PHILADELPHIA -- While seat belts save lives, the straps can unintentionally maim and even kill young children in crashes. Now, researchers hope to develop safer restraints by using a better crash-test dummy - one that includes a simulated child abdomen.
For more than a decade, it has been clear that the abdomen is the second most commonly injured body area in seat-belted youngsters, after the head. With the abdominal insert, safety engineers can at last measure precisely what happens to this vital region in the average 4-to-8-year-old.
Ford Motor Co. engineers spent three years working with experts from Children's Hospital of Philadelphia, the University of Virginia, Wayne State University in Detroit, and the Japanese seat-belt manufacturer Takata Corp. to develop a simulated abdomen that fits into the standard 6-year-old-size crash-test dummy.
This month, Ford will present the prototype to the Society of Automotive Engineers, the first step toward making it available to the entire auto industry, said Stephen W. Rouhana, Ford's senior technical leader on the project.
Technically, a crash dummy is an "anthropomorphic test device." Equipping one with an imitation kiddie abdomen may sound simple, especially considering that the industry already has come up with a pregnant version.
But simple it was not. Researchers had to parse the biomechanics of child seat-belt injuries. Then they re-created the injuries in an animal model. Finally, they built a gizmo that behaved like abdominal tissue - taking into account variables such as muscle tension.
Children's Hospital's Center for Injury Research and Prevention provided its expertise on crash injuries in children ages 4 to 8. At those ages, bioengineer Kristy Arbogast explained, youngsters are usually too big for toddler safety seats but too small for lap and shoulder harnesses.
The lap belt, which rests on the bony pelvis of an adult, often rides up a child's cartilage-soft pelvis to the stomach. Children may add to this belly-binding effect by sitting on the edge of the seat because their legs are short.
"They scoot forward on the seat so their knees can bend comfortably," Arbogast said. The shoulder belt tends to cut across children's necks, so they often put the annoying strap under an arm or behind the back.
To study the biomechanics of improper belt placement, poor posture, or misuse of the shoulder belt, Arbogast and colleagues crunched an accident database and conducted in-depth crash investigations. They found specific patterns of abdominal injuries. The seat-belted children were either propelled forward head-first over the lap belt, or their pelvises slipped under it.
The crushing force of the lap belt - or the lap and shoulder belts - variously injured the liver, spleen, pancreas, bowel, colon, bladder, ribs, even lungs.
"The belt would almost go right through the abdomen to the lower spine," said Arbogast, lead author of the study, published in June. "We saw several cases of partial paralysis. We also saw children with serious injuries in relatively minor crashes. The driver sustained only minor bruises."
Booster seats, studies have shown, can reduce the risk of crash injury in 4-to-8-year-olds almost 60 percent. Thirty-eight states now have laws requiring the transitional safety seats.
But it's not an ideal fix. Only about half of children who need boosters actually use them. And while boosters can improve seat-belt fit, the child's body remains inherently more fragile than an adult's.
With researchers armed with an understanding of the mechanics of injury, their next step was to figure out how much force would cause it. After university researchers did some testing on anesthetized pigs, Ford's experts had to build the contraption that would "feel" these forces as a human abdomen would. They invented a flexible silicone shell filled with liquid silicone and equipped with light sensors.
During a crash test, the seat belt compresses the shell, causing light-emitting sensors in three spots on the front to move toward light-receiving sensors at the back. These record the change in light intensity, which is then converted into the key indicators - the speed and depth of abdominal penetration.
"The sensors tell not only how severe the crash is, but how the seat belt deformed the abdomen and the risk of injury," said University of Virginia biomedical engineer Richard W. Kent.
"A child could walk out of a fender-bender with significant injury, or walk away from a serious accident with scratches.
"Until now, there was no way to predict."
Ford's Rouhana said he hoped that sharing the imitation abdomen with the industry in the coming months would give safety engineers "the ability to do out-of-the-box thinking" to create better restraint systems.
Arbogast, meanwhile, looks forward to sparing mothers from arguments like the one she has with her daughter, who at age 10 is still shorter than 57 inches - small enough to need a booster seat.
"She gives me a hard time every now and then," Arbogast said. "I tell her: 'This is what Mom does. She studies how to make kids safer. So you're stuck with it.'"