Professor Yves Catonne answers journalists' questions at a hotel in Los Angeles December 15, 2009, one day after assessing the health of French rock star Johnny Hallyday. Hallyday had surgery at the Cedars-Sinai hospital where he was admitted on December 7, 2009, his publicists said. Hallyday, one of France's most popular entertainers in a career spanning almost 50 years, has been suffering health problems recently. REUTERS/Benoit Tessier (UNITED STATES - Tags: HEALTH SOCIETY)