5 Modelling of the Brain for Injury Simulation and Prevention
121
Acute subdural hematoma (ASDH) describes an abnormal blood collection
between the dura and arachnoid maters. ASDHs are one of the most frequently seen
forms of high severity acute head injuries. There is evidence that ASDH is usually
formed within the first several minutes and certainly by the end of the first hour after
a severe impact. Many researchers believe that the cause of ASDH is the rupture of
parasagittal bridging veins. Hence, relative motions between the brain and skull
are a good predictor to estimate the risk of ASDH. While this hypothesis may have
clinical correlation in a number of cases, Maxeiner and Wolff [65] showed that there
was an equal probability of ASDH caused by bridging vein rupture and by cortical
artery rupture. Moreover, Shenkin [90] reviewed 39 consecutive cases of ASDH
and found that there was a high incidence rate of cortical artery rupture (61.5%).
Additionally, relative motions between the brain and skull measured by Hardy et al.
[30] indicated that relative motions in the peripheral region of the cortex were less
than those measured in the central region of the brain. For these reasons, we cannot
confirm the precise injury mechanisms of ASDH until new experiments are carried
out.
Subarachnoid hematoma (SAH) or haemorrhage is the result of ruptured corticomeningeal vessels or bridging veins upon blunt impact. As the haemorrhage occurs
in the CSF space, intracranial pressure is not likely to rise significantly, and this
injury type does not present a significant challenge in clinical practice. Additionally,
it is computationally too expensive to explicitly model these cortico-meningeal
vessels. Hence, this type of brain injury has been mostly ignored by most FE models.
Similarly, epidural hematoma (EPH) is seen in less than 5% of TBI cases and has a
low mortality rate. Although there is no space between the skull and dura, there is
a natural epidural space around the spinal cord for the haemorrhage to move into.
Consequently, simulating the risk of EPH is not a great concern to many researchers.
5.3.6 Acquisition of Experimental Data Specifically Conducted
for Model Validation
As mentioned in Sect. 5.2, only limited datasets are available to validate FE
models. These datasets can be grouped into two categories: laboratory experiments
and reconstructed real-world data. Practically, any FE head model that has been
validated include the use of intracranial pressure data from the oft-cited Test 37
reported by Nahum et al. [71] probably due to the fact that this was the only
time history data presented in the paper. Note that the same publication [71] also
included peak data in tabular form, reporting on a number of experiments in
which intracranial pressures were measured. For example, there were padded and
rigid impacts, using three different impactor masses (2.7, 5.23, 5.59 kg) and six
different velocities (4.36, 6.3, 8.69, 8.75, 9.94, 12.95 m/s). Some of the intracranial
pressure data did not make sense from a mechanical point of view and were
121
Acute subdural hematoma (ASDH) describes an abnormal blood collection
between the dura and arachnoid maters. ASDHs are one of the most frequently seen
forms of high severity acute head injuries. There is evidence that ASDH is usually
formed within the first several minutes and certainly by the end of the first hour after
a severe impact. Many researchers believe that the cause of ASDH is the rupture of
parasagittal bridging veins. Hence, relative motions between the brain and skull
are a good predictor to estimate the risk of ASDH. While this hypothesis may have
clinical correlation in a number of cases, Maxeiner and Wolff [65] showed that there
was an equal probability of ASDH caused by bridging vein rupture and by cortical
artery rupture. Moreover, Shenkin [90] reviewed 39 consecutive cases of ASDH
and found that there was a high incidence rate of cortical artery rupture (61.5%).
Additionally, relative motions between the brain and skull measured by Hardy et al.
[30] indicated that relative motions in the peripheral region of the cortex were less
than those measured in the central region of the brain. For these reasons, we cannot
confirm the precise injury mechanisms of ASDH until new experiments are carried
out.
Subarachnoid hematoma (SAH) or haemorrhage is the result of ruptured corticomeningeal vessels or bridging veins upon blunt impact. As the haemorrhage occurs
in the CSF space, intracranial pressure is not likely to rise significantly, and this
injury type does not present a significant challenge in clinical practice. Additionally,
it is computationally too expensive to explicitly model these cortico-meningeal
vessels. Hence, this type of brain injury has been mostly ignored by most FE models.
Similarly, epidural hematoma (EPH) is seen in less than 5% of TBI cases and has a
low mortality rate. Although there is no space between the skull and dura, there is
a natural epidural space around the spinal cord for the haemorrhage to move into.
Consequently, simulating the risk of EPH is not a great concern to many researchers.
5.3.6 Acquisition of Experimental Data Specifically Conducted
for Model Validation
As mentioned in Sect. 5.2, only limited datasets are available to validate FE
models. These datasets can be grouped into two categories: laboratory experiments
and reconstructed real-world data. Practically, any FE head model that has been
validated include the use of intracranial pressure data from the oft-cited Test 37
reported by Nahum et al. [71] probably due to the fact that this was the only
time history data presented in the paper. Note that the same publication [71] also
included peak data in tabular form, reporting on a number of experiments in
which intracranial pressures were measured. For example, there were padded and
rigid impacts, using three different impactor masses (2.7, 5.23, 5.59 kg) and six
different velocities (4.36, 6.3, 8.69, 8.75, 9.94, 12.95 m/s). Some of the intracranial
pressure data did not make sense from a mechanical point of view and were