EE WAS BEGINNIGN TO TROUBLESHOOT A REPORTED STEERING PROBLEM WITH TRUCK, EE WAS SITTING IN SEATM RESTING LEFT ARM ON STEERING WHEEL WHILE REMOVING SHROUD SCREWS UNDER CONSOLE, WHEEL INDEPENDENTLY TURNED THROUGH2-3 REVS, LEFT ARM BECAME CAUGHT IN WHEEL AND WEDGED AGAINST RETARDER LEVER, ARM BROKE BETWEEN ELBOW AND SHOULDER.