RADIO-OPAQUE AGENTS IN BONE-CEMENT INCREASE BONE-RESORPTION

A heavy infiltrate of foreign-body macrophages is commonly seen in the fibrous membrane which surrounds an aseptically loose cemented implan t, This is in response to particles of polymethylmethacrylate (PMRW) b one cement and other biomaterials. We have previously shown that monoc ytes and macrophages responding to particles of bone cement are capabl e of differentiating into osteoclastic cells which resorb bone. To det ermine whether the radio-opaque additives barium sulphate (BaSO4) and zirconium dioxide (ZrO2) influence this process, particles of PMMA wit h and without these agents were added to mouse monocytes and coculture d with osteoblast-like cells on bone slices, Osteoclast differentiatio n, as shown by the presence of the osteoclast-associated enzyme tartra te-resistant acid phosphatase (TRAP) and lacunar bone resorption,,vas observed in all cocultures. The addition of PMMA alone to these cocult ures caused no increase in TRAP expression or bone resorption relative to control cocultures, Adding PMMA particles containing BaSO4 or ZrO2 , however, caused an increase in TRAP expression and a highly signific ant increase in bone resorption, Particles containing BaSO4 mere assoc iated with 50% more bone resorption than those containing ZrO2. Our re sults suggest that radio-opaque agents in bone cement may contribute t o the bone resorption of aseptic loosening by enhancing macrophage-ost eoclast differentiation, and that PMMA containing BaSO4 is likely to b e associated with more osteolysis than that containing ZrO2.