High resolution quantitative computed tomography-based assessment of trabecular microstructure and strength estimates by finite-element analysis of the spine, but not DXA, reflects vertebral fracture status in men with glucocorticoid-induced osteoporosis

Predicting physiological hip joint loads with inverse bone remodeling using clinically available QCT images

BACKGROUND AND OBJECTIVE

Assessing joint-level loading conditions in vivo is challenging due to invasive measurement or complex computation. Inverse bone remodeling (IBR) offers a different approach by recovering the loading conditions directly from computed tomography (CT) images of the bone microstructure by finding the magnitudes to a set of load cases that load the bone optimally, i.e., maximally homogeneously. An efficient IBR method was recently proposed based on homogenized finite element (hFE) models. This study compared the hip joint load predictions of hFE-based IBR with clinically feasible CT scans to those obtained with the current gold standard, micro-FE-based IBR.

METHODS

A set of 20 proximal femora was scanned ex vivo, both with a clinical quantitative CT (QCT) scanner (0.3 mm resolution) and an Xtreme CT II (XCT2) scanner (0.03 mm resolution). Finite element (FE) models with decreasing complexity were automatically created from those images. Micro-FE (µFE) models based on XCT2 images served as a baseline. hFE models based on the QCT images were created as clinically feasible models. Further intermediate models were created to trace sources of errors. IBR was applied to predict the optimal scaling factors of twelve unit load cases distributed over the femoral head.

RESULTS

The predicted loads of the newly developed workflow for QCT images within IBR followed a trend seen previously with hFE models created from high-resolution images, such as XCT2. The peak load magnitudes of µFE and hFE-based IBR were well correlated (R²=76.8 %), and the overall distribution of the loads was similar. However, an additional peak load calibration was required to obtain quantitative agreement (CCC=82.8 %).

CONCLUSIONS

A thorough comparison of µFE-based IBR and hFE-based IBR using QCT data was performed for the first time. A clinically feasible workflow, including a peak calibration, is presented, allowing for fast prediction of physiological peak hip joint loads.

Standardization of bone mineral density and microstructure from high-resolution CT-scans of the spine in a multicenter setting

PURPOSE

Quantitative Computed Tomography (QCT) has not fully addressed the need to reduce intra- and inter-scanner variability for Osteoporosis and bone-related studies, which can lead to inaccuracies when pooling data from different CT manufacturers, models, devices, or protocols. In this context, the aim of this work was to develop ex vivo methods for the standardization of bone mineral density and microstructural parameters.

MATERIALS AND METHODS

Six human vertebral body specimens embedded in poly-methyl methacrylate (PMMA) were scanned ex vivo inside an anthropomorphic abdomen phantom in eight different CT-scanners. We measured 3D trabecular and cortical bone mineral density (Tb.BMD and Ct.BMD at the peeled spongiosa and the vertical cortex, respectively), trabecular separation (Tb.Sp) and cortical thickness (Ct.Th). Standardization of Tb.BMD and Ct.BMD across CT-scanners was conducted by correcting for the influence of PMMA and kernel related differences in the segmented cortical volume. For Tb.BMD and Ct.BMD two CT-scanners, where the majority of the patients were scanned, were used as reference. For Tb.Sp standardization we accounted for the image binarization threshold and used high-resolution peripheral QCT (HR-pQCT) as reference. Cross-calibration factors were obtained for each CT-scanner from which the cross-calibrated measures xTb.BMD, xCt.BMD and xTb.Sp were computed both ex vivo and in vivo. Agreement of the ex vivo measurements with respect to the references was quantified with Lin's concordance correlation coefficient (rCCC) before and after standardization. For the clinical in vivo part of the study, 152 patients (24M, 128F) undergoing long-term bisphosphonate treatment had their T12 or L1 vertebrae scanned with the same CT-scanners and protocols as for ex vivo. Statistical bone fracture models were conducted before and after cross-calibration to assess the performance of the standardization procedure in vivo.

RESULTS

After cross-calibration the overall ex vivo mean Tb.BMD across CT-scanners was basically maintained, changing only from 119.0 mgHA/cm3 to 119.4 mgHA/cm3. The mean Ct.BMD raised from 420.4 mgHA/cm3 to 441.1 mgHA/cm3. Tb.BMD showed a small variability (SD of means) across centers of 2.7 mgHA/cm3. For Ct.BMD additional kernel related thickness correction reduced this variability from 31.7 mgHA/cm3 to 22.4 mgHA/cm3. Non-standardized Tb.Sp showed a mean of 2.63 mm across CT-scanners, which after standardization was corrected to 1.18 mm. Agreement to the reference measurements was markedly improved after standardization (before: the rccc [min, max] for Tb.BMD, Ct.BMD and Tb.Sp was [0.64, 0.92], [0.40, 0.89] and [0.57, 0.99], respectively; after standardization: [0.98, 0.99], [0.96, 0.99] and [0.78, 0.99], respectively). For in vivo, Tb.BMD and Ct.BMD showed a mean (SD of means) across CT-scanners before standardization of 72.3 (7.6) mgHA/cm3 and 352.4 (44.6) mgHA/cm3, respectively and after standardization 72.6 (7.0) mgHA/cm3 and 370.7 (31.0) mgHA/cm3, respectively. Non-standardized Tb.Sp showed a mean (SD of means) of 3.55 (2.42) mm across CT-scanners, which after standardization was corrected to 1.65 mm (0.16) mm. The cross-calibrated xTb.BMD showed a highly statistical significance in prevalent fracture classification (p = 0.0001) similar to Tb.BMD (p = 0.0002). For xCt.BMD a trend was observed in improving fracture prediction, albeit not significant (p = 0.14), compared to Ct.BMD (p = 0.23). xTb.Sp demonstrated improved fracture prediction (p = 0.024) compared to a non-standardized Tb.Sp (p > 0.1).

CONCLUSION

The improved inter-scanner agreement with corresponding reduced variability underscores the importance of cross-calibration of bone mineral density and microstructural parameters. For the in vivo application of the methods, cross-calibrated Tb.Sp improved fracture prediction in patients, whereas cross-calibrated BMD had no discernible impact, possibly due to the distribution of patients across the participating CT-centers and the already high fracture classification power of Tb.BMD.

Individuals with heterogenous trabecular bone texture by clinical magnetic resonance imaging have lower bone strength and stiffness by quantitative computed tomography-based finite element analysis

Opportunistic screening is essential to improve the identification of individuals with osteoporosis. Our group has utilized image texture features to assess bone quality using clinical MRIs. We have previously demonstrated that greater heterogeneity of MRI texture related to history of fragility fractures, lower bone density, and worse microarchitecture. The present study investigated relationships between MRI-based texture features and biomechanical properties of bone using CT-based finite element analyses (FEAs). We hypothesized that individuals with greater texture heterogeneity would have lower stiffness and failure load. Thirty individuals included in this prospective study had CT and MRI of L1 and L2 vertebrae. Using T1-weighted MR images, a gray-level co-occurrence matrix was generated to characterize the distribution and spatial organization of voxelar signal intensities to derive the following texture features: contrast (variability), entropy (disorder), angular second moment (ASM; uniformity), and inverse difference moment (IDM; homogeneity). Features were calculated in five directions relative to the image plane. Whole-bone stiffness and failure load were calculated from phantom-calibrated lumbar QCT. Mean age of subjects was 59 ± 11 yr (57% female). Individuals with lower vertebral stiffness had greater texture heterogeneity; specifically, higher contrast (r = -0.54, p < .01), higher entropy (r = -0.52, p < .01), lower IDM (r = 0.54, p < .01) and lower ASM (r = 0.51, p < .01). Lower vertebral failure load and lower vBMD were similarly associated with greater texture heterogeneity. Relationships were unchanged when using the average of texture in all directions or the vertical direction in isolation. In summary, individuals with more heterogeneous MRI-based trabecular texture had lower stiffness and failure load by FEA, and lower vBMD by central quantitative CT. These results-the first relating MRI-based texture features and biomechanical properties of bone-provide further support that MRI-based texture measurements can be used to opportunistically detect skeletal fragility.

Effects of Denosumab and Bisphosphonates on Glucocorticoid-induced Osteoporosis in Patients with Neuroimmunological Disorders

Objective Although patients with neuroimmunological disorders often need to be treated with glucocorticoids and are at risk of developing glucocorticoid-induced osteoporosis, no research has focused on the treatment of glucocorticoid-induced osteoporosis in such patients. Methods We compared the efficacy of denosumab and bisphosphonates in glucocorticoid-induced osteoporosis in neuroimmunological diseases. In 57 patients with neuroimmunological disorders treated with corticosteroids (34 with neuromyelitis optica spectrum disorders, 16 with myasthenia gravis, and 7 with others), we retrospectively studied the long-term effects of denosumab (n=23) and bisphosphonates (n=34) on spine and total hip bone mineral density (BMD) measured by dual energy X-ray absorptiometry. Results There were no significant differences in the age, lumbar spine BMD, or mean dose or duration of prednisolone administration at baseline between the denosumab and bisphosphonate groups. During the follow-up period of up to 6 years, the increase in the lumbar spine and total hip BMD was greater in the denosumab group than in the bisphosphonate group (p<0.01). Insufficient bone fractures were observed in 2 (9%) of the 23 patients in the denosumab group and in 2 (6%) of the 34 patients in the bisphosphonate group (not significant). Conclusion Denosumab is more effective than bisphosphonates in increasing the BMD of patients with neuroimmunological disorders receiving glucocorticoids.

The impact of androgen deprivation therapy on bone microarchitecture in men with prostate cancer: A longitudinal observational study (The ANTELOPE Study)

Introduction

Androgen Deprivation Therapy (ADT) for prostate cancer (PC) has substantial negative impacts on the musculoskeletal system and body composition. Many studies have focused on the effects of ADT on areal bone mineral density (aBMD), but aBMD does not capture key determinants of bone strength and fracture risk, for example volumetric bone density (vBMD), geometry, cortical thickness and porosity, trabecular parameters and rate of remodelling. More specialist imaging techniques such as high-resolution peripheral quantitative computed tomography (HR-pQCT) have become available to evaluate these parameters. Although it has previously been demonstrated that bone microarchitectural deterioration occurs in men undergoing ADT, the aim of the ANTELOPE study was to examine longitudinal changes in bone microstructure alongside a range of musculoskeletal parameters and frailty, comparing men with PC receiving ADT alone or ADT plus chemotherapy for metastatic disease, with a healthy age-matched population.

Methods

We used HR-pQCT to investigate effects of 12 months of ADT on vBMD and microstructural parameters, complemented by assessment of changes in aBMD, serum bone turnover markers, sex hormones, body composition, grip strength, physical and muscle function, frailty and fracture risk. We studied three groups: Group A - men with localised/locally advanced PC due to commence ADT; Group B - men with newly diagnosed hormone-sensitive, metastatic PC, starting ADT alongside docetaxel chemotherapy and steroids; Group C - healthy, age-matched men. The primary endpoint was change in vBMD (Group A vs Group C) at the distal radius.

Results

Ninety-nine participants underwent baseline study assessments (Group A: n = 38, Group B: n = 30 and Group C: n = 31). Seventy-five participants completed all study assessments (Group A (29), Group B (18), Group C (28). At baseline, there were no significant differences between Groups A and C in any of the BMD or bone microstructure outcomes of interest. After 12 months of ADT treatment, there was a significantly greater decrease in vBMD (p < 0.001) in Group A (mean 12-month change = -13.7 mg HA/cm3, -4.1 %) compared to Group C (mean 12-month change = -1.3 mg HA/cm3, -0.4 %), demonstrating achievement of primary outcome. Similar effects were observed when comparing the change in vBMD between Group B (mean 12-month change = -13.5 mg HA/cm3, -4.3 %) and Group C. These changes were mirrored in aBMD. ADT resulted in microstructural deterioration, a reduction in estimated bone strength and an increase in bone turnover. There was evidence of increase in total fat mass and trunkal fat mass in ADT-treated patients, with marked loss in upper limb mass, along with BMI gain. Frailty increased and physical performance and strength deteriorated in both ADT groups, relative to the healthy control group.

Conclusion

The study showed that ADT has profound effects on vBMD, aBMD, bone microstructure and strength and body composition, and important impacts on frailty and physical performance. Whilst DXA remains a valuable tool (changes in aBMD are of the same magnitude as those observed for vBMD), HR-pQCT should be considered for assessing the effects of anti-androgens and other newer PC therapies on bone, as well as potential mitigation by bone-targeted agents.

Characterizing Bone Phenotypes Related to Skeletal Fragility Using Advanced Medical Imaging

PURPOSE OF REVIEW

Summarize the recent literature that investigates how advanced medical imaging has contributed to our understanding of skeletal phenotypes and fracture risk across the lifespan.

RECENT FINDINGS

Characterization of bone phenotypes on the macro-scale using advanced imaging has shown that while wide bones are generally stronger than narrow bones, they may be more susceptible to age-related declines in bone strength. On the micro-scale, HR-pQCT has been used to identify bone microarchitecture phenotypes that improve stratification of fracture risk based on phenotype-specific risk factors. Adolescence is a key phase for bone development, with distinct sex-specific growth patterns and significant within-sex bone property variability. However, longitudinal studies are needed to evaluate how early skeletal growth impacts adult bone phenotypes and fracture risk. Metabolic and rare bone diseases amplify fracture risk, but the interplay between bone phenotypes and disease remains unclear. Although bone phenotyping is a promising approach to improve fracture risk assessment, the clinical availability of advanced imaging is still limited. Consequently, alternative strategies for assessing and managing fracture risk include vertebral fracture assessment from clinically available medical imaging modalities/techniques or from fracture risk assessment tools based on clinical risk factors. Bone fragility is not solely determined by its density but by a combination of bone geometry, distribution of bone mass, microarchitecture, and the intrinsic material properties of bone tissue. As such, different individuals can exhibit distinct bone phenotypes, which may predispose them to be more vulnerable or resilient to certain perturbations that influence bone strength.

High prevalence of vertebral fractures associated with preoperative cortisol levels in patients with recent diagnosis of Cushing disease

BACKGROUND/OBJECTIVE

Morphometric vertebral fractures (VFs) and osteopathy are prevalent and clinically significant complications of Cushing disease (CD). However whether they represent an early occurrence in the natural progression of the disease is an ongoing debate. This study aimed to assess the prevalence and determinants of VFs in patients newly diagnosed with CD.

PATIENTS AND METHODS

This cross-sectional case-control study recruited 75 newly diagnosed CD patients and compared them with a control group of individuals without pituitary disorders or secondary forms of osteoporosis. Demographic, clinical and biochemical data were collected. The VFs were assessed using preoperative lateral chest radiography.

RESULTS

We found a significantly higher prevalence of VFs in the CD group than in the control group (58.7% vs. 14.5%; P < 0.001). Among the CD patients with VFs, 27 (61.4%) showed moderate/severe VFs. The CD patients with VFs had significantly higher preoperative 8 am serum cortisol (8ASC) levels than those without VFs (P < 0.001). The preoperative 4 pm adrenocorticotropic hormone (ACTH) levels (P = 0.031), preoperative 0 am ACTH levels (P = 0.021) and systolic blood pressure were slightly higher in CD patients with VFs than in those without VFs (P = 0.028). A binary multiple logistic analysis showed that 8ASC was an independent predictor of VF risk (P = 0.003). The optimal cut-off value of the preoperative serum 8ASC level for predicting VFs was 22.18 ng/mL.

CONCLUSIONS

This is the first study reporting a high prevalence of radiologic VFs in recently diagnosed CD patients. VFs may represent an early manifestation of CD and may be related to cortisol levels. Therefore, VF assessment should be included in the workup during CD diagnosis.

Quantitative CT screening improved lumbar BMD evaluation in older patients compared to dual-energy X-ray absorptiometry

BACKGROUND

Robust evidence on whether diagnostic discordance exists between lumbar osteoporosis detected by quantitative computed tomography (QCT) vs. dual-energy X-ray absorptiometry (DXA) is still lacking. In this study involving a relatively large prospective cohort of older men (aged > 60 years) and postmenopausal women, we assessed lumbar QCT-derived volumetric bone mineral density (vBMD) and DXA-derived area BMD and evaluated their predictive performance for prevalent vertebral fracture (VF).

METHODS

A total of 501 patients who underwent spinal surgery from September 2020 to September 2022 were enrolled. The criteria recommended by the American College of Radiology and the World Health Organization were used for lumbar osteoporosis diagnosis. The osteoporosis detection rates between QCT and DXA were compared. QCT-vBMD was plotted against the DXA T score, and the line of best fit was calculated based on linear regression. Multivariate logistic regression was used to analyze the associations between risk factors and VF. Receiver operating characteristic curve analysis was performed, and the corresponding area under the curve (AUC) was calculated.

RESULTS

QCT screening showed that 60.7% of patients had osteoporosis, whereas DXA screening showed that 50.7% of patients had osteoporosis. Diagnoses were concordant for 325 (64.9%) patients. In all, 205 patients suffered a VF of at least one anatomic level. Of these, 84.4% (173/205) were diagnosed with osteoporosis by QCT, while only 73.2% (150/205) were diagnosed by DXA. Multivariate logistic regression showed that osteoporosis detected by QCT exhibited a stronger relationship with VF than that detected by DXA (unadjusted OR, 6.81 vs. 5.04; adjusted OR, 3.44 vs. 2.66). For discrimination between patients with and without VF, QCT-vBMD (AUC = 0.802) showed better performance than DXA T score (AUC = 0.76).

CONCLUSION

In older patients undergoing spinal surgery, QCT-vBMD is more helpful than DXA in terms of osteoporosis detection rate and prediction of patients with prevalent VFs.

Trabecular bone score, bone marrow fat and vertebral fractures in cushing syndrome

OBJECTIVE

Prediction of fragility fractures in Cushing syndrome (CS) is a challenge since dual energy X-ray absorptiometry (DXA) measurement of bone mineral density (BMD) does not capture all the alterations in bone microstructure induced by glucocorticoid excess. In this study we investigated the relationship between trabecular bone score (TBS), bone marrow fat (BMF) and vertebral fractures (VFs) in endogenous CS.

DESIGN

Cross-sectional.

METHODS

Thirty subjects (7 M and 23 F, mean age 44.8 ± 13.4 yrs, range: 25-71) with active hypercortisolism were evaluated for VFs by quantitative morphometry, BMD and TBS by lumbar spine DXA and BMF by single-voxel magnetic resonance spectroscopy of vertebral body of L3.

RESULTS

Subjects with VFs (17 cases; 56.7%) had higher BMF (P = 0.014) and lower BMD T-score (P = 0.012) and TBS (P = 0.004) as compared to those without VFs. Prevalence of VFs resulted to be significantly higher in individuals with impaired TBS as compared to those with normal TBS (77.8% vs. 25.0%; P = 0.008). Among patients with VFs, only 6 (35.3%) had either osteoporosis or "low BMD for age". In logistic regression analysis, impaired TBS maintained the significant association with VFs [odds ratio (OR) 6.60, 95% C.I. 1.07-40.61; P = 0.042] independently of BMF (OR 1.03, 95% C.I. 0.99-1.08; P = 0.152).

CONCLUSIONS

TBS might be more accurate than BMF in identifying subjects with active CS and skeletal fragility at risk of VFs.

SIGNIFICANCE STATEMENT

Excess in glucocorticoids is associated with alterations in bone remodeling and metabolism, leading to fragility fractures regardless of bone mineral density, making more challenging for the clinician the identification of high-risk population and the definition of preventing strategies. In this context, instrumental parameters suggestive of bone quality alterations and predictive of increased fracture risk are needed. In this study, we found CS patients to have bone quality alterations as indicated by the decreased trabecular bone score and increased bone marrow fat, as measured by DEXA and MRI respectively. Both parameters were associated with high risk of VFs, and were inversely correlated, although TBS seems to be more accurate than BMF in fractures prediction in this clinical setting.

Dual-Layer Spectral-Computed Tomography Enhances the Separability of Calcium-Based Implant Material from Bone: An Ex Vivo Quantitative Imaging Study

Local treatment of bone loss with an injection of a resorbable, calcium-based implant material to replace bone has a long history of clinical use. The in vivo discrimination of changes in bone versus implant is challenging with standard computed tomography (CT). However, spectral-CT techniques enable the separation between tissues of similar densities but different chemical compositions. Dual-layer spectral-CT imaging and postprocessing analysis methods were applied to investigate the separability of AGN1 (a triphasic calcium-based implant) and bone after AGN1 injection in n = 10 male cadaveric femurs ex vivo. Using the area under the curve (AUC) from receiver-operating characteristic (ROC) analyses, the separability of AGN1 from bone was assessed for AGN1 (postoperatively) versus compact and versus femoral neck cancellous bone (both preoperatively). CT techniques included conventional Hounsfield (HU) and density-equivalent units (BMD, mg hydroxyapatite [HA]/cm³ ) and spectral-CT measures of effective atomic number (Zeff) and electron density (ED). The samples had a wide range of femoral neck BMD (55.66 to 241.71 mg HA/cm³ ). At the injection site average BMD, HU, Zeff, and ED increased from 69.5 mg HA/cm³ , 109 HU, 104.38 EDW, and 8.30 Zeff in the preoperative to 1233 mg HA/cm³ , 1741 HU, 181.27 EDW, and 13.55 Zeff in the postoperative CT scan, respectively. For compact bone at the femoral shaft the preoperative values were 1124.15 mg HA/cm³ , 1648 HU, 177 EDW, and 13.06 Zeff and were maintained postoperatively. Zeff showed substantially sharper distributions and significantly greater separability compared to ED, BMD, and HU (all p < 0.002, for both regions) with average AUCs for BMD, HU, ED, and Zeff of 0.670, 0.640, 0.645, and 0.753 for AGN1 versus compact and 0.996, 0.995, 0.994, and 0.998 for AGN1 versus femoral neck cancellous sites, respectively. Spectral-CT permits better discrimination of calcium-based implants like AGN1 from bone ex vivo. Our results warrant application of spectral-CT in patients undergoing procedures with similar implants. © 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).

Prevention and Treatment of Glucocorticoid-Induced Osteoporosis in Adults: Consensus Recommendations From the Belgian Bone Club

Glucocorticoids are effective immunomodulatory drugs used for many inflammatory disorders as well as in transplant recipients. However, both iatrogenic and endogenous glucocorticoid excess are also associated with several side effects including an increased risk of osteoporosis and fractures. Glucocorticoid-induced osteoporosis (GIOP) is a common secondary cause of osteoporosis in adults. Despite availability of clear evidence and international guidelines for the prevention of GIOP, a large treatment gap remains. In this narrative review, the Belgian Bone Club (BBC) updates its 2006 consensus recommendations for the prevention and treatment of GIOP in adults. The pathophysiology of GIOP is multifactorial. The BBC strongly advises non-pharmacological measures including physical exercise, smoking cessation and avoidance of alcohol abuse in all adults at risk for osteoporosis. Glucocorticoids are associated with impaired intestinal calcium absorption; the BBC therefore strongly recommend sufficient calcium intake and avoidance of vitamin D deficiency. We recommend assessment of fracture risk, taking age, sex, menopausal status, prior fractures, glucocorticoid dose, other clinical risk factors and bone mineral density into account. Placebo-controlled randomized controlled trials have demonstrated the efficacy of alendronate, risedronate, zoledronate, denosumab and teriparatide in GIOP. We suggest monitoring by dual-energy X-ray absorptiometry (DXA) and vertebral fracture identification one year after glucocorticoid initiation. The trabecular bone score might be considered during DXA monitoring. Extended femur scans might be considered at the time of DXA imaging in glucocorticoid users on long-term (≥ 3 years) antiresorptive therapy. Bone turnover markers may be considered for monitoring treatment with anti-resorptive or osteoanabolic drugs in GIOP. Although the pathophysiology of solid organ and hematopoietic stem cell transplantation-induced osteoporosis extends beyond GIOP alone, the BBC recommends similar evaluation, prevention, treatment and follow-up principles in these patients. Efforts to close the treatment gap in GIOP and implement available effective fracture prevention strategies into clinical practice in primary, secondary and tertiary care are urgently needed.

Dose-efficient assessment of trabecular microstructure using ultra-high-resolution photon-counting CT

Photon-counting (PC) detectors for clinical computed tomography (CT) may offer improved imaging capabilities compared to conventional energy-integrating (EI) detectors, e.g. superior spatial resolution and detective efficiency. We here investigate if PCCT can reduce the administered dose in examinations aimed at quantifying trabecular bone microstructure. Five human vertebral bodies were scanned three times in an abdomen phantom (QRM, Germany) using an experimental dual-source CT (Somatom CounT, Siemens Healthineers, Germany) housing an EI detector (0.60 mm pixel size at the iso-center) and a PC detector (0.25 mm pixel size). A tube voltage of 120 kV was used. Tube current-time product for EICT was 355 mAs (23.8 mGy CTDI_{32 cm}). Dose-matched UHR-PCCT (UHRdm, 23.8 mGy) and noise-matched acquisitions (UHRnm, 10.5 mGy) were performed and reconstructed to a voxel size of 0.156 mm using a sharp kernel. Measurements of bone mineral density (BMD) and trabecular separation (Tb.Sp) and Tb.Sp percentiles reflecting the different scales of the trabecular interspacing were performed and compared to a gold-standard measurement using a peripheral CT device (XtremeCT, SCANCO Medical, Switzerland) with an isotropic voxel size of 0.082 mm and 6.6 mGy CTDI_{10 cm}. The image noise was quantified and the relative error with respect to the gold-standard along with the agreement between CT protocols using Lin's concordance correlation coefficient (r_CCC) were calculated. The Mean ± StdDev of the measured image noise levels in EICT was 109.6 ± 3.9 HU. UHRdm acquisitions (same dose as EICT) showed a significantly lower noise level of 78.6 ± 4.6 HU (p = 0.0122). UHRnm (44% dose of EICT) showed a noise level of 115.8 ± 3.7 HU, very similar to EICT at the same spatial resolution. For BMD the overall Mean ± StdDev for EI, UHRdm and UHRnm were 114.8 ± 28.6 mgHA/cm³, 121.6 ± 28.8 mgHA/cm³ and 121.5 ± 28.6 mgHA/cm³, respectively, compared to 123.1 ± 25.5 mgHA/cm³ for XtremeCT. For Tb.Sp these values were 1.86 ± 0.54 mm, 1.80 ± 0.56 mm and 1.84 ± 0.52 mm, respectively, compared to 1.66 ± 0.48 mm for XtremeCT. The ranking of the vertebrae with regard to Tb.Sp data was maintained throughout all Tb.Sp percentiles and among the CT protocols and the gold-standard. The agreement between protocols was very good for all comparisons: UHRnm vs. EICT (BMD r_CCC = 0.97; Tb.Sp r_CCC = 0.998), UHRnm vs. UHRdm (BMD r_CCC = 0.998; Tb.Sp r_CCC = 0.993) and UHRdm vs. EICT (BMD r_CCC = 0.97; Tb.Sp r_CCC = 0.991). Consequently, the relative RMS-errors from linear regressions against the gold-standard for EICT, UHRdm and UHRnm were very similar for BMD (7.1%, 5.2% and 5.4%) and for Tb.Sp (3.3%, 3.3% and 2.9%), with a much lower radiation dose for UHRnm. Short-term reproducibility for BMD measurements was similar and below 0.2% for all protocols, but for Tb.Sp showed better results for UHR (about 1/3 of the level for EICT). In conclusion, CT with UHR-PC detectors demonstrated lower image noise and better reproducibility for assessments of bone microstructure at similar dose levels. For UHRnm, radiation exposure levels could be reduced by 56% without deterioration of performance levels in the assessment of bone mineral density and bone microstructure.

Challenges in the diagnosis and management of glucocorticoid-induced osteoporosis in younger and older adults

OBJECTIVE

Glucocorticoids constitute a considerable risk for developing osteoporosis in both younger and older adults. However, currently available bone imaging modalities and fracture-risk assessment tools do not adequately capture the dramatic changes in bone microarchitecture, heterogeneity of glucocorticoid exposure, the impact of chronic disease and other osteoporosis risk factors on the assessment of osteoporosis in these individuals.

DESIGN

A narrative review is presented, following a systematic search of the literature from 2000 to 2021.

RESULTS

Our current appreciation of glucocorticoid-induced osteoporosis (GIO) is focused on older populations, with limited evidence to guide the investigation, risk assessment and treatment in premenopausal women and men less than 50 years. The impact of the underlying chronic disease on secondary osteoporosis in these younger adults is also poorly understood.

CONCLUSION

Through this narrative review, we provide a comprehensive overview of and recommendations for optimising the management of this common cause of secondary osteoporosis younger and older adults.

Estimation of fracture risk by the FRAX tool in patients with systemic lupus erythematosus: a 10-year longitudinal validation study

BACKGROUND

The fracture risk assessment tool has been widely used to stratify the 10-year fracture risk to guide therapy. Using the actual fracture data of a 10-year longitudinal cohort of older patients with systemic lupus erythematosus, we reported an underestimation of the tool in predicting major symptomatic osteoporotic fractures. Treatment of osteoporosis in systemic lupus erythematosus should not be based on fracture risk estimation alone. Relevant time-dependent risk factors should be taken into account for an individualized decision.

OBJECTIVE

To compare the observed fracture incidence in a 10-year longitudinal cohort of patients with systemic lupus erythematosus (SLE) with the fracture risk prediction from the fracture risk assessment (FRAX) tool.

METHODS

Adult patients (⩾40 years) with SLE who had a first DEXA scan performed in 2005-2009 were studied. The 10-year rates of major osteoporotic and hip fractures were estimated by FRAX using clinical data at DEXA with adjustment for prednisolone dosage. The actual incidence of clinical fractures at 10 years was compared with the estimated rates. Factors associated with new fractures were studied by logistic regression.

RESULTS

A total of 229 SLE patients were studied (age: 50.2 ± 6.6 years, 93% women). Glucocorticoid was used in 148 (65%) patients at baseline (mean dose: 7.3 ± 6.9 mg/day; 34% ⩾ 7.5 mg/day). Osteoporosis (bone mineral density T score ⩽ -2.5) at the hip, femoral neck, or spine was present in 61 (27%) patients. The estimated 10-year risk of major osteoporotic and hip fractures by FRAX was 3.4 ± 4.5% and 0.95 ± 2.3%, respectively. After 10 years, three patients developed hip fracture, 6 patients had limb fractures and 20 patients had symptomatic vertebral fractures (major osteoporotic fracture 12.7%, hip fracture 1.3%). The actual major osteoporotic fracture rate was significantly higher than the FRAX estimation (12.7% vs 3.4%; p < 0.001). Logistic regression revealed that osteoporosis (odds ratio (OR): 4.07 [1.51-10.9]), previous fragility fracture (OR: 3.18 [1.02-9.90]), and a parental history of fracture (OR: 4.44 [1.16-17.0]) were independently associated with new clinical fractures at 10 years.

CONCLUSION

The FRAX tool underestimates the major clinical fracture risk at 10 years in patients with SLE.

Osteoporosis Due to Hormone Imbalance: An Overview of the Effects of Estrogen Deficiency and Glucocorticoid Overuse on Bone Turnover

Osteoporosis is a serious health issue among aging postmenopausal women. The majority of postmenopausal women with osteoporosis have bone loss related to estrogen deficiency. The rapid bone loss results from an increase in bone turnover with an imbalance between bone resorption and bone formation. Osteoporosis can also result from excessive glucocorticoid usage, which induces bone demineralization with significant changes of spatial heterogeneities of bone at microscale, indicating potential risk of fracture. This review is a summary of current literature about the molecular mechanisms of actions, the risk factors, and treatment of estrogen deficiency related osteoporosis (EDOP) and glucocorticoid induced osteoporosis (GIOP). Estrogen binds with estrogen receptor to promote the expression of osteoprotegerin (OPG), and to suppress the action of nuclear factor-κβ ligand (RANKL), thus inhibiting osteoclast formation and bone resorptive activity. It can also activate Wnt/β-catenin signaling to increase osteogenesis, and upregulate BMP signaling to promote mesenchymal stem cell differentiation from pre-osteoblasts to osteoblasts, rather than adipocytes. The lack of estrogen will alter the expression of estrogen target genes, increasing the secretion of IL-1, IL-6, and tumor necrosis factor (TNF). On the other hand, excessive glucocorticoids interfere the canonical BMP pathway and inhibit Wnt protein production, causing mesenchymal progenitor cells to differentiate toward adipocytes rather than osteoblasts. It can also increase RANKL/OPG ratio to promote bone resorption by enhancing the maturation and activation of osteoclast. Moreover, excess glucocorticoids are associated with osteoblast and osteocyte apoptosis, resulting in declined bone formation. The main focuses of treatment for EDOP and GIOP are somewhat different. Avoiding excessive glucocorticoid use is mandatory in patients with GIOP. In contrast, appropriate estrogen supplement is deemed the primary treatment for females with EDOP of various causes. Other pharmacological treatments include bisphosphonate, teriparatide, and RANKL inhibitors. Nevertheless, more detailed actions of EDOP and GIOP along with the safety and effectiveness of medications for treating osteoporosis warrant further investigation.

Pharmacology and toxicology of eteplirsen and SRP-5051 for DMD exon 51 skipping: an update

Duchenne muscular dystrophy (DMD) afflicts 1 in 5000 newborn males, leading to progressive muscle weakening and the loss of ambulation between the ages of 8 and 12. Typically, DMD patients pass away from heart failure or respiratory failure. Currently, there is no cure, though exon-skipping therapy including eteplirsen (brand name Exondys 51), a synthetic antisense oligonucleotide designed to skip exon 51 of the dystrophin gene, is considered especially promising. Applicable to approximately 14% of DMD patients, a phosphorodiamidate morpholino oligomer (PMO) antisense oligonucleotide eteplirsen received accelerated approval by the US Food and Drug Administration (FDA) in 2016. Throughout clinical trials, eteplirsen has been well tolerated by patients with no serious drug-related adverse events. The most common events observed are balance disorder, vomiting, and skin rash. Despite its safety and promise of functional benefits, eteplirsen remains controversial due to its low production of dystrophin. In addition, unmodified PMOs have limited efficacy in the heart. To address these concerns of efficacy, eteplirsen has been conjugated to a proprietary cell-penetrating peptide; the conjugate is called SRP-5051. Compared to eteplirsen, SRP-5051 aims to better prompt exon-skipping and dystrophin production but may have greater toxicity concerns. This paper reviews and discusses the available information on the efficacy, safety, and tolerability data of eteplirsen and SRP-5051 from preclinical and clinical trials. Issues faced by eteplirsen and SRP-5051, including efficacy and safety, are identified. Lastly, the current state of eteplirsen and exon-skipping therapy in general as a strategy for the treatment of DMD are discussed.

Implications of gender-based variabilities in bone mineral density and hemoglobin levels

BACKGROUND

Studies reported that there is a relationship between volumetric bone mineral density (vBMD) and hemoglobin (HGB) in sickle cell anemia, chronic obstructive pulmonary disease, inflammatory bowel disease, and chronic kidney disease, it is not clear whether this association exists in normal populations or different genders. In order to further clarify the relationship between vBMD and HGB, and provide the basis for the diagnosis of related diseases, this study was conducted in the physical examination population.

METHODS

A cross-sectional study was conducted on a health check-up population from Wannan area of China from January to December 2018. The study involved 1238 individuals aged 23 to 85 years. Linear regression analysis and smooth curve were applied to determine the relationship of HGB and vBMD.

RESULTS

The average level of vBMD in the population was 130.11 ± 79.51 mg/cm³, after adjusting for age, body mass index (BMI), systolic blood pressure (SBP), diastolic blood pressure (DBP), total cholesterol (TC), triglycerides (TG), glucose (GLU), high-density lipoprotein (HDL) and low-density lipoprotein (LDL). A U-shape relationship was established between vBMD and HGB, the cut off value of HGB was 130 g/L. After gender stratification, the results showed a U-shaped curve relationship between vBMD and HGB in male group, and a linear relationship between vBMD and HGB in female group. The vBMD decreased with HGB when HGB < 120 g/L, and increased when HGB ≥ 120 g/L in male group.

CONCLUSION

The relationship between vBMD and HGB in the male physical examination population presents a U-shaped curve.

The Role of BMP Signaling in Osteoclast Regulation

The osteogenic effects of Bone Morphogenetic Proteins (BMPs) were delineated in 1965 when Urist et al. showed that BMPs could induce ectopic bone formation. In subsequent decades, the effects of BMPs on bone formation and maintenance were established. BMPs induce proliferation in osteoprogenitor cells and increase mineralization activity in osteoblasts. The role of BMPs in bone homeostasis and repair led to the approval of BMP2 by the Federal Drug Administration (FDA) for anterior lumbar interbody fusion (ALIF) to increase the bone formation in the treated area. However, the use of BMP2 for treatment of degenerative bone diseases such as osteoporosis is still uncertain as patients treated with BMP2 results in the stimulation of not only osteoblast mineralization, but also osteoclast absorption, leading to early bone graft subsidence. The increase in absorption activity is the result of direct stimulation of osteoclasts by BMP2 working synergistically with the RANK signaling pathway. The dual effect of BMPs on bone resorption and mineralization highlights the essential role of BMP-signaling in bone homeostasis, making it a putative therapeutic target for diseases like osteoporosis. Before the BMP pathway can be utilized in the treatment of osteoporosis a better understanding of how BMP-signaling regulates osteoclasts must be established.

Glucocorticoid- and Transplantation-Induced Osteoporosis

Glucocorticoid-induced osteoporosis is the most common cause of secondary osteoporosis; nonetheless, it remains an undertreated condition. Transplantation-induced osteoporosis encompasses a broad range of unique pathogenetic features with distinct characteristics dependent on the transplanted organ. Understanding the pathogenesis of bone loss is key to recommending osteoporosis therapy in these patients. This review summarizes recent advances and addresses current issues in these fields.

High-Resolution Cone-Beam Computed Tomography is a Fast and Promising Technique to Quantify Bone Microstructure and Mechanics of the Distal Radius

Obtaining high-resolution scans of bones and joints for clinical applications is challenging. HR-pQCT is considered the best technology to acquire high-resolution images of the peripheral skeleton in vivo, but a breakthrough for widespread clinical applications is still lacking. Recently, we showed on trapezia that CBCT is a promising alternative providing a larger FOV at a shorter scanning time. The goals of this study were to evaluate the accuracy of CBCT in quantifying trabecular bone microstructural and predicted mechanical parameters of the distal radius, the most often investigated skeletal site with HR-pQCT, and to compare it with HR-pQCT. Nineteen radii were scanned with four scanners: (1) HR-pQCT (XtremeCT, Scanco Medical AG, @ (voxel size) 82 μm), (2) HR-pQCT (XtremeCT-II, Scanco, @60.7 μm), (3) CBCT (NewTom 5G, Cefla, @75 μm) reconstructed and segmented using in-house developed software and (4) microCT (VivaCT40, Scanco, @19 μm-gold standard). The following parameters were evaluated: predicted stiffness, strength, bone volume fraction (BV/TV) and trabecular thickness (Tb.Th), separation (Tb.Sp) and number (Tb.N). The overall accuracy of CBCT with in-house optimized algorithms in quantifying bone microstructural parameters was comparable (R² = 0.79) to XtremeCT (R² = 0.76) and slightly worse than XtremeCT-II (R² = 0.86) which were both processed with the standard manufacturer's technique. CBCT had higher accuracy for BV/TV and Tb.Th but lower for Tb.Sp and Tb.N compared to XtremeCT. Regarding the mechanical parameters, all scanners had high accuracy (R² [Formula: see text] 0.96). While HR-pQCT is optimized for research, the fast scanning time and good accuracy renders CBCT a promising technique for high-resolution clinical scanning.

Rehabilitation in Osteoporosis - therapeutic chalenge?

Introduction. Osteoporosis is a disease of the entire skeleton, characterized by decrease bone mass and microarhitectural alterations of bone tissue, which result in increased bone fragility and predisposition to bone fractures. Materials and methods. Accesing standard medical databases: Medline, Embase, Database, Pubmed and the Cochrane Register of Controled Studies to review new pharmacological studies and non-pharmacological terapies in osteoporosis. Statistical analysis performed from the data extracted from the observation sheets from June 2019 to December 2019 by Dr. Liliana Stanciu. Results and discussions. The complex balneo-physical-kinetic treatment is an important link in the treatment of the disabling pathology for the patient, with an important clinical resonance. Conclusion. Osteoporosis is a pathology that decreases the patient’s quality of life. There are complementary therapies to pharmacological treatment with immediate and long lasting results. Keywords: mud, osteoporosis, balneal, hormones,

Conventional finite element models estimate the strength of metastatic human vertebrae despite alterations of the bone's tissue and structure

INTRODUCTION

Pathologic vertebral fractures are a major clinical concern in the management of cancer patients with metastatic spine disease. These fractures are a direct consequence of the effect of bone metastases on the anatomy and structure of the vertebral bone. The goals of this study were twofold. First, we evaluated the effect of lytic, blastic and mixed (both lytic and blastic) metastases on the bone structure, on its material properties, and on the overall vertebral strength. Second, we tested the ability of bone mineral content (BMC) measurements and standard FE methodologies to predict the strength of real metastatic vertebral bodies.

METHODS

Fifty-seven vertebral bodies from eleven cadaver spines containing lytic, blastic, and mixed metastatic lesions from donors with breast, esophageal, kidney, lung, or prostate cancer were scanned using micro-computed tomography (μCT). Based on radiographic review, twelve vertebrae were selected for nanoindentation testing, while the remaining forty-five vertebrae were used for assessing their compressive strength. The μCT reconstruction was exploited to measure the vertebral BMC and to establish two finite element models. 1) a micro finite element (μFE) model derived at an image resolution of 24.5 μm and 2) homogenized FE (hFE) model derived at a resolution of 0.98 mm. Statistical analyses were conducted to measure the effect of the bone metastases on BV/TV, indentation modulus (E_it), ratio of plastic/total work (W_Pl/W_tot), and in vitro vertebral strength (F_exp). The predictive value of BMC, μFE stiffness, and hFE strength were evaluated against the in vitro measurements.

RESULTS

Blastic vertebral bodies exhibit significantly higher BV/TV compared to the mixed (p = 0.0205) and lytic (p = 0.0216) vertebral bodies. No significant differences were found between lytic and mixed vertebrae (p = 0.7584). Blastic bone tissue exhibited a 5.8% lower median E_it (p< 0.001) and a 3.3% lower median W_pl/W_tot (p<0.001) compared to non-involved bone tissue. No significant differences were measured between lytic and non-involved bone tissues. F_exp ranged from 1.9 to 13.8 kN, was strongly associated with hFE strength (R²=0.78, p< 0.001) and moderately associated with BMC (R²=0.66, p< 0.001) and μFE stiffness (R²=0.66, p< 0.001), independently of the lesion type.

DISCUSSION

Our findings show that tumour-induced osteoblastic metastases lead to slightly, but significantly lower bone tissue properties compared to controls, while osteolytic lesions appear to have a negligible impact. These effects may be attributed to the lower mineralization and woven nature of bone forming in blastic lesions whilst the material properties of bone in osteolytic vertebrae appeared little changed. The moderate association between BMC- and FE-based predictions to fracture strength suggest that vertebral strength is affected by the changes of bone mass induced by the metastatic lesions, rather than altered tissue properties. In a broader context, standard hFE approaches generated from CTs at clinical resolution are robust to the lesion type when predicting vertebral strength. These findings open the door for the development of FE-based prediction tools that overcomes the limitations of BMC in accounting for shape and size of the metastatic lesions. Such tools may help clinicians to decide whether a patient needs the prophylactic fixation of an impending fracture.

MicroRNA-218 competes with differentiation media in the induction of osteogenic differentiation of mesenchymal stem cell by regulating β-catenin inhibitors

Osteoporosis, a systemic skeletal disorder specified by low bone mass, is associated with bone fragility and the raised risk of fractures. Activation of the Wnt/β-catenin signaling pathway has been directly demonstrated as a prominent biological event in the prevention of osteoporosis. Recently, critical roles of microRNAs (miRNAs) were further revealed in Wnt/β-catenin signaling activation and thereby contributing to the development and maintenance of the human skeleton. In this study, we investigated whether miR-218 can significantly promote the osteogenic differentiation of mesenchymal stem cells in conditional media by regulating β-catenin signaling inhibitors. The pre-miRNA nucleotide sequence of miR-218 was cloned into the pEGP-miR vector. Next, human adipose tissue-derived mesenchymal stem cells (AD-MSCs) were isolated, characterized, and transfected using pEGP-miR-218.Subsequently, the osteogenic potential of AD-MSCs was investigated in different treated groups using alkaline phosphatase (ALP)activity, calcium mineral deposition, and the expression of osteogenesis-related genes. Finally, negative regulators of Wnt signaling targeted by miR-218 were bioinformatically predicted. Our results indicated a significant increase in the ALP activity, mineralization, and osteogenesis-related genes expression in the AD-MSCs transfected with pEGP-miR-218. Also, the bioinformatic surveys and gene expression results showed that adenomatosis polyposis coli (APC) and glycogen synthase kinase 3 (GSK3-β) were downregulated in the transfected AD-MSCs in both differential and conditional media. This study provided evidence that miR-218 can promote osteogenic differentiation of AD-MSCs even in conditional media. Therefore, our findings suggest miR-218 as a putative novel therapeutic candidate in the context of osteoporosis and other bone metabolism-related diseases.

Regional improvements in lumbosacropelvic Hounsfield units following teriparatide treatment

OBJECTIVE

Opportunistic Hounsfield unit (HU) determination from CT imaging has been increasingly used to estimate bone mineral density (BMD) in conjunction with assessments from dual energy x-ray absorptiometry (DXA). The authors sought to compare the effect of teriparatide on HUs across different regions in the pelvis, sacrum, and lumbar spine, as a surrogate measure for the effects of teriparatide on lumbosacropelvic instrumentation.

METHODS

A single-institution retrospective review of patients who had been treated with at least 6 months of teriparatide was performed. All patients had at least baseline DXA as well as pre- and post-teriparatide CT imaging. HUs were measured in the pedicle, lamina, and vertebral body of the lumbar spine, in the sciatic notch, and at the S1 and S2 levels at three different points (ilium, sacral body, and sacral ala).

RESULTS

Forty patients with an average age of 67 years underwent a mean of 20 months of teriparatide therapy. Mean HUs of the lumbar lamina, pedicles, and vertebral body were significantly different from each other before teriparatide treatment: 343 ± 114, 219 ± 89.2, and 111 ± 48.1, respectively (p < 0.001). Mean HUs at the S1 level for the ilium, sacral ala, and sacral body were also significantly different from each other: 124 ± 90.1, −10.7 ± 61.9, and 99.1 ± 72.1, respectively (p < 0.001). The mean HUs at the S2 level for the ilium and sacral body were not significantly different from each other, although the mean HU at the sacral ala (−11.9 ± 52.6) was significantly lower than those at the ilium and sacral body (p = 0.003 and 0.006, respectively). HU improvement occurred in most regions following teriparatide treatment. In the lumbar spine, the mean lamina HU increased from 343 to 400 (p < 0.001), the mean pedicle HU increased from 219 to 242 (p = 0.04), and the mean vertebral body HU increased from 111 to 134 (p < 0.001). There were also significant increases in the S1 sacral body (99.1 to 130, p < 0.05), S1 ilium (124 vs 165, p = 0.01), S1 sacral ala (−10.7 vs 3.68, p = 0.04), and S2 sacral body (168 vs 189, p < 0.05).

CONCLUSIONS

There was significant regional variation in lumbar and sacropelvic HUs, with most regions significantly increasing following teriparatide treatment. The sacropelvic area had lower HU values than the lumbar spine, more regional variation, and a higher degree of correlation with BMD as measured on DXA. While teriparatide treatment resulted in HUs > 110 in the majority of the lumbosacral spine, the HUs in the sacral ala remained suggestive of severe osteoporosis, which may limit the effectiveness of fixation in this region.

Investigation of bone matrix composition, architecture and mechanical properties reflect structure-function relationship of cortical bone in glucocorticoid induced osteoporosis

Glucocorticoid induced osteoporosis (GIOP) is the most common negative consequence of long-term glucocorticoid treatment, leading to increased fracture risk followed by loss of mobility and high mortality risk. These biologically induced changes in bone quality at molecular level lead to changes both in bone matrix architecture and bone matrix composition. However, the quantitative details of changes in bone quality - and especially their link to reduced macroscale mechanical properties are still largely missing. In this study, a mouse model for glucocorticoid-induced osteoporosis (GIOP) was used to investigate mechanical and material alterations in bone cortex (natural nanocomposite) at different scale. By combining quantitative backscattered electron (qBSE) imaging, nanoindentation and high brilliance synchrotron X-ray nanomechanical imaging on a genetically modified mouse model of GIOP, we were able to quantify the local indentation modulus, mineralization distribution and the alterations of nanoscale structures and deformation mechanisms in the mid-diaphysis of femur, and relate them to the macroscopic mechanical changes. Our results showed clear and significant changes in terms of material quality of bone at nanoscale and microscale, which manifests itself in development of spatial heterogeneities in mineralization and indentation moduli across the bone organ, with potential implications for increased fracture risk.

Overview of treatment approaches to osteoporosis

Efficient therapies are available for the treatment of osteoporosis. Anti-resorptive therapies, including bisphosphonates and denosumab, increase bone mineral density (BMD) and reduce the risk of fractures by 20-70%. Bone-forming or dual-action treatments stimulate bone formation and increase BMD more than the anti-resorptive therapies. Two studies have demonstrated that these treatments are superior to anti-resorptives in preventing fractures in patients with severe osteoporosis. Bone-forming or dual-action treatments should be followed by anti-resorptive treatment to maintain the fracture risk reduction. The BMD gains seen with bone-forming and dual-action treatments are greater in treatment-naïve patients compared to patients pretreated with anti-resorptive treatments. However, the antifracture efficacy seems to be preserved. Treatment failure will often lead to switch of treatment from orally to parentally administrated anti-resorptives treatment or from anti-resorptive to bone-forming or dual-action treatment. Osteoporosis is a chronic condition and therefore needs a long-term management plan with a personalized approach to treatment. LINKED ARTICLES: This article is part of a themed issue on The molecular pharmacology of bone and cancer-related bone diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.9/issuetoc.

X-ray-based quantitative osteoporosis imaging at the spine

Osteoporosis is a metabolic bone disease with a high prevalence that affects the population worldwide, particularly the elderly. It is often due to fractures associated with bone fragility that the diagnosis of osteoporosis becomes clinically evident. However, early diagnosis would be necessary to initiate therapy and to prevent occurrence of further fractures, thus reducing morbidity and mortality. X-ray-based imaging plays a key role for fracture risk assessment and monitoring of osteoporosis. Whereas over decades dual-energy X-ray absorptiometry (DXA) has been the main method used and still reflects the reference standard, another modality reemerges with quantitative computed tomography (QCT) because of its three-dimensional advantages and the opportunistic exploitation of routine CT scans. Against this background, this article intends to review and evaluate recent advances in the field of X-ray-based quantitative imaging of osteoporosis at the spine. First, standard DXA with the recent addition of trabecular bone score (TBS) is presented. Secondly, standard QCT, dual-energy BMD quantification, and opportunistic BMD screening in non-dedicated CT exams are discussed. Lastly, finite element analysis and microstructural parameter analysis are reviewed.

Differences in Trabecular Microarchitecture and Simplified Boundary Conditions Limit the Accuracy of Quantitative Computed Tomography-Based Finite Element Models of Vertebral Failure

Vertebral fractures are common in the elderly, but efforts to reduce their incidence have been hampered by incomplete understanding of the failure processes that are involved. This study's goal was to elucidate failure processes in the lumbar vertebra and to assess the accuracy of quantitative computed tomography (QCT)-based finite element (FE) simulations of these processes. Following QCT scanning, spine segments (n = 27) consisting of L1 with adjacent intervertebral disks and neighboring endplates of T12 and L2 were compressed axially in a stepwise manner. A microcomputed tomography scan was performed at each loading step. The resulting time-lapse series of images was analyzed using digital volume correlation (DVC) to quantify deformations throughout the vertebral body. While some diversity among vertebrae was observed on how these deformations progressed, common features were large strains that developed progressively in the superior third and, concomitantly, in the midtransverse plane, in a manner that was associated with spatial variations in microstructural parameters such as connectivity density. Results of FE simulations corresponded qualitatively to the measured failure patterns when boundary conditions were derived from DVC displacements at the endplate. However, quantitative correspondence was often poor, particularly when boundary conditions were simplified to uniform compressive loading. These findings suggest that variations in trabecular microstructure are one cause of the differences in failure patterns among vertebrae and that both the lack of incorporation of these variations into QCT-based FE models and the oversimplification of boundary conditions limit the accuracy of these models in simulating vertebral failure.

Improved accuracy in the assessment of vertebral cortical thickness by quantitative computed tomography using the Iterative Convolution OptimizatioN (ICON) method

Vertebral whole bone strength is substantially affected by cortical bone properties. Disease and therapy may affect cancellous and cortical bone differently. Unlike Dual X-ray Absorptiometry (DXA), Quantitative Computed Tomography (QCT) permits selective assessment of cortical and cancellous bone, but image quality limits the accuracy. We present an image processing method specifically adopted to thin cortices that substantially improves accuracy. Ten human vertebrae embedded in epoxy resin were imaged using clinical QCT and High-Resolution QCT (HR-QCT) protocols, both acquired on a clinical whole body CT scanner, whereas high resolution peripheral QCT (HR-pQCT) was used as gold standard. Microstructural variables and BMD were calculated using in-house software StructuralInsight for QCT and HR-QCT and the manufacturer's μCT evaluation software for HR-pQCT. An adjusted measure, a deconvolved cortical thickness (dcCt.Th), corrected for partial volume effects, was derived applying the new Iterative Convolution OptimizatioN (ICON) method. Direct measurements of cortical thickness (Ct.Th) showed substantial overestimation with mean ± standard deviation of 1.8 ± 0.5 mm for QCT and 1.5 ± 0.3 mm for HR-QCT compared to 0.37 ± 0.07 mm using HR-pQCT. Correlations of both QCT (r² = 0.05, p > 0.5.) and HR-QCT (r² = 0.38, p = 0.060) with the gold standard HR-pQCT were not significant. Also QCT-based BMD and BMC as well as HR-QCT-based BMD did not show a significant correlation with the gold standard approach. Only HR-QCT-based BMC showed a modest correlation (r² = 0.59, p = 0.01) After applying ICON corrections, dcCt.Th resulted in 0.52 ± 0.09 mm for QCT and 0.43 ± 0.07 mm for HR-QCT, both significantly correlated to HR-pQCT (r² = 0.75, p = 0.0012 and r² = 0.93, p < 0.0001, respectively). The average overestimation bias of Ct.Th was reduced from (402 ± 157)% to (45 ± 17)% for QCT and from (330 ± 69)% to (19 ± 8)% for HR-QCT. Due to inaccurate segmentation uncorrected QCT-based Ct.Th measures as well as BMD and BMC showed no correlation to HR-pQCT and thus such bias cortical data can be misleading. The application of ICON reduced random overestimation bias to about 50 μm and 20 μm for QCT and HR-QCT, respectively, leading to a recovery of a significant correlation with the reference data of HR-pQCT. This reveals the potential for fairly accurate assessment of cortical thickness, allowing to better characterize cortical mechanical competence. These results warrant testing of the performance in vivo.

Prediction of incident vertebral fracture using CT-based finite element analysis

Prior studies show vertebral strength from computed tomography-based finite element analysis may be associated with vertebral fracture risk. We found vertebral strength had a strong association with new vertebral fractures, suggesting that vertebral strength measures identify those at risk for vertebral fracture and may be a useful clinical tool.

INTRODUCTION

We aimed to determine the association between vertebral strength by quantitative computed tomography (CT)-based finite element analysis (FEA) and incident vertebral fracture (VF). In addition, we examined sensitivity and specificity of previously proposed diagnostic thresholds for fragile bone strength and low BMD in predicting VF.

METHODS

In a case-control study, 26 incident VF cases (13 men, 13 women) and 62 age- and sex-matched controls aged 50 to 85 years were selected from the Framingham multi-detector computed tomography cohort. Vertebral compressive strength, integral vBMD, trabecular vBMD, CT-based BMC, and CT-based aBMD were measured from CT scans of the lumbar spine.

RESULTS

Lower vertebral strength at baseline was associated with an increased risk of new or worsening VF after adjusting for age, BMI, and prevalent VF status (odds ratio (OR) = 5.2 per 1 SD decrease, 95% CI 1.3-19.8). Area under receiver operating characteristic (ROC) curve comparisons revealed that vertebral strength better predicted incident VF than CT-based aBMD (AUC = 0.804 vs. 0.715, p = 0.05) but was not better than integral vBMD (AUC = 0.815) or CT-based BMC (AUC = 0.794). Additionally, proposed fragile bone strength thresholds trended toward better sensitivity for identifying VF than that of aBMD-classified osteoporosis (0.46 vs. 0.23, p = 0.09).

CONCLUSION

This study shows an association between vertebral strength measures and incident vertebral fracture in men and women. Though limited by a small sample size, our findings also suggest that bone strength estimates by CT-based FEA provide equivalent or better ability to predict incident vertebral fracture compared to CT-based aBMD. Our study confirms that CT-based estimates of vertebral strength from FEA are useful for identifying patients who are at high risk for vertebral fracture.

Collagen proton fraction from ultrashort echo time magnetization transfer (UTE-MT) MRI modelling correlates significantly with cortical bone porosity measured with micro-computed tomography (μCT)

Intracortical bone porosity is a key microstructural parameter that determines bone mechanical properties. While clinical MRI visualizes the cortical bone with a signal void, ultrashort echo time (UTE) MRI can acquire high signal from cortical bone, thus enabling quantitative assessments. Magnetization transfer (MT) imaging combined with UTE-MRI can indirectly assess protons in the bone collagenous matrix, which are inversely related to porosity. This study aimed to examine UTE-MT MRI techniques to evaluate intracortical bone porosity. Eighteen human cortical bone specimens from the tibial and fibular midshafts were scanned using UTE-MT sequences on a clinical 3 T MRI scanner and on a high-resolution micro-computed tomography (μCT) scanner. A series of MT pulse saturation powers (500°, 1000°, 1500°) and frequency offsets (2, 5, 10, 20, 50 kHz) were used to measure the macromolecular fraction (MMF) and macromolecular T2 (T2MM ) using a two-pool MT model. The measurements were made on 136 different regions of interest (ROIs). ROIs were selected at three cortical bone layers (from endosteum to periosteum) and four anatomical sites (anterior, mid-medial, mid-lateral, and posterior) to provide a wide range of porosity. MMF showed moderate to strong correlations with intracortical bone porosity (R = -0.67 to -0.73, p < 0.01) and bone mineral density (BMD) (R = +0.46 to +0.70, p < 0.01). Comparing the average MMF between cortical bone layers revealed a significant increase from the endosteum towards the periosteum. Such a pattern was in agreement with porosity reduction and BMD increase towards the periosteum. These results suggest that the two-pool UTE-MT technique can potentially serve as a novel and accurate tool to assess intracortical bone porosity.

Determinants of bone damage: An ex-vivo study on porcine vertebrae

Bone's resistance to fracture depends on several factors, such as bone mass, microarchitecture, and tissue material properties. The clinical assessment of bone strength is generally performed by Dual-X Ray Photon Absorptiometry (DXA), measuring bone mineral density (BMD) and trabecular bone score (TBS). Although it is considered the major predictor of bone strength, BMD only accounts for about 70% of fragility fractures, while the remaining 30% could be described by bone "quality" impairment parameters, mainly related to tissue microarchitecture. The assessment of bone microarchitecture generally requires more invasive techniques, which are not applicable in routine clinical practice, or X-Ray based imaging techniques, requiring a longer post-processing. Another important aspect is the presence of local damage in the bony tissue that may also affect the prediction of bone strength and fracture risk. To provide a more comprehensive analysis of bone quality and quantity, and to assess the effect of damage, here we adopt a framework that includes clinical, morphological, and mechanical analyses, carried out by means of DXA, μCT and mechanical compressive testing, respectively. This study has been carried out on trabecular bones, taken from porcine trabecular vertebrae, for the similarity with human lumbar spine. This study confirms that no single method can provide a complete characterization of bone tissue, and the combination of complementary characterization techniques is required for an accurate and exhaustive description of bone status. BMD and TBS have shown to be complementary parameters to assess bone strength, the former assessing the bone quantity and resistance to damage, and the latter the bone quality and the presence of damage accumulation without being able to predict the risk of fracture.

Bone matrix development in steroid-induced osteoporosis is associated with a consistently reduced fibrillar stiffness linked to altered bone mineral quality

Glucocorticoid-induced osteoporosis (GIOP) is a major secondary form of osteoporosis, with the fracture risk significantly elevated - at similar levels of bone mineral density - in patients taking glucocorticoids compared with non-users. The adverse bone structural changes at multiple hierarchical levels in GIOP, and their mechanistic consequences leading to reduced load-bearing capacity, are not clearly understood. Here we combine experimental X-ray nanoscale mechanical imaging with analytical modelling of the bone matrix mechanics to determine mechanisms causing bone material quality deterioration during development of GIOP. In situ synchrotron small-angle X-ray diffraction combined with tensile testing was used to measure nanoscale deformation mechanisms in a murine model of GIOP, due to a corticotrophin-releasing hormone promoter mutation, at multiple ages (8-, 12-, 24- and 36 weeks), complemented by quantitative micro-computed tomography and backscattered electron imaging to determine mineral concentrations. We develop a two-level hierarchical model of the bone matrix (mineralized fibril and lamella) to predict fibrillar mechanical response as a function of architectural parameters of the mineralized matrix. The fibrillar elastic modulus of GIOP-bone is lower than healthy bone throughout development, and nearly constant in time, in contrast to the progressively increasing stiffness in healthy bone. The lower mineral platelet aspect ratio value for GIOP compared to healthy bone in the multiscale model can explain the fibrillar deformation. Consistent with this result, independent measurement of mineral platelet lengths from wide-angle X-ray diffraction finds a shorter mineral platelet length in GIOP. Our results show how lowered mineralization combined with altered mineral nanostructure in GIOP leads to lowered mechanical competence.

SIGNIFICANCE STATEMENT

Increased fragility in musculoskeletal disorders like osteoporosis are believed to arise due to alterations in bone structure at multiple length-scales from the organ down to the supramolecular-level, where collagen molecules and elongated mineral nanoparticles form stiff fibrils. However, the nature of these molecular-level alterations are not known. Here we used X-ray scattering to determine both how bone fibrils deform in secondary osteoporosis, as well as how the fibril orientation and mineral nanoparticle structure changes. We found that osteoporotic fibrils become less stiff both because the mineral nanoparticles became shorter and less efficient at transferring load from collagen, and because the fibrils are more randomly oriented. These results will help in the design of new composite musculoskeletal implants for bone repair.

Phase 1 trial of vamorolone, a first-in-class steroid, shows improvements in side effects via biomarkers bridged to clinical outcomes

BACKGROUND

Glucocorticoid drugs are highly effective anti-inflammatory agents, but chronic use is associated with extensive pharmacodynamic safety concerns that have a considerable negative impact on patient quality of life.

PURPOSE

Vamorolone (VBP15) is a first-in-class steroidal multi-functional drug that shows potent inhibition of pro-inflammatory NFkB pathways via high-affinity binding to the glucocorticoid receptor, high affinity antagonism for the mineralocorticoid receptor, and membrane stabilization properties. Pre-clinical data in multiple mouse models of inflammation showed retention of anti-inflammatory efficacy, but loss of most or all side effects.

EXPERIMENTAL APPROACH

We report first-in-human Phase 1 clinical trials (86 healthy adult males), with single ascending doses (0.1-20.0 mg/kg), and multiple ascending doses (1.0-20 mg/kg/day; 14 days treatment).

KEY RESULTS

Vamorolone was well-tolerated at all dose levels. Vamorolone showed pharmacokinetic and metabolism profiles similar to prednisone. Biomarker studies showed loss of side effects of traditional glucocorticoid drugs (bone fragility, metabolic disturbance, immune suppression). Suppression of the adrenal axis was 10-fold less than prednisone. The crystallographic structure of vamorolone was solved, and compared to prednisone and dexamethasone. There was overlap in structure, but differences in conformation at the C-ring where glucocorticoids interact with Asn564 of the glucocorticoid receptor. The predicted loss of Asn564 binding to vamorolone may underlie the loss of gene transcriptional activity.

CONCLUSIONS AND INTERPRETATIONS

Vamorolone is a dissociative steroid that retains high affinity binding and nuclear translocation of both glucocorticoid (agonist) and mineralocorticoid (antagonist) receptors, but does not show pharmacodynamic safety concerns of existing glucocorticoid drugs at up to 20 mg/kg/day.

Opportunistic Bone Density Measurement on Abdomen and Pelvis Computed Tomography to Predict Fracture Risk in Women Aged 50 to 64 Years Without Osteoporosis Risk Factors

OBJECTIVE

The aim of this study is to evaluate opportunistic vertebral bone density measurement in abdominal and pelvic computed tomography (CT) to predict future osteoporotic fracture in women aged 50 to 64 years without known osteoporosis risk factors.

METHODS

Consecutive female patients 50 to 64 years old without osteoporosis risk factors with 2 CT examinations more than 10 years apart were included. Vertebral height and bone density in each vertebra from T10 to L5 were measured. Vertebral fractures were diagnosed on CT preformed 10 years after the original CT and through online medical records.

RESULTS

Thirty (15%) of 199 patients developed osteoporotic fracture. Bone density was lower in patients who developed fractures compared with those who did not (P < 0.05). Development of osteoporotic fracture of any grade was predicted for patients having bone density less than 180 HU at L4 with sensitivity of 90% (95% confidence interval, 74%-97%) and specificity of 43% (95% confidence interval, 34%-50%).

CONCLUSIONS

Opportunistic bone density screening can identify women at elevated risk of developing fractures within 10 years.

Bone quality changes associated with aging and disease: a review

Bone quality encompasses all the characteristics of bone that, in addition to density, contribute to its resistance to fracture. In this review, we consider changes in architecture, porosity, and composition, including collagen structure, mineral composition, and crystal size. These factors all are known to vary with tissue and animal ages, and health status. Bone morphology and presence of microcracks, which also contribute to bone quality, will not be discussed in this review. Correlations with mechanical performance for collagen cross-linking, crystallinity, and carbonate content are contrasted with mineral content. Age-dependent changes in humans and rodents are discussed in relation to rodent models of disease. Examples are osteoporosis, osteomalacia, osteogenesis imperfecta (OI), and osteopetrosis in both humans and animal models. Each of these conditions, along with aging, is associated with increased fracture risk for distinct reasons.

Vertebral Imaging in the Diagnosis of Osteoporosis: a Clinician's Perspective

PURPOSE OF REVIEW

Vertebral fractures are the most common osteoporotic fracture and result in functional decline and excess mortality. Dual-energy x-ray absorptiometry (DXA) is the gold standard for the diagnosis of osteoporosis to identify patients at risk for fragility fractures; however, advances in imaging have expanded the role of computed tomography (CT) and magnetic resonance imaging (MRI) in evaluating bone health.

RECENT FINDINGS

The utility of CT and MRI in the assessment of bone density is starting to gain traction, particularly when used opportunistically. DXA, conventional radiography, CT, and MRI can all be used to assess for vertebral fractures, and MRI can determine the acuity of fractures. Finally, advances in imaging allow for non-invasive assessment of measures of bone quality, including microarchitecture, bone strength, and bone turnover, to help identify and treat at-risk patients prior to sustaining a vertebral fracture. CT and MRI techniques remain primarily research tools to assess metabolic bone dysfunction, while use of DXA can be clinically expanded beyond measurement of bone density to assess for vertebral fractures and bone architecture to improve fracture risk assessment and guide treatment.

Phase-field boundary conditions for the voxel finite cell method: Surface-free stress analysis of CT-based bone structures

The voxel finite cell method uses unfitted finite element meshes and voxel quadrature rules to seamlessly transfer computed tomography data into patient-specific bone discretizations. The method, however, still requires the explicit parametrization of boundary surfaces to impose traction and displacement boundary conditions, which constitutes a potential roadblock to automation. We explore a phase-field-based formulation for imposing traction and displacement constraints in a diffuse sense. Its essential component is a diffuse geometry model generated from metastable phase-field solutions of the Allen-Cahn problem that assumes the imaging data as initial condition. Phase-field approximations of the boundary and its gradient are then used to transfer all boundary terms in the variational formulation into volumetric terms. We show that in the context of the voxel finite cell method, diffuse boundary conditions achieve the same accuracy as boundary conditions defined over explicit sharp surfaces, if the inherent length scales, ie, the interface width of the phase field, the voxel spacing, and the mesh size, are properly related. We demonstrate the flexibility of the new method by analyzing stresses in a human femur and a vertebral body.

Advances in the evaluation of bone health in kidney transplant patients

Bone disease related to chronic kidney disease and, particularly, to kidney transplant patients is a common cause or morbidity and mortality, especially due to a higher risk of osteoporotic fractures. Despite the fact that this has been known for decades, to date, an appropriate diagnostic strategy has yet to be established. Apart from bone biopsy, which is invasive and scarcely used, no other technique is available to accurately establish the risk of fracture in kidney patients. Techniques applied to the general population, such as bone densitometry, have not been subjected to sufficient external validation and their use is not systematic. This means that the identification of patients at risk of fracture and therefore those who are candidates for preventive strategies is an unmet need. Bone strength, defined as the ability of the bone to resist fracture, is determined by bone mineral density (measured by bone densitometry), trabecular architecture and bone tissue quality. The trabecular bone score estimates bone microarchitecture, and low values have been described as an independent predictor of increased fracture risk. Bone microindentation is a minimally invasive technique that measures resistance of the bone to micro-cracks (microscopic separation of mineralised collagen fibres), and therefore bone tissue biomechanical properties. The superiority over bone densitometry of the correlation between the parameters measured by trabecular bone score and microindentation with the risk of fracture in diverse populations led us to test its feasibility in chronic kidney disease and kidney transplant patients.

Quantitative Computed Tomography-Current Status and New Developments

This review focuses on new developments and current controversies in the field of quantitative computed tomography. Recent positions of the International Society for Clinical Densitometry acknowledged the clinical value of quantitative computed tomography of the spine and the hip using clinical whole-body computed tomography (CT) scanners. Opportunistic screening summarizes a number of new approaches describing the dual use of clinical CT scans. For example, CT scans may have been taken for tumor diagnosis but may also be used for the prediction of high or low fracture risks as an additional benefit for the patient. The assessment of the cortical parameters is another topic of current research. In CT images of the spine and the hip, a number of techniques have been developed to determine the thickness, mass, and bone density of the cortex. In higher-spatial resolution peripheral CT images of the radius and tibia obtained from special purpose scanners, 1 focus is the measurement of cortical porosity. Two different approaches, one based on the direct segmentation of the pores and one based on cortical density, will be reviewed.

Site-Specific Variations in Bone Mineral Density under Systemic Conditions Inducing Osteoporosis in Minipigs

Osteoporosis is a systemic bone disease with an increasing prevalence in the elderly population. There is conflicting opinion about whether osteoporosis affects the alveolar bone of the jaws and whether it poses a risk to the osseointegration of dental implants. The aim of the present study was to evaluate the effects of systemic glucocorticoid administration on the jaw bone density of minipigs. Thirty-seven adult female minipigs were randomly divided into two groups. Quantitative computed tomography (QCT) was used to assess bone mineral density BMD of the lumbar spine as well as the mandible and maxilla, and blood was drawn. One group of minipigs initially received 1.0 mg prednisolone per kg body weight daily for 2 months. The dose was tapered to 0.5 mg per kg body weight per day thereafter. The animals in the other group served as controls and received placebo. QCT and blood analysis were repeated after 6 and 9 months. BMD was compared between the two groups by measuring Hounsfield units, and serum levels of several bone metabolic markers were also assessed. A decrease in BMD was observed in the jaws from baseline to 9 months. This was more pronounced in the prednisolone group. Statistically significant differences were reached for the mandible (p < 0.001) and the maxilla (p < 0.001). The administration of glucocorticoids reduced the BMD in the jaws of minipigs. The described model shows promise in the evaluation of osseointegration of dental implants in bone that is compromised by osteoporosis.

Clinical experience with microindentation in vivo in humans

Densitometry and imaging techniques are currently used in clinical settings to measure bone quantity and spatial structure. Recently, Reference Point Indentation has opened the possibility of directly assessing the mechanical characteristics of cortical bone in living individuals, adding a new dimension to the assessment of bone strength. Impact microindentation was specifically developed for clinical studies and has been tested in several populations where there are discrepancies between bone density and fracture propensity, such as type 2 diabetes, atypical femoral fracture, stress fractures, glucocorticoid treatment, patients with osteopenia and fragility fractures, and individuals infected with HIV, among others. Microindentation will complement, not replace, existing bone analysis methods, particularly where bone mineral density does not fully explain fracture propensity. The available evidence provides solid proof of concept; future studies will fully define the role of microindentation for the assessment of bone health both in clinics and in 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.

Finite Element-Based Mechanical Assessment of Bone Quality on the Basis of In Vivo Images

Beyond bone mineral density (BMD), bone quality designates the mechanical integrity of bone tissue. In vivo images based on X-ray attenuation, such as CT reconstructions, provide size, shape, and local BMD distribution and may be exploited as input for finite element analysis (FEA) to assess bone fragility. Further key input parameters of FEA are the material properties of bone tissue. This review discusses the main determinants of bone mechanical properties and emphasizes the added value, as well as the important assumptions underlying finite element analysis. Bone tissue is a sophisticated, multiscale composite material that undergoes remodeling but exhibits a rather narrow band of tissue mineralization. Mechanically, bone tissue behaves elastically under physiologic loads and yields by cracking beyond critical strain levels. Through adequate cell-orchestrated modeling, trabecular bone tunes its mechanical properties by volume fraction and fabric. With proper calibration, these mechanical properties may be incorporated in quantitative CT-based finite element analysis that has been validated extensively with ex vivo experiments and has been applied increasingly in clinical trials to assess treatment efficacy against osteoporosis.

TECHNOLOGIES FOR STRAIN ASSESSMENT FROM WHOLE BONE TO MINERALIZED OSTEOID LEVEL: A CRITICAL REVIEW

Bone has distinctive structures and mechanical properties at the whole bone, perilacunar and mineralized osteoid levels. A systematic understanding of bone strain magnitudes at different anatomical levels and their internal interactions is the prerequisite to advances in bone mechanobiology. However, due to the intrinsic shortcomings of the strain-measuring technologies, the systematic assessment of bone strain at different anatomical levels under physiological conditions and a deep understanding of their internal interactions are still restricted. To promote technological advances and provide systematic and valuable information for mechanical engineers and bone biomechanical researchers, the most useful methods for measuring bone strain at different anatomical levels are demonstrated in this review, and suggestions for the future development of the technologies and their potential integrated applications are proposed.

Trabecular Bone Score (TBS) and TBS-Adjusted Fracture Risk Assessment Tool are Potential Supplementary Tools for the Discrimination of Morphometric Vertebral Fractures in Postmenopausal Women With Type 2 Diabetes

Type 2 diabetes mellitus (T2DM) is associated with fracture risk but, paradoxically, greater bone mineral density (BMD). The trabecular bone score (TBS) has been proposed as an index of bone microarchitecture associated with bone quality. This study compared the performance of TBS, BMD, and original and TBS-adjusted Fracture Risk Assessment Tool (FRAX®) scores in the discrimination of vertebral fractures (VFs) in T2DM patients. This retrospective study enrolled 169 Korean postmenopausal women with T2DM. Lateral plain radiographs of the thoracolumbar spine were taken. Lumbar spine and femur neck BMDs were obtained using dual-energy X-ray absorptiometry (DXA). TBS was obtained using the TBS iNsight software program (Med-Imaps, Pessac, France) with BMD DXA images (L1-L4). VFs were diagnosed when at least 1 of the 3 height measurements was decreased by >25% compared to the nearest uncompressed vertebral body. Among the subjects, 34 women (20.1%) had VFs. Significantly lower TBS (p = 0.008) and higher TBS-adjusted FRAX scores were shown (p = 0.019) in the group with VFs compared to the group without VFs. In contrast, there were no significant differences in BMD and original FRAX scores between the 2 groups. Odds ratios (ORs) per standard deviation decrease in BMD or TBS and per standard deviation increase in the FRAX score were estimated with adjustment for age. TBS (OR = 1.8, 95% confidence interval [CI]: 1.1-2.7, p = 0.011) and TBS-adjusted FRAX score (OR = 2.0, 95% confidence interval: 1.1-3.5, p = 0.020) showed statistically significant ORs but the others did not. TBS and TBS-adjusted FRAX could be supplementary tools to discriminate osteoporotic fractures in T2DM.

Synchrotron Imaging Assessment of Bone Quality

Bone is a complex hierarchical structure, and its principal function is to resist mechanical forces and fracture. Bone strength depends not only on the quantity of bone tissue but also on the shape and hierarchical structure. The hierarchical levels are interrelated, especially the micro-architecture, collagen and mineral components; hence, analysis of their specific roles in bone strength and stiffness is difficult. Synchrotron imaging technologies including micro-CT and small/wide angle X-ray scattering/diffraction are becoming increasingly popular for studying bone because the images can resolve deformations in the micro-architecture and collagen-mineral matrix under in situ mechanical loading. Synchrotron cannot be directly applied in vivo due to the high radiation dose but will allow researchers to carry out systematic multifaceted studies of bone ex vivo. Identifying characteristics of aging and disease will underpin future efforts to generate novel devices and interventional therapies for assessing and promoting healthy aging. With our own research work as examples, this paper introduces how synchrotron imaging technology can be used with in situ testing in bone research.