PARKED FACING DOWNHILL WITH VEHICLE IN PARK AND PARKING BRAKE ON. CAR WOULD NOT CHANGE GEAR USING COLUMN LEVER. GOT OUT OF VEHICLE TO CHECK UNDER HOOD FOR A PROBLEM. NOTICE CABLE DISCONNECTED FROM LEVER ON TRANSMISSION. WHEN I WAS ABOUT TO REACH IN TO GET THE CABLE, THE VEHICLE POPPED OUT OF GEAR AND ROLLED DOWN HILL, THE HOOD SLAMMED MY ARM TRAPPING IT AS THE VEHICLE ROLLED DOWNHILL. I BECAME TRAPPED BETWEEN ANOTHER CAR AS IT PUSHED ME 20 FEET DOWNHILL. ANOTHER PASSER BY WAS ABLE TO GET IN THE VEHICLE AND PUT THE BRAKE WHILE I PRIED MY ARM OUT CAUSING NERVE DAMAGE. THE HOOD WOULD NOT RELEASE WHILE MY ARM WAS STUCK. *TR