Panel calls for FDA to issue safety advice for metal-on-metal hip replacements

BMJ 2012; 345 doi: (Published 03 July 2012) Cite this as: BMJ 2012;345:e4542
  1. Bob Roehr
  1. 1Washington, DC

An FDA advisory committee inquiry into metal-on-metal hip replacements was unable to determine whether all such implants were at risk of becoming damaged and shedding cobalt and chromium ions with effect on surrounding muscle tissue.

The committee spent two days wrestling with issues surrounding the 750 000 metal-on-metal hip replacements that have been done in the US. The agency was trying to sort out often conflicting data and interpretations of those data in updating its policy on the devices.

Two recent investigations by the BMJ have raised serious concerns about the regulation of medical devices and problems with metal-on-metal implants caused by metal ions leaking into the body.1 2 After publication of the articles, the UK’s Medicines and Healthcare Products Regulatory Agency recommended that all patients with metal-on-metal hip implants with a femoral diameter of ≥36 mm have annual blood tests to check metal ion concentrations in their blood for the rest of their lives and that patients with hip symptoms indicative of problems with the joint, such as swelling, pain, or limping, also undergo annual magnetic resonance imaging.3

At the end of two days of presentations and discussions, the FDA committee was asked to advise on nine questions, often with multiple subparts.

Metal-on-metal devices initially were used because they were believed to be more durable and better suited to younger, more physically active patients compared with the then available alternatives. But experience has shown that they can also become damaged and shed cobalt and chromium ions with effect on surrounding muscle tissue.

However, the available data left the panel unwilling to say if this was a class effect common to all metal-on-metal devices; was unique to some device designs; was dependent on the angle of implantation by surgeons; or a combination of those factors.

None of the panellists would ban the devices, though they thought use should be quite limited. Part of their reasoning was the improvement seen in poly-based devices over the ensuing years.

They were not willing to make comparisons with other types of devices because they had not been presented data on those other devices. Raj Rao, from the Medical College of Wisconsin, said, “In the absence of comparative data, I think it is difficult for this panel to make definitive conclusions.”

Panelist William O’Brien, a device specialist at the University of Michigan, Ann Arbor, cautioned that the advice applies only to current generation cobalt/chromium alloy devices. It is possible that other more corrosion resistant alloys might be developed in the future.

Only those patients who are symptomatic should undergo blood screening for metal ion levels and imaging for potential tissue damage, they said. There is insufficient reason to screen asymptomatic patients, and those tests can carry their own risks.

The University of Minnesota’s Edward Cheng said one should screen only if you believe it will change management of the patient.

Adolph Yates, from the University of Pittsburgh Medical Center, would readily agree to a patient request for a metal ion screening test because “most times it comes back normal and they can sleep better.”

The committee recommended that the FDA establish reference ranges of what constitute safe, intermediate, and unsafe levels of cobalt and chromium in blood and tissue.

It urged the FDA to take the lead in providing more information to the public in both considering hip replacement surgery and for those who are already living with the devices. That may include adding warning notices to the device label.

Scott Evans, a clinical trials statistician at Harvard University, noted that there are ample data on hip implants but they are primarily from observational studies and registries “with high levels of uncertainties.”

He argued for appropriately designed prospective studies to answer the remaining questions, otherwise “we are going to continue to dance around the true answers.”

Cheng said, despite the meeting’s focus on problems associated with metal-on-metal devices, patients should “take comfort in knowing that the vast majority of these joints are functioning successfully and failures are rare.”

He added, “The absolute risk remains small . . . You do not have a ticking time bomb [implanted in your hip] but instead a joint that needs continued monitoring, and we have some tools to perform that monitoring. Additional surgery may never be needed,” but tools are available for the few who need it.


Cite this as: BMJ 2012;345:e4542


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