Uniformly low serum cobalt levels after modular dual-mobility total hip arthroplasties with ceramic heads A PROSPECTIVE STUDY IN HIGH-RISK PATIENTS

Aims Modular dual-mobility constructs reduce the risk of dislocation after revision total hip arthroplasty (THA). However, questions about metal ions from the cobalt-chromium (CoCr) liner persist, and are particularly germane to patients being revised for adverse local tissue reactions (ALTR) to metal. We determined the early-to mid-term serum Co and Cr levels after modular dual-mobility components were used in revision and complex primary THAs, and specifically included patients revised for ALTR. Patients and Methods Serum Co and Cr levels were measured prospectively in 24 patients with a modular dual-mobility construct and a ceramic femoral head. Patients with CoCr heads or contralateral THAs with CoCr heads were excluded. The mean age was 63 years (35 to 83), with 13 patients (54%) being female. The mean follow-up was four years (2 to 7). Indications for modular dual-mobility were prosthetic joint infection treated with two-stage exchange and subsequent reimplantation (n = 8), ALTR revision (n = 7), complex primary THA (n = 7), recurrent instability (n = 1), and periprosthetic femoral fracture (n = 1). The mean preoperative Co and Cr in patients revised for an ALTR were 29.7 mu g/l (2 to 146) and 21.5 mu g/l (1 to 113), respectively. Results Mean Co and Cr levels were 0.30 mu g/l and 0.76 mu g/l, respectively, at the most recent follow-up. No patient had a Co level = 1 mu g/l. Only one patient had a Cr level = 1 mu g/l. That patient's Cr level was 12 mu g/l at 57 months after revision THA for ALTR (and decreased tenfold from a preoperative Cr of 113 mu g/l). Conclusion At a mean of four years, no patient with a modular dual-mobility construct and ceramic femoral head had elevated Co levels, including seven patients revised specifically for ALTR. While further studies are required, we support the selective use of a modular dual-mobility construct in revision and complex primary THAs for patients at high risk for instability.