Systemic Cobalt Toxicity From Chrome-Cobalt Hip Implants
A new research study synthesizes data on systemic arthroprosthetic cobaltism, a recently described syndrome that results from wear or corrosion of chrome-cobalt hip replacement components.
This syndrome is important, the authors say, because millions of hip devices implanted in the past decade use chrome-cobalt components. The authors evaluated nine different symptom categories and a category of medical utilization.
The researchers identified 25 patients reported between 2001 and 2014, with a substantial increase in case reports over the past three years. The symptoms were diverse and involved the hip (84%), cardiovascular system (60%), audiovestibular system (52%), peripheral motor-sensory system (48%), thyroid (48%), psychological functioning (32%), visual system (32%), and the hematological, oncological, or immune system (20%), according to the article’s abstract. The research was published in June in the Journal of Patient Safety.
According to the National Institutes of Health (NIH), cobalt poisoning has recently been seen from the wear and tear of some cobalt/chromium metal-on-metal hip implants. In these implants, the artificial hip socket is created by fitting a metal ball into a metal cup. In the course of normal movement, cobalt particles are released as the metal ball grinds against the metal cup. These metal particles (ions) can be released into the hip socket and sometimes the bloodstream, causing cobalt toxicity.
The researchers found the mean latency from implantation of the device to presentation or revision surgery was 41 months (range of 9 to 99 months). The mean blood cobalt level, B[Co], was 324 μg/L; four patients had levels less than 20 μg/L. The B[Co] but not blood chromium level was highly associated with a quantitative measure of overall symptom severity (r2, 0.81; P < 0.001). Mean B[Co] and symptom scores were substantially higher in patients with revisions of failed ceramic-on-ceramic prostheses than those with primary metal-on-metal prostheses.
For 20 patients (80%), the researchers had documentation of hip explantation, but the reporting of symptoms was non-systematic and incomplete, making analysis impossible. But for 19 of the patients, at least some of the symptoms improved. The twentieth patient died of cobalt cardiomyopathy two months after hip resection. Despite symptom improvement, at least some symptoms attributable to cobaltism persisted after removal of the cobalt-containing device, the authors say.
When metal-on-metal (MoM) hip implants were introduced to the market, manufacturers expected the hips would be more durable than older designs made from a combination of materials. But the devices instead proved problematic, with patients experiencing higher than expected early failure rates and injuries and complications requiring many recipients to undergo additional surgery. DePuy Orthopaedics, Biomet, Stryker, and Smith & Nephew are among the manufacturers that have recalled MoM hips. Thousands of hip recipients sued manufacturers over injuries and complications they allege are the result of to defective design of the devices. In the last year, Stryker and Biomet have reached settlements in multidistrict litigations over their MoM hips.
The authors of the study conclude that systemic cobaltism is an increasingly recognized complication of wear or corrosion of chrome-cobalt hip implants. It may involve a large number of organ systems, and may occur with relatively low B[Co]. The authors note an urgent need to better determine the overall scope of the problem and to develop screening and management strategies.
