Employee stepped in between the grader blade and tire to start up the ladder to the cab of grader. He twisted left knee and fell to the ground. He stated that he heard a popping noise and was unable to put any weight on or stand. He was transported to ER and X-ray showed nothing broke. He seen Family Dr. on May 1, 2009 and returned to work on May 4, 2009. LTA began on May 26, 2009.