OSTEOCLASTIC DIFFERENTIATION BY MONONUCLEAR PHAGOCYTES CONTAINING BIOMATERIAL PARTICLES

Aseptic loosening of implant components is a common and important comp lication of both cemented and uncemented prosthetic joint replacements . Wear particles derived from organic polymer and metal implant biomat erials are commonly found within macrophages and macrophage polykaryon s in the fibrous membrane between loose implant components and the hos t bone undergoing resorption. In order to deter-mine whether biomateri al particle-containing, foreign-body macrophages may contribute to per iprosthetio bone resorption. we cultured murine monocytes that had pha gocytosed particles of biomaterials commonly employed in bone implant surgery [polymethylmethacrylate (PMMA), ultra-high molecular weight po lyethylene (PE), titanium and chromium-cobalt] on bone slices and glas s coverslips with UMR 106 osteoblast-like stromal cells in the presenc e of 1.25-dihydroxy-vitamin D-3. Under these conditions, all biomateri al particle-containing. foreign-body macrophages differentiated into o steoclastic cells, i.e. tartrate-resistant acid, phosphatase (TRAP)-po sitive multinucleated cells capable of extensive lacunar bone resorpti on. This study shows that particle phagocytosis by macrophages does no t abrogate the ability of these cells to undergo osteoclast differenti ation. These findings emphasise the importance of the foreign-body mac rophage response to biomaterial wear particles in the pathogenesis of aseptic loosening.