(Reuters) - As concerns mount over the safety of metal-on-metal hip implants, U.S. health regulators are seeking advice on how best to minimize risks for the more than 500,000 patients who have received the devices.

All-metal artificial hips were developed to be more durable than traditional implants, which combine a ceramic or metal ball with a plastic socket. Johnson & Johnson is the biggest manufacturer of the all-metal devices, and other device makers include Zimmer Holdings Inc and Wright Medical Group .

J&J recalled its ASR all-metal hip implant in 2010, and has since set aside $3 billion to cover legal costs related to patient claims. Recent studies have shown such products may fail at higher rates than their predecessors, and may leach high concentrations of metal ions into the bloodstream.

The U.S. Food and Drug Administration will convene outside experts for a two-day meeting starting on Wednesday, asking for guidance from doctors, manufacturers, researchers and the public on how to monitor patients who get the implants or need them replaced.

The discussion will not address whether to impose more rigorous testing standards on companies who already make the devices, the agency said in documents posted ahead of the meeting.

The FDA also does not plan to ask for guidance on changing review requirements that must be met before the implants can be sold in the United States, or whether to remove existing implants from the market.

But these are some of the key questions for researchers like Art Sedrakyan of Weill Cornell Medical College, who has written extensively about the safety issues with the all-metal hip implants. He believes the larger type of metal-on-metal hip implants should no longer be used.

Having a lot of alternatives to these implants, it's just very clear that the potential harms outweigh any benefits that are possible to imagine, he said in an interview.

The FDA said about 400,000 Americans get a hip replaced or repaired each year in order to make it easier to walk and to alleviate pain from joint problems, including arthritis.

In 2010, about 27 percent of those implants were all-metal, a decrease from about 40 percent in 2008, the FDA said, likely due to the increased attention on the devices' safety problems.

In April, British health regulators advised surgeons to stop using a type of metal-on-metal hip implant because of the high risk for patients needing repeat surgery compared to other devices. They have also told doctors to conduct life-long tests for some patients who get all-metal implants.

The warning was issued for implant cups or heads made by Finsbury Orthopaedics, a unit of J&J, used in combination with femoral stems made by Stryker Corp.

The devices can produce debris that can leak chromium and cobalt ions into the blood, causing health problems and potential damage to chromosomes.

The FDA's meeting follows a May 2011 order from the agency requiring manufacturers of metal-on-metal implants to collect more safety data on the devices.

But a recent article in the New England Journal of Medicine, co-authored by Sedrakyan, highlighted the delays in the studies. By mid-June, over a year since the order, the FDA and companies had agreed on study design for less than a quarter of the devices.

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