Letter to the Editor: Is There a Cardiotoxicity Associated With Metallic Head Hip Prostheses? A Cohort Study in the French National Health Insurance Databases

To the Editor, We read the recent study by Lassalle and colleagues [6] with great interest. Using a large observational cohort, the authors examined the relationship between hip prostheses with metal femoral heads and cardiotoxicity. Evidence suggests that a small proportion of patients treated with metal-on-metal (MoM) hip arthroplasties will experience serious health problems related to high cobalt and chromium-ion concentrations [2, 16] but that a larger proportion of patients with MoM THAs will undergo premature revisions caused by metallurgical problems related to their THAs [9, 12, 14]. In the occupational setting, high metal ion exposure can lead to developing certain cancers—hexavalent chromium, for example, is carcinogenic [15]. But analyses involving large cohorts from the National Joint Registries for England and Wales, as well as from Finland have not demonstrated any increased risk of cancer or mortality in patients with MoM hip arthroplasties compared with conventional THA patients at up to 7 years [5, 7, 13]. Still, given the long latency period for cancer development, longer-term followup is needed before drawing firm conclusions. Dietary cobalt excess can cause cardiomyopathy (first reported in 1967 as “Quebec beer-drinkers” cardiomyopathy [10]). Researchers also have reported instances of cardiomyopathy resulting from cobalt toxicity in MoM hip arthroplasty patients, which can be fatal [8]. Older male patients with an ASR XL MoM hip arthroplasty, which was recalled in 2010, had a three-fold increased risk of hospital admission due to cardiac failure compared with conventional THA patients [3]. However, these patients were older than the typical MoM hip arthroplasty population, and the study included small subgroups, calling into question its generalizability. Two recent large studies from the National Joint Registry (n = 535,776) and the United States (n = 53,658) demonstrated that MoM hip arthroplasty patients were not at increased risk of heart failure compared with non-MoM hip arthroplasty patients, with the latter also observing no difference in the risks of arrhythmia, myocardial infarction or cardiomyopathy [4, 11]. Another study reported that MoM hip arthroplasty patients with high blood metal ions had no detectable heart pathology on cardiac MRI or echocardiographic examination [1]. The recent study by Lassalle and colleagues [6] suggests that systemic problems may be much more global and might involve all THAs using metal femoral heads. Their analysis of 255,350 patients from the French national database reported an increased risk of cardiomyopathy and heart failure in patients with metal femoral heads (MoM hip arthroplasty and metal-on-polyethylene bearings) compared with ceramic femoral heads (ceramic-on-ceramic and ceramic-on-polyethylene bearings), persisting after adjustment for confounding factors and various sensitivity analyses. The authors suggested that cardiac function should be regularly monitored in patients with metallic head THAs. We feel this statement is a substantial leap from the findings presented, and that there are important unacknowledged limitations in the study. The main study limitation relates to the oversimplification of the problem by focusing only on femoral head material (metal or ceramic). The stem material (usually cobalt-chrome, stainless steel, or titanium) is just as important, and represents a major confounding factor that was not accounted for. Ceramic heads coupled with cobalt-chrome stems may generate metal ion release through fretting and corrosion at the head-neck junction. A further limitation in the study is the lack of a control group of individuals without THA. Knowing the true incidence of dilated cardiomyopathy and heart failure in unexposed age- and sex-matched control groups is paramount when interpreting the incidence presented in the arthroplasty population. This is even more important given that the authors reported only a small increase in the risk in the metal-head group. Finally, it would have been useful to present data on cardiovascular-specific mortality given that this would be the worst-possible outcome if patients did develop cardiotoxicity following THA. There remains a small risk of THA patients developing systemic problems but most of the current evidence suggests that this is not a common problem, even among patients with MoM hip arthroplasties. As there may be a long latency period before developing any systemic effects, extended followup of large international cohorts is required to detect any future problems. These analyses must include all types of THA constructs, but importantly should account for all of the materials within the construct and not just the femoral head material. This will help determine how commonly serious, systemic health complications occur in patients who undergo THA.

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