In an unusual move, the Food and Drug Administration has ordered all producers of a popular category of artificial hip to undertake studies of the implants, which have been linked to high early failure rates and severe health effects in some patients. Under the order, producers of "metal-on-metal" hips will have to conduct studies of patients who received the device to determine, among other things, whether the implants are shedding high levels of metallic debris. Some patients have encountered that problem, including soft tissue damage that has disabled them. In a telephone interview on Tuesday, William H. Maisel, MD, the deputy director for science at the FDA's Center for Devices and Radiological Health, said the order marks the broadest use of the agency's authority to conduct studies of devices after approval for sale.