FIG. 2.

The “particle disease” theory in brief. Macrophages are activated by wear particles to produce chemokines and inflammatory mediators. Chemokines recruit additional monocytes into interface tissue, and inflammatory cytokines lead to increased ostoclastogenesis and bone resorption, primarily by increasing receptor activator of Nf-κB ligand (RANKL) and decresing osteoprotegeing (OPG) production from local fibroblasts and osteoblast. The exact mechanisms by which wear particles are recognized by macrophages and thus cause macrophage activation is still incompletely understood.