WHILE CHANGING A FLAT TIRES ON FREIGHT TRAILER #74-303 THE JACK WAS HANGING UP AND NOT GOING UNDER THE AXLE AS EE PUSH AND TWISTED TRYING TO FORCE THE JACK UNDER THE AXLE HE FELT PAIN IN HIS RIGHT WRIST, HE GOT THE JACK UNDER THE AXLE AND FINISH CHANGING OUT THE TIRE. HE DID NOT THINK HE HAD HURT HIMSELF UNTIL LATER THAT NIGHT. AND REPORTED IT TO HIS SUPERVISOR THE NEXT MORNING.