By LINDA A. JOHNSONTRENTON, N.J. (AP) â¿¿ Federal prosecutors are investigating Johnson & Johnson's practices in marketing a line of hip replacements recalled in 2010 because many had to be replaced within a few years â¿¿ part of a string of more than 30 product recalls by the health care giant in the last 3 1/2 years. The U.S. Attorney's Office in Massachusetts and the Civil Division of the U.S. Justice Department last August sent Johnson & Johnson an "informal request" for information about its ASR hip replacements, J&J reported in a regulatory filing Friday. The company's annual report to the Securities and Exchange Commission states that the government has asked for additional documents from DePuy Synthes and two related subsidiaries. They have turned over the documents and are cooperating fully with investigators, the filing states. DePuy Synthes is one of the world's biggest makers of joint replacements, surgical trauma equipment and other orthopedic surgery products. The filing didn't specify what the government is looking for, but J&J has had legal problems before over its artificial joints. Just days before the ASR systems were recalled, the Food and Drug Administration told DePuy to stop marketing its Corail Hip System for two unapproved uses. And in 2007, J&J agreed to pay $84.7 million in fines as part of a settlement of a sweeping investigation by the Justice Department into alleged kickbacks. J&J and the four other top U.S. makers of replacement hips and knees were accused of paying surgeons to get them to use their products exclusively, from at least 2002 through 2006. DePuy recalled two artificial joint systems â¿¿ the ASR Hip Resurfacing System and the ASR XL Acetabular System â¿¿ in August 2010 because of unexpectedly high rates of failure. That means they caused pain and difficulty walking because they no longer fit perfectly, or that tiny pieces of metal had flaked off inside the patient's body, allegedly causing immune system problems in some people. More than 90,000 of systems were recalled in the U.S. and other countries.