I WAS STRUCK FROM THE REAR ON THE LEFT CORNER WHILE IN THE CENTER LANE OF I-435 RIGHT BEFORE AN EXIT.. DIFERENTIAL SPEED OF APPROX.25 MPH. THE SEAT SLID BACK ON THE TRACKS AND THE SEAT BACK FAILED LEAVING ME LOOKING AT THE CEILING. MY FEET NO LONGER REACHED THE PEDALS AND MY HANDS BARELY REACHED THE STEERING WHEEL. THE CAR WENT ACROSS 2 LANES OF TRAFIC INTO A DITCH AND PARTIALLY UP AN EMBANKMENT. HAD THE SEAT NOT FAILED I WOULD HAVE BEEN ABLE TO CONTROL THE CAR AND STAYED ON THE ROAD. THE DAMAGE ESTIMATE SHOWED $3000 OF THE TOTAL $5000 TO BE IN THE FRONT END ! I WAS ALMOST HIT BY AN 18 WHEELER OR SIMILAR SIZED TRUCK AS I WAS CROSSING THE TWO LANES OF TRAFFIC TOWARD THE DITCH. AS THIS WAS A DIVIDED INTERSTATE I COULD HAVE BEEN THROWN THE OTHER WAY ACROSS THE MEDIAN INTO ONCOMMING TRAFFIC.(LUCKILY WE HAVE A CABLE BARIER SYSTEM IN PLACE.) THE POINT IS, LOSS OF CONTROL OVER A REAR END COLLISION BECAUSE THE DRIVERS SEAT FAILS IS NOT ACCEPTABLE.*AK