EE WAS REMOVING FRONT DIFFERENTIAL DRAIN PLUG FROM A 992 LOADER USING A 3/4 INCH BREAKER BAR AND 1/2 INCH SOCKET WHEN HE FELT A STRAIN IN HIS LOWER BACK. HE DID NOT CEASE WORK NOR SEEK MEDICAL ATTENTION UNTIL 8/15/02 WHEN HE NOTIFIED MINE MANAGEMENT HE WAS UNDER PHYSICIANS CARE AND ORDERED OFF WORK.