New Medical Devices Aren’t Always Improved

The right hip joint has the metal-and-plastic artificial hip implant that is proving to be better than the newer all-metal implant.

Think just because you’re getting a new medical device that it must be “new and improved”? According to an article by Barry Meier in The New York Times, it doesn’t play out that way for medical devices designed to be hip replacements. “New” isn’t always “improved.”

The new metal-on-metal hip implants were considered by device makers and surgeons to be a significant improvement over previous hip devices that used both metal and plastic. But federal regulators and medical researchers are now racing to determine how many patients have been injured by the devices because the devices shed dangerous metallic debris.

Meier reports:

In a highly unusual move, the Food and Drug Administration last month ordered manufacturers of all metal hips to undertake emergency studies of patients. And lawmakers and others are now calling for a tightening of how the F.D.A. scrutinizes new implants — both before and after they are sold.

In the course of his reporting, Meier shows how the innovation’s sparkle caused experts to embrace a product without convincing evidence that it was better or even as good as the existing devices.

Some experts told Meier that they only used a special type of metal-on-metal implant known as a resurfacing device in relatively tall and middle-aged men because data showed that they worked for that small demographic. But metal hips were marketed to everyone. Meier says that about 65% of the implants went to women and older patients, two groups who now appear to be most vulnerable to the device’s breakdown.

Meier reports:

Last year, DePuy, the orthopedics division of Johnson & Johnson, recalled one of its all-metal hips, the ASR, which was failing at a high rate. Another manufacturer, Zimmer Holdings, also briefly halted sales of one of its metal models, the Durom.  DePuy, Zimmer and other companies and doctors have said that most patients who received metal hips have done well.

The modern artificial hip was developed in the 1960s by a British surgeon, John Charnley. Its idea is pretty simple — it mimics the ball and socket of the human hip by using a metal “ball,” made of cobalt and chromium, at the top of the thigh bone and a “cup,” made of plastic, as the artificial hip socket.

Metal-on-metal implants, where the cup is also made of a metal alloy, were attempted during those early decades, but tests had found that patients had metal particles in their blood or organs, raising concerns about long-term health risks like cancer.

By 1996, Jonathan Black, an industry consultant and professor emeritus of bioengineering at Clemson University, had written in the medical literature that the metal-on-metal design was risky because little was known about the biological chaos that metallic debris might unleash in the body.

Meier writes:

At the time, Mr. Black estimates, the all-metal implants accounted for only a tiny fraction of some 250,000 hips implanted annually in the United States. By 2008, they were used in one out of every three hip procedures.

What happened? In essence, the old technology was repackaged as new and cutting-edge, and warnings like Mr. Black’s were ignored and considered no longer relevant. This new generation of devices was manufactured differently and reflected better designs, advocates argued.

Companies and surgeons began promoting the new implants as the next big step in orthopedics, one that would let patients, particularly middle-age ones, do strenuous physical activities because their mechanics were more natural. And patients, intrigued by ads featuring celebrity athletes, also wanted such devices.

Most all-metal hips don’t have to undergo clinical trials before sale because of the way FDA rules currently stand. Instead, they were tested in labs on machines that simulate millions of steps to study the forces exerted by years of motion. Such wear is inevitable in an artificial hip, and tests showed that some plastic “sockets” shed particles that led to bone loss in some patients.

Similar tests of the all-metal implants did not highlight the same issue. But with hindsight being 20/20, testing experts now say the simulations were based on idealized conditions and didn’t reflect what really happens in a human body. All-metal devices are less forgiving than metal-and-plastic ones to small variations in how they were implanted, with parts sometimes banging together and generating debris.

Worse, damage from debris generated by metal implants is more serious than that caused by plastic. In some patients, the bits of metal has caused crippling tissue and muscle damage, and produced neurological problems in others.

Source: “In Medicine, New Isn’t Always Improved,” The New York Times, 06/25/11
Public domain image from the National Institutes of Health, used under Fair Use: Reporting.