Seven months after transplantation, the patient underwent hip imaging and measurement of serum cobalt levels because of safety concerns with her prosthesis. Pelvic MRI showed bilateral thin-walled fluid collections caused by a reaction to the metal implants, and her serum cobalt level was 287.6 mcg/L (reference value <1.0). Eleven months after heart transplantation, the patient’s original left hip prosthesis was replaced. Nine weeks later, she underwent another procedure to replace her right hip prosthesis.
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Explore This IssueSeptember 2014
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After both hip implants were replaced, the patient’s serum cobalt levels rapidly decreased and her left ventricular ejection fraction returned to normal. She also reported feeling stronger each day.
The remarkable nature of these case studies is that ‘hip pain was not a prominent feature,’ Dr. Bunning says.
Absorbing a large amount of cobalt over long periods of time can lead to significant health issues.6 Two telling symptoms are cardiomyopathy and hypothyroidism, Dr. Bunning noted, but additional signs and symptoms may include lassitude; neuropathy, including loss of taste, smell and hearing; focal and diffuse weakness; and rashes.
Before the three cases presented in early 2014, cobalt toxicity has been reported in the literature. Perhaps the seminal report was of the so-called Quebec beer-drinkers’ cardiomyopathy.7 In the 48 cases reported in 1967, the patients preferred the same brand of beer, which investigators learned used cobalt sulfate to improve the stability of the foam. In 2011, an Australian report was published telling of two patients who experienced cobalt toxicity from metal-on-metal total hip replacements.8
When the components of metal-on-metal hip prostheses rub together, they can shed metal ions that enter the bloodstream, Dr. Bunning explained. Somewhat of a surprise, he added, is that corrosion at the modular junction in metal-on-polyethylene implants can cause the same issue. A 2012 paper showed that in 15 cases, corrosion at the head–neck taper of metal-on-polyethylene implants can cause adverse local tissue reactions, including elevated serum cobalt and chromium levels.9
Cobalt toxicity related to hip implants is likely to become more prevalent, Dr. Bunning says, especially because it has been determined that in addition to metal-on-metal prosthetics, cobalt toxicity is also a possible complication of metal-on-polyethylene implants.
The potential issues of metal-on-metal implants recently garnered the attention of the U.S. Food and Drug Administration, which issued a safety communication in January 2013.10 The FDA’s recommendation is to conduct “follow-up of asymptomatic patients with metal-on-metal hip implants, including physical examinations and routine radiographs” about every one to two years. If the hip is performing normally, the FDA stated it is unnecessary to “routinely perform additional soft tissue imaging or assess metal ion levels in the blood.”