To investigate the pathogenesis of articular prosthesis osteolysis, and to clarify the role of OPG, RANKL and RANK on osteolysis in aseptic loosening of hip prostheses.

We examined the mRNAs of OPG, RANKL and RANK from cultured peripheral mononuclear cells and the tissue surrounding failed hip prostheses by RT-PCR and gel electrophoresis and performed immunohistochemistry for RANKL and RANK in the periprosthetic tissue of revised hip replacement therapy.

RANKL was detected in 32% and RANK was detected in 20% of the periprosthetic tissues of failed hip prostheses. Proliferative responses of cultured PBMCs occurred in cells with the titanium, cobalt and LPS, and highest response was observed in cells with cobalt particles. The mRNAs of RANKL and OPG were expressed in the periprosthetic tissues of loosened hip prostheses, but RANK mRNA was not detected. OPG mRNA was not detected in cultured PBMCs with any particles, RANKL mRNA was detected in cultured PBMCs with titanium and cobalt particles by RT-PCR, and RANK mRNA was detected in PBMCs with cobalt particles, but not with titanium.

Osteolysis around the failed hip prosthesis may be related to activation of the OPG-ANKLRANK system. It is suggested that OPG, RANKL and RANK are major mediators of osteolysis in failed hip prosthesis.