Early failure of metal-on-metal hip arthroplasties is a current concern because tissue damage resulting from periprosthetic metallosis can compromise subsequent revision arthroplasty1,2. The United Kingdom’s Medicines and Healthcare products Regulatory Agency has advised that patients with metal-on-metal implants who have pain, prosthetic malposition, or implants that are known to have excessive failure rates should be evaluated with the measurement of serum cobalt. A serum cobalt level of >7 μg/L indicates possible periprosthetic metallosis3,4. A normal serum cobalt level is 0.19 μg/L, and 95% of those who are unexposed to cobalt have a value of <0.41 μg/L5. A serum cobalt level of >1 μg/L indicates excessive cobalt exposure, and levels of >5 μg/L are considered toxic6.
In excess, cobalt blocks cellular metabolism and can damage multiple organs. Cobalt poisoning (cobaltism) from beer additives, industrial exposure, or medicinal use is well known. Cobaltism can result in tinnitus, vertigo, deafness, blindness, optic nerve atrophy, convulsions, headaches, peripheral neuropathy, cardiomyopathy, and hypothyroidism7,8. Including the two cases in the present report, there are at least six case reports of cobaltism related to arthroplasty implants (arthroprosthetic cobaltism)7,9-12. These four patients presented with combinations of deafness, blindness, cognitive decline, headaches, convulsions, fatigue, weakness, peripheral neuropathy, heart failure, and hypothyroidism. All of these patients had periprosthetic metallosis due to wear of steel femoral heads by ceramic, and all had a serum cobalt level of >60 μg/L. The two …
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