Extensive research has demonstrated increased levels of blood metal ions caused by corrosion or wear of the metal after prosthetic implantations. However, metal ion levels in the joint fluid immediately after prosthetic implantation have not been investigated. We measured the concentrations of metal ions in the joint fluid immediately after total knee arthroplasty in seven patients. Fluid specimens from the joint were obtained from the suction drain 3 days after the operation. We determined the levels of Ni2+, Co2+, Cr3+, and Fe3+ using inductively coupled plasma atomic emission spectrometry (ICP-AES). Six of the seven patients exhibited high levels of Fe3+, which may have been derived from the accumulated hemoglobin of the red blood cells released following postoperative hemorrhage. Ni2+ ions could be detected in one patient, and Cr3+ ions in another. These ions are probably the result of mechanical friction between the bonesaw and the cutting guide during osteotomy. We further investigated the effects of metal ions on bone-resorbing cytokine production by synoviocytes and bone marrow macrophages in vitro. The results clearly indicated that the metal ion levels detected in the joint fluid specimens were sufficient to stimulate production of these cytokines. Finally, it should be emphasized that the metal ions detected in the joint fluid in the early stages after prosthetic implantation potentially produce bone-resorbing cytokines and possibly cause subsequent periprosthetic osteolysis.
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