Hardware-in-the-loop-simulator for testing of knee endoprostheses

Abstract

A major problem of total knee endoprostheses is the instability of the artificial joint. Contributing factors are, for example, insufficient ligament structure, inappropriate implant design or implant malposition. Despite increasing clinical experiences the reoperation rate caused by knee instability has not reduced significantly during the last years. There are still numerous open questions about influence parameters on postoperative instability of total knee endoprostheses. Because in vivo measurements of the joint stability behaviour are not possible, a novel mechatronical hard-ware-in-the-loop (HiL) simulator for joint endoprostheses is presented. HiL simulations allow the analysis of physical system components in a virtual environment simulated by a computer. By means of the HiL joint simulator the kinematic and dynamic behaviour of the total knee endoprosthesis is simulated in order to evaluate experimentally the influencing parameters. The femoral and tibial knee implant components which represent the physical component of the HiL simulator are fixed to artificial bone. The femoral component is moved and loaded by an industrial robot capable to apply physiological forces and torques. The dynamics of the physiological movements including the preload of the ligaments as well as soft tissue and muscular forces are simulated by a biomechanical multibody model. The biomechanical model and the robot with the implants mutually interact and represent a closed-loop control system. The new concept of the HiL joint simulator provides a comparative investigation of actual total knee implants under exactly reproducible conditions. It is the basis for optimising influence parameters considering the individual implant design and positioning as well as bone and ligament conditions of the patients.