THE AIRPLANE WAS PARKED AT THE PASSENGER TERMINAL WITH BOTH ENGINES SHUT DOWN AS PASSENGERS DEPLANED. REPORTEDLY, TWO RAMP AGENTS WERE POSITIONED AT THE BOTTOM OF THE AIRSTAIR DOOR AND WERE ASSISTING THE DEPLANING PASSENGERS. HOWEVER, ACCORDING TO THE WIFE OF THE INJURED PASSENGER, HER HUSBAND, A DIABETIC, WAS NOT ASSISTED BY THE TWO AGENTS. AS THE PASSENGER STEPPED FROM THE LAST STEP TO THE GROUND (APPROXIMATELY 18 INCHES) HE FELL AND BROKE HIS HIP. A NORTHWEST AIRLINK OFFICIAL STATED THAT A STEP WAS NOT POSITIONED BELOW THE FINAL AIRSTAIR STEP AS REQUIRED BY VERBAL COMPANY POLICY. A WRITTEN POLICY REGARDING THIS MATTER IS BEING FORMULATED AND WILL BE INSERTED INTO THE STATION MANUAL. SUBSEQUENT TO THIS ACCIDENT, ALL RAMP AGENTS HAVE BEEN RETRAINED IN THE USE OF THE ADDITIONAL STEP REQUIREMENT FOR THE JETSTREAM AIRPLANES.