Advisors narrowly backed an experimental Medtronic Inc. spine implant that uses a protein to stimulate bone grown and reduce lower-back pain. The committee of Food and Drug Administration advisers voted 6-5 that the benefits of the Amplify device outweighed risks. Three panelists abstained. The FDA will consider the recommendation as it decides whether to approve Amplify, which could help Medtronic boost the spine business that now accounts for 22 percent of the company's sales. Amplify contains a genetically engineered form of a protein to help fuse vertebrae by promoting bone growth. Medtronic said Amplify offered a safe and effective alternative to standard fusion surgery using a piece of a patient's hip bone implanted in the spine. FDA reviewers, however, voiced concern about cancer cases seen in some patients treated with Amplify.