Experimental protocol to develop and validate a 3D patient-specific Finite Element Model of human knee joint after Total Knee Arthroplasty: Squat analysis

In some cases of degenerative knee condition, total knee arthroplasty (TKA) can be a successful surgical treatment to restore the knee’s functionality, if carried out correctly. Since each patient has different bone shapes and soft tissues mechanical properties, the 3D complex roto-translation movement and the kinetics of the knee change as well. For these reasons, nowadays, several methodologies are carried out to analyse and predict the three-dimensional behaviour of a native or post-arthroplasty knee. To overcome the limitations of the in vivo analysis, such as low amount of analysed specimens for specific boundary conditions, and of the cadaver tests, in terms of high costs, lack of repeatability and ethical issues, the use of numerical modelling is becoming a fundamental tool to better understand the patient-specific knee joint anatomy and functionality.The purpose of this research project was to produce a protocol in order to develop and validate a patient specific finite element model comparing numerical outcomes, in terms of kinematics and kinetics, with in vitro results obtained during cadaver test performed on the same specimen under the same boundary conditions.Guide lines about experimental test were given, showing step by step the surgical specimen preparation and all the procedures to calibrate and utilise maps pressure sensors and motion capture systems. CT images, mechanical properties estimated through tensile test of ligaments, and boundary conditions applied during the experimental test, were used to develop the patient-specific Finite Element model. Therefore, the same active motor task simulated with the cadaver specimen was reproduced with a numerical approach.A final comparison analysis between numerical and experimental outcomes showed that, the tibiofemoral kinematics were validated both in terms of translations and rotations. Instead, regarding to kinetics, while the patellofemoral contact areas and contact pressures predicted using FE model were validated for the main significant flexion angles, it could be validated only the tibiofemoral contact areas because the relative contact pressures measured during the cadaver test resulted uncorrected and in disagreement with the literature.