ARLINGTON, Va., Aug. 12, 2003 -- Babies are more vulnerable to serious head injury during a fall than had been previously thought, according to new research that may also begin to help child abuse investigators distinguish between accidental and intentional injury.

Whitaker investigator Susan Margulies of the University of Pennsylvania found that rotational forces generated by a baby's head hitting a hard surface can cause widespread, potentially serious brain injury. This can include internal bleeding, which can damage tissue and alter brain function, and nerve cell damage, which can impair thinking, sensation, and other mental functions.

Infant falls are often dismissed as relatively benign because the head is assumed to be moving in a straight line at impact, Margulies said. Linear motions are associated with such localized injuries as skull fractures.

Rotational movements, however, can produce more widespread and serious brain injury. "We found that when the head contacted a firm surface before the body, significant rotational motions were produced," Margulies said. Her study was published in the July issue of the Journal of Neurosurgery.

These findings may also help distinguish between accidental falls and injury sustained by intentionally striking a child's head against a hard surface, although more research is needed before such results could make a clear difference in abuse investigations.

"Traumatic brain injury is the most common cause of death in childhood, and child abuse is believed to be responsible for at least half of infant brain injuries," Margulies said. "While accidental falls are a frequent cause of pediatric trauma, they are also a common explanation given by caretakers in suspected abuse cases."

Margulies and her colleagues used an infant "crash test dummy" to measure rotational forces, which are rapid changes in velocity as the head contacts a hard surface and then violently rebounds. The lifelike doll resembling a 6-week-old infant is equipped with sensors to measure rotational velocity and acceleration. These forces increase with higher falls and harder surfaces.

The doll was suspended from a scaffold and allowed to fall 134 times from heights of 1, 3 and 5 feet onto surfaces commonly found in a home: a concrete floor, .25-inch-thick carpet padding, and a 4-inch-thick foam pad, simulating a crib mattress. Volunteers also shook the doll vigorously and struck its head against each of the three surfaces.

The 5-foot-fall onto concrete produced enough force to cause serious brain injury, the researchers found. But intentional head strikes onto hard surfaces produced significantly greater force.

"Based on this evidence, our data suggest that inflicted impacts are much more likely than falls or shaking to lead to brain injury," Margulies said. These injuries could include internal bleeding and prolonged or permanent nerve damage.

There has been a widespread assumption that children are the physiological equivalent of miniature adults and are affected similarly in cases of head trauma. But Margulies and others are accumulating evidence that young children do not always respond to trauma the same way adults do.

"Learning more about pediatric brain injuries will help us develop protective devices -- helmets, playground surfaces, car seats -- that better meet their specific needs," she said.

Collaborators include Michael Prange and Brittany Coats of Pennsylvania and Ann-Christine Duhaime of Hitchcock Medical Center in Hanover, N.H. Margulies received a Whitaker Biomedical Engineering Research Grant in 1992 for work in the lung.