Up to now, the interaction mechanisms between cartilage and synovial fluid within diarthrodial joints are not fully understood. These joints are able to function effectively over the lifetime of an individual even under very high loads, which requires minimal wear of cartilage. In particular, the reason for the extremely low coefficients of friction has still to be explained.
The goal of this contribution is to numerically investigate the interaction between articular cartilage and synovial fluid in diarthrodial joints. In this connection, we already developed an appropriate continuum model of the articulating tissue layers as highly anisotropic and heteregeneously charged biphasic solid-fluid aggregates based on the Theory of Porous Media (TPM). The calibration of the previously elaborated model is the next concern. To this end, a sensitivity analysis is performed to identify the relevant constitutive parameters governing the cartilage response during indentation tests. The remaining parameters are then estimated numerically using a direct search algorithm. Next, a sequential solution algorithm has to be developed in order to solve the complex contact problem at the interface between synovial fluid and articular cartilage. Thereby, the fluid and cartilage domains are iteratively calculated until equilibrium is reached. For the moment, simulations are performed on a 3-d hip-joint geometry reconstructed from MRI data, which proceed from a continuum-mechanical description of the synovial fluid gap. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)