Why is it so hard to Assess Metal on Metal Hips

On July 5^th, The New England Journal of Medicine published an article regarding the difficulties and the delays associated with diagnosing problems associated with metal on metal hip implants.

Over half a million Americans received metal on metal hip implants, which doctors believed would be stronger than the traditional ceramic or plastic prosthetics. Recently, it came to light that these metal on metal devices had a high early failure rate compared to implants made of alternative material.

Surgeons started using metal on metal implants in 2003. It’s been almost a decade, and the FDA is just now starting the investigate the safety of these devices? Why is that? Why was there such a delay in investigating the safety of metal on metal hip implants?

These devices were approved under the FDA’s 510(k) rule, which requires device manufacturers to prove they are substantially similar to devices already on the market to gain approval. There was no pre-market study with these devices prior to FDA approval. Once one device got on the market, it opened up the flood gates for the rest. Following the recalls of popular devices such as Johnson & Johnson’s DePuy ASR and Pinnacle devices, the FDA began receiving adverse event reports from several other manufacturers. This lead the FDA’s May 2011 Order for Post Market Study.

It Is very difficult to assess Post Market Studies. There is no set protocol in place for this type of study. To develop one, would be very time consuming to the FDA, and would require a large amount of resources. Thus, the studies are not conducted by the FDA, rather the device manufacturers themselves. Many critics are skeptical of what the results will be. Parameters and results could possibly be manipulated to show a favorable view of data that would prove otherwise since there is no incentive for the manufactures to produce information proving their device is faulty.

The fact that it is not an organized study, and the individual manufacturers are producing results that they see fit makes it difficult to study the safety and effectiveness of metal on metal hip implants as a whole. Different interpretations of data, reported differently could make one device seem more effective than another when that might not really be the case. Should one manufacturer choose to be dishonest and report false data, that device might be deemed safer than the competitors, when in reality it could be more dangerous.

Perhaps, the one universal component of the study, is the biggest flaw. The FDA could only order the manufacturers to survey the devices for 3 years. These devices generally are said to have a lifetime of 15 years. The five year mark is the cut off for early failure. Devices that will fail in year 4 or year 5, will not be counted in the study as an early failure rate. Thus, any ineffective device that can make it past the 3 year mark, will be deemed as effective.

The New England Journal of Medicine offered a few recommendations that could help make the study more of a success. The main suggestion was collaboration between the FDA and the manufacturers to establish a protocol land the ability for the FDA to ensure the manufacturers are initiating the study in a timely manner. The Second suggestion was harmonized study methods for the multiple manufactures that would include a cross-product data pool. Lastly, the industry itself needs an infrastructure improvement. The creation of a comprehensive national device registry with unique identifiers will give data systems the ability to “talk” to each other. Something like this would allow for the tracking and comparison of devices.

The NEJM is on the right track. Something needs to be done. The Manufacturers should not have as much control over these studies. Independent cross-product studies are the best way to measure the effectiveness of the market as a whole, as well as the individual devices.