DRIVING ON SEMI-CLEAR ROAD ABOUT 40 MPH, AIR TEMPERATURE WAS -7 DEGREES. HIT BLACK ICE AND WENT OFF THE ROAD AND INTO A DITCH. THE EXPLORER HIT A TREE STUMP ON THE FRONT LEFT CORNER OF BUMPER AND WHEEL. THE TRUCK DID NOT ROLL OVER DURING THE ACCIDENT. BOTH THE DRIVER AND PASSENGER WERE WEARING THE SEAT BELT/SHOULDER BELT. BOTH FRONTAL AIR BAGS FAILED TO DEPLOY. THE DRIVER SUSTAINED A FRACTURE/COMPRESSION OF THE L1 VERTBRAE (SPINE) DUE TO THE SEAT BELT (SEAT-BELT SYNDROME). THE TRUCK SUSTAINED HEAVY DAMAGE TO THE FRONT, FRONT WHEEL AND ENGINE AREA. THE REPAIR MECHANIC DID PERFORM A CHECK OF THE AIR BAG SYSTEM DURING THE REPAIR OF THE VEHICLE AND THE SYSTEM CHECKED OUT AS NORMAL. NO AIR BAG SYSTEM PART HAD BEEN REPLACED DURING THE REPAIR. *AK