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Posttraumatic osteoarthritis (PTOA) results in joint pain, loss of joint function, and impaired quality of daily life in patients with limited treatment options. We previously demonstrated that epidermal growth factor receptor (EGFR) signaling is essential for maintaining chondroprogenitors during articular cartilage development and homeostasis. Here, we used a nonsurgical, loading-induced PTOA mouse model to investigate the protective action of EGFR signaling. A single bout of cyclic tibial loading at a peak force of 6 N injured cartilage at the posterior aspect of lateral femoral condyle. Similar loading at a peak force of 9 N ruptured the anterior cruciate ligament, causing additional cartilage damage at the medial compartment and ectopic cartilage formation in meniscus and synovium. Constitutively overexpression of an EGFR ligand, heparin binding EGF-like growth factor (HBEGF), in chondrocytes significantly reduced cartilage injury length, synovitis, and pain after 6 N loading and mitigated medial side cartilage damage and ectopic cartilage formation after 9 N loading. Mechanistically, overactivation of EGFR signaling protected chondrocytes from loading-induced apoptosis and loss of proliferative ability and lubricant synthesis. Overexpressing HBEGF in adult cartilage starting right before 6 N loading had similar beneficial effects. In contrast, inactivating EGFR in adult cartilage led to accelerated PTOA progression with elevated cartilage Mankin score and synovitis score and increased ectopic cartilage formation. As a therapeutic approach, we constructed a nanoparticle conjugated with the EGFR ligand TGFα. Intra-articular injections of this nanoconstruct once every 3 weeks for 12 weeks partially mitigated PTOA symptoms in cartilage and synovium after 6 N loading. Our findings demonstrate the anabolic actions of EGFR signaling in maintaining articular cartilage during PTOA development and shed light on developing a novel nanomedicine for PTOA. © 2022 American Society for Bone and Mineral Research (ASBMR)., (© 2022 American Society for Bone and Mineral Research (ASBMR).)

Anabolic agents, such as intermittent parathyroid hormone (PTH), exert their treatment efficacy through activation of two distinct bone formation processes, namely, remodeling-based bone formation (RBF, bone formation coupled with prior bone resorption) and modeling-based bone formation (MBF, bone formation without prior activation of bone resorption). However, if not followed by an antiresorptive agent, treatment benefit was quickly lost upon withdrawal from anabolic agents. By using in vivo micro-computed tomography imaging and multiplex cryohistology with sequential immunofluorescence staining, we investigated the temporal response of newly formed bone tissue from MBF and RBF and the preexisting bone tissue to withdrawal from PTH treatment and the associated cellular activity in an ovariectomized (OVX) rat model. We first demonstrated continued mineral apposition at both RBF and MBF sites following PTH discontinuation, resulting in an extended anabolic effect after 1-week withdrawal from PTH. It was further discovered that MBF sites had a greater contribution than RBF sites to the extended anabolic effect upon early withdrawal from PTH, evidenced by a higher percentage of alkaline phosphatase-positive (ALP+) surfaces and far greater bone formation activity at MBF versus RBF sites. Furthermore, significant bone loss occurred after 3 weeks of discontinuation from PTH, resulting from marked loss of newly formed bone tissue from RBF and preexisting bone tissue prior to treatment. In contrast, MBF surfaces had a delayed increase of tartrate-resistant acid phosphatase activity following PTH discontinuation. As a result, newly formed bone tissue from MBF had greater resistance to PTH discontinuation-induced bone loss than those from RBF and preexisting bone. Understanding various responses of two distinct bone formation types and preexisting bone to anabolic treatment discontinuation is critical to inform the design of follow-up treatment or cyclic treatment strategies to maximize treatment benefit of anabolic agents. © 2022 American Society for Bone and Mineral Research (ASBMR)., (© 2022 American Society for Bone and Mineral Research (ASBMR).)

Despite the potent effect of intermittent parathyroid hormone (PTH) treatment on promoting new bone formation, bone mineral density (BMD) rapidly decreases upon discontinuation of PTH administration. To uncover the mechanisms behind this adverse phenomenon, we investigated the immediate responses in bone microstructure and bone cell activities to PTH treatment withdrawal and the associated long-term consequences. Unexpectedly, intact female and estrogen-deficient female rats had distinct responses to the discontinuation of PTH treatment. Significant tibial bone loss and bone microarchitecture deterioration occurred in estrogen-deficient rats, with the treatment benefits of PTH completely lost 9 weeks after discontinuation. In contrast, no adverse effect was observed in intact rats, with sustained treatment benefit 9 weeks after discontinuation. Intriguingly, there is an extended anabolic period during the first week of treatment withdrawal in estrogen-deficient rats, during which no significant change occurred in the number of osteoclasts, whereas the number of osteoblasts remained elevated compared with vehicle-treated rats. However, increases in number of osteoclasts and decreases in number of osteoblasts occurred 2 weeks after discontinuation of PTH treatment, leading to significant reduction in bone mass and bone microarchitecture. To leverage the extended anabolic period upon early withdrawal from PTH, a cyclic administration regimen with repeated cycles of on and off PTH treatment was explored. We demonstrated that the cyclic treatment regimen efficiently alleviated the PTH withdrawal-induced bone loss, improved bone mass, bone microarchitecture, and whole-bone mechanical properties, and extended the treatment duration. © 2021 American Society for Bone and Mineral Research (ASBMR)., (© 2021 American Society for Bone and Mineral Research (ASBMR).)

Atrophic nonunion represents an extremely challenging clinical dilemma for both physicians and fracture patients alike, but its underlying mechanisms are still largely unknown. Here, we established a mouse model that recapitulates clinical atrophic nonunion through the administration of focal radiation to the long bone midshaft 2 weeks before a closed, semistabilized, transverse fracture. Strikingly, fractures in previously irradiated bone showed no bony bridging with a 100% nonunion rate. Radiation triggered distinct repair responses, separated by the fracture line: a less robust callus formation at the proximal side (close to the knee) and bony atrophy at the distal side (close to the ankle) characterized by sustained fibrotic cells and type I collagen-rich matrix. These fibrotic cells, similar to human nonunion samples, lacked osteogenic and chondrogenic differentiation and exhibited impaired blood vessel infiltration. Mechanistically, focal radiation reduced the numbers of periosteal mesenchymal progenitors and blood vessels and blunted injury-induced proliferation of mesenchymal progenitors shortly after fracture, with greater damage particularly at the distal side. In culture, radiation drastically suppressed proliferation of periosteal mesenchymal progenitors. Radiation did not affect hypoxia-induced periosteal cell chondrogenesis but greatly reduced osteogenic differentiation. Lineage tracing using multiple reporter mouse models revealed that mesenchymal progenitors within the bone marrow or along the periosteal bone surface did not contribute to nonunion fibrosis. Therefore, we conclude that atrophic nonunion fractures are caused by severe damage to the periosteal mesenchymal progenitors and are accompanied by an extraskeletal, fibro-cellular response. In addition, we present this radiation-induced periosteal damage model as a new, clinically relevant tool to study the biologic basis of therapies for atrophic nonunion. © 2018 American Society for Bone and Mineral Research., (© 2018 American Society for Bone and Mineral Research.)

The female skeleton undergoes substantial structural changes during the course of reproduction. Although bone mineral density recovers postweaning, reproduction may induce permanent alterations in maternal bone microarchitecture. However, epidemiological studies suggest that a history of pregnancy and/or lactation does not increase the risk of postmenopausal osteoporosis or fracture and may even have a protective effect. Our study aimed to explain this paradox by using a rat model, combined with in vivo micro-computed tomography (μCT) imaging and bone histomorphometry, to track the changes in bone structure and cellular activities in response to estrogen deficiency following ovariectomy (OVX) in rats with and without a reproductive history. Our results demonstrated that a history of reproduction results in an altered skeletal response to estrogen-deficiency-induced bone loss later in life. Prior to OVX, rats with a reproductive history had lower trabecular bone mass, altered trabecular microarchitecture, and more robust cortical structure at the proximal tibia when compared to virgins. After OVX, these rats underwent a lower rate of trabecular bone loss than virgins, with minimal structural deterioration. As a result, by 12 weeks post-OVX, rats with a reproductive history had similar trabecular bone mass, elevated trabecular thickness, and increased robustness of cortical bone when compared to virgins, resulting in greater bone stiffness. Further evaluation suggested that reproductive-history-induced differences in post-OVX trabecular bone loss were likely due to differences in baseline trabecular microarchitecture, particularly trabecular thickness. Rats with a reproductive history had a larger population of thick trabeculae, which may be protective against post-OVX trabecular connectivity deterioration and bone loss. Taken together, these findings indicate that reproduction-associated changes in bone microarchitecture appear to reduce the rate of bone loss induced by estrogen deficiency later in life, and thereby exert a long-term protective effect on bone strength. © 2018 American Society for Bone and Mineral Research., (© 2018 American Society for Bone and Mineral Research.)

Postmenopausal osteoporosis is often treated with bisphosphonates (eg, alendronate, [ALN]), but oversuppression of bone turnover by long-term bisphosphonate treatment may decrease bone tissue heterogeneity. Thus, alternate treatment strategies after long-term bisphosphonates are of great clinical interest. The objective of the current study was to determine the effect of intermittent parathyroid hormone (PTH) following 12 weeks of ALN (a bisphosphonate) treatment in 6-month-old, ovariectomized (OVX) rats on bone microarchitecture, bone remodeling dynamics, and bone mechanical properties at multiple length scales. By using in vivo μCT and 3D in vivo dynamic bone histomorphometry techniques, we demonstrated the efficacy of PTH following ALN therapy for stimulating new bone formation, and increasing trabecular thickness and bone volume fraction. In healthy bone, resorption and formation are coupled and balanced to sustain bone mass. OVX results in resorption outpacing formation, and subsequent bone loss and reduction in bone tissue modulus and tissue heterogeneity. We showed that ALN treatment effectively reduced bone resorption activity and regained the balance with bone formation, preventing additional bone loss. However, ALN treatment also resulted in significant reductions in the heterogeneity of bone tissue mineral density and tissue modulus. On the other hand, PTH treatment was able to shift the bone remodeling balance in favor of formation, with or without a prior treatment with ALN. Moreover, by altering the tissue mineralization, PTH alleviated the reduction in heterogeneity of tissue material properties induced by prolonged ALN treatment. Furthermore, switching to PTH treatment from ALN improved bone's postyield mechanical properties at both the whole bone and apparent level compared to ALN alone. The current findings suggest that intermittent PTH treatment should be considered as a viable treatment option for patients with prior treatment with bisphosphonates. © 2017 American Society for Bone and Mineral Research., (© 2017 American Society for Bone and Mineral Research.)

Pregnancy, lactation, and weaning result in dramatic changes in maternal calcium metabolism. In particular, the increased calcium demand during lactation causes a substantial degree of maternal bone loss. This reproductive bone loss has been suggested to be largely reversible, as multiple clinical studies have found that parity and lactation history have no adverse effect on postmenopausal fracture risk. However, the precise effects of pregnancy, lactation, and post-weaning recovery on maternal bone structure are not well understood. Our study aimed to address this question by longitudinally tracking changes in trabecular and cortical bone microarchitecture at the proximal tibia in rats throughout three cycles of pregnancy, lactation, and post-weaning using in vivo μCT. We found that the trabecular thickness underwent a reversible deterioration during pregnancy and lactation, which was fully recovered after weaning, whereas other parameters of trabecular microarchitecture (including trabecular number, spacing, connectivity density, and structure model index) underwent a more permanent deterioration, which recovered minimally. Thus, pregnancy and lactation resulted in both transient and long-lasting alterations in trabecular microstructure. In the meantime, multiple reproductive cycles appeared to improve the robustness of cortical bone (resulting in an elevated cortical area and polar moment of inertia), as well as increase the proportion of the total load carried by the cortical bone at the proximal tibia. Taken together, changes in the cortical and trabecular compartments suggest that whereas rat tibial trabecular bone appears to be highly involved in maintaining calcium homeostasis during female reproduction, cortical bone adapts to increase its load-bearing capacity, allowing the overall mechanical function of the tibia to be maintained. © 2017 American Society for Bone and Mineral Research., (© 2017 American Society for Bone and Mineral Research.)

Focal radiotherapy is frequently associated with skeletal damage within the radiation field. Our previous in vitro study showed that activation of Wnt/β-catenin pathway can overcome radiation-induced DNA damage and apoptosis of osteoblastic cells. Neutralization of circulating sclerostin with a monoclonal antibody (Scl-Ab) is an innovative approach for treating osteoporosis by enhancing Wnt/β-catenin signaling in bone. Together with the fact that focal radiation increases sclerostin amount in bone, we sought to determine whether weekly treatment with Scl-Ab would prevent focal radiotherapy-induced osteoporosis in mice. Micro-CT and histomorphometric analyses demonstrated that Scl-Ab blocked trabecular bone structural deterioration after radiation by partially preserving osteoblast number and activity. Consistently, trabecular bone in sclerostin null mice was resistant to radiation via the same mechanism. Scl-Ab accelerated DNA repair in osteoblasts after radiation by reducing the number of γ-H2AX foci, a DNA double-strand break marker, and increasing the amount of Ku70, a DNA repair protein, thus protecting osteoblasts from radiation-induced apoptosis. In osteocytes, apart from using similar DNA repair mechanism to rescue osteocyte apoptosis, Scl-Ab restored the osteocyte canaliculi structure that was otherwise damaged by radiation. Using a lineage tracing approach that labels all mesenchymal lineage cells in the endosteal bone marrow, we demonstrated that radiation damage to mesenchymal progenitors mainly involves shifting their fate to adipocytes and arresting their proliferation ability but not inducing apoptosis, which are different mechanisms from radiation damage to mature bone forming cells. Scl-Ab treatment partially blocked the lineage shift but had no effect on the loss of proliferation potential. Taken together, our studies provide proof-of-principle evidence for a novel use of Scl-Ab as a therapeutic treatment for radiation-induced osteoporosis and establish molecular and cellular mechanisms that support such treatment. © 2016 American Society for Bone and Mineral Research., (© 2016 American Society for Bone and Mineral Research.)

Asian women have lower rates of hip and forearm fractures compared to other racial groups despite lower areal bone mineral density (aBMD). We have demonstrated microarchitectural differences, including greater cortical thickness (Ct.Th) and cortical volumetric BMD (Ct.BMD), in Chinese American versus white women. Yet it is not known whether greater Ct.BMD in Chinese American women is a result of greater tissue mineral density (TMD) or reduced cortical porosity (Ct.Po). Using an advanced segmentation algorithm based on high-resolution peripheral quantitative computed tomography (HR-pQCT) images, we tested the hypothesis that Chinese American women have better cortical skeletal integrity owing to lower Ct.Po and higher Ct.TMD compared with white women. A total of 78 Chinese American women (49 premenopausal and 29 postmenopausal) and 114 white women (46 premenopausal and 68 postmenopausal) were studied. Premenopausal Chinese American versus white women had greater Ct.Th, Ct.BMD, and Ct.TMD at both the radius and tibia, and decreased Ct.Po (p < 0.05). A similar pattern was observed between postmenopausal Chinese American and white women. As expected, postmenopausal versus premenopausal women had lower Ct.BMD at the radius and tibia in both races (p < 0.001). Ct.Po largely increased between premenopausal and postmenopausal women, whereas Ct.TMD decreased by 3% to 8% (p < 0.001) in both races. Age-related differences in Ct.Po and Ct.TMD did not differ by race. In summary, both reduced Ct.Po and greater Ct.TMD explain higher Ct.BMD in Chinese American versus white women. Thicker and preserved cortical bone structure in Chinese American women may contribute to greater resistance to fracture compared to white women., (© 2014 American Society for Bone and Mineral Research.)

The majority of fragility fractures occur in women with osteopenia rather than osteoporosis as determined by dual‐energy X‐ray absorptiometry (DXA). However, it is difficult to identify which women with osteopenia are at greatest risk. We performed this study to determine whether osteopenic women with and without fractures had differences in trabecular morphology and biomechanical properties of bone. We hypothesized that women with fractures would have fewer trabecular plates, less trabecular connectivity, and lower stiffness. We enrolled 117 postmenopausal women with osteopenia by DXA (mean age 66 years; 58 with fragility fractures and 59 nonfractured controls). All had areal bone mineral density (aBMD) measured by DXA. Trabecular and cortical volumetric bone mineral density (vBMD), trabecular microarchitecture, and cortical porosity were measured by high‐resolution peripheral computed tomography (HR‐pQCT) of the distal radius and tibia. HR‐pQCT scans were subjected to finite element analysis to estimate whole bone stiffness and individual trabecula segmentation (ITS) to evaluate trabecular type (as plate or rod), orientation, and connectivity.Groups had similar age, race, body mass index (BMI), and mean T‐scores. Fracture subjects had lower cortical and trabecular vBMD, thinner cortices, and thinner, more widely separated trabeculae. By ITS, fracture subjects had fewer trabecular plates, less axially aligned trabeculae, and less trabecular connectivity. Whole bone stiffness was lower in women with fractures. Cortical porosity did not differ. Differences in cortical bone were found at both sites, whereas trabecular differences were more pronounced at the radius.In summary, postmenopausal women with osteopenia and fractures had lower cortical and trabecular vBMD; thinner, more widely separated and rodlike trabecular structure; less trabecular connectivity; and lower whole bone stiffness compared with controls,despite similar aBMD by DXA. Our results suggest that in addition to trabecular and cortical bone loss, changes in plate and rod structure may be important mechanisms of fracture in postmenopausal women with osteopenia.

Although high-resolution peripheral quantitative computed tomography (HR-pQCT) has advanced clinical assessment of trabecular bone microstructure, nonlinear microstructural finite element (µFE) prediction of yield strength using a HR-pQCT voxel model is impractical for clinical use due to its prohibitively high computational costs. The goal of this study was to develop an efficient HR-pQCT-based plate and rod (PR) modeling technique to fill the unmet clinical need for fast bone strength estimation. By using an individual trabecula segmentation (ITS) technique to segment the trabecular structure into individual plates and rods, a patient-specific PR model was implemented by modeling each trabecular plate with multiple shell elements and each rod with a beam element. To validate this modeling technique, predictions by HR-pQCT PR model were compared with those of the registered high-resolution micro-computed tomography (HR-µCT) voxel model of 19 trabecular subvolumes from human cadaveric tibia samples. Both the Young's modulus and yield strength of HR-pQCT PR models strongly correlated with those of µCT voxel models (r²  = 0.91 and 0.86). Notably, the HR-pQCT PR models achieved major reductions in element number (>40-fold) and computer central processing unit (CPU) time (>1200-fold). Then, we applied PR model µFE analysis to HR-pQCT images of 60 postmenopausal women with (n = 30) and without (n = 30) a history of vertebral fracture. HR-pQCT PR model revealed significantly lower Young's modulus and yield strength at the radius and tibia in fracture subjects compared to controls. Moreover, these mechanical measurements remained significantly lower in fracture subjects at both sites after adjustment for areal bone mineral density (aBMD) T-score at the ultradistal radius or total hip. In conclusion, we validated a novel HR-pQCT PR model of human trabecular bone against µCT voxel models and demonstrated its ability to discriminate vertebral fracture status in postmenopausal women. This accurate nonlinear µFE prediction of the HR-pQCT PR model, which requires only seconds of desktop computer time, has tremendous promise for clinical assessment of bone strength., (Copyright © 2013 American Society for Bone and Mineral Research.)

Compared to white women, premenopausal Chinese-American women have more plate-like trabecular (Tb) bone. It is unclear whether these findings are relevant to postmenopausal women and if there are racial differences in the deterioration of bone microarchitecture with aging. We applied individual trabecula segmentation and finite element analysis to high-resolution peripheral quantitative computed tomography images in premenopausal and postmenopausal Chinese-American and white women to quantify within-race age-related differences in Tb plate-versus-rod microarchitecture and bone stiffness. Race-menopause status interactions were assessed. Comparisons between races within menopause status were adjusted for age, height and weight. Comparisons between premenopausal and postmenopausal women were adjusted for height and weight. Adjusted analyses at the radius indicated that premenopausal Chinese-Americans had a higher plate bone volume fraction (pBV/TV), Tb plate-to-rod ratio (P-R ratio), and greater plate-plate junction densities (P-P Junc.D) versus white women (all p < 0.01), resulting in 27% higher Tb stiffness (p < 0.05). Greater cortical thickness and density (Ct.Th and Dcort) and more Tb plates led to 19% greater whole bone stiffness (p < 0.05). Postmenopausal Chinese-Americans had similar pBV/TV and P-P Junc.D, yet a higher P-R ratio versus white women. Postmenopausal Chinese-American versus white women had greater Ct.Th, Dcort, and relatively intact Tb plates, resulting in similar Tb stiffness but 12% greater whole bone stiffness (p < 0.05). In both races, Ct.Th and Dcort were lower in postmenopausal versus premenopausal women and there were no differences between races. Tb plate parameters were also lower in postmenopausal versus premenopausal women, but age-related differences in pBV/TV, P-R ratio, and P-P Junc D were greater (p < 0.05) in Chinese-Americans versus white women. There are advantages in cortical and Tb bone in premenopausal Chinese-American women. Within-race cross-sectional differences between premenopausal and postmenopausal women suggest greater loss of plate-like Tb bone with aging in Chinese-Americans, though thicker cortices and more plate-like Tb bone persists., (Copyright © 2013 American Society for Bone and Mineral Research.)

Despite the dramatic bone loss that occurs during lactation, bone mineral density rapidly recovers after offspring are weaned and milk production stops. The goal of this study is to quantify site-specific changes in bone quantity and quality during and after lactation in a mouse model. We used micro computed tomography (µCT), individual trabecula segmentation (ITS), digital topological analysis (DTA)-based tissue mineral density (TMD) analysis, and micro finite element analysis (µFEA) to quantify the effects of lactation and weaning on bone microarchitecture, mineralization, and stiffness at the spine, tibia, and femur. We found a significant decrease in trabecular plate microarchitecture, tissue mineralization of the trabecular surface, trabecular central skeleton, and intervening envelopes, and whole bone stiffness in lactating versus nulliparous mice at all three sites. In recovered mice, all these different aspects of bone quality were comparable to nulliparous mice at the spine. In contrast, trabecular plate microarchitecture and whole bone stiffness at the tibia and femur in recovered mice were lower than nulliparous mice, as were central trabecular tissue mineralization and cortical structure at the femur. These findings are consistent with clinical observations of partial recovery of femoral bone mineral density BMD after lactation in humans. The observed differences in trabecular surface tissue mineralization in nulliparous, lactating, and recovered mice are consistent with prior observations that maternal bone turnover shifts from resorption to formation at the time of pup weaning. The significant differences in trabecular central tissue mineralization during these three states suggest that osteocytes may contribute to the reversible loss of mineral during and after lactation. Future studies are necessary to determine whether differing functions of various bone cells at individual skeletal sites cause site-specific skeletal changes during and after lactation., (Copyright © 2012 American Society for Bone and Mineral Research.)

Osteoporosis is typically diagnosed by dual-energy X-ray absorptiometry (DXA) measurements of areal bone mineral density (aBMD). Emerging technologies, such as high-resolution peripheral quantitative computed tomography (HR-pQCT), may increase the diagnostic accuracy of DXA and enhance our mechanistic understanding of decreased bone strength in osteoporosis. Women with (n = 68) and without (n = 101) a history of postmenopausal fragility fracture had aBMD measured by DXA, trabecular plate and rod microarchitecture measured by HR-pQCT image-based individual trabecula segmentation (ITS) analysis, and whole bone and trabecular bone stiffness by microfinite element analysis (µFEA) of HR-pQCT images at the radius and tibia. DXA T-scores were similar in women with and without fractures at the spine, hip, and 1/3 radius, but lower in fracture subjects at the ultradistal radius. Trabecular microarchitecture of fracture subjects was characterized by preferential reductions in trabecular plate bone volume, number, and connectivity over rod trabecular parameters, loss of axially aligned trabeculae, and a more rod-like trabecular network. In addition, decreased thickness and size of trabecular plates were observed at the tibia. The differences between groups were greater at the radius than the tibia for plate number, rod bone volume fraction and number, and plate-rod and rod-rod junction densities. Most differences between groups remained after adjustment for T-score by DXA. At a fixed bone volume fraction, trabecular plate volume, number, and connectivity were directly associated with bone stiffness. In contrast, rod volume, number, and connectivity were inversely associated with bone stiffness. In summary, HR-pQCT-based ITS and µFEA measurements discriminate fracture status in postmenopausal women independent of DXA measurements. Moreover, these results suggest that preferential loss of plate-like trabeculae contribute to lower trabecular bone and whole bone stiffness in women with fractures. We conclude that HR-pQCT-based ITS and µFEA measurements increase our understanding of the microstructural pathogenesis of fragility fracture in postmenopausal women.

Individual trabecula segmentation (ITS), a rigorous model-independent 3D morphological analysis, has been developed to assess trabecular plate and rod microstructure separately based on micro-computed tomographic (µCT) images. We examined the influence of the limited spatial resolution, noise, and artifact of high-resolution peripheral quantitative CT (HR-pQCT) on ITS measurements of human tibial trabecular bone. In comparison with measurements from "gold standard" µCT images (25 µm), decreased spatial resolution (40, 60, and 80 µm) of µCT had minimal influence on the correlations of the scale of trabecular plates (ie, plate bone volume fraction, thickness, and surface area) and the orientation (ie, axial bone volume fraction) and structural type (ie, plate tissue fraction) of the trabecular network. ITS measurements of HR-pQCT images correlated significantly with those of µCT images at a similar voxel size (80 µm, r = 0.71-0.94); correlations were stronger for plate-related parameters, suggesting that measurements of trabecular rods are more subject to noise and artifact associated with HR-pQCT imaging technology. In comparison with measurements of "gold standard" µCT images, the percent absolute errors of HR-pQCT measurements such as axial and plate bone volume fraction, plate number and tissue fraction, and plate and rod thickness (3.5% to 10.3%) were comparable with those of bone volume fraction (9.3%). For both HR-pQCT and µCT images, measurements of the scale and junction densities of trabecular plates and orientation and structural type were strong and positive indicators of the elastic modulus of trabecular bone (r = 0.59-0.95). We conclude that ITS measurements of HR-pQCT images are highly reflective of trabecular bone microarchitecture from a biomechanical perspective., (Copyright © 2011 American Society for Bone and Mineral Research.)

Despite lower areal bone mineral density (aBMD), Chinese-American women have fewer fractures than white women. We hypothesized that better skeletal microstructure in Chinese-American women in part could account for this paradox. Individual trabecula segmentation (ITS), a novel image-analysis technique, and micro-finite-element analysis (µFEA) were applied to high-resolution peripheral quantitative computed tomography (HR-pQCT) images to determine bone microarchitecture and strength in premenopausal Chinese-American and white women. Chinese-American women had 95% and 80% higher plate bone volume fraction at the distal radius and tibia, respectively, as well as 20% and 18% higher plate number density compared with white women (p < .001). With similar rodlike characteristics, the plate-to-rod ratio was twice as high in the Chinese-American than in white trabecular bone (p < .001). Plate-rod junction density, a parameter indicating trabecular network connections, was 37% and 29% greater at the distal radius and tibia, respectively, in Chinese-American women (p < .002). Moreover, the orientation of the trabecular bone network was more axially aligned in Chinese-American women because axial bone volume fraction was 51% and 32% higher at the distal radius and tibia, respectively, than in white women (p < .001). These striking differences in trabecular bone microstructure translated into 55% to 68% (distal radius, p < .001) and 29% to 43% (distal tibia, p < .01) greater trabecular bone strength, as assessed by Young's moduli, in the Chinese-American versus the white group. The observation that Chinese-American women have a major microstructural advantage over white women may help to explain why their risk of fracture is lower despite their lower BMD., (Copyright © 2011 American Society for Bone and Mineral Research.)

Chinese-American women have lower rates of hip and forearm fracture than white women despite lower areal bone density (aBMD) by dual X-ray absorptiometry (DXA). We recently reported higher trabecular (D(trab) ) and cortical (D(comp) ) bone density as well as greater trabecular (Tb.Th) and cortical thickness (C.Th) but smaller bone area (CSA), as measured by high-resolution peripheral quantitative computed tomography (HR-pQCT), in premenopausal Chinese-American compared with white women. These findings may help to account for the lower fracture rate among Chinese-American women but were limited to measurements in premenopausal women. This study was designed to extend these investigations to postmenopausal Chinese-American (n = 29) and white (n = 68) women. Radius CSA was 10% smaller in the Chinese-American versus the white group (p = .008), whereas their C.Th and D(comp) values were 18% and 6% greater (p < .001 for both). Tibial HR-pQCT results for cortical bone were similar to the radius, but Tb.Th was 11% greater in Chinese-American versus white women (p = .007). Tibial trabecular number and spacing were 17% lower and 20% greater, respectively, in Chinese-American women (p < .0001 for both). There were no differences in trabecular or whole-bone stiffness estimated by microstructural finite-element analysis, but Chinese-American women had a greater percentage of load carried by the cortical bone compartment at the distal radius and tibia. There was no difference in load distribution at the proximal radius or tibia. Whole-bone finite-element analysis may indicate that the thicker, more dense cortical bone and thicker trabeculae in postmenopausal Chinese-American women compensate for fewer trabeculae and smaller bone size., (Copyright © 2011 American Society for Bone and Mineral Research.)

Strontium (Sr) exerts an anabolic and antiresorptive effect on bone, but the mechanism remains unknown. Osteoprotegerin (OPG) expressed by osteoblasts plays an important role in regulating bone homeostasis by inhibiting osteoclastogenesis and bone resorption. This study aims at evaluating the role of OPG in Sr-mediated inhibition of osteoclastogenesis and bone resorption. Six-week-old Opg knockout (KO) male mice and their wild-type (WT) littermates were treated orally with vehicle (Veh) or Sr compound (4 mmol/kg) daily for 8 weeks. Bone mass and microstructure in the lumbar spine (L(4)) and proximal tibia were analyzed with micro-computed tomography (µCT). Bone remodeling was evaluated with serum biochemical analysis and static and dynamic bone histomorphometry. Osteoclast differentiation potential and gene expression were analyzed in bone marrow cells. The findings demonstrate that Sr compound treatment results in greater bone volume and trabecular number than Veh treatment in WT mice. The anabolic response of trabecular bone to Sr treatment is attenuated in KO mice. Although Sr treatment significantly decreases in vitro osteoclastogenesis and bone resorption in WT mice, these effects are attenuated in KO mice. Furthermore, Sr treatment profoundly increases Opg gene expression in the tibias and OPG protein levels in the sera of WT mice. This study concludes that the inhibition of osteoclastogenesis and bone resorption is possibly associated with OPG upregulation by Sr treatment., (Copyright © 2011 American Society for Bone and Mineral Research.)

Vertebral strength, a key etiologic factor of osteoporotic fracture, may be affected by the relative amount of vertically oriented trabeculae. To better understand this issue, we performed experimental compression testing, high-resolution micro-computed tomography (µCT), and micro-finite-element analysis on 16 elderly human thoracic ninth (T(9)) whole vertebral bodies (ages 77.5 ± 10.1 years). Individual trabeculae segmentation of the µCT images was used to classify the trabeculae by their orientation. We found that the bone volume fraction (BV/TV) of just the vertical trabeculae accounted for substantially more of the observed variation in measured vertebral strength than did the bone volume fraction of all trabeculae (r(2) = 0.83 versus 0.59, p < .005). The bone volume fraction of the oblique or horizontal trabeculae was not associated with vertebral strength. Finite-element analysis indicated that removal of the cortical shell did not appreciably alter these trends; it also revealed that the major load paths occur through parallel columns of vertically oriented bone. Taken together, these findings suggest that variation in vertebral strength across individuals is due primarily to variations in the bone volume fraction of vertical trabeculae. The vertical tissue fraction, a new bone quality parameter that we introduced to reflect these findings, was both a significant predictor of vertebral strength alone (r(2) = 0.81) and after accounting for variations in total bone volume fraction in multiple regression (total R(2) = 0.93). We conclude that the vertical tissue fraction is a potentially powerful microarchitectural determinant of vertebral strength., (Copyright © 2011 American Society for Bone and Mineral Research.)

Measurement of areal bone mineral density (aBMD) by dual-energy x-ray absorptiometry (DXA) has been shown to predict fracture risk. High-resolution peripheral quantitative computed tomography (HR-pQCT) yields additional information about volumetric BMD (vBMD), microarchitecture, and strength that may increase understanding of fracture susceptibility. Women with (n = 68) and without (n = 101) a history of postmenopausal fragility fracture had aBMD measured by DXA and trabecular and cortical vBMD and trabecular microarchitecture of the radius and tibia measured by HR-pQCT. Finite-element analysis (FEA) of HR-pQCT scans was performed to estimate bone stiffness. DXA T-scores were similar in women with and without fracture at the spine, hip, and one-third radius but lower in patients with fracture at the ultradistal radius (p < .01). At the radius fracture, patients had lower total density, cortical thickness, trabecular density, number, thickness, higher trabecular separation and network heterogeneity (p < .0001 to .04). At the tibia, total, cortical, and trabecular density and cortical and trabecular thickness were lower in fracture patients (p < .0001 to .03). The differences between groups were greater at the radius than at the tibia for inner trabecular density, number, trabecular separation, and network heterogeneity (p < .01 to .05). Stiffness was reduced in fracture patients, more markedly at the radius (41% to 44%) than at the tibia (15% to 20%). Women with fractures had reduced vBMD, microarchitectural deterioration, and decreased strength. These differences were more prominent at the radius than at the tibia. HR-pQCT and FEA measurements of peripheral sites are associated with fracture prevalence and may increase understanding of the role of microarchitectural deterioration in fracture susceptibility. © 2010 American Society for Bone and Mineral Research., (Copyright © 2010 American Society for Bone and Mineral Research.)

High-resolution peripheral quantitative computed tomography (HR-pQCT) is a new in vivo imaging technique for assessing 3D microstructure of cortical and trabecular bone at the distal radius and tibia. No studies have investigated the extent to which measurements of the peripheral skeleton by HR-pQCT reflect those of the spine and hip, where the most serious fractures occur. To address this research question, we performed dual-energy X-ray absorptiometry (DXA), central QCT (cQCT), HR-pQCT, and image-based finite-element analyses on 69 premenopausal women to evaluate relationships among cortical and trabecular bone density, geometry, microstructure, and stiffness of the lumbar spine, proximal femur, distal radius, and distal tibia. Significant correlations were found between the stiffness of the two peripheral sites (r = 0.86), two central sites (r = 0.49), and between the peripheral and central skeletal sites (r = 0.56-0.70). These associations were explained in part by significant correlations in areal bone mineral density (aBMD), volumetric bone mineral density (vBMD), and cross-sectional area (CSA) between the multiple skeletal sites. For the prediction of proximal femoral stiffness, vBMD (r = 0.75) and stiffness (r = 0.69) of the distal tibia by HR-pQCT were comparable with direct measurements of the proximal femur: aBMD of the hip by DXA (r = 0.70) and vBMD of the hip by cQCT (r = 0.64). For the prediction of vertebral stiffness, trabecular vBMD (r = 0.58) and stiffness (r = 0.70) of distal radius by HR-pQCT were comparable with direct measurements of lumbar spine: aBMD by DXA (r = 0.78) and vBMD by cQCT (r = 0.67). Our results suggest that bone density and microstructural and mechanical properties measured by HR-pQCT of the distal radius and tibia reflect the mechanical competence of the central skeleton.

Micro magnetic resonance imaging (µMRI) is an in vivo imaging method that permits 3D quantification of cortical and trabecular bone microstructure. µMR images can also be used for building microstructural finite element (µFE) models to assess bone stiffness, which highly correlates with bone's resistance to fractures. In order for µMRI-based microstructural and µFE analyses to become standard clinical tools for assessing bone quality, validation with a current gold standard, namely, high-resolution micro computed tomography (µCT), is required. Microstructural measurements of 25 human cadaveric distal tibias were performed for the registered µMR and µCT images, respectively. Next, whole bone stiffness, trabecular bone stiffness, and elastic moduli of cubic subvolumes of trabecular bone in both µMR and µCT images were determined by voxel-based µFE analysis. The bone volume fraction (BV/TV), trabecular number (Tb.N*), trabecular spacing (Tb.Sp*), cortical thickness (Ct.Th), and structure model index (SMI) based on µMRI showed strong correlations with µCT measurements (r(2) = 0.67 to 0.97), and bone surface-to-volume ratio (BS/BV), connectivity density (Conn.D), and degree of anisotropy (DA) had significant but moderate correlations (r(2) = 0.33 to 0.51). Each of these measurements also contributed to one or many of the µFE-predicted mechanical properties. However, model-independent trabecular thickness (Tb.Th*) based on µMRI had no correlation with the µCT measurement and did not contribute to any mechanical measurement. Furthermore, the whole bone and trabecular bone stiffness based on µMRI were highly correlated with those of µCT images (r(2) = 0.86 and 0.96), suggesting that µMRI-based µFE analyses can directly and accurately quantify whole bone mechanical competence. In contrast, the elastic moduli of the µMRI trabecular bone subvolume had significant but only moderate correlations with their gold standards (r(2) = 0.40 to 0.58). We conclude that most microstructural and mechanical properties of the distal tibia can be derived efficiently from µMR images and can provide additional information regarding bone quality., (© 2010 American Society for Bone and Mineral Research.)

Idiopathic osteoporosis (IOP) in premenopausal women is a poorly understood entity in which otherwise healthy women have low-trauma fracture or very low bone mineral density (BMD). In this study, we applied individual trabeculae segmentation (ITS)-based morphological analysis to high-resolution peripheral quantitative computed tomography (HR-pQCT) images of the distal radius and distal tibia to gain greater insight into skeletal microarchitecture in premenopausal women with IOP. HR-pQCT scans were performed for 26 normal control individuals and 31 women with IOP. A cubic subvolume was extracted from the trabecular bone compartment and subjected to ITS-based analysis. Three Young's moduli and three shear moduli were calculated by micro-finite element (microFE) analysis. ITS-based morphological analysis of HR-pQCT images detected significantly decreased trabecular plate and rod bone volume fraction and number, decreased axial bone volume fraction in the longitudinal axis, increased rod length, and decreased rod-to-rod, plate-to-rod, and plate-to-plate junction densities at the distal radius and distal tibia in women with IOP. However, trabecular plate and rod thickness did not differ. A more rod-like trabecular microstructure was found in the distal radius, but not in the distal tibia. Most ITS measurements contributed significantly to the elastic moduli of trabecular bone independent of bone volume fraction (BV/TV). At a fixed BV/TV, plate-like trabeculae contributed positively to the mechanical properties of trabecular bone. The results suggest that ITS-based morphological analysis of HR-pQCT images is a sensitive and promising clinical tool for the investigation of trabecular bone microstructure in human studies of osteoporosis., (2010 American Society for Bone and Mineral Research.)

High-resolution peripheral quantitative computed tomography (HR-pQCT) is a newly developed in vivo clinical imaging modality. It can assess the 3D microstructure of cortical and trabecular bone at the distal radius and tibia and is suitable as an input for microstructural finite element (microFE) analysis to evaluate bone's mechanical competence. In order for microstructural and image-based microFE analyses to become standard clinical tools, validation with a current gold standard, namely, high-resolution micro-computed tomography (microCT), is required. Microstructural measurements of 19 human cadaveric distal tibiae were performed for the registered HR-pQCT and microCT images, respectively. Next, whole bone stiffness, trabecular bone stiffness, and elastic moduli of cubic subvolumes of trabecular bone in both HR-pQCT and microCT images were determined by microFE analysis. The standard HR-pQCT patient protocol measurements, derived bone volume fraction (BV/TV(d)), trabecular number (Tb.N*), trabecular thickness (Tb.Th), trabecular spacing (Tb.Sp), and cortical thickness (Ct.Th), as well as the voxel-based direct measurements, BV/TV, Tb.N*, Tb.Th*, Tb.Sp*, Ct.Th, bone surface-to-volume ratio (BS/BV), structure model index (SMI), and connectivity density (Conn.D), correlated well with their respective gold standards, and both contributed to microFE-predicted mechanical properties in either single or multiple linear regressions. The mechanical measurements, although overestimated by HR-pQCT, correlated highly with their gold standards. Moreover, elastic moduli of cubic subvolumes of trabecular bone predicted whole bone or trabecular bone stiffness in distal tibia. We conclude that microstructural measurements and mechanical parameters of distal tibia can be efficiently derived from HR-pQCT images and provide additional information regarding bone fragility., (Copyright 2010 American Society for Bone and Mineral Research.)

Osteoporosis is a major public health problem in men. Hypogonadal men have decreased BMD and deteriorated trabecular bone architecture compared with eugonadal men. Testosterone treatment improves their BMD and trabecular structure. We tested the hypothesis that testosterone replacement in hypogonadal men would also improve their bone's mechanical properties. Ten untreated severely hypogonadal and 10 eugonadal men were selected. The hypogonadal men were treated with a testosterone gel for 24 mo to maintain their serum testosterone concentrations within the normal range. Each subject was assessed before and after 6, 12, and 24 mo of testosterone treatment by microMRI of the distal tibia. A subvolume of each microMR image was converted to a microfinite element (microFE) model, and six analyses were performed, representing three compression and three shear tests. The anisotropic stiffness tensor was calculated, from which the orthotropic elastic material constants were derived. Changes in microarchitecture were also quantified using newly developed individual trabeculae segmentation (ITS)-based and standard morphological analyses. The accuracy of these techniques was examined with simulated microMR images. Significant differences in four estimated anisotropic elastic material constants and most morphological parameters were detected between the eugonadal and hypogonadal men. No significant change in estimated elastic moduli and morphological parameters was detected in the eugonadal group over 24 mo. After 24 mo of treatment, significant increases in estimated elastic moduli E(22) (9.0%), E(33) (5.1%), G(23) (7.2%), and G(12) (9.4%) of hypogonadal men were detected. These increases were accompanied by significant increases in trabecular plate thickness. These results suggest that 24 mo of testosterone treatment of hypogonadal men improves estimated elastic moduli of tibial trabecular bone by increased trabecular plate thickness.

Unlabelled: Trabecular plates and rods are important microarchitectural features in determining mechanical properties of trabecular bone. A complete volumetric decomposition of individual trabecular plates and rods was used to assess the orientation and morphology of 71 human trabecular bone samples. The ITS-based morphological analyses better characterize microarchitecture and help predict anisotropic mechanical properties of trabecular bone., Introduction: Standard morphological analyses of trabecular architecture lack explicit segmentations of individual trabecular plates and rods. In this study, a complete volumetric decomposition technique was developed to segment trabecular bone microstructure into individual plates and rods. Contributions of trabecular type-associated morphological parameters to the anisotropic elastic moduli of trabecular bone were studied., Materials and Methods: Seventy-one human trabecular bone samples from the femoral neck (FN), tibia, and vertebral body (VB) were imaged using muCT or serial milling. Complete volumetric decomposition was applied to segment trabecular bone microstructure into individual plates and rods. The orientation of each individual trabecula was determined, and the axial bone volume fractions (aBV/TV), axially aligned bone volume fraction along each orthotropic axis, were correlated with the elastic moduli. The microstructural type-associated morphological parameters were derived and compared with standard morphological parameters. Their contributions to the anisotropic elastic moduli, calculated by finite element analysis (FEA), were evaluated and compared., Results: The distribution of trabecular orientation suggested that longitudinal plates and transverse rods dominate at all three anatomic sites. aBV/TV along each axis, in general, showed a better correlation with the axial elastic modulus (r(2) = 0.95 approximately 0.99) compared with BV/TV (r(2) = 0.93 approximately 0.94). The plate-associated morphological parameters generally showed higher correlations with the corresponding standard morphological parameters than the rod-associated parameters. Multiple linear regression models of six elastic moduli with individual trabeculae segmentation (ITS)-based morphological parameters (adjusted r(2) = 0.95 approximately 0.98) performed equally well as those with standard morphological parameters (adjusted r(2) = 0.94 approximately 0.97) but revealed specific contributions from individual trabecular plates or rods., Conclusions: The ITS-based morphological analyses provide a better characterization of the morphology and trabecular orientation of trabecular bone. The axial loading of trabecular bone is mainly sustained by the axially aligned trabecular bone volume. Results suggest that trabecular plates dominate the overall elastic properties of trabecular bone.