Design optimization of a knee joint for an active transfemoral prosthesis for weight reduction

This paper describes the optimized design of a knee joint for an active transfemoral prosthesis with a fully active knee joint. The active transfemoral prosthesis which can help amputees to walk naturally with a powered motor has been actively developed around the world with advances in battery technology and others. However, most of them are designed for level walking, especially in South Korea, research about active prosthesis is insufficiently carried out, also depends on foreign technology. Therefore, this study focuses on the development of prosthetic knee joint that can overcome complex walking environment including stair walking. The developed prosthesis has one degree of freedom at the knee joint and can mimic the human walking mechanism. The prosthetic knee joint has a simple high-torque mechanism comprising a flat BLDC motor, harmonic drive, and pulley to generate the torque required for walking on stairs, which requires the largest torque. As one of the most important factors for comfort and fatigue, the total weight of the prosthesis should be minimized. Topology optimization was carried out to reduce the weight, and an advanced knee joint design was developed based on the optimization. The structural safety was validated via finite element analysis and a strain experiment under working conditions.

     

A one-degree-of-freedom spherical mechanism for human knee joint modelling

In-depth comprehension of human knee kinematics is necessary in prosthesis and orthosis design and in surgical planning but requires complex mathematical models. Models based on one-degree-of-freedom equivalent mechanisms have replicated well the passive relative motion between the femur and tibia, i.e. the knee joint motion in virtually unloaded conditions. In these mechanisms, fibres within the anterior and posterior cruciate and medial collateral ligaments were taken as isometric and anatomical articulating surfaces as rigid. A new one-degree-of-freedom mechanism is analysed in the present study, which includes isometric fibres within the two cruciates and a spherical pair at the pivot point of the nearly spherical motion as measured for this joint. Bounded optimization was applied to the mechanism to refine parameter first estimates from experimental measurements on four lower-limb specimens and to best-fit the experimental motion of these knees. Relevant results from computer simulations were compared with those from one previous equivalent mechanism, which proved to be very accurate in a former investigation. The spherical mechanism represented knee motion with good accuracy, despite its simple structure. With respect to the previous more complex mechanism, the less satisfactory results in terms of replication of natural motion were counterbalanced by a reduction of computational costs, by an improvement in numerical stability of the mathematical model, and by a reduction of the overall mechanical complexity of the mechanism. These advantages can make the new mechanism preferable to the previous ones in certain applications, such as the design of prostheses, orthoses, and exoskeletons, and musculoskeletal modelling of the lower limb.     

膝关节三维模型的构建

通过对逆向工程技术的研究,提出了一种构建膝关节三维模型的新方法。首先,分别对已有膝关节假体原型和志愿者的股骨远端及胫骨近段进行数据的采集;其次,利用逆向工程软件Geomagic和Mimics分别对膝关节假体原型的点云数据和股骨远端和胫骨近端的CT图像进行处理,然后利用三维软件PRO/E进行再设计;最后按顺序在PRO/E软件中装配成膝关节三维模型。模型的建立为进一步进行膝关节生物力学分析提供了方法与平台,同时也为人工膝关节模型数据库的建立提供了方法。     

Design and control of an active artificial knee joint

A passive above knee prosthesis being currently in use does not respond adequately to the needs of daily living activities of an amputee due to its limited functions. Therefore, this study deals with design and testing of an active above knee prosthesis. The essential part of this prosthesis is the knee joint actuator based on active control of basic flexion and extension functions of the knee joint with the motor. The imitation of walking gait pattern by the proposed prosthesis was provided with a trajectory control scheme for the knee joint angle in accordance with the necessity of rule-based control approach.     

智能假肢膝关节的优化设计及运动学分析

智能假肢膝关节是一种代偿下肢缺失功能的机械电子装置,可以采用双摇杆机构实现对假肢膝关节运动特性的模拟。针对假肢膝关节行走过程中能量消耗过大、稳定性较差的问题,以假肢膝关节机构峰值驱动力矩最小为优化目标,建立了优化模型;在满足性能与结构的约束条件下,运用复合形法对该模型进行优化求解,得到了假肢膝关节机构的最佳结构参数;在此基础上,利用ADAMS软件进行了虚拟运动仿真。结果表明:优化后的智能假肢膝关节具有优良的仿生性能,其峰值驱动力矩相比优化前降低了40%,驱动力矩变化范围缩小36%,大大地提升了智能假肢膝关节的稳定性与续航能力。     

Reconsideration on the use of elastic models to predict the instantaneous load response of the knee joint

Fluid pressurization in articular cartilages and menisci plays an important role in the mechanical function of the knee joint. However, fluid pressure has not been incorporated in previous finite element modelling of the knee, instead elastic models of the knee are widely used. It is believed that an elastic model can be used to predict the instantaneous load response of the knee as long as large effective moduli for the cartilaginous tissues are used. In the present study, the instantaneous response of the knee was obtained from a proposed model including fluid pressure and fibril reinforcement in the cartilaginous tissues. The results were then compared with those obtained from an elastic model using the effective modulus method. It was found that the deformations and contact pressures predicted by the two models were substantially different. An unconfined compression of a tissue disc was used to help understand the issue. It was clear that a full equivalence between the instantaneous and elastic responses could not be established even for this simple case. A partial equivalence in stress could be conditionally established for a given unconfined compression, but it was not valid for a different magnitude of compression. The instantaneous deformation of the intact tissues in the joint was even more difficult to determine using the effective modulus method. The results thus obtained were further compromised because of the uncertainty over the choice of effective modulus. The tissue non-linearity was one of the factors that made it difficult to establish the equivalence in stress. The pressurized tissue behaved differently from a solid material when non-linear fibril reinforcement was presented. The direct prediction of the instantaneous response using the proposed poromechanical model had the advantage of determining the fluid pressure and incompressible deformation.     

定制髋关节假体数字化设计与制造技术研究

针对人体的髋关节具有个性化特征以及传统假体与股骨匹配后力传递不稳定等问题,对人体髋关节假体数字化设计、有限元力传递分析、基于机器人磨削的数字化加工进行了研究,提出了在设计、仿真和加工过程中将髋关节假体模型统一的方法,实现了定制式假体数字化设计、有限元力传递的分析和机器人磨削加工的一体化,初步建立了髋关节假体的数字化设计与制造、产品生命周期的服务模型,为数字化设计与制造技术在髋关节假体等骨科植入物中的应用建立了基础。实验结果表明:采用机器人数字化磨削加工定制式假体,保持机器人软件空间与实际工作空间一致,可以有效提高假体的制造精度,实现假体与股骨髓腔的最优匹配。     

A 12-station anatomic hip joint simulator

A novel 12-station hip joint simulator with an anatomic position of the prosthesis was designed and built. The motion of the simulator consists of flexion-extension and abduction-adduction. The load is of the double-peak type. The validation test was done with three similar 28 mm CoCr-polyethylene joints in diluted calf serum lubricant for 3.3 x 10(6) cycles. The bearing surfaces of the polyethylene cups were burnished, the CoCr heads were undamaged, the wear particles were in the 0.1-1 microm size range, and the mean wear factor of the polyethylene cups was 5.7 x 10(-7) mm(3)/N m. These essential observations were in good agreement with clinical findings. In addition, three similar 50 mm CoCr/CoCr joints, representing the contemporary large-diameter metal-on-metal articulation were tested. The wear of the CoCr/CoCr joints was calculated from the Co and Cr concentrations of the used lubricant quantified with atomic absorption spectroscopy. The bearing surfaces of the CoCr/CoCr joints showed mild criss-cross scratching only. The average wear factor of polyethylene cups was 275 times that of the CoCr/CoCr joints. The tribological behaviour of the large-dia. CoCr/CoCr appeared to be dominated by fluid film lubrication, as indicated by very low frictional heating and wear, making it tribologically superior to the conventional CoCr/polyethylene, and therefore very interesting clinically. In conclusion, the simulator proved to be a valid, reliable, practical, economical, and easy-to-operate tool for wear studies of various hip replacement designs.     

3-RRR平面并联微动机器人的运动学分析

运动学分析是并联机器人机构分析中的首要问题,是进行机构动力学分析、精度分析的基础,而全柔性微动机器人机构的首要目标就是精确实现所需的运动。因此对其运动学的研究在机构学领域占有重要的地位。本文对平面并联微动机器人进行了建立伪刚性模型,采用闭环矢量原理建立理论运动学线性模型,得到理论Jacobian矩阵,其次对该机构进行实验分析,得到工作平台的实验输出位移和方位角(Jacobian矩阵);然后用ANSYS软件对其进行有限元分析,得到有限元运动学模型(Jacobian矩阵值),最后通过分析比较该机构的理论运动学方程、实验运动学方程和有限元运动学方程,得到输出平台适用的运动学方程。     

A review of probabilistic analysis in orthopaedic biomechanics

Probabilistic analysis methods are being increasingly applied in the orthopaedics and biomechanics literature to account for uncertainty and variability in subject geometries, properties of various structures, kinematics and joint loading, as well as uncertainty in implant alignment. As a complement to experiments, finite element modelling, and statistical analysis, probabilistic analysis provides a method of characterizing the potential impact of variability in parameters on performance. This paper presents an overview of probabilistic analysis and a review of biomechanics literature utilizing probabilistic methods in structural reliability, kinematics, joint mechanics, musculoskeletal modelling, and patient-specific representations. The aim of this review paper is to demonstrate the wide range of applications of probabilistic methods and to aid researchers and clinicians in better understanding probabilistic analyses.     

A five-station hip joint simulator for wear rate studies.

The aim of the work has been the development of a hip joint simulator for comparative wear rate studies of long duration. A five-station apparatus has been designed, constructed and tested. Five total hip joints can be tested at the same time in identical conditions. The flexion-extension motion and the superior-inferior component of the joint contact force are incorporated. The motion is electromechanical and the loading pneumatic. The angle and load waveforms are fixed and simulate level walking. For accurate wear measurements each station employs a control prosthesis. The conditions of the control prosthesis in regard to loading, exposure to lubricant and environment temperature (37 +/- 1 degree C) are identical to those of the test prosthesis. The acetabular cups can be readily removed for periodic wear measurements and reassembled in exactly the original position. Extensive tests have shown that the simulator is a practical and reliable instrument in the wear rate studies of various designs of total hip joint.     

Elasto-plastic contact analysis of an ultra-high molecular weight polyethylene tibial component based on geometrical measurement from a retrieved knee prosthesis

The wear phenomenon of ultra-high molecular weight polyethylene (UHMWPE) in knee and hip prostheses is one of the major restriction factors on the longevity of these implants. Especially in retrieved knee prostheses with anatomical design, the predominant types of wear on UHMWPE tibial components are delamination and pitting. These fatigue wear patterns of UHMWPE are believed to result from repeated plastic deformation owing to high contact stresses. In this study, the elasto-plastic contact analysis of the UHWMPE tibial insert, based on geometrical measurement for retrieved knee prosthesis, was performed using the finite element method (FEM) to investigate the plastic deformation behaviour in the UHMWPE tibial component. The results suggest that the maximum plastic strain below the surface is closely related to subsurface crack initiation and delamination of the retrieved UHMWPE tibial component. The worn surface whose macroscopic geometrical congruity had been improved due to wear after joint replacement showed lower contact stress at macroscopic level.     

Mechanics of the passive knee joint. Part 2: interaction between the ligaments and the articular surfaces in guiding the joint motion

The aim of this study was to examine how the interaction between ligament tensions and contact forces guides the knee joint through its specific pattern of passive motion. A computer model was built based on cadaver data. The passive motion and the ligament lengthening and force patterns predicted by the model were verified with data from the literature. The contribution of each ligament and contact force was measured in terms of the rotational moment that it produced about the tibial medial plateau and the anterior-posterior (AP) force that it exerted on the tibia. The high tension of the anterior cruciate ligament (ACL) and the geometric constraints of the anterior horns of the menisci were found to be key features that stabilized the knee at full extension. The mutual effect of the cruciates was found as the reason for the screw-home mechanism at early flexion. Past 300, the AP component of contact force on the convex geometry of the lateral tibial plateau and tension of the lateral collateral ligament (LCL) were identified as elements that control the joint motion. From 60 degrees to 90 degrees, reduction in the tension of the ACL was determined as a reason for continuation of the tibial anterior translation. From 90 degrees to 120 degrees, increase in the tension of the posterior cruciate ligament and the AP component of the contact force on the convex geometry of the lateral tibial plateau pushed the tibia more anteriorly. This anterior translation was limited by the constraining effects of the ACL tension and the AP component of the contact force on the medial meniscus. The important guiding role observed for the LCL suggests that it should not be overlooked in knee models.     

假肢膝关节四杆机构的优化与仿真

从满足人体运动过程中假肢与人体的协调性出发,对假肢膝关节部位的构型进行选取,并对该机构进行了运动学分析;针对个人膝关节瞬心轨迹曲线,提出该机构尺寸参数的优化数学模型,对该机构的参数进行优化,使目标函数中机构瞬心坐标与人体膝关节瞬时转动中心理想值之差最小,即该机构的实际瞬心轨迹与理想的膝关节瞬心轨迹相接近,满足人体下假肢膝关节机构协调性的设计要求,通过Matlab优化工具箱进行优化计算并获得机构模型,又应用AD-AMS对机构模型进行运动学仿真,验证优化结果的可用性。     

整体弹性关节平面并联微动机器人ANSYS有限元分析

对整体弹性关节平面并联机器人建立刚性模型,采用闭环线型原理建立理论运动学线性模型(Jacobian矩阵),然后用ANSYS软件对其进行有限元分析,得到有限元运动学模型(Jacobian矩阵值),最后讨论两者关系,发现有限元模型比理论模型要精确.     

Future trends in the use of X-ray fluoroscopy for the measurement and modelling of joint motion

Knowledge of three-dimensional skeletal kinematics during functional activities such as walking, is required for accurate modelling of joint motion and loading, and is important in identifying the effects of injury and disease. For example, accurate measurement of joint kinematics is essential in understanding the pathogenesis of osteoarthritis and its symptoms and for developing strategies to alleviate joint pain. Bi-plane X-ray fluoroscopy has the capacity to accurately and non-invasively measure human joint motion in vivo. Joint kinematics obtained using bi-plane X-ray fluoroscopy will aid in the development of more complex musculoskeletal models, which may be used to assess joint function and disease and plan surgical interventions and post-operative rehabilitation strategies. At present, however, commercial C-arm systems constrain the motion of the subject within the imaging field of view, thus precluding recording of motions such as overground gait. These fluoroscopy systems also operate at low frame rates and therefore cannot accurately capture high-speed joint motion during tasks such as running and throwing. In the future, bi-plane fluoroscopy systems may include computer-controlled tracking for the measurement of joint kinematics over entire cycles of overground gait without constraining motion of the subject. High-speed cameras will facilitate measurement of high-impulse joint motions, and computationally efficient pose-estimation software may provide a fast and fully automated process for quantification of natural joint motion.     

Dynamic characteristics of a magnetorheological pin joint for civil structures

Magnetorheological (MR) pin joint is a novel device in which its joint moment resistance can be controlled in real-time by altering the applied magnetic field. The smart pin joint is intended to be used as a controllable connector between the columns and beams of a civil structure to instantaneously shift the structural natural frequencies in order to avoid resonance and therefore to reduce unwanted vibrations and hence prevent structural damage. As an intrinsically nonlinear device, modelling of this MR fluid based device is a challenging task and makes the design of a suitable control algorithm a cumbersome situation. Aimed at its application in civil structure, the main purpose of this paper is to test and characterise the hysteretic behaviour of MR pin joint. A test scheme is designed to obtain the dynamic performance of MR pin joint in the dominant earthquake frequency range. Some unique phenomena different from those of MR damper are observed through the experimental testing. A computationally-efficient model is proposed by introducing a hyperbolic element to accurately reproduce its dynamic behaviour and to further facilitate the design of a suitable control algorithm. Comprehensive investigations on the model accuracy and dependences of the proposed model on loading condition (frequency and amplitude) and input current level are reported in the last section of this paper.     

Knee and hip joint forces--sensitivity to the degrees of freedom classification at the knee

Previous research has demonstrated that the number of degrees of freedom (DOF) modelled at a given joint affects the antagonistic muscle activity predicted by inverse dynamics optimization techniques. This higher level of muscle activity in turn results in greater joint contact forces. For instance, modelling the knee as a 3 DOF joint has been shown to result in higher hip and knee joint forces commensurate with a higher level of muscular activity than when the knee is modelled with 1 DOF. In this study, a previously described musculoskeletal model of the lower limb was used to evaluate the sensitivity of the knee and hip joint contact forces to the DOF at the knee during vertical jumping in both a 1 and a 3 DOF knee model. The 3 DOF knee was found to predict higher tibiofemoral and hip joint contact forces and lower patellofemoral joint contact forces. The magnitude of the difference in hip contact force was at least as significant as that found in previous research exploring the effect of subject-specific hip geometry on hip contact force. This study therefore demonstrates a key sensitivity of knee and hip joint contact force calculations to the DOF at the knee. Finally, it is argued that the results of this study highlight an important physiological question with practical implications for the loading of the structures of the knee; that is, the relative interaction of muscular, ligamentous, and articular structures in creating moment equilibrium at the knee.     

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.