Thoughts on bone biomechanics

Simple simulations of stresses and strains in several types of localised anatomical features have been modelled using basic biomechanical thinking, experimental stress analysis employing photo-elastic methods and theoretical stress and strain analysis using a finite elements approach where the computational program utilises fast LaGrangian analysis of continua. The studies are providing results showing that, for given load proportions, the particular forms of some bones and bony architectural features seem related to stresses and strains that are relatively evenly distributed across surfaces (and therefore mechanically optimal). The results particularly show how apparently opposite (paradoxical) situations can readily occur within anatomical systems. They also provide strong biological information relevant to the assessment of such features of bone architecture in phylogenetic investigations. They even give information relevant to clinical problems.     

Impact of bone events on survival in solitary bone plasmacytoma

BackgroundAlthough much studied in multiple myeloma, bone events (BE) can also cause important morbidity in bone plasmacytoma patients. To our knowledge, the effect of BE on overall survival (OS) and progression to multiple myeloma free-survival (MPFS) also has never been studied.Patients and MethodsFifty-nine patients treated from 2008 to 2017 were retrospectively assessed. All patients had histological proof of disease and were treated with radical radiotherapy (RT). Available clinical information for at least 6 months follow-up or until death had to be available. BE were described as one of the following events in the index bone: fractures, osteomyelitis, chronic pain, surgery or loss of limb function after RT.ResultsMean age at diagnosis was 57.3 years (18–80); most male (67.8%). Mean OS, bone event free-survival (BEFS), local progression-free survival (LPFS) and MPFS were 41, 36, 37 and 19 months, respectively. There were 15 deaths. BEFS (p = 0.008) and age>55y (p = 0.044) were associated with MPFS. Only BEFS correlated with OS (p = 0.029). BE was independently associated with both MPFS and OS in multivariate analysis.ConclusionBE and survival end-points were correlated. BE should be investigated in prospective trials.     

Repair of bone defects using dynamic fabricated tissue-engineered bone based on a bio-derived porous bone scaffold

Fabrication and transplantation of tissue-engineered bones in a rotating wall vessel bioreactor (RWVB) was studied in the present study aiming to repair segmental bone defects. Osteoblasts were transfected with green fluorescent protein prior to seeding on bio-derived porous bone scaffolds at a density of 1?×?10⁶?cells/mL and cultured in an RWVB for one week. For comparison, constructs were also cultured in a static condition. Morphology and structure of fabricated bones were examined using an inverted microscope, scanning electron microscope and histology analysis via hematoxylin–eosin and toluidine blue staining. Moreover, an animal model for repairing segmental bone defects of a Zelanian rabbit was used to assess the efficacy and biosafety of fabricated bones. In conclusion, tissue-engineered bones grew favorably in RWVB. In animal study, a preliminary repair of bone defects was noticed only in the experimental group after 4 weeks of implantation. Using RWVB, the fabricated tissue-engineered bone constructs were approved with better bio-capability in repairing the segmental bone defect.     

Effect of irradiation on autogenous bone transplantation in rat parietal bone

To determine the appropriate time for bone reconstruction after irradiation, the healing process after autogenous iliac bone transplantation in the irradiated parietal bone was examined by scanning electron microscopy and light microscopy. Bone transplantation was carried out at the second and the fourth weeks after Cobalt-sixty (60Co) irradiation with calculated dose and fractionation. Animals without irradiation were used as control. The results show the appearance of mesenchymal cells and blood vessels around the transplantation to be extremely few one week after transplantation which was carried out at the second week after irradiation. These inhibitions were still seen two weeks after transplantation. Four weeks after transplantation, there were no differences in the bone formation among the experimental groups. Bone formation in the transplantation at the fourth week after irradiation was similar to that of the control group. Microvascularization in the transplantation at the second week after irradiation was inhibited one week after transplantation. The delay in bone healing was responsible for the retardation of revascularization and caused microcirculatory failures as well as the damage of osteogenic cells. It is quite clear that damaged cells and tissues recovered by the elapse of time under the irradiation procedure employed in this study and also that bone formation was carried out in the physiological process. We think that bone transplantation after irradiation should be done after recovery from the radiation damage to the periosteal cells and the blood vessels.     

Oestrogen action on bone cells

Sex steroids have an important impact on bone physiology. Oestrogen (E) appears to be the most important sex steroid in preventing osteoporosis in women. Despite the overwhelming evidence that oestrogens modulate bone growth and turnover in vivo, oestrogen receptors (ER) were detected only recently. Two forms of ER have been discovered so far, ERalpha and ERbeta. Both have been detected in osteoblasts and osteoclasts as well. A number of growth factors and cytokines appear to modulate bone resorption in vitro and in vivo. Among others, interleukin-1 and -6 and tumor necrosis factor alpha and beta were found to be extremely potent stimulators of bone resorption. Binding of different cytokines to their receptors in osteoblasts result in the release of soluble factors that act directly on osteoclasts to modulate their recruitment or activity. Thus, E, apart from the direct regulation of osteoclasts, which it achieves through its receptors, can inhibit the release of osteoclast stimulatory factors or enhance the release of osteoclast inhibitory factors. In general, E is an inhibitor of bone resorption that decreases both osteoclast numbers and activity. Recently, it has also been shown that it promotes apoptosis. Moreover, it also has anabolic effects on osteoblasts. However, E action on osteoclasts is superior in comparison with that on osteoblasts. Recent data have shown that transforming growth factor beta (TGFbeta) mediates the actions of E in bone. Following the example of raloxifene it may be proved that the role of TGFbeta in the actions of E in bone is central and has not only academic interest. More data are needed to elucidate this issue. Finally, recent data suggest the importance of E for bone maturation and development of peak bone mass in men. It seems likely that both E and androgens are required for the growth and maintenance of the adult male skeleton.     

Effects of physical training on bone mineral density and bone metabolism

The purpose of this study was to examine the influences of long-term walking training and walking and jumping training on bone mineral density (BMD) and bone metabolism. Data from 28 healthy premenopausal women was assessed. The subjects were divided into the walking group (WG; 17 women mean+/-SE age 35+/-2 years), and the walking and jumping group (WJG; 11 women mean+/-SE age 39+/-1 years). BMD was measured in the lumbar spine and proximal femur using dual energy X-ray absorptiometry (DXA). As markers of bone metabolism, this study was to measure bone formation markers, bone-alkaline phosphatase (B-ALP: measured by enzyme immunoassay/EIA) and osteocalcin (BGP: by radioimmunoassay/RI) as well as bone resorption markers, parathyroid hormone (PTH: measured by/RI) and type I collagen cross-linked N-telopeptides (NTx: by EIA). Despite the significant decrease in body weight (p<0.05), no corresponding decrease in BMD was observed. Moreover, no significant difference in bone markers BGP, PTH, and NTx was observed. B-ALP was significantly increased (p<0.05) after one year, and the rate of this increase was greater in the WJG than in the WG. It is thus concluded that walking training for one year is beneficial for the promotion of bone formation, and that jumping stimulus maintain BMD effectively.     

Update on Wnt signaling in bone cell biology and bone disease

For more than a decade, Wnt signaling pathways have been the focus of intense research activity in bone biology laboratories because of their importance in skeletal development, bone mass maintenance, and therapeutic potential for regenerative medicine. It is evident that even subtle alterations in the intensity, amplitude, location, and duration of Wnt signaling pathways affects skeletal development, as well as bone remodeling, regeneration, and repair during a lifespan. Here we review recent advances and discrepancies in how Wnt/Lrp5 signaling regulates osteoblasts and osteocytes, introduce new players in Wnt signaling pathways that have important roles in bone development, discuss emerging areas such as the role of Wnt signaling in osteoclastogenesis, and summarize progress made in translating basic studies to clinical therapeutics and diagnostics centered around inhibiting Wnt pathway antagonists, such as sclerostin, Dkk1 and Sfrp1. Emphasis is placed on the plethora of genetic studies in mouse models and genome wide association studies that reveal the requirement for and crucial roles of Wnt pathway components during skeletal development and disease.     

Effect of guided bone regeneration on bone quality surrounding dental implants

Bone quality as well as its quantity at the implant interface is responsible for determining stability of the implant system. The objective of this study is to examine the nanoindentation based elastic modulus (E) at different bone regions adjacent to titanium dental implants with guided bone regeneration (GBR) treated with DBM and BMP-2 during different post-implantation periods. Six adult male beagle dogs were used to create circumferential defects with buccal bone removal at each implantation site of mandibles. The implant systems were randomly assigned to only GBR (control), GBR with demineralized bone matrix (DBM), and GBR with DBM + recombinant human bone morphogenetic protein-2 (rhBMP-2) (BMP) groups. Three animals were sacrificed at each 4 and 8 weeks of post-implantation healing periods. Following buccolingual dissection, the E values were assessed at the defects (Defect), interfacial bone tissue adjacent to the implant (Interface), and pre-existing bone tissue away from the implant (Pre-existing). The E values of BMP group had significantly higher than control and DBM groups for interface and defect regions at 4 weeks of post-implantation period and for the defect region at 8 weeks (p < 0.043). DBM group had higher E values than control group only for the defect region at 4 weeks (p < 0.001). The current results indicate that treatment of rhBMP-2 with GBR accelerates bone tissue mineralization for longer healing period because the GBR likely facilitates a microenvironment to provide more metabolites with open space of the defect region surrounding the implant.     

Direct action of 1,25-dihydroxyvitamin D on bone: VDRKO bone shows excessive bone formation in normal mineral condition

In the present study, the direct role of Vitamin D in bone metabolism was investigated. Vitamin D has been suggested to be an important hormone for bone metabolism, but there has been little evidence that Vitamin D actively participates in this process. Here, we show the direct action of Vitamin D by transplanting the bone of the Vitamin D receptor null mutant mice (VDR-/-) to the wild-type mouse. This procedure allowed us to investigate the changes in the bone without VDR in the normal humoral environment. Unexpectedly, the volume and the density of the VDR-/- bone transplanted to the wild-type mouse were significantly increased compared with the control (wild-type bone transplanted to the wild-type mouse). We show that Vitamin D has key roles in bone metabolism negatively.     

Dependence of ultrasonic attenuation on bone mass and microstructure in bovine cortical bone

The development of the axial transmission technique now enables in vivo evaluation of cortical bone quality, which plays an important role in bone fragility. Cortical bone is a complex multiscale material, which may be made of different types of microstructure. The interaction between ultrasound and cortical bone remains unclear and most studies have been confined to wave speed analysis. The first aim of this study is to investigate the dependence of the frequency-dependent attenuation on the type of bone microstructure. The second goal is to determine whether broadband ultrasonic attenuation (BUA) is related to volumetric bone mineral density (vBMD) and mass density. Parallelepipedic samples of bovine cortical bone were cut from three specimens and tested in the axial, radial and tangential directions using an ultrasonic transmission device. BUA was evaluated over a 1-MHz wide bandwidth around 4MHz. In addition, the microstructure of each sample was determined using an optical microscope. BUA values measured in porotic microstructure are significantly higher than in Haversian microstructure. The lowest BUA values are obtained for plexiform microstructure. For all structures, BUA in the axial direction is significantly smaller than in the radial and tangential directions. Moreover, BUA is correlated with both vBMD and density (determination coefficient (R2) equal to 0.44 and 0.65, respectively, in the axial direction). BUA variations can be explained by scattering and viscoelastic mechanisms. This study suggests that BUA measurements have the potential to discriminate among different cortical bone microstructures in addition to providing material properties.     

Effect of alendronate on osteoclast differentiation and bone volume in transplanted bone.

Alendronate, one of the bisphosphonates, is known to have an inhibitory effect on bone resorption. The purpose of this study was to investigate the effects of alendronate on ectopic bone graft resorption and to determine the optimal dose in the mouse. The grafted bone in the control group disappeared due to resorption by osteoclasts within 5 weeks. In the experimental groups, the area of bone tissue decreased by only 20-40% at 5 weeks post-operatively. At 8 and 9 weeks after surgery, the decreased area of bone structure was significantly less in all the 10(-4) M injected alendronate-immersed groups than in the 10(-4) M non-injected alendronate-immersed. At 9 weeks after surgery, the number of osteoclasts were significantly less in the 10(-4) M injected alendronate-treated groups than in the 10(-4) M non-injected alendronate-treated groups. These results suggest that alendronate inhibits resorption of ectopic bone graft at concentrations of 10(-4) and 10(-6) M.     

Role of angiogenesis on bone formation

Angiogenesis and bone formation are coupled during skeletal development and fracture healing. This relationship, although known for some time, has not been properly explored. Advances in the discovery of how angiogenesis is regulated in physiological processes like embryogenesis, endometrial regeneration and wound healing or in pathologies such as cancer have provided a deeper understanding of how angiogenic factors may interact with bone cells to improve bone formation and bone regeneration. The lack of oxygen (hypoxia) and the subsequent generation of angiogenic factors have been shown to be critical in the development of a regular skeleton and achieving successful bone regeneration and fracture healing. Given that vascular status is important for a proper bone homeostasis, defining the roles of osteoblasts, osteoclasts, endothelial cells and angiogenic factors and their interactions in bone is a key issue for the development of new strategies to manage bone pathologies and nonfused fractures.     

大豆异黄酮对去卵巢大鼠骨密度及骨代谢影响的实验研究

目的 探讨大豆异黄酮对去卵巢大鼠骨丢失的防治作用及其作用机理。方法 选用卵巢切除大鼠所诱发的骨质疏松模型,给与大豆异黄酮治疗。三个月后测定大鼠骨密度及骨代谢相关生化指标。结果 大豆异黄酮可提高卵巢切除大鼠的骨密度及血清雌激素水平,降低尿钙（Ca),尿磷（P）及尿羟脯氨酸（HOP）的排泄,同时降低血清总碱性磷酸酶（ALP）,骨碱性磷酸酶（BALP）,及抗酒石酸酸性磷酸酶（TRACP）的活性,还可使血清骨钙素（BGP）的浓度降低,促使卵巢切除大鼠子宫的相对重量增加,其作用与剂量相关。结论 小剂量大豆异黄酮有类似雌激素样作用,可有效防治卵巢切除大鼠的骨量丢失,其作用机制可能是通过降低骨转换率实现的。     

Effect of ifosfamide on bone healing

The effect of ifosfamide on bone healing was tested in a controlled experiment of fibular osteotomy in immature rabbits. Standardized shaft osteotomy was implemented in 10 experimental subjects (group 2) and 10 controls (group 1). Experimental animals received a 50 mg/kg ifosfamide dose by intraperitoneal injection on the fourth post-operative day, and for five days thereafter, while controls received injections of distilled water. After five weeks, all animals were submitted to pharmacological euthanasia and the resulting bone callus samples were studied with histomorphometry, using hematoxylin-eosin stain. Group 2 presented smaller bone volume (69.03% versus 84.98%), larger fibrosis volume (30.96% versus 15.02%), and larger resorption surface (22.02% versus 16.17%) than group 1 (all p< or = 0.05). We conclude that ifosfamide is able to alter the physiological bone healing process by producing a less mature callus (characterized by a smaller quantity of bone tissue), a larger quantity of fibrous tissue, and a smaller resorption surface.     

Lack of effect of spaceflight on bone mass and bone formation in group-housed rats

As part ofan experiment to study the role of corticosteroids in bone changesduring spaceflight, male Sprague-Dawley rats (6 wk old, 165 g bodyweight) were placed in orbit for 17 days, in groups of six, inanimal-enclosure modules (AEMs) aboard the space shuttle Columbia(STS-78). Control rats were group housed in a similar manner inground-based AEMs or standard vivarium cages. Adrenal hypertrophyoccurred in flight rats, but bone histomorphometric analyses revealed alack of significant changes in bone mass and bone formation in theseanimals. Cancellous bone volume and osteoblast surface in the proximaltibial metaphysis were nearly the same in flight and ground-based rats.Normal levels of cancellous bone mass and bone formation were alsodetected in the lumbar vertebrae and femoral necks of flight rats. Inthe tibial diaphysis, periosteal bone formation rate was found to beidentical in flight and ground-based rats. The results indicate that,under conditions of group housing in AEMs, spaceflight has minimaleffects on bone mass and bone formation in rapidly growingrats. These findings emphasize the need to investigate theimportance of rat age, strain, and especially housing conditions forstudies of the skeletal effects of spaceflight.

     

High bone density and bone health

The aim of this paper is to review the main aspects related to high bone density (HBD) as well as to discuss the physiologic mechanisms involved in bone health. There are still no well-defined criteria for identification of individuals with HBD and there are few studies on the topic. Most studies demonstrate that overweight, male gender, black ethnic background, physical activity, calcium and fluoride intake and use of medications such as statins and thiazide diuretics play a relevant and positive role on bone mineral density. Moreover, it is known that individuals with certain diseases such as obesity, diabetes, estrogen receptor-positive breast or endometrial cancer have greater bone density than healthy individuals, as well as athletes having higher bone density than non-athletes does not necessarily mean that they have healthy bones. A better understanding of risk and protective factors may help in the management of patients with bone frailty and have applicability in the treatment and in the prevention of osteoporosis, especially intervening on non-modifiable risk factors.     

The influence of exercise on bone morphogenic enzyme activity of immature equine subchondral bone

This study aimed at the determination of the influence of exercise on the levels of a number of bone morphogenic enzymes in subchondral bone and at the comparison of these data with other (subchondral) bone-related parameters that have been investigated in the same experimental population.Forty-three foals were reared until weaning at 5 months of age under similar conditions, except for the type and amount of exercise. Fifteen foals remained at pasture (Pasture group and also control group), 14 foals were kept in box stalls (Box group) and 14 foals were kept in the same box stalls but were subjected daily to an increasing number of gallop sprints (Training group). After weaning 8 foals from each group were euthanised. All remaining 19 animals were housed together in a loose box with access to a small paddock to study a possible reversibility of exercise-induced effects. Post mortem subchondral bone samples were collected from the femoropatellar joint and analysed for the bone morphogenic enzymes alkaline phosphatase (ALP), tartrate resistant acid phosphatase (TRAP) and lysyl oxidase (LO). Data were compared to calcium content, numbers of collagen cross-links, bone mineral density (BMD) and cross-sectional area (CSA) collected in other bone-related studies in the same group of experimental animals.At 5 months of age, ALP levels were significantly lower and TRAP levels higher in both the Box and the Training group, making the ALP : TRAP ratio reversed in relation to the Pasture group. LO levels were lower in the Box group only. The ALP and TRAP data corresponded with changes in CSA, but not with calcium and BMD, the levels of which were the same in the Training and Pasture groups. The LO levels corresponded nicely with hydroxylysylpyridinoline (HP) and lysylpyridinoline (LP) cross-links. At 11 months of age ALP and TRAP levels had reached similar levels in most groups, normalising the ALP : TRAP ratio. TRAP levels in the former Training group lagged somewhat behind. LO levels were still significantly lower in the former Box rest group.It is concluded that the overall increase in bone mass (characterised by the change in CSA) is apparently related to continuous, evenly distributed exercise as in the Pasture group (natural situation). This process seems to be related with ALP and TRAP levels and their ratio. For normal cross-link levels and BMD, short heavy bouts of exercise superimposed on a basic rest regimen seem sufficient. However, both data from this study and from earlier studies suggest that this latter exercise regimen might have a long-term deleterious effect.     

Effect of bone strain on cortical bone structure in macaques (Macaca mulatta)

It has recently been shown that the consistency of food significantly affects levels of bone strain in the mandible during mastication (Hylander, '79a). Mandibular bone histology was examined to test the effects of a diet of hard food compared to a diet of soft food in two group of monkeys. One group of rhesus macaques (Macaca mulatta) was fed a diet of commercially prepared hard biscuits. The second group was fed a soft diet the consistency of fudge. Both diets were nutritionally adequate for normal growth and development. As a control for other factors influencing cortical bone structure, fibular morphology was also examined. At the end of the test period, mandibular and fibular tissue samples from the two groups were prepared to determine the amount of secondary Haversian bone present. Mandibular depth at M₂ and fibular anteroposterior diameter were also measured and compared between the two dietary groups. The soft-diet monkeys showed low levels of remodeling in their mandibles. There were large patches of unremodeled bone and resorption spaces were common. The hard-diet monkeys exhibited more extensive evidence of secondary Haversian remodeling in their mandibles. The hard-diet monkeys also had deeper mandibles. In contrast, the fibulae from the two groups had similar mean diameters and showed comparable levels of secondary remodeling. We infer that the higher mandibular bone remodeling levels in the hard-diet monkeys represent an adaptive response to remove and replace fatigued mandibular bone due to higher stress levels associated with the ingestion and mastication of hard foods. We also infer that greater depth of the mandible at M₂ found in the harddiet group represents an adaptive response to higher stress levels associated with the ingestion and mastication of hard foods.     

Dynamic culture improves MSC adhesion on freeze-dried bone as a scaffold for bone engineering

AIM:To investigate the interaction between mesenchymal stem cells(MSCs) and bone grafts using two different cultivation methods:static and dynamic.METHODS:MSCs were isolated from rat bone marrow.MSC culture was analyzed according to the morphology,cell differentiation potential,and surface molecular markers.Before cell culture,freeze-dried bone(FDB) was maintained in culture for 3 d in order to verify culture medium pH.MSCs were co-cultured with FDB using two different cultivation methods:static co-culture(two-dimensional) and dynamic co-culture(threedimensional).After 24 h of cultivation by dynamic or static methods,histological analysis of Cell adhesion on FDB was performed.Cell viability was assessed by the Trypan Blue exclusion method on days 0,3 and 6 after dynamic or static culture.Adherent cells were detached from FDB surface,stained with Trypan Blue,and quantified to determine whether the cells remained on the graft surface in prolonged non-dynamic culture.Statistical analyses were performed with SPSS and a P < 0.05 was considered significant.RESULTS:The results showed a clear potential for adipogenic and osteogenic differentiation of MSC cultures.Rat MSCs were positive for CD44,CD90 and CD29 and negative for CD34,CD45 and CD11bc.FDBs were maintained in culture for 3 d and the results showed there was no significant variation in the culture medium pH with FDB compared to pure medium pH(P > 0.05).In histological analysis,there was a significant difference in the amount of adhered cells on FDB between the two cultivation methods(P < 0.05).The MSCs in the dynamic co-culture method demonstrated greater adhesion on the bone surface than in static co-culture method.On day 0,the cell viability in the dynamic system was significantly higher than in the static system(P < 0.05).There was a statistical difference in cell viability between days 0,3 and 6 after dynamic culture(P < 0.05).In static culture,cell viability on day 6 was significantly lower than on day 3 and 0(P < 0.05).CONCLUSION:An alternative cultivation method was developed to improve the MSCs adhesion on FDB,demonstrating that dynamic co-culture provides a superior environment over static conditions.     

Effect of bed rest immobilization on metabolic turnover of bone and bone mineral density

Immobilization induces abnormal bone metabolism and severe decalcification of bone. To investigate the effect of middle-term immobilization on bone metabolism, we studied 10 young healthy males and females during bed rest for 20 days. Bone mineral density (BMD) rapidly decreased in both lumbar and metacarpal bones. No bone showed consistent BMD alterations, partial increase and partial decrease, and both lumbar and metacarpal bone showed similar rapid BMD change. Urinary excretion of pyridinoline tended to slightly increase by day 10, and to decline by day 20 (mean +/-SE: 34.2 +/-7.4, 26.3+/-4.6 nmol day-1, respectively). Neither alkaline phosphatase (isoform III) nor tartrate-resistant acid phosphatase, changed, suggesting that in the early stage of immobilization bone matrix in some part might increase or be resorbed without any activation of osteoblast or osteoclast, resulting in rapid calcification or decalcification, respectively.