Strain Rate Dependent Response and Fluid Load Support of the Knee Joint Under Compression

Abstract

The human knee joint is subjected to loading changes during daily activities. The investigation of the load response mechanisms within the knee contributes to the prevention, diagnosis and treatment of injury and disease of the joint. The load response of articular cartilage in the joint highly depends on the compression rate. This response has been extensively investigated in vitro with tissue discs, but not sufficiently examined in situ and in vivo within the intact joint. Computational simulation is a widely used tool to study this response. The development of imaging techniques has contributed to obtaining an accurate geometry of the knee joint, whose behaviour can then be simulated considering realistic contact conditions during knee compression. The role of the complex anatomy of the knee and its interplay between the various tissues needs to be considered in simulations and in vitro and in vivo studies to understand joint mechanics. This research is intended to deepen the understanding of the stress relaxation and creep response of the knee joint when the realistic human or animal geometry is considered. The objectives of this research are to (1) determine the compression rate-dependent response of the healthy and meniscectomized knee joints, (2) explore the role of fluid load support in healthy porcine knee joints subjected to compression and (3) evaluate the creep response of human knee joint in vivo using a combined imaging approach of MRI and dual fluoroscopy. Results from porcine joint tests revealed significant nonlinear compression-rate dependent load response and the influence of tissue hydration. A human subject test showed the feasibility of studying the creep response of the human joint in vivo, which may be used to validate a geometrically accurate model for computational simulations. This research will provide a better understanding of load share between the fluid pressure and tissue matrices within the knee joint, and how the load share changes with a compression rate that varies in daily activity.