Compressive strength,ash weight,and volume of vertebral trabecular bone in experimental fluorosis in pigs

Summary The aim of the investigation was to measure the effect of fluoride on vertebral trabecular bone compressive strength and to correlate this with fluoride-induced changes in bone density. This correlation would express changes in the quality of bone during fluoride treatment. Pigs were used in the experiment because their trabecular bone structure and remodeling sequences are very similar to the human. Eight animals receiving a supplement of 2 mg F⁻/kg b.w. per day from age 8–14 months were compared with 8 control animals. Morphologic measurements in the animals receiving fluoride supplement showed a significant increase of 17% in bone density and a smaller, insignificant increase of 3% in ash weight analyses. Meanwhile, the mechanical parameters for the fluorotic animals were unchanged (maximum compressive strength, maximum stiffness, and energy-absorption capacity) or decreased (normalized compressive strength=maximum compressive load corrected for ash density). It is concluded that the increased bone mass during the initial stages of fluoride treatment does not necessarily indicate an improved bone quality. The discrepancy between bone mass and strength could be either a permanent or a temporary phenomenon and requires further investigation.     

Cnaical significance of changes in cortital and trabeular bone density after menopause

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Prediction of cortical bone porosity in vitro by microcomputed tomography

The high importance of intracortical porosity for mechanical strength of cortical bone has been established. The contribution of other parameters of microstructure such as osteon dimensions for strength is in discussion. The aim of this study was to evaluate the predictive value of microcomputed tomography (mCT) for porosity and other microstructural parameters of cortical bone in cortical bone biopsies. Femoral cortical bone specimens from the middiaphysis of 24 patients were harvested during the procedure of total hip replacement at the location where normally one hole (? 4.5 mm) for the relief of the intramedullary pressure is placed. In vitro intracortical porosity and bone mineral density (BMD) measurements by mCT were compared with structural parameters assessed in histological sections of the same specimens. A strong correlation was found between intracortical porosity measured by mCT and histological porosity (r = 0.95, P <0.0001). Porosity measured by mCT was also a strong predictor for other parameters describing dimensions of porous structures. BMD?1 was associated with osteonal area (r = -0.76, P <0.0001). We consider the measurement of porosity by mCT as a very potent procedure for assessing intracortical porosity and parameters related to porous structures of cortical bone nondestructively in vitro.     

Oophorectomy and cortical bone remodeling in the beagle

Summary Cortical bone remodeling measurements were carried out on the ribs of 6 spayed and five control Beagle dams which had been subjected to a period of observation equal to more than one sigma of cortical bone remodeling activity. The results of the measurements of static and dynamic parameters indicate that the lack of ovarian hormones does not produce a major alteration in the rates of cortical bone remodeling, but does result in an increase in the number of resorption spaces per mm² of cortical bone without altering the parameters of bone function. This latter fact supports the hypothesis that decreased levels of circulatory ovarian hormones may influence the duration of the resorption activity as well as possibly uncoupling the resorption/formation (R/F) mechanism of the bone remodeling unit.     

Re-evaluating the toughness of human cortical bone

Data for fracture in human humeral cortical bone are re-analyzed to assess the validity for this material of linear-elastic fracture mechanics (LEFM), which is the standard method of analyzing toughness and one basis for analyzing clinical data relating to bone quality. A nonlinear fracture model, which is based on representing the damage zone in the bone by a cohesive model, is calibrated against a number of sets of test data for normal (not diseased or aged) human cortical bone taken from cadavers. The data consist of load vs. load-point displacement measurements from standard compact–tension fracture tests. Conventional LEFM is unable to account for the shape of the load–displacement curves, but the nonlinear model overcomes this deficiency. Calibration of the nonlinear model against one data curve leads to predictions of the peak load and the displacement to peak load for two other data curves that are, for this limited test set, more accurate than those made using LEFM. Furthermore, prior observations of damage mechanisms in bone are incompatible with the modeling assumption of LEFM that all nonlinearity is confined to a zone much smaller than the specimen and the crack length. The predictions of the cohesive model and the prior observations concur that the length of the nonlinear zone in human cortical bone varies in the range 3–10 mm, which is comparable to or larger than naturally-occurring bones and the specimens used to test them. We infer that LEFM is not an accurate model for cortical bone. The fracture toughness of bone deduced via LEFM from test data will not generally be a material constant, but will take different values for different crack lengths and test configurations. The accuracy of using LEFM or single-parameter fracture toughness for analyzing the significance of data from clinical studies is called into question. The nonlinear cohesive zone model is proposed to be a more accurate model of bone and the traction-displacement or cohesive law is hypothesized to be a material property. The cohesive law contains a more complete representation of the mechanics of material failure than the single-parameter fracture toughness and may therefore provide a superior measure of bone quality, e.g., for assessing the efficacy of therapy for osteoporosis.     

A model of osteon closure in cortical bone

Summary A model of osteon closure is presented that incorporates some physiologic features of cortical bone remodeling, such as matrix synthesizing activity of osteoblasts, their burial as osteocytes, and elimination of cells. A simplified version of the model assumes a constant osteoblast activity throughout radial closure. An extended version allows for varible osteoblasts activity and is based on Lee's law of radial closure kinetics. The model calculations (extended model) show that both in humans and beagle dogs osteoblast activity steadily decreases during radial closure of the osteon. The potential of the model is also illustrated by calculating the dynamic change of the geometrical shape of the closing cone and the time dependence of the osteoid seam width, number of osteoblasts and bone formation rate in the closing cone.     

Effects of a high fat-sucrose diet on cortical bone morphology and biomechanics

Summary High fat-sucrose (HFS) diets can reportedly produce glucose intolerance and hyperinsulinemia that may indirectly have deleterious effects on bone. The effects of a high-fat diet on calcium absorption, bone calcium content, and bone mechanical properties, however, remain controversial. Thus, we examined the morphological and biomechanical adaptations in limb bones of rats that were fed a HFS diet. Female Sprague-Dawley rats (8 weeks old) were randomly assigned to two groups, either a control group (n=9) fed a standard diet (low-fat complex-carbohydrate) or an experimental group (n=9) fed a HFS diet for 10 weeks. The right tibia and second metatarsus (MT) were fractured in three-point bending, and contralateral bones were used for morphological and histological analyses. HFS tibias had significantly lower maximum load and failure energy, and tensile stress at the proportional limit for both HFS tibia and MT was significantly less than controls. In addition, the elastic modulus and density of the HFS MT was significantly lower than controls. Geometry of the tibial mid-diaphysial cross section did not differ for the two diets, but the cortical cross-sectional area of HFS MT increased significantly compared to control MT. The total number of osteons in the middiaphysis of HFS MT decreased, but tibial and MT porosities did not change with the HFS diet. Our results suggest that the deleterious effects of the HFS diet may be more related to changes in the material properties of the cortical bone rather than to osteoporotic changes in the bone.     

Torsional strength reduction due to cortical defects in bone

This study correlated torsional strength reduction with circular defect size in cortical bone, to define the "stress riser" and "open-section" effect of the defects. The experimental model was developed and verified. Circular defects from 10 to 60% of bone diameter were then created in paired sheep femora and the bones loaded to failure. Contrary to theory, this experimental study suggests that small defects (10%) of bone diameter cause no significant torsional strength reduction. A 20% defect caused a 34% decrease in strength, representing the "stress riser" dimension. Defects between 20 and 60% of bone diameter decreased strength linearly as a function of defect size, and thus no discrete "open section" dimension was identified. For circular defects, we were unable to demonstrate a discrete "open-section" effect at which dramatic strength reduction is observed. These data may prove to be helpful when planning surgery that involves placing defects in bone such as for infection, biopsy, and prosthesis removal. The accepted guideline to avoid defects of greater than 50% of the bone diameter may be too great. Our data reveal this 62% reduction in torque strength and 88% energy to failure exist with a 50% circular defect.     

补肾中药复方延缓老年雄性大鼠股骨皮质骨、松质骨骨量增龄性丢失的实验研究

目的　研究补肾中药复方延缓老年大鼠股骨皮质骨 、松质骨骨量增龄性丢失的作用。方法３６只２４月龄 Ｓ Ｄ 雄性大鼠随机分为２４月龄本底对照组、３０月龄增龄对照组、补肾中药复方低剂量组、补肾中药复方高剂量组,每组各９只。低剂量组、高剂量组均自２４月龄给药至３０月龄。各组相应处理以后分别测定各组大鼠左侧股骨以松质骨为主的近段、远段以及以皮质骨为主的中段的骨密度。结果　补肾中药复方低剂量组大鼠股骨各段骨密度增龄性减少率出现延缓的趋势;高剂量的补肾中药复方则能明显延缓股骨各段骨密度增龄性减少率。结论　补肾中药复方具有量效依赖性地延缓大鼠皮质骨、松质骨增龄性骨丢失的作用     

高钙饮食对老年雌性大鼠皮质骨的影响

目的研究高钙饮食对老年雌性大鼠皮质骨的保健作用。方法按照食料中钙含量不同,大鼠随机分为3组,分别喂饲低钙饲料(0.1?)、中钙饲料(0.6?)、高钙饲料(1.2?),持续12w。采用pQCT技术测定股骨中段皮质骨相关参数。结果高钙组大鼠股骨中段皮质骨的骨密度和骨矿含量都明显升高。高钙饮食显著提高皮质骨面积及皮质骨厚度,而对股骨中段外周面积和内周面积没有明显影响。结论高钙饮食能够提高老年雌性大鼠皮质骨的骨量、面积和厚度,从而维护皮质骨的骨骼健康。     

Mechanisms of cortical bone loss from the metacarpal following digital amputation

Immobilization bone loss, whether due to whole body immobilization or local causes, is associated with an initial rapid phase of trabecular bone loss, but the long-term effects of immobilization on cortical bone are not well described. We have studied metacarpal morphometry in 16 men who had undergone partial or complete traumatic digital amputations 4–71 years earlier. Noninvolved metacarpals from the affected and unaffected hands were used as controls. Cortical bone width was significantly reduced in the metacarpals proximal to the amputated digits (P=0.001). In the 7 subjects who suffered amputation before the age of 19, the cortical bone deficit was primarily due to a reduction in the total width of the medullary shaft (P=0.007), whereas medullary width was not changed. In these subjects the metacarpal was also significantly reduced in length, by a mean 2.9 mm (P=0.035). In the 9 subjects who had their amputation after the age of 19, both a reduction in total width and an increase in medullary width (P=0.017) accounted for the cortical bone deficit. The deficit in total width was related to the time since amputation (P=0.008) and could be accounted for by loss of the normal age-related increase in total width (0.01 mm/year). We conclude that in this model of immobilization osteoporosis, the metacarpal proximal to the amputated digit demonstrates cortical osteopenia. An inhibition of the periosteal bone formation, which is responsible for the normal age-related gain in total width, is an important factor in this bone loss, which thus differs from normal age-related bone loss (which is endosteal) and from bone loss following acute immobilization (which is from trabecular sites). The pattern of cortical bone loss differs according to the age at amputation.     

皮质骨机械性显微损伤的形态分析及其研究价值

目的拟观察骨钉植入所造成的鼠皮质骨机械性显微损伤的形态特征。方法在成年（12个月）大鼠胫骨中段钻入直径1．2mm的含螺纹的克氏针。钻孔骨段经碱性品红染色，甲基丙烯酸甲酯包埋后作100μm厚的横截面切片。骨切片在普通光镜、荧光显微镜和激光共聚焦显微镜下进行观察，并对显微损伤的范围进行定量分析。结果普通光镜和荧光显微镜均可以发现针孔周围的弥散性损伤和线性裂纹，而荧光显微镜能显示普通光镜下难以分辨的染色较弱的显微损伤；激光共聚焦显微镜则具有更高的分辨率，能发现光镜下的片状损伤由很多细小的交叉裂纹组成。定量分析结果显示，损伤骨的厚度一般小于100μm，而荧光显微镜显示的损伤骨表面比率、损伤骨厚度和损伤骨面积均大于普通光镜所示（P〈0．05）。结论螺钉植入造成的周围皮质骨显微损伤包括弥散性损伤和线性裂纹。两者均可由极微细的裂纹聚合而成。荧光显微镜由于对碱性品红有更高的敏感性，因儿能提供更为准确的定量分析结果。     

短期应用糖皮质激素对大鼠皮质骨和松质骨的不同影响

目的探讨短期使用糖皮质激素对大鼠不同部位骨骼的形态结构和生物力学的影响。方法20只3月龄SD雌性大鼠随机分为2组:①正常对照组(Ctrl);②糖皮质激素组(dexamethasone,Dex)。每只大鼠适应性喂养1周后,灌胃6周,取左侧胫骨上段(proximal tibia metaphyses,PTM)和中段(middle part of tibia shaft,TX)进行骨形态计量学检测,取左侧股骨(Left Femur,LF)和第5腰椎(the5th Lumbar Vertebra,LV5)进行骨生物力学检测。结果Ctrl组大鼠的体重随时间(6周)逐渐增加;而Dex组大鼠的体重增加缓慢,甚至出现体重下降的情况,两组大鼠的体重差异具有显著性。与Ctrl组比,Dex组大鼠软组织中:肝、脾、肾、子宫和胸腺重量显著性减少。骨形态计量学静态参数显示:与Ctrl组相比,Dex组大鼠TX段皮质骨的骨量明显降低,骨髓腔增大。动态参数显示:Dex组大鼠的骨内膜面荧光周长百分率、骨形成率明显降低,而骨吸收百分率增加;骨外膜面动态参数无显著性变化,两组大鼠PTM松质骨无论静态参数或动态参数与对照组比无统计学上的显著性变化。Dex也没有弱化LF和LV5的力学性能(最大载荷,最大应力,最大应变)。结论短期、少量使用Dex(45d,2.5mg·kg-1,twice per week),仅使大鼠皮质骨丢失,由于几何形状的变化,并不改变生物力学的性能。以这种方式使用Dex,不仅不影响松质骨,也不改变大鼠的生物力学性能。此结论提示Dex短期使用对不同部位的骨骼影响不同,先出现皮质骨的变化。因此需要重视对糖皮质激素导致皮质骨变化的观察和研究。     

卵巢切除对大鼠皮质骨结构和力学性能的影响

目的：研究卵巢切除大鼠皮质骨的几何学改变和力学性能改变,探讨雌激素缺乏时皮质骨改变的发生机理。方法：选雌性SD大鼠56只,分为Sham组和OVX组,动物分别在4、12、20和28周时处死7只,取其胫骨备用。左侧于近3/5和远2/5交界部切断,在电镜下摄片,计测截面总面积、皮质骨面积、骨外径周长、骨髓腔面积和骨内径周长。右侧以近3/5与远2/5交界点为加载点进行三点弯曲力学实验。结果：Sham组术后4周至28周胫骨截面总面积和骨外径周长逐渐增加。（P＜0.005),而髓腔面积和内径周长变化不明显。OVX组截面总面积和外径周长也有逐渐增加趋势。但差异无显性。而内径周长和髓腔面积都明显增加,在相同时期显大于Sham组（P＜0.005),而皮质骨面积却与Sham组差异无显性。三点弯曲试验结果表明,从4-28周实验对照两组抗弯强度和刚度均逐渐增加,但两组间差异无显性。在各时期骨组织材料力学性能也无显性差异。结论：卵巢切除对皮质骨的影响主要表现在使骨髓控扩大,对骨外膜的影响较小,在短期内皮质骨的力学性能无明显影响。     

河北省农村青少年人群骨密度调查

本文对河北省农村７～１９岁青少年人群５４８５人用单光子骨矿仪测量挠骨远端１／３处骨密度，同时测量身高、体重。结果男、女性别间７～１４岁身高、７～１５岁体重与骨密度差异不显著（ｐ＞０．０５），其后男性均高于女性，差异显著（ｐ＜０．０５）；两性骨密度与年龄、身高、体重均呈明显正相关（均为ｐ＜０．００１），性别间相关系数比较，男性大于女性，差别显著（ｐ＜０．０１）；两性在青春前期和青春中期身高、体重和骨密度增长率均高于学龄期和青春后期；生活在不同地区男、女性骨密度比较，沿海区高于平原区，平原区高于山区，差别均有显著意义（均为ｐ＜０．００１）。由于青少年生长发育较快，特别在青春前期和青春中期身高、体重和骨密度增长率最快，因此应对此期青少年注意补充足够的营养物质和矿物质，尤其对经济、生活条件较差的地区更应加以关照，保障健康发育防止骨畸形和骨折发生、本调查对青少年医疗保健有指导意义。     

The effects of continuous progestogen treatment on cortical bone remodeling activity in beagles

Summary Cortical bone remodeling measurements were carried out on the ribs of 6 spayed and 5 progestogen-treated spayed Beagle dams which had been subjected to a period of observation equal to more than 1 sigma of intact canine bone remodeling activity. Analyses of static and dynamic features indicated that continuous medroxyprogesterone acetate replacement therapy altered the rates of cortical bone remodeling activity. In the progestogen-treated dams, more Basic Multicellular Units (BMUs) were activated, exhibiting shortened resorption and formation times. Thus, this progestogen appears to play a significant role in regulating cortical bone cell activity and, as such, suggests that progesterone may play a part in the prevention or slowing down of cortical bone loss in females following menopause or oophorectomy.     

Estimation of mechanical properties of cortical bone by computed tomography

It is difficult to assess from conventional x-rays the amount of loading that a bone can tolerate. The question therefore was asked whether the mechanical properties of cortical bone could be estimated by using a computed tomography (CT) system typically employed in the clinical setting. In vitro cross sectional diaphyseal scans of adult human tibiae were made using a GE 9800 scanner and linear attenuation coefficients determined in several regions of the central cross sections. Samples from the mid-diaphyses of these tibiae were harvested, tested in three-point bending to failure, and mechanical properties as well as density and ash fraction determined. The respective relationships between CT measurements, mechanical properties, and physical properties were calculated using regression analysis. In addition, a solid calibration phantom (tricalciumphosphate) was scanned to evaluate the variability of CT measurements. The physical parameters measured in this study were found to be comparable with data from other authors but correlations were moderate to weak. Linear regression revealed the following correlation coefficients with CT data: r = 0.55 (Young's modulus), r = 0.50 (strength), r = 0.65 (apparent density) and r = 0.46 (ash fraction). The correlation coefficients of these regressions for both linear and power fits were not significantly different. A high linear correlation (r = 0.99) was found between the chamber densities and the measured attenuation coefficients, but accuracy varied between 2 and 6%. The small range of specimen mechanical properties as well as the limitations inherent with the methods employed may explain these results. We conclude that clinical equipment as used in this study is not sufficient to accurately estimate the mechanical properties of cortical bone.     

基于体素的股骨近端骨密度和骨皮质厚度的测量及可重复性研究

目的研究基于定量CT(quantitative computed tomography,QCT)的股骨近段骨密度和骨皮质厚度体素化测量的可重复性,为髋部骨折研究提供技术支持。方法选择28例短时间内QCT扫描两次的髋部骨折患者,其中男性6例,女性22例。从QCT影像中手动分割出股骨近段结构。借助体素形态学分析(voxel-based morphometry,VBM)思想,选择一个形状和结构适中的股骨近段结构作为标准模板,通过三维弹性配准算法将其他股骨近段映射到标准模板上。采用最小二乘和列文伯格-马夸尔特(Levenberg-Marquardt)方法将CT值转化成体素化的骨密度和骨皮质厚度值。最后,使用统计参数图(statistical parametric mapping,SPM)方法对28例患者短时间内两次QCT扫描数据的股骨近段骨密度和骨皮质厚度进行统计分析,获取三维统计参数图。结果所选28例骨折患者短时间内两次QCT扫描数据的股骨近段骨密度和骨皮质厚度的测量结果差异无统计学意义(P0.05),一致性均较好,说明测量结果较为准确。结论股骨近段骨密度和骨皮质厚度的测量方法具有较好的可重复性,为髋部骨折风险评估提供有效手段。     

Effect of aging on trabecular and compact bone components of proximal and ultradistal radius

Bone densitometry has become a major tool for osteoporosis risk assessment. The traditional dual-energy X-ray absorptiometry (DXA) methods are able to evaluate the bone mineral content (BMC; mg/cm) and the areal density (BMD; mg/cm²), but only quantitative computed tomography (QCT) has the potential to measure the true volumetric bone density in the sense of mass per unit volume (mg/cm³). Peripheral QCT (pQCT) measurements were carried out at the non-dominant radius using a Stratec XCT 960 (Unitrem, Roma) in 241 postmenopausal and 29 premenopausal women. The sites of evaluation were both the ultradistal and the proximal radius. The technique used has a coefficient of variation of 2% and it allows separation of the bone section into trabecular and cortical bone on the basis of density threshold. Bone mass of radius, hip and spine was also evaluated by DXA procedures. The bone density data obtained by pQCT were significantly correlated with all DXA measurements. The correlation coefficients between their respective BMD values ranged from 0.48 to 0.75, but for the BMC values of the radius the correlation coefficients ranged from 0.82 to 0.93. The BMD values measured by DXA, but not by pQCT, were positively related with patient heights. All pQCT density measurements, including those obtained at the proximal radius and containing exclusively cortical bone, where negatively related with age and years since menopause. A partial volume effect, which is increasingly relevant the thinner are the bone cortices, might explain that. However, by applying increasing density thresholds, cortical bone density seems to decrease with age as a consequence of a gradual density diminution from the inner part of the bone cortex outwards. Trabecular bone density decreases with aging, but its overall mass does not change as a consequence of an age-related enlargement of trabecular area. Thus, the proportion of trabecular bone over total bone rises, and this might be relevant for our understanding of the age-related changes in bone turnover and rate of bone loss.     

Effect of aging on the toughness of human cortical bone: evaluation by R-curves

Age-related deterioration of the fracture properties of bone, coupled with increased life expectancy, is responsible for increasing incidence of bone fracture in the elderly, and hence, an understanding of how its fracture properties degrade with age is essential. The present study describes ex vivo fracture experiments to quantitatively assess the effect of aging on the fracture toughness properties of human cortical bone in the longitudinal direction. Because cortical bone exhibits rising crack-growth resistance with crack extension, unlike most previous studies, the toughness is evaluated in terms of resistance-curve (R-curve) behavior, measured for bone taken from wide range of age groups (34–99 years). Using this approach, both the ex vivo crack-initiation and crack-growth toughness are determined and are found to deteriorate with age; the initiation toughness decreases some 40% over 6 decades from 40 to 100 years, while the growth toughness is effectively eliminated over the same age range. The reduction in crack-growth toughness is considered to be associated primarily with a degradation in the degree of extrinsic toughening, in particular, involving crack bridging in the wake of the crack.