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)
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)
Pittsburgh Penguins' Robert Bortuzzo (41) and Deryk Engelland (5) hit Washington Capitals' Troy Brouwer (20) in the NHL hockey game between the Pittsburgh Penguins and the Washington Capitals on Thursday, Feb. 7, 2013 in Pittsburgh. (AP Photo/Keith Srakocic)
Washington Capitals defenseman Mike Green, left, celebrates his goal with Alex Ovechkin (8), of Russia, and Wojtek Wolski (17), of Poland, during the first period of an NHL hockey game against the Pittsburgh Penguins, Sunday, Feb. 3, 2013, in Washington. (AP Photo/Nick Wass)
Washington Capitals defenseman Mike Green (52) skates with the puck against the Pittsburgh Penguins during the second period of an NHL hockey game, Sunday, Feb. 3, 2013, in Washington. (AP Photo/Nick Wass)
Ottawa Senators defenseman Erik Karlsson (65) limps off the ice as a team trainer arrives to help him after Karlsson collided with Pittsburgh Penguins left wing Matt Cooke during the second period of an NHL hockey game in Pittsburgh on Wednesday, Feb. 13, 2013. Karlsson did not return to the game. The Penguins won 4-2. (AP Photo/Gene J. Puskar)
Ottawa Senators defenseman Erik Karlsson (65) grimaces as he falls to the ice after colliding with Pittsburgh Penguins left wing Matt Cooke, left, during the second period of an NHL hockey game in Pittsburgh Wednesday, Feb. 13, 2013. Karlsson was helped off the ice. (AP Photo/Gene J. Puskar)
Ottawa Senators defenseman Erik Karlsson (65) grimaces as he falls to the ice after colliding with Pittsburgh Penguins left wing Matt Cooke, left, during the second period of an NHL hockey game in Pittsburgh Wednesday, Feb. 13, 2013. Karlsson was helped off the ice. (AP Photo/Gene J. Puskar)
Pittsburgh Penguins' Robert Bortuzzo (41) and Deryk Engelland (5) hit Washington Capitals' Troy Brouwer (20) in the NHL hockey game between the Pittsburgh Penguins and the Washington Capitals on Thursday, Feb. 7, 2013 in Pittsburgh. (AP Photo/Keith Srakocic)
