Biomechanics of Skull Fracture

Abstract

This study was conducted to determine the biomechanics of the human head under quasistatic and dynamic loads. Twelve unembalmed intact human cadaver heads were tested to failure using an electrohydraulic testing device. Quasistatic loading was done at a rate of 2.5 mm/s. Impact loading tests were conducted at a rate of 7.1 to 8.0 m/s. Vertex, parietal, temporal, frontal, and occipital regions were selected as the loading sites. Pathological alterations were determined by pretest and posttest radiography, close-up computed tomography (CT) images, macroscopic evaluation, and defleshing techniques. Biomechanical force-deflection response, stiffness, and energy-absorbing characteristics were obtained. Results indicated the skull to have nonlinear structural response. The failure loads, deflections, stiffness, and energies ranged from 4.5 to 14.1 kN, 3.4 to 16.6 mm, 467 to 5867 N/mm, and 14.1 to 68.5 J, respectively. The overall mean values of these parameters for quasistatic and dynamic loads were 6.4 kN (+/- 1.1), 12.0 mm (+/- 1.6), 812 N/mm (+/- 139), 33.5 J (+/- 8.5), and 11.9 kN (+/-0.9), 5.8 mm (+/- 1.0), 4023 N/mm (+/- 541), 28.0 J (+/- 5.1), respectively. It should be emphasized that these values do not account for the individual variations in the anatomical locations on the cranium of the specimens. While the X-rays and CT scans identified the fracture, the precise direction and location of the impact on the skull were not apparent in these images. Fracture widths were consistently wider at sites remote from the loading region. Consequently, based on retrospective images, it may not be appropriate to extrapolate the anatomical region that sustained the impact forces. The quantified biomechanical response parameters will assist in the development and validation of finite element models of head injury.

Reconstruction of real world head injury accidents resulting from falls using multibody dynamics

“…They are also not excessively high considering that all of these people sustained moderately severe head injury. Forces on the head, similarly, fall within more acceptable levels compared to the literature, and the only case that still exceeds the highest fracture limit found by Yoganandan et al [16] and Allsop et al [17] (Case 3) is one that actually did have skull fracture. With regards to angular acceleration figures for these simulations, they do reduce significantly, but not by the same factor that linear acceleration does.…”

“…Thomson et al [25] found angular acceleration values of between 7 and 30 krad/s 2 in reconstructions of severe head injury accidents involving vehicles). Force values for all of these simulations apart from Case 1 also exceed the highest tolerance limits established for skull fracture (14.1 kN [16] or 17.0 kN [17]), with fracture actually only occurring in two cases. In many simulations, these limits are exceeded by a great amount -enough to suggest much more extensive fracture of the skull than the relatively simple linear fractures present in the two cases showing skull fracture.…”

“…This is because of the definite relationship between force applied to the skull, and failure of cranial bone. Yoganandan et al [16] investigated levels of force required to fracture the skulls of 12 unembalmed cadavers. Using a hemispherical impactor with a 48 mm radius, they carried out impacts to various locations on the skull at a rate of 7.1 to 8.0 m/s.…”

“…Other authors, however, have obtained alternative force-deflection characteristics for the head from cadaveric head impacts. Yoganandan et al [16] provide force/deflection curves for unembalmed cadaver heads under dynamic loading. Force/deflection responses from these impacts were recorded at various locations on the cranium (the vertex, frontal bone, parietal bone, occipital bone and temporal bone) and results were plotted to produce an average force-deflection curve.…”

“…This is in line with the observations of Thomson et al [25] that HIC values can increase by over 500% when Hybrid III properties are used to model head contact compared to cadaveric head contact properties from the literature. The MADYMO default curves are based on tests performed on the EEVC headform, while the alternative values are based on impacts carried out by Yoganandan et al [16] using unembalmed cadaver heads. Yoganandan's force-deflection characteristics are consistent with those estimated by Allsop et al (17) and Manavais et al (9) for skull bone -ground impact interactions.…”