Dynamic analysis of the knee after total joint arthroplasty by hardware-in-the-loop simulation

尽管植入物设计复杂，但四分之一的患者对全膝关节置换术后的临床和功能结果仍不满意。不满以及发生的并发症通常导致患者活动受限，随后种植体失败需要翻修手术。然而，到目前为止，还无法通过现有的测试方法来研究生理环境下膝关节内假体的失效机制以及运动学和载荷情况。本研究的目的是开发一种基于机器人的测试系统，以高精度地研究膝关节内假体的关节运动学和动态稳定性行为。该方法考虑到邻近的韧带和囊结构，并允许评估植入物组件和手术技术。通过比较天然膝关节和全膝关节置换术后的运动模式，揭示了频繁和潜在的失败原因。到目前为止，相关的韧带、囊膜和肌肉结构在可重复条件下的实验设置中还没有得到充分的解决。因此，我们的方法是将邻近的软组织结构实现为生物力学模型。真正的植入部件由工业机器人作为执行器系统移动和装载。同时，生物力学模型在硬件在环（HiL）控制回路中与机器人进行通信，实时交换运动学和力数据。因此，在考虑软组织结构和真实接触条件的情况下，以一种可重复和独特的方式产生膝关节内假体的运动和载荷。在初步工作中，我们已经成功地实施了全髋关节置换术的HiL环境。然而，由于膝关节的复杂性，需要一种优化的方法来研究膝关节内假体。因此，必须通过使用机器人测试尸体膝盖来确定周围韧带和荚膜结构的固有运动学以及力学特性。在此基础上建立了生物力学模型。此外，物理装置的感觉和控制系统适应膝关节，随后进行了HiL环境的配置和验证。基于HiL模拟，考虑了种植体设计、种植体定位和手术技术的变化，并评估了它们对关节运动学和负载情况的影响。此外，为了确定人工膝关节内的应力、应变和接触压力，将HiL模拟结果作为边界条件进行了有限元分析。

Despite sophisticated implant designs every fourth patient remains dissatisfied with the clinical and functional outcome after total knee arthroplasty. Discontentment as well as occurring complications usually result into restricted mobility of the patient and subsequent implant failure requiring revision surgery. However, it has not been possible so far to investigate failure mechanisms as well as kinematics and load situation of knee endoprostheses under physiological circumstances by use of established testing methods.The objective of this proposal is to develop a novel robot-based test system in order to investigate knee endoprostheses with respect to joint kinematics and dynamic stability behavior with high accuracy. The approach is taking into account adjacent ligaments and capsular structures, and allows for evaluation of implant components and surgical techniques. Frequent and potential failure causes are revealed by comparing motion patterns of native knee joints and after total knee arthroplasty.Relevant ligaments, capsular and muscular structures have been insufficiently addressed in experimental setups under reproducible conditions so far. Hence, our approach is to implement the adjacent soft tissue structures into a biomechanical model. The real implant components are moved and loaded by an industrial robot serving as actuator system. At the same time, the biomechanical model communicates with the robot within a Hardware-in-the-Loop (HiL) control loop exchanging kinematic and force data in real time. As a result, the movement and loading of knee endoprostheses are generated taking into consideration soft tissue structures and real contact conditions in a reproducible and unique manner.In preliminary work we have already successfully implemented the HiL environment for total hip replacements. However, an optimised approach is required for investigating knee endoprostheses due to the complexity of the knee joint. Hence, the native kinematics as well as the mechanical properties of surrounding ligaments and capsular structures have to be identified by testing cadaveric knees using the robot. Based on the gained data the biomechanical model is built-up. Furthermore, the sensory and control system of the physical setup is adapted to the knee joint followed by the configuration and the validation of the HiL environment. Based on HiL simulations variations of implant designs, implant positioning and surgical techniques are considered and their impact on joint kinematics and load situation will be evaluated. Moreover, finite element analyses are conducted using the results of the HiL simulations as boundary conditions in order to determine stresses, strains and contact pressure in the artificial knee joint.