PHILADELPHIA Scientists at the University of Pennsylvania have demonstrated that an infant skull is only a fraction as strong as that of an adult, a finding that could greatly enhance the safety of young children. The results, published in the most recent issue of the Journal of Biomechanical Engi-neering, indicate that at birth a child skull has just one-eighth the strength of an adult skull.

The study also found that infantsskulls can undergo six-fold larger de-formations before fracture, making blows to infantsmalleable skulls far more likely to intrude into the cranial cavity although its authors caution that it not clear whether the larger deformations necessarily result in more severe brain injuries.

"While it long been suspected that infantsskulls are not only thin but also made of bone less sturdy than that in adultsskulls, this work is the first rigorous examination of the issue," said lead author Susan S. Margulies, Ph.D., an associate professor of bioengineering at Penn. "Despite this evidence con-firming the fragility of children skulls, researchersunderstanding of the actual mechanisms of pediatric head injury remains very limited."

Safety experts say the work should help make a variety of products and environments safer from children bicycle helmets and car seats to the surfaces upon which playgrounds are built.

"Certainly any further information on the mechanical properties of in-fant skulls will help us set standards and modify standards as appropriate," said Walter Henderson, a member of the public playground equipment com-mittee of the American Society for Testing and Materials, which sets safety standards for products worldwide. "Very little is known about infantsskulls, and a better body of knowledge will help us enact better standards."

Mr. Henderson, of Henderson Consulting Services in Mechanicsburg, Pa., said Dr. Margulies work will likely play a role as the ASTM reviews its playground safety standards for children younger than 2.

A child skull is incompletely fused at birth, and the Penn researchers have also found that the sutures joining the skull bony plates have less than half the strength of the bone, allowing the skull to deform and distort the in-fant brain beneath. The skull and sutures reach adult thickness and strength only during early adolescence.

"Unlike adults, children who suffer head injuries usually can reliably relay to us how their injuries happened," Dr. Margulies said. "To help pre-vent serious head injuries among children, we like to know the mechanisms by which these injuries occur, and we like to better understand the mechani-cal properties of children skulls."

Kirk L. Thibault, Ph.D., a former graduate student at Penn, joined Dr. Margulies in the research. Their work was supported by the Center for Injury Research and Prevention at the Centers for Disease Control.