Stress wave effects in a finite element analysis of an impulsively loaded articular joint.

A dynamic contact finite element formulation was used to study transient stresses in the impulsively loaded rabbit knee, an established experimental model of mechanically induced osteoarthrosis. The computations were used to test the hypothesis that stress wave propagation and reflection, from juxtarticular interfaces of material property discontinuity, could be responsible for markedly increased levels of transient local cartilage stress. The finite element results demonstrated intuitively credible stress wave propagation and interfacial reflection phenomena. However, the magnitude of these waves was not nearly large enough to appreciably alter the quasi-static stress distributions otherwise prevailing. Thus, local stress wave reflection from interfaces of modulus discontinuity (for example the cartilage/subchondral plate) probably does not contribute appreciably to the heightened tissue sensitivity to impulsive loading experimentally observed in this animal model.     

Spatial and temporal changes of subchondral bone proceed to articular cartilage degeneration in rats subjected to knee immobilization

This study was aimed to investigate the spatial and temporal changes of subchondral bone and its overlying articular cartilage in rats following knee immobilization. A total of 36 male Wistar rats (11–13 months old) were assigned randomly and evenly into 3 groups. For each group, knee joints in 6 rats were immobilized unilaterally for 1, 4, or 8 weeks, respectively, while the remaining rats were allowed free activity and served as external control groups. For each animal, femurs at both sides were dissected after sacrificed. The distal part of femur was examined by micro‐CT. Subsequently, femoral condyles were collected for further histological observation and analysis. For articular cartilage, significant changes were observed only at 4 and 8 weeks of immobilization. The thickness of articular cartilage and chondrocytes numbers decreased with time. However, significant changes in subchondral bone were defined by micro‐CT following immobilization in a time‐dependent manner. Immobilization led to a thinner and more porous subchondral bone plate, as well as a reduction in trabecular thickness and separation with a more rod‐like architecture. Changes in subchondral bone occurred earlier than in articular cartilage. More importantly, immobilization‐induced changes in subchondral bone may contribute, at least partially, to changes in its overlying articular cartilage. Microsc. Res. Tech. 79:209–218, 2016. © 2016 Wiley Periodicals, Inc.     

Effects of acetabular resurfacing component material and fixation on the strain distribution in the pelvis

A 3D finite element (FE) model of an implanted pelvis was developed as part of a project investigating an all-polymer hip resurfacing design. The model was used to compare this novel design with a metal-on-metal design in current use and a metal-on-polymer design typical of early resurfacing implants. The model included forces representing the actions of 22 muscles as well as variable cancellous bone stiffness and variable cortical shell thickness. The hip joint reaction force was applied via contact modelled between the femoral and acetabular components of the resurfacing prosthesis. Five load cases representing time points through the gait cycle were analysed. The effect of varying fixation conditions was also investigated. The highest cancellous bone strain levels were found at mid-stance, not heel-strike. Remote from the acetabulum there was little effect of prosthesis material and fixation upon the von Mises stresses and maximum principal strains. Implant material appeared to have little effect upon cancellous bone strain failure with both bended and unbonded bone-implant interfaces. The unbonded implants increased stresses in the subchondral bone at the centre of the acetabulum and increased cancellous bone loading, resembling behaviour obtained previously for the intact acetabulum.     

Development of artificial articular cartilage

Attempts have been made to develop an artificial articular cartilage on the basis of a new viewpoint of joint biomechanics in which the lubrication and load-bearing mechanisms of natural and artificial joints are compared. Polyvinyl alcohol hydrogel (PVA-H), 'a rubber-like gel', was investigated as an artificial articular cartilage and the mechanical properties of this gel were improved through a new synthetic process. In this article the biocompatibility and various mechanical properties of the new improved PVA-H is reported from the perspective of its usefulness as an artificial articular cartilage. As regards lubrication, the changes in thickness and fluid pressure of the gap formed between a glass plate and the specimen under loading were measured and it was found that PVA-H had a thicker fluid film under higher pressures than polyethylene (PE) did. The momentary stress transmitted through the specimen revealed that PVA-H had a lower peak stress and a longer duration of sustained stress than PE, suggesting a better damping effect. The wear factor of PVA-H was approximately five times that of PE. Histological studies of the articular cartilage and synovial membranes around PVA-H implanted for 8-52 weeks showed neither inflammation nor degenerative changes. The artificial articular cartilage made from PVA-H could be attached to the underlying bone using a composite osteochondral device made from titanium fibre mesh. In the second phase of this work, the damage to the tibial articular surface after replacement of the femoral surface in dogs was studied. Pairs of implants made of alumina, titanium or PVA-H on titanium fibre mesh were inserted into the femoral condyles. The two hard materials caused marked pathological changes in the articular cartilage and menisci, but the hydrogel composite replacement caused minimal damage. The composite osteochondral device became rapidly attached to host bone by ingrowth into the supporting mesh. The clinical implications of the possible use of this material in articular resurfacing and joint replacement are discussed.     

低碳钢焊缝金属强度组配对焊接残余应力分布的影响规律

采用热弹塑性有限元方法,对平板对接接头中焊缝金属强度组配对焊接残余应力分布的影响进行了研究。结果表明,对于高组配接头,纵向残余应力的峰值接近焊缝金属的屈服极限,出现在焊缝中心。对于低组配接头,纵向残余应力的峰值接近母材的屈服极限,并发生在焊缝附近。随着对含有残余应力的接头施加外载,焊缝金属强度组配对纵向应力分布的影响依然存在,但残余应力的影响在减小。对承受外载的焊接接头,逐步卸除外载后,焊缝横截面     

Response of the donor and recipient cells in mesenchymal cell transplantation to cartilage defect

To facilitate the repair of articular cartilage defects, autologous mesenchymal cells from bone marrow or periosteum were transplanted in a rabbit model. Two weeks after the transplantation of the mesenchymal cells, the whole area of the original defect was occupied by cartilage. From the deep area of the reparative cartilage, which contacted with host bone, chondrocytes became hypertrophic and the invasion of bone with vasculature started, until the replacement reached the natural junction of the host cartilage and the subchondral bone about 4 weeks after transplantation. Twelve weeks after the transplantation, the repair cartilage in the defect became a little thinner than the adjacent normal cartilage, which became a little thinner 24 weeks after the transplantation (the longest observation period in the study). Large, full-thickness defects of the weight-bearing region of the articular cartilage were repaired with hyaline-like cartilage after implantation of autologous mesenchymal cells. The repair process by mesenchymal cell transplantation was explained as follows: The donor transplanted cell differentiated into cartilage and the defects were completely filled with cartilage. Then, mesenchymal cells that entered the chondrogenic lineage rapidly progressed through this lineage to the hypertrophic state, which was then the target for erosion and vascular invasion. Although this vasculature and the newly formed bone were considered to be host-derived, there was no evidence to that effect. To prove this, suitable experimental marking of these donor cells is needed. In the case of chondrocyte transplantation, the repair cartilage maintained its thickness to the full depth of the original defect; the tissue derived from the implanted chondrocytes was not invaded by vessels or replaced by subchondral bone.     

The significance of axial stresses and out-of-plane restraints on the design of rotors

The importance of axial stresses in rotors and the effect of out-of-plane restraints at the hub, on the in-plane stresses are investigated by using the finite element technique, with a hexahedral isoparametric element. The stresses in a non-dimensional form are compared with the plane stress solution. The probable mode of deformation of rotors of various axial thicknesses is given. The use of the above method in the analysis of an asymmetric rotor is also demonstrated.     

Numerical analysis of stress shielding of platedhuman femur using 3-dimensional finite element method

Conventional compression bone fracture plates sometimes cause osteoporosis under the plate due to their high rigidity. In order to prevent the osteopenia, many researchers have attempted various types of bone plates. To meet the same purpose, a new concept bone plate which have a vicoelastic washer between plate and screw head is introduced. The washer is made of a biocompatible polymer (ultra high molecular weight polyethylene, UHMWPE). This research was performed first to establish a more realistic and detailed plated-bone system using finite element method and second to investigate the effect of the UHMWPE washer on the stress shielding comparing with the conventional plate model. Three-dinensional finite element meshes of the human femur with the conventional and new concept bone plate were generated and the comparative stress analysis of the stress shielding was performed with static half-stance loading condition. The results of analysis showed that the new and conventional bone plate transfer the stress through the bone average 15% and 10% that of the intact bone respecively. However, the local stress in the bone under the new bone plate have increased about 13-150% that of the conventional bone plate depending on the region. Earlier preliminary animal studies showed some promising results. It is suggested that the in vivo and FEM results support the feasibility of the new concept bone plate.     

残余应力对对焊接头疲劳性能的影响

利用线弹性断裂力学（ＬＥＦＭ）理论、迭加原理和有限元分析方法,就残余应力对对焊接头的疲劳性能的影响进行了理论分析。采用有限板中边界裂纹及中心穿透裂纹的Ｂｕｅｃｋｎｅｒ及Ｋａｎａｚａｗａ权函数,计算对应对焊接头中的各种残余应力分布的残余应力强度因子。建立了考虑不同残余应力水平影响的表面裂纹疲劳模型,估算对焊接头疲劳寿命及疲劳强度,并与试验数据进行比较验证。     

Effects of ageing on the biomechanical properties of rat articular cartilage

Previous studies have demonstrated that male Sprague Dawley (SD) rats experience age-related bone loss with the same characteristics as that in ageing men. As articular cartilage, like bone, is a critical component of the health and function of the musculoskeletal system, the authors hypothesized that articular cartilage in the untreated male SD rats could be a suitable model for studying the age-related deterioration of articular cartilage in men. To test this hypothesis, male SD rats were killed at between 6 and 27 months. The right femur of each rat was removed. The effects of ageing on the structural integrity of the distal femoral articular cartilage were studied by biomechanical testing with a creep indentation apparatus. The aggregate modulus, Poisson's ratio, permeability, thickness, and percentage recovery of articular cartilage were determined using finite element/non-linear optimization modelling. No significant differences were observed in these biomechanical properties of the distal femoral articular cartilage as a function of age. Therefore, untreated male SD rats appear to be unsuitable for studying the age-related changes of articular cartilage as they occur in men. However, and more intriguingly, it is also possible that ageing does not affect the biomechanical properties of articular cartilage in the absence of cartilage pathology.     

基于ANSYS的二级三环减速器内齿环板的强度分析

介绍了二级三环减速器的结构组成。用ANSYS软件对内齿环板进行有限元应力、应变分析,得到应力云图和变形图。结果表明,在危险工况下,厚度为30mm的r8齿环板变形很小,刚度足够,最大应力值符合要求但是强度较富裕。将内齿环板的厚度减小5mm,刚度无变化,最大应力值接近许用值,强度仍满足要求。表明结构优化设计的结果最佳。详细阐述的ANSYS求解步骤可作为类似构件有限元分析的参考。     

磁共振显微线圈高分辨成像技术在腕关节病变中的临床应用

目的探讨磁共振显微线圈高分辨成像技术在腕关节病变中的临床应用。方法收集2018年12月至2019年12月45例腕关节类风湿关节炎患者、30例手腕关节骨性关节炎患者、40例腕部撞击综合症损伤患者作为研究对象,分别使用磁共振常规线圈及显微线圈技术对其部位进行扫描。比较分析两种诊断方式的诊断准确率及对软骨侵蚀、关节积液和滑膜增厚的诊出情况。结果显微线圈技术对腕关节类风湿关节炎、手腕关节骨性关节炎、腕部撞击综合症损伤的诊断准确率分别为97.78%、96.67%、97.50%,均显著高于常规线圈技术的60.00%、50.00%、60.00%,差异有统计学意义(P<0.05)。显微线圈技术对软骨侵蚀、关节积液和滑膜增厚的诊出情况显著优于常规线圈技术,差异有统计学意义(P<0.05)。经显微线圈技术MRI增强扫描检测:腕关节类风湿关节炎患者右手近端指间关节周围软组织增厚,关节周围可见少量积液,增强扫描指间关节滑膜呈明显增厚并强化。骨性关节炎患者可见关节面下骨质异常信号,表现为“虫蚀状”或小斑片状软骨下骨质缺损区。结论磁共振显微线圈高分辨成像技术能够显著提高腕关节病变的诊断准确率,提高对软骨侵蚀、关节积液和滑膜增厚的诊出情况,值得广泛推广。     

Generalized buckling analysis of laminated plates with random material properties using stochastic finite elements

A generalized layer-wise stochastic finite element formulation is developed for the buckling analysis of both homogeneous and laminated plates with random material properties. The pre-buckled stresses are considered in the derivation of geometric stiffness matrix and the effect of variation in these stresses on the mean and coefficient of variation of buckling strength is studied. The mean buckling strength of plates under uniform stress assumption exactly matches with those reported in the literature. However, it is shown that the actual mean buckling strength of plates can be significantly different based on the pre-buckled stress analysis which depends on boundary constraints, principal material directions, aspect and thickness ratios of plates. The statistics of buckling strength is determined using a Taylor series expansion based mean centered first order perturbation technique. The stochastic finite element solutions obtained using layer-wise plate theory is also validated with analytical solutions presented in this paper. Parametric studies are conducted for different aspect ratios, ply orientations and boundary conditions.     

一种考虑胶瘤的胶接简化有限元模型:应力与刚度分析

胶接接头中总存在胶瘤,由于建模复杂,胶接接头有限元分析中胶瘤常被忽略.但胶瘤能减少峰值应力,提高结构强度和刚度.为此,提出一种简化的胶接有限元模型,即用壳单元代表胶瘤,体单元代表被粘体和胶层,并用弹性理论建立壳单元等效厚度公式.以体单元精细模型结果作为对比的真实解,考察五种载荷工况下,单搭接头简化有限元模型的胶层应力和刚度.分析表明,壳单元等效厚度公式正确,胶接简化有限元模型精度高,可用于诸如汽车等大型结构中;用壳单元简单模型可定量分析胶瘤大小和形状对接头应力和总体刚度性能的影响.     

The effect of glycosaminoglycan depletion on the friction and deformation of articular cartilage

Glycosaminoglycans (GAGs) have been shown to be responsible for the interstitial fluid pressurization of articular cartilage and hence its compressive stiffness and load-bearing properties. Contradictory evidence has been presented in the literature on the effect of depleting GAGs on the friction properties of articular cartilage. The aim of this study was to investigate the effect of depleting GAGs on the friction and deformation characteristics of articular cartilage under different tribological conditions. A pin-on-plate machine was utilized to measure the coefficient of friction of native and chondroitinase ABC (CaseABC)-treated articular cartilage under two different models: static (4 mm/s start-up velocity) and dynamic (4 mm/s sliding velocity; 4 mm stroke length) under a load of 25 N (0.4 MPa contact stress) and with phosphate-buffered saline as the lubricant. Indentation tests were carried out at 1 N and 2 N loads (0.14 MPa and 0.28 MPa contact stress levels) to study the deformation characteristics of both native and GAG-depleted cartilage samples. CaseABC treatment rendered the cartilage tissue soft owing to the loss of compressive stiffness and a sulphated-sugar assay confirmed the loss of GAGs from the cartilage samples. CaseABC treatment significantly increased (by more than 50 per cent) the friction levels in the dynamic model (p < 0.05) at higher loading times owing to the loss of biphasic lubrication. CaseABC treatment had no effect on friction in the static model in which the cartilage surfaces did not have an opportunity to recover fluid because of static loading unlike the cartilage tissue in the dynamic model, in which translation of the cartilage surfaces was involved, ensuring effective biphasic lubrication. Therefore the depletion of GAGs had a smaller effect on the coefficient of friction for the static model. Indentation tests showed that GAG-depleted cartilage samples had a lower elastic modulus and higher permeability than native tissue. These results corroborate the role of GAGs in the compressive and friction properties of articular cartilage and emphasize the need for developing strategies to control GAG loss from diseased articular cartilage tissue.     

Characterization of compressive deformation behavior of multi-layer porous composite materials for articular tissue engineering

Regeneration of articular layered tissues consisting of cartilage and cancellous bone has been a critical issue in orthopedics. Tissue engineering technology for such large-scale damaged layered tissue may be developed by using layered scaffold with stem cells. In this study, therefore, a novel multi-layer scaffold consisting of a porous poly (?-caprolactone) (PCL) layer for cartilage regeneration and a porous composite layer of poly (L-lactic acid) (PLLA) and hydroxyapatite (HAp) for bone regeneration was developed. The microstructure of the scaffold was characterized by a field emission scanning electron microscope (FE-SEM). Compression tests were also performed to understand the stress-strain behavior. FE-SEM observation clearly showed that an interlayer exists between the PCL and the composite layers. The compressive stress-strain relation is characterized by a stepwise behavior including the first and the second steps. The first modulus corresponding to the first step is mainly related to the deformation of the PCL layer; on the other hand, the second modulus is related to both solidified PCL layer and the composite layer and increases with increase of HAp content of the composite layer. It is also found that the classical mechanics theory and three-dimensional finite element model can predict the first modulus reasonably well.     

Arch-shaped versus flat arthrodesis of the ankle joint: strength measurements using synthetic cancellous bone

The aim of this study was to see if preservation of the arch shape of the ankle at arthrodesis contributes to stability. The ankle joint was simulated by paired blocks of a synthetic material corresponding to rheumatoid cancellous bone with low stiffness and strength. Flat end constructs with and without subchondral bone were compared with arch-shape constructs with and without subchondral bone. The pairs were fixed with two screws simulating an arthrodesis. These constructs were then tested to failure in four-point bending and torque. In four-point bending the subchondral bone increased the strength, regardless of shape. Stiffness was higher in the arch-shaped specimens but was not influenced by the subchondral bone. In torque, both arch-shape and subchondral bone increase the strength. Stiffness was increased by arch-shape but not subchondral bone. The results imply that the arch-shape and subchondral bone should be preserved when performing an ankle arthrodesis, especially in weak rheumatoid bone.     

The effect of cartilage deformation on the laxity of the knee joint

In this paper, deformation of the articular cartilage layers is incorporated into an existing two-dimensional quasi-static model of the knee joint. The new model relates the applied force and the joint displacement, as measured in the Lachmann drawer test, and allows the effect of cartilage deformation on the knee joint laxity to be determined. The new model augments the previous knee model by calculating the tibio-femoral contact force subject to an approximate 'thin-layer' constitutive equation, and a method is described for finding the configuration of the knee under a specified load, in terms of a displacement from a zero-load reference configuration. The results show that inclusion of deformable cartilage layers can cause a reduction of between 10 and 35 per cent in the force required to produce a given tibial displacement, over the range of flexion angles considered. The presence of cartilage deformation was found to be an important modifier of the loading response but is secondary to the effect of ligamentous extension. The flexion angle dependence of passive joint laxity is much more strongly influenced by fibre recruitment in the ligaments than by cartilage deformation.     

板厚对不同胶粘剂胶焊单搭接头中应力分布影响的数值分析

采用三维弹塑性有限元分析方法,研究了板厚对胶焊单搭接头中有效应力分布的影响。计算结果表明,板厚对不同胶粘剂胶焊接头中的有效应力分布有不同影响。对酚醛树脂胶粘剂胶焊接头,搭接区边缘应力高于焊点边缘,搭接区边缘是裂纹的起裂位置;随板厚增加,搭接区边缘的峰应力减小而焊点边缘应力变化不大,使应力分布趋于均匀,对提高接头强度有利。对丙烯酸酯胶粘剂胶焊接头刚好相反。     

Stress analysis in elastic joint structures

A new inverse problem approach is introduced to analyse the stresses in the overlap elastic joint structures consisting of two adherents and an adhesive interlayer. Displacements in the elements of a joint are expressed in terms of some initially unknown contact stresses by solving the boundary-value problem for each element considered separately. The contact stresses are calculated from the matching continuity conditions for the displacements. Contact tearing and shear stresses, three-dimensional stress distribution in the bulk of adhesive interlayer, and the maximum stress values are calculated for different ratios of thicknesses and material properties of the adherents and the adhesive interlayer. The present study represents a new alternative modelling approach to stress analysis in the elastic joint structures.