Falls are the most common unintentional injury modality among infants, as well as the most common history provided by caretakers in cases of suspected child abuse. Skull fracture is a common finding for both violence-related and unintentional head injuries, and it is not clear what fall heights cause skull fracture in young children.

Material property testing of human infant skull and suture, anthropomorphic surrogate simulations, and finite element modeling were combined to determine the fall heights capable of creating skull fracture. The ultimate stress of human adult cranial bone at high test rates is more than 5 times higher than pediatric cranial bone, indicating a lower threshold for fracture. However, adult cranial bone was found to be 48 times stiffer than pediatric cranial bone, and pediatric cranial suture was able deform over 100% before failure, producing an infant skullcase that may significantly deform before fracture, increasing the potential for brain deformation and injury upon impact.

Angular accelerations calculated from surrogate simulations of head-first falls from 1-3 feet reveal that drops onto mattress produce significantly lower rotational accelerations than carpet and concrete. Drops onto carpet pad were not significantly different than concrete due to compression of the carpet pad and underlying concrete surface. Sagittal and axial rotation accounted for the majority of head motion during all drops.

Using measured material property data and loads from the surrogate simulations, a 3D finite element model of a 1-½ month old infant head predicted that a 280 N impact force onto the occiput would result in a 50% probability of skull fracture in infants. Based on the range of forces calculated for the fall simulations of average head-first impacts, we conclude that there is ≥ 50% probability of skull fracture in infants with head-first impact to the occiput from falls of 1-3 feet onto carpet pad and concrete, but not onto a mattress.

By defining biomechanical tolerances of pediatric tissues and mechanisms of injury, better accident prevention methods may be developed, and clinicians will be better equipped to make objective assessments of injury etiologies in infants.