The effects of PTH,loading and surgical insult on cancellous bone at the bone–implant interface in the rabbit

Enhancing the quantity and quality of cancellous bone with anabolic pharmacologic agents may lead to more successful outcomes of non-cemented joint replacements. Using a novel rabbit model of cancellous bone loading, we examined two specific questions regarding bone formation at the bone–implant interface: (1) does the administration of intermittent PTH, a potent anabolic agent, and mechanical loading individually and combined enhance the peri-implant cancellous bone volume fraction; and, (2) does surgical trauma enhance the anabolic effect of PTH on peri-implant bone volume fraction. In this model, PTH enhanced peri-implant bone volume fraction by 30% in loaded bone, while mechanical loading alone increased bone volume fraction modestly (+ 10%). Combined mechanical loading and PTH treatment had no synergistic effect on any cancellous parameters. However, a strong combined effect was found in bone volume fraction with combined surgery and PTH treatment (+ 34%) compared to intact control limbs. Adaptive changes in the cancellous bone tissue included increased ultimate stress and enhanced remodeling activity. The number of proliferative osteoblasts increased as did their expression of pro-collagen 1 and PTH receptor 1, and the number of TRAP positive osteoclasts also increased. In summary, both loading and intermittent PTH treatment enhanced peri-implant bone volume, and surgery and PTH treatment had a strong combined effect. This finding is of clinical importance since enhancing early osseointegration in the post-surgical period has numerous potential benefits.     

Skin wound trauma,following high-dose radiation exposure,amplifies and prolongs skeletal tissue loss

The present study investigated the detrimental effects of non-lethal, high-dose (whole body) γ-irradiation on bone, and the impact that radiation combined with skin trauma (i.e. combined injury) has on long-term skeletal tissue health. Recovery of bone after an acute dose of radiation (RI; 8 Gy), skin wounding (15–20% of total body skin surface), or combined injury (RI + Wound; CI) was determined 3, 7, 30, and 120 days post-irradiation in female B6D2F1 mice and compared to non-irradiated mice (SHAM) at each time-point. CI mice demonstrated long-term (day 120) elevations in serum TRAP 5b (osteoclast number) and sclerostin (bone formation inhibitor), and suppression of osteocalcin levels through 30 days as compared to SHAM (p < 0.05). Radiation-induced reductions in distal femur trabecular bone volume fraction and trabecular number through 120 days post-exposure were significantly greater than non-irradiated mice (p < 0.05) and were exacerbated in CI mice by day 30 (p < 0.05). Negative alterations in trabecular bone microarchitecture were coupled with extended reductions in cancellous bone formation rate in both RI and CI mice as compared to Sham (p < 0.05). Increased osteoclast surface in CI animals was observed for 3 days after irradiation and remained elevated through 120 days (p < 0.01). These results demonstrate a long-term, exacerbated response of bone to radiation when coupled with non-lethal wound trauma. Changes in cancellous bone after combined trauma were derived from extended reductions in osteoblast-driven bone formation and increases in osteoclast activity.     

Aging diminishes lamellar and woven bone formation induced by tibial compression in adult C57BL/6

Aging purportedly diminishes the ability of the skeleton to respond to mechanical loading, but recent data show that old age did not impair loading-induced accrual of bone in BALB/c mice. Here, we hypothesized that aging limits the response of the tibia to axial compression over a range of adult ages in the commonly used C57BL/6. We subjected the right tibia of old (22 month), middle-aged (12 month) and young-adult (5 month) female C57BL/6 mice to peak periosteal strains (measured near the mid-diaphysis) of − 2200 με and − 3000 με (n = 12–15/age/strain) via axial tibial compression (4 Hz, 1200 cycles/day, 5 days/week, 2 weeks). The left tibia served as a non-loaded, contralateral control. In mice of every age, tibial compression that engendered a peak strain of − 2200 με did not alter cortical bone volume but loading to a peak strain of − 3000 με increased cortical bone volume due in part to woven bone formation. Both loading magnitudes increased total volume, medullary volume and periosteal bone formation parameters (MS/BS, BFR/BS) near the cortical midshaft. Compared to the increase in total volume and bone formation parameters of 5-month mice, increases were less in 12- and 22-month mice by 45–63%. Moreover, woven bone incidence was greatest in 5-month mice. Similarly, tibial loading at − 3000 με increased trabecular BV/TV of 5-month mice by 18% (from 0.085 mm³/mm³), but trabecular BV/TV did not change in 12- or 22-month mice, perhaps due to low initial BV/TV (0.032 and 0.038 mm³/mm³, respectively). In conclusion, these data show that while young-adult C57BL/6 mice had greater periosteal bone formation following loading than middle-aged or old mice, aging did not eliminate the ability of the tibia to accrue cortical bone.     

Fatigue-induced microdamage in cancellous bone occurs distant from resorption cavities and trabecular surfaces

Impaired bone toughness is increasingly recognized as a contributor to fragility fractures. At the tissue level, toughness is related to the ability of bone tissue to resist the development of microscopic cracks or other tissue damage. While most of our understanding of microdamage is derived from studies of cortical bone, the majority of fragility fractures occur in regions of the skeleton dominated by cancellous bone. The development of tissue microdamage in cancellous bone may differ from that in cortical bone due to differences in microstructure and tissue ultrastructure. To gain insight into how microdamage accumulates in cancellous bone we determined the changes in number, size and location of microdamage sites following different amounts of cyclic compressive loading. Human vertebral cancellous bone specimens (n = 32, 10 male donors, 6 female donors, age 76 ± 8.8, mean ± SD) were subjected to sub-failure cyclic compressive loading and microdamage was evaluated in three-dimensions. Only a few large microdamage sites (the largest 10%) accounted for 70% of all microdamage caused by cyclic loading. The number of large microdamage sites was a better predictor of reductions in Young’s modulus caused by cyclic loading than overall damage volume fraction (DV/BV). The majority of microdamage volume (69.12 ± 7.04%) was located more than 30 μm (the average erosion depth) from trabecular surfaces, suggesting that microdamage occurs primarily within interstitial regions of cancellous bone. Additionally, microdamage was less likely to be near resorption cavities than other bone surfaces (p < 0.05), challenging the idea that stress risers caused by resorption cavities influence fatigue failure of cancellous bone. Together, these findings suggest that reductions in apparent level mechanical performance during fatigue loading are the result of only a few large microdamage sites and that microdamage accumulation in fatigue is likely dominated by heterogeneity in tissue material properties rather than stress concentrations caused by micro-scale geometry.     

High doses of ionizing radiation on bone repair: is there effect outside the irradiated site?

Local ionizing radiation causes damage to bone metabolism, it reduces blood supply and cellularity over time. Recent studies indicate that radiation promotes biological response outside the treatment field. The aim of this study was to investigate the effects of ionizing radiation on bone repair outside the irradiated field. Ten healthy male Wistar rats were used; and five animals were submitted to radiotherapy on the left femur. After 4 weeks, in all animals were created bone defects in the right and left femurs. Seven days after surgery, animals were euthanized. The femurs were removed and randomly divided into 3 groups (n = 5): Control (C) (right femur of the non-irradiated animals); Local ionizing radiation (IR) (left femur of the irradiated animals); Contralateral ionizing radiation (CIR) (right femur of the irradiated animals). The femurs were processed and embedded in paraffin; and bone histologic sections were evaluated to quantify the bone neoformation. Histomorphometric analysis showed that there was no significant difference between groups C (24.6 ± 7.04) and CIR (25.3 ± 4.31); and IR group not showed bone neoformation. The results suggest that ionizing radiation affects bone repair, but does not interfere in bone repair distant from the primary irradiated site.     

Biomechanical comparison of plate and screw fixation in anterior pelvic ring fractures with low bone mineral density

IntroductionOsteosynthesis of anterior pubic ramus fractures can be challenging, especially in poor bone quality. The aim of the present study was to compare plate and retrograde endomedullary screw fixation of the superior pubic ramus with low bone mineral density (BMD).Materials and methodsTwelve human cadaveric hemi-pelvises were analyzed in a matched pair study design. BMD of the specimens was 35 ± 30 mgHA/cm³, as measured in the fifth lumbar vertebra. A simulated two-fragment superior pubic ramus fracture model was fixed with either a 7.3-mm cannulated retrograde screw (Group 1) or a 10-hole 3.5-mm reconstruction plate (Group 2). Cyclic progressively increasing axial loading was applied through the acetabulum. Relative interfragmentary movements were captured using an optical motion tracking system.ResultsInitial axial construct stiffness was 424 ± 116.1 N/mm in Group 1 and 464 ± 69.7 N/mm in Group 2, with no significant difference (p = 0.345). Displacement and gap angle at the fracture site during cyclic loading were significantly higher in Group 1 compared to Group 2. Cycles to failure, based on clinically relevant criteria, were significantly lower in Group 1 (3469 ± 1837) compared to Group 2 (10,226 ± 3295) (p = 0.028). Failure mode in Group 1 was characterized by screw cutting through the cancellous bone. In Group 2 the specimens exclusively failed by plate bending.ConclusionsFrom biomechanical point of view, pubic ramus stabilization with plate osteosynthesis is superior compared to a single retrograde screw fixation in osteoporotic bone. However, the extensive surgical approach needed for plating must be considered.     

Bone's responses to mechanical loading are impaired in type 1 diabetes

Diabetes adversely impacts many organ systems including the skeleton. Clinical trials have revealed a startling elevation in fracture risk in diabetic patients. Bone fractures can be life threatening: nearly 1 in 6 hip fracture patients die within one year. Because physical exercise is proven to improve bone properties and reduce fracture risk in non-diabetic subjects, we tested its efficacy in type 1 diabetes. We hypothesized that diabetic bone's response to anabolic mechanical loading would be attenuated, partially due to impaired mechanosensing of osteocytes under hyperglycemia. Heterozygous C57BL/6-Ins2^Akita/J (Akita) male and female diabetic mice and their age- and gender-matched wild-type (WT) C57BL/6J controls (7-month-old, N = 5–7 mice/group) were subjected to unilateral axial ulnar loading with a peak strain of 3500 με at 2 Hz and 3 min/day for 5 days. The Akita female mice, which exhibited a relatively normal body weight and a mild 40% elevation of blood glucose level, responded with increased bone formation (+ 6.5% in Ct.B.Ar, and 4 to 36-fold increase in Ec.BFR/BS and Ps.BFR/BS), and the loading effects, in terms of changes of static and dynamic indices, did not differ between Akita and WT females (p ≥ 0.1). However, loading-induced anabolic effects were greatly diminished in Akita males, which exhibited reduced body weight, severe hyperglycemia (+ 230%), diminished bone formation (ΔCt.B.Ar: 0.003 vs. 0.030 mm², p = 0.005), and suppressed periosteal bone appositions (ΔPs.BFR/BS, p = 0.02). Hyperglycemia (25 mM glucose) was further found to impair the flow-induced intracellular calcium signaling in MLO-Y4 osteocytes, and significantly inhibited the flow-induced downstream responses including reduction in apoptosis and sRANKL secretion and PGE₂ release. These results, along with previous findings showing adverse effects of hyperglycemia on osteoblasts and mesenchymal stem cells, suggest that failure to maintain normal glucose levels may impair bone's responses to mechanical loading in diabetics.     

Paradoxical Sost gene expression response to mechanical unloading in metaphyseal bone

The Sost gene encodes Sclerostin, an inhibitor of Wnt-signaling, generally considered a main response gene to mechanical loading in bone. Several papers describe that unloading leads to upregulation of Sost, which in turn may lead to loss of bone. These studies were based on whole bone homogenates or cortical bone. By serendipity, we noted an opposite response to unloading in the proximal rat tibia. Therefore, we hypothesized that Sost-expression in response to changes in mechanical load is bone site specific.One hind limb of male, 3 month old rats was unloaded by paralyzing the extensors with Botulinium toxin A (Botox) injections. A series of experiments compared the expression of Sost mRNA in the unloaded and contralateral, loaded limbs, after 3 or 10 days, in metaphyseal cancellous bone, metaphyseal cortical bone, and diaphyseal cortical bone. We also conducted μCT to confirm changes in bone volume density related to unloading.Sost mRNA expression in the cancellous metaphyseal bone was downregulated almost 2-fold, both 3 days and 10 days after unloading (P < 0.05). A similar tendency was seen in the metaphyseal cortical bone, in which Sost was 1.5-fold downregulated (P < 0.05) after 10 days, but not significantly changed after 3 days. In contrast, diaphyseal cortical Sost expression was instead upregulated 1.4-fold (P < 0.05) following 3-day unloading, while there was no significant change after 10 days. Cancellous bone volume density was 58% lower (P < 0.001, compared to cage controls) in the unloaded limb but not significantly affected in the loaded limb.The results suggest that Sost mRNA expression in metaphyseal bone responds to mechanical unloading in an opposite direction to that observed in diaphyseal cortical bone. This proposes a more complex expression pattern for Sost in response to unloading. Therapeutics that target Sclerostin during altered loading conditions may result in local bone mass changes that are difficult to predict.     

Cortical and trabecular bone adaptation to incremental load magnitudes using the mouse tibial axial compression loading model

The mouse tibial axial compression loading model has recently been described to allow simultaneous exploration of cortical and trabecular bone adaptation within the same loaded element. However, the model frequently induces cortical woven bone formation and has produced inconsistent results with regards to trabecular bone adaptation. The aim of this study was to investigate bone adaptation to incremental load magnitudes using the mouse tibial axial compression loading model, with the ultimate goal of revealing a load that simultaneously induced lamellar cortical and trabecular bone adaptation. Adult (16 weeks old) female C57BL/6 mice were randomly divided into three load magnitude groups (5, 7 and 9 N), and had their right tibia axially loaded using a continuous 2-Hz haversine waveform for 360 cycles/day, 3 days/week for 4 consecutive weeks. In vivo peripheral quantitative computed tomography was used to longitudinally assess midshaft tibia cortical bone adaptation, while ex vivo micro-computed tomography and histomorphometry were used to assess both midshaft tibia cortical and proximal tibia trabecular bone adaptation. A dose response to loading magnitude was observed within cortical bone, with increasing load magnitude inducing increasing levels of lamellar cortical bone adaptation within the upper two thirds of the tibial diaphysis. Greatest cortical bone adaptation was observed at the midshaft where there was a 42% increase in estimated mechanical properties (polar moment of inertia) in the highest (9 N) load group. A dose response to load magnitude was not clearly evident within trabecular bone, with only the highest load (9 N) being able to induce measureable adaptation (31% increase in trabecular bone volume fraction at the proximal tibia). The ultimate finding was that a load of 9 N (engendering a tensile strain of 1833 με on medial surface of the midshaft tibia) was able to simultaneously induce measurable lamellar cortical and trabecular bone adaptation when using the mouse tibial axial compression loading model in 16 week old female C57BL/6 mice. This finding will help plan future studies aimed at exploring simultaneous lamellar cortical and trabecular bone adaptation within the same loaded element.     

Anabolic action of parathyroid hormone (PTH) does not compromise bone matrix mineral composition or maturation

Intermittent administration of parathyroid hormone (PTH) is used to stimulate bone formation in patients with osteoporosis. A reduction in the degree of matrix mineralisation has been reported during treatment, which may reflect either production of undermineralised matrix or a greater proportion of new matrix within the bone samples assessed. To explore these alternatives, high resolution synchrotron-based Fourier Transform Infrared Microspectroscopy (sFTIRM) coupled with calcein labelling was used in a region of non-remodelling cortical bone to determine bone composition during anabolic PTH treatment compared with region-matched samples from controls.8 week old male C57BL/6 mice were treated with vehicle or 50 μg/kg PTH, 5 times/week for 4 weeks (n = 7–9/group). Histomorphometry confirmed greater trabecular and periosteal bone formation and 3-point bending tests confirmed greater femoral strength in PTH-treated mice. Dual calcein labels were used to match bone regions by time-since-mineralisation (bone age) and composition was measured by sFTIRM in six 15 μm² regions at increasing depth perpendicular to the most immature bone on the medial periosteal edge; this allowed in situ measurement of progressive changes in bone matrix during its maturation.The sFTIRM method was validated in vehicle-treated bones where the expected progressive increases in mineral:matrix ratio and collagen crosslink type ratio were detected with increasing bone maturity. We also observed a gradual increase in carbonate content that strongly correlated with an increase in longitudinal stretch of the collagen triple helix (amide I:amide II ratio). PTH treatment did not alter the progressive changes in any of these parameters from the periosteal edge through to the more mature bone.These data provide new information about how the bone matrix matures in situ and confirm that bone deposited during PTH treatment undergoes normal collagen maturation and normal mineral accrual.     

Knee loading protects against osteonecrosis of the femoral head by enhancing vessel remodeling and bone healing

Osteonecrosis of the femoral head is a serious orthopedic problem. Moderate loads with knee loading promote bone formation, but their effects on osteonecrosis have not been investigated. Using a rat model, we examined a hypothesis that knee loading enhances vessel remodeling and bone healing through the modulation of the fate of bone marrow-derived cells. In this study, osteonecrosis was induced by transecting the ligamentum teres followed by a tight ligature around the femoral neck. For knee loading, 5 N loads were laterally applied to the knee at 15 Hz for 5 min/day for 5 weeks. Changes in bone mineral density (BMD) and bone mineral content (BMC) of the femur were measured by pDEXA, and ink infusion was performed to evaluate vessel remodeling. Femoral heads were harvested for histomorphometry, and bone marrow-derived cells were isolated to examine osteoclast development and osteoblast differentiation. The results showed that osteonecrosis significantly induced bone loss, and knee loading stimulated both vessel remodeling and bone healing. The osteonecrosis group exhibited the lowest trabecular BV/TV (p < 0.001) in the femoral head, and lowest femoral BMD and BMC (both p < 0.01). However, knee loading increased trabecular BV/TV (p < 0.05) as well as BMD (p < 0.05) and BMC (p < 0.01). Osteonecrosis decreased the vessel volume (p < 0.001), vessel number (p < 0.001) and VEGF expression (p < 0.01), and knee loading increased them (p < 0.001, p < 0.001 and p < 0.01). Osteonecrosis activated osteoclast development, and knee loading reduced its formation, migration, adhesion and the level of “pit” formation (p < 0.001, p < 0.01, p < 0.001 and p < 0.001). Furthermore, knee loading significantly increased osteoblast differentiation and CFU-F (both p < 0.001). A significantly positive correlation was observed between vessel remodeling and bone healing (both p < 0.01). These results indicate that knee loading could be effective in repair osteonecrosis of the femoral head in a rat model. This effect might be attributed to promoting vessel remodeling, suppressing osteoclast development, and increasing osteoblast and fibroblast differentiation. In summary, the current study suggests that knee loading might potentially be employed as a non-invasive therapy for osteonecrosis of the femoral head.     

Heavy ion irradiation and unloading effects on mouse lumbar vertebral microarchitecture,mechanical properties and tissue stresses

Astronauts are exposed to both musculoskeletal disuse and heavy ion radiation in space. Disuse alters the magnitude and direction of forces placed upon the skeleton causing bone remodeling, while energy deposited by ionizing radiation causes free radical formation and can lead to DNA strand breaks and oxidative damage to tissues. Radiation and disuse each result in a net loss of mineralized tissue in the adult, although the combined effects, subsequent consequences for mechanical properties and potential for recovery may differ. First, we examined how a high dose (2 Gy) of heavy ion radiation (⁵⁶Fe) causes loss of mineralized tissue in the lumbar vertebrae of skeletally mature (4 months old), male, C57BL/6 mice using microcomputed tomography and determined the influence of structural changes on mechanical properties using whole bone compression tests and finite element analyses. Next, we tested if a low dose (0.5 Gy) of heavy particle radiation prevents skeletal recovery from a 14-day period of hindlimb unloading. Irradiation with a high dose of ⁵⁶Fe (2 Gy) caused bone loss (?14%) in the cancellous-rich centrum of the fourth lumbar vertebra (L4) 1 month later, increased trabecular stresses (+ 27%), increased the propensity for trabecular buckling and shifted stresses to the cortex. As expected, hindlimb unloading (14 days) alone adversely affected microarchitectural and mechanical stiffness of lumbar vertebrae, although the reduction in yield force was not statistically significant (?17%). Irradiation with a low dose of ⁵⁶Fe (0.5 Gy) did not affect vertebrae in normally loaded mice, but significantly reduced compressive yield force in vertebrae of unloaded mice relative to sham-irradiated controls (?24%). Irradiation did not impair the recovery of trabecular bone volume fraction that occurs after hindlimb unloaded mice are released to ambulate normally, although microarchitectural differences persisted 28 days later (96% increase in ratio of rod- to plate-like trabeculae). In summary, ⁵⁶Fe irradiation (0.5 Gy) of unloaded mice contributed to a reduction in compressive strength and partially prevented recovery of cancellous microarchitecture from adaptive responses of lumbar vertebrae to skeletal unloading. Thus, irradiation with heavy ions may accelerate or worsen the loss of skeletal integrity triggered by musculoskeletal disuse.     

Rapidly growing Brtl/+ mouse model of osteogenesis imperfecta improves bone mass and strength with sclerostin antibody treatment

Osteogenesis imperfecta (OI) is a heritable collagen-related bone dysplasia, characterized by brittle bones with increased fracture risk that presents most severely in children. Anti-resorptive bisphosphonates are frequently used to treat pediatric OI and controlled clinical trials have shown that bisphosphonate therapy improves vertebral outcomes but has little benefit on long bone fracture rate. New treatments which increase bone mass throughout the pediatric OI skeleton would be beneficial. Sclerostin antibody (Scl-Ab) is a potential candidate anabolic therapy for pediatric OI and functions by stimulating osteoblastic bone formation via the canonical Wnt signaling pathway. To explore the effect of Scl-Ab on the rapidly growing OI skeleton, we treated rapidly growing 3 week old Brtl/+ mice, harboring a typical heterozygous OI-causing Gly → Cys substitution on col1a1, for 5 weeks with Scl-Ab. Scl-Ab had anabolic effects in Brtl/+ and led to new cortical bone formation and increased cortical bone mass. This anabolic action resulted in improved mechanical strength to WT Veh levels without altering the underlying brittle nature of the material. While Scl-Ab was anabolic in trabecular bone of the distal femur in both genotypes, the effect was less strong in these rapidly growing Brtl/+ mice compared to WT. In conclusion, Scl-Ab was able to stimulate bone formation in a rapidly growing Brtl/+ murine model of OI, and represents a potential new therapy to improve bone mass and reduce fracture risk in pediatric OI.     

Low dose PTH improves metaphyseal bone healing more when muscles are paralyzed

Stimulation of bone formation by PTH is related to mechanosensitivity. The response to PTH treatment in intact bone could therefore be blunted by unloading. We studied the effects of mechanical loading on the response to PTH treatment in bone healing. Most fractures occur in the metaphyses, therefor we used a model for metaphyseal bone injury.One hind leg of 20 male SD rats was unloaded via intramuscular botulinum toxin injections. Two weeks later, the proximal unloaded tibia had lost 78% of its trabecular contents. At this time-point, the rats received bilateral proximal tibiae screw implants. Ten of the 20 rats were given daily injections of 5 μg/kg PTH (1–34). After two weeks of healing, screw fixation was measured by pull-out, and microCT of the distal femur cancellous compartment was performed. Pull-out force provided an estimate for cancellous bone formation after trauma.PTH more than doubled the pull-out force in the unloaded limbs (from 14 to 30 N), but increased it by less than half in the loaded ones (from 30 to 44 N). In relative terms, PTH had a stronger effect on pull-out force in unloaded bone than in loaded bone (p = 0.03).The results suggest that PTH treatment for stimulation of bone healing does not require simultaneous mechanical stimulation.     

Three-dimensional microarchitecture of adolescent cancellous bone

This study investigated microarchitectural, mechanical, collagen and mineral properties of normal adolescent cancellous bone, and compared them with adult and aging cancellous bone, to obtain more insight into the subchondral bone adaptations during development and growth.Twenty-three human proximal tibiae were harvested and divided into 3 groups according to their ages: adolescence (9 to 17 years, n = 6), young adult (18 to 24 years, n = 9), and adult (25 to 30 years, n = 8). Twelve cubic cancellous bone samples with dimensions of 8 × 8 × 8 mm³ were produced from each tibia, 6 from each medial and lateral condyle. These samples were micro-CT scanned (vivaCT 40, Scanco Medical AG, Switzerland) resulting in cubic voxel sizes of 10.5 ? 10.5 ? 10.5 μm³. Microarchitectural properties were calculated. The samples were then tested in compression followed by collagen and mineral determination.Interestingly, the adolescent cancellous bone had similar bone volume fraction (BV/TV), structure type (plate, rod or mixtures), and connectivity (3-D trabecular networks) as the adult cancellous bone. The adolescent cancellous bone had significantly lower bone surface density (bone surface per total volume of specimen) but higher collagen concentration (collagen weight per dry weight of specimen) than the adult cancellous bone; and significant greater trabecular separation (mean distance between trabeculae), significant lower trabecular number (number of trabeculae per volume), tissue density (dry weight per volume of bone matrix excluding marrow space) and mineral concentration (ash weight per dry weight of specimen) than the young adult and adult cancellous bones. Despite these differences, ultimate stress and failure energy were not significantly different among the three groups, only the Young's modulus in anterior-posterior direction was significantly lower in adolescence. Apparent density appears to be the single best predictor of mechanical properties.In conclusion, adolescent cancellous bone has similar bone volume fraction, structure type, and connectivity as the young adult and adult cancellous bones, and significant lower tissue density, bone surface density and mineral concentration but higher collagen concentration than in the young adult and adult bone. Despite these differences, the mechanical properties did not show significant difference among the three groups except less stiffness in anterior-posterior direction in the adolescents.     

Whole body vibration improves osseointegration by up-regulating osteoblastic activity but down-regulating osteoblast-mediated osteoclastogenesis via ERK1/2 pathway

Due to the reduction in bone mass and deterioration in bone microarchitecture, osteoporosis is an important risk factor for impairing implant osseointegration. Recently, low-magnitude, high-frequency (LMHF) vibration (LM: < 1 ×g; HF: 20–90 Hz) has been shown to exhibit anabolic, but anti-resorptive effects on skeletal homeostasis. Therefore, we hypothesized that LMHF loading, in terms of whole body vibration (WBV), may improve implant fixation under osteoporotic status. In the in vivo study, WBV treatment (magnitude: 0.3 g, frequency: 40 Hz, time: 30 min/12 h, 5 days/week) was applied after hydroxyapatite-coated titanium implants were inserted in the bilateral tibiae of ovariectomized rats. The bone mass and the osteospecific gene expressions were measured at 12 weeks post implantation. In the in vitro study, the cellular and molecular mechanisms underlying osteoblastic and osteoclastic activities were fully investigated using various experimental assays. Micro-CT examination showed that WBV could enhance osseointegration by improving microstructure parameters surrounding implants. WBV-regulated gene levels in favor of bone formation over resorption may be the reason for the favorable adaptive bone remolding on bone-implant surface. The in vitro study showed that vibration (magnitude: 0.3 g, frequency: 40 Hz, time: 30 min/12 h) up-regulated osteoblast differentiation, matrix synthesis and mineralization. However, mechanically regulated osteoclastic activity was mainly through the effect on osteoblastic cells producing osteoclastogenesis-associated key soluble factors, including RANKL and M-CSF. Osteoblasts were therefore the direct target cells during the mechanotransduction process. The ERK1/2 pathway was demonstrated to play an essential role in vibration-induced enhancement of bone formation and decreased bone resorption. Our data suggests that WBV was a helpful non-pharmacological intervention for improving osseointegration under osteoporosis.     

Voxel size and measures of individual resorption cavities in three-dimensional images of cancellous bone

Cavities formed by osteoclasts on the surface of cancellous bone during bone remodeling (resorption cavities) are believed to act as stress risers and impair cancellous bone strength and stiffness. Although resorption cavities are readily detected as eroded surfaces in histology sections, identification of resorption cavities in three-dimensional images of cancellous bone has been rare. Here we use sub-micrometer resolution images of rat lumbar vertebral cancellous bone obtained through serial milling (n = 5) to determine how measures of the number and surface area of resorption cavities are influenced by image resolution. Three-dimensional images of a 1 mm cube of cancellous bone were collected at 0.7 × 0.7 × 5.0 μm/voxel using fluorescence based serial milling and uniformly coarsened to four other resolutions ranging from 1.4 × 1.4 × 5.0 to 11.2 × 11.2 × 10 μm/voxel. Cavities were identified in the three-dimensional image as an indentation on the cancellous bone surface and were confirmed as eroded surfaces by viewing two-dimensional cross-sections (mimicking histology techniques). The number of cavities observed in the 0.7 × 0.7 × 5.0 μm/voxel images (22.0 ± 1.43, mean ± SD) was not significantly different from that in the 1.4 × 1.4 × 5.0 μm/voxel images (19.2 ± 2.59) and an average of 79% of the cavities observed at both of these resolutions were coincident. However, at lower resolutions, cavity detection was confounded by low sensitivity (< 20%) and high false positive rates (> 40%). Our results demonstrate that when image voxel size exceeds 1.4 × 1.4 × 5.0 μm/voxel identification of resorption cavities by bone surface morphology is highly inaccurate. Experimental and computational studies of resorption cavities in three-dimensional images of cancellous bone may therefore require images to be collected at resolutions of 1.4 μm/pixel in-plane or better to ensure consistent identification of resorption cavities.     

The effects of multiple high-resolution peripheral quantitative computed tomography scans on bone healing in a rabbit radial bone defect model

The use of in vivo high-resolution computed tomography (CT) scanners provides the unique opportunity for evaluating temporal progression in healing of bone defects. However, these in vivo scanners impose ionizing radiation that could affect the healing and morphology of the bone. The primary objective of this study was to determine the effects of in vivo scanning at 2-week intervals on bone healing of a critical sized radial defect in rabbits and to investigate the effect of this radiation protocol on bone marrow cell viability using clinically applicable radiation doses. Thirty male rabbits were randomized into three groups: two groups received a 15 mm defect in the left radius that was filled with an autologous bone graft (DEF-CT and DEF-SHAM), and one group acted as an intact control (INT-CT). The duration of the study was 6 weeks. DEF-CT and INT-CT had high-resolution CT scans performed at 2-week intervals. The total cumulative radiation dose was 81.6 mGy per animal. DEF-SHAM received sham CT scans at the same time points. In group DEF-CT, the bone volume (BV) in the defect increased significantly over time (p ≤ 0.002, for all comparisons); the bone mineral density (BMD) in the defect decreased over time and was significantly lower at weeks 4 and 6 than at weeks 0 and 2 (p < 0.001, for all comparisons). In group INT-CT, BV and BMD did not change over time (p = 1, for all comparison). The BV (p = 0.50) and the BMD (p = 0.37) in the defect as measured by microCT scan during ex vivo analysis was not significantly different between DEF-CT and DEF-SHAM. Similarly, histomorphometry showed no significant difference in the total bone area (p = 0.22) and percentage bone within the defect (p = 0.24) between these groups.Bone marrow analysis of the left (radiated) and right (non-radiated) radius of the INT-CT group via a Colony Forming Units (CFU) assay demonstrated an average of 25.3 and 28.5 colonies for radiated and non-radiated radii, respectively (p = 0.72).In conclusion, there was no significant difference in bone healing between radiated and non-radiated radius defects in rabbits. This is an important finding as it demonstrates that serial in vivo high resolution-CT imaging can not only provide accurate tissue regeneration data, but it can also be used to reduce the number of temporal cohorts within an experimental design.     

Dexmedetomidine acts as an oxidative damage prophylactic in rats exposed to ionizing radiation

Study objectiveTo investigate the effects of dexmedetomidine on oxidative injury caused by ionizing radiation.DesignRandomized controlled experimental study.SettingDepartment of radiation oncology and research laboratory of an academic hospital.InterventionsTwenty-eight rats were randomized to 4 groups (n = 7 per group). Group S rats were administered physiologic serum; group SR rats were administered physiologic serum and 10 Gy external ionizing radiation. Groups D100 and D200 were administered 100 and 200 μg/kg dexmedetomidine intraperitoneally, respectively, 45 minutes before ionizing radiation.MeasurementsLiver, kidney, lung, and thyroid tissue and serum levels of antioxidant enzymes (glutathione peroxidase [GPX], superoxide dismutase, and catalase) and oxidative metabolites (advanced oxidation protein products, malondialdehyde, and nitrate/nitrite, and serum ischemia-modified albumin) were measured 6 hours postprocedure.Main resultsIn group SR, IR decreased antioxidant enzyme levels and increased oxidative metabolite levels (P < .05). In plasma, antioxidant enzyme levels were higher and oxidative metabolite levels were lower in groups D100 and D200 than in group SR (P < .01). In tissues, hepatic and lung GPX levels were higher in groups D100 and D200 than in group SR (P < .001). Renal and thyroid GPX levels were higher in D200 than in group SR (P < .01). Thyroid superoxide dismutase levels were higher in groups D100 and D200 than in group SR (P < .01). Renal, lung, and thyroid catalase levels were higher in group D200 than in group SR (P < .01). Hepatic, renal, and lung advanced oxidation protein products and malondialdehyde levels were lower in groups D100 and D200 than in group SR (P < .01). Hepatic, renal, and lung nitrate/nitrite levels were lower in group D200 than in group SR (P < .05).ConclusionsDexmedetomidine preserves the antioxidant enzyme levels and reduces toxic oxidant metabolites. Therefore, it can provide protection from oxidative injury caused by ionizing radiation.