When I asked my father if he had a metal-on-metal (MOM) hip replacement, he said, “Yeah, I probably have had one of those.”
After four hip replacements (three on the right, one of the left), it goes without saying that he has probably had most materials that hip replacements are made of in his body. He even had a replacement break. He kept the pieces after the 10-hour surgery to take them out, partially for my uncle to bring to UCLA to show his fourth-year med students. If you’re nice, my dad will show them to you.
Whatever amount of dark humor my dad approaches his medical maladies, he still had to be tested for chromium levels that have been mandated by FDA as a result of recent complications with MOMs. Although FDA advised against using them for most patients back in July, up until recently the devices had been a Class III, but did not require a premarket approval (PMA) in order to come to the commercial market.
MOMs were considered to be preamendment devices, which means that they have been classified at this level since 1976. Even though they are classified as Class III by FDA, previous to the change they could go through the same submission process as a class 2 device, which means that they could come to market with a 510(k).
There are two main concerns regarding MOMs that FDA is looking at. One of them is device failure (failing at five years while other traditional artificial hip replacements fail at 15). The other is the shedding of particles in the typically chromium-based MOMs, which certain patients’ bodies may fight rather aggressively if there is a hypersensitivity.
Peper Long, associate director for external relations for CDRH, says that these two elements need to be examined further, and FDA is seeking more information. “[It’s] what we have been requesting from postmarket for manufacturers,” she says. “We want a better understanding of the failure rate and the mode of failure, as well as the ions in the blood stream, and whether there is any connection between the two.”
According to Dan McLain, president of Walker Downey and Associates, not everyone will necessarily have a reaction to chromium ions. Part of the reason why this has been getting so much attention, he says, is that chromium is a known carcinogen. He explains that the problem isn’t the chemical itself, but the presence of unknown metal ions in the body.
“They sequester,” he says of the chromium ions. “We don’t readily pass them, unlike many of the other foreign objects [in our bodies]. With metal ions tend to accumulate, and over time, they may cause damage.”
Len Czuba, president of Czuba Enterprises, echoed this statement. He says part of the issue is the replacements themselves and the materials that they are made of. With the shedding that occurs with MOMs, the body cannot digest the materials properly, which has the potential to weaken the tissue around the implant. This would be the case beyond just chromium levels—even stainless steel would cause a similar reaction, with the oxidation and moisture in the body causing the implant to weaken.
The new regulations may make MOMs more difficult to sell in the long term, and there is a good chance that the devices may completely disappear from the market. Many surgeons have been abandoning MOMs, such as consulting surgeons at Johnson & Johnson’s DePuy Orthopaedics unit, even as they were selling their Articular Surface Replacement.
Reina V. Slutske is the assistant editor for MD+DI.