Mechanical properties and anthropometry of the human infant head.

The adult head has been studied extensively and computationally modeled for impact, however there have been few studies that attempt to quantify the mechanical properties of the pediatric skull. Likewise, little documentation of pediatric anthropometry exists. We hypothesize that the properties of the human pediatric skull differ from the human adult skull and exhibit viscoelastic structural properties. Quasi-static and dynamic compression tests were performed using the whole head of three human neonate specimens (ages 1 to 11 days old). Whole head compression tests were performed in a MTS servo-hydraulic actuator. Testing was conducted using nondestructive quasi-static, and constant velocity protocols in the anterior-posterior and right-left directions. In addition, the pediatric head specimens were dropped from 15cm and 30cm and impact force-time histories were measured for five different locations: vertex, occiput, forehead, right and left parietal region. The compression stiffness values increased with an increase in velocity but were not significantly different between the anterior-posterior and right-left directions. Peak head acceleration during the head impact tests did not significantly vary between the five different impact locations. A three parameter model that included damping represented the pediatric head impact data more accurately than a simple mass-spring system. The compressive and impact stiffness of the pediatric heads were significantly more compliant than published adult values. Also, infant head dimensions, center of gravity and moment of inertia (Iyy) were determined. The CRABI 6-month dummy impact response was similar to the infant cadaver for impacts to the vertex, occiput, and forehead but dramatically stiffer in lateral impacts. These pediatric head anthropomorphic, compression, and impact data will provide a basis to validate whole head models and compare with ATD performance in similar exposures.