Osteolysis model with continuous infusion of polyethylene particles.

Several in vivo studies have investigated bone to implant interface tissues after a single injection of wear particles into animal joints. However, in the clinical setting, wear debris are generated continuously rather than periodically. Histomorphologic findings and the gene expression of bone resorbing cytokines in reactive membranes were analyzed in response to continuous infusion of polyethylene particles with an osmotic pump. In this model, it took only 6 weeks for proliferative fibrous tissue to form, which penetrated the subchondral bone to communicate with the bone marrow. In addition, tartrate resistant acid phosphatase positive osteoclastlike cells were found in empty lacunae. According to the analysis of gene expression, only tumor necrosis factor alpha messenger ribonucleic acid was expressed specifically in the fibrous tissue of rats infused with particles from 4 weeks after surgery. This finding suggests that tumor necrosis factor alpha may play a major role in fibrous tissue formation and osteoclastic bone resorption caused by wear debris around implants. In addition, this in vivo model seems useful for investigating the mechanism of membrane formation and associated bone resorption around implants in a situation more similar to human prostheses than in conventional models.