Measurement of laxity in the anterior cruciate ligament-deficient knee: a comparison of three different methods in vitro

The aim of this study was to compare in-vitro measurements of anteroposterior laxity in the anterior cruciate ligament (ACL)-deficient knee using three different methods: an Instron materials-testing machine, then a KT-2000 arthrometer, and finally by Roentgen stereophotogrammetric analysis (RSA). Eight ACL-deficient human cadaver knees were used. Total displacement was measured between 90 N anterior and 90 N posterior tibiofemoral drawer forces at both 20 degrees and 90 degrees knee flexion. Laxity ranged from 11.5 to 27.6 mm at 20 degrees and from 8.7 to 23.9 mm at 90degrees. A statistically significant difference was not found between the mean RSA and KT-2000 measurements. However, the mean Instron measurements of laxity were significantly (3-4 mm) higher than both RSA and KT-2000 measurements. The clinical methods of RSA and the KT-2000 measurements agreed well but appeared to underestimate tibiofemoral anteroposterior laxity compared with the materials-testing machine. These findings may be helpful in the future comparison of different studies.     

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.     

In-vitro measurement of the human knee joint motion during quadriceps leg raising

This paper represents a three-dimensional motion analysis of the human knee joint under given conditions of loading and constraint. As the knee is extended by a known force applied to the quadriceps tendon, relative displacements of the femur, tibia, and patella are measured using a video motion analysis system. The most prominent motion of the tibia is external rotation and anterior displacement relative to the femur during knee extension. The patellar flexion angle decreases from 70° to 0°. The moment arm of the knee extensor mechanism exhibits a characteristic bell shape which peaks somewhere in the 40°–60° region of flexion. In general, the quadriceps force results primarily from an increase in the torque exerted by the weight of the lower leg. In the range of 20°–60°, the quardricep force needed to extend the leg remains relatively constant. As the knee approaches full extension, the moment arm decreases due to the fact that the posterior capsule and the ACL begin to tighten in this region. Consequently, the quadriceps force increases rapidly.     

Objective measurement of knee laxity and stiffness with reference to knee injury diagnosis. Part 2: Results

Equipment capable of objective knee analysis has been used to obtain data from 85 'normal' healthy knees, 47 patients suffering with knee disorders, and three cadaveric knee joints. Among the 'normals' it was found that there was a correlation between body weight and stiffness and laxity. A lower stiffness and higher laxity was recorded at 20 degrees of knee flexion than at 90 degrees. Using relative-paired difference analysis the variables affected by different injuries in patients were identified and are presented. In a separate analysis a multi-variate technique is used to interpret the data. The technique could be used to predict or diagnose knee injury, and as such may be highly useful to clinicians.     

Robotic control in knee joint replacement surgery

A brief history of robotic systems in knee arthroplasty is provided. The place of autonomous robots is then discussed and compared to more recent 'hands-on' robotic systems that can be more cost effective. The case is made for robotic systems to have a clear justification, with improved benefits compared to those from cheaper navigation systems. A number of more recent, smaller, robot systems for knee arthroplasty are also described. A specific example is given of an active constraint medical robot, the ACROBOT system, used in a prospective randomized controlled trial of unicondylar robotic knee arthroplasty in which the robot was compared to conventional surgery. The results of the trial are presented together with a discussion of the need for measures of accuracy to be introduced so that the efficacy of the robotic surgery can be immediately identified, rather than have to wait for a number of years before long-term clinical improvements can be demonstrated.     

Validation of the soft tissue restraints in a force-controlled knee simulator

In vitro testing of total knee replacements (TKRs) is important both at the design stage and after the production of the final components. It can predict long-term in vivo wear of TKRs. The two philosophies for knee testing are to drive the motion by displacement or to drive the motion by force. Both methods have advantages and disadvantages. For force control an accurate simulation of soft tissue restraints is required. This study was devised to assess the accuracy of the soft tissue restraints of the force-controlled Stanmore knee simulator in simulating the restraining forces of the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL). In order to do this, human cadaver knee joints were subjected to the ISO Standard Walking Cycle. The resulting kinematics were monitored when the soft tissue structures were intact, when the ACL and PCL were resected, and when they were simulated by springs positioned anteriorly and posteriorly. The stiffness of the springs was determined from the literature. Two different stiffnesses of springs were used which were 7.24 N/mm (designated as soft springs) and 33.8 N/mm (designated as hard springs). All the intact knees showed displacements that were within the range of the machine. Cutting the ACL and PCL resulted in anterior and posterior motion and internal external rotation that were significantly greater than the intact knee. Results showed that when the ACL and PCL were cut hard springs positioned anterior and posterior to the knee returned the knee to near normal anterior-posterior (AP) motion. Using hard springs in the posterior position in any condition reduced rotational displacements. Therefore using springs in a force-controlled simulator is a compromise. More accuracy may be obtained using springs that are of intermediate stiffness.     

In-plane dead reckoning with knee and waist attached gyroscopes

This paper presents a Micro-Electro-Mechanical (MEM)-based system which comprises of two inertial sensors (gyroscopes) for indoor personal navigation. In this system, the position and orientation of a moving person on a flat surface (zero-slope) is determined through strategically placed sensors on the waist and knee of the human body. From the knee attached gyroscope, this system takes advantage of the repetitive angular displacement during each step of the walking person to bound the angular displacement error. Our algorithm continuously estimates the heading by integrating the measured angular rates from the waist attached gyroscope. Results show that on a flat surface, the average tracking error of 0.1935 m with a standard deviation 0.0512 m for total distance traveled of 62.32 m.     

旋转调制式激光惯导系统综述

对激光惯导系统导航精度提高方法进行了分析,认为旋转调制技术是提高激光惯导系统长航时导航精度的一种有效可行的方法,并对旋转调制技术国外发展现状、技术原理、工程实现方案及关键技术进行了阐述。     

The research of PNS based on micro inertial sensors

In order to reduce the dependence of pedestrian navigation on satellite navigation system and wireless communication, a new method is proposed to construct pedestrian navigation system (PNS) based on micro inertial technology. In this paper, the distributed system structure is arranged on human feet and trunk, and the key technologies, namely the system initial alignment, the error correction, the precise gait-phase detection, the effect and the inhibition of environmental magnetic field, have been studied. Besides, theories and applications of the key technologies are also discussed, and the performance of the PNS has been analyzed in the environment of electromagnetic interference. Experimental results show that the positioning error of the route with electromagnetic interference accounts for 2% of the travel distance. The key technologies proposed in the study can effectively improve the positioning accuracy of PNS, and independently achieve longer time personal navigation in the attenuate or even invalid global navigation satellite system (GNSS) and wireless communication signal environment.     

基于低压电力线载波通信的助航灯光控制系统设计

机场助航灯光系统是保证飞机安全升降的必要设施。随着机场设备管理的现代化,要求助航灯光系统能进行智能检测和控制。该文重点研究了新型恒流调光器和基于低压电力线载波通信的助航灯光状况控制系统。不仅增加了对灯光系统的控制功能,而且在交流恒流调光电源中引入SPWM控制策略,改善了供电质量。     

Reconstruction of the anterior cruciate ligament.

Ligaments are strong collagenous structures that act as constraints on joint motion, thus confining the articular surfaces to more or less the same paths. In so doing they prevent arbitrary apposition of these surfaces from occurring and resulting in abnormal stresses which may damage the joint surfaces. Ligaments rupture due to excessive loads, particularly those resulting from trauma occurring during sporting events or motor vehicle accidents. Knee and ankle joints have the highest frequency of ligamentous injuries. This paper is a brief review of the current approaches to the reconstruction of the knee ligaments with specific reference to the anterior cruciate ligament (ACL) being the most frequently reconstructed. This is not only because it is frequently injured but also because of the debilitating consequences of such an injury. Approaches ranging from the conservative to those that advocate the use of frank prosthetic replacement have been adopted by surgeons at both ends of the spectrum. Following a discussion of the rationale for reconstruction of the ACL, the mechanical and biological considerations of the reconstructive procedure are discussed. The different methods of ACL reconstruction are reviewed. These include: (a) primary repair, (b) reconstruction with different tissues, including autogenous allografts and xenografts, (c) reconstruction employing different synthetic devices. A brief discussion of the procedures used for reconstruction with different types of tissue and of the surviving examples of the synthetic devices will follow.     

A position based kinematic method for the analysis of human gait

Human joint motion can be kinematically described in three planes, typically the frontal, sagittal, and transverse, and related to experimentally measured data. The selection of reference systems is a prerequisite for accurate kinematic analysis and resulting development of the equations of motion. Moreover, the development of analysis techniques for the minimization of errors, due to skin movement or body deformation, during experiments involving human locomotion is a critically important step, without which accurate results in this type of experiment are an impossibility. The traditional kinematic analysis method is the Angular-based method (ABM), which utilizes the Euler angle or the Bryant angle. However, this analysis method tends to increase cumulative errors due to skin movement. Therefore, the objective of this study was to propose a new kinematic analysis method, Position-based method (PBM), which directly applies position displacement data to represent locomotion. The PBM presented here was designed to minimize cumulative errors via considerations of angle changes and translational motion between markers occurring due to skin movements. In order to verify the efficacy and accuracy of the developed PBM, the mean value of joint dislocation at the knee during one gait cycle and the pattern of three dimensional translation motion of the tibiofemoral joint at the knee, in both flexion and extension, were accessed via ABM and via new method, PBM, with a Local Reference system (LRS) and Segmental Reference system (SRS), and then the data were compared between the two techniques. Our results indicate that the proposed PBM resulted in improved accuracy in terms of motion analysis, as compared to ABM, with the LRS and SRS.     

基于FTA与TRIZ的机电产品故障分析

将TRIZ中的标准解反向转换,得到可以分析系统故障原因的方法.并替代传统FTA中"列举故障原因"所采用的方法,提出一个结合了FTA和TRIZ优点、能够对系统故障进行定性和定量分析的综合方案.     

A computerized bioskills system for surgical skills training in total knee replacement

Although all agree that the results of total knee replacement (TKR) are primarily determined by surgical skill, there are few satisfactory alternatives to the 'apprenticeship' model of surgical training. A system capable of evaluating errors of instrument alignment in TKR has been developed and demonstrated. This system also makes it possible quantitatively to assess the source of errors in final component position and limb alignment. This study demonstrates the use of a computer-based system to analyse the surgical skills in TKR through detailed quantitative analysis of the technical accuracy of each step of the procedure. Twelve surgeons implanted a posterior-stabilized TKR in 12 fresh cadavers using the same set of surgical instruments. During each procedure, the position and orientation of the femur, tibia, each surgical instrument, and the trial components were measured with an infrared coordinate measurement system. Through analysis of these data, the sources and relative magnitudes of errors in position and alignment of each instrument were determined, as well as its contribution to the final limb alignment, component positioning and ligament balance. Perfect balancing of the flexion and extension gaps was uncommon (0/15). Under standardized loading, the opening of the joint laterally exceeded the opening medially by an average of approximately 4 mm in both extension (4.1 +/- 2.1 mm) and flexion (3.8 +/- 3.4 mm). In addition, the overall separation of the femur and the tibia was greater in flexion than extension by an average of 4.6 mm. The most significant errors occurred in locating the anterior/posterior position of the entry point in the distal femur (SD = 8.4 mm) and the correct rotational alignment of the tibial tray (SD = 13.2 degrees). On a case-by-case basis, the relative contributions of errors in individual instrument alignments to the final limb alignment and soft tissue balancing were identified. The results indicate that discrete steps in the surgical procedure make the largest contributions to the ultimate alignment and laxity of the prosthetic knee. Utilization of this method of analysis and feedback in orthopaedic training is expected rapidly to enhance surgical skills without the risks of patient exposure.     

水面多传感器组合导航系统技术研究

研究了INS、GPS、Doppler计程仪组成的水面多传感器组合导航技术,给出了设计方案;介绍了一种修正的自适应卡尔曼滤波算法,并应用于组合导航系统.仿真结果表明,该算法可以有效的抑制滤波发散,提高了组合导航系统的精度.     

Vision coupled GPS/INS scheme for helicopter navigation

This paper presents a framework for a GPS/INS/vision-based helicopter navigation system. The conventional GPS/INS algorithm has weak points such as GPS blockage and jamming, while the helicopter is a speedy and highly dynamic vehicle that may easily lose a GPS signal. A vision sensor is not affected by signal jamming, and the navigation error of such a system does not accumulate. Hence, a GPS/INS/vision-aided navigation scheme was implemented to provide the robust localization suitable for helicopter operations in various environments. The core algorithm is the vision-based SLAM (simultaneous localization and mapping) technique. Flight tests were performed to verify the SLAM-aided vision navigation algorithm. During the tests, it was confirmed that the developed system is sufficiently robust under GPS blockage conditions. The system design, software algorithm, and flight test results are described in this paper.     

轮式移动机器人轨迹跟踪的预测控制

自动导航小车 (AGV)是一种移载用轮式移动机器人 (WMR) ,主要用于现代化的无人生产车间中实现物料的搬运。为完成搬运任务 ,其控制系统必须具备定位、路径规划和导航等功能。考虑到其工作任务的特殊性 ,作者设计了一种运动控制系统———组合导航预测控制系统。理论分析和仿真结果均表明 ,该控制系统是有效可靠的。     

Virtual assembly planning and assembly-oriented quantitative evaluation of product assemblability

Assembly motion navigation and assemblability evaluation play key roles in assembly design, assembly operation analysis, and assembly planning. The accurate positioning of parts and realistic simulation of the assembly process are the premise of the evaluation and optimization of product design. The product assemblability evaluation is needed during the initial design stage in order to identify potential assembly problems. This paper presents a motion navigation method based on force guidance, which achieves a realistic simulation of the assembly process. A novel approach to assemblability and assembly sequence analysis and evaluation is developed. The calculation methods of assembly force, contact force, and assembly torque under the influences of part properties, visual, and human factors etc. are given. Quantitative evaluation of component assemblability (CA) according to the assembly time and assembly trial times is developed. Then, from an overall perspective, a product assemblability (PA) evaluation system is established on the basis of assemblability of each component and the assembly sequence is optimized according to the PA evaluation results. This algorithm has been applied to a self-developed desktop virtual assembly prototype system. An example is illustrated, and the results prove that this algorithm provides a realistic and accurate assembly motion navigation in virtual space and gives a correct and appropriate quantitative evaluation of the product assemblability.     

Prototype Information System for High-Precision Navigation in Global Satellite Systems

An information system permitting the timely construction of constellations of navigation satellites on the basis of data files provided by various analysis centers is described. In this approach, realistic results may be obtained in simulating the operation of instruments receiving signals from global navigation satellite systems (GNSS). The proposed architecture and functional capabilities of the information system are outlined. It is shown to be more effective in modeling the actual ephemeris data of GNSS than the traditional method of integrating the satellites’ equations of motion.     

捷联惯导/天文导航/合成孔径雷达组合导航系统

设计了适用于巡航导弹的捷联惯性/天文导航/合成孔径雷达(SINS/CNS/SAR)组合导航系统,针对巡航导弹对导航系统高精度和自主性的要求以及其匀速、等高状态飞行的特性,突出工程实用性,对SINS/CNS/SAR组合导航采用非线性建模,非线性的无迹卡尔曼滤波(UKF)方法进行各子滤波器的滤波,非线性的模型和滤波方法更符合实际,因而提高了系统精度,而子滤波器之间的信息融合过程选择基于信息分配因子实时调整的联邦滤波器,大大增强了系统的容错性和实时性。提出了一种新的可观测度计算方法,简化了可观测度的计算。数字和半实物仿真实验表明组合导航系统对于巡航导弹高空长航的飞行环境具有很强适用性,该组合导航系统不但适用于巡航导弹,也适用于无人机等其他一些长航时飞行器,具有重大的工程应用价值。