LONDON (AP) - British experts at the world's biggest artificial joint registry said doctors should stop using metal-on-metal hip replacements, citing an analysis showing they have to be fixed or replaced more often than other implants.
All metal hip joints were already under scrutiny over questions about how long they last, and one major manufacturer recalled its product over a year ago. Last year, regulators in the U.S. asked makers to conduct safety studies on them. Most artificial hip joints are plastic or ceramic.
Earlier this month, the British agency that regulates medical devices warned that patients with these joints should have yearly blood tests to make sure no dangerous metals are seeping into their bodies. It also advised patients with symptoms such as pain, swelling or reduced movement to get MRI scans to check for muscle damage in case the joints need to be removed.
In the new study, experts analyzed data for more than 400,000 hip replacements from the National Joint Registry of England and Wales between 2003 and 2011. More than 31,000 of those were metal-on-metal devices.
After five years, about 6 percent of people with the metal-on-metal variety needed surgery to fix or replace them. That compares with just 1.7 to 2.3 percent of people who had ceramic or plastic joints.
Doctors usually expect hip joints to last at least a decade. The study was published online Tuesday in the journal, Lancet. It was paid for by the National Joint Registry.
Ashley Blom, head of orthopedic research at the University of Bristol and one of the study authors, emphasized most people with a metal hip haven't needed a replacement. But with so many alternatives, he said there was no reason to take that risk.
"If I were a patient, I would not choose a metal-on-metal hip," he said.
He said the rates of failing metal hips were likely an underestimate since not all patients report their symptoms or have surgery to fix the problem.
In 2010, DePuy, part of Johnson & Johnson, recalled a metal hip implant after it was linked to high failure rates. Blom said the new analysis suggests the problem applies to all metal-on-metal hips, not just one brand. Doctors began using metal-on-metal implants after laboratory tests suggested the devices would be more resistant to wear and reduced the chances of dislocation. They aren't sure why that isn't the case once they are used in patients.
Last year, the U.S. Food and Drug Administration asked all manufacturers of metal-on-metal hips to conduct safety studies. Use of the devices has dropped dramatically in recent years worldwide. In the U.K., only about 5 percent of patients are believed to be getting the metal hips.
In the U.S., estimates are about 500,000 people have them.
Some experts called for tighter regulation, warning there might be similar problems with other joint replacements, such as those for knees and shoulders.
"I wouldn't be surprised if this was just the beginning of the storm," said Art Sedrakyan, an associate professor of public health at Weill Cornell Medical College in New York, who authored an accompanying commentary in Lancet. "A lot of products have been allowed onto the market without clinical evidence they work."