Doctors are trying something radically new in an attempt to get a quadriplegic back on his feet. They injected pig cells into the spine of a 50-year-old man in an experimental procedure that officials say is the first of its kind. The doctors at Albany Medical Center in New York hope the cells will grow as they would in a developing pig and create a new connection in Charles Dederick's spine. If electric impulses can again flow from Dederick's brain, they could send signals to the muscles and possibly allow him to walk again. Dederick , whose spine was damaged in a motorcycle accident four years ago, says he feels no difference yet. It was the first of a dozen similar human experiments approved by the Food and Drug Administration.