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

• Applicants: Professor Dr. Rainer Bader; Privatdozent Dr.-Ing. Daniel Klüß; Professor Dr.-Ing. Christoph Woernle
• Subject Area: Applied Mechanics, Statics and Dynamics ; Automation, Mechatronics, Control Systems, Intelligent Technical Systems, Robotics
• Term: from 2013 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 235922259

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.

• DFG Programme: Research Grants