An investigation of the stress distribution generated in articular cartilage by crystal aggregates of varying material properties

Several joint diseases are associated with the deposition of crystals within the articular cartilage. A variety of crystal aggregates have previously been identified throughout the thickness of the cartilage. A linear elastic finite element model representing instantaneous, or short-term, loading conditions has been developed of a large crystal aggregate surrounded by articular cartilage. The material properties of the aggregate and the cartilage were varied and the resultant shear stress and equivalent strain distribution in the surrounding cartilage studied in order to provide some indication of the relative potential of various types of crystal aggregate to cause damage to the articular cartilage. Results indicated that aggregates with a Young's modulus either much less, or much greater, than that of the surrounding cartilage generated the maximum shear stress and equivalent strain concentrations at the interface between the aggregate and the cartilage. Also, that highly compressible aggregates, with a very low Poisson's ratio, generated higher shear stress and equivalent strain concentrations in the surrounding cartilage than aggregates of a more incompressible nature. Under conditions of short-term loading these results suggest that crystal aggregates present within the cartilage layer will increase the shear stress and equivalent strain concentrations in the surrounding cartilage, and therefore have the potential to cause damage to the cartilage