Modeling the steady-state deformation of the solid phase of articular cartilage

The transient response of articular cartilage (AC) to compressive loads has been described by complex multicomponent models. However, the steady-state behaviour is determined by the collagen network which is heterogeneous through the depth of the tissue, a characteristic which is omitted from most theoretical models. Experimental data are now available on the local responses of the network to compressive loads and the aim of this study was to develop minimal models capable of simulating this behaviour. A series of finite element models (FEMs) of AC under load were developed of increasing complexity, assuming the AC was i) completely homogeneous, ii) layered and isotropic and iii) layered and anisotropic. The geometry of the layered cartilage model was based on the recent experimental data. It is shown that a layered transversely isotropic elastic model is required to accurately recreate the experimental data. Stress distributions within the models are analysed, and the relevance of this work to transient modeling of AC is discussed. The work presented is a fundamental step forward in the understanding of the distribution of local physiological stresses and strains in AC, and has applications in modeling chondrocyte mechanotransduction as well as the effects of pathogenesis.