The Celtics  announced Tuesday afternoon that guard J.R. Giddens underwent successful left knee arthroscopic surgery at the New England Baptist Hospital. The surgery was performed by team physician, Dr. Brian McKeon and assisted by John Rand. No timetable has been set for his return. Giddens, a 6-foot-5 guard, has appeared in 21 games for the Celtics this season and registered season-highs of six points and seven rebounds against New Jersey on Jan. 13. In four games on assignment for the Maine Red Claws of the NBA Development League this season, he averaged 18.0 points, 4.5 rebounds, 3.0 assists and 1.0 steal in 31.8 minutes per game.