In vivo knee joint loading and kinematics – the interplay between movement and loading at the patello-femoral and tibio-femoral joints.

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While total knee arthroplasty is a generally very successful treatment for knee osteoarthritis, about 20% of patients later turn out to be not satisfied with their functional post-operative outcome. A substantial patient population suffers from not yet fully understood post-operative symptoms, such as anterior knee pain. Progress towards solving the remaining problems of knee joint replacement requires a better understanding of the mechanical interaction between the patello-femoral and tibio-femoral joints. However, measuring the precise internal loading and kinematics of the knee during dynamic activities is extremely challenging; as a result no appropriate data is available so far. Over the last few years, a tight collaboration between the Charité-Berlin and the ETH-Zürich allowed us to capture a worldwide unique dataset of synchronized in vivo tibio-femoral loads and internal joint kinematics. The simultaneous measurement of these two key parameters, along with whole body motion, ground reaction forces and muscle activity, now provides the basis for the present application, which aims to gain an understanding of the underlying knee mechanics in a replaced joint. Concurrently, we will quantify the patient-specific patello-femoral loads, how they relate to the dynamic movements within the patello-femoral and tibio-femoral joints, and how antagonist muscle co-contraction affects the total joint forces and the pressure distributions at the articulating surfaces. In particular, we will develop a technology platform that enables us to identify adverse combinations of implantation parameters, that may lead to excessive loading of the joint structures. After validation against in vivo knee load measurements and muscle activation from EMG, the musculoskeletal loading determined through advanced subject specific models will serve as input to detailed contact analyses with the goal to unravel the loading distribution at the articulating surfaces. Although this specific dataset of in vivo forces and kinematics is limited to a patient cohort of six, it is globally the largest available dataset, and within this project we aim at establishing it as a benchmark for later analyses of other implants or patient kinematic data. In doing so, we will also lay the technological foundation to evaluate other implant designs and implantation methods, beyond the validated instrumented implants used here.