Cortical Bone Microarchitecture Research Articles

Moderate chronic kidney disease impairs bone quality in C57Bl/6J mice

Chronic kidney disease (CKD) increases bone fracture risk. While the causes of bone fragility in CKD are not clear, the disrupted mineral homeostasis inherent to CKD may cause material quality changes to bone tissue. In this study, 11-week-old male C57Bl/6J mice underwent either 5/6th nephrectomy (5/6 Nx) or sham surgeries. Mice were fed a normal chow diet and euthanized 11weeks post-surgery. Moderate CKD with high bone turnover was established in the 5/6 Nx group as determined through serum chemistry and bone gene expression assays. We compared nanoindentation modulus and mineral volume fraction (assessed through quantitative backscattered scanning electron microscopy) at matched sites in arrays placed on the cortical bone of the tibia mid-diaphysis. Trabecular and cortical bone microarchitecture and whole bone strength were also evaluated. We found that moderate CKD minimally affected bone microarchitecture and did not influence whole bone strength. Meanwhile, bone material quality decreased with CKD; a pattern of altered tissue maturation was observed with 5/6 Nx whereby the newest 60μm of bone tissue adjacent to the periosteal surface had lower indentation modulus and mineral volume fraction than more interior, older bone. The variance of modulus and mineral volume fraction was also altered following 5/6 Nx, implying that tissue-scale heterogeneity may be negatively affected by CKD. The observed lower bone material quality may play a role in the decreased fracture resistance that is clinically associated with human CKD.

Sclerostin Antibody Treatment Increases Bone Formation, Bone Mass, and Bone Strength of Intact Bones in Adult Male Rats.

We investigated the systemic effect of sclerostin monoclonal antibody (Scl-Ab) treatment on intact non-operated bones in an open osteotomy male Sprague Dawley (SD) rat model. Six-month-old male SD rats were subjected to transverse osteotomy at the right femur mid-shaft. Rats were injected subcutaneously with vehicle or Scl-Ab (25 mg/kg, 2 times per week) treatment for 9 weeks. Compared with vehicle control, Scl-Ab treatment significantly improved trabecular and cortical bone mass and microarchitecture at L5 vertebrae and left femora by micro-CT at week 6 and 9. Mechanical testing showed that Scl-Ab treatment resulted in significantly higher stiffness, energy to failure and ultimate load at the femora at week 9. Mineral apposition rate, mineralizing surface and bone formation rate on the trabecular bone in the distal femora was significantly increased in Scl-Ab group at week 6 and 9. The administered Scl-Ab was localized in the osteocytes and beta-catenin was strongly expressed in osteoblasts. Scl-Ab treatment significantly increased serum P1NP level and there was no between-group difference in serum level of CTX-1. In conclusion, Scl-Ab treatment could induce rapid and sustained increase in bone formation, bone mass and bone strength in non-operated bones. Sclerostin inhibition might be advantageous to prevent secondary fracture(s).

Role of endocortical contouring methods on precision of HR-pQCT-derived cortical micro-architecture in postmenopausal women and young adults

Precision errors of cortical bone micro-architecture from high-resolution peripheral quantitative computed tomography (pQCT) ranged from 1 to 16% and did not differ between automatic or manually modified endocortical contour methods in postmenopausal women or young adults. In postmenopausal women, manually modified contours led to generally higher cortical bone properties when compared to the automated method. First, the objective of the study was to define in vivo precision errors (coefficient of variation root mean square (CV%RMS)) and least significant change (LSC) for cortical bone micro-architecture using two endocortical contouring methods: automatic (AUTO) and manually modified (MOD) in two groups (postmenopausal women and young adults) from high-resolution pQCT (HR-pQCT) scans. Second, it was to compare precision errors and bone outcomes obtained with both methods within and between groups. Using HR-pQCT, we scanned twice the distal radius and tibia of 34 postmenopausal women (mean age ± SD 74 ± 7years) and 30 young adults (27 ± 9years). Cortical micro-architecture was determined using AUTO and MOD contour methods. CV%RMS and LSC were calculated. Repeated measures and multivariate ANOVA were used to compare mean CV% and bone outcomes between the methods within and between the groups. Significance was accepted at P < 0.05. CV%RMS ranged from 0.9 to 16.3%. Within-group precision did not differ between evaluation methods. Compared to young adults, postmenopausal women had better precision for radial cortical porosity (precision difference 9.3%) and pore volume (7.5%) with MOD. Young adults had better precision for cortical thickness (0.8%, MOD) and tibial cortical density (0.2%, AUTO). In postmenopausal women, MOD resulted in 0.2-54% higher values for most cortical outcomes, as well as 6-8% lower radial and tibial cortical BMD and 2% lower tibial cortical thickness. Results suggest that AUTO and MOD endocortical contour methods provide comparable repeatability. In postmenopausal women, manual modification of endocortical contours led to generally higher cortical bone properties when compared to the automated method, while no between-method differences were observed in young adults.

Bone status of adult female butyrylcholinesterase gene-deficient mice

Butyrylcholinesterase (BChE) degrades acetylcholine in addition to acetylcholinesterase (AChE) which is involved in embryonic development of limbs. Since BChE is expressed by osteoblast-like cells we asked whether it is functional in adult bone remodeling. We addressed this issue by analyzing BChE gene-deficient mice (BChE-KO).Bones were extracted from 16-week old female BChE-KO and corresponding wild type mice (WT). Femoral bones were used for biomechanical testing and μCT evaluation of cancellous and cortical bone. Also vertebrae Th12 and L1 were investigated with μCT while L3 was used for tartrate-resistant acidic phosphatase (TRAP) histomorphometry and Th10 for gene expression analysis by means of real-time RT-PCR.BChE-KO did not reveal significant differences in biomechanical bone strength and bone mineral density determined by μCT. Microarchitecture of cancellous and cortical bone showed an increase in μCT parameters like trabecular thickness, trabecular separation, and relative cortical bone area of femoral BChE-KO bone compared to WT. In vertebrae no changes of microstructure and mRNA expression were detected. However, osteoclast histomorphometry with TRAP stained sections demonstrated a significant increase in relative osteoclast number.In conclusion, in adult murine bone the role of BChE is limited to bone specific changes in microarchitecture and to an increase in relative number of bone resorbing osteoclasts whereas the main collagen resorbing enzyme Cathepsin-K (CtsK) was stably expressed. Besides, AChE might be able to compensate the lack of BChE. Thus, further analyses using bone tissue specific AChE BChE cre–lox double knockout mice would be helpful.

Bone Geometry, Volumetric Density, Microarchitecture, and Estimated Bone Strength Assessed by HR-pQCT in Adult Patients With Type 1 Diabetes Mellitus.

The primary goal of this cross-sectional in vivo study was to assess peripheral bone microarchitecture, bone strength, and bone remodeling in adult type 1 diabetes (T1D) patients with and without diabetic microvascular disease (MVD+ and MVD-, respectively) and to compare them with age-, gender-, and height-matched healthy control subjects (CoMVD+ and CoMVD-, respectively). The secondary goal was to assess differences in MVD- and MVD+ patients. Fifty-five patients with T1DM (MVD+ group: n = 29) were recruited from the Funen Diabetes Database. Dual-energy X-ray absorptiometry (DXA), high-resolution peripheral quantitative computed tomography (HR-pQCT) of the ultradistal radius and tibia, and biochemical markers of bone turnover were performed in all participants. There were no significant differences in HR-pQCT parameters between MVD- and CoMVD- subjects. In contrast, MVD+ patients had larger total and trabecular bone areas (p = 0.04 and p = 0.02, respectively), lower total, trabecular, and cortical volumetric bone mineral density (vBMD) (p < 0.01, p < 0.04, and p < 0.02, respectively), and thinner cortex (p = 0.03) at the radius, and lower total and trabecular vBMD (p = 0.01 and p = 0.02, respectively) at the tibia in comparison to CoMVD+. MVD+ patients also exhibited lower total and trabecular vBMD (radius p = 0.01, tibia p < 0.01), trabecular thickness (radius p = 0.01), estimated bone strength, and greater trabecular separation (radius p = 0.01, tibia p < 0.01) and network inhomogeneity (radius p = 0.01, tibia p < 0.01) in comparison to MVD- patients. These differences remained significant after adjustment for age, body mass index, gender, disease duration, and glycemic control (average glycated hemoglobin over the previous 3 years). Although biochemical markers of bone turnover were significantly lower in MVD+ and MVD- groups in comparison to controls, they were similar between the MVD+ and MVD- groups. The results of our study suggest that the presence of MVD was associated with deficits in cortical and trabecular bone vBMD and microarchitecture that could partly explain the excess skeletal fragility observed in these patients.

Skeletal changes through the lifespan--from growth to senescence.

Age-related fragility fractures are an enormous public health problem. Both acquisition of bone mass during growth and bone loss associated with ageing affect fracture risk late in life. The development of high-resolution peripheral quantitative CT (HRpQCT) has enabled in vivo assessment of changes in the microarchitecture of trabecular and cortical bone throughout life. Studies using HRpQCT have demonstrated that the transient increase in distal forearm fractures during adolescent growth is associated with alterations in cortical bone, which include cortical thinning and increased porosity. Children with distal forearm fractures in the setting of mild, but not moderate, trauma also have increased deficits in cortical bone at the distal radius and in bone mass systemically. Moreover, these children transition into young adulthood with reduced peak bone mass. Elderly men, but not elderly women, with a history of childhood forearm fractures have an increased risk of osteoporotic fractures. With ageing, men lose trabecular bone primarily by thinning of trabeculae, whereas the number of trabeculae is reduced in women, which is much more destabilizing from a biomechanical perspective. However, age-related losses of cortical bone and increases in cortical porosity seem to have a much larger role than previously recognized, and increased cortical porosity might characterize patients at increased risk of fragility fractures.

Serum sclerostin: the missing link in the bone-vessel cross-talk in hemodialysis patients?

We found for the first time that in maintenance hemodialysis patients, higher sclerostin serum level was associated with severe abdominal aortic calcification (AAC). In addition, cortical bone microarchitecture (density and thickness) assessed by high-resolution peripheral quantitative computed tomography (HR-pQCT) at tibia was also independently associated with severe AAC. These results suggest that sclerostin may be involved in the association of mineral and bone disorder with vascular calcification in hemodialysis patients. Severe abdominal aortic calcifications are predictive of high cardiovascular mortality in maintenance hemodialysis (MHD) patients. In patients with end-stage renal disease, a high aortic calcification score was associated with lower bone turnover on bone biopsies. Thus, we hypothesized that sclerostin, a Wnt pathway inhibitor mainly secreted by osteocytes and acting on osteoblasts to reduce bone formation, may be associated with vascular calcifications in MHD patients. Fifty-three MHD patients, aged 53years [35-63] (median [Q1-Q3]) were included. Serum was sampled before the MHD session to assay sclerostin. Framingham score was computed and the abdominal aortic calcification (AAC) score was assessed according to Kauppila method on lateral spine imaging using DEXA. Tibia bone status was evaluated by high-resolution peripheral quantitative computed tomography (HR-pQCT). Patients were distributed into two groups according to their AAC score: patients with mild or without AAC (score below 6) versus patients with severe AAC (score of 6 and above). In multivariate analysis, after adjustment on age, dialysis duration and diabetes, serum sclerostin and cortical thickness were independently associated with severe AAC (odds ratio (OR) = 1.43 for each 0.1ng/mL increase [95% confidence interval (CI) 1.10-1.83]; p = 0.006 and 0.16 for 1 SD increase [0.03-0.73]; p = 0.018, respectively). A second cardiovascular model adjusted on Framingham score and the above mentioned confounders showed similar results. Elevated sclerostin serum level and poorer tibia cortical bone structure by HR-pQCT were positively and independently associated with higher odds of severe AAC in MHD patients. Serum sclerostin may become a biomarker of mineral and bone disorder and vascular risk in MHD patients.

Abnormal Skeletal Strength and Microarchitecture in Women With Celiac Disease.

Osteoporosis is often a presenting sign of celiac disease (CD). Whether skeletal fragility in CD is associated with microarchitectural abnormalities is not known. The objective of the study was to evaluate microarchitecture and biomechanical properties of bone in CD. This was a case-control study. The study was conducted at a university hospital outpatient facility. Patients included premenopausal women with newly diagnosed CD (n = 33) and healthy controls (n = 33). Areal bone mineral density by dual-energy x-ray absorptiometry was measured as was trabecular and cortical volumetric bone mineral density (vBMD) and microarchitecture by high-resolution peripheral computed tomography of the distal radius and tibia. Whole-bone stiffness estimated by finite element analysis. PTH, 25-hydroxyvitamin D, and bone turnover markers were also measured. Groups had similar age, race, and body mass index. Both groups had sufficient 25-hydroxyvitamin D and normal calcium and PTH. Areal bone mineral density was lower in CD. By high-resolution peripheral computed tomography, CD had lower trabecular vBMD, fewer, more widely, and irregularly spaced trabeculae at both the radius and tibia (8%-33%). At the tibia, they also had lower total density (8%) and thinner cortices (10%). Whole-bone stiffness and failure load were lower (11%-21%) in CD at both sites. Biomechanical deficits were associated with trabecular abnormalities. Women with CD had abnormal vBMD and microarchitecture at both the radius and tibia. Trabecular bone was preferentially affected. These deficits were associated with lower estimates of skeletal strength. These findings suggest a potential structural mechanism for skeletal fragility in CD and support further research into the pathogenesis of fracture in this population.

New Insights Into Androgen and Estrogen Receptor Regulation of the Male Skeleton.

Beginning with the report in 1994 that an adult male with homozygous loss of estrogen receptor α (ERα) had unfused epiphyses and osteopenia,(1) there is now considerable evidence from observational and interventional studies (summarized in Khosla and colleagues(2)) that estrogen is the dominant regulator of bone metabolism in men. Indeed, a legitimate argument can be made that testosterone is largely a prohormone for the skeleton, with its effects on bone mediated principally via aromatization to estrogen, although it remains likely that testosterone contributes to bone size via effects on periosteal apposition and perhaps indirectly to bone mass by increasing muscle mass.

Piroxicam treatment augments bone abnormalities in interleukin-10 knockout mice.

Osteoporosis and fractures are common complications of inflammatory bowel disease. The pathogenesis is multifactorial and has been partly attributed to intestinal inflammation. The aim of this study was to evaluate bone status and assess the association between bone loss and gut inflammation in an experimental colitis model. Colitis was induced in interleukin-10 knockout mice (PAC IL-10 k.o.) by peroral administration of piroxicam for 12 days. The degree of colitis was assessed by clinical, macroscopic, and microscopic evaluation. Trabecular and cortical bone microarchitecture of tibia were determined using micro-computed tomography. Moreover, the serum levels of bone formation and bone resorption biomarkers were measured, and inflammatory protein profiling was performed on colons. PAC IL-10 k.o. mice developed severe colitis, characterized by hyperplasia and focal transmural inflammation, which was consistent with Crohn's disease-like pathology. The gut inflammation was accompanied by a 14% and 12% reduction in trabecular thickness relative to piroxicam-treated wild type and untreated wild type mice, respectively (P < 0.001). The trabecular bone structure was also changed in PAC IL-10 k.o. mice, whereas no differences in cortical bone geometry were observed. The trabecular thickness was inversely correlated with serum levels of CTX (r = -0.93, P = 0.006). Moreover, numerous inflammatory mediators, including RANKL and osteoprotegerin, were significantly increased in the colon of PAC IL-10 k.o. mice. PAC IL-10 k.o. mice develop bone loss and changed trabecular structure, as a result of increased bone resorption. Thus, the PAC IL-10 k.o. model could be a useful experimental model in preclinical research of inflammatory bowel disease-associated bone loss.

Effects of long-term doxycycline on bone quality and strength in diabetic male DBA/2J mice

In type 1 diabetes, diabetic bone disease (DBD) is characterized by decreased bone mineral density, a state of low bone turnover and an increased risk of fracture. Animal models of DBD demonstrate that acquired alterations in trabecular and cortical bone microarchitecture contribute to decreased bone strength in diabetes. With anti-collagenolytic and anti-inflammatory properties, tetracycline derivatives may prevent diabetes-related decreases in bone strength. To determine if doxycycline, a tetracycline class antibiotic, can prevent the development of DBD in a model of long-term diabetes, male DBA/2J mice, with or without diabetes, were treated with doxycycline-containing chow for 10weeks (dose range, 28–92mg/kg/day). Long-term doxycycline exposure was not deleterious to the microarchitecture or biomechanical properties of healthy bones in male DBA/2J mice. Doxycycline treatment also did not prevent or alleviate the deleterious changes in trabecular microarchitecture, cortical structure, and biomechanical properties of bone induced by chronic diabetes.

In vivo imaging of rat cortical bone porosity by synchrotron phase contrast micro computed tomography

Cortical bone is a dynamic tissue which undergoes adaptive and pathological changes throughout life. Direct longitudinal tracking of this remodeling process holds great promise for improving our understanding of bone development, maintenance and senescence. The application of in vivo micro-computed tomography (micro-CT) has enabled longitudinal tracking of trabecular bone microarchitecture with commercially available scanners generally operating in the 10–20 µm voxel range with absorbed doses reported between 0.5 and 1 Gy. Imaging of cortical bone microarchitecture (porosity) requires higher resolution and thus in vivo imaging of these structures has not been achieved due to excessive radiation dose. In this study we tested the hypothesis that synchrotron propagation phase contrast micro-CT can enable in vivo imaging of cortical porosity in rats at doses comparable to those currently employed for trabecular bone imaging. Synchrotron imaging experiments were conducted at the Canadian Light Source using the bending magnet beamline of the BioMedical Imaging and Therapy (BMIT) facility. Protocol optimization (propagation distance, projection number) was conducted ex vivo on rat (Sprague-Dawley) forelimbs with dose determined by ion chamber and lithium fluoride crystal thermoluminescent dosimeters. Comparative ex vivo imaging was performed using laboratory in vivo scanning systems, identifying a range of doses between 1.2–3.6 Gy for common protocols. A final in vivo synchrotron protocol involving a 2.5 Gy dose was implemented with live rats. The resulting images demonstrated improved delineation of cortical porosity through the improved edge enhancement effect of phase contrast, opening the door to novel experimental studies involving the longitudinal tracking of remodeling.

Defects in cortical microarchitecture among African-American women with type 2 diabetes

Patients with type 2 diabetes mellitus (DM2) have increased fracture risk. We found that African-American women with DM2 have increased cortical porosity and lower cortical bone density at the radius than non-diabetic controls. These cortical deficits are associated with hyperglycemia and may contribute to skeletal fragility associated with DM2. Fracture risk is increased in patients with type 2 diabetes mellitus (DM2) despite normal areal bone mineral density (aBMD). DM2 is more common in African-Americans than in Caucasians. It is not known whether African-American women with DM2 have deficits in bone microstructure. We measured aBMD at the spine and hip by DXA, and volumetric BMD (vBMD) and microarchitecture at the distal radius and tibia by HR-pQCT in 22 DM2 and 78 non-diabetic African-American women participating in the Study of Women Across the Nation (SWAN). We also measured fasting glucose and HOMA-IR. Age, weight, and aBMD at all sites were similar in both groups. At the radius, cortical porosity was 26% greater, while cortical vBMD and tissue mineral density were lower in women with DM2 than in controls. There were no differences in radius total vBMD or trabecular vBMD between groups. Despite inferior cortical bone properties at the radius, FEA-estimated failure load was similar between groups. Tibia vBMD and microarchitecture were also similar between groups. There were no significant associations between cortical parameters and duration of DM2 or HOMA-IR. However, among women with DM2, higher fasting glucose levels were associated with lower cortical vBMD (r=-0.54, p=0.018). DM2 and higher fasting glucose are associated with unfavorable cortical bone microarchitecture at the distal radius in African-American women. These structural deficits may contribute to the increased fracture risk among women with DM2. Further, our results suggest that hyperglycemia may be involved in mechanisms of skeletal fragility associated with DM2.

Skeletal deterioration following ovarian failure: can some features be a direct consequence of estrogen loss while others are more related to physical inactivity?

Findings on experimental animals show that ovarian failure is accompanied by a decrease in motor activity. As mechanical loading has a vital role in the maintenance of skeletal health, our aim was to determine to what extent this decrease in motor activity contributes to ovariectomy-induced bone loss. Thirty-two female Wistar rats were ovariectomized or sham-operated and housed in standard cages or with access to running wheels for 36 weeks with their running distance monitored. Markers of bone turnover were assayed in the serum, and bone geometry, trabecular and cortical bone microarchitecture, mineralization degree, and biomechanical properties were assessed in the femur. Differences between groups were determined by one-way ANOVA. Although reduced motor activity and sex steroid deficiency both resulted in decreases in trabecular bone volume, trabecular number decreases were mostly associated with sex steroid deficiency, whereas trabecular thickness decreases were mostly associated with sedentary behavior. Cortical bone appeared to be more sensitive to variations in motor activity, whereas bone turnover rate and bone tissue mineralization degree seemed to be primarily affected by sex steroid deficiency, even though they were further aggravated by sedentary behavior. Increases in femur length were mostly a consequence of sex steroid deficiency, whereas femoral neck length was also influenced by sedentary behavior. Differences in mechanical properties resulted mostly from differences in physical activity. Both the direct effect of sex steroid deficiency and the indirect effect of motor activity changes are implicated in bone loss following ovariectomy.

High-resolution peripheral quantitative CT imaging: Cortical porosity, poor trabecular bone microarchitecture, and low bone strength in lung transplant recipients.

To characterize bone microarchitecture and quantify bone strength in lung transplant (LT) recipients by using high-resolution (HR) peripheral quantitative computed tomographic (CT) imaging of the ultradistal radius. After study approval by the local ethics committee, all participants provided written informed consent. Included were 118 participants (58 LT recipients [mean age, 46.8 years ± 1.9; 30 women, 28 men] and 60 control participants [mean age, 39.9 years ± 1.9; 41 women, 19 men]) between April 2010 and May 2012. HR peripheral quantitative CT of the ultradistal radius was performed and evaluated for bone mineral density and trabecular and cortical bone microarchitecture. Mechanical competence was quantified by microfinite element analysis. Differences between LT recipients and control participants were determined by using two-way factorial analysis of covariance with age adjustment. Total and trabecular bone mineral density were significantly lower (-13.4% and -16.4%, respectively; P = .001) in LT recipients than in healthy control participants. LT recipients had lower trabecular number (-9.7%; P = .004) and lower trabecular thickness (-8.1%; P = .025). Trabecular separation and trabecular network heterogeneity were higher (+24.3% and +63.9%, respectively; P = .007 and P = .012, respectively) in LT recipients. Moreover, there was pronounced cortical porosity (+31.3%; P = .035) and lower cortical thickness (-10.2%, P = .005) after LT. In addition, mechanical competence was impaired, which was reflected by low stiffness (-15.0%; P < .001), low failure force (-14.8%; P < .001), and low bone strength (-14.6%; P < .001). Men and women with recent LT showed severe deficits in cortical and trabecular bone microarchitecture. Poor bone microarchitecture and low bone strength are likely to contribute to high fracture susceptibility observed in LT recipients.

The role of patient-mode high-resolution peripheral quantitative computed tomography indices in the prediction of failure strength of the elderly women's thoracic vertebral body.

The correlations between the failure load of 20 T12 vertebral bodies, their patient-mode high-resolution peripheral quantitative computed tomography (HR-pQCT) indices, and the L1 areal bone mineral density (aBMD) were investigated. For the prediction of the T12 vertebral failure load, the T12 HR-pQCT microarchitectural parameters added significant information to that of L1 aBMD and to that of cortical BMD, but not to that of T12 vertebral BMD and not to that of T12 trabecular BMD. HR-pQCT is a new in vivo imaging technique for assessing the three-dimensional microarchitecture of cortical and trabecular bone at the distal radius and tibia. But little is known about this technique in the direct measurement of vertebral body. Twenty female donors with the mean age of 80.1 (7.6) years were included in the study. Dual X-ray absorptiometry of the lumbar spine and femur was performed. The spinal specimens (T11/T12/L1) were dissected, scanned using HR-pQCT scanner, and mechanically tested under 4° wedge compression. The L1 aBMD, T12 patient-mode HR-pQCT indices, and T12 vertebral failure loads were analyzed. For the prediction of vertebral failure load, the inclusion of BV/TV into L1 aBMD was the best model (R (2) = 0.52), Tb.N and Tb.Sp added significant information to the L1 aBMD and to the cortical BMD, but none of the vertebral microarchitectural parameters yielded additional significant information to the trabecular BMD (or BV/TV) and to the vertebral BMD. Vertebral microarchitectural parameters obtained from the patient-mode HR-pQCT analysis provide significant information on bone strength complementary to that of aBMD and to that of cortical BMD, but not to that of vertebral BMD and not to that of trabecular BMD.

Microstructural properties of the mid-facial bones in relation to the distribution of occlusal loading

Although the concept of the occlusal load transfer through the facial skeleton along the buttresses has been extensively studied, there has been no study to link microarchitecture of the mid-facial bones to the occlusal load distribution. The aim of this study was to analyze micro-structural properties of the mid-facial bones in relation to occlusal stress. The study was performed by combining the three-dimensional finite element analysis (3D FEA) and micro-computed tomography analysis (micro-CT). Clenching was simulated on the computer model of the adult male human skull which was also used as a source of bone specimens. After the FEA was run, stress was measured at the specific sites in cortical shell and trabecular bone of the model along and between the buttresses. From the corresponding sites on the skull, twenty-five cortical and thirteen cancellous bone specimens were harvested. The specimens were classified into high stress or low stress group based on the stress levels measured via the FEA. Micro-architecture of each specimen was assessed by micro-CT. In the high stress group, cortical bone showed a tendency toward greater thickness and density, lower porosity, and greater pore separation. Stress-related differences in microstructure between the groups were more pronounced in trabecular bone, which showed significantly greater bone volume fraction (BV/TV) and trabecular thickness (Tb.Th) in the high stress group. Our results suggest that the mid-facial bones in the adult dentate male skull exhibit regional variations in cortical and trabecular bone micro-architecture that could be a consequence of different occlusal stress.

Moderate-intensity rotating magnetic fields do not affect bone quality and bone remodeling in hindlimb suspended rats.

Abundant evidence has substantiated the positive effects of pulsed electromagnetic fields (PEMF) and static magnetic fields (SMF) on inhibiting osteopenia and promoting fracture healing. However, the osteogenic potential of rotating magnetic fields (RMF), another common electromagnetic application modality, remains poorly characterized thus far, although numerous commercial RMF treatment devices have been available on the market. Herein the impacts of RMF on osteoporotic bone microarchitecture, bone strength and bone metabolism were systematically investigated in hindlimb-unloaded (HU) rats. Thirty two 3-month-old male Sprague-Dawley rats were randomly assigned to the Control (n = 10), HU (n = 10) and HU with RMF exposure (HU+RMF, n = 12) groups. Rats in the HU+RMF group were subjected to daily 2-hour exposure to moderate-intensity RMF (ranging from 0.60 T to 0.38 T) at 7 Hz for 4 weeks. HU caused significant decreases in body mass and soleus muscle mass of rats, which were not obviously altered by RMF. Three-point bending test showed that the mechanical properties of femurs in HU rats, including maximum load, stiffness, energy absorption and elastic modulus were not markedly affected by RMF. µCT analysis demonstrated that 4-week RMF did not significantly prevent HU-induced deterioration of femoral trabecular and cortical bone microarchitecture. Serum biochemical analysis showed that RMF did not significantly change HU-induced decrease in serum bone formation markers and increase in bone resorption markers. Bone histomorphometric analysis further confirmed that RMF showed no impacts on bone remodeling in HU rats, as evidenced by unchanged mineral apposition rate, bone formation rate, osteoblast numbers and osteoclast numbers in cancellous bone. Together, our findings reveal that RMF do not significantly affect bone microstructure, bone mechanical strength and bone remodeling in HU-induced disuse osteoporotic rats. Our study indicates potentially obvious waveform-dependent effects of electromagnetic fields-stimulated osteogenesis, suggesting that RMF, at least in the present form, might not be an optimal modality for inhibiting disuse osteopenia/osteoporosis.

Analysis of Cortical Bone Structures in Perimenopausal Female Patients With Recent Fragility Fractures

Aims: The aim of this study was to investigate trabecular and cortical bone microstructure in perimenopausal patients with atraumatic peripheral or vertebral fractures. We hypothesize that in perimenopausal women cortical bone is more affected by osteoporosis than trabecular bone. Methods: We consecutively investigated 26 perimenopausal treatment naive female patients (mean age: 47.8 yrs) with peripheral fractures (PG) and compared them to ageand sex-matched healthy controls (CG; n538; mean age 42.7 yrs). Patients had an average of two atraumatic fractures, but were otherwise healthy. The distal radius and the ultradistal tibia of all patients were scanned on an HRpQCT scanner (XtremeCT, SCANCO Medical, Br€uttisellen, Switzerland). Trabecular bone volume fraction (BV/TV) from the volumetric BMD of the trabecular compartment (Tb.BMD), the peripheral region adjacent to the cortex (pTb.BMD) and the central trabecular region (mTb.BMD) were analyzed. From the binary trabecular ridge image, trabecular number (Tb.N) was measured using the direct 3D distance transform approach. Based on the densitometric BV/TV and direct Tb.N, trabecular thickness (Tb.Th) and trabecular separation (Tb.Sp) were derived using traditional plate model assumptions, as has been described previously (Boutroy et al., JCEM 2005). To assess cortical bone microarchitecture, the trabecular and cortical compartment were segmented by automated algorithm (Burghardt et al., JBMR 2009). We analyzed cortical BMD (Ct.BMD), cortical porosity (Ct.Po), cortical pore volume (Ct.Po.V), cortical pore diameter (Ct.Po.Dm) and cortical pore diameter distribution (Ct.Po.Dm.SD). Results: Structural analysis by HR-pQCT showed significant differences between patients and healthy controls regarding cortical but not trabecular parameters at both sites. At the radius patients had increased cortical pore volume (7.74 4.97mm vs. 5.29 3.78; p!0.01), increased cortical pore diameter (0.17 0.03mm vs. 0.15 0.02mm; p! 0.001) and an increased distribution of cortical pore diameters (7 3% vs. 4 3%; p!0.01) compared to controls. In addition, at the tibia cortical pore volume (61.15 30.66mm; p!0.01) and also cortical porosity (7 4% vs. 4 3%; p!0.01) were significantly increased. Strong correlations of cortical parameters were found between the tibia and radius. In addition, most cortical structure parameters were correlated with age in patients and controls. Conclusion: Our results suggest that bone fragility and fracture susceptibility in perimenopausal females are likely to contribute to poor cortical bone strength and increased cortical porosity. However, HR-pQCT resolution is limited and cortical porosity, analyzed by different algorithm, was reported to be much higher. Disclosure of Interest: None Declared

Characterizing microarchitectural changes at the distal radius and tibia in postmenopausal women using HR-pQCT.

Limited prospective evidence exists regarding bone microarchitectural deterioration. We report annual changes in trabecular and cortical bone microarchitecture at the distal radius and tibia in postmenopausal women. Lost trabeculae with corresponding increase in trabecular thickness at the radius and thinning tibial cortex indicated trabecularization of the cortex at both sites. Osteoporosis is characterized by low bone mass and the deterioration of bone microarchitecture. However, limited prospective evidence exists regarding bone microarchitectural changes in postmenopausal women: a population prone to sustaining osteoporotic fractures. Our primary objective was to characterize the annual change in bone area, density, and microarchitecture at the distal radius and distal tibia in postmenopausal women. Distal radius and tibia were measured using high-resolution peripheral quantitative computed tomography (HR-pQCT) at baseline and 1 year later in 51 women (mean age ± SD, 77 ± 7 years) randomly sampled from the Saskatoon cohort of the Canadian Multicentre Osteoporosis Study (CaMos). We used repeated measures analysis of variance (ANOVA) with Bonferroni adjustment for multiple comparisons to characterize the mean annual change in total density, cortical perimeter, trabecular and cortical bone area, density, content, and microarchitecture. Significant changes were accepted at P < 0.05. At the distal radius in women without bone-altering drugs, total density (-1.7%) and trabecular number (-6.4%) decreased, while trabecular thickness (+6.0%), separation (+8.6%), and heterogeneity (+12.1%) increased. At their distal tibia, cortical area (-4.5%), density (-1.9%), content (-6.3%), and thickness (-4.4%) decreased, while trabecular area (+0.4%) increased. The observed loss of trabeculae with concomitant increase in trabecular size at the distal radius and the declined cortical thickness, density, and content at the distal tibia indicated a site-specific trabecularization of the cortical bone in postmenopausal women.