Development of a dynamic hip joint simulation model

Abstract

Synovial joints, like the hip joint, has unique characteristics. In order to study these characteristics by making use of mathematical techniques, it is necessary to develop a model simulating the dynamic forces and joint movements during joint operation. Once this is available, the effect of the synovial fluid lubricant properties can be added by describing its behaviour as a component of the hip joint simulation model. This was the ultimate aim of this research effort. With this work a model based on fundamental principles, like the equations of mass and motion, was developed and validated experimentally with a hip joint simulator. It is also shown that the effect of the lubricant properties can be studied by adding the relevant rheological equations. These fluid properties can have a significant effect on the joint under typical joint operations like dynamic loading and movement. To develop a model with relative complexity, certain simplifying assumptions have to be made. In this study, the fluid was assumed to have no boundary interactions with the articulating surfaces. It is known that complex rheological interaction exists in these systems. Although certain assumptions were made during development, model results are promising and a firm basis was established for subsequent research. In future, the model needs to be extended to simulate the continuous, multi-cycle operation of a human joint, with accurate geometrical descriptions of articulating surfaces and known components of synovial joints like articular cartilage. The model could then contain lubrication mechanisms known to prevail in synovial joints, with accurate rheological models of synovial fluid which will play an increasing role under typical joint operations.