A Multiscale Model of the Cartilage Bone Interface to Investigate the Initiation of Osteoarthritis

The initiation of cartilage degeneration has been linked to the onset of subchondral bone remodelling and osteophyte formation at the cartilage-bone interface. As such, Osteoarthritis (OA) is defined as the thinning of cartilage and/or osteophyte formation. Cartilage adjacent to healthy bone has a characteristic stress distribution when loaded within a healthy range. This loading is then transferred to the subchrondal bone, where remodelling maintain a bone strength and structure to cope with everyday loads. We have developed a framework to model the cartilage bone interface using a hierarchy of models at the whole knee level, micro level and cellular level. Whole knee loads determine the boundary conditions for micro models. The micro models then capture the remodeling of bone and change in cartilage stiffness. The amount of bone forming cells (osteoblasts), bone resorbing cells (osteoclasts) and the rate of cartilage cell (chondrocyte) metabolism under the influence of inflammation cells (cytokines) are determined from cell models. The cell models respond to strain from the micro models. The current model predicts that altered loads initiate bone thickening (cartilage thinning), osteophyte formation, cartilage stiffening and ultimately cartilage degeneration.