Stresses in the local collagen network of articular cartilage: a poroviscoelastic fibril-reinforced finite element study.

Osteoarthritis (OA) is a multifactorial disease, resulting in diarthrodial joint wear and eventually destruction. Swelling of cartilage, which is proportional to the amount of collagen damage, is an initial event of cartilage degeneration, so damage to the collagen fibril network is likely to be one of the earliest signs of OA cartilage degeneration. We propose that the local stresses and strains in the collagen fibrils, which cause the damage, cannot be determined dependably without taking the local arcade-like collagen-fibril structure into account. We investigate this using a poroviscoelastic fibril-reinforced FEA model. The constitutive fibril properties were determined by fitting numerical data to experimental results of unconfined compression and indentation tests on samples of bovine patellar articular cartilage. It was demonstrated that with this model the stresses and strains in the collagen fibrils can be calculated. It was also exhibited that fibrils with different orientations at the same location can be loaded differently, depending on the local architecture of the collagen network. To the best of our knowledge, the present model is the first that can account for these features. We conclude that the local stresses and strains in the articular cartilage are highly influenced by the local morphology of the collagen-fibril network.