EMPLOYEE WAS STANDING ON A LADDER, TIGHTENING A BOLT. WHILE APPLYING PRESSURE TO WRENCH, THE WRENCH SLIPPED OFF THE NUT CAUSING HIS RIGHT ELBOW TO HIT A WRUNG ON LADDER; THIS RESULTED IN CONTUSION TO THE ELBOY WHICH EVENTUALLY RESULTEDIN A SUBLUXED ULNER NERVE. THIS INJURY DIDN'T BECOME REPORTABLE UNTIL FINAL DIAGNOSIS RESULTEDIN SURGERY AND LOST TIME.