A new knee simulator has been developed at Ghent University. This simulator provides the unique opportunity of evaluating the knee kinematics during activities of daily living. The simulator therefore controls the position of the ankle in the sagittal plane while keeping the hip at a fixed position. This approach provides full kinematic freedom to the knee. To evaluate and validate the performance of the simulator, the development of and comparison with a numerical simulation model is discussed in this paper. Both a two and three dimensional simulation model have been developed using the AnyBody Modelling System (AMS). In the two dimensional model, the knee joint is represented by a hinge. Similarly, the ankle and hip joint are represented by a hinge joint and a variable amplitude quadriceps and hamstrings force is applied. In line with this simulation model, a hinge model was created that could be mounted in the UGent knee simulator to evaluate the performance of the simulated model. The hinge model thereby performs a cyclic motion under varying simulated muscle loads while recording the ankle reaction forces. In addition to the two dimensional model, a three dimensional model has been developed. More specifically, a model is built of a sawbone leg holding a posterior stabilised single radius total knee implant. The physical sawbone model contains simplified medial and lateral collateral ligaments. In line with the boundary conditions of the UGent knee simulator, the simulated hip contains a single rotational degree of freedom and the ankle holds four degrees of freedom (three rotations, single translation). In the simulations, the knee is modelled using the force-dependent kinematics (FDK) method built in the AMS. This leaves the knee with six degrees of freedom that are controlled by the ligament tension in combination with the applied quadriceps load and shape of the implant. The physical sawbone model goes through five cycles in the UGent simulator using while recording the kinematics of the femur and tibia using a set of markers rigidly attached to the femur and tibia bone. The position of the implant with respect to the markers was evaluated by CT-scanning the sawbone model.Background
Methods
Biomechanical joint contact pressure distribution measurements have proven to be a very valuable tool in orthopaedic research to investigate the influence of surgical techniques such as total knee arthroplasty (TKA) on the human knee joint. Quantification of the in vitro tibiofemoral and patellofemoral contact pressure distribution before and after the intervention are an important measure to evaluate the impact of the surgery. The K scan pressure sensor from Tekscan (South Boston USA) is a commonly reported device for these in vitro pressure measurements. Despite the large interest in the sensor, the effective measurement accuracy for in vitro biomechanical joint contact measurement still remains a big question and therefore the reliability of these measurements should be questioned. Reliable contact pressure measurements can only be done if the sensor behaviour is fully understood. Therefore, a tailored multi-axial testing machine has been designed to profoundly investigate and characterise the sensor behaviour. This test setup is unique through its ability to apply a predefined tangential force or sliding velocity to the sensor's interface next to a normal force. Dynamic effects occurring in knee joint motion can thus be simulated while evaluating the effect on the contact pressure measurements.Background
Methods
