EE STEPPED BACK OFF OF EXCAVATOR TRACKS WHILE SERVICING UNIT. EE LANDED ON HIS FEET, BUT STATES HE HEARD POP IN RIGHT KNEE. EE DID NOT REPORT INJURY TO OFFICE UNTIL 3/29/05. EE WORKED REGULAR HOURS UNTIL 5/20/05, THE DAY HE HAD ARTHROSCOPIC SURGERY TO RIGHT KNEE.