Effects of cobalt-chrome alloy wear particles on the morphology, viability and phagocytic activity of murine macrophages in vitro.

Metallic wear particles were prepared from orthopaedic cobalt-chrome alloy by milling in medium supplemented with 20% foetal calf serum to maintain particle dispersion. The size distribution of particles was determined by sedimentation and centrifugation and particle concentration was assessed using light extinction. Monolayers of mouse peritoneal macrophages were exposed to metal particles at different concentrations for varying periods. After 4 h of exposure to particle concentrations exceeding 30 micrograms/ml there was a progressive decline in cell viability, and light and electron microscopy showed that surviving cells had assumed remarkably smooth profiles and contained abundant endocytosed metal. Phagocytic uptake of polystyrene spherules was inhibited markedly by exposure to metal particles even at concentrations at which macrophages remained 100% viable, and preceded the reduction of viability at higher concentrations. The findings are consistent with a pathological role for the metallic wear particles observed frequently within macrophages in the synovial tissues around loose artificial joints in humans.