Modelling of the conlyde elements within a biomechanical knee model

Abstract

The main purposes of this work are to present a computational multibody model able to capture some of the fundamental properties of the knee joint and to simulate human gait during the stance phase, which includes the kinetics of the real knee articulation. The research question is whether an accurate modeling of the condyle contact in the knee will lead to reproduction of the complex combination of flexion/extension, abduction/adduction and tibial rotation observed in the real knee? In a simple manner, the developed model is composed by two anatomic segments, the tibia and the femur, whose characteristics are functions of the geometric and anatomic properties of the real bones. The biomechanical model characterization is developed under the framework of multibody systems methodologies using Cartesian coordinates. The type of approach used in the proposed knee model is the surface contact conditions between ellipsoids, representing the two femoral condyles, and points, representing the tibial plateau and the menisci. These elements are closely fitted to the actual knee geometry, which is based on a parameter optimization process to represent experimental data published in the thematic literature. Kinematic data in the form of flexion/extension patterns are imposed on the model, and the resulting patterns of secondary knee movements are analyzed and compared with data obtained from in vivo bone results. From the computational simulations performed, it was observed that the knee model approximates the average secondary motion patterns observed in the literature. However, the studies performed also revealed considerable inter-individual differences in the secondary motion patterns, and it was subsequently investigated whether the model was able to reproduce these differences with reasonable variations of bone shape parameters. This was accomplished by a parameter study, in which the main variables that define the geometry of condyles were considered. The data also reveal a difference in secondary kinematics of the knee in flexion versus extension. The likely explanation for this fact is the elastic component of the secondary motions created by the combination of joint forces and soft tissue deformations. The model proposed throughout this work is, therefore, used to investigate whether this observed behavior can be explained by reasonable elastic deformations of the points representing the menisci in the model.