MECHANIC WAS ASSISTING ON PALLET CAR CHANGEOUT FOR LINE 1 FURNACE. A CAR WINCH PULL CHAIN CAUGHT AND DAMAGED A PIECE OF GRATING. THE MECHANIC INADVERTENTLY STEPPED ON IT, TWISTING HIS LEFT A NKLE. AS TIME PASSED, HIS BACK BECAME SORE. HE RECENTLY BEGAN PHYSICAL THERAPY FOR A BACK STRAIN, ATTRIBUTED TO THIS INCIDENT. THE GRATING WAS REPAIRED.