Cathepsin K in aseptic hip prosthesis loosening: Expression in osteoclastswithout polyethylene wear particles

Objective. To investigate the expression of the bone matrix degrading cyste ine proteinase cathepsin K and to determine the colocalization of cathepsin K with polyethylene (PE) particles in tissue specimens of patients with as eptic hip prosthesis loosening (AHPL). Methods, The expression of cathepsin K was studied by immunohistochemistry in tissue specimens of 9 patients with aseptically loosened acetabular comp onents of failed cementless total hip replacements. The expression of cathe psin K was compared to that of the macrophage marker CD68 by serial section analysis. Double labeling of the expression of cathepsin K or CD68 by immu nohistochemistry and of PE particles by modified Oil Red staining method wa s performed. Results, Cathepsin K could be predominantly detected in osteoclasts attache d to the bone tissue. while only a few (CD68+) mononuclear and multinucleat ed foreign body giant cells (MGC) were positive for this enzyme. By double labeling with Oil Red staining we found the majority of CD68 positive cells of the periprosthetic tissue that were colocalized with PE particles. Howe ver, cathepsin K-expressing osteoclasts could not be stained with Oil Red. Conclusion. The present data suggest that in AHPL neither mononuclear cells nor MGC but rather osteoclasts are mainly involved in cathepsin K mediated bone matrix destruction. Using double labeling of immunohistochemistry and Oil Red staining we observed that the cathepsin K-expressing osteoclasts d id not include PE particles.