Synovial macrophage response to aluminium oxide ceramic and cobalt-chrome alloy wear particles in rats.

The tissue response to intra-articular injection into rat knees of similar concentrations of sterile cobalt-chrome (Co-Cr) alloy and aluminium oxide (AL2O3) ceramic prosthesis wear particles was assessed at 1, 4 and 13 wk. A semiquantitative method of histological assessment showed a correlation between the numbers of particles and macrophage response in the tissues, and a difference in the response to different concentrations of Co-Cr particles. At 1 wk, the macrophage response to Co-Cr particles was significantly greater (p less than or equal to 0.01) than that to AL2O3 particles but no difference was detected at 4 and 13 wk. The difference may be due to necrosis of macrophages induced by Co-Cr particles.