Augmenting Osteoporosis Imaging with Machine Learning.

PURPOSE OF REVIEW: In this paper, we discuss how recent advancements in image processing and machine learning (ML) are shaping a new and exciting era for the osteoporosis imaging field. With this paper, we want to give the reader a basic exposure to the ML concepts that are necessary to build effective solutions for image processing and interpretation, while presenting an overview of the state of the art in the application of machine learning techniques for the assessment of bone structure, osteoporosis diagnosis, fracture detection, and risk prediction. RECENT FINDINGS: ML effort in the osteoporosis imaging field is largely characterized by "low-cost" bone quality estimation and osteoporosis diagnosis, fracture detection, and risk prediction, but also automatized and standardized large-scale data analysis and data-driven imaging biomarker discovery. Our effort is not intended to be a systematic review, but an opportunity to review key studies in the recent osteoporosis imaging research landscape with the ultimate goal of discussing specific design choices, giving the reader pointers to possible solutions of regression, segmentation, and classification tasks as well as discussing common mistakes.

Update on Imaging-Based Measurement of Bone Mineral Density and Quality.

PURPOSE OF REVIEW: Patients with inflammatory arthropathies have a high rate of fragility fractures. Diagnostic assessment and monitoring of bone density and quality are therefore critically important. Here, we review standard and advanced techniques to measure bone density and quality, specifically focusing on patients with inflammatory arthropathies. RECENT FINDINGS: Current standard procedures are dual-energy X-ray absorptiometry (DXA) and quantitative computed tomography (QCT). DXA-based newer methods include trabecular bone score (TBS) and vertebral fracture assessment (VFA). More advanced imaging methods to measure bone quality include high-resolution peripheral quantitative computed tomography (HR-pQCT) as well as multi-detector CT (MD-CT) and magnetic resonance imaging (MRI). Quantitative ultrasound has shown promise but is not standard to assess bone fragility. While there are limitations, DXA remains the standard technique to measure density in patients with rheumatological disorders. Newer modalities to measure bone quality may allow better characterization of bone fragility but currently are not standard of care procedures.

Detection of Lumbar Spine Osseous Metastases Using Dual-Energy CT: Phantom Results and Preliminary Clinical Validation.

OBJECTIVE: The purpose of this study was to evaluate the sensitivity, tumor conspicuity, and image quality of different material decomposition images of phantoms and patients with nearly isodense bone metastases using rapid-kilovoltage-switching dual-energy CT (DECT). MATERIALS AND METHODS: Fifty-one semianthropomorphic lumbar spine phantoms embedded with 75 simulated tumors were scanned without and with outer torso-attenuating encasement under the same scan settings. Two radiologists independently reviewed the 70-keV virtual monochromatic and material decomposition images (hydroxyapatite-water, water-hydroxyapatite, cortical bone-water, water-cortical bone). The sensitivity of tumor detection, tumor conspicuity (on a 3-point scale), and image quality (on a 3-point scale) were recorded by two independent readers. McNemar and Wilcoxon signed rank tests were used to compare results between the image reconstructions. Six clinical abdominopelvic DECT scans (three men, three women; mean age, 52 years) with nine nearly isodense lumbar spine tumors missed in the clinical report but confirmed on other scans were also evaluated. RESULTS: The hydroxyapatite-water material decomposition algorithm showed improved sensitivity for isodense lesion detection (without torso phantom encasement, 94% vs 82%, p = 0.031; with torso phantom encasement, 38% vs 18%, p = 0.013), and higher tumor conspicuity scores (p < 0.0001) compared with 70-keV virtual monoenergetic images. Artifacts were more prevalent with all material decomposition images than with 70-keV virtual monoenergetic images. Similar results were seen in the patient study. CONCLUSION: Dual-energy CT with hydroxyapatite-water material decomposition may improve the detection of bone marrow metastases, especially for subtle isodense tumors. Further study in prospective clinical scans is warranted.

Validation of bone marrow fat quantification in the presence of trabecular bone using MRI.

BACKGROUND: To validate six-echo, chemical-shift based MRI with T2 * correction for the quantification of bone marrow fat content in the presence of trabecular bone. METHODS: Ten bone phantoms were made using trabecular bone cores extracted from the distal femur and proximal tibia of 20 human cadaveric knees. Bone marrow was removed from the cores and the marrow spaces were filled with water-fat gelatin to mimic bone marrow of known fat fractions. A chemical-shift based water-fat separation method with T2 * correction was used to generate fat fraction maps. The proton density fat fractions (PDFF) between marrow regions with and without bone were compared with the reference standard of known fat fraction using the squared Pearson correlation coefficient and unpaired t-test. RESULTS: Strong correlations were found between the known fat fraction and measured PDFF in marrow without trabecular bone (R(2) = 0.99; slope = 0.99, intercept = 0.94) as well as in marrow with trabecular bone (R(2) = 0.97; slope = 1.0, intercept = -3.58). Measured PDFF between regions with and without bone were not significantly different (P = 0.5). However, PDFF was systematically underestimated by -3.2% fat fraction in regions containing trabecular bone. CONCLUSION: Our implementation of a six-echo chemical-shift based MRI pulse sequence with T2 * correction provided an accurate means of determining fat content in bone marrow in the presence of trabecular bone.

Effect of intraspecimen spatial variation in tissue mineral density on the apparent stiffness of trabecular bone.

This study investigated the effects of intraspecimen variations in tissue mineral density(TMD) on the apparent-level stiffness of human trabecular bone. High-resolution finite element (FE) models were created for each of 12 human trabecular bone specimens,using both microcomputed tomography (lCT) and "gold-standard" synchrotron radiation lCT (SRlCT) data. Our results confirm that incorporating TMD spatial variation reduces the calculated apparent stiffness compared to homogeneous TMD models. This effect exists for both lCT- and SRlCT-based FE models, but is exaggerated in lCT based models. This study provides a direct comparison of lCT to SRlCT data and is thereby able to conclude that the influence of including TMD heterogeneity is overestimated in lCT-based models.

Microvascular disease not type 2 diabetes is associated with increased cortical porosity: A study of cortical bone microstructure and intracortical vessel characteristics.

Introduction: Fracture risk is elevated in type 2 diabetes (T2D) despite normal or even high bone mineral density (BMD). Microvascular disease (MVD) is a diabetic complication, but also associated with other diseases, for example chronic kidney disease. We hypothesize that increased fracture risk in T2D could be due to increased cortical porosity (Ct.Po) driven by expansion of the vascular network in MVD. The purpose of this study was to investigate associations of T2D and MVD with cortical microstructure and intracortical vessel parameters. Methods: The study group consisted of 75 participants (38 with T2D and 37 without T2D). High-resolution peripheral quantitative CT (HR-pQCT) and dynamic contrast-enhanced MRI (DCE-MRI) of the ultra-distal tibia were performed to assess cortical bone and intracortical vessels (outcomes). MVD was defined as ≥1 manifestation including neuropathy, nephropathy, or retinopathy based on clinical exams in all participants. Adjusted means of outcomes were compared between groups with/without T2D or between participants with/without MVD in both groups using linear regression models adjusting for age, sex, BMI, and T2D as applicable. Results: MVD was found in 21 (55 %) participants with T2D and in 9 (24 %) participants without T2D. In T2D, cortical pore diameter (Ct.Po.Dm) and diameter distribution (Ct.Po.Dm.SD) were significantly higher by 14.6 µm (3.6 %, 95 % confidence interval [CI]: 2.70, 26.5 µm, p = 0.017) and by 8.73 µm (4.8 %, CI: 0.79, 16.7 µm, p = 0.032), respectively. In MVD, but not in T2D, cortical porosity was significantly higher by 2.25 % (relative increase = 12.9 %, CI: 0.53, 3.97 %, p = 0.011) and cortical BMD (Ct.BMD) was significantly lower by -43.6 mg/cm3 (2.6 %, CI: -77.4, -9.81 mg/cm3, p = 0.012). In T2D, vessel volume and vessel diameter were significantly higher by 0.02 mm3 (13.3 %, CI: 0.004, 0.04 mm3, p = 0.017) and 15.4 µm (2.9 %, CI: 0.42, 30.4 µm, p = 0.044), respectively. In MVD, vessel density was significantly higher by 0.11 mm-3 (17.8 %, CI: 0.01, 0.21 mm-3, p = 0.033) and vessel volume and diameter were significantly lower by -0.02 mm3 (13.7 %, CI: -0.04, -0.004 mm3, p = 0.015) and - 14.6 µm (2.8 %, CI: -29.1, -0.11 µm, p = 0.048), respectively. Conclusions: The presence of MVD, rather than T2D, was associated with increased cortical porosity. Increased porosity in MVD was coupled with a larger number of smaller vessels, which could indicate upregulation of neovascularization triggered by ischemia. It is unclear why higher variability and average diameters of pores in T2D were accompanied by larger vessels.

MR-based techniques for intracortical vessel visualization and characterization: understanding the impact of microvascular disease on skeletal health.

PURPOSE OF REVIEW: The relationships between bone vasculature and bone microstructure and strength remain incompletely understood. Addressing this gap will require in vivo imaging capabilities. We describe the relevant vascular anatomy of compact bone, review current magnetic resonance imaging (MRI)-based techniques that allow in vivo assessment of intracortical vasculature, and finally present preliminary studies that apply these techniques to investigate changes in intracortical vessels in aging and disease. RECENT FINDINGS: Ultra-short echo time MRI (UTE MRI), dynamic contrast-enhanced MRI (DCE-MRI), and susceptibility-weighted MRI techniques are able to probe intracortical vasculature. Applied to patients with type 2 diabetes, DCE-MRI was able to find significantly larger intracortical vessels compared to nondiabetic controls. Using the same technique, a significantly larger number of smaller vessels was observed in patients with microvascular disease compared to those without. Preliminary data on perfusion MRI showed decreased cortical perfusion with age. SUMMARY: Development of in vivo techniques for intracortical vessel visualization and characterization will enable the exploration of interactions between the vascular and skeletal systems, and further our understanding of drivers of cortical pore expansion. As we investigate potential pathways of cortical pore expansion, appropriate treatment and prevention strategies will be clarified.

A Laplace-Hamming Binarization Approach for Second-Generation HR-pQCT Rescues Fine Feature Segmentation.

Although second-generation high-resolution peripheral quantitative computed tomography (XCTII) provides the highest-resolution in vivo bone microstructure assessment, the manufacturer's standard image processing protocol omits fine features in both trabecular and cortical compartments. To optimize fine structure segmentation, we implemented a binarization approach based on a Laplace-Hamming (LH) segmentation and documented the reproducibility and accuracy of XCTII structure segmentation using both the standard Gaussian-based binarization and the proposed LH segmentation approach. To evaluate reproducibility, 20 volunteers (9 women, 11 men; aged 23-75 years) were recruited, and three repeat scans of the radii and tibias were acquired using the manufacturer's standard in vivo protocol. To evaluate accuracy, cadaveric structure phantoms (14 radii, 6 tibias) were scanned on XCTII using the same standard in vivo protocol and on µCT at 24.5 µm resolution. XCTII images were analyzed twice-first, with the manufacturer's standard patient evaluation protocol and, second, with the proposed LH segmentation approach. The LH approach rescued fine features evident in the grayscale images but omitted or overrepresented (thickened) by the standard approach. The LH approach significantly reduced error in trabecular volume fraction (BV/TV) and thickness (Tb.Th) compared with the standard approach; however, higher error was introduced for trabecular separation (Tb.Sp). The LH approach improved the correlation between XCTII and µCT for cortical porosity (Ct.Po) and significantly reduced error in cortical pore diameter (Ct.Po.Dm) compared with the standard approach. The LH approach resulted in improved precision compared with the standard approach for BV/TV, Tb.Th, Ct.Po, and Ct.Po.Dm at the radius and for Ct.Po at the tibia. Our results suggest that the proposed LH approach produces substantially improved binary masks, reduces proportional bias, and provides greater accuracy and reproducibility in important outcome metrics, all due to more accurate segmentation of the fine features in both trabecular and cortical compartments. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Differential bone adaptation to mechanical unloading and reloading in young, old, and osteocyte deficient mice.

Mechanical unloading causes rapid loss of bone structure and strength, which gradually recovers after resuming normal loading. However, it is not well established how this adaptation to unloading and reloading changes with age. Clinically, elderly patients are more prone to musculoskeletal injury and longer periods of bedrest, therefore it is important to understand how periods of disuse will affect overall skeletal health of aged subjects. Bone also undergoes an age-related decrease in osteocyte density, which may impair mechanoresponsiveness. In this study, we examined bone adaptation during unloading and subsequent reloading in mice. Specifically, we examined the differences in bone adaptation between young mice (3-month-old), old mice (18-month-old), and transgenic mice that exhibit diminished osteocyte density at a young age (3-month-old BCL-2 transgenic mice). Mice underwent 14 days of hindlimb unloading followed by up to 14 days of reloading. We analyzed trabecular and cortical bone structure in the femur, mechanical properties of the femoral cortical diaphysis, osteocyte density and cell death in cortical bone, and serum levels of inflammatory cytokines. We found that young mice lost ~10% cortical bone volume and 27-42% trabecular bone volume during unloading and early reloading, with modest recovery of metaphyseal trabecular bone and near total recovery of epiphyseal trabecular bone, but no recovery of cortical bone after 14 days of reloading. Old mice lost 12-14% cortical bone volume and 35-50% trabecular bone volume during unloading and early reloading but had diminished recovery of trabecular bone during reloading and no recovery of cortical bone. In BCL-2 transgenic mice, no cortical bone loss was observed during unloading or reloading, but 28-31% trabecular bone loss occurred during unloading and early reloading, with little to no recovery during reloading. No significant differences in circulating inflammatory cytokine levels were observed due to unloading and reloading in any of the experimental groups. These results illustrate important differences in bone adaptation in older and osteocyte deficient mice, suggesting a possible period of vulnerability in skeletal health in older subjects during and following a period of disuse that may affect skeletal health in elderly patients.

Bone Marrow Adiposity Alterations in Type 2 Diabetes Are Sex-Specific and Associated with Serum Lipid Levels.

Type 2 diabetes (T2D) has negative effects on skeletal health. A proposed mechanism of diabetic bone disease connects hyperlipidemia to increased bone marrow adiposity and decreased bone quality. Previous research on Type 1 diabetes reported positive associations between serum lipid levels and marrow adiposity, but no data exist for T2D. In addition, marrow adiposity is sex-dependent in healthy populations, but sex has not been addressed adequately in previous reports of marrow adiposity in T2D. The purpose of this study was to quantify associations of marrow adiposity and composition with T2D status, serum lipid levels, and sex. T2D patients and normoglycemic controls (n = 39/37) were included. Single-voxel magnetic resonance spectroscopy (MRS) was performed at the spine and tibia. Quantitative MRS outcomes of marrow adiposity and composition were calculated. Linear regression models were used to compare MRS outcomes among groups and to evaluate associations of MRS outcomes with serum lipid levels. All analyses were performed on sex-stratified subgroups. Total, unsaturated, and saturated fat content at the spine were lower in T2D participants compared to controls in age-adjusted models; these differences were significant in men but not in women. In our study cohort, total cholesterol, low-density lipoprotein (LDL), and high-density lipoprotein (HDL) were lower in T2D participants compared to controls. Adjustment for LDL, HDL, and statin use attenuated the association of T2D status with unsaturated fat but not saturated fat in men. Further analysis confirmed significant associations between serum lipid levels and MRS outcomes. Specifically, we found a positive association between LDL cholesterol and total marrow fat in the male T2D group and a negative association between HDL and total marrow fat in the female T2D group. In conclusion, our results suggest that marrow adiposity and composition are associated with lipid levels as well as T2D status, and these relationships are sex-specific. © 2023 American Society for Bone and Mineral Research (ASBMR).

Diabetes Risk Factors and Bone Microarchitecture as Assessed by High-Resolution Peripheral Quantitative Computed Tomography in Adults With Long-Standing Type 1 Diabetes.

OBJECTIVE: To determine whether type 1 diabetes and its complications are associated with bone geometry and microarchitecture. RESEARCH DESIGN AND METHODS: This cross-sectional study was embedded in a long-term observational study. High-resolution peripheral quantitative computed tomography (HR-pQCT) scans of the distal radius and distal and diaphyseal tibia were performed in a subset of 183 participants with type 1 diabetes from the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications (DCCT/EDIC) study and 94 control participants without diabetes. HbA1c, skin advanced glycation end products (AGEs), and diabetes-related complications were assessed in EDIC participants with >30 years of follow-up. RESULTS: Compared with control participants (aged 60 ± 8 years, 65% female), EDIC participants (aged 60 ± 7 years, diabetes duration 38 ± 5 years, 51% female) had lower total bone mineral density (BMD) at the distal radius (-7.9% [95% CI -15.2%, -0.6%]; P = 0.030) and distal tibia (-11.3% [95% CI -18.5%, -4.2%]; P = 0.001); larger total area at all sites (distal radius 4.7% [95% CI 0.5%, 8.8%; P = 0.030]; distal tibia 5.9% [95% CI 2.1%, 9.8%; P = 0.003]; diaphyseal tibia 3.4% [95% CI 0.8%, 6.1%; P = 0.011]); and poorer radius trabecular and cortical microarchitecture. Estimated failure load was similar between the two groups. Among EDIC participants, higher HbA1c, AGE levels, and macroalbuminuria were associated with lower total BMD. Macroalbuminuria was associated with larger total area and lower cortical thickness at the distal radius. Higher HbA1c and AGE levels and lower glomerular filtration rate, peripheral neuropathy, and retinopathy were associated with deficits in trabecular microarchitecture. CONCLUSIONS: Type 1 diabetes is associated with lower BMD, larger bone area, and poorer trabecular microarchitecture. Among participants with type 1 diabetes, suboptimal glycemic control, AGE accumulation, and microvascular complications are associated with deficits in bone microarchitecture and lower BMD.

The effect of voxel size on high-resolution peripheral computed tomography measurements of trabecular and cortical bone microstructure.

PURPOSE: Accurate quantification of bone microstructure plays a significant role in understanding bone mechanics and response to disease or treatment. High-resolution peripheral quantitative computed tomography (HR-pQCT) allows for the quantification of trabecular and cortical structure in vivo, with the capability of generating images at multiple voxel sizes (41, 82, and 123 µm). The aim of this study was to characterize the effect of voxel size on structural measures of trabecular and cortical bone and to determine accuracy in reference to micro-CT ([micro sign]CT), the gold standard for bone microstructure quantification. METHODS: Seventeen radii from human cadaver specimens were imaged at each HR-pQCT voxel size and subsequently imaged using [micro sign]CT. Bone density and microstructural assessment was performed in both the trabecular and cortical compartments, including cortical porosity quantification. Two distinct analysis techniques were applied to the 41 µm HR-pQCT data: the standard clinical indirect analysis and a direct analysis requiring no density or structural model assumptions. Analysis parameters were adjusted to enable segmentation and structure extraction at each voxel size. RESULTS: For trabecular microstructural measures, the 41 µm HR-pQCT data displayed the strongest correlations and smallest errors compared to [micro sign]CT data. The direct analysis technique applied to the 41 µm data yielded an additional improvement in accuracy, especially for measures of trabecular thickness. The 123 µm data performed poorly, with all microstructural measures either having moderate or nonsignificant correlations with [micro sign]CT data. Trabecular densitometric measures showed strong correlations to [micro sign]CT data across all voxel sizes. Cortical thickness was strongly correlated with [micro sign]CT values across all HR-pQCT voxel sizes. The accuracy of cortical porosity parameters was highly dependent on voxel size; again, the 41 µm data was most strongly correlated. Measures of cortical density and pore diameter at all HR-pQCT voxel sizes had either weak or nonsignificant correlations. CONCLUSIONS: This study demonstrates the effect of voxel size on the accuracy of HR-pQCT measurements of trabecular and cortical microstructure and presents parameters for HR-pQCT analysis at nonstandard resolutions. For all parameters measured, correlations were strongest at 41 µm. Weak correlations for porosity measures indicate that a better understanding of pore structure and resolution dependence is needed.

Cortical Bone Loss Following Gastric Bypass Surgery Is Not Primarily Endocortical.

Roux-en Y gastric bypass (RYGB) surgery is an effective treatment for obesity; however, it may negatively impact skeletal health by increasing fracture risk. This increase may be the result not only of decreased bone mineral density but also of changes in bone microstructure, for example, increased cortical porosity. Increased tibial and radial cortical porosity of patients undergoing RYGB surgery has been observed as early as 6 months postoperatively; however, local microstructural changes and associated biological mechanisms driving this increase remain unclear. To provide insight, we studied the spatial distribution of cortical porosity in 42 women and men (aged 46 ± 12 years) after RYGB surgery. Distal tibias and radii were evaluated with high-resolution peripheral quantitative computed tomography (HR-pQCT) preoperatively and at 12 months postoperatively. Laminar analysis was used to determine cortical pore number and size within the endosteal, midcortical, and periosteal layers of the cortex. Paired t tests were used to compare baseline versus follow-up porosity parameters in each layer. Mixed models were used to compare longitudinal changes in laminar analysis outcomes between layers. We found that the midcortical (0.927 ± 0.607 mm-2 to 1.069 ± 0.654 mm-2 , p = 0.004; 0.439 ± 0.293 mm-2 to 0.509 ± 0.343 mm-2 , p = 0.03) and periosteal (0.642 ± 0.412 mm-2 to 0.843 ± 0.452 mm-2 , p < 0.0001; 0.171 ± 0.101 mm-2 to 0.230 ± 0.160 mm-2 , p = 0.003) layers underwent the greatest increases in porosity over the 12-month period at the distal tibia and radius, respectively. The endosteal layer, which had the greatest porosity at baseline, did not undergo significant porosity increase over the same period (1.234 ± 0.402 mm-2 to 1.259 ± 0.413 mm-2 , p = 0.49; 0.584 ± 0.290 mm-2 to 0.620 ± 0.299 mm-2 , p = 0.35) at the distal tibia and radius, respectively. An alternative baseline-mapping approach for endosteal boundary definition confirmed that cortical bone loss was not primarily endosteal. These findings indicate that increases in cortical porosity happen in regions distant from the endosteal surface, suggesting that the underlying mechanism driving the increase in cortical porosity is not merely endosteal trabecularization. © 2022 American Society for Bone and Mineral Research (ASBMR).

Bone marrow adipose tissue composition and glycemic improvements after gastric bypass surgery.

Fracture risk is increased in type 2 diabetes, which may in part be due to altered bone marrow adiposity. Cross sectional studies have reported that people with type 2 diabetes have lower unsaturated BMAT lipid levels than people without diabetes, although there are limited data on longitudinal changes. We hypothesized that Roux-en-Y gastric bypass (RYGB), which dramatically improves glycemic status, would have differential effects on BMAT composition, with increases in the unsaturated lipid index in people with diabetes. Given reports that axial BMAT is responsive to metabolic stimuli while appendicular BMAT is stable, we hypothesized that BMAT changes would occur at the spine but not the tibia. We enrolled 30 obese women, stratified by diabetes status, and used magnetic resonance spectroscopy to measure BMAT at the spine in all participants, and the tibia in a subset (n = 19). At baseline, BMAT parameters were similar between those with and without diabetes, except tibial marrow fat content was lower in women with diabetes (97.4 % ± 1.0 % versus 98.2 % ± 0.4 %, p = 0.04). Six months after surgery, both groups experienced similar weight loss of 27 kg ± 7 kg. At the spine, there was a significant interaction between diabetes status and changes in both marrow fat content and the unsaturated lipid index (p = 0.02, p < 0.01 for differences, respectively). Women with diabetes had a trend towards a decline in marrow fat content (-4.3 % ± 8.2 %, p = 0.09) and increase in the unsaturated lipid index (+1.1 % ± 1.5 %, p = 0.02). In contrast, BMAT parameters did not significantly change in women without diabetes. In all women, changes in the unsaturated lipid index inversely correlated with hemoglobin A1c changes (r = -0.47, p = 0.02). At the tibia, there was little BMAT change by diabetes status. Our results suggest that vertebral BMAT composition is responsive to changes in glycemic control after RYGB.

A timeseries analysis of the fracture callus extracellular matrix proteome during bone fracture healing.

While most bones fully self-heal, certain diseases require bone allograft to assist with fracture healing. Bone allografts offer promise as treatments for such fractures due to their osteogenic properties. However, current bone allografts made of decellularized bone extracellular matrix (ECM) have high failure rates, and thus grafts which improve fracture healing outcomes are needed. Understanding specific changes to the ECM proteome during normal fracture healing would enable the identification of key proteins that could be used enhance osteogenicity of bone allograft. Here, we performed a timeseries analysis of the fracture callus in mice to investigate proteomic and mineralization changes to the ECM at key stages of fracture healing. We found that changes to the ECM proteome largely coincide with the distinct phases of fracture healing. Basement membrane proteins (AGRN, COL4, LAMA), cartilage proteins (COL2A1, ACAN), and collagen crosslinking enzymes (LOXL, PLOD, ITIH) were initially upregulated, followed by bone specific proteoglycans and collagens (IBSP, COL1A1). Various tissue proteases (MMP2, 9, 13, 14; CTSK, CTSG, ELANE) were expressed at different levels throughout fracture healing. These changes coordinated with mineralization of the fracture callus, which increased steeply during the initial stages of healing. Interestingly the later timepoint was characterized by a response to wound healing and high expression of clotting factors (F2, 7, 9, 10). We identified ELANE and ITIH2 as tissue remodeling enzymes having no prior known involvement with fracture healing. This data can be further mined to identify regenerative proteins for enhanced bone graft design.

Microstructural abnormalities are evident by histology but not HR-pQCT at the periosteal cortex of the human tibia under CVD and T2D conditions.

Cortical bone microstructure deficits may increase fracture risk in individuals with cardiovascular disease and diabetes. High resolution peripheral quantitative computed tomography (HR-pQCT) enables in vivo microstructure characterization but is limited in its ability to visualize important biological features. We conducted histological analyses and HR-pQCT imaging of distal tibia bone samples from 6 donors with cardiovascular disease (CVD) and type 2 diabetes mellitus (T2D). Histology but not HR-pQCT identified previously undocumented morphopathological deficits that may contribute to cortical bone fragility. These observations may provide guidance for improved HR-pQCT microstructural characterization as well as insight into mechanisms of cortical bone degradation.

Longitudinal Evolution of Bone Microarchitecture and Bone Strength in Type 2 Diabetic Postmenopausal Women With and Without History of Fragility Fractures-A 5-Year Follow-Up Study Using High Resolution Peripheral Quantitative Computed Tomography.

Introduction: Diabetic bone disease is characterized by an increased fracture risk which may be partly attributed to deficits in cortical bone quality such as higher cortical porosity. However, the temporal evolution of bone microarchitecture, strength, and particularly of cortical porosity in diabetic bone disease is still unknown. Here, we aimed to prospectively characterize the 5-year changes in bone microarchitecture, strength, and cortical porosity in type 2 diabetic (T2D) postmenopausal women with (DMFx) and without history of fragility fractures (DM) and to compare those to nondiabetic fracture free controls (Co) using high resolution peripheral quantitative computed tomography (HR-pQCT). Methods: Thirty-two women underwent baseline HR-pQCT scanning of the ultradistal tibia and radius and a FU-scan 5 years later. Bone microarchitectural parameters, including cortical porosity, and bone strength estimates via µFEA were calculated for each timepoint and annualized. Linear regression models (adjusted for race and change in BMI) were used to compare the annualized percent changes in microarchitectural parameters between groups. Results: At baseline at the tibia, DMFx subjects exhibited the highest porosity of the three groups (66.3% greater Ct.Po, 71.9% higher Ct.Po.Volume than DM subjects, p < 0.022). Longitudinally, porosity increased significantly over time in all three groups and at similar annual rates, while DMFx exhibited the greatest annual decreases in bone strength indices (compared to DM 4.7× and 6.7× greater decreases in failure load [F] and stiffness [K], p < 0.025; compared to Co 14.1× and 22.2× greater decreases in F and K, p < 0.020). Conclusion: Our data suggest that despite different baseline levels in cortical porosity, T2D women with and without fractures experienced long-term porosity increases at a rate similar to non-diabetics. However, the annual loss in bone strength was greatest in T2D women with a history of a fragility fractures. This suggests a potentially non-linear course of cortical porosity development in T2D bone disease: major porosity may develop early in the course of disease, followed by a smaller steady annual increase in porosity which in turn can still have a detrimental effect on bone strength-depending on the amount of early cortical pre-damage.

Assessment of trabecular bone structure using MDCT: comparison of 64- and 320-slice CT using HR-pQCT as the reference standard.

OBJECTIVES: The aim of our study was to perform trabecular bone structure analysis with images from 64- and 320-slice multidetector computed tomography (MDCT) and to compare these with high-resolution peripheral computed tomography (HR-pQCT). MATERIALS AND METHODS: Twenty human cadaver distal forearm specimens were imaged on a 64- and 320-slice MDCT system at 120 kVp, 200 mA and 135 kVp, 400 mA (in-plane pixel size 234 microm; slice thickness 500 microm). HR-pQCT imaging was performed at an isotropic voxel size of 41 microm. Bone volume fraction (BV/TV), trabecular number (Tb.N), thickness (Tb.Th) and separation (Tb.Sp) were computed. RESULTS: MDCT-derived BV/TV and Tb.Sp were highly correlated (r = 0.92-0.96, p < 0.0001) with the corresponding HR-pQCT parameters. Tb.Th was the only structure measure that did not yield any significant correlation. CONCLUSION: The 64- and 320-slice MDCT systems both perform equally well in depicting trabecular bone architecture. However, because of constrained resolutions accurate derivation of trabecular bone measures is limited to only a subset of microarchitectural parameters.

Soft tissue variations influence HR-pQCT density measurements in a spatially dependent manner.

OBJECTIVE: Significant weight loss following treatments for obesity undermines bone metabolism and increases bone turnover and fracture incidence. High resolution peripheral quantitative computed tomography (HR-pQCT) is widely used in skeletal heath assessment research to provide noninvasive bone parameter measurement (e.g. volumetric bone mineral density (vBMD)) with minimal radiation exposure. However, variation in body composition among study groups or longitudinal variations within individuals undergoing significant weight change will generate artifacts and errors in HR-pQCT data. The purpose of this study is to determine the influence of these artifacts on the measurement of vBMD. METHODS: We designed a custom-made hydroxyapatite (HA)-polymer phantom surrounded by layers of reusable gel pack and hydrogenated fat to mimic the distal tibia and the surrounding lean and fat tissue. Four different thicknesses of fat were used to mimic the soft tissue of increasingly overweight individuals. We then evaluated how a change in soft tissue thickness influenced image quality and vBMD quantification within total, trabecular, and cortical bone compartments. Based on these data, we applied a data correction to previously acquired clinical data in a cohort of gastric bypass patients. RESULTS: In the phantom measurements, total, trabecular, and cortical vBMD increased as soft tissue thickness decreased. The impact of soft tissue thickness on vBMD varied by anatomic quadrant. When applying the soft tissue data correction to a set of clinical data, we found that soft tissue reduction following bariatric surgery can lead to a clinically significant underestimation of bone loss in longitudinal data, and that the effect is most severe in the cortical compartment. CONCLUSION: HR-pQCT-based vBMD measurement accuracy is influenced by soft tissue thickness and is spatially inhomogeneous. Our results suggest that variations in soft tissue thickness must be considered in HR-pQCT studies, particularly in studies enrolling cohorts with differing body composition or in studies of longitudinal weight change.

Factors associated with bone microstructural alterations assessed by HR-pQCT in long-term HIV-infected individuals.

PURPOSE: In adults with long-term HIV infection, low bone density and increased fracture risk have emerged as significant comorbidities. Our aim was to assess the association of exercise, nutrition, and medications with bone quality in adults with long-term HIV infection. METHODS: Forty-three adults with HIV infection were enrolled (median BMI 25.7, range 18.2-35.6 kg/m2; median age 57, range 50-69 years). Participants underwent ultradistal radius and tibia high-resolution peripheral quantitative CT (HR-pQCT). Questionnaires included the revised Community Healthy Activities Model Program for Seniors (CHAMPS), the Mini Nutritional Assessment (MNA) as well as medication assessments. Multivariable linear regression models were used to evaluate the association of exercise, nutritional status, tenofovir disoproxil fumarate (TDF) and protease inhibitor (PI) use with bone density and microstructure, adjusting for demographic risk factors. RESULTS: In regression models, higher nutrition scores were associated with higher tibia cortical thickness (R2 = 0.23; ß = 0.03; p = 0.044) and higher radius cortical BMD (R2 = 0.43; ß = 8.4; p = 0.026). Higher weekly frequency of all physical activities was significantly associated with higher radius trabecular BMD (R2 = 0.38; ß = 0.96; p = 0.050), higher radius trabecular number (R2 = 0.31; ß = 0.01; p = 0.026), lower tibia and radius trabecular separation (tibia: R2 = 0.30; ß = -0.003; p = 0.038; radius: R2 = 0.35; ß = -0.003; p = 0.021), and higher radius bone stiffness (R2 = 0.45; ß = 0.38; p = 0.047). Higher frequency of bone loading physical activities was significantly associated with higher tibia trabecular density (R2 = 0.44; ß = 4.06; p = 0.036), higher tibia bone stiffness (R2 = 0.46; ß = 3.06; p = 0.050), and higher tibia estimated failure load (R2 = 0.46; ß = 0.17; p = 0.049). TDF used in combination with a PI was associated with lower radius trabecular BMD (R2 = 0.39; ß = -41.2; p = 0.042), lower radius trabecular number (R2 = 0.34; ß = -0.44; p = 0.009) and greater radius trabecular separation (R2 = 0.42; ß = 0.16; p = 0.002), while TDF use without a PI was not associated with reduced bone quality. CONCLUSIONS: In adults with HIV infection, malnutrition is associated with poor cortical bone quality, while reduced frequency of physical activities and specifically reduced frequency of mechanical loading activities are associated with deficient trabecular bone structure and reduced estimates of bone strength. TDF use in combination with a PI is associated with deleterious effects on trabecular bone structure.