Abstract
Introduction: Cobalt-chrome particles from metal hip implants can accumulate in the liver, spleen, lymph nodes and bone marrow of patients. This is a concern as studies have reported neoplastic changes in cells of patients with metal implants. The aims of this study were to determine the effect of wear particles generated by metal-on-metal and ceramic-on-metal implants from hip simulations upon the viability of L929 cells and to determine their genotoxic potential when cultured with primary human fibroblasts.
Methods: Particles were generated in a 10 station Prosim hip simulator run with water as lubricant under microseparation and standard conditions. Bearings comprised medical grade HIPed ‘BIOLOX Forte’ alumina ceramic femoral heads against Ultima metal CoCr acetabular cups (CoM) and wrought CoCr alloy ASTM F1537 femoral heads and acetabular cups (MoM). Particles were sterilised at 1800C for 4 hours and cultured with L929 fibroblasts at particle volume(μm3):cell number ratios of 500:1, 100:1, 50:1, 5:1, 0.5:1, 0.05:1, 0.005:1 and 0.0005:1. Camptothecin (1 and 2μg.ml-1) and latex beads (100μm3 per cell) were used as positive and negative controls. Cultures were for 0, 1, 2, 3, 4 and 5 days at 37oC in 5%(v/v) CO2 in air. Cell viability was assessed using the ATPlite assay. Sterile particles were cultured with primary human fibroblasts at particle volume (μm3):cell number ratios of 50:1, 5:1 and 0.5:1. Cells were exposed to 30%(v/v) H2O2 (positive control) and latex beads (50μm3 per cell; negative control). Cells were cultured for 24 hours and 5 days at 37oC in 5%(v/v) CO2 in air. Genotoxicity was assessed using the comet assay. Statistical analysis between the cell-only negative controls and the cells with the particles at various concentrations, were determined by ANOVA and calculating the minimum significant difference (MSD;p< 0.05) using the T-method.
Results: Particle volume(μm3):cell ratios of 500:1, 100:1 and 50:1 caused a significant decrease in cell viability over 5 days. Wear particles from MoM implants under microseparation wear conditions were also significantly reduced viability at particle volume(μm3):cell ratios of 5:1 over 5 days. Particles from MoM implants under standard wear conditions and CoM implants under both wear conditions resulted in increases in tail length and tail moment relative to the cells only negative control for all treatment groups after 24 hours. These decreased by day 5. Tail length and tail moment were increased at 24 hours relative to day 5 for each of the three particle types. Particles generated by MoM implants under microseparation conditions had different effects upon cells. Tail lengths increased between days 1and 5 for all particle concentrations. A significant increase in tail moments between days 1 and 5 was recorded.
Discussion: This study has shown that metal particles can cause cytotoxic effects and immediate DNA damage to fibroblasts in vitro. Particles were found to reduce cell viability over 5 days and this may account for the decreases in tail length and moments between 1 and 5 days for three particle types. This is of concern as MoM and CoM implants are designed to be implanted into young patients and, despite their low wear rates generate circa 1013 particles per mm3 of wear.
Correspondence should be addressed to Dr Carlos Wigderowitz, Honorary Secretary of BORS, Division of Surgery & Oncology, Section of Orthopaedic & Trauma Surgery, Ninewells Hospital & Medical School Tort Centre, Dundee, DD1 9SY.
