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.