Two More Studies Reveal Metal-on-Metal Hip Implants Injuries

Metal-on-metal hip replacement devices have come under fierce scrutiny in recent years, following the high-profile recall of DePuy Orthopaedics’ ASR hip implant devices, which were failing prematurely at unexpectedly high rates.

Since, a number of studies have found evidence that the devices can shed dangerous amounts of chromium and cobalt into patients’ bloodstreams, leading to early implant failure, adverse local tissue reactions, bone and tissue loss, the development of pseudotumors, and other long-term health problems. Now, a new study reveals that cobalt is being seen in high levels in patients implanted with the devices. In fact, according to the peer-reviewed journal, Human & Experimental Toxicology, cobalt is known for its toxic effects on the thyroid, heart and the blood system as well as causing occupational lung disease, allergic reactions, and—potentially—cancer.

Recently, said the journal, high levels of cobalt have been seen in patients implanted with metal-on-metal hip replacement devices who report symptoms including noise or ringing in the ear (tinnitus), deafness, dizziness (vertigo), visual changes or vision loss as a result of optic atrophy, tremor, and peripheral neuropathy (nerve damage on both sides of the body). The exposure, believed linked to cobalt-chromium alloyed orthopedic implants, such as replacement hip devices, appears to be caused by fretting and shedding of device materials.

In April 2010 the United Kingdom’s Medical Products and Healthcare Devices Regulatory Agency released a medical device alert recommending patients undergo follow-up of after receiving a metal-on-metal hip replacement no less that once a year for the first five years following surgery to determine if the devices are leading to toxicity, said Human & Experimental Toxicology. Earlier this summer, we wrote that the U.S. Food & Drug Administration’s (FDA) Orthopaedic and Rehabilitation Devices Panel recommended that new warnings be included on the labels for metal-on-metal hip implants and that patients undergo regular monitoring to ensure their devices are not failing.

About one million of these devices have been implanted, globally, over the past 15 years, leaving these patients at possible risk for cobalt toxicity, the researchers noted, said Human & Experimental Toxicology.

The research noted that other studies have found that cobalt levels increased following implantation with an artificial hip device and during later follow up, and that the release of these metal ions is a well-document outcome following hip arthroplasty implants, specifically, metal-on-metal hip replacement devices. Levels were higher in the first two years following surgery and, again, when devices began to fail, said the researchers, according to Human & Experimental Toxicology. The most frequent route of cobalt exposure in modern times is through the release of cobalt ions from these metal devices, they added.

Meanwhile, population-based registry data from the Nordic Arthroplasty Register Association (NARA) and The National Joint Registry of England and Wales revealed that patient outcomes following hip resurfacing arthroplasty (HRA) are inferior to conventional total hip arthroplasty (THA). The researchers reviewed short-term survival in 4,401 HRA procedures from the Finnish Arthroplasty Register and compared these to 48,409 THAs performed during the same time period and found that Articular Surface Replacement (a type of HRA), specifically DePuy ASR, resulted in both an inferior outcome as well as increased risks for revision surgery, when compared to other implants, said Acta Orthopaedica.

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