In vivo serum metal ion levels in primary anatomic and reverse total shoulder arthroplasty after 5-year follow-up

Background: Elevated metal ions may be indicative of prosthesis wear or failure. Despite the fact there are no metal-on-metal articulations in shoulder arthroplasty, there are several metal-on-metal junctions, which could potentially lead to metal wear and debris. Direct metal-on-metal wear can also occur due to polyethylene component failure, wear, or dissociation. The primary aim of this study was to quantify in vivo metal ion levels in anatomic and reverse shoulder arthroplasty at 5-year minimum follow-up to evaluate if serum metal ion levels increase over time. The secondary aim was to investigate if the type of shoulder arthroplasty implant, reverse or anatomic, is associated with concentration of circulating ions. Methods: This was an institutional review board–approved prospective cohort study. Patients were recruited in person at routine 5-year follow-up appointments. Consented participants had a standard blood draw that was processed at a commercial laboratory using established techniques. Chromium, cobalt, and titanium levels were measured. Results: Fifty-three subjects were eligible and enrolled in the study. Thirty-eight participants underwent aTSA and 15 underwent reverse shoulder arthroplasty. No participant had serum titanium levels above the minimum detection threshold of 10.0 ng/L and only 1 participant had cobalt levels above the minimum detection threshold of 1.0 μg/L. The mean blood concentration of chromium was 0.89 ± 0.45 μg/L (median = 0.80, interquartile range = 0.60-1.10). Conclusion: Few cases of metallosis have been reported after shoulder arthroplasty; however, it is important to establish expected circulating metal ion levels. In addition to evaluation for potential systemic toxicity, the values may be important in future research to evaluate wear and implant failure. Future research should focus on serum metal ion levels in patients who have received multiple joint arthroplasties, as well as attempting to elucidate any differences between surgical and implant factors.