HiL simulation for testing joint stability after total knee arthroplasty

Instability of total knee replacements (TKRs) remains one of the most prevalent complications after total knee arthroplasty. Especially the actual event of instability involving complex interactions between implant components and soft tissue structures is not well understood. Therefore, the purpose of this work is to introduce a novel approach for testing TKRs with respect to stability of the artificial knee joint based on a mechatronic hardware-in-the-loop (HiL) test system. The mechanical test setup is composed of an industrial robot with a compliant support for the endoprosthesis to be tested. It interacts with a biomechanical multibody model consisting of all relevant body parts of the lower extremity incorporating ligament structures of the knee joint. According to the movement angles and reaction forces/torque provided by the multibody model, the robot rotates and loads the femoral component with respect to the tibial component. The resulting position and loading of the femoral component are measured and fed back into the model, thus closing the control loop for HiL simulations. The functional principle of the HiL simulation is proven by simulating a passive flexion movement of a bicondylar, posterior cruciate ligament retaining TKR using the described biomechanical multibody model.