Some of the nation’s leading orthopedic surgeons have reduced or stopped use of a popular category of artificial hips amid concerns that the devices are causing severe tissue and bone damage in some patients, often requiring replacement surgery within a year or two. In recent years, such devices, known as "metal on metal" implants, have been used in about one-third of the approximately 250,000 hip replacements performed annually in the U.S., the New York Times reports.