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Brain/Skull Relative Displacement Magnitude Due to Blunt Head Impact: New Experimental Data and Model
Technical Paper
99SC22
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English
Abstract
Relative motion between the brain and skull may explain many
types of brain injury such as intracerebral hematomas due to
bridging veins rupture [1] and cerebral contusions. However, no
experimental methods have been developed to measure the magnitude
of this motion. Consequently, relative motion between the brain and
skull predicted by analytical tools has never been validated. In
this study, radio opaque markers were placed in the skull and
neutral density markers were placed in the brain in two vertical
columns in the occipitoparietal and temporoparietal regions. A
bi-planar, high-speed x-ray system was used to track the motion of
these markers. Due to limitations in current technology to record
the x-ray image on high-speed video cameras, only low- speed (﹤ 4m/s) impact data were available.
A previously developed finite element model of the brain
simulating blunt head impact was used to study the feasibility of
using this model to obtain relative displacement of the same
magnitude as that obtained experimentally. The model simulated the
scalp, three-layered skull, dura, falx, tentorium, pia, cerebral
spinal fluid (CSF), venous sinuses, ventricles, cerebrum (gray and
white matter), cerebellum, brain stem, and parasagittal bridging
veins. No sliding was allowed between any component structures of
the model, and a layer of solid elements with low shear modulus was
used to model the CSF. However, this approach was not able to
predict relative motions over 1 mm between the brain and skull.
In this study, the model was modified. Although the CSF remained
as a layer of material with a low shear modulus, a sliding
interface was introduced to simulate the interaction between the
CSF and pia matter. With this change in place, the model
predictions corresponded with brain displacement data obtained from
cadaveric experiments. The relative skull/brain displacement-time
histories predicted by the new model agreed well with those
obtained experimentally. The model was also run at higher impact
speeds to obtain intracranial pressure as well as displacement
histories. The computed coup/contrecoup pressures and contact
forces predicted by the model compared favorably with the
experimental data published by Nahum et al., [2]. Simulation results
reproduced the translational acceleration injury mechanism
(coup/contrecoup) proposed by Gurdjian and Lissner [3].