deletion in osteoclast progenitors increased trabecular bone volume (+20%) due to reduced osteoclast numbers (-32%), whereas osteoblast numbers were enhanced (+25%). Conclusions: This study confirms that high systemic T3 in global Mct8-knockout mice masks the direct effect of Mct8. Moreover, it identifies Mct8 as a critical regulator of trabecular vs. cortical bone by regulating T3 uptake and highlights its cell intrinsic role in osteoclast and osteoblast progenitors.

Ultrasound-Based Estimates of Cortical Bone Thickness and Porosity Are Associated With Nontraumatic Fractures in Postmenopausal Women: A Pilot Study

Recent ultrasound (US) axial transmission techniques exploit the multimode waveguide response of long bones to yield estimates of cortical bone structure characteristics. This pilot cross-sectional study aimed to evaluate the performance at the one-third distal radius of a bidirectional axial transmission technique (BDAT) to discriminate between fractured and nonfractured postmenopausal women. Cortical thickness (Ct.Th) and porosity (Ct.Po) estimates were obtained for 201 postmenopausal women: 109 were nonfractured (62.6 ± 7.8 years), 92 with one or more nontraumatic fractures (68.8 ± 9.2 years), 17 with hip fractures (66.1 ± 10.3 years), 32 with vertebral fractures (72.4 ± 7.9 years), and 17 with wrist fractures (67.8 ± 9.6 years). The areal bone mineral density (aBMD) was obtained using DXA at the femur and spine. Femoral aBMD correlated weakly, but significantly with Ct.Th (R = 0.23, p < 0.001) and Ct.Po (R = -0.15, p < 0.05). Femoral aBMD and both US parameters were significantly different between the subgroup of all nontraumatic fractures combined and the control group (p < 0.05). The main findings were that (1) Ct.Po was discriminant for all nontraumatic fractures combined (OR = 1.39; area under the receiver operating characteristic curve [AUC] equal to 0.71), for vertebral (OR = 1.96; AUC = 0.84) and wrist fractures (OR = 1.80; AUC = 0.71), whereas Ct.Th was discriminant for hip fractures only (OR = 2.01; AUC = 0.72); there was a significant association (2) between increased Ct.Po and vertebral and wrist fractures when these fractures were not associated with any measured aBMD variables; (3) between increased Ct.Po and all nontraumatic fractures combined independently of aBMD neck; and (4) between decreased Ct.Th and hip fractures independently of aBMD femur. BDAT variables showed comparable performance to that of aBMD neck with all types of fractures (OR = 1.48; AUC = 0.72) and that of aBMD femur with hip fractures (OR = 2.21; AUC = 0.70). If these results are confirmed in prospective studies, cortical BDAT measurements may be considered useful for assessing fracture risk in postmenopausal women. © 2019 American Society for Bone and Mineral Research.