Metal-on-Metal Implants — High Failure Rates, Low Safety Monitoring

Even though more than 93,000 patients have been implanted with the now recalled DePuy metal-on-metal hip, the U.S. Food and Drug Administration wants to start a conversation.

It seems a little like the proverbial “closing the barn door after the horse has already escaped”.

The federal agency will convene a panel of experts as well as metal-on-metal hip injured patients at a two-day expert advisory panel meeting June 27 and 28, 2012.

The expert panelists, yet to be named, will look at the total hip replacement systems which consist of a metal ball or femoral head that fits into a metal cup in the hip bone, also known as the acetabular component. The other type of MoM hip is the resurfacing system. That is made up of a trimmed femoral head that has a metal covering with a metal cup in the hip bone.

It was one year ago in May that the FDA finally ordered manufacturers of metal hips to conduct post-market surveillance to collect more data on patient injuries after the hips have been implanted. While the UK has a National Joint Registry, the U.S. does not, so the FDA is ordering manufacturers to essentially monitor their own success or failures.

Wouldn’t it be better to conduct those safety studies before the hips are implanted? It sounds simple doesn’t it, but that is not the way it happens.

The majority of these metal hips are approved for market based on the assurances of the manufacturers that they are the “substantial equivalent” of another hip already on the market. That is all that’s required of the 510(k) process which is an approval for marketing, sort of a notification to the FDA of what the manufacturer plans to get the hips on the market. Understanding as we do, that many of these major corporations are more interested in quick profits and aggressive marketing than patient safety, it is time for the FDA to step-up before the injuries occur.

What sort of injuries?

In the case of metal-on-metal hips, patients are experiencing higher than normal rates of cobalt and chromium in the bloodstream as the metal debris flakes from the movement of the hip. Infection is not uncommon, nor are repeated surgeries to remove not just the metal components but the destroyed muscle and tissue left behind. Many of these patients will never be able to walk again.

To be discussed are the failure rates and modes; the metal ion testing; imaging methods; local and systemic complications; patient risk factors; and considerations for follow-up after surgery.

Interestingly, in making its announcement, the FDA says its job “protects the public health by assuring the safety, effectiveness, and security of human and veterinary drugs, vaccines and other biological products for human use, and medical devices.”

If only that were true.