Deuterium nuclear magnetic resonance unambiguously quantifies pore and collagen‐bound water in cortical bone

Bone water (BW) plays a pivotal role in nutrient transport and conferring bone with its viscoelastic mechanical properties. BW is partitioned between the pore spaces of the Haversian and lacuno‐canalicular system, and water predominantly bound to the matrix proteins (essentially collagen). The general model of BW is that the former predominantly experiences fast isotropic molecular reorientation, whereas water in the bone matrix undergoes slower anisotropic rotational diffusion. Here, we provide direct evidence for the correctness of this model and show that unambiguous quantification in situ of these two functionally and dynamically different BW fractions is possible. The approach chosen relies on nuclear magnetic resonance (NMR) of deuterium (²H) that unambiguously separates and quantifies the two fractions on the basis of their distinguishing microdynamic properties. Twenty‐four specimens of the human tibial cortex from 6 donors (3 male, 3 female, ages 27–83 years) were cored and ²H spectra recorded at 62 MHz (9.4 Tesla) on a Bruker Instruments DMX 400 spectrometer after exchange of native BW with ²H₂O. Spectra consisted of a doublet signal resulting from quadrupole interaction of water bound to collagen. Doublet splittings were found to depend on the orientation of the osteonal axis with respect to the magnetic field direction (8.2 and 4.3 kHz for parallel and perpendicular orientation, respectively). In contrast, the isotropically reorienting pore‐resident water yielded a single resonance line superimposed on the doublet. Nulling of the singlet resonance allowed separation of the two fractions. The results indicate that in human cortical bone 60% to 80% of detectable BW is collagen‐bound. Porosity determined as the difference between total BW and collagen bound water fraction was found to strongly parallel micro–computed tomography (µCT)‐based measurements (R² = 0.91). Our method provides means for direct validation of emerging relaxation‐based measurements of cortical bone porosity by proton MRI. © 2012 American Society for Bone and Mineral Research © 2012 American Society for Bone and Mineral Research     

Magnetic resonance imaging measurements of bone density and cross-sectional geometry

Magnetic resonance imaging (MRI) is commonly used in the assessment of the musculoskeletal system and associated pathology. The ability of MRI to measure the signals from water and lipid protons enables quantitative measurements of bone porosity. The goal of this investigation was to demonstrate that the density and cross-sectional geometry of whole bones can be noninvasively measured using MRI. Ten trabecular specimens cored from whale vertebrae were used to compare apparent bone density measured directly, and using a quantitative MRI algorithm. Bone density and several cross-sectional geometric properties were also measured using MRI in the distal tibia of 14 volunteers. The MRI measurements were compared with measurements made using quantitative-computed tomography (QCT). A proton density sequence was used for all MRI studies. A porosity phantom was included in the MRI examinations and used to convert the MRI signal intensity to bone volume fraction. Bone density and cross-sectional bone geometry were calculated from the bone volume fractions by assuming constant tissue properties. The apparent density of trabecular bone cores measured directly and using quantitative MRI were linearly related (r²= 0.959; P < 0.01). A strong linear relation also existed between MRI and QCT measurements of ash density (r²= 0.923; P < 0.01) and cross-sectional geometric properties (r²= 0.976–0.992; P < 0.01). MRI data can be used to measure bone density and cross-sectional geometry of whole bones if a proton density sequence is used to homogenize differences in marrow composition and a porosity phatom is used for slice-specific volume fraction calibration. Received: 3 November 1998 / Accepted: 1 July 1999     

Femoral Neck External Size but not aBMD Predicts Structural and Mass Changes for Women Transitioning Through Menopause

The impact of adult bone traits on changes in bone structure and mass during aging is not well understood. Having shown that intracortical remodeling correlates with external size of adult long bones led us to hypothesize that age‐related changes in bone traits also depend on external bone size. We analyzed hip dual‐energy X‐ray absorptiometry images acquired longitudinally over 14 years for 198 midlife women transitioning through menopause. The 14‐year change in bone mineral content (BMC, R² = 0.03, p = 0.015) and bone area (R² = 0.13, p = 0.001), but not areal bone mineral density (aBMD, R² = 0.00, p = 0.931) correlated negatively with baseline femoral neck external size, adjusted for body size using the residuals from a linear regression between baseline bone area and height. The dependence of the 14‐year changes in BMC and bone area on baseline bone area remained significant after adjusting for race/ethnicity, postmenopausal hormone use, the 14‐year change in weight, and baseline aBMD, weight, height, and age. Women were sorted into tertiles using the baseline bone area‐height residuals. The 14‐year change in BMC (p = 0.009) and bone area (p = 0.001) but not aBMD (p = 0.788) differed across the tertiles. This suggested that women showed similar changes in aBMD for different structural and biological reasons: women with narrow femoral necks showed smaller changes in BMC but greater increases in bone area compared to women with wide femoral necks who showed greater losses in BMC but without large compensatory increases in bone area. This finding is opposite to expectations that periosteal expansion acts to mechanically offset bone loss. Thus, changes in femoral neck structure and mass during menopause vary widely among women and are predicted by baseline external bone size but not aBMD. How these different structural and mass changes affect individual strength‐decline trajectories remains to be determined. © 2017 American Society for Bone and Mineral Research.     

Early Changes in Bone Density,Microarchitecture, Bone Resorption,and Inflammation Predict the Clinical Outcome 12 Weeks After Conservatively Treated Distal Radius Fractures: An Exploratory Study

Fracture healing is an active process with early changes in bone and inflammation. We performed an exploratory study evaluating the association between early changes in densitometric, structural, biomechanical, and biochemical bone parameters during the first weeks of fracture healing and wrist‐specific pain and disability at 12 weeks in postmenopausal women with a conservatively treated distal radius fracture. Eighteen patients (aged 64 ± 8 years) were evaluated at 1 to 2 and 3 to 4 weeks postfracture, using high‐resolution peripheral quantitative computed tomography (HR‐pQCT), micro‐finite element analysis, serum procollagen type‐I N‐terminal propeptide (P1NP), carboxy‐terminal telopeptide of type I collagen (ICTP), and high‐sensitive C‐reactive protein (hsCRP). After 12 weeks, patients rated their pain and disability using Patient Rated Wrist Evaluation (PRWE) questionnaire. Additionally, Quick Disability of the Arm Shoulder and Hand (QuickDASH) questionnaire and active wrist range of motion was evaluated. Linear regression models were used to study the relationship between changes in bone parameters and in hsCRP from visit 1 to 2 and PRWE score after 12 weeks. A lower PRWE outcome, indicating better outcome, was significantly related to an early increase in trabecular bone mineral density (BMD) (β ?0.96 [95% CI ?1.75 to ?0.16], R² = 0.37), in torsional stiffness (?0.14 [?0.28 to ?0.004], R² = 0.31), and to an early decrease in trabecular separation (209 [15 to 402], R² = 0.33) and in ICTP (12.1 [0.0 to 24.1], R² = 0.34). Similar results were found for QuickDASH. Higher total dorsal and palmar flexion range of motion was significantly related to early increase in hsCRP (9.62 [3.90 to 15.34], R² = 0.52). This exploratory study indicates that the assessment of early changes in trabecular BMD, trabecular separation, calculated torsional stiffness, bone resorption marker ICTP, and hsCRP after a distal radius fracture provides valuable information regarding the 12‐week clinical outcome in terms of pain, disability, and range of motion and validates its use in studies on the process of early fracture healing. © 2014 American Society for Bone and Mineral Research.     

Quantitative ultrasound of cortical bone in the femoral neck predicts femur strength: Results of a pilot study

A significant risk of femoral neck (FN) fracture exists for men and women with an areal bone mineral density (aBMD) higher than the osteoporotic range, as measured with dual‐energy X‐ray absorptiometry (DXA). Separately measuring the cortical and trabecular FN compartments and combining the results would likely be a critical aspect of enhancing the diagnostic capabilities of a new technique. Because the cortical shell determines a large part of FN strength a novel quantitative ultrasound (QUS) technique that probes the FN cortical compartment was implemented. The sensitivity of the method to variations of FN cortical properties and FN strength was tested. Nine femurs (women, mean age 83 years) were subjected to QUS to measure the through transmission time‐of‐flight (TOF) at the FN and mechanical tests to assess strength. Quantitative computed tomography (QCT) scans were performed to enable analysis of the dependence of TOF on bone parameters. DXA was also performed for reference. An ultrasound wave propagating circumferentially in the cortical shell was measured in all specimens. Its TOF was not influenced by the properties of the trabecular compartment. Averaged TOF for nine FN measurement positions/orientations was significantly correlated to strength (R² = 0.79) and FN cortical QCT variables: total BMD (R² = 0.54); regional BMD in the inferoanterior (R² = 0.90) and superoanterior (R² = 0.57) quadrants; and moment of inertia (R² = 0.71). The results of this study demonstrate that QUS can perform a targeted measurement of the FN cortical compartment. Because the method involves mechanical guided waves, the QUS variable is related to the geometric and material properties of the cortical shell (cortical thickness, tissue elasticity, and porosity). This work opens the way to a multimodal QUS assessment of the proximal femur, combining our approach targeting the cortical shell with the existing modality sensitive to the trabecular compartment. In vivo feasibility of our approach has to be confirmed with experimental data in patients. © 2013 American Society for Bone and Mineral Research     

In Vivo UTE‐MRI Reveals Positive Effects of Raloxifene on Skeletal‐Bound Water in Skeletally Mature Beagle Dogs

Raloxifene positively affects mechanical properties of the bone matrix in part through modification of skeletal‐bound water. The goal of this study was to determine if raloxifene‐induced alterations in skeletal hydration could be measured in vivo using ultra‐short echotime magnetic resonance imaging (UTE‐MRI). Twelve skeletally mature female beagle dogs (n = 6/group) were treated for 6 months with oral doses of saline vehicle (VEH, 1 mL/kg/d) or raloxifene (RAL, 0.5 mg/kg/d). After 6 months of treatment, all animals underwent in vivo UTE‐MRI of the proximal tibial cortical bone. UTE‐MRI signal intensity versus echotime curves were analyzed by fitting a double exponential to determine the short and long relaxation times of water with the bone (dependent estimations of bound and free water, respectively). Raloxifene‐treated animals had significantly higher bound water (+14%; p = 0.05) and lower free water (–20%) compared with vehicle‐treated animals. These data provide the first evidence that drug‐induced changes in skeletal hydration can be noninvasively assessed using UTE‐MRI. © 2015 American Society for Bone and Mineral Research. © 2015 American Society for Bone and Mineral Research.     

Identifying Novel Clinical Surrogates to Assess Human Bone Fracture Toughness

Fracture risk does not solely depend on strength but also on fracture toughness; ie, the ability of bone material to resist crack initiation and propagation. Because resistance to crack growth largely depends on bone properties at the tissue level, including collagen characteristics, current X‐ray based assessment tools may not be suitable to identify age‐related, disease‐related, or treatment‐related changes in fracture toughness. To identify useful clinical surrogates that could improve the assessment of fracture resistance, we investigated the potential of ¹H nuclear magnetic resonance spectroscopy (NMR) and reference point indentation (RPI) to explain age‐related variance in fracture toughness. Harvested from cadaveric femurs (62 human donors), single‐edge notched beam (SENB) specimens of cortical bone underwent fracture toughness testing (R‐curve method). NMR‐derived bound water showed the strongest correlation with fracture toughness properties (r = 0.63 for crack initiation, r = 0.35 for crack growth, and r = 0.45 for overall fracture toughness; p < 0.01). Multivariate analyses indicated that the age‐related decrease in different fracture toughness properties were best explained by a combination of NMR properties including pore water and RPI‐derived tissue stiffness with age as a significant covariate (adjusted R² = 53.3%, 23.9%, and 35.2% for crack initiation, crack growth, and overall toughness, respectively; p < 0.001). These findings reflect the existence of many contributors to fracture toughness and emphasize the utility of a multimodal assessment of fracture resistance. Exploring the mechanistic origin of fracture toughness, glycation‐mediated nonenzymatic collagen crosslinks and intracortical porosity are possible determinants of bone fracture toughness and could explain the sensitivity of NMR to changes in fracture toughness. Assuming fracture toughness is clinically important to the ability of bone to resist fracture, our results suggest that improvements in fracture risk assessment could potentially be achieved by accounting for water distribution (quantitative ultrashort echo time magnetic resonance imaging) and by a local measure of tissue resistance to indentation, RPI. © 2015 American Society for Bone and Mineral Research.     

Changes in 3-dimensional bone structure indices in hypoparathyroid patients treated with PTH(1-84): a randomized controlled study

Hypoparathyroidism (hypoPT) is characterized by a state of low bone turnover and high bone mineral density (BMD) despite conventional treatment with calcium supplements and active vitamin D analogues. To assess effects of PTH substitution therapy on 3‐dimensional bone structure, we randomized 62 patients with hypoPT into 24 weeks of treatment with either PTH(1‐84) 100 µg/day subcutaneously or similar placebo as an add‐on therapy. Micro‐computed tomography was performed on 44 iliac crest bone biopsies (23 on PTH treatment) obtained after 24 weeks of treatment. Compared with placebo, PTH caused a 27% lower trabecular thickness (p < 0.01) and 4% lower trabecular bone tissue density (p < 0.01), whereas connectivity density was 34% higher (p < 0.05). Trabecular tunneling was evident in 11 (48%) of the biopsies from the PTH group. Patients with tunneling had significantly higher levels of biochemical markers of bone resorption and formation. At cortical bone, number of Haversian canals per area was 139% higher (p = 0.01) in the PTH group, causing a tendency toward an increased cortical porosity (p = 0.09). At different subregions of the hip, areal BMD (aBMD) and volumetric BMD (vBMD), as assessed by dual‐energy X‐ray absorptiometry (DXA) and quantitative computed tomography (QCT), decreased significantly by 1% to 4% in the PTH group. However, at the lumbar spine, aBMD decreased by 1.8% (p < 0.05), whereas vBMD increased by 12.8% (p = 0.02) in the PTH compared with the placebo group. © 2012 American Society for Bone and Mineral Research.     

Inflammatory Bowel Disease in a Rodent Model Alters Osteocyte Protein Levels Controlling Bone Turnover

Bone loss is a common comorbidity of inflammatory bowel disease (IBD), leading to elevated fracture risk in these patients. Inflammatory factors associated with IBD cause increased bone resorption and decreased bone formation with multiple factors implicated as instigators of these alterations. In this project, we examined the influence of IBD on osteocyte proteins in male rats (2 months old) divided into two groups: induced gut inflammation via 2,4,6‐trinitrobenzenesulfonic acid (TNBS) enema, and vehicle control. We examined the prevalence of two pro‐inflammatory cytokines, tumor necrosis factor‐α (TNF‐α) and interleukin‐6 (IL‐6), an anti‐inflammatory cytokine, interleukin‐10 (IL‐10), the anabolic factor insulin‐like growth factor‐I (IGF‐I), osteoclastogenesis regulators RANKL and OPG, and the bone formation inhibitor sclerostin in osteocytes in three bone compartments 4 weeks after initiation of gut inflammation. Histomorphometry of the proximal tibia and fourth lumbar vertebra revealed lower bone volume, lower bone formation rate (BFR), lower osteoid surface (OS), and higher osteoclast surface (Oc.S) with TNBS. Tibial mid‐shaft periosteal BFR was also lower with TNBS. Immunohistochemical staining of the distal femur demonstrated that %TNF‐α⁺, %IL‐6⁺, %RANKL⁺, and %OPG⁺ osteocytes were elevated in cancellous bone in TNBS animals compared to vehicle. These changes were coincident with increased bone resorption. With regression analysis, %RANKL⁺ osteocytes statistically predicted the increase in cancellous Oc.S (R² = 0.565). Increased %sclerostin⁺ osteocytes observed in the TNBS treatment predicted declines in cancellous OS (R² = 0.581) as well as BFR in cancellous and cortical bone (R² = 0.674, R² = 0.908, respectively). Contrary to our hypothesis, %IGF‐I⁺ osteocytes increased in TNBS animals. In conclusion, the IBD model produced a systemic inflammation that altered the regulatory protein profile in osteocytes that control bone resorption and bone formation, likely contributing to IBD‐induced bone loss. These data highlight a potential mechanistic role of osteocytes in inflammatory bone loss associated with IBD and systemic inflammation. © 2017 American Society for Bone and Mineral Research.     

Assessment of Bone Fragility in Patients With Multiple Myeloma Using QCT‐Based Finite Element Modeling

Multiple myeloma (MM) is a malignant plasma cell disease associated with severe bone destruction. Surgical intervention is often required to prevent vertebral body collapse and resulting neurological complications; however, its necessity is determined by measuring lesion size or number, without considering bone biomechanics. Finite element (FE) modeling, which simulates the physiological loading, may improve the prediction of fragility. To test this, we developed a quantitative computed tomography (QCT)‐based FE model of the vertebra and applied it to a dataset of MM patients with and without prevalent fracture. FE models were generated from vertebral QCT scans of the T₁₂ (T₁₁ if T₁₂ was fractured) of 104 MM patients, 45 with fracture and 59 without, using a low‐dose scan protocol (1.5 mm slice thickness, 4.0 to 6.5 mSv effective dose). A calibration phantom enabled the conversion of the CT Hounsfield units to FE material properties. Compressive loading of the vertebral body was simulated and the stiffness, yield load, and work to yield determined. To compare the parameters between fracture and nonfracture groups, t tests were used, and standardized odds ratios (sOR, normalized to standard deviation) and 95% confidence intervals were calculated. FE parameters were compared to mineral and structural parameters using linear regression. Patients with fracture showed lower vertebral stiffness (–15.2%; p = 0.010; sOR = 1.73; 95% CI, 1.11 to 2.70), yield force (–21.5%; p = 0.002; sOR = 2.09; 95% CI, 1.27 to 3.43), and work to yield (–27.4%; p = 0.001; sOR = 2.28; 95% CI, 1.33 to 3.92) compared to nonfracture patients. All parameters correlated significantly with vBMD (stiffness: R² = 0.57, yield force: R² = 0.59, work to yield: R² = 0.50, p < 0.001), BV/TV (stiffness: R² = 0.56, yield force: R² = 0.58, work to yield: R² = 0.49, p < 0.001), and Tb.Sp (stiffness: R² = 0.51, yield force: R² = 0.53, work to yield: R² = 0.45, p < 0.001). FE modeling identified MM patients with compromised mechanical integrity of the vertebra. Higher sOR values were obtained for the biomechanical compared to structural or mineral measures, suggesting that FE modeling improves fragility assessment in these patients. © 2016 American Society for Bone and Mineral Research.     

Multiscale Predictors of Femoral Neck In Situ Strength in Aging Women: Contributions of BMD,Cortical Porosity,Reference Point Indentation,and Nonenzymatic Glycation

The diagnosis of fracture risk relies almost solely on quantifying bone mass, yet bone strength is governed by factors at multiple scales including composition and structure that contribute to fracture resistance. Furthermore, aging and conditions such as diabetes mellitus alter fracture incidence independently of bone mass. Therefore, it is critical to incorporate other factors that contribute to bone strength in order to improve diagnostic specificity of fracture risk. We examined the correlation between femoral neck fracture strength in aging female cadavers and areal bone mineral density, along with other clinically accessible measures of bone quality including whole‐bone cortical porosity (Ct.Po), bone material mechanical behavior measured by reference point indentation (RPI), and accumulation of advanced glycation end‐products (AGEs). All measurements were found to be significant predictors of femoral neck fracture strength, with areal bone mineral density (aBMD) being the single strongest correlate (aBMD: r = 0.755, p < 0.001; Ct.Po: r = –0.500, p < 0.001; RPI: r = –0.478, p < 0.001; AGEs: r = –0.336, p = 0.016). RPI‐derived measurements were not correlated with tissue mineral density or local cortical porosity as confirmed by micro–computed tomography (μCT). Multiple reverse stepwise regression revealed that the inclusion of aBMD and any other factor significantly improve the prediction of bone strength over univariate predictions. Combining bone assays at multiple scales such as aBMD with tibial Ct.Po (r = 0.835; p < 0.001), tibial difference in indentation depth between the first and 20th cycle (IDI) (r = 0.883; p < 0.001), or tibial AGEs (r = 0.822; p < 0.001) significantly improves the prediction of femoral neck strength over any factor alone, suggesting that this personalized approach could greatly enhance bone strength and fracture risk assessment with the potential to guide clinical management strategies for at‐risk populations. © 2015 American Society for Bone and Mineral Research.     

Quantitative ultrashort echo time (UTE) MRI of human cortical bone: correlation with porosity and biomechanical properties

In this study we describe the use of ultrashort echo time (UTE) magnetic resonance imaging (MRI) to evaluate short and long T2* components as well as the water content of cortical bone. Fourteen human cadaveric distal femur and proximal tibia were sectioned to produce 44 rectangular slabs of cortical bone for quantitative UTE MR imaging, microcomputed tomography (µCT), and biomechanical testing. A two‐dimensional (2D) UTE pulse sequence with a minimal nominal TE of 8 µseconds was used together with bicomponent analysis to quantify the bound and free water in cortical bone using a clinical 3T scanner. Total water concentration was measured using a 3D UTE sequence together with a reference water phantom. UTE MR measures of water content (total, free, and bound), T2* (short and long), and short and long T2* fractions were compared with porosity assessed with µCT, as well as elastic (modulus, yield stress, and strain) and failure (ultimate stress, failure strain, and energy) properties, using Pearson correlation. Porosity significantly correlated positively with total (R² = 0.23; p < 0.01) and free (R² = 0.31; p < 0.001) water content as well as long T2* fraction (R² = 0.25; p < 0.001), and negatively with short T2* fraction and short T2* (R² = 0.24; p < 0.01). Failure strain significantly correlated positively with short T2* (R² = 0.29; p < 0.001), ultimate stress significantly correlated negatively with total (R² = 0.25; p < 0.001) and bound (R² = 0.22; p < 0.01) water content, and failure energy significantly correlated positively with both short (R² = 0 30; p < 0.001) and long (R² = 0.17; p < 0.01) T2* values. These results suggest that UTE MR measures are sensitive to the structure and failure properties of human cortical bone, and may provide a novel way of evaluating cortical bone quality. © 2012 American Society for Bone and Mineral Research.     

Understanding Age‐Induced Cortical Porosity in Women: The Accumulation and Coalescence of Eroded Cavities Upon Existing Intracortical Canals Is the Main Contributor

Intracortical bone remodeling normally ensures maintenance of the cortical bone matrix and strength, but during aging, this remodeling generates excessive porosity. The mechanism behind the age‐induced cortical porosity is poorly understood and addressed in the present study. This study consists of a histomorphometric analysis of sections of iliac bone specimens from 35 women (age 16–78 years). First, the study shows that the age‐induced cortical porosity reflects an increased pore size rather than an increased pore density. Second, it establishes a novel histomorphometric classification of the pores, which is based on the characteristics of the remodeling sites to which each pore is associated. It takes into consideration (i) the stage of the remodeling event at the level where the pore is sectioned, (ii) whether the event corresponds with the generation of a new pore through penetrative tunneling (type 1 pores) or with remodeling of an existing pore (type 2 pores), and (iii) in the latter case, whether or not the new remodeling event leads to the coalescence of pores. Of note, the advantage of this classification is to relate porosity with its generation mechanism. Third, it demonstrates that aging and porosity are correlated with: a shift from type 1 to type 2 pores, reflecting that the remodeling of existing pores is higher; an accumulation of eroded type 2 pores, reflecting an extended resorption‐reversal phase; and a coalescence of these eroded type 2 pores into enlarged coalescing type 2 cavities. Collectively, this study supports the notion, that age‐related increase in cortical porosity is the result of intracortical remodeling sites upon existing pores, with an extended reversal‐resorption phase (eroded type 2 pores) that may likely result in a delayed or absent initiation of the subsequent bone formation. © 2017 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals Inc.     

Subpixel Enhancement of Nonuniform Tissue (SPENT): A Novel MRI Technique for Quantifying BMD

BMD is commonly obtained with DXA, but this is confounded by the length and composition of tissues that the X‐ray must traverse. Subpixel enhancement of nonuniform tissue (SPENT) is a novel MRI technique that can provide (direction specific) information based on the subvoxel structural uniformity of a sample. We hypothesized that the SPENT signal would be related to BMD. This hypothesis was tested using (1) 2D computer simulation of a simplified bone structure and (2) in vitro experiments. Simulation results suggested that a resolution of 610–800 μm was required for SPENT to be correlated well with the simulated bone volume fraction (BVF) and, at this resolution, a modest signal‐to‐noise ratio (SNR > 5) was required for reasonable data quality. For the experiments, 15‐mm³ human trabecular bone samples were used (1) to quantify BMD (through both physical measurement and DXA) and (2) to perform MRI on a 7T system. Standard and SPENT images were obtained. Normalized SPENT (NSPENT) images were calculated by pixel‐by‐pixel division of the SPENT images by the standard proton density images to remove any dependence on proton density and coil uniformity from the SPENT images. The average NSPENT values were determined over the sample volume and compared with the reference BMD measurements. Each of the individual NSPENT directions was highly correlated with BMD (x‐NSPENT, R² = 0.73, p < 0.001; y‐NSPENT, R² = 0.76, p < 0.001; z‐NSPENT, R² = 0.89, p < 0.001). With all three individual NSPENT directions combined, the correlation with BMD was found to be the highest (xyz‐NSPENT, R² = 0.95, p < 0.001). The results suggest that the SPENT technique can provide a noninvasive measure of BMD at resolution and SNR levels achievable in vivo.     

The Estimation of Second‐Generation HR‐pQCT From First‐Generation HR‐pQCT Using In Vivo Cross‐Calibration

Second‐generation high‐resolution peripheral quantitative computed tomography (HR‐pQCT) provides the highest resolution in vivo to assess bone density and microarchitecture in 3D. Although strong agreement of most outcomes measured with first‐ (XCTI) and second‐ (XCTII) generation HR‐pQCT has been demonstrated, the ability to use the two systems interchangeably is unknown. From in vivo measurements, we determined the limits of estimating XCTII data from XCTI scans conducted in vivo and whether that estimation can be improved by linear cross‐calibration equations. These data are crucial as the research field transitions to the new technology. Our study design established cross‐calibration equations by scanning 62 individuals on both systems on the same day and then tested those cross‐calibrations on the same cohort 6 months later so that estimated (denoted as XCTII*) and “true” XCTII parameters could be compared. We calculated the generalized least‐significant change (GLSC) for those predictions. There was strong agreement between both systems for density (R² > 0.94), macroarchitecture (R² > 0.95), and most microarchitecture outcomes with the exception of trabecular thickness (Tb.Th, R² = 0.51 to 0.67). Linear regression equations largely eliminated the systematic error between XCTII and XCTII* and produced a good estimation of most outcomes, with individual error estimates between 0.2% and 3.4%, with the exception of Tt.BMD. Between‐system GLSC was similar to within‐XCTI LSC (eg, 8.3 to 41.9 mg HA/cm³ for density outcomes). We found that differences between outcomes assessed with XCTI and XCTII can be largely eliminated by cross‐calibration. Tb.Th is poorly estimated because it is measured more accurately by XCTII than XCTI. It may be possible to use cross‐calibration for most outcomes when both scanner generations are used for multicenter and longitudinal studies. © 2017 American Society for Bone and Mineral Research.     

Naturally Occurring Stable Calcium Isotope Ratios in Body Compartments Provide a Novel Biomarker of Bone Mineral Balance in Children and Young Adults

Serum calcium (Ca), bone biomarkers, and radiological imaging do not allow accurate evaluation of bone mineral balance (BMB), a key determinant of bone mineral density (BMD) and fracture risk. We studied naturally occurring stable (non-radioactive) Ca isotopes in different body pools as a potential biomarker of BMB. ⁴²Ca and ⁴⁴Ca are absorbed from our diet and sequestered into different body compartments following kinetic principles of isotope fractionation; isotopically light ⁴²Ca is preferentially incorporated into bone, whereas heavier ⁴⁴Ca preferentially remains in blood and is excreted in urine and feces. Their ratio (δ^44/42Ca) in serum and urine increases during bone formation and decreases with bone resorption. In 117 healthy participants, we measured Ca isotopes, biomarkers, and BMD by dual-energy X-ray absorptiometry (DXA) and tibial peripheral quantitative CT (pQCT). ⁴⁴Ca and ⁴²Ca were measured by multi-collector ionization-coupled plasma mass-spectrometry in serum, urine, and feces. The relationship between bone Ca gain and loss was calculated using a compartment model. δ^44/42Ca_serum and δ^44/42Ca_urine were higher in children (n = 66, median age 13 years) compared with adults (n = 51, median age 28 years; p < 0.0001 and p = 0.008, respectively). δ^44/42Ca_serum increased with height in boys (p < 0.001, R² = 0.65) and was greatest at Tanner stage 4. δ^44/42Ca_serum correlated positively with biomarkers of bone formation (25-hydroxyvitaminD [p < 0.0001, R² = 0.37] and alkaline phosphatase [p = 0.009, R² = 0.18]) and negatively with bone resorption marker parathyroid hormone (PTH; p = 0.03, R² = 0.13). δ^44/42Ca_serum strongly positively correlated with tibial cortical BMD Z-score (n = 62; p < 0.001, R² = 0.39) but not DXA. Independent predictors of tibial cortical BMD Z-score were δ^44/42Ca_serum (p = 0.004, β = 0.37), 25-hydroxyvitaminD (p = 0.04, β = 0.19) and PTH (p = 0.03, β = −0.13), together predicting 76% of variability. In conclusion, naturally occurring Ca isotope ratios in different body compartments may provide a novel, non-invasive method of assessing bone mineralization. Defining an accurate biomarker of BMB could form the basis of future studies investigating Ca dynamics in disease states and the impact of treatments that affect bone homeostasis. © 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).     

Genetic and Environmental Variances of Bone Microarchitecture and Bone Remodeling Markers: A Twin Study

All genetic and environmental factors contributing to differences in bone structure between individuals mediate their effects through the final common cellular pathway of bone modeling and remodeling. We hypothesized that genetic factors account for most of the population variance of cortical and trabecular microstructure, in particular intracortical porosity and medullary size – void volumes (porosity), which establish the internal bone surface areas or interfaces upon which modeling and remodeling deposit or remove bone to configure bone microarchitecture. Microarchitecture of the distal tibia and distal radius and remodeling markers were measured for 95 monozygotic (MZ) and 66 dizygotic (DZ) white female twin pairs aged 40 to 61 years. Images obtained using high‐resolution peripheral quantitative computed tomography were analyzed using StrAx1.0, a nonthreshold‐based software that quantifies cortical matrix and porosity. Genetic and environmental components of variance were estimated under the assumptions of the classic twin model. The data were consistent with the proportion of variance accounted for by genetic factors being: 72% to 81% (standard errors ～18%) for the distal tibial total, cortical, and medullary cross‐sectional area (CSA); 67% and 61% for total cortical porosity, before and after adjusting for total CSA, respectively; 51% for trabecular volumetric bone mineral density (vBMD; all p < 0.001). For the corresponding distal radius traits, genetic factors accounted for 47% to 68% of the variance (all p ≤ 0.001). Cross‐twin cross‐trait correlations between tibial cortical porosity and medullary CSA were higher for MZ (r_MZ = 0.49) than DZ (r_DZ = 0.27) pairs before (p = 0.024), but not after (p = 0.258), adjusting for total CSA. For the remodeling markers, the data were consistent with genetic factors accounting for 55% to 62% of the variance. We infer that middle‐aged women differ in their bone microarchitecture and remodeling markers more because of differences in their genetic factors than differences in their environment. © 2014 American Society for Bone and Mineral Research.     

Trabecular Bone Structure Analysis in the Osteoporotic Spine Using a Clinical In Vivo Setup for 64‐Slice MDCT Imaging: Comparison to μCT Imaging and μFE Modeling

Assessment of trabecular microarchitecture may improve estimation of biomechanical strength, but visualization of trabecular bone structure in vivo is challenging. We tested the feasibility of assessing trabecular microarchitecture in the spine using multidetector CT (MDCT) on intact human cadavers in an experimental in vivo–like setup. BMD, bone structure (e.g., bone volume/total volume = BV/TV; trabecular thickness = Tb.Th; structure model index = SMI) and bone texture parameters were evaluated in 45 lumbar vertebral bodies using MDCT (mean in‐plane pixel size, 274 μm²; slice thickness, 500 μm). These measures were correlated with structure measures assessed with μCT at an isotropic spatial resolution of 16 μm and to microfinite element models (μFE) of apparent modulus and stiffness. MDCT‐derived BMD and structure measures showed significant correlations to the density and structure obtained by μCT (BMD, R² = 0.86, p < 0.0001; BV/TV, R² = 0.64, p < 0.0001; Tb.Th, R² = 0.36, p < 0.01). When comparing μCT‐derived measures with μFE models, the following correlations (p < 0.001) were found for apparent modulus and stiffness, respectively: BMD (R² = 0.58 and 0.66), BV/TV (R² = 0.44 and 0.58), and SMI (R² = 0.44 and 0.49). However, the overall highest correlation (p < 0.001) with μFE app. modulus (R² = 0.75) and stiffness (R² = 0.76) was achieved by the combination of QCT‐derived BMD with the bone texture measure Minkowski Dimension. In summary, although still limited by its spatial resolution, trabecular bone structure assessment using MDCT is overall feasible. However, when comparing with μFE‐derived bone properties, BMD is superior compared with single parameters for microarchitecture, and correlations further improve when combining with texture measures.     

Assessment of Bone Health in Patients With Type 1 Gaucher Disease Using Impact Microindentation

Gaucher disease (GD), one of the most common lysosomal disorders (a global population incidence of 1:50,000), is characterized by beta‐glucocerebrosidase deficiency. Some studies have demonstrated bone infiltration in up to 80% of patients, even if asymptomatic. Bone disorder remains the main cause of morbidity in these patients, along with osteoporosis, avascular necrosis, and bone infarcts. Enzyme replacement therapy (ERT) has been shown to improve these symptoms. This cross‐sectional study included patients with type 1 Gaucher disease (GD1) selected from the Catalan Study Group on GD. Clinical data were collected and a general laboratory workup was performed. Bone mineral density (BMD) was measured at the lumbar spine and hip using dual‐energy X‐ray absorptiometry (DXA). Patients with bone infarcts or any other focal lesion in the area of indentation visible on imaging were excluded. Bone Material Strength index (BMSi) was measured by bone impact microindentation using an Osteoprobe instrument. Analysis of covariance (ANCOVA) models were fitted to adjust for age, sex, weight, and height. Sixteen patients with GD1 and 29 age‐ and sex‐matched controls were included. GD1 was associated with significantly lower BMSi (adjusted beta –9.30; 95% CI, –15.18 to –3.42; p = 0.004) and reduced lumbar BMD (adjusted beta –0.14; 95% CI, –0.22 to –0.06; p = 0.002) and total hip BMD (adjusted beta –0.09; 95% CI, –0.15 to –0.03; p = 0.006), compared to GD1‐free controls. Chitotriosidase levels were negatively correlated with BMSi (linear R² = 51.6%, p = 0.004). Bone tissue mechanical characteristics were deteriorated in patients with GD1. BMSi was correlated with chitotriosidase, the marker of GD activity. Bone disorder requires special consideration in this group of patients, and microindentation could be an appropriate tool for assessing and managing their bone health. © 2017 American Society for Bone and Mineral Research.     

Serum uric acid is associated with bone health in older men: A cross‐sectional population‐based study

Serum uric acid (UA) is a strong endogenous antioxidant. Since oxidative stress has been linked to osteoporosis, we examined the association between serum UA levels and bone mineral density (BMD), prevalent vertebral and nonvertebral fractures, and laboratory measures such as calcitropic hormones and bone turnover marker levels. This cross‐sectional analysis consisted of 1705 community‐dwelling men aged 70 years or over who participated in the baseline part of the Concord Health and Ageing in Men Project (CHAMP), a population‐based study of older men in Sydney, Australia. BMD at all sites was significantly higher among men with serum UA levels above the group median than among men with UA levels below the median. In multiple regression analyses adjusted for potential confounders, serum UA remained associated with BMD at all sites (β = 0.12 to 0.14, p < .001), serum calcium (β = 0.11, p = .001), parathyroid hormone (β = 0.09, p = .002), 25‐hydroxyvitamin D (β = 0.09, p = .005), and was negatively associated with urinary excretion amino‐terminal cross‐linked telopeptide of type 1 collagen (β = –0.09, p = .006). Overall, serum UA accounted for 1.0% to 1.44% of the variances in BMD (R² = 0.10 to 0.22). In multiple logistic regression analyses, above‐median serum UA levels were associated with a lower prevalence of osteoporosis at the femoral neck [odds ratio (OR) = 0.42, 95% confidence interval (CI) 0.22–0.81, p = .010) and lumbar spine (OR = 0.44, 95% CI 0.23–0.86, p = .016) and a lower prevalence of vertebral (OR = 0.62, 95% CI 0.43–0.91, p = .015) and nonvertebral (OR = 0.51, 95% CI 0.29–0.89, p = .018) fractures. In conclusion, higher serum UA levels are associated with higher BMD at all skeletal sites and with a lower prevalence of vertebral and nonvertebral fractures in older men. © 2011 American Society for Bone and Mineral Research.