Constitutive Modeling and Algorithmic Implementation of a Plasticity-like Model for Trabecular Bone Structures

Trabecular bone is a highly porous orthotropic cellular solid material present inside human bones such as the femur (hip bone) and vertebra (spine). In this study, an infinitesimal plasticity-like model with isotropic/kinematic hardening is developed to describe yielding of trabecular bone at the continuum level. One of the unique features of this formulation is the development of the plasticity-like model in strain space for a yield envelope expressed in terms of principal strains having asymmetric yield behavior. An implicit return-mapping approach is adopted to obtain a symmetric algorithmic tangent modulus and a step-by-step procedure of algorithmic implementation is derived. To investigate the performance of this approach in a full-scale finite element simulation, the model is implemented in a non-linear finite element analysis program and several test problems including the simulation of loading of the human femur structures are analyzed. The results show good agreement with the experimental data.     

Experimental errors in the application of photoelastic coatings on human femurs with uncemented hip stems

The investigation of the stress distribution in the proximal femur is of primary relevance when testing hip prostheses. Most of the in-vitro research to date, has been conducted with strain gauges. However, the photoelastic coatings provide a field vision of the state of strain and of the most stressed points. The purpose of this work was to validate the application of photoelastic coatings to intact and implanted human femurs. Coatings of various thickness were bonded to two regions: the surface of the diaphysis, and the resection surface of the neck. A theoretical study was conducted on a geometrical model of the diaphysis to quantify some of the experimental errors. The reinforcing effect was found to be far the most important source of error for the coating of the diaphysis. Other possible sources of error such as Poisson's coefficient mismatch, incorrect light incidence angle and uneven coating thickness were also examined. Due to the uneven distribution of such errors, any correction seems impossible. The results must therefore be considered only qualitatively, as a complement to the strain gauging. The coating of the resection surface of the neck of the femur suffers much less from the reinforcing effect, but the coating is more sensitive to Poisson's coefficient mismatch. In this second application, quantitative results can be satisfactorily obtained.     

Correlative light and backscattered electron microscopy of bone--part II: automated image analysis

Detailed studies of biological phenomena often involve multiple microscopy and imaging modes and media. For bone biology, various forms of light and electron microscopy are used to study the microscopic structure of bone. Integrating information from the different sources is necessary to understand how different aspects of the bone structure interact. To accomplish this, methods were developed to prepare and image thin sections for correlative light microscopy (LM) and backscattered electron imaging in the scanning electron microscope (BSE-SEM). Images of the same fields of view may then be analyzed for degrees of relationships between specimen features not observed by LM or SEM alone. These methods are applied here to study possible associations between the degree of bone mineralization and pattern of collagen fiber orientation in the mid-shaft of the human femur. The "relational images" obtained allow us to examine the relationship between these two variables, both objectively and quantitatively.     

运用快速成型技术的人工骨骼实体模型重建

将快速成型技术运用于骨骼实体模型的三维重建研究中,以人体下肢股骨近端为例,通过对原始CT图像数据进行阈值分割,提取股骨近端轮廓曲线,拟合成数字模型.利用快速成型机可以将股骨近端的数字模型实体化,得到与实际骨骼拟合程度较高的实体模型.     

Organ Weights in NPC1 Mutant Mice Partly Normalized by Various Pharmacological Treatment Approaches

Niemann-Pick Type C1 (NPC1, MIM 257220) is a rare, progressive, lethal, inherited autosomal-recessive endolysosomal storage disease caused by mutations in the NPC1 leading to intracellular lipid storage. We analyzed mostly not jet known alterations of the weights of 14 different organs in the BALB/cNctr-Npc1^m1N/-J Jackson Npc1 mice in female and male Npc1^+/+ and Npc1^−/− mice under various treatment strategies. Mice were treated with (i) no therapy, (ii) vehicle injection, (iii) a combination of miglustat, allopregnanolone, and 2-hydroxypropyl-ß-cyclodextrin (HPßCD), (iv) miglustat, and (v) HPßCD alone starting at P7 and repeated weekly throughout life. The 12 respective male and female wild-type mice groups were evaluated in parallel. In total, 351 mice (176 Npc1^+/+, 175 Npc1^−/−) were dissected at P65. In both sexes, the body weights of None and Sham Npc1^−/− mice were lower than those of respective Npc1^+/+ mice. The influence of the Npc1 mutation and/or sex on the weights of various organs, however, differed considerably. In males, Npc1^+/+ and Npc1^−/− mice had comparable absolute weights of lungs, spleen, and adrenal glands. In Npc1^−/− mice, smaller weights of hearts, livers, kidneys, testes, vesicular, and scent glands were found. In female Npc1^−/− mice, ovaries, and uteri were significantly smaller. In Npc1^−/− mice, relative organ weights, i.e., normalized with body weights, were sex-specifically altered to different extents by the different therapies. The combination of miglustat, allopregnanolone, and the sterol chelator HPßCD partly normalized the weights of more organs than miglustat or HPßCD mono-therapies.     

60Coγ射线急慢性照射对小鼠骨、牙和毛发ESR信号的影响

对昆明种雄性小白鼠给予不同剂量的急性或慢性60Co γ射线整体照射(剂量范围为0-3.0Gy),分离小鼠股骨、牙齿和毛发并进行前处理后,用电子自旋共振谱仪(ESR)测定各自的信号强度.结果表明,小鼠牙齿和毛发信号无特征性峰.小鼠股骨ESR信号呈现特征峰,无论是急性照射还是慢性照射,小鼠股骨ESR信号强度随着照射剂量的增大而增高,呈现良好的直线关系.保存在福尔马林溶液中的小鼠股骨,其ESR信号强度在保存7d时明显降低(p＜0.001),在室温干燥条件下保存453d的股骨ESR信号强度无明显改变.说明,小鼠股骨的最适保存条件为室温干燥.     

Hexahedral mesh development of free-formed geometry: The human femur exemplified

The objective of the present research is to develop a standard hexahedral Finite Element (FE) model of the human femur accounting for the material characteristics of cortical bone, cancellous bone and bone marrow. The anatomical data were acquired from the Visible Human Project. A detailed outline of the steps necessary in developing hexahedral FE meshes from computed tomography (CT) data is provided, along with a section on modelling strategies providing comprehensive suggestions on how to overcome meshing difficulties due to geometrical non-linearities. The stress and deformation results are discussed.     

A Method to Improve Experimental Validation of Finite‐Element Models of Long Bones

Abstract: Finite‐element (FE) simulations are extremely sensitive to boundary conditions, including the position of applied forces. This is particularly critical for FE models of bones, where the lack of a univocal reference system makes identifying the boundary conditions difficult. The aims of this work were to design a transducer (FP‐transducer) to accurately determine the position of the resultant joint force during in vitro tests, and to assess its accuracy for future application in validating numerical models of long bones. A strain gauge‐based transducer was designed to indirectly measure the position of the force applied to the long bones during in vitro tests, by measuring the reaction moments about two perpendicular axes, generated by the force applied. Validation tests were performed to quantify the intrinsic precision of the FP‐transducer (by applying calibrated forces at known locations), and the overall accuracy when the FP‐transducer was included in a typical set‐up for long bone testing. The intrinsic accuracy of the FP‐transducer when used to calculate the position of an offset force was satisfactory (0.66 mm). The overall accuracy of the FP‐transducer in measuring the position of the applied force, when included in a typical set‐up for long bone testing was 0.85 mm. In vitro validation of FE models of long bones may, therefore, be improved, thanks to a more accurate determination of the force application point.     

高龄患者股骨颈骨质疏松性骨折45例治疗体会

目的探讨高龄患者股骨颈骨质疏松性骨折的手术方法及临床疗效。方法回顾性分析我院2000年4月-2007年9月收治的45例高龄股骨颈骨质疏松性骨折的临床资料。结果均顺利完成手术,术后发生并发症5例,随访32例。结论对于高龄股骨颈骨质疏松性骨折应早期固定,进行功能锻炼,恢复髋关节活动。