EE ALLEGES THAT INJURY OCCURRED WHILE HE WAS DESCENDING THE STAIRWELL FROM THE 5TH FLOOR OF THE MILL BUILDING. EE STOPPED TO OBSERVE MILL OPERATION. WHEN HE STARTED AGAINS, HIS LEFT FOOT BECAM E STUCK ON THE FLOOR GRATING AND IN TURNING RIGHT, HIS LEFT KNEE ""POPPED"". EE CONTINUED TO WORK UNTIL 5-25-00 WHEN TREATMENT FOR HIS KNEE & ASSOCIATED SORE BACK REQUIRED TIME OFF WORK.