Serum levels of cobalt and chromium in patients with Sikomet metal–metal total hip replacements

Metal/metal total hip replacements (M/M THRs) made of CoCr‐based alloys were reintroduced in hip arthroplasty in order to avoid the problem of polyethylene wear and consequently to diminish the wear debris‐related osteolysis. Emerging concerns accompanying the reintroduction of M/M THRs are related to the possibility increase of Co and Cr serum levels and, therefore, a careful surveillance of M/M patients is recommended. In the present work three groups of patients with Sikomet SM21 low‐carbon alloy were investigated: retrospective group, prospective group and revision group. The investigation of these different groups of patients provided data concerning the metal concentration as a function of time in situ, as well as time ex situ, i.e., following the removal of M/M bearing. A retrospective group of 25 patients sampled at average 60 ± 20 months postoperatively showed a 3‐fold increase in cobalt and a 4.4‐fold increase in chromium compared with the control group. In the prospective group of seven patients both cobalt and chromium increase with time and at average 140 ± 80 days achieved a significant increase compared with preoperative values. An important contribution of this study to the current knowledge on M/M bearings is achieved by the measurements in the revision group of 10 patients, where we observed a decline of serum Co and Cr levels following the removal of M/M articulation. While the link between the increase in metal serum levels and the presence of M/M THR is proved, the biological impact of these results remains to be elucidated.