After setting cement plug the crew was to lay out the cement line. The chicksan was removed from the “Pump- In” sub. The connection between the pump-in sub and drill pipe was to be broken with the use of the Iron Roughneck™ so the sub could be removed with a chain tong. The Iron Roughneck™ Operator was asked to repeat this action to ensure the sub was loose enough to use a chain tong. He was then instructed to remove the Iron Roughneck™ but by mistake began to back out the sub. Just as he did this the IP placed his hand on the Iron Roughneck™ to assist in its removal from the sub. The pump-in sub with Lo-Torque valve spun and caught the IP’s fingers. He suffered severe injuries to the ring finger resulting in three quarters of it being amputated. The middle and index fingers sustained fractures and cuts.