The synovial response to intra-articular Co-Cr-Mo particles in guinea pigs

The histology and cytology of the tissue response to an intra-articular insertion of Co-Cr-Mo particles has been studied in the guinea pig knee joint. Following insertion, particles became incorporated into synovial tissue in two ways: (A) by incorporation in the intimal (surface) cell layer; (B) by growth of granulation tissue into metal-containing debris initially adherent to the synovial surface, leading to its incorporation in the subintimal tissue (i.e. beneath the surface), with subintimal fibrosis. Small particles of Co-Cr-Mo were phagocytosed by intimal cells, macrophages, multinucleate giant cells (macrophage polykaryons) and fibroblasts; large particles remained extracellular. Metal particles persisted in the synovial fluid, intimal cell layer and subintimal tissue for many months after metal insertion. As an unexpected finding, no zones of tissue necrosis were observed in the long-term (3 months to 1 year) response to Co-Cr-Mo particles incorporated in subintimal tissue. Lymphatic transport of metal particles from the knee area to inguinal lymph nodes was observed.