2. Author's personal copy
1570 R. Coimbra et al. / Accident Analysis and Prevention 40 (2008) 1569–1575
acceleration of the head’s center of gravity during a crash. Crash
testing is currently conducted in the US to assess compliance with
Federal Motor Vehicle Safety Standards (FMVSS) and as advisory
tests under the New Car Assessment Program (NCAP) for con-
sumers. Frontal crash tests, assessing FMVSS 208, are conducted by
the US National Highway Traffic Safety Administration using 50th
percentile male anthropomorphic dummies in test vehicles trav-
eling at 35 miles per hour (mph) (56 kilometers per hour (km/h))
speed and impacting a rigid barrier in a full frontal impact (NHTSA,
2007). Offset and extreme offset (i.e., corner) frontal impacts are
not currently part of the federal testing program for FMVSS. How-
ever, under NCAP, offset frontal crash tests are conducted at 40 mph
(64 km/h) into a deformable barrier to provide information on these
types of frontal impacts.
Previous research shows crash characteristics influence injury
patterns and severity (Augenstein et al., 2003). Crash severity, as
measured by delta V, is associated with clinically important brain
injury (Al-Salamah et al., 2004). The Principal Direction of Force
(PDOF) (e.g., frontal, side, rear) has been associated with injury pat-
terns and severity for occupants involved in motor vehicle crashes
(Augenstein et al., 2003). One study comparing fatally injured
restrained occupants found more serious head injuries occurred
during frontal impacts with less than 30% of damage distribution
across the frontal plane compared to distributed impacts (Lindquist
et al., 2006). The impact type affects head acceleration (Zhang et al.,
2006) and the direction of head motion has been shown to influ-
ence brain injury patterns (Miller et al., 1998). The percentage of the
vehicle plane damaged also may result in different injury patterns
and severity.
Real world crashes occur under different conditions (e.g., differ-
ent speeds) than crash tests. Human occupants also may respond
differently (based on height, weight, position, and other fac-
tors) compared to anthropomorphic dummies. Additionally, not all
frontal crashes involve damage distributed widely across the front
plane of the vehicle. Often there are impacts damaging only part of
the frontal plane or just the corner where the front and side planes
meet. This variation in damage distribution may influence how
occupants sustain injury during frontal crashes. Studying severe
real world crashes investigated through the Crash Injury Research
and Engineering Network (CIREN) (NHTSA, 2002) may provide use-
ful information on occupant injuries under impact circumstances
not currently covered by crash testing.
This research used the CIREN database to study front seat occu-
pants with brain injury who were in frontal impacts with a differing
percentage of damage distribution across the frontal plane. We
hypothesized that brain injury patterns, severity, and causes may
vary depending upon the damage distribution (distributed, offset,
or corner) during frontal impacts. Because our study focuses on
brain-injured occupants, it does not assess primary prevention of
brain injuries during crashes.
2. Materials and methods
2.1. Study population source
The National Highway Traffic Safety Administration (NHTSA)
funds CIREN, an ongoing study of occupant injuries associated
with motor vehicle crashes. Trauma centers and medical examiners
identify potential cases for inclusion in the CIREN program. Multi-
ple CIREN Centers throughout the United States participate in this
multidisciplinary research program to study severe crashes and the
resulting injuries using a modified National Automotive Sampling
System (NASS) protocol (NCSA, 2007). In addition to injury severity,
the occupant vehicle must be a late model year (6–8 years earlier
than the crash year) vehicle meeting current federal safety stan-
dards. Occupants dying at the scene as well as those transported to
trauma centers are included.
Medical data are obtained by personal interviews with occu-
pants, medical chart review, and evaluation of diagnostic images
including radiographs, computed tomography (CT) images, and
magnetic resonance imaging (MRI) scans. After all crash and med-
ical data are obtained, a multidisciplinary team (trauma surgeons,
orthopedic surgeons, trauma nurses, biomechanical engineers, and
crash investigators) at each center reviews each case to determine
how the injury occurred during the crash and assign the source of
each injury. For example, the interdisciplinary review team may
determine, whether a brain injury was caused by hard contact
between the occupant’s head with an interior vehicle component,
or due to a soft contact with the deployed airbag, or due to linear
or rotational acceleration without any contact. In some cases, it is
not possible to determine the cause of injury and these are iden-
tified as unknowns. This information regarding injury causation is
unique to the CIREN database and provides information regarding
which vehicle component causes a specific injury or if there was
no identified contact with the interior vehicle. An additional qual-
ity control process with an independent external review of all data
(and supporting crash and medical information) for each case is
conducted after data entry is complete.
We used all available CIREN data (1997–2007) to identify occu-
pants in frontal crashes. These included vehicle to vehicle crashes
and crashes with either fixed or non-fixed objects. In crashes with
multiple impacts, the frontal impact ranked as the most severe by
the crash investigator was selected for study. We used the Collision
Deformation Classification (CDC) (SAE, 1980) to identify vehicles
with deformation along the frontal plane that were in crashes with
a Principal Direction of Force equal to 11, 12, or 1 o’clock (using a
clock face superimposed along the longitudinal axis of the vehi-
cle with the center at the point of impact). The CDC also was used
to further classify these impacts based on the damage distribution
across the frontal plane. Distributed impacts were defined as having
a wide damage distribution area (greater than 66% of the vehi-
cle’s frontal plane). Offset impacts were defined as impacts with
35–65% of damage across the frontal plane. Extreme offset (corner)
impacts were defined as impacts occurring at one of the vehicle’s
front corners.
Only adult (>13 years old) drivers or passengers sitting in the
front right “outboard” position were included in the study. Next
occupants who sustained brain injury (based on Abbreviated Injury
Scale (AIS) 1998 update edition) codes (AAAM, 1998) in frontal
crashes were identified. Minor (AIS 1) brain injuries were excluded
from analyses. Scalp lacerations, cranial nerve injury, and secondary
injury (e.g., compression) also were excluded.
2.2. Occupant variable definitions
Occupant variables used in the analyses include age (in years),
gender, seat position (driver or passenger), and safety belt use. Anal-
yses were not stratified by driver status because both drivers and
passenger kinematics would be similar because these were “head
on” frontal impacts with an 11, 12, or 1 o’clock PDOF. Safety belt
design and proper use (e.g., presence of a pre-tensioner, manual,
automatic) was not considered in this study. All safety belt use by
an occupant, regardless of safety belt design or whether there was
proper use, was considered use for analytic purposes.
2.3. Injury coding
AIS codes were assigned using medical records and diagnos-
tic tests (e.g., radiographs, CT scans, MRI) by trauma center or
3. Author's personal copy
R. Coimbra et al. / Accident Analysis and Prevention 40 (2008) 1569–1575 1571
CIREN center staff. Injury body region and severity coding for
CIREN follows the NASS Guidelines based on the AIS developed by
the Association of Advancement for Automotive Medicine (AAAM)
(AAAM, 1998). Because of AIS coding guidelines, concussion would
not be coded unless it was the only brain injury. Loss of conscious-
ness would be coded only if it was the only brain injury or if it
was more severe than an underlying intracranial injury. The AIS is
an anatomical injury scoring system ranging from minor (AIS 1),
moderate (AIS 2), serious (AIS 3), severe (AIS 4), critical (AIS 5) to
maximum (AIS 6) severity. It was originally developed to measure
injury severity for blunt force trauma occurring during motor vehi-
cle crashes. The Glasgow Coma Scale (GCS) also was used to assess
brain injury severity. If an occupant had more than one recorded
GCS, the lowest recorded GCS was used for analyses. Diffuse brain
injuries were defined as concussions, loss of consciousness, and
diffuse axonal injury (DAI).
2.4. Crash variable definitions
Crash related variables used in the analysis include: Princi-
pal Direction of Force, delta V (change in velocity at the time of
impact), frontal air bag deployment, and residual intrusion (mea-
sured in centimeters) into the passenger compartment at the
occupant’s seat position. The PDOF during the impact was recorded
using a clock reference system, with clockwise rotation beginning
at the front of the vehicle (12 o’clock). The delta V was deter-
mined by WinSmash computer algorithms (Stucki and Fessahaie,
1996).
2.5. Statistical analysis
The CIREN database (1997–2006) was queried for occupants
with brain injuries. As necessary, case summaries and case files
were reviewed to validate data or fill in missing information. Cases
with variables coded as unknown are excluded from analyses based
on that variable. Data were edited in Excel and imported into SAS®
software (Release 9.1) (SAS, 2004) for further editing, recoding,
and analyses. Logistic regression was used to identify predictive
variables for brain injury severity while controlling for potential
confounders (age, gender, delta V, intrusion >15 centimeters (cm),
airbag deployment, delta V, seat position (driver versus passenger),
and safety belt use). A p-value of less than 0.05 was considered sta-
tistically significant. Chi-square or Fisher Exact statistics and odds
ratios (OR) with 95% confidence limits (CL) were used to assess
statistical differences. Differences were considered statistically sig-
nificant based on a 0.05 level. The Hosmer–Lemshow Goodness
of Fit Chi-square was used to test the fit of the logistic regression
models (Hosmer et al., 1991).
3. Results
Out of 1706 occupants involved in frontal impacts in the CIREN
database, there were 708 (41.5%) occupants in distributed frontal
impacts, 613 (35.9%) in offset impacts, and 92 (5.4%) in cor-
ner impacts. There were 418 occupants (13.3%) with AIS 2 or
greater brain injury identified in the CIREN database. Because
some occupants had more than one brain injury, overall there
were 671 brain injuries. The type of brain injuries is summarized
in Table 1. Although 22% of occupants had either a concus-
sion or loss of consciousness, only 2% had diffuse axonal injury
(DAI). Twenty percent had a subarachnoid hemorrhage, almost
14% had a cerebral contusion, and 12% had a basal skull frac-
ture.
Table 1
Brain injuries of occupants in distributed, offset, and corner frontal impacts
Brain injurya
N (%)b
Skull fractures
Base0 51(12.2)
Vault 31(7.4)
Focal injury
Hemorrhage
Subdural 43(10.3)
Subarachnoid 84(20.1)
Intraventricular/intracerebral 8(1.9)
Epidural 1(0.2)
Contusions/lacerations
Cerebrum (frontal, temporal/parietal, occipital) 57(13.7)
Brain stem 13(3.2)
Cerebellum 2(0.4)
Diffuse injury
Concussion/loss of consciousness 91(21.8)
Diffuse axonal injury 7(1.7)
a
Occupants could have more than one brain injury.
b
Percent is based on number of occupants with a specific type of brain injury so
adds to over 100%.
3.1. Occupant characteristics
When separated into different categories based on the vehicle’s
frontal plane damage distribution there were 171 occupants in dis-
tributed impacts, 177 occupants in offset frontal impacts, and 70 in
corner impacts. Table 2 summarizes occupant, vehicle, and crash
characteristics for brain-injured occupants by the three different
impact categories. Occupants in the three categories were similar
on the basis of age, gender, seat position, and safety belt use with
no significant differences.
3.2. Vehicle and crash characteristics
Vehicle and crash characteristics also are shown in Table 2.
The mean delta V was significantly different for occupants
in both distributed and offset impacts compared to those in
corner impacts. Corner impacts were less severe based on a
lower delta V. There was no significant difference in mean
delta V comparing occupants in distributed to offset impacts.
Most of the occupants were protected by deploying frontal
airbags. There was a significant difference in residual intru-
sion >15 cm with more intrusion occurring in offset and corner
impacts.
3.3. Brain injury patterns and severity
Overall, there was no statistically significant difference for
brain injury severity (based on Glasgow Coma Scale <9, or
brain injury AIS > 2, or brain injury AIS > 3) comparing occu-
pants in the different impact categories. Even when stratified
by safety belt use there were no significant differences between
the categories. Although not statistically significant, brain injuries
of occupants who were in corner impacts were more severe
based on their GCS and greater percentage of intracranial
hemorrhage.
Fig. 1 shows the type of brain injury by frontal impact cate-
gory and whether the injured occupant was wearing a safety belt.
Overall, the patterns were similar and there were no significant
differences. Occupants in distributed and offset impacts who were
using a safety belt had injuries that would be considered less seri-
ous (e.g., concussions) and occupants not wearing their safety belts
had more severe injuries (e.g., contusions and lacerations). For cor-
4. Author's personal copy
1572 R. Coimbra et al. / Accident Analysis and Prevention 40 (2008) 1569–1575
Table 2
Occupant and crash characteristics by driver status and impact category
Distributed (N = 171) Offset (N = 177) Corner (N = 70)
Occupant characteristics
Age (years)
Mean, median, range 40, 37, 13–86 40, 36, 13–85 41, 35, 16–94
Male gender 82 (49.4%) 100 (56.5%) 44 (62.9%)
Driver 140 (81.9%) 151 (85.3%) 61 (87.1%)
Safety belt use 95 (56.2%) 98 (55.4%) 45 (65.2%)
Glasgow Coma Scale < 9 29 (23.6%) 32 (25.2%) 13 (28.3%)
Vehicle and crash characteristics
Delta V (km/h)a
Mean, median, range 51,47, 15–137 49, 46, 12–126 30, 25, 12–94
Vehicle year 1998 (1988–2006) 1997 (1987–2006) 1998 (1990–2004)
Vehicle curb weight
Mean, median, range 1411, 316, 831–2903 1445, 344, 320–2518 1467, 369, 900–2422
Frontal air bag deployment 146 (85.4%) 150 (84.7%) 62 (88.6%)
Intrusion at occupants location >15 cma
77 (46.4%) 99 (57.2%) 67 (67.2%)
S.D., Standard deviation.
a
Statistically significant (Chi-square = 9.26, 2, p = 0.01).
ner impacts there was less difference based on safety belt use but
occupants wearing their belts suffered more serious injuries (more
hemorrhage and fewer concussions).
There were no statistically significant differences in the pro-
portional distribution of fractures, focal, and diffuse brain injury,
comparing occupants wearing their safety belt to unbelted occu-
pants within each impact category. Also, no significant differences
in the percentage of fracture, focal, and diffuse brain injury was
found comparing belted occupants in different impact categories
or comparing unbelted occupants in different impact categories.
Occupants in distributed impacts who were wearing their safety
belts had 57.3% diffuse brain injury, 32.9% focal injuries, and 9.8%
fractures. For unbelted occupants in distributed impacts, there were
47.0% diffuse injuries, 40.9% focal, and 12.1% fractures. For belted
and unbelted occupants in offset frontals there was a similar dis-
tribution with 55.7% (belted) and 42.3% (unbelted) with diffuse
injury, 33.6% (belted) and 41.3% (unbelted) focal injury, and 10.7%
(belted) and 16.3% (unbelted) with fractures. Finally, for occupants
in corner impacts, 39.3% (belted) and 44.5% (unbelted) were diffuse
injury, focal injuries (50.8% for belted, 47.4% for unbelted), and pro-
portionally fewer injuries were fractures (9.8% for belted, 9.1% for
Fig. 1. Type of brain injury of occupants by impact category and safety belt use.
unbelted). One interesting finding was that for both distributed and
offset impacts, there was proportionally more diffuse brain injury
(mostly concussions) if the occupant was wearing their safety
belt.
Fig. 2 shows sources of brain injuries for occupants, stratified by
safety belt use, for the three different categories of impacts studied.
For each impact category if the occupant was wearing a safety belt,
they were less likely to have injuries associated with “hard” con-
tact with vehicle interior components (including the windshield,
instrument panel, roof, or roof rails). However, for brain injuries
caused by contact with the air bag (soft contacts) the pattern was
less clear and safety belts did not appear to be protective. Occu-
pants were significantly more likely to have brain injury caused by
contact with the air bag if involved in distributed (OR = 5.04, 95% CL
2.8, 9.03) and offset crashes (OR = 3.50, 95% CL 1.96, 6.25). Within
each impact category, occupants wearing their safety belts had a
greater proportion of diffuse brain injury compared to focal brain
injury and fractures. Although a few occupants sustained severe
DAI, most diffuse brain injury was less serious (e.g., concussions).
Different types of brain injuries also had different sources when
compared overall, although because of small numbers, the statisti-
Fig. 2. Sources of brain injury by occupant safety belt use and impact category (WS,
windshield; IP, instrument panel; other includes exterior objects, other vehicles or
objects, safety belt, not else specified, interior objects).
5. Author's personal copy
R. Coimbra et al. / Accident Analysis and Prevention 40 (2008) 1569–1575 1573
Table 3
Logistic regression models predicting severe brain injury based on Glasgow Coma Scale < 9
Independent variables Adjusted odds ratios (95% confidence limits)
All impact categories Distributed Offset Corner
Safety belt use 0.46 (0.28, 0.76)a
0.61 (0.27, 1.37) 0.25 (0.11, 0.57)a
2.32 (0.32, 16.9)
Frontal intrusion >15 cm 1.34 (0.76, 2.34) 4.35 (1.51, 12.5)a
1.20 (0.51, 2.82) 0.26 (0.04, 1.61)
Impact category 1.33 (0.90, 1.97) N/A N/A N/A
Driver 1.00 (0.72, 1.38) 0.96 (0.59, 1.59) 1.14 (0.67, 1.94) 0.72 (0.26, 2.05)
Age 0.99 (0.97, 1.00) 0.99 (0.98, 1.02) 0.98 (0.96, 1.00) 0.97 (0.93, 1.02)
Deployed airbag 0.83 (0.38, 1.83) 0.54 (0.14, 2.03) 0.95 (0.31, 2.89) N/Ab
Gender 0.73 (0.44, 1.21) 0.59 (0.26, 1.37) 0.96 (0.46, 2.01) 0.20 (0.03, 1.52)
Delta V 1.01 (1.00, 1.03) 1.00 (0.97, 1.02) 1.03 (1.00, 1.05) 1.04 (0.96, 1.13)
a
Statistically significant odds ratio.
b
Not included in model to improve model validity.
cal significance was not tested. For example, almost 9% of occupants
with concussions or loss of consciousness had non-contact sources
and 35% of their brain injury was caused by soft contact with the
airbag. Occupants with contusions have different sources; less than
1% had non-contact sources and 11% had contusions caused by the
airbag. For these occupants, 32% of their contusions were caused
by hard contact with the roof, roof rails, or pillars.
There were also differences comparing belted and unbelted
occupant brain injury sources regardless of impact category.
Restrained occupants had more non-contact brain injury (i.e., no
interior vehicle contacts with the head were identified) compared
to unrestrained occupants who had more contact brain injuries
caused by the occupant’s head hitting the roof, roof rails, wind-
shield, or instrument panel.
3.4. Multivariate analyses
Logistic regression models were used to calculate adjusted odds
ratios for predictive factors for severe brain injury (based on AIS > 2
or GCS < 9). Table 3 demonstrates that when potential confounders
are controlled by inclusion in the model, the impact category
was not predictive of severe brain injury. Wearing a safety belt
was protective against severe brain injury when other potential
confounders (e.g., frontal airbag deployment) were controlled for.
These occupants were less than half as likely to have severe brain
injury (OR = 0.46).
Logistic regression models also were stratified by impact cate-
gory to determine if predictive factors were the same for the three
categories of frontal impact (Table 3). For occupants in distributed
frontal impacts, intrusion at the occupant’s seat position was four
times more likely to result in severe brain injury (OR = 4.35). For
occupants in offset frontal impacts, safety belt use was protec-
tive (OR = 0.25). There were no significant predictive factors for
occupants in corner impacts. When brain injury severity based on
AIS > 2 was used as a measure of severity, similar significant results
for safety belt use being protective in offset impacts were found
as shown in Table 4. Intrusion also was significantly predictive
of severe brain injury overall (OR = 2.01) and for both distributed
(OR = 3.33) and offset impacts (OR = 2.52).
4. Discussion
Over 3/4 of the frontal impacts in CIREN are distributed or
offset impacts. Although corner impacts account for a small pro-
portion (5%) of the frontal impacts, these impacts may present
a challenge for preventing serious brain injury. We used CIREN
data to compare brain-injured occupants in frontal crashes with
a different damage distribution across the frontal plane. Only
occupants sustaining moderate (AIS 2) or greater severity brain
injury were included in the study. Brain injury patterns and over-
all severity were similar for occupants, regardless of the damage
distribution across the frontal vehicle plane when the PDOF was
the same (11, 12, 1 o’clock), suggesting that variation in damage
distribution does not affect occupant brain injury patterns and
severity.
Crash factors, especially the Principal Direction of Force, may
influence occupant injury patterns and severity (Augenstein et al.,
2003; Loo et al., 1996). In general, occupants move in a direc-
tion opposite to the PDOF which is important in determining
which vehicle components may be contacted during impact, pos-
sibly resulting in injury. Occupants in impacts involving greater
vehicle rotation (such as may occur in corner impacts) may
not always move directly opposite and parallel to the PDOF
(Bready et al., 2002). Our study found that occupants with brain
injury from corner frontal impacts may differ from brain-injured
occupants in impacts involving more of the frontal plane (dis-
tributed and offset). However, this finding may be partially related
to the small number of occupants in corner impacts and the
study restriction to the higher end of the brain injury spec-
trum.
Table 4
Logistic regression models predicting severe brain injury based on brain injury AIS > 2
Independent variables Adjusted odds ratios (95% confidence limits)
All impact categories Distributed Offset Corner
Safety belt use 0.59 (0.36, 0.96)a
0.69 (0.31, 1.56)a
0.40 (0.19, 0.35)a
1.06 (0.17, 6.48)
Frontal intrusion >15 cm 2.09 (1.20, 3.64)a
3.33 (1.20, 9.29)a
2.52 (1.10, 5.78)a
0.32 (0.06, 1.73)
Impact category 0.83 (0.57, 1.22) N/A N/A N/A
Driver 1.35 (0.98, 1.86) 1.47 (0.89, 2.44) 1.31 (0.79, 2.17) 1.27 (0.47, 3.47)
Age 1.01 (0.99, 1.02) 1.02 (1.00, 1.05) 1.01 (0.99, 1.03) 0.97 (0.34, 1.01)
Deployed airbag 1.06 (0.49, 2.27) 0.69 (0.20, 2.45) 1.67 (0.54, 5.19) N/Ab
Gender 1.04 (0.64, 1.69) 0.90 (0.40, 2.03) 1.05 (0.52, 2.13) 2.59 (0.39, 16.8)
Delta V 1.00 (0.99, 1.02) 1.00 (0.98, 1.03) 1.00 (0.98, 1.02) 0.99 (0.93, 1.05)
a
Statistically significant odds ratio.
b
Not included in model to improve model validity.
6. Author's personal copy
1574 R. Coimbra et al. / Accident Analysis and Prevention 40 (2008) 1569–1575
4.1. Brain injury severity
We found differences in predictive factors for severe brain injury
(based on both GCS and AIS) using multivariate analysis, depend-
ing upon the damage distribution across the frontal plane. Logistic
regression models showed that wearing a safety belt was pro-
tective against serious brain injury only for occupants in offset
impacts. Again, our finding is restricted to occupants with more
severe brain injuries and does not address whether brain injury
is prevented. Previous research has shown that safety belt use
decreased brain injuries in occupants (Pintar et al., 2000; Siegel
et al., 1993).
Safety belts are accepted as the most important safety system
in motor vehicles that occupants can use to prevent brain injury
and to decrease the severity of brain injury (Smith-Seemiller et al.,
1997). Indeed, safety belts are designed and tested to prevent injury
during frontal impacts. However, safety belt performance may dif-
fer in extreme offset (corner) impacts because there may be more
rotation of the vehicle during this type of crash. Our results sug-
gest further research looking at serious brain injury in occupants
involved in corner impacts may be useful.
Because this study focused on frontal crashes and more current
model years, it is not surprising that about 85–89% of brain-injured
occupants were protected by deploying frontal airbags. Our study
criteria specified occupants had to have sustained brain injury;
therefore, it was not possible to assess the role of airbags in prevent-
ing brain injury in this analysis. Although safety belts are typically
considered the most important safety system, airbags are also an
important component of the vehicle safety system and when used
in conjunction with safety belts, may prevent serious injury. Airbag
deployment did not significantly protect against brain injury sever-
ity in our study as found in another study (McGwin et al., 2003).
Other research has shown that for car-to-car frontal crashes, airbags
decreased the mean GCS (Siegel et al., 2001). Another study assess-
ing air bag effectiveness concluded that brain injury is reduced
when occupants in frontal crashes are using both airbags and safety
belts (Pintar et al., 2000).
Intrusion into the passenger compartment may be important
in causing injury because it increases the potential for contact with
interior vehicle components. Intrusion was found to be significantly
predictive of serious (AIS 2 or greater) brain injury, while control-
ling for other potential confounders, only for distributed impacts
but not offset or corner impacts. When GCS is used as a measure of
severity, intrusion was significantly predictive for distributed and
offset impact, but not for corner impacts. Other research has shown
the importance of intrusion into the passenger compartment for
causing injury to occupants (Loo et al., 1996; Nirula et al., 2003;
Stucki et al., 1998).
4.2. Brain injury sources
Overall, restrained occupants, regardless of whether they were
in distributed, offset, or corner impacts had a greater percentage of
non-contact injury compared to occupants not wearing safety belts.
Biomechanical research indicates that brain injury is more likely
with sudden deceleration of the brain during hard contact (Zhang
et al., 2007). Non-contact injuries may be less severe because there
is a more continuous deceleration (Zhang et al., 2007). This sup-
ports the importance of restraint use to prevent hard contact with
interior vehicle components and decrease the chance for serious
brain injury.
As documented in our study, brain injuries may occur without
any contact. These brain injuries occurred with no identified con-
tact with the vehicle interior or objects outside the vehicle. The
mechanism of this injury differs from brain injuries occurring from
hard contacts and may require different approaches for prevention.
Determination of the biomechanical mechanism of brain injury was
outside the scope of the current study. However, the CIREN database
is being expanded to include this information. Future studies focus-
ing on the mechanism of brain injury may be useful to further
address the role of linear and rotational acceleration in causing
brain injury.
4.3. Implications for crash testing
Our results support that safety belt use prevents serious brain
injury for occupants in offset frontal crashes. Our research sug-
gests that extreme offset (corner) frontal impacts may not have
the same predictive factors for severe brain injury as distributed
and offset impacts. Because current crash tests are based on dis-
tributed and offset frontal impacts, these tests may not be useful in
assessing safety system performance and vehicle crashworthiness
for corner impacts. Other research found that crash testing ratings
and actual crash injury occurrence was not always in agreement
(Farmer, 2005; Nirula et al., 2004).
4.4. Limitations
CIREN is not a population-based study and occupants may not
be representative of all occupants injured in motor vehicle crashes.
This current study is limited to studying brain-injured occupants
and does not assess the frequency of occurrence of brain injury
in occupants in frontal impacts. It only compares occupants with
brain injury (of at least AIS 2 severity) for these different impact
types. Occupants in this specific study are likely to also have seri-
ous injury to other body regions because the CIREN database is
specifically designed to study persons severely injured in motor
vehicle crashes. Because occupants must be seriously injured to
meet CIREN inclusion criteria, it is not possible to assess the benefit
of safety belts and other safety systems (e.g., air bags) for occu-
pants sustaining only minor injury. Inclusion as a CIREN case may
be based on serious (AIS > 2) injury to body regions other than the
brain. It is unclear whether occupants with brain injury may be
less likely to participate in CIREN; this also may bias results if more
severely brain-injured occupants are less likely be included than
those with less severe brain injury.
We did not explore the association between seat locations (i.e.,
driver versus right front passenger) because there were only 13
passengers with brain injury included in the study. However, the
vehicle interior differs on the driver side compared to the passen-
ger side and this may impact the nature, severity, and sources of
brain injury. Therefore, it may be useful to study the impact of
seat location as the number of passengers increases in the CIREN
database.
Possible bias is introduced when CIREN cases with missing data
are excluded from analyses based on specific variables. Another
limitation is that the WinSmash algorithm used to determine delta
V may not be as accurate for corner impacts. Furthermore, almost
half of the corner impacts had missing delta V and were not
included in analyses based on this variable. This further restricts
conclusions based on the limited number of corner impacts avail-
able for study. As more CIREN data become available, it would
be useful to further study occupants in extreme offset (corner)
impacts.
4.5. Summary
This study found no significant difference in brain injury sever-
ity comparing occupants in distributed, offset, and corner frontal
impacts. This study also illustrates how “real world” crashes can
