RT Journal A1 Jacobs, Joshua J. T1 Commentary on an article by Stephen S. Tower, MD: “Arthroprosthetic Cobaltism: Neurological and Cardiac Manifestations in Two Patients with Metal-on-Metal Arthroplasty. A Case Report” JF The Journal of Bone & Joint Surgery JO The Journal of Bone & Joint Surgery YR 2010 FD December 1 VO 92 IS 17 SP e35 1 OP 2 DO 10.2106/JBJS.J.01657 UL http://dx.doi.org/10.2106/JBJS.J.01657 AB This issue of The Journal of Bone and Joint Surgery includes a report on two patients with metal-on-metal total hip replacements who developed systemic neurological and cardiac complications associated with an elevation in serum cobalt levels. Causality is suggested by the fact that the systemic symptoms improved in at least one of the two patients following revision surgery. The report is unusual because of the rarity of the occurrence of metal-induced systemic complications in patients with total hip replacement and the fact that the author was one of the patients. As millions of patients worldwide have undergone total hip replacement, these cases represent rare events indeed.