EE STEERED ATV FULL RIGHT & STEERING LOCKED. TO AVOID MACHINE TIPPING OVER, HE USED LEFT FOOT ON GROUND TO STABILIZE THE UNIT WHILE STOPPING. THE MAIN FRAME BROKE CAUSING STEERING TO LOCK. INI TIAL MEDICAL FINDINGS WERE NEGATIVE BUT LATER MRI REVEALED NECESSITY FOR SURGERY. EE PERFORMED FULL JOB DUTIES PRIOR TO SURGERY, WHICH OCCURRED ON 5/9/03, THEN HE WAS PLACED ON RESTRICTIONS.