Metal-on-Metal Hip Implants Not Thoroughly Tested

Chicago, ILWhile not the market leader in the hip replacement industry, Zimmer hip is nonetheless poised to share in the projected $8.6 billion implant market by the year 2017. That's just six years away. However, it does speak to the growing need for the largest segment of the baby boom population moving through middle age into the retirement demographic and requiring joint replacement at a scale not yet seen.

That's why a column by writer Barry Meier, appearing June 26 in The New York Times, is so troubling. It points to the current state of the artificial implant industry—especially hips—and, specifically, troubles with metal-on-metal hip implants, a design that is part of the Zimmer hip replacement line.

It has been revealed that as far back as 1996 an industry consultant warned in a published article that the metal-on-metal design of any artificial hip manufacturer (not just Zimmer Inc.) posed significant risk. Jonathan Black, professor emeritus of bioengineering at Clemson University, noted 15 years ago that the aftereffects of metallic debris had not been properly studied—nor could it, given the statistical impossibility of conducting sufficient studies to prove the assumed superiority of metal-on-metal implants over the more traditional—and highly effective—metal and plastic design that had been around since the 1960s.

Earlier cursory tests of metal-on-metal implants are said to have revealed the presence of metal particles in organs and the bloodstreams of test patients, even then.

Metal-on-metal implants have been failing at a higher and faster rate than more traditional implants. Zimmer, for its part, temporarily halted sales of the Zimmer Durom Cup for that very reason. However, Zimmer postulated that the failures had more to do with improper installation than a potentially defective design, and undertook additional training for surgeons.

Surgeons, for the most part, were excited about the concept of metal-on-metal implants such as Zimmer Durom Cup hip replacement. They were easier to implant and afforded—on paper, at least—the promise of increased durability and mobility for the patient.

However, it was revealed on Sunday in The New York Times that rules observed by the US Food and Drug Administration (FDA) do not require manufacturers of metal hip implants to undertake clinical trials before bringing a new product to market—partly because the "new" product is substantially similar to that which is already available.

Instead, the hip implants are tested in laboratories and testing facilities on devices that simulate real-world use. However, it has since been revealed that such tests were conducted based on idealized conditions, according to a device-testing expert at Los Angeles Orthopaedic Hospital.

Other doctors were skeptical of metal-on-metal implants from the beginning. Nadim J. Hallab, identified in The New York Times as an implants expert at Chicago's Rush University Medical Center, noted, "I never thought this was going to fly." In contrast, Dr. Larry Dorr was an early advocate of the Zimmer Durom Cup. "I thought this could be a home run," he said in comments published Sunday in The New York Times. "Instead, it turned out to be a strikeout."

The move last month by the FDA to require metal-on-metal hip implant manufacturers to conduct emergency studies of patients having received metal-on-metal implants—including the Zimmer defective hip—was described as highly unusual.