A LIFTING EXTENSION WAS PLACED ON A 988A FRONT END LOADER TO ASSIST EE AND A COWORKER IN THE REMOVAL & REPAIRING OF A HOUSE ROLLER ON A 4500 DRAGLINE. THE WEIGHT OF ROLLER SHIFTED, CAUSING CHAIN TO SLIP. THIS CAUSED THE BOOM EXTENSION TO LURCH UPWARD, STRIKING EE UNDER THE BEEK OF HIS HARD HAT, CAUSING A LACERATION TO HIS FOREHEAD REQUIRING 16 STITCHES TO CLOSE.