Contact mechanics modelling of articular cartilage and applications

Osteoarthritis (OA) is a degenerative disease of articular cartilage. The normal cartilage is known to be an excellent bearing material with remarkable lubricating properties and very low frictional co-efficient and wear and generally survives the lifetime of a person. The contact mechanics of the articular cartilage was investigated in this study. The contact mechanics of the cartilage surface against both rigid metallic and cartilage surfaces was investigated using finite element method. Axisymmetric and two-dimensional plane stain models were developed to examine consolidation and sliding respectively.

A new contact detection algorithm was developed to be used with ABAQUS (ABAQUS., 2005) which was more generic in nature. Two versions were developed; one for the indenter-cartilage models and the other for the cartilage-cartilage models. The first algorithm and the corresponding model were validated against the previous study (Warner, 2000) for the indentation of the articular cartilage using a rigid spherical indenter. The second algorithm and the model were validated against the study by Federico and colleagues (Federico et al., 2004) for the cartilage-cartilage configuration. The results presented in these studies could be reproduced with high degree of accuracy. The first algorithm was also applied to derive the mechanical properties of the cartilage from the experimental indentation measurements as well as to study its behaviour.

All the sliding models showed the interstitial fluid pressurization persisted over a long time period. This fluid load support of the cartilage had been shown to contribute towards lowering the frictional co-efficient (Forster et al., 1995; Krishnan et al., 2005).

The model of a rigid plate sliding over the cartilage covering it entirely during the course of sliding showed similar results as consolidation. The fluid exudation suggested in the weeping lubrication (McCutchen, 1959; McCutchen, 1962) mechanism was also observed in this model.

In the model of a rigid cylindrical indenter sliding over cartilage the fluid pressurization was found to decrease initially before attaining the steady value. The stress shielding phenomenon of the cartilage was also observed as in other models. The self generating lubrication (Mow and Lai, 1980) phenomena and boosted lubrication (Maroudas, 1967; Walker et al., 1968) were observed in this model.