Ottawa Senators defenseman Erik Karlsson (65) limps off the ice after injuring his left left in a collision with Pittsburgh Penguins left wing Matt Cooke during the second period of an NHL hockey game in Pittsburgh Wednesday, Feb. 13, 2013. Karlsson did not return to the game. The Penguins won 4-2. (AP Photo/Gene J. Puskar)

Photo by: Gene J. Puskar

Ottawa Senators defenseman Erik Karlsson (65) limps off the ice after injuring his left left in a collision with Pittsburgh Penguins left wing Matt Cooke during the second period of an NHL hockey game in Pittsburgh Wednesday, Feb. 13, 2013. Karlsson did not return to the game. The Penguins won 4-2. (AP Photo/Gene J. Puskar)