EE WAS WALKING AROUND THE CAT 16G GRADER DURING HIS PRE-SHIFT EXAM OF THE EQUIPMENT. AS HE STEPPED AROUND THE RIGHT FRONT WHEEL OF THE GRADER, HIS FOOT SLIPPED & HE FELL TO THE GROUND SPRAININ G HIS LEFT KNEE. HE WORKED UNTIL NOON WHEN SWELLING & PAIN DEVELOPED. HIS KNEE WAS IMMOBILIZED AT THE E.R. & HE HAS BEEN RESTRICTED UNTIL FEB. 4. THE GROUND WAS FROZEN WITH SOME ICY AREAS.