Penguins defenseman Paul Martin has a broken tibia and will miss the next four to six weeks, coach Dan Bylsma said today. Martin apparently got hurt blocking a shot Monday in the third period of a 4-3 overtime loss at Boston and played at least some on the broken leg afterward. He has been paired defensively with Brooks Orpik and plays in all situations. He is the Penguins' leader in ice time with an average of 25 minutes, 16 seconds a game. Recently he had supplanted Kris Letang on the team's top power-play unit. Letang will resume that role with Martin out