Time Dependent Behaviour of Trabecular Bone at Multiple Load Levels

The deformation of bone when subjected to loads is not instantaneous but varies with time. To investigate this time-dependent behaviour sixteen bovine trabecular bone specimens were subjected to compressive loading, creep, unloading and recovery at multiple load levels corresponding to apparent strains of 2000–25,000 με. We found that: the time-dependent response of trabecular bone comprises of both recoverable and irrecoverable strains; the strain response is nonlinearly related to applied load levels; and the response is linked to bone volume fraction. Although majority of strain is recovered after the load-creep-unload-recovery cycle some residual strain always exists. The analysis of results indicates that trabecular bone becomes stiffer initially and then experiences stiffness degradation with the increasing load levels. Steady state creep rate was found to be dependent on applied stress level and bone volume fraction with a power law relationship.     

股骨头坏死中松质骨微观力学特性的演变规律

目的采用结合显微CT和显微有限元分析方法,即基于显微CT图像建立三维有限元模型并进行数值模拟仿真分析,无创研究不同分期的坏死股骨头松质骨的微结构和微观力学性能,以期了解在股骨头坏死的发展过程中,松质骨微结构和微观力学特性的变化规律,为临床预测股骨头坏死提供理论基础。方法采集10例股骨头坏死患者的股骨头标本的显微CT图像,按照国际骨循环研究学会分期标准分为Ⅱ期样本3例,Ⅲ期3例,Ⅳ期4例。将图像中骨组织进行阈值分割,分区域建立坏死区、侧向区、硬化区和远端区的松质骨块三维有限元模型(边长8 mm),并根据CT值赋予非均匀材料属性。利用ImageJ软件中的BoneJ插件通过识别显微CT组图像,计算测量各区域松质骨的微结构参数,包括骨体积分数、骨小梁厚度、骨小梁间隙、结构模型指数。对松质骨块施加表观应变为1%的压缩载荷,计算骨组织应力和松质骨表观刚度等参数,对比分析各分期、各分区结果。结果在松质骨微结构方面,Ⅳ期较Ⅱ期的股骨头内部硬化区和坏死区的变化最为明显,硬化区的骨体积分数不断上升,骨小梁间隙下降,结构模型指数减小,而坏死区域与之相反;在骨组织微观受力方面,Ⅱ期到Ⅲ期坏死区域的应力并没有明显变化,而硬化区域随着分期增加应力不断上升,侧向区的应力不断下降。表观刚度变化与应力变化一致。结论随着股骨头坏死程度的加剧,硬化区的松质骨微结构和力学性能变化最大,应作为临床早期诊断中重点关注的区域。此外,微结构参数并不能准确体现松质骨的力学行为,而股骨头塌陷最终取决于其力学特性,因此结合有限元分析方法可更加全面了解股骨头坏死的微观力学演变规律。     

Shear Stress Distribution in the Trabeculae of Human Vertebral Bone

The statistical distribution of von Mises stress in the trabeculae of human vertebral cancellous bone was estimated using large-scale finite element models. The goal was to test the hypothesis that average trabecular von Mises stress is correlated to the maximum trabecular level von Mises stress. The hypothesis was proposed to explain the close experimental correlation between apparent strength and stiffness of human cancellous bone tissue. A three-parameter Weibull function described the probability distribution of the estimated von Mises stress (r²) > 0.99 for each of 23 cases). The mean von Mises stress was linearly related to the standard deviation (r²=0.63) supporting the hypothesis that average and maximum magnitude stress would be correlated. The coefficient of variation (COV) of the von Mises stress was nonlinearly related to apparent compressive strength, apparent stiffness, and bone volume fraction (adjusted r²=0.66, 0.56, 0.54, respectively) by a saturating exponential function [COV=A+B exp(–x/C)]. The COV of the stress was higher for low volume fraction tissue (<0.12) consistent with the weakness of low volume fraction tissue and suggesting that stress variation is better controlled in higher volume fraction tissue. We propose that the average stress and standard deviation of the stress are both controlled by bone remodeling in response to applied loading. © 2000 Biomedical Engineering Society. PAC00: 8719Rr     

Trabecular Shear Stresses Predict <Emphasis Type="Italic">In Vivo</Emphasis> Linear Microcrack Density but not Diffuse Damage in Human Vertebral Cancellous Bone

Linear microcracks and diffuse damage (staining over a broad region) are two types of microscopic damage known to occur in vivo in human vertebral trabecular bone. These damage types might be associated with vertebral failure. Using microcomputed tomography and finite element analysis for specimens of cancellous bone, we estimated the stresses in the trabeculae of human vertebral tissue for inferosuperior loading. Microdamage was quantified histologically. The density of in vivo linear microcracks was, but the diffuse damage area was not, related to the estimates of von Mises stress distribution in the tissue. In vivo linear microcrack density increased with increasing coefficient of variation of the trabecular von Mises stress and with increasing average trabecular von Mises stress generated per superoinferior apparent axial stress. Nonlinear increase in linear crack density, similar to the increase of the coefficient of variation of trabecular shear stresses, with decreasing bone stiffness and bone volume fraction suggests that damage may accumulate rather rapidly in diseases associated with low bone density due to the dramatic increase of shear stresses in the tissue. © 2003 Biomedical Engineering Society. PAC2003: 8719Rr, 8719Xx, 8759Ls, 8759Fm, 8710+e     

Adaptations of Trabecular Bone to Low Magnitude Vibrations Result in More Uniform Stress and Strain Under Load

Extremely low magnitude mechanical stimuli (<10 microstrain) induced at high frequencies are anabolic to trabecular bone. Here, we used finite element (FE) modeling to investigate the mechanical implications of a one year mechanical intervention. Adult female sheep stood with their hindlimbs either on a vibrating plate (30 Hz, 0.3 g) for 20 min/d, 5 d/wk or on an inactive plate. Microcomputed tomography data of 1 cm bone cubes extracted from the medial femoral condyles were transformed into FE meshes. Simulated compressive loads applied to the trabecular meshes in the three orthogonal directions indicated that the low level mechanical intervention significantly increased the apparent trabecular tissue stiffness of the femoral condyle in the longitudinal (+17%, p < 0.02), anterior–posterior (+29%, p < 0.01), and medial-lateral (+37%, p < 0.01) direction, thus reducing apparent strain magnitudes for a given applied load. For a given apparent input strain (or stress), the resultant stresses and strains within trabeculae were more uniformly distributed in the off-axis loading directions in cubes of mechanically loaded sheep. These data suggest that trabecular bone responds to low level mechanical loads with intricate adaptations beyond a simple reduction in apparent strain magnitude, producing a structure that is stiffer and less prone to fracture for a given load. © 2003 Biomedical Engineering Society.     

Development of fetal trabecular micro-architecture in the humerus and femur

It is widely accepted that during postnatal development trabecular bone adapts to the prevailing loading environment via modelling. However, very little is known about the mechanisms (whether it is predominantly modelling or remodelling) or controls (such as whether loading influences development) of fetal bone growth. In order to make inferences about these factors, we assessed the pattern of fetal trabecular development in the humerus and femur via histomorphometric parameter quantification. Growth and development (between 4 and 9 months prenatal) of trabecular architecture (i.e. thickness, number and bone volume fraction) was compared across upper and lower limb bones, proximal and distal regions, and sexes. The data presented here indicate that during prenatal development trabeculae became thicker and less numerous, whilst bone volume fraction remained constant. This partly mimics the pattern of early postnatal development (0-2 years) described by other researchers. Thickness was reported to increase whilst number reduced, but bone volume fraction decreased. This is perhaps because the balance of bone modelling (deposition vs. resorption) changes post partum. Published histological data suggest that bone deposition slows after birth, while resorption rates remain constant. Hence, fetal development may be characterized by relatively high rates of modelling and, particularly, bone deposition in comparison to postnatal. With respect to measures of thickness, number and bone volume fraction prenatal development was not bone, site, or sex specific, whilst postnatally these measures of architecture diverge. This is despite reported developmental variation in the frequency, speed and amplitude of fetal movements (which begin after 11 weeks and continue until birth), and probably therefore loading induced by muscular contractions. This may be because prenatal limb bone micro-architecture follows a generalised predetermined growth trajectory (or genetic blueprint), as appears to be the case for gross distribution of trabecular tissue.     

Osseous microarchitecture of the scaphoid: Cadaveric study of regional variations and clinical implications

Bone strength and structure are closely associated with fracture and screw fixation, however osseous micro architecture on scaphoid has not been clearly addressed. We conducted histomorphometric study of the scaphoid using micro CT to find regional variations and differences in the scaphoid to provide better understanding of fracture mechanism and suggest optimal screw position. We divided scaphoid into eight regions and collected regional data from eleven different cadaveric scaphoids. A computer program was used to measure parameters, which includes mean subchondral bone thickness, bone mineral density for bone density parameters, and tissue mineral density, trabecular thickness, trabecular spacing, trabecular number and bone volume fraction for bone quality parameters. All bone strength parameters were measured the maximum value in the regions where scaphoid articulates with radius. Articular regions presented higher bone strength parameters and thicker subchondral bone. The minimum value of trabecular number was in midcarpal side of waist portion. There was trend of higher subchondral bone thickness in the scaphoid which articulates with capitate and radius. This histomorphometric study showed regional variation of the scaphoid in terms of bone density and quality parameters. Waist portion presented thick subchondral and trabecular bone for high cross section moment of inertia against bending. Three point bending for scaphoid fracture and vertical screw placement are suggested based on these variations.     

Subchondral bone morphology in the metacarpus of racehorses in training changes with distance from the articular surface but not with age

The repetitive large loads generated during high‐speed training and racing commonly cause subchondral bone injuries in the metacarpal condyles of racehorses. Adaptive bone modelling leads to focal sclerosis at the site of highest loading in the palmar aspect of the metacarpal condyles. Information on whether and how adaptive modelling of subchondral bone changes during the career of a racehorse is sparse. The aim of this cross‐sectional study was to describe the changes in subchondral bone micromorphology in the area of highest loading in the palmar aspect of the metacarpal condyle in thoroughbred racehorses as a function of age and training. Bone morphology parameters derived from micro‐CT images were evaluated using principal component analysis and mixed‐effects linear regression models. The largest differences in micromorphology were observed in untrained horses between the age of 16 and 20 months. Age and duration of a training period had no influence on tissue mineral density, bone volume fraction or number and area of closed pores to a depth of 5.1 mm from the articular surface in 2‐ to 4‐year‐old racehorses in training. Horses with subchondral bone injuries had more pores in cross‐section compared with horses without subchondral bone injuries. Differences in bone volume fraction were due to the volume of less mineralised bone. Tissue mineral density increased and bone volume fraction decreased with increasing distance from the articular surface up to 5.1 mm from the articular surface. Further research is required to elucidate the biomechanical and pathophysiological consequences of these gradients of micromorphological parameters in the subchondral bone.     

Predicting time-dependent remodeling of bone around immediately loaded dental implants with different designs

The purpose of this study was to predict time-dependent biomechanics of bone around cylindrical screw dental implants with different macrogeometric designs under simulated immediate loading condition. The remodeling of bone around a parallel-sided and a tapered dental implant of same length was studied under 100 N oblique load by implementing the Stanford theory into three-dimensional finite element models. The results of the analyses were examined in five time intervals consisting loading immediately after implant placement, and after 1, 2, 3 and 4 weeks following implantation. Maximum principal stress, minimum principal stress, and strain energy density in peri-implant bone and displacement in x-(implant lateral direction with a projection of the oblique force) and y-(implant longitudinal direction) axes of the implant were evaluated. The highest value of the maximum and minimum principal stresses around both implants increased in cortical bone and decreased in trabecular bone. The maximum and minimum principal stresses in cortical bone were higher around the tapered cylindrical implant, but stresses in the trabecular bone were higher around the parallel-sided cylindrical implant. Strain energy density around both implants increased in cortical bone, slightly decreased in trabecular bone, and higher values were obtained for the parallel-sided cylindrical implant. Displacement values slightly decreased in time in x-axis, and an initial decrease followed by a slight increase was observed in the y-axis. Bone responded differently in remodeling for the two implant designs under immediate loading, where the cortical bone carried the highest load. Application of oblique loading resulted in increase of stiffness in the peri-implant bone.     

Baby steps towards linking calcaneal trabecular bone ontogeny and the development of bipedal human gait

Trabecular bone structure in adulthood is a product of a process of modelling during ontogeny and remodelling throughout life. Insight into ontogeny is essential to understand the functional significance of trabecular bone structural variation observed in adults. The complex shape and loading of the human calcaneus provides a natural experiment to test the relationship between trabecular morphology and locomotor development. We investigated the relationship between calcaneal trabecular bone structure and predicted changes in loading related to development of gait and body size in growing children. We sampled three main trabecular regions of the calcanei using micro-computed tomography scans of 35 individuals aged between neonate to adult from the Norris Farms #36 site (1300 AD, USA) and from Cambridge (1200–1500 AD, UK). Trabecular properties were calculated in volumes of interest placed beneath the calcaneocuboid joint, plantar ligaments, and posterior talar facet. At birth, thin trabecular struts are arranged in a dense and relatively isotropic structure. Bone volume fraction strongly decreases in the first year of life, whereas anisotropy and mean trabecular thickness increase. Dorsal compressive trabecular bands appear around the onset of bipedal walking, although plantar tensile bands develop prior to predicted propulsive toe-off. Bone volume fraction and anisotropy increase until the age of 8, when gait has largely matured. Connectivity density gradually reduces, whereas trabeculae gradually thicken from birth until adulthood. This study demonstrates that three different regions of the calcaneus develop into distinct adult morphologies through varying developmental trajectories. These results are similar to previous reports of ontogeny in human long bones and are suggestive of a relationship between the mechanical environment and trabecular bone architecture in the human calcaneus during growth. However, controlled experiments combined with more detailed biomechanical models of gait maturation are necessary to establish skeletal markers linking growth to loading. This has the potential to be a novel source of information for understanding loading levels, activity patterns, and perhaps life history in the fossil record.     

Investigation of the failure behaviour of vertebral trabecular architectures under uni-axial compression and wedge action loading conditions

Vertebral wedge fractures are associated with combined compression and flexure loading and are the most common fracture type for human vertebrae. In this study, rapid prototype (RP) biomodels of human vertebral trabecular bone were mechanically tested under uni-axial compression loading and also under wedge action loading (combination of compression and flexure loading) to investigate the mode of failure and the ultimate loads that could be sustained under these different loading conditions. Two types of trabecular bone models were manufactured and tested: baseline models which were directly derived from μCT scans of human thoracic vertebrae, and osteoporotic models which were generated from the baseline models using a custom-developed bone loss algorithm. The ultimate load for each model under compression and wedge action loading was determined and a video was recorded of each test so that failure mechanisms could be evaluated. The results of the RP model mechanical tests showed that the ultimate loads that could be supported by vertebral trabecular architectures under wedge action loading were less than those that could be supported under uni-axial compression loading by up to 26%. Also, the percentage reduction in strength from the baseline value due to osteoporotic bone loss was slightly less for the wedge action loading compared to uni-axial compression loading. Analysis of the videos for each test revealed that failure occurred in localised regions of the trabecular structure due to bending and buckling of thin vertical struts. These results suggest that vertebral trabecular bone is more susceptible to failure from wedge action loading compared to uni-axial compression loading, although this effect is not exacerbated by osteoporotic bone loss.     

The three-dimensional microstructure of the trabecular bone in the mandible

This study investigated the three dimensional (3D) trabecular microstructure of the alveolar and basal bone in the mandible using micro-CT and compared the morphometric values of the different sites. Ten specimens were prepared and scanned using a micro-CT system. Both the alveolar and basal trabecular bone of the premolar region in the mandible were measured for the structural analysis. Cross-sectional 1024×1024 pixel images were created. From the two-dimensional (2D) images produced, 3D structural images were reconstructed. After scanning the specimen, the volumes of interest (VOI) of the alveolar and basal bone regions were selected from the 3D reconstruction images, and the structural parameters such as bone volume fraction, bone surface density, trabecular thickness, trabecular separation, trabecular number and structural model index were analyzed. The trabecular structure showed a marked variation within the sites of the specimen, especially in the basal trabecular bone inferior to the mandibular canal. In both the alveolar and basal bone regions, a mixture of both plate-like and rod-like structures was observed. The alveolar region showed a more compact, plate-type trabecular structure than the basal regions. In parametric comparison with the basal bone, the alveolar bone generally had a higher bone volume fraction, bone trabecular thickness and trabecular number, and lower bone surface density, trabecular separation and structural model index. The alveolar bone consisted of a compact bone structure with a large amount of thick plate-type trabecular bone, which was effectively resistant to the masticatory forces. As the measurements were made closer to the basal bone, a loose structure was observed with lower bone volume and fewer, thin, rod-like trabeculae.     

股骨近端主张力骨小梁生物力学特性

目的 研究股骨近端主张力骨小梁的生物力学性能,为解释股骨颈骨折后股骨头坏死的发生原因提供实验依据.方法 取8个正常国人(45 ～60岁)尸体股骨,排除畸形、骨折等病变.将近端主张力骨小梁系统从外侧到内侧分成3个区,在每个区内沿主张力小梁方向及与其垂直方向切取骨小梁试件,并分别在EnduraTEC ELF3200生物力学...     

Trabecular architecture of the great ape and human femoral head

Studies of femoral trabecular structure have shown that the orientation and volume of bone are associated with variation in loading and could be informative about individual joint positioning during locomotion. In this study, we analyse for the first time trabecular bone patterns throughout the femoral head using a whole‐epiphysis approach to investigate how potential trabecular variation in humans and great apes relates to differences in locomotor modes. Trabecular architecture was analysed using microCT scans of Pan troglodytes (n = 20), Gorilla gorilla (n = 14), Pongo sp. (n = 5) and Homo sapiens (n = 12) in medtool 4.1. Our results revealed differences in bone volume fraction (BV/TV) distribution patterns, as well as overall trabecular parameters of the femoral head between great apes and humans. Pan and Gorilla showed two regions of high BV/TV in the femoral head, consistent with hip posture and loading during two discrete locomotor modes: knuckle‐walking and climbing. Most Pongo specimens also displayed two regions of high BV/TV, but these regions were less discrete and there was more variability across the sample. In contrast, Homo showed only one main region of high BV/TV in the femoral head and had the lowest BV/TV, as well as the most anisotropic trabeculae. The Homo trabecular structure is consistent with stereotypical loading with a more extended hip compared with great apes, which is characteristic of modern human bipedalism. Our results suggest that holistic evaluations of femoral head trabecular architecture can reveal previously undetected patterns linked to locomotor behaviour in extant apes and can provide further insight into hip joint loading in fossil hominins and other primates.     

The ability of quantitative ultrasound to predict the mechanical properties of trabecular bone under different strain rates

The ability of quantitative ultrasound to predict the mechanical properties of trabecular bone under different strain rates was investigated. Ultrasound velocity (UV) and broadband attenuation (BUA) were measured for 60 specimens of human trabecular bone. Samples were divided into two equal groups and loaded in compression at the strain rates of 0.0004 and 0.08 s⁻¹. The ultimate strength, elastic modulus, and energy absorption capacity were determined for each specimen. Specimens tested at 0.08 s⁻¹ had a mean value of strength 63% higher than the specimens tested at 0.0004 s⁻¹. The elastic modulus and energy absorption capacity were 82% and 42% higher, respectively, for the higher strain rate. UV and BUA were significantly associated with most mechanical properties at both strain rates. All mechanical properties were also correlated strongly with a linear combination of UV and BUA for both the low and high loading rates. The use of ultrasound parameters may provide good clinical means for assessing the resistance of trabecular bone to both low and high energy trauma.     

激素性股骨头坏死与股骨颈骨折患者股骨头内骨小梁形态学对比研究

目的利用微计算机断层扫描技术(Micro-CT)对比分析激素性股骨头坏死与股骨颈骨折患者的股骨头内骨小梁的结构特点。 方法选取2016年9月至2017年9月因股骨颈骨折与激素性股骨头坏死于大连大学附属中山医院行人工全髋关节置换术的患者,分别设为骨折组与坏死组,每组各20例(20髋),术中完整取出股骨头作为研究材料。应用计算机对股骨头进行三维重建,利用x、y、z轴各2个相互平行的平面将股骨头分割成27个区域,27个区域的编号规则：分为内侧、中间、外侧3个区,每组按照由前向后、由上向下的顺序编为1～9号。内侧区编号为m1、m2……m9;中间区编号为c1、c2……c9;外侧区编号为l1、l2……l9。对样本进行Micro-CT断层扫描,获取股骨头样本的计算机三维图像。手工选取兴趣区,采用骨体积分数、骨小梁厚度、骨小梁数量、骨小梁间隙等三维空间参数分别对2组股骨头内骨小梁进行评价。数据比较采用t检验和单因素方差分析。 结果在骨折组中,将股骨头按矢状面分割为内侧区、中间区、外侧区进行对比,中间区表现为骨体积分数均值最大、厚度均值最大、数量均值最大、间隙均值最小的优势骨小梁区域,差异均有统计学意义(F＝36.59、73.50、38.60、48.50,P值均小于0.05);将股骨头按冠状面分割为前区、中间区、后区进行对比,前区表现为骨体积分数均值最大、厚度均值最大、数量均值最大、间隙均值最小,差异均有统计学意义(F＝69.50、43.92、85.40、36.00,P值均小于0.05);将股骨头按水平面分割为上区、中间区、下区进行对比,上区表现为骨体积分数均值最大、厚度均值最大、数量均值最大、间隙均值最小,差异均有统计学意义(F＝37.03、29.47、255.50、45.50,P值均小于0.05)。对比坏死组股骨头不同部位骨小梁微结构参数,如果将股骨头分为内侧区、中间区、外侧区,中间区表现为骨体积分数均值最大、厚度均值最大、数量均值最大、间隙均值最小的优势骨小梁区域,差异均有统计学意义(F＝41.42、26.60、400.00、36.00,P值均小于0.05);如果将股骨头分为上区、中间区、下区,上区表现为骨体积分数均值最大、厚度均值最大、数量均值最大、间隙均值最小,差异均有统计学意义(F＝52.99、25.33、28.50、37.33,P值均小于0.05);如果将股骨头分为前区、中间区、后区,前区表现为骨体积分数均值最大、厚度均值最大、数量均值最大、间隙均值最小,差异均有统计学意义(F＝2 567.17、57.29、42.11、41.17,P值均小于0.05)。与坏死组相比,骨折组骨小梁骨体积分数均值更大,差异有统计学意义(t＝4.90,P＝0.01)、骨小梁厚度均值更大,差异有统计学意义(t＝－4.17,P＝0.01)、骨小梁数量均值更大,差异有统计学意义(t＝－31.37,P＝0.01),骨小梁间隙均值更小,差异有统计学意义(t＝－7.12,P＝0.01)。 结论激素对于坏死股骨头的影响不仅仅是坏死区,包括硬化区、正常骨小梁区,即对于整个股骨头都产生了影响。     

不同角度载荷下股骨头骨小梁的生物力学特性

目的 探讨不同角度载荷对股骨头骨小梁形态学与力学性能的影响,为研究股骨头坏死、塌陷的生物力学机制提供理论依据。方法 利用12月龄羊股骨头和人尸体股骨头分别制作羊股骨头骨小梁试件94个和人股骨头骨小梁试件43个。按照受力方向与骨小梁主压力方向之间的不同夹角,将骨小梁以10°间隔分为内翻10°、0°和外翻10°、20°、30°共计5组,模拟股骨颈骨折内固定术后不同戈登（Garden）对线指数下的复位情况。通过分别对羊股骨头骨小梁进行micro-CT扫描、计算与压缩破坏试验以及对人尸体股骨头骨小梁进行循环压缩试验,分析不同受力方向下股骨头骨小梁的骨体积分数（BV/TV）、骨表面积/骨体积（BS/BV）、骨小梁平均厚度（Tb.Th）、骨小梁数量（Tb.N）、骨小梁间距（Tb.Sp）等形态学指标以及弹性模量、极限强度、屈服强度、初始弹性模量、循环次数等力学指标。结果 加载方向与骨小梁的主压力方向之间夹角为0°时,BV/TV、Tb.Th以及弹性模量、极限强度、屈服强度、初始弹性模量、循环次数均为最大,而BS/BV与Tb.N为最小,并随着夹角增大前者呈递减而后者呈递增趋势。结论 12月龄羊股骨头骨小梁BV/TV与极限强度随受力方向与骨小梁主压力方向之间夹角变化的趋势与人股骨头骨小梁一致;加载方向与主压力骨小梁之间夹角增大时,股骨头骨小梁形态学与力学性能均下降;Garden指数偏离160°越大时,股骨头内骨小梁越易发生损伤。     

Similar damage initiation but different failure behavior in trabecular and cortical bone tissue

The mechanical properties of bone tissue are reflected in its micro- and nanostructure as well as in its composition. Numerous studies have compared the elastic mechanical properties of cortical and trabecular bone tissue and concluded that cortical bone tissue is stiffer than trabecular bone tissue. This study compared the progression of microdamage leading to fracture and the related local strains during this process in trabecular and cortical bone tissue. Unmachined single bovine trabeculae and similarly-sized cortical bovine bone samples were mechanically tested in three-point bending and concomitantly imaged to assess local strains using a digital image correlation technique. The bone whitening effect was used to detect microdamage formation and propagation. This study found that cortical bone tissue exhibits significantly lower maximum strains (trabecular 36.6%±14% vs. cortical 22.9%±7.4%) and less accumulated damage (trabecular 16100±8800 pix/mm2 vs. cortical 8000±3400 pix/mm2) at failure. However, no difference was detected for the maximum local strain at whitening onset (trabecular 5.8%±2.6% vs. cortical 7.2%±3.1%). The differences in elastic modulus and mineral distribution in the two tissues were investigated, using nanoindentation and micro-Raman imaging, to explain the different mechanical properties found. While cortical bone was found to be overall stiffer and more highly mineralized, no apparent differences were noted in the distribution of modulus values or mineral density along the specimen diameter. Therefore, differences in the mechanical behavior of trabecular and cortical bone tissue are likely to be in large part due to microstructural (i.e. orientation and distribution of cement lines) and collagen related compositional differences.     

不同角度载荷下股骨头骨小梁的生物力学特性

目的探讨不同角度载荷对股骨头骨小梁形态学与力学性能的影响,为研究股骨头坏死、塌陷的生物力学机制提供理论依据。方法利用12月龄羊股骨头和人尸体股骨头分别制作羊股骨头骨小梁试件94个和人股骨头骨小梁试件43个。按照受力方向与骨小梁主压力方向之间的不同夹角,将骨小梁以10°间隔分为内翻10°、0°和外翻10°、20°、30°共计5组,模拟股骨颈骨折内固定术后不同戈登(Garden)对线指数下的复位情况。通过分别对羊股骨头骨小梁进行micro-CT扫描、计算与压缩破坏试验以及对人尸体股骨头骨小梁进行循环压缩试验,分析不同受力方向下股骨头骨小梁的骨体积分数(BV/TV)、骨表面积/骨体积(BS/BV)、骨小梁平均厚度(Tb.Th)、骨小梁数量(Tb.N)、骨小梁间距(Tb.Sp)等形态学指标以及弹性模量、极限强度、屈服强度、初始弹性模量、循环次数等力学指标。结果加载方向与骨小梁的主压力方向之间夹角为0°时,BV/TV、Tb.Th以及弹性模量、极限强度、屈服强度、初始弹性模量、循环次数均为最大,而BS/BV与Tb.N为最小,并随着夹角增大前者呈递减而后者呈递增趋势。结论 12月龄羊股骨头骨小梁BV/TV与极限强度随受力方向与骨小梁主压力方向之间夹角变化的趋势与人股骨头骨小梁一致;加载方向与主压力骨小梁之间夹角增大时,股骨头骨小梁形态学与力学性能均下降;Garden指数偏离160°越大时,股骨头内骨小梁越易发生损伤。     

不同角度载荷下股骨头骨小梁的生物力学特性

目的 探讨不同角度载荷对股骨头骨小梁形态学与力学性能的影响,为研究股骨头坏死、塌陷的生物力学机制提供理论依据。方法 利用12月龄羊股骨头和人尸体股骨头分别制作羊股骨头骨小梁试件94个和人股骨头骨小梁试件43个。按照受力方向与骨小梁主压力方向之间的不同夹角,将骨小梁以10°间隔分为内翻10°、0°和外翻10°、20°、30°共计5组,模拟股骨颈骨折内固定术后不同戈登（Garden）对线指数下的复位情况。通过分别对羊股骨头骨小梁进行micro-CT扫描、计算与压缩破坏试验以及对人尸体股骨头骨小梁进行循环压缩试验,分析不同受力方向下股骨头骨小梁的骨体积分数（BV/TV）、骨表面积/骨体积（BS/BV）、骨小梁平均厚度（Tb.Th）、骨小梁数量（Tb.N）、骨小梁间距（Tb.Sp）等形态学指标以及弹性模量、极限强度、屈服强度、初始弹性模量、循环次数等力学指标。结果 加载方向与骨小梁的主压力方向之间夹角为0°时,BV/TV、Tb.Th以及弹性模量、极限强度、屈服强度、初始弹性模量、循环次数均为最大,而BS/BV与Tb.N为最小,并随着夹角增大前者呈递减而后者呈递增趋势。结论 12月龄羊股骨头骨小梁BV/TV与极限强度随受力方向与骨小梁主压力方向之间夹角变化的趋势与人股骨头骨小梁一致;加载方向与主压力骨小梁之间夹角增大时,股骨头骨小梁形态学与力学性能均下降;Garden指数偏离160°越大时,股骨头内骨小梁越易发生损伤。