In a car accident where there is a strong possibility of a neck fracture, the patient is usually placed on a backboard to immobilize the spine.
But what if the victim is sitting? You don't want him/her to climb out of the car, then lie down on a backboard. So here is when you use a KED.
A KED is basically a smaller backboard meant to go between the seat and the victim. After putting a neck collar on to protect the C-Spine, the EMTs all at the same time gently push the victim forward, so that the KED can be slipped behind them. It's like a back cushion, though it's made from hard plastic. Usually someone (the head stabilization person) is seated behind the victim, if they can get there to hold the head in place until a collar comes on.
After that, straps on the side are fastened around the torso, under the arms. 2 straps are placed around the head to keep the neck immobilized and held down.
Once secured,the rescue workers slowly rotate the victim so his back is to the car door, and lower him so he/she is horizontal. If someone can get in the other seat, they will lift the legs and aid in carrying the victim out.
It is standard protocol for every ambulance to have one of these, and the EMT's are trained in its use. However, the KED is not used always, such as in a critical patient (ie Cardiac arrest, which takes priority over possible spinal problems), known to EMT's as scoop and run.