WHILE UNLOADING BOLTS AND PLATES OUT OF A SCOOP BUCKET ONTO THE BOLTER, EMPLOYEE PICKED UP 5 TO 6 BOLTS TOOK ONE STEP BACK INTO A HOLE FORCING HIS LEFT KNEE BACKWARD. NOTE: OPERATIONS WERE IDL E FROM 12/21/02 THRU 1/2/03. REPORT IS WITHIN 10 DAY LIMIT.