Structural analysis of cortical porosity applied to HR-pQCT data

Osteocyte mitochondria regulate angiogenesis of transcortical vessels

Transcortical vessels (TCVs) provide effective communication between bone marrow vascular system and external circulation. Although osteocytes are in close contact with them, it is not clear whether osteocytes regulate the homeostasis of TCVs. Here, we show that osteocytes maintain the normal network of TCVs by transferring mitochondria to the endothelial cells of TCV. Partial ablation of osteocytes causes TCV regression. Inhibition of mitochondrial transfer by conditional knockout of Rhot1 in osteocytes also leads to regression of the TCV network. By contrast, acquisition of osteocyte mitochondria by endothelial cells efficiently restores endothelial dysfunction. Administration of osteocyte mitochondria resultes in acceleration of the angiogenesis and healing of the cortical bone defect. Our results provide new insights into osteocyte-TCV interactions and inspire the potential application of mitochondrial therapy for bone-related diseases.

A novel visceral adiposity index predicts bone loss in female early rheumatoid arthritis patients detected by HR-pQCT

The purpose of this prospective study is to compare the Chinese visceral adiposity index (CVAI) between early rheumatoid arthritis (ERA) patients and healthy controls; and to assess the relationship between CVAI and the bone microstructure using high-resolution peripheral quantitative computed tomography (HR-pQCT) in ERA patients. 104 female ERA and 100 age-, gender- and BMI-matched healthy controls were recruited for the comparison of CVAI. All ERA patients were prospectively followed for 1 year. HR-pQCT scan of the distal radius, tibia and second metacarpal head were performed at baseline and after one-year. ERA patients were divided into two sub-groups according to the median CVAI value (65.73) (low CVAI and high CVAI groups). CVAI in the ERA group was significantly higher than the controls group (p = 0.01). At baseline, the high CVAI group had a higher ESR level (p = 0.004) while the cortical volumetric bone mineral density (vBMD) was lower (at both the distal radius and tibia, all p < 0.05) compared to the low CVAI group. Linear regression analysis revealed that a higher baseline CVAI was an independent predictor of a lower cortical vBMD at month 12 (distal radius: B = - 0.626, p = 0.022, 95%CI - 1.914  to  - 0.153; tibia: B = - 0.394, p = 0.003, 95%CI - 1.366 to - 0.290); and a greater reduction in trabecular vBMD (tibia: B = 0.444, p = 0.001, 95%CI 0.018-0.063; distal radius: B = 0.356, p = 0.008, 95%CI 0.403-0.063). In summary, CVAI is an independent predictor of trabecular bone loss in female patients with ERA, which may be augmented by a chronic inflammatory state in patients with visceral dysfunction of fat metabolism.Trial registration: http://Clinicaltrial.gov no: NCT01768923, 16/01/2013.

High-resolution ex vivo analysis of the degradation and osseointegration of Mg-xGd implant screws in 3D

Biodegradable magnesium (Mg) alloys can revolutionize osteosynthesis, because they have mechanical properties similar to those of the bone, and degrade over time, avoiding the need of removal surgery. However, they are not yet routinely applied because their degradation behavior is not fully understood.

In this study we have investigated and quantified the degradation and osseointegration behavior of two biodegradable Mg alloys based on gadolinium (Gd) at high resolution.

Mg-5Gd and Mg-10Gd screws were inserted in rat tibia for 4, 8 and 12 weeks. Afterward, the degradation rate and degradation homogeneity, as well as bone-to-implant interface, were studied with synchrotron radiation micro computed tomography and histology. Titanium (Ti) and polyether ether ketone (PEEK) were used as controls material to evaluate osseointegration.

Our results showed that Mg-5Gd degraded faster and less homogeneously than Mg-10Gd. Both alloys gradually form a stable degradation layer at the interface and were surrounded by new bone tissue. The results were correlated to in vitro data obtained from the same material and shape. The average bone-to-implant contact of the Mg-xGd implants was comparable to that of Ti and higher than for PEEK. The results suggest that both Mg-xGd alloys are suitable as materials for bone implants.

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High-resolution non-destructive synchrotron micro computed tomography of biodegradable Mg alloys ex vivo.

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Mg-xGd implants exhibit a high bone-to-implant contact, similar to titanium implants.

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Initially Mg-xGd implants are surrounded by a lesser bone volume fraction but reach similar levels as reference materials.

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Mg-xGd implants degrade at rates lower than 1 mm a⁻¹ in vivo, decreasing to less than 0.4 mm a⁻¹ after 12 weeks.

Mechanical and morphological properties of parietal bone in patients with sagittal craniosynostosis

Limited information is available on the effect of sagittal craniosynostosis (CS) on morphological and material properties of the parietal bone. Understanding these properties would not only provide an insight into bone response to surgical procedures but also improve the accuracy of computational models simulating these surgeries. The aim of the present study was to characterise the mechanical and microstructural properties of the cortical table and diploe in parietal bone of patients affected by sagittal CS. Twelve samples were collected from pediatric patients (11 males, and 1 female; age 5.2 ± 1.3 months) surgically treated for sagittal CS. Samples were imaged using micro-computed tomography (micro-CT); and mechanical properties were extracted by means of micro-CT based finite element modelling (micro-FE) of three-point bending test, calibrated using sample-specific experimental data. Reference point indentation (RPI) was used to validate the micro-FE output. Bone samples were classified based on their macrostructure as unilaminar or trilaminar (sandwich) structure. The elastic moduli obtained using RPI and micro-FE approaches for cortical tables (E_RPI 3973.33 ± 268.45 MPa and E_micro-FE 3438.11 ± 387.38 MPa) in the sandwich structure and diploe (E_RPI1958.17 ± 563.79 MPa and E_micro-FE 1960.66 ± 492.44 MPa) in unilaminar samples were in strong agreement (r = 0.86, p < .01). We found that the elastic modulus of cortical tables and diploe were correlated with bone mineral density. Changes in the microstructure and mechanical properties of bone specimens were found to be irrespective of patients' age. Although younger patients are reported to benefit more from surgical intervention as skull is more malleable, understanding the material properties is critical to better predict the surgical outcome in patients <1 year old since age-related changes were minimal.

Bone Density around Titanium Dental Implants Coating Tested/Coated with Chitosan or Melatonin: An Evaluation via Microtomography in Jaws of Beagle Dogs

Peri-implant bone density plays an important role in the osseointegration of dental implants. The aim of the study was to evaluate via micro-CT, in Hounsfield units, the bone density around dental implants coated with chitosan and melatonin and to compare it with the bone density around implants with a conventional etched surface after 12 weeks of immediate post-extraction placement in the jaws of Beagle dogs. Six dogs were used, and 48 implants were randomly placed: three groups—melatonin, chitosan, and control. Seven 10 mm × 10 mm regions of interest were defined in each implant (2 in the crestal zone, 4 in the medial zone, and 1 in the apical zone). A total of 336 sites were studied with the AMIDE tool, using the Norton and Gamble classification to assess bone density. The effect on bone density of surface coating variables (chitosan, melatonin, and control) at the crestal, medial, and apical sites and the implant positions (P2, P3, P4, and M1) was analyzed at bivariate and multivariate levels (linear regression). Adjusted effects on bone density did not indicate statistical significance for surface coatings (p = 0.653) but did for different levels of ROIs (p < 0.001) and for positions of the implants (p = 0.032). Micro-CT, with appropriate software, proved to be a powerful tool for measuring osseointegration.

Determinants of Bone Material Strength and Cortical Porosity in Patients with Type 2 Diabetes Mellitus

CONTEXT

Reduced bone material strength index (BMSi) and increased cortical porosity (CtPo) have emerged as potentially contributing to fracture risk in type 2 diabetes mellitus (T2DM) patients.

OBJECTIVE

To determine whether BMSi or CtPo are related to other diabetic complications.

DESIGN

Cross-sectional observational study.

SETTING

Subjects recruited from a random sample of southeast Minnesota residents.

PARTICIPANTS

A total of 171 T2DM patients (mean age, 68.8 years) and 108 age-matched nondiabetic controls (mean age, 67.3 years).

MAIN MEASURES

Bone material strength index was measured using microindentation, skin advanced glycation end-products (AGEs) measured using autofluorescence, high-resolution peripheral quantitative computed tomography at the distal radius and tibia, assessment of diabetic microvascular complications including urine microalbuminuria, retinopathy, neuropathy, and vascular disease (ankle brachial index and transcutaneous oxygen tension [TcPO2]). All analyses were adjusted for age, sex, and body mass index.

RESULTS

Skin AGEs were negatively correlated with the BMSi in both T2DM (r = -0.30, P < 0.001) and control (r = -0.23, P = 0.020) subjects. In relating diabetic complications to CtPo, we found that T2DM patients with clinically significant peripheral vascular disease (TcPO2 ≤ 40 mm Hg) had higher (+21.0%, P = 0.031) CtPo at the distal tibia as compared to controls; in these subjects, CtPo was negatively correlated with TcPO2 at both the distal tibia (r = -0.39, P = 0.041) and radius (r = -0.41, P = 0.029).

CONCLUSIONS

Our findings demonstrate that bone material properties are related to AGE accumulation regardless of diabetes status, while CtPo in T2DM patients is linked to TcPO2, a measure of microvascular blood flow.

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.

Finite Element Analysis-Based Vertebral Bone Strength Prediction Using MDCT Data: How Low Can We Go?

Objective: To study the impact of dose reduction in MDCT images through tube current reduction or sparse sampling on the vertebral bone strength prediction using finite element (FE) analysis for fracture risk assessment. Methods: Routine MDCT data covering lumbar vertebrae of 12 subjects (six male; six female; 74.70 ± 9.13 years old) were included in this study. Sparsely sampled and virtually reduced tube current-based MDCT images were computed using statistical iterative reconstruction (SIR) with reduced dose levels at 50, 25, and 10% of the tube current and original projections, respectively. Subject-specific static non-linear FE analyses were performed on vertebra models (L1, L2, and L3) 3-D-reconstructed from those dose-reduced MDCT images to predict bone strength. Coefficient of correlation (R²), Bland-Altman plots, and root mean square coefficient of variation (RMSCV) were calculated to find the variation in the FE-predicted strength at different dose levels, using high-intensity dose-based strength as the reference. Results: FE-predicted failure loads were not significantly affected by up to 90% dose reduction through sparse sampling (R² = 0.93, RMSCV = 8.6% for 50%; R² = 0.89, RMSCV = 11.90% for 75%; R² = 0.86, RMSCV = 11.30% for 90%) and up to 50% dose reduction through tube current reduction method (R² = 0.96, RMSCV = 12.06%). However, further reduction in dose with the tube current reduction method affected the ability to predict the failure load accurately (R² = 0.88, RMSCV = 22.04% for 75%; R² = 0.43, RMSCV = 54.18% for 90%). Conclusion: Results from this study suggest that a 50% radiation dose reduction through reduced tube current and a 90% radiation dose reduction through sparse sampling can be used to predict vertebral bone strength. Our findings suggest that the sparse sampling-based method performs better than the tube current-reduction method in generating images required for FE-based bone strength prediction models.

The generation of enlarged eroded pores upon existing intracortical canals is a major contributor to endocortical trabecularization

The gradual conversion of cortical bone into trabecular bone on the endocortical surface contributes substantially to thinning of the cortical bone. The purpose of the present study was to characterize the intracortical canals (3D) and pores (2D) in human fibular bone, to identify the intracortical remodeling events leading to this endocortical trabecularization. The analysis was conducted in fibular diaphyseal bone specimens obtained from 20 patients (6 women and 14 men, age range 41-75 years). μCT revealed that endosteal bone had a higher cortical porosity (p< 0.05) and canals with a larger diameter (p< 0.05) than periosteal bone, while the canal spacing and number were similar in the endosteal and periosteal half. Histological analysis showed that the endosteal half versus the periosteal half: (i) had a higher likelihood of being non-quiescent type 2 pores (i.e. remodeling of existing pores) than other pore types (OR = 1.6, p< 0.01); (ii) that the non-quiescent type 2 pores contributed to a higher porosity (p< 0.001); and that (iii) amongst these pores especially eroded type 2 pores contributed to the elevated cortical porosity (p< 0.001). In conclusion, we propose that endocortical trabecularization results from the accumulation of eroded cavities upon existing intracortical canals, favored by delayed initiation of bone formation.

Next-generation imaging of the skeletal system and its blood supply

Bone is organized in a hierarchical 3D architecture. Traditionally, analysis of the skeletal system was based on bone mass assessment by radiographic methods or on the examination of bone structure by 2D histological sections. Advanced imaging technologies and big data analysis now enable the unprecedented examination of bone and provide new insights into its 3D macrostructure and microstructure. These technologies comprise ex vivo and in vivo methods including high-resolution computed tomography (CT), synchrotron-based imaging, X-ray microscopy, ultra-high-field magnetic resonance imaging (MRI), light-sheet fluorescence microscopy, confocal and intravital two-photon imaging. In concert, these techniques have been used to detect and quantify a novel vascular system of trans-cortical vessels in bone. Furthermore, structures such as the lacunar network, which harbours and connects osteocytes, become accessible for 3D imaging and quantification using these methods. Next-generation imaging of the skeletal system and its blood supply are anticipated to contribute to an entirely new understanding of bone tissue composition and function, from macroscale to nanoscale, in health and disease. These insights could provide the basis for early detection and precision-type intervention of bone disorders in the future.

Use of Micro-Computed Tomography for Bone Evaluation in Dentistry

Micro computed tomography (µCT) follows the same principle of computed-tomography used for patients, however providing higher-resolution. Using a non-destructive approach, samples can be scanned, and each section obtained is used to build a volume using tridimensional reconstruction. For bone analysis, it is possible to obtain information about the tissue's microarchitecture and composition. According to the characteristics of the bone sample (e.g. human or animal origin, long or irregular shape, epiphysis or diaphysis region) the pre-scanning parameters must be defined. The resolution (i.e. voxel size) should be chosen taking into account the features that will be evaluated, and the necessity to identify inner structures (e.g. bone channels and osteocyte lacunae). The region of interest should be delimited, and the threshold that defines the bone tissue set in order to proceed with binarization to separate the voxels representing bone from the other structures (channels, resorption areas, and medullary space). Cancellous bone is evaluated by means of the trabeculae characteristics and their connectivity. The cortex is evaluated in relation to the thickness and porosity. Bone mineral density can also be measured, by the amount of hydroxyapatite. Other parameters such as structure-model-index, anisotropy, and fractal dimension can be assessed. In conclusion, intrinsic and extrinsic determinants of bone quality can be assessed by µCT. In dentistry, this method can be used for evaluating bone loss, alterations in bone metabolism, or the effects of using drugs that impair bone remodeling, and also to assess the success rate of bone repair or surgical procedures.

A study of intracortical porosity's area fractions and aspect ratios using computer vision and pulse-coupled neural networks

Employing computer vision (CV) and optimized pulse-coupled neural networks (PCNN), this work automatically quantifies the geometrical attributes of intracortical bone porosity (namely lacunae and canaliculi (L-C), Haversian canals, and resorption cavities). Fifty pathological slides of cortical bone (× 20 magnification) were prepared from middiaphysis of bovine forelegs collected fresh from butcher. Biopsies were subdivided into sectors encircling arcs (θ of 10°) and radial distances (R) originating from the bone's geometric center toward posterior regions and spanning 3.3 mm. Microscopically, each pore is classified according to whether it belonged to primary or secondary osteon. Globally, each pore is assigned as being located in anterior or posterior regions. For each pore, area and major/minor axes lengths were determined as raw measures from which derived geometric measures, namely, area fraction (AF) and aspect ratio (AR), were derived. Said measures were plotted versus R (for different angles). Plots of AF and AR trends were found to vary linearly along the radial distance. Area fractions (%) significantly decreased linearly with R (p < 0.01) in the anterior region. In the posterior region, area fraction values are flat versus R. These findings are indicative of maturing osteons at the outer cortex with predominately near circular-shaped pores. Graphical abstract (Left) Grids of slides (magnified at 20X) of intra-cortical bone showing Lacunar-canalicular porosity (LCP). Areas marked with the dotted square represent a group of 25 images. The dashed line is a hand-drawn line that demarcates the anterior and posterior regions and the solid line is the best-fit arc radii (R =16.4 mm) of the dashed demarcation line. (Right) Images rotated in the polar coordinate system with their respective angles and radii shown.

Effects of Gastric Bypass Surgery on Bone Mass and Microarchitecture Occur Early and Particularly Impact Postmenopausal Women

Roux-en-Y gastric bypass (RYGB) surgery is a highly effective treatment for obesity but negatively affects the skeleton. Studies of skeletal effects have generally examined areal bone mineral density (BMD) by dual-energy X-ray absorptiometry (DXA), but DXA may be inaccurate in the setting of marked weight loss. Further, as a result of modestly sized samples of mostly premenopausal women and very few men, effects of RYGB by sex and menopausal status are unknown. We prospectively studied the effects of RYGB on skeletal health, including axial and appendicular volumetric BMD and appendicular bone microarchitecture and estimated strength. Obese adults (N = 48; 27 premenopausal and 11 postmenopausal women, 10 men) with mean ± SD body mass index (BMI) 44 ± 7 kg/m² were assessed before and 6 and 12 months after RYGB. Participants underwent spine and hip DXA, spine QCT, radius and tibia HR-pQCT, and laboratory evaluation. Mean 12-month weight loss was 37 kg (30% of preoperative weight). Overall median 12-month increase in serum collagen type I C-telopeptide (CTx) was 278% (p < 0.0001), with greater increases in postmenopausal than premenopausal women (p = 0.049). Femoral neck BMD by DXA decreased by mean 5.0% and 8.0% over 6 and 12 months (p < 0.0001). Spinal BMD by QCT decreased by mean 6.6% and 8.1% (p < 0.0001); declines were larger among postmenopausal than premenopausal women (11.6% versus 6.0% at 12 months, p = 0.02). Radial and tibial BMD and estimated strength by HR-pQCT declined. At the tibia, detrimental changes in trabecular microarchitecture were apparent at 6 and 12 months. Cortical porosity increased at the radius and tibia, with more dramatic 12-month increases among postmenopausal than premenopausal women or men at the tibia (51.4% versus 18.3% versus 3.0%, p < 0.01 between groups). In conclusion, detrimental effects of RYGB on axial and appendicular bone mass and microarchitecture are detectable as early as 6 months postoperatively. Postmenopausal women are at highest risk for skeletal consequences and may warrant targeted screening or interventions. © 2017 American Society for Bone and Mineral Research.

Cortical Fractal Analysis and Collagen Crosslinks Content in Femoral Neck After Osteoporotic Fracture in Postmenopausal Women: Comparison with Osteoarthritis

The femoral neck (FN) has been previously characterized by thinner cortices in osteoporotic fracture (HF) when compared to hip osteoarthritis (HOA). The purposes of this study were to complete the previous investigations on FNs from HF and HOA by analyzing the complexity of the cortical structure and to approach the intrinsic properties of cortical bone by assessing the collagen crosslink contents. FN samples were obtained during arthroplasty in 35 postmenopausal women (HF; n = 17; mean age 79 ± 2 years; HOA; n = 18; mean age 66 ± 2 years). The cortical fractal dimension (Ct.FD) and lacunarity (Ct.Lac) derived from high-resolution peripheral quantitative tomography (isotropic voxel size: 82 μm) images of FN by using Ctan software and Fraclac running in ImageJ were analyzed. The collagen crosslinks content [pyridinoline, deoxypyridinoline, pentosidine (PEN)] were assessed in cortical bone. Ct.FD was significantly lower (p < 0.0001) in HF than HOA reflecting a decreased complexity and was correlated to the age and BMD. In two sub-groups, BMD- and age-matched, respectively, Ct.FD remained significantly lower in HF than HOA (p < 0.001). Ct.Lac was not different between HF and HOA. PEN content was two times higher in HF than HOA (p < 0.0001) independently of age. In conclusion, FN with HF was characterized by a less complex cortical texture and higher PEN content than HOA. In addition to the decreased bone mass and BMD previously reported, these modifications contribute to the lower bone quality in HF than HOA in postmenopausal women.

Skeletal Microstructure and Estimated Bone Strength Improve Following Parathyroidectomy in Primary Hyperparathyroidism

Context

High-resolution peripheral quantitative computed tomography (HRpQCT) is a noninvasive imaging technology that can provide insight into skeletal microstructure and strength. In asymptomatic primary hyperparathyroidism (PHPT), HRpQCT imaging has demonstrated both decreased cortical and trabecular indices, consistent with evidence for increased fracture risk. There are limited data regarding changes in HRpQCT parameters postparathyroidectomy.

Objective

To evaluate changes in skeletal microstructure by HRpQCT in subjects with PHPT after parathyroidectomy.

Design

We studied 29 subjects with PHPT (21 women, 8 men) with HRpQCT at baseline and 6, 12, 18, and 24 months postparathyroidectomy.

Main Outcome Measures

Volumetric bone mineral density, microarchitectural indices, and finite element analysis at the distal radius and tibia.

Results

At both the radius and tibia, there were significant improvements in total, cortical, and trabecular volumetric bone density as early as 6 months postparathyroidectomy (24-month values for total volumetric bone density, radius: +2.8 ± 4%, tibia: +4.4 ± 4%; P < 0.0001 for both), cortical thickness (radius: +1.1 ± 2%, tibia: +2.0 ± 3%; P < 0.01 for both), and trabecular bone volume (radius: +3.8 ± 5%, tibia: +3.2 ± 4%; P < 0.0001 for both). At both sites, by finite element analysis, stiffness and failure load were improved starting at 6 months postparathyroidectomy (24-month values for failure load, radius: +6.2 ± 6%, tibia: +4.8 ± 7%; P < 0.0001 for both).

Conclusions

These results provide information about skeletal microarchitecture in subjects with PHPT followed through 2 years after parathyroidectomy. Estimated bone strength is improved, consistent with data showing decreased fracture risk postparathyroidectomy.

The Reliability of a Semi-automated Algorithm for Detection of Cortical Interruptions in Finger Joints on High Resolution CT Compared to MicroCT

We developed a semi-automated algorithm for the detection of cortical interruptions in finger joints using high-resolution peripheral quantitative computed tomography (HR-pQCT). Here, we tested its reliability compared to microCT (µCT) as gold standard. Nineteen joints of 10 female anatomic index fingers were imaged by HR-pQCT and µCT (82 and 18 µm isotropic voxel sizes, respectively). The algorithm was applied for detection of cortical interruptions of different minimum diameters (range >0.16 to >0.50 mm). Reliability was tested at the joint level with intra-class correlation coefficient (ICC) for the number of interruptions and interruption surface, and at the level of a single interruption for matching between HR-pQCT and µCT with a fixed interruption diameter (>0.10 mm) on µCT. The positive predictive value (PPV_0.10mm) and sensitivity_0.10mm were evaluated. The mean number of interruptions per joint depended on the diameter cut-off and ranged from 3.4 to 53.5 on HR-pQCT and from 1.8 to 45.1 on µCT for interruptions >0.50 to >0.16 mm, respectively. Reliability at the joint level was almost perfect (ICC ≥0.81) for both the number and surface of interruptions >0.16 and >0.33 mm. As expected, the PPV_0.10mm increased with increasing interruption diameter from 84.9 to 100%, for interruptions >0.16 and >0.50 mm, respectively. However, the sensitivity_0.10mm decreased with increasing interruption diameter from 62.4 to 4.7%. This semi-automated algorithm for HR-pQCT in finger joints performed best for the detection of cortical interruptions with a minimum diameter of >0.16 or >0.33 mm, showing almost perfect reliability at the joint level and interruptions matched with those on µCT.

In vivo assessment of bone structure and estimated bone strength by first- and second-generation HR-pQCT

Bone strength is dependent on bone density and microstructure. High-resolution peripheral quantitative computed tomography (HR-pQCT) can measure microstructure but is somewhat limited due to its resolution. We compared a new HR-pQCT scanner to existing technology and found very good agreement for most parameters. This study will be important when interpreting results from different devices.

INTRODUCTION

Recently, a second-generation HR-pQCT scanner (XCT2) has been developed with a higher nominal isotropic resolution (61 μm) compared to the first-generation device (XCT1, 82 μm). It is unclear how in vivo measurements from these two devices compare. In this study, we obtained and analyzed in vivo XCT1 and XCT2 measurements of bone microarchitecture and estimated strength.

METHODS

We scanned 51 adults (16 men and 35 women, age 44.8 ± 16.0) on both XCT2 and XCT1 on the same day. We first compared XCT1 and XCT2 measurements obtained using their respective standard patient protocols. In XCT1, microarchitecture parameters were derived, while XCT2 measurements were directly measured. We also compared XCT2-D with XCT1 by finding the overlapping regions of interest and using the standard patient protocol for XCT1.

RESULTS

We obtained excellent agreement between XCT1 and XCT2 for most of the volumetric bone mineral density (vBMD), trabecular and cortical measurements (All R (2) > 0.820) except for cortical porosity at the radius (R (2) = 0.638), trabecular number (R (2) = 0.694, 0.787) and trabecular thickness (R (2) = 0.569, 0.527) at both radius and tibia, respectively. XCT1 and XCT2-D measurements also had excellent agreement for most of the measurements (all R (2) > 0.870) except trabecular number (R (2) = 0.524, 0.706), trabecular thickness (R (2) = 0.758, 0.734) at both radius and tibia, respectively, and trabecular separation (R (2) = 0.656) at the radius.

CONCLUSION

While some caution should be exercised for parameters that are more dependent on image resolution, results from our study indicate that second-generation scans can be compared to more widely available first-generation data and may be beneficial for multicenter and longitudinal studies using both scanner generations.

Cortical bone laminar analysis reveals increased midcortical and periosteal porosity in type 2 diabetic postmenopausal women with history of fragility fractures compared to fracture-free diabetics

We investigated the characteristics and spatial distribution of cortical bone pores in postmenopausal women with type 2 diabetes (T2D). High porosity in the midcortical and periosteal layers in T2D subjects with fragility fractures suggests that these cortical zones might be particularly susceptible to T2D-induced toxicity and may reflect cortical microangiopathy.

INTRODUCTION

Elevated cortical porosity is regarded as one of the main contributors to the high skeletal fragility in T2D. However, to date, it remains unclear if diabetic cortical porosity results from vascular cortical changes or from an expansion in bone marrow space. Here, we used a novel cortical laminar analysis technique to investigate the characteristics and spatial radial distribution of cortical pores in a T2D group with prior history of fragility fractures (DMFx, assigned high-risk group) and a fracture-free T2D group (DM, assigned low-risk group) and to compare their results to non-diabetic controls with (Fx) and without fragility fractures (Co).

METHODS

Eighty postmenopausal women (n = 20/group) underwent high-resolution peripheral quantitative computed tomography (HR-pQCT) of the distal tibia and radius. Cortical bone was divided into three layers of equal width including an endosteal, midcortical, and periosteal layer. Within each layer, total pore area (TPA), total pore number (TPN), and average pore area (APA) were calculated. Statistical analysis employed Mann-Whitney tests and ANOVA with post hoc tests.

RESULTS

Compared to the DM group, DMFx subjects exhibited +90 to +365 % elevated global porosity (p = 0.001). Cortical laminar analysis revealed that this increased porosity was for both skeletal sites confined to the midcortical layer, followed by the periosteal layer (midcortical +1327 % TPA, p ≤ 0.001, periosteal +634 % TPA, p = 0.002), and was associated in both layers and skeletal sites with high TPN (+430 % TPN, p < 0.001) and high APA (+71.5 % APA, p < 0.001).

CONCLUSION

High porosity in the midcortical and periosteal layers in the high-risk T2D group suggests that these cortical zones might be particularly susceptible to T2D-induced toxicity and may reflect cortical microangiopathy.

In Vivo Characterization of Cortical Bone Using Guided Waves Measured by Axial Transmission

Cortical bone loss is not fully assessed by the current X-ray methods, and there is an unmet need in identifying women at risk of osteoporotic fracture, who should receive a treatment. The last decade has seen the emergence of the ultrasound (US) axial transmission (AT) techniques to assess a cortical bone. Recent AT techniques exploit the multimode waveguide response of the long bones such as the radius. A recent ex vivo study by our group evidenced that a multimode AT approach can yield simultaneous estimates of cortical thickness (Ct.Th) and stiffness. The aim of this paper is to move one step forward to evaluate the feasibility of measuring multimode guided waves (GW) in vivo and to infer from it cortical thickness. Measurements were taken on the forearm of 14 healthy subjects with the goal to test the accuracy of the estimated thickness using the bidirectional AT method implemented on a dedicated 1-MHz linear US array. This setup allows determining in vivo the dispersion curves of GW transmitted in the cortical layer of the radius. An inverse procedure based on the comparison between the measured and modeled dispersion curves predicted by a 2-D transverse isotropic free plate waveguide model allowed an estimation of cortical thickness, despite the presence of soft tissue. The Ct.Th values were validated by comparison with the site-matched estimates derived from X-ray high-resolution peripheral quantitative computed tomography. Results showed a significant correlation between both measurements ( r² = 0.7 , , and [Formula: see text] mm). This pilot study demonstrates the potential of bidirectional AT for the in vivo assessment of cortical thickness, a bone strength-related factor.

Changes in cortical bone channels network and osteocyte organization after the use of zoledronic acid

OBJECTIVE

The aim of this study was to evaluate the effects of zoledronic acid (ZA) on the cortical bone channels network (CBCN) and osteocyte organization in relation to the bone channels.

MATERIALS AND METHODS

Eighteen male Wistar rats were divided into control (CG) and test groups (TG). Twelve animals from TG received 3 ZA doses (7.5 µg/kg), and 6 animals from CG did not receive any medication. TG animals were euthanized at 14 (n = 6) and 75 (n = 6) dadys after drug injection. CBCN was analyzed in mandibles and tibias using computational routines. The osteocyte organization was qualitatively evaluated in tibias using a three-dimensional reconstruction of images from serial histological sections.

RESULTS

Significant differences in CBCN of tibia were found between the treated and untreated rats, with a wider range of sizes and shapes of the channels after the use of ZA (channels area p = 0.0063, channels area SD p = 0.0276) and less bone matrix (bone volume p = 0.0388). The alterations in the channels' morphology were more evident at 75 days after the drug injection (channels perimeter p = 0.0286). No differences were found in mandibles CBCN. The osteocyte distribution revealed more variable patterns of cell distribution in ZA groups, with non-homogeneous distribution of cells in relation to the bone channels.

CONCLUSION

Zoledronic acid induces structural changes in CBCN and modifies the osteocyte arrangement in cortical bone in the tibia; also, the variability in the morphology of bone channels became more evident after a certain time of the use of the drug.

Spatial distribution of intracortical porosity varies across age and sex

Cortical bone porosity is a major determinant of strength, stiffness, and fracture toughness of cortical tissue. The goal of this work was to investigate changes in spatial distribution and microstructure of cortical porosity associated with aging in men and women. The specific aims were to: 1) develop an automated technique for spatial analysis of cortical microstructure based on HR-pQCT data, and; 2) apply this technique to explore sex- and age-specific spatial distribution and microstructure of porosity within the cortex. We evaluated HR-pQCT images of the distal tibia from a cross-sectional cohort of 145 individuals, characterizing detectable pores as being in the endosteal, midcortical, or periosteal layers of the cortex. Metrics describing porosity, pore number, and pore size were quantified within each layer and compared across sexes, age groups, and cortical layers. The elderly cohort (65-78 years, n=22) displayed higher values than the young cohort (20-29 years, n=29) for all parameters both globally and within each layer. While all three layers displayed significant age-related porosity increases, the greatest difference in porosity between the young and elderly cohort was in the midcortical layer (+344%, p<0.001). Similarly, the midcortical layer reflected the greatest differences between young and elderly cohorts in both pore number (+243%, p<0.001) and size (+28%, p<0.001). Females displayed greater age-related changes in porosity and pore number than males. Females and males displayed comparable small to non-significant changes with age in pore size. In summary, considerable variability exists in the spatial distribution of detectable cortical porosity at the distal tibia, and this variability is dependent on age and sex. Intracortical pore distribution analysis may ultimately provide insight into both mechanisms of pore network expansion and biomechanical consequences of pore distribution.

The influence of disuse on bone microstructure and mechanics assessed by HR-pQCT

Numerous clinical cohorts are exposed to reduced skeletal loading and associated bone loss, including surgical patients, stroke and spinal cord injury victims, and women on bed rest during pregnancy. In this context, understanding disuse-related bone loss is critical to developing interventions to prevent fractures and the associated morbidity, mortality, and cost to the health care system. The aim of this pilot study was to use high-resolution peripheral QCT (HR-pQCT) to examine changes in trabecular and cortical microstructure and biomechanics during a period of non weight bearing (WB) and during recovery following return to normal WB. Surgical patients requiring a 6-week non WB period (n=12, 34.8±7.7 yrs) were scanned at the affected and contralateral tibia prior to surgery, after the 6-week non WB period, and 6 and 13 weeks after returning to full WB. At the affected ultradistal tibia, integral vBMD (including both trabecular and cortical compartments) decreased with respect to baseline (-1.2%), trabecular number increased (+5.6%), while trabecular thickness (-5.4%), separation (-4.6%), and heterogeneity (-7.2%) decreased (all p<0.05). Six weeks after return to full WB, trabecular structure measures reverted to baseline levels. In contrast, integral vBMD continued to decrease after 6 (-2.0%, p<0.05) and 13 weeks (-2.5%, p=0.07) of full WB. At the affected distal site, the disuse period resulted in increased porosity (+16.1%, p<0.005), which remained elevated after 6 weeks (+16.8%, p<0.01) and after 13 weeks (+16.2%, p<0.05). A novel topological analysis applied to the distal tibia cortex demonstrated increased number of canals with surface topology ("slabs" +21.7%, p<0.01) and curve topology ("tubes" +15.0%, p<0.05) as well as increased number of canal junctions (+21.4%, p<0.05) following the disuse period. Porosity increased uniformly through increases in both pore size and number. Finite element analysis at the ultradistal tibia showed decreased stiffness and failure load (-2.8% and -2.4%, p<0.01) following non WB. These biomechanical predictions remained depressed following 6 and 13 weeks of full WB. Finite element analysis at the distal site followed similar trends. Our results suggest that detectable microstructural and biomechanical degradation occurs--particularly within the cortical compartment--as a result of non WB and persists following return to normal loading. A better understanding of these microstructural changes and their short- and long-term influence on biomechanics may have clinical relevance in the context of disuse-related fracture prevention.