Cardinals pitcher Chris Carpenter, sidelined since opening day with an elbow injury, will undergo arthroscopic surgery early next week after suffering a setback in his rehab program. Carpenter, a 15-game winner last year and the NL Cy Young award winner in 2005, will be out at least three months, the team said Saturday. An exam on Friday with Dr. George Paletta, the team's medical supervisor, revealed recurrent swelling, stiffness and loss of motion.