Reassuring early serum metal ion levels with a specific modular dual mobility system

The popularity of modular dual mobility (MDM) acetabular components has increased. Concerns have been raised about the potential for corrosion related complications in these modular implants. The purpose of this study was to prospectively monitor serum ion levels in a series of patients with a modular dual mobility system.

Twenty-six patients with the Zimmer Biomet G7 DM construct were enrolled and followed for a minimum of one year. Serum cobalt, chromium, and titanium levels were obtained prior to six-weeks postoperatively and at one and two-years postoperatively. Five-year labs were obtained if previous labs were elevated.

At 0-6 weeks postoperatively, 4/26 patients had mildly elevated cobalt levels (1-2.8 μg/L) and 2/26 had mildly elevated chromium levels (1.6, 2.0 μg/L). None of the 19 patients showed elevated cobalt levels at one or two years, while 4/19 reported mildly elevated chromium levels (1.1-1.3 μg/L) at one-year with a slight decrease (1-1.4 μg/L) at two-years. No patients at any time point had metal ion levels exceeding the initial early threshold of 5 μg/L. No patient was symptomatic and no MRIs were indicated or obtained.

In this series of a specific modular DM system, the early mildly elevated cobalt levels in four patients all subsequently normalized. Chromium was mildly elevated in four patients through year two. While these findings are reassuring in the short term as mildly elevated chromium (<2 μg/L) has not been associated with clinical toxicity, additional follow-up is needed to establish the long-term safety and efficacy of this specific modular DM implant.