Andrew MacDonald led the Islanders in ice time and blocked shots this season, and he and Travis Hamonic have been the top defense pair assigned to either Sidney Crosby's or Evgeni Malkin's line all series.
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But the Isles will have to adjust after MacDonald suffered a broken hand, according to a source, in the second period of the 6-4 win in Game 4.
"It's a big blow for us, a tough break," said Hamonic, who played 28:42 Tuesday night as the Isles rotated mostly four defensemen through the third period. "You don't really realize how many tough minutes he plays until he's not out there. We all have to adjust."
MacDonald appeared to suffer the injury at the 13-minute mark of the second, either on a hit by Craig Adams or a subsequent shot from the point. MacDonald was without his stick and held Adams for a penalty, then skated off to the dressing room holding his arm.
Thomas Hickey has not played since Game 1 and Radek Martinek, the only Islander on the roster who has played a postseason game with the team before, is also available.
Martin, Cooke scrap
Matt Martin got shoved into the Penguins bench in the third period by Matt Cooke, and the two exchanged some shoves, part of the nastiness that ensued late in Game 4. Brenden Morrow pounded Casey Cizikas when the Isles center wouldn't let go of Morrow's stick, and Martin was in the middle of a game-ending melee.
"I think it's inevitable in a series," Jarome Iginla said. "The longer it goes on, the more you stare at the same people across the line and the more desperate each team gets and the more you dislike each other."