The compressive stiffness of human pediatric heads

Abstract

Head injury is a persistent and costly problem for both children and adults. Globally, approximately 10 million people are hospitalized each year for head injuries. Knowing the structural properties of the head is important for modeling the response of the head in impact, and for providing insights into mechanisms of head injury. Hence, the goal of this study was to measure the sub-injurious structural stiffness of whole pediatric heads. 12 cadaveric pediatric (20-week-gestation to 16 years old) heads were tested in a battery of viscoelastic compression tests. The heads were compressed in both the lateral and anterior-posterior directions to 5% of gauge length at normalized deformation rates of 0.0005/s, 0.01/s, 0.1/s, and 0.3/s. Because of the non-linear nature of the response, linear regression models were used to calculate toe region (<2.5%) and elastic region (>2.5%) stiffness separately so that meaningful comparisons could be made across rate, age, and direction. The results showed that age was the dominant factor in predicting the structural stiffness of the human head. A large and statistically significant increase in the stiffness of both the toe region and the elastic region was observed with increasing age (p<0.0001), but no significant difference was seen across direction or normalized deformation rate. The stiffness of the elastic region increased from as low as 5 N/mm in the neonate to >4500 N/mm in the 16 year old. The changes in stiffness with age may be attributed to the disappearance of soft sutures and the thickening of skull bones with age.

Preliminary observations of the sequence of damage in excised human juvenile cranial bone at speeds equivalent to falls from 1.6 m

“…Specimens #1 and #2 were more flexible than the other specimens as visible bending occurred before they fractured. This is consistent with previous literature where the infant skull has been found to be more compliant than a child or adult skull [13,26,27].…”

A Review of the Compressive Stiffness of the Human Head

“…A series of A-P and lateral non-destructive compression loads were applied to adult ( N = 6) 19 and pediatric ( N = 12) 21 , 35 heads. Loading rates were normalized by the head length and width, respectively for A-P and lateral tests, to produce consistent strain rates (0.0005, 0.01, 0.1, 0.3 1/s).…”

“…This response was observed for some destructive quasistatic and dynamic tests, and with dry, embalmed and fresh-frozen heads, 42 and was thought to arise from rate-dependent fracture mechanics of the skull. 9 The bilinear response was absent in non-destructive 21 , 22 , 35 and destructive 4 , 6 studies that calculated deformation from acceleration-time data, which is likely a limitation of the instrumentation. For studies that measured deformation directly during frontal impacts 1 , 2 , 9 , 46 the peak force was achieved in approximately one millisecond.…”

Bilateral Parietal Skull Fractures in Infants Attributable to Accidental Falls

“…The authors hypothesized that the pliable infant skull could bend in such a way that 2 separate, distant fractures could occur. Loyd et al [26] conducted mechanical compression tests on 12 cadaveric pediatric heads of different ages by applying bilateral loads. While these authors avoided fractures so that their specimens could be used more than once, valuable information about infant skull stiffness was obtained.…”