When metal-on-metal hip implants were introduced, they were marketed at being a superior type of hip replacement. Consumers were told that, compared to the older metal-on-plastic and metal-on-ceramic implants, all-metal hip implants were more durable and less likely to dislocate, making it a better option for younger, more active patients. Within recent years, however, researchers have found that all-metal hip implants have a serious flaw; the device releases tiny metal particles when the surfaces of the implant rub together, such as when the patient walks or runs. The U.S. Food and Drug Administration (FDA) recently issued new guidelines for patients implanted with these devices, advising them to speak with their doctor if they experience symptoms such as pain or swelling.
What is a Metal-on-Metal Hip Implant?
A metal-on-metal hip implant is an implant made of all metal components. A hip replacement consists of a cup, which acts as the hip socket, and a long stem with a ball on top acting as the femur (thighbone). These components interact with each other to mimic the natural motion of the hip. With a metal-on-metal hip implant, both of these components are made of metal. The problem is that sometimes when the patient walks or runs, these surfaces grind against each other and release metal ions into the body.
Metal-on-metal hip implants gained notoriety in 2010, after Johnson & Johnson recalled 93,000 DePuy ASR hip implants worldwide. The recall was based on data showing that the hips failed in 13 percent of patients within five years. A typical hip implant is expected to last up to 15 years.
FDA Looking for Stricter Regulations, Metal Hips Never Tested
After Johnson & Johnson recalled the DePuy ASR, researchers found that the problems were common to all types of metal-on-metal hip implants. In light of this, the FDA asked a number of manufacturers to conduct post market studies to find out whether they release dangerous amounts of metal ions.
Believe it or not, metal-on-metal hip implants were never tested for safety before they were released onto the market. Because of a regulatory loophole known as the 510(k) route, manufacturers are allowed to sell these devices without any clinical testing as long as they can prove that it is similar enough to a previously approved device, even if that previous device had poor clinical performance or is no longer in use. The 510(k) was supposed to only be a temporary route for metal hips, but the FDA never got around to finalizing regulations. In light of all the issues that have come up, the agency is now trying to close the loophole by requiring manufacturers to prove that metal hip implants are safe and effective.
The FDA has also issued new guidelines for patients with metal-on-metal hips. In a Safety Communication issued last week, the agency warned about the risk of “adverse local tissue reaction”, which is what can occur when the metallic debris from the device gets absorbed into the muscle and tissues surrounding the implant. For the first time, the FDA recommended metal ion testing for patients experiencing symptoms such as pain, swelling, limited mobility or sounds coming from the hip (clicking, popping, squeaking). Even if patients do not have symptoms, they are still advised to talk with their doctors and have regular physical examinations. Diagnostic imaging such as CT scans and MRIs are also recommended for assessing the tissues surrounding the hip implant.