Mechanical Properties of the Hindlimb Bones of Bullfrogs and Cane Toads in Bending and Torsion

When compared with most vertebrates, frogs use a novel style of jumping locomotion powered by the hindlimbs. Hindlimb bones of frogs must withstand the potentially erratic loads associated with such saltatory locomotion. To evaluate the load bearing capacity of anuran limb bones, we used three‐point bending, torsion, and hardness tests to measure the mechanical properties of the femur and tibiofibula from adults of two species that use different jumping styles: explosively jumping bullfrogs (Rana (Lithobates) catesbeiana) and cyclically hopping cane toads (Bufo (Chaunus) marinus). Yield stress and strain values for R. catesbeiana and B. marinus hindlimb bones are within the range of values previously reported for other vertebrates. However, anuran hindlimb bones generally stand out as having higher yield stresses in bending than those of closely related, nonsaltatory salamanders, highlighting the importance of considering phylogenetic context in comparisons of bone functional capacity and adaptation. Stiffness values for both frog species tested were also high, which may facilitate efficient transmission of muscular forces while jumping. Elevated stiffness may also contribute to some discrepancies between determinations of bone properties via hardness versus bending tests. In comparisons between species, B. marinus bones showed significantly higher bending yield stresses than R. catesbeiana, whereas R. catesbeiana bones showed significantly higher torsional yield stresses than B. marinus. These differences may correlate with differences in jumping style and limb anatomy between ranid and bufonid frogs, suggesting that evolutionary changes in bone mechanical properties may help to accommodate new functional demands that emerge in lineages. Anat Rec, 292:935–944, 2009. © 2009 Wiley‐Liss, Inc.     

Quantifying morphological adaptations using direct measurements: The carnivoran appendicular skeleton as a case study

Here, I study whether locomotor adaptations can be detected in limb bones using a univariate approach, and whether those results are affected by size and/or shared evolutionary history. Ultimately, it tests whether classical papers on locomotor adaptations should be trusted. To do that, I analyzed the effect of several factors (size, taxonomic group, and locomotor habit) on limb bone morphology using a set of 43 measurements of the scapula, long bones, and calcaneus, of 435 specimens belonging to 143 carnivoran species. Size was the main factor affecting limb morphology. Size-corrected analyses revealed artifactual differences between various locomotion-related categories in the analyses of raw data. Additionally, several between-group differences were new to the size-corrected analyses, suggesting that they were masked by the size-effect. Phylogeny had also an important effect, although it only became apparent after removing the effect of size, probably due to the strong covariation of both factors. Regarding locomotor adaptations, locomotor type was used to represent locomotor specialization, and utilized habitat as an indicator of the capacity to adopt different modes of locomotion (running, swimming, climbing, and digging) and thus maximize resource exploitation by being capable of navigating all the substrates in the habitat they use. Locomotor type produced better results than utilized habitat, suggesting that carnivorans use locomotor specialization to minimize locomotion costs. The characteristic limb bone morphology for each locomotor type studied is described, including several adaptations and trends that are novel to the present study. Finally, the results presented here support the hypothesis of a “viverrid-like”, forest-dwelling carnivoran ancestor, either arboreal or terrestrial.     

Adaptation of diaphyseal structure with aging and increased mechanical usage in the adult rat: a histomorphometrical and biomechanical study

The experimental increase in mechanical usage or overloading of the left hindlimb was produced by immobilization of the contralateral hindlimb. The right hindlimb was placed in a flexed position against the body and was immobilized using an elastic bandage. Some control animals were sacrificed initially at time zero and increased mechanical usage and age-matched control animals were sacrificed after 2, 10, 18, and 26 weeks of treatment. All animals received double bone fluorochrome labeling prior to sacrifice. Cortical bone histomorphometry and cross-sectional moments of inertia were determined. Marrow cavity enlargement and total cross-sectional area expansion represented the age-related cortical bone changes. Increased mechanical usage enhanced periosteal bone modeling in the formation mode and dampened endocortical bone remodeling and bone modeling in the resorption mode (resorption drift) to create a slight positive bone balance. These observations are in general agreement with Frost's postulate for mechanical effects on bone modeling and remodeling (Frost, H.M. 1987b. Bone "mass" and the "mechanostat." A proposal. Anat. Rec. 219: 1-9). The maximum moment of inertia did not change significantly in either control or overloaded tibial shafts. The minimum and polar moment of inertias in overloaded bones increases over those of controls at 18 and 26 weeks of the experiment.     

动载荷作用下骨重建力学调控机制

目的探讨动载荷作用下骨重建的力学调控机制。方法对骨重建力学调控机制进行分析,吸纳力学疲劳强度理论思想,提出动载荷作用下骨重建力学调控机制;选取损伤作为力学激励,建立动载荷骨重建模型;分析动态载荷成骨效果优于静态载荷现象,数值模拟运动防治骨质疏松。结果动态载荷成骨效果优于静态载荷现象得到较为合理的解释;运动量增加10%~30%,骨密度增加3.13%~8.61%。结论动载荷作用下骨重建的力学调控机制可为机械振动防治骨代谢相关疾病提供理论指导,是骨重建力学调控理论的补充和完善。     

不同力学激励对骨重建数值模拟的影响

目的研究采用应变能密度、等效应力、等效应变3种不同力学激励对骨重建数值模拟结果的影响。方法建立股骨近端的二维有限元模型,基于力学稳态理论的重建控制方程并结合有限元法,分别用3种不同力学激励模拟股骨近端的内部结构及密度分布,并与CT数据计算得到的骨密度值进行定量分析比较。结果 3种力学激励模拟得到的重建结果均能反映出股骨近端的主要特征结构,但采用等效应力作为激励时得到的股骨密度曲线图的趋势和数值都与CT图像数据更为一致。结论在骨重建力学调控机制中,应力可能起主导作用。准确预测和模拟骨重建过程将对矫形外科、骨伤治疗、人工假体的优化和个体化设计等临床实践提供理论依据。     

Dynamics of recovery of morphometrical variables and pQCT-derived cortical bone properties after a short-term protein restriction in maturing rats

Severe protein restriction during the post-weaning period in the rat markedly reduces femoral bone mass and produces a number of alterations in the shaft biomechanical properties. Body weight and femur length show an immediate and complete catch-up during nutritional rehabilitation. The aim of the present investigation was to assess whether the accelerated bone growth that occurs during protein rehabilitation is accompanied by recovery of cortical bone properties. The dynamics of the recovery of both material and geometric properties were thus evaluated on the femoral diaphyses in 45-day old female rats after a 10-day period of dietary protein restriction by peripheral quantitative computed tomography (pQCT). Protein starvation led to marked reduction of both body weight and femoral length (37% and 14% at day 10, respectively) which showed a complete catch-up after 30 d of protein refeeding. Protein restriction was associated with the interruption of the natural increase in cortical area (CtCSA), volumetric cortical bone mineral content (vCtBMC) and volumetric cortical bone mineral density (vCtBMD) which were 19.7, 25.8, and 14%, respectively, in malnourished than in control rats at the end of the protein starvation period. These parameters recovered completely during protein refeeding. Treatment also reduced by 30% both rectangular (xCSMI) and polar (pCSMI) moments of inertia. Although an improvement of these architectural indicators occurred with time, an approximately 20% deficit was still present at the end of the observation period (70 d), as was the bone strength index (BSI). It is concluded that protein restriction affected the adaptation of diaphyseal design which should reduce the mechanical competence of the femoral diaphysis because of an inadequate architectural distribution of cortical bone, and that the alteration did not show complete catch-up during the studied period.     

Bilateral symmetry of biomechanical properties in mouse femora

Bone healing and remodeling are commonly examined in animal models by comparing one femur (experimental) to the contralateral femur (control) with the assumption that they are identical with respect to their biomechanical properties. While past studies have characterized the symmetry in geometrical properties in many types of animal bones, few studies have compared the symmetry in the biomechanical properties. The purpose of this study was to determine whether there is symmetry in the mechanical properties of mouse femora. Strain gauges were attached to the posterior surface of the femora of C57BL/6 mice, parallel to the long axis of the bone. The femora were mechanically tested in cantilever bending while strain values were recorded. Moments of inertia, cortical areas, and moduli of elasticity were determined from strains and cross-sectional properties. Mouse femora demonstrated an average strain difference of 0.4% in tension and 1.4% in compression. Elastic moduli differed by 6.6% and 0.9% in tension and compression, respectively, and failure strength differed by an average of 2.0%. Statistical analysis showed there were no significant differences in strain, modulus, or failure load values for the mice, indicating mechanical and geometrical symmetry of mouse femora in cantilever bending.     

An experimental study on the biomechanical properties of the cancellous bones of distal femur

OBJECTIVES: To study the comprehensive biomechanical properties of the cancellous bone of distal femur through a series of mechanical tests, and provide relevant subjects with the basic technical data. BACKGROUNDS: The study on bone mechanics is a commonly used approach to evaluate the biomechanical competency of bone. The biomechanical properties of bone have come to be the precondition of the further research of these relevant clinical subjects. METHODS: In this paper, comprehensive items of mechanical properties of the cancellous bones of distal femur were conducted, and many valuable test results were obtained through a series of mechanical tests, which comprised tensile test, compression test, torsion test, shear test, bending test and impact test. The specimens were extracted from the normal corpses of Chinese donors died from acute head injury. As another key problem in this kind of experiment, the sampling and fixing method of cancellous bones specimens was developed and optimized in this research. RESULTS: A series of the experimental data of mechanical properties of cancellous bones were obtained in the tests, these experimental data include tensile strength, compression strength, yield tensile strength, modulus of elasticity, torsion strength, shear strength, torsion modulus, bending strength, yield shear limit and impact toughness, which can reflect the complex mechanical competency of bone, being of great value and practice in clinic and further research on cancellous bones. The mechanical properties of the cancellous bones of distal femur were analyzed and discussed. CONCLUSIONS: The biomechanical properties of the cancellous bones have a close relationship with individual difference. Comprehensive items of the mechanical properties of the bone can evaluate the mechanical performance of the bone better, and can provide more valuable data to relevant research.     

Regional variation in the mechanical properties of cortical bone from the porcine femur

Despite the widespread use of porcine bone as a substitute for human bone in the development of surgical technique and the use of fixation devices, relatively few studies have reported on the mechanical behaviour of porcine long bones. Regional variation in the mechanical properties of cortical bone from porcine femora was investigated using three-point bending and cutting tests. Results were related to measurements of bone architecture and composition and Rutherford backscattering spectrometry (RBS) was used to calculate the calcium to phosphorus ratio. There was significant, but limited, regional variation in the strength of the femur with bone from the distal, posterior quadrant (241.4 ± 10.43 MPa) being significantly stronger than that of the lateral quadrant (162.3 ± 17.96 MPa). Cortical bone was also anisotropic; samples cut transverse to the bone's axis were around six times tougher than those cut parallel to the axis (p<0.05). This corresponded with a significant negative correlation between the Young's modulus and toughness when cut along the longitudinal axis. RBS analysis of cortical bone samples gave a Ca:P ratio of 1.37 ± 0.035, somewhat lower than that reported for cortical bone of adult human femora. These results indicate that the mechanical properties of cortical bone show significant, but limited, variation around the porcine femur and that this should be taken into consideration when sampling and choosing an appropriate animal model for orthopaedic biomechanics research.     

Linear and Geometric Morphometric Analysis of Long Bone Scaling Patterns in Jurassic Neosauropod Dinosaurs: Their Functional and Paleobiological Implications

Neosauropod dinosaurs were gigantic, herbivorous dinosaurs. Given that the limb skeleton is essentially a plastic, mobile framework that supports and moves the body, analysis of long bone scaling can reveal limb adaptations that supported neosauropod gigantism. Previously, analyses of linear dimensions have revealed a relatively isometric scaling pattern for the humerus and femur of neosauropods. Here, a combined scaling analysis of humerus and femur linear dimensions, cortical area, and shape across six neosauropod taxa is used to test the hypothesis that neosauropod long bones scaled isometrically and to investigate the paleobiological implications of these trends. A combination of linear regression and geometric morphometrics analyses of neosauropod humeri and femora were performed using traditional and thin‐plate splines approaches. The neosauropod sample was very homogeneous, and linear analyses revealed that nearly all humerus and femur dimensions, including cortical area, scale with isometry against maximum length. Thin‐plate splines analyses showed that little to no significant shape change occurs with increasing length or cortical area for the humerus or femur. Even with the exclusion of the long‐limbed Brachiosaurus, the overall trends were consistently isometric. These results suggest that the mechanical advantage of limb‐moving muscles and the relative range of limb movement decreased with increasing size. The isometric signal for neosauropod long bone dimensions and shape suggests these dinosaurs may have reached the upper limit of vertebrate long bone mechanics. Perhaps, like stilt‐walkers, the absolutely long limbs of the largest neosauropods allowed for efficient locomotion at gigantic size with few ontogenetic changes. Anat Rec, 290:1089–1111, 2007. © 2007 Wiley‐Liss, Inc.     

Microanatomical Record of Cortical Bone Remodeling and High Vascularity in a Fossil Giant Rat Midshaft Femur

Rat cortical bone does not typically undergo secondary (Haversian) remodeling. Haversian organization of rat bone has been mainly observed in experimental settings following biomechanical or dietary manipulation. Here, we report an observation of cortical secondary osteons within a histological femur cross-section from an extinct (late Quaternary) form of Timorese giant rat (Murinae gen. et sp. indet). The medio-lateral midshaft diameter of its femur, used as a measure of bone size, is 6.15 mm and indicates a heavier than normal skeletal frame. We compare this sample to bone histology in a small rat's midshaft femur of 2.33 mm diameter. A complete lack of Haversian bone remodeling characteristics is noted for the smaller sample, which is dominated by radial vascular canals. The giant rat shows clear secondary osteons and diffuse vascularity mainly composed of tightly packed longitudinal canals across its cortex. It appears that rat cortical bone can undergo bone remodeling, and is organized in a highly vascularized manner, in insular giant cases. Our findings from Timor align with results reported in experimental rat model skeletal biology literature and other insular fossil rat material. Where macroanatomical examination is limited, histological observations on fossil rat limb bones have the potential to aid reconstructions of life history and skeletal growth aspects in these rodents. Anat Rec, 302:1934–1940, 2019. © 2019 American Association for Anatomy     

Limb bone morphology,bone strength,and cursoriality in lagomorphs

The primary aim of this study is to broadly evaluate the relationship between cursoriality (i.e. anatomical and physiological specialization for running) and limb bone morphology in lagomorphs. Relative to most previous studies of cursoriality, our focus on a size‐restricted, taxonomically narrow group of mammals permits us to evaluate the degree to which ‘cursorial specialization’ affects locomotor anatomy independently of broader allometric and phylogenetic trends that might obscure such a relationship. We collected linear morphometrics and μCT data on 737 limb bones covering three lagomorph species that differ in degree of cursoriality: pikas (Ochotona princeps, non‐cursorial), jackrabbits (Lepus californicus, highly cursorial), and rabbits (Sylvilagus bachmani, level of cursoriality intermediate between pikas and jackrabbits). We evaluated two hypotheses: cursoriality should be associated with (i) lower limb joint mechanical advantage (i.e. high ‘displacement advantage’, permitting more cursorial species to cycle their limbs more quickly) and (ii) longer, more gracile limb bones, particularly at the distal segments (as a means of decreasing rotational inertia). As predicted, highly cursorial jackrabbits are typically marked by the lowest mechanical advantage and the longest distal segments, non‐cursorial pikas display the highest mechanical advantage and the shortest distal segments, and rabbits generally display intermediate values for these variables. Variation in long bone robusticity followed a proximodistal gradient. Whereas proximal limb bone robusticity declined with cursoriality, distal limb bone robusticity generally remained constant across the three species. The association between long, structurally gracile limb bones and decreased maximal bending strength suggests that the more cursorial lagomorphs compromise proximal limb bone integrity to improve locomotor economy. In contrast, the integrity of distal limb bones is maintained with increasing cursoriality, suggesting that the safety factor takes priority over locomotor economy in those regions of the postcranial skeleton that experience higher loading during locomotion. Overall, these findings support the hypothesis that cursoriality is associated with a common suite of morphological adaptations across a range of body sizes and radiations.     

Correlation between wing bone microstructure and different flight styles: The case of the griffon vulture (gyps fulvus) and greater flamingo (phoenicopterus roseus)

Flying is the main means of locomotion for most avian species, and it requires a series of adaptations of the skeleton and of feather distribution on the wing. Flight type is directly associated with the mechanical constraints during flight, which condition both the morphology and microscopic structure of the bones. Three primary flight styles are adopted by avian species: flapping, gliding, and soaring, with different loads among the main wing bones. The purpose of this study was to evaluate the cross-sectional microstructure of the most important skeletal wing bones, humerus, radius, ulna, and carpometacarpus, in griffon vultures (Gyps fulvus) and greater flamingos (Phoenicopterus roseus). These two species show a flapping and soaring flight style, respectively. Densitometry, morphology, and laminarity index were assessed from the main bones of the wing of 10 griffon vultures and 10 flamingos. Regarding bone mineral content, griffon vultures generally displayed a higher mineral density than flamingos. Regarding the morphology of the crucial wing bones involved in flight, while a very slightly longer humerus was observed in the radius and ulna of flamingos, the ulna in griffons was clearly longer than other bones. The laminarity index was significantly higher in griffons. The results of the present study highlight how the mechanics of different types of flight may affect the biomechanical properties of the wing bones most engaged during flight.     

Interpreting the three‐dimensional orientation of vascular canals and cross‐sectional geometry of cortical bone in birds and bats

Cortical bone porosity and specifically the orientation of vascular canals is an area of growing interest in biomedical research and comparative/paleontological anatomy. The potential to explain microstructural adaptation is of great interest. However, the determinants of the development of canal orientation remain unclear. Previous studies of birds have shown higher proportions of circumferential canals (called laminarity) in flight bones than in hindlimb bones, and interpreted this as a sign that circumferential canals are a feature for resistance to the torsional loading created by flight. We defined the laminarity index as the percentage of circumferential canal length out of the total canal length. In this study we examined the vascular canal network in the humerus and femur of a sample of 31 bird and 24 bat species using synchrotron micro‐computed tomography (micro‐CT) to look for a connection between canal orientation and functional loading. The use of micro‐CT provides a full three‐dimensional (3D) map of the vascular canal network and provides measurements of the 3D orientation of each canal in the whole cross‐section of the bone cortex. We measured several cross‐sectional geometric parameters and strength indices including principal and polar area moments of inertia, principal and polar section moduli, circularity, buckling ratio, and a weighted cortical thickness index. We found that bat cortices are relatively thicker and poorly vascularized, whereas those of birds are thinner and more highly vascularized, and that according to our cross‐sectional geometric parameters, bird bones have a greater resistance to torsional stress than the bats; in particular, the humerus in birds is more adapted to resist torsional stresses than the femur. Our results show that birds have a significantly (P = 0.031) higher laminarity index than bats, with birds having a mean laminarity index of 0.183 in the humerus and 0.232 in the femur, and bats having a mean laminarity index of 0.118 in the humerus and 0.119 in the femur. Counter to our expectation, the birds had a significantly higher laminarity index in the femur than in the humerus (P = 0.035). To evaluate whether this discrepancy was a consequence of methodology we conducted a comparison between our 3D method and an analogue to two‐dimensional (2D) histological measurements. This comparison revealed that 2D methods significantly underestimate (P < 0.001) the amount of longitudinal canals by an average of 20% and significantly overestimate (P < 0.001) the laminarity index by an average of 7.7%, systematically mis‐estimating indices of vascular canal orientations. In comparison with our 3D results, our approximated 2D measurement had the same results for comparisons between the birds and bats but found significant differences only in the longitudinal index between the humerus and the femur for both groups. The differences between our 3D and pseudo‐2D results indicate that differences between our findings and the literature may be partially based in methodology. Overall, our results do not support the hypothesis that the bones of flight are more laminar, suggesting a complex relation between functional loading and microstructural adaptation.     

Exploring Femoral Diaphyseal Shape Variation in Wild and Captive Chimpanzees by Means of Morphometric Mapping: A Test of Wolff's Law

Long bone shafts (diaphyses) serve as load‐bearing structures during locomotion, implying a close relationship between diaphyseal form and its locomotor function. Diaphyseal form‐function relationships, however, are complex, as they are mediated by various factors such as developmental programs, evolutionary adaptation, and functional adaptation through bone remodeling during an individual's lifetime. The effects of the latter process (“Wolff's Law”) are best assessed by comparing diaphyseal morphologies of conspecific individuals under different locomotor regimes. Here we use morphometric mapping (MM) to analyze the morphology of entire femoral diaphyses in an ontogenetic series of wild and captive common chimpanzees (Pan troglodytes troglodytes). MM reveals patterns of variation of diaphyseal structural and functional properties, which cannot be recognized with conventional cross‐sectional analysis and/or geometric morphometric methods. Our data show that diaphyseal shape, cortical bone distribution and inferred cross‐sectional biomechanical properties vary both along ontogenetic trajectories and independent of ontogeny. Mean ontogenetic trajectories of wild and captive chimpanzees, however, were found to be statistically identical. This indicates that the basic developmental program of the diaphysis is not altered by different loading conditions. Significant differences in diaphyseal shape between groups could only be identified in the distal diaphysis, where wild chimpanzees exhibit higher mediolateral relative to anteroposterior cortical bone thickness. Overall, thus, the hypothesis that Wolff's Law predominantly governs long bone diaphyseal morphology is rejected. Anat Rec, 2011. © 2011 Wiley‐Liss, Inc.     

Bone's mechanostat: a 2003 update

The still-evolving mechanostat hypothesis for bones inserts tissue-level realities into the former knowledge gap between bone's organ-level and cell-level realities. It concerns load-bearing bones in postnatal free-living bony vertebrates, physiologic bone loading, and how bones adapt their strength to the mechanical loads on them. Voluntary mechanical usage determines most of the postnatal strength of healthy bones in ways that minimize nontraumatic fractures and create a bone-strength safety factor. The mechanostat hypothesis predicts 32 things that occur, including the gross anatomical bone abnormalities in osteogenesis imperfecta; it distinguishes postnatal situations from baseline conditions at birth; it distinguishes bones that carry typical voluntary loads from bones that have other chief functions; and it distinguishes traumatic from nontraumatic fractures. It provides functional definitions of mechanical bone competence, bone quality, osteopenias, and osteoporoses. It includes permissive hormonal and other effects on bones, a marrow mediator mechanism, some limitations of clinical densitometry, a cause of bone "mass" plateaus during treatment, an "adaptational lag" in some children, and some vibration effects on bones. The mechanostat hypothesis may have analogs in nonosseous skeletal organs as well.     

利用生物力学方法评价振动在骨质疏松康复过程中的作用

目的 通过研究基于Micro CT数据的大鼠股骨皮质骨材料性质与力学性能的关系,探讨振动在对抗骨量丢失过程中的生物力学评价方法。方法 Wistar大鼠35只,尾部悬吊建立废用性骨质疏松模型,随机分为间歇振动1、3、5、7 d和持续振动组。实施35 Hz、0.3 g的机械振动,8周后处死,取其左侧股骨行Micro CT扫描,建立皮质骨三维有限元模型,计算获得其表观和组织水平的力学参数。通过主元素分析法从材料分布、间歇振动天数、体积分数中提取主元素。结果 提取出了能够全面反映振动下皮质骨材料性质的3个主元素,并建立起主元素与表观和细观力学参数之间的回归方程。影响皮质骨力学性能的主要因素为材料分布,体积分数与间歇振动天数的影响次之。结论 皮质骨的材料性质能够反映其力学性能的变化,通过材料性质与力学性能的关系可以评估骨强度,为骨质疏松的振动防治及其康复过程的评价提供理论依据。     

Whole-bone scaling of the avian pelvic limb

Birds form the largest extant group of bipedal animals and occupy a broad range of body masses, from grams to hundreds of kilograms. Additionally, birds occupy distinct niches of locomotor behaviour, from totally flightless strong runners such as the ratites (moa, kiwi, ostrich) to birds that may walk, dabble on water or fly. We apply a whole-bone approach to investigate allometric scaling trends in the pelvic limb bones (femur, tibiotarsus, tarsometatarsus) from extant and recently extinct birds of greatly different size, and compare scaling between birds in four locomotor groups; flightless, burst-flying, dabbling and flying. We also compare scaling of birds' femoral cross-sectional properties to data previously collected from cats. Scaling exponents were not significantly different between the different locomotor style groups, but elevations of the scaling relationships revealed that dabblers (ducks, geese, swans) have particularly short and slender femora compared with other birds of similar body mass. In common with cats, but less pronounced in birds, the proximal and distal extrema of the bones scaled more strongly than the diaphysis, and in larger birds the diaphysis occupied a smaller proportion of bone length than in smaller birds. Cats and birds have similar femoral cross-sectional area (CSA) for the same body mass, yet birds' bone material is located further from the bone's long axis, leading to higher second and polar moments of area and a greater inferred resistance to bending and twisting. The discrepancy in the relationship between outer diameter to CSA may underlie birds' reputation for having 'light' bones.     

仙珍骨宝干预泼尼松诱发大鼠的骨丢失

背景：仙珍骨宝胶囊由蛇床子、淫羊藿等制成,对糖皮质激素、维甲酸等诱发的骨质疏松有一定的预防作用。 目的：建立泼尼松诱发大鼠骨质疏松模型,通过骨形态计量学和骨生物力学等方法探讨仙珍骨宝对大鼠不同部位骨骼的影响。 方法：32只SD大鼠随机分成对照组、模型组和仙珍骨宝高、低剂量组。后3组给予泼尼松3.5 mg/(kg•d)灌胃建立骨质疏松模型。仙珍骨宝高、低剂量组大鼠在泼尼松灌胃1 h后给予仙珍骨宝胶囊0.95 g/(kg•d)、0.475 g/(kg•d)。 结果与结论：与对照组比较,模型组大鼠股骨骨密度、弹性载荷、最大载荷和断裂载荷均下降,胫骨上段动态参数标记周长百分数、骨表面形成率、骨转换率均降低,但静态参数骨小梁面积百分数、骨小梁数量、骨小梁厚度和骨小梁分离度无明显变化。胫骨中段皮质骨形态计量学参数均无明显变化。与模型组比较,仙珍骨宝高剂量组股骨密度、骨生物力学参数,胫骨上段标记周长百分数、骨表面形成率和骨转换率增加,但胫骨中段的骨形态计量学参数无明显变化。与模型组比较,仙珍骨宝低剂量组各项参数均无明显变化。提示高剂量仙珍骨宝促进骨形成,可预防泼尼松所致大鼠股骨骨密度及生物力学的降低,但对胫骨中段皮质骨无明显影响。     

松质骨微观骨小梁结构的生物力学有限元分析

股骨松质骨具有骨小梁的微观结构,其单元特性影响了股骨的整体力学性能.找到适当的单元形状与骨小梁分布特点可以帮助人们有效地进行松质骨及股骨整体的生物力学特性分析.本文采用不同结构的微观骨小梁单元模型,分析各单元的生物力学特性,并采用有限元方法,对由不同骨小梁单元及不同分布形式构成的股骨模型进行生物力学分析,获得了骨小梁单元密度与单元生物力学特性的关系的综合分析结果,找到了较好的微观骨小梁单元模型及总体布局形式,并应用于股骨松质骨建模.仿松质骨的骨小梁结构可以有效提高整体生物力学性能,所获得的微观单元优化结构可以应用于仿生结构材料的制造.