Ceramic-on-ceramic (CoC) articulations in total hip arthroplasty (THA) have low wear, but the unique risk of fracture. After revision for CoC fracture, ceramic third bodies can lead to runaway wear of cobalt chrome (CoCr) causing extremely elevated blood cobalt. We present five cases of ceramic liner fractures revised to a CoCr head associated with the rapid development of severe cobalt toxicity. We identified 5 cases of fractured CoC THA treated with revision to CoCr on highly cross-linked polyethylene (HXLPE) – three to conventional bearings and two to modular dual mobility bearings (CoCr acetabular liner, CoCr femoral head, and HXLPE). Mean follow up was 2.5 years after CoCr/HXLPE re-revision. Symptoms of cobalt toxicity occurred at average 9.5 months after revision for ceramic fracture (range 6–12). All patients developed vision and hearing loss, balance difficulties, and peripheral neuropathy. Several had cardiomyopathy, endocrinopathy, and local skin discoloration. Two reported hip pain. Re-revision for cobalt toxicity occurred at an average of 22 months (range 10–36) after revision for ceramic fracture. Average serum cobalt level at re-revision was 991 μg/L (range 734–1302, normal <1 μg/L). All CoCr heads exhibited massive wear with asphericity; deep tissues exhibited prominent metallosis. Treatment consisted of debridement and revision to a ceramic head with HXLPE. Serum cobalt improved to an average of 25 μg/L at final follow up. All patients reported partial improvement in vision and hearing; peripheral neuropathy and balance did not recover. Systemic cobalt toxicity is a rare but devastating complication of ceramic fracture in THA treated with cobalt-alloy bearings. Cobalt alloy bearings should be avoided in this setting. The diagnosis of systemic cobalt toxicity requires a high index of suspicion and was typically delayed following systemic symptoms. Debridement and revision to a ceramic-on-HXLPE leads to improvement but not resolution of cobalt toxicity complications.
Circulating cobalt and chromium from metal-on-metal implants cause rare but fatal autopsy-diagnosed cardiotoxicity. Concern exists that milder cardiotoxicity may be common and under-recognized. Unacceptably high failure rates of metal-on-metal hip implants have prompted regulatory authorities to issue worldwide safety alerts. Despite this, approximately 1 million patients continue to live with metal-on-metal implants, putting them at risk of systemic toxicity. Although blood cobalt and chromium levels are easily measured and track local toxicity, no non-invasive tests for organ deposition exist. We recently demonstrated the utilisation of a T2* protocol (cardiovascular MRI) to detect cobalt and chromium deposition within the liver of a patient with elevated blood cobalt levels (confirmed by liver biopsy tissue analysis and X-ray fluorescence spectroscopy). We sought to detect and constrain the correlation between blood metal ions and a comprehensive panel of established markers of early cardiotoxicity. In addition we applied T2* protocols with the aim of detecting cardiac metal deposition. 90 patients were recruited through RNOH clinics into this prospective single centre blinded study. Patients were divided into 3 age and gender-matched groups according to type of implant and blood metal ion levels as follows: [Group A] Non-metal bearing hip implants; [Group B] Metal-on-metal implants, low blood metal ion levels (<7ppb); and [Group C] Metal-on-metal implants, high blood levels (>7ppb). All underwent detailed cardiovascular phenotyping using cardiac MRI (with T2*, T1 and ECV mapping, in addition to LV size and ejection fraction), advanced echocardiography (LV size and ejection fraction), and cardiac blood biomarker (Troponin and BNP) sampling in the same sitting at the Heart Hospital London. Primary outcomes were pre-specified. See study flow diagram – figure 1. (The study was registered with Blood cobalt levels were significantly different between groups (0.17ppb (range 0·10–0·47, SD 0·08) vs. 2·47 (0·72–6·9, SD 1·81) vs. 30·0 (7·54–118.0, SD 29·1) respectively for groups A, B and C). No significant between-group differences were found for LV size, ejection fraction (CMR or echocardiography), LA size, T1, T2*, ECV, BNP or troponin, with all results within normal ranges. There was no relationship between blood cobalt levels and either left ventricular ejection fraction or T2* (r=-0·022 and r=-0·108 respectively). Although small, the study was sufficiently powered to detect, as a minimum, a difference in ejection fraction of 4.8% (Cohen's d effect size 0·8). Using best available technologies, exposure of patients with metal-on-metal hip implants to high (but not extreme) blood cobalt and chromium levels has no detectable effect on the heart. We believe these findings will offer reassurance to one million patients worldwide living with a metal-on-metal hip implant and will support clinicians caring for such patients. For any figures or tables, please contact the authors directly by clicking on ‘Info & Metrics’ above to access author contact details.
