Changes in blood ion levels after removal of metal-on-metal hip replacements

Abstract

Background and purposeIn patients with metal-on-metal (MoM) hip prostheses, pain and joint effusions may be associated with elevated blood levels of cobalt and chromium ions. Since little is known about the kinetics of metal ion clearance from the body and the rate of resolution of elevated blood ion levels, we examined the time course of cobalt and chromium ion levels after revision of MoM hip replacements.Patients and methodsWe included 16 patients (13 female) who underwent revision of a painful MoM hip (large diameter, modern bearing) without fracture or infection, and who had a minimum of 4 blood metal ion measurements over an average period of 6.1 (0–12) months after revision.ResultsAverage blood ion concentrations at the time of revision were 22 ppb for chromium and 43 ppb for cobalt. The change in ion levels after revision surgery varied extensively between patients. In many cases, over the second and third months after revision surgery ion levels decreased to 50% of the values measured at revision. Decay of chromium levels occurred more slowly than decay of cobalt levels, with a 9% lag in return to normal levels. The rate of decay of both metals followed second-order (exponential) kinetics more closely than first-order (linear) kinetics.InterpretationThe elimination of cobalt and chromium from the blood of patients who have undergone revision of painful MoM hip arthroplasties follows an exponential decay curve with a half-life of approximately 50 days. Elevated blood levels of cobalt and chromium ions can persist for at least 1 year after revision, especially in patients with high levels of exposure.

Follow-Up of Metal-on-Metal Hip Arthroplasty Patients Is Currently Not Evidence Based or Cost Effective

“…In another study repeating blood metal ions at a mean of 27 months in 205 patients with mainly high-risk ASR HRs, no significant difference in cobalt concentration was demonstrated with time since HR [34]. Two studies repeating blood metal ions following revision both observed that most patients have significantly decreased or normal concentrations three-months after bearing exchange, though chromium decreases at a slower rate than cobalt [58,59].…”

Revision of Metal-on-metal Hip Prostheses Results in Marked Reduction of Blood Cobalt and Chromium Ion Concentrations

“…High revision rates have been reported for these hips [2,27], and a few metal-on-metal implants have been recalled [16]. The effect of revision surgery of a metal-on-metal prosthesis on circulating Co and Cr levels as systemic exposure has been described only in relatively small cohorts [4,12,25]. Further, some studies [7-9, 14, 15, 17, 18, 23, 28] have reported clinical scores after revision surgery in cohorts that have included several metal-on-metal designs revised for various indications.…”

“…However, the reduction in blood and serum Co and Cr after removal of poorly functioning metal-on-metal components has been described only in small cohorts [4,12,25]. In addition, improving [7,8,14,17,23,28,31] and poor [18] clinical scores have been reported for revisions of hip resurfacings with metal-on-metal systems, whereas similar studies of THAs with metal-on-metal systems are scarce [13,15,23].…”

Effects of chronic cobalt and chromium exposure after metal‐on‐metal hip resurfacing: An epigenome‐wide association pilot study

“…Patients with MOM HR that present with a pathology due to elevated circulating metal concentrations, subsequently undergo a revision surgery that eventually reduces the concentrations of metal in circulation. 23,24 It is therefore the patient population with a well-functioning MOM hip replacement which have low-level chronic exposure to circulating metals, for whom the longer term outcomes are unclear. The exposure cohort in the study consisted of a metal exposure group of 35 patients with a well-functioning MOM HR.…”