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Cement particles containing radio-opacifiers stimulate pro-osteolytic cytokine production from a human monocytic cell line

Yeovil District Hospital, Higher Kingston, Yeovil, Somerset BA21 4AT, UK.

M. H. Stone, FRCS Ed, Consultant Orthopaedic Surgeon

Leeds General Infirmary, Great George Street, Leeds LS1 3EX, UK.

E. Ingham, PhD, Professor of Medical Immunology; and J. Fisher, PhD, Prfessor of Mechanical Engineering

The University of Leeds, Woodhouse Lane, Leeds, West Yorkshire LS2 9JT, UK.

Correspondence should be sent to Mr D. L. Shardlow.

Proponents of the biological theory of aseptic loosening have in recent years tended to concentrate on the production and distribution of particulate ultra-high-molecular-weight polyethylene (UHMWPE) debris around the potential joint space. However, mechanical loading of cemented implants with the differing elastic moduli of metal stems, polymethylmethacrylate (PMMA) cement and bone can result in relative micromotion, implying the potential for production of metal and PMMA particles from the stem-cement interface by fretting wear.

In order to investigate the production and biological reactivity of debris from this interface, PMMA and metal particulate debris was produced by sliding wear of PMMA pins containing barium sulphate and zirconium dioxide against a Vaquasheened stainless steel counterface. This debris was characterised by SEM, energy-dispersive analysis by X-ray (EDAX) and image analysis, then added to cell cultures of a human monocytic cell line, U937, and stimulation of pro-osteolytic cytokines measured by ELISA.

Large quantities of PMMA cement debris were generated by the sliding wear of PMMA pins against Vaquasheened stainless steel plates in the method developed for this study. Both cements stimulated the release of pro-osteolytic TNF from the U937 monocytic cell line, in a dose-dependent fashion. There was a trend towards greater TNF release with Palacos cement than CMW cement at the same dose. Palacos particles also caused significant release of IL-6, another pro-osteolytic cytokine, while CMW did not. The particulate cement debris produced did not stimulate the release of GM-CSF or IL1ß from the U937 cells. These results may explain the cytokine pathway responsible for bone resorption caused by particulate PMMA debris.

Radio-opaque additives are of value in surgical practice and clinical studies to quantify the relevance of these in vitro findings are required before the use of cement containing radio-opacifier is constrained.