Parker, et al. v. NGM Insurance Company, et al

Filing 94

ORDER AND REASONS - IT IS ORDERED that Plaintiffs 64 motion in limine to exclude Dr. Charles Ted Bain is GRANTED, and Dr. Bain is hereby excluded from testifying as an expert in this case. IT IS FURTHER ORDERED that Defendants 46 motion in limi ne to exclude Dr. David Barczyk on timeliness grounds is DENIED AS MOOT. IT IS FURTHER ORDERED that Defendants 65 motion in limine to exclude Dr. Barczyk under Federal Rule of Evidence 702 and Daubert is DENIED AS MOOT. Signed by Judge Susie Morgan. (Attachments: # 1 Attachment 1, # 2 Attachment 2) (bwn)

INCIDENCE OF THORACIC AND LUMBAR SPINE
INJURIES FOR RESTRAINED OCCUPANTS IN FRONTAL
COLLISIONS
Darrin Richards, M.S., P.Eng.1
Michael Carhart, Ph.D. 1,2
Christine Raasch, Ph.D. 1
Janine Pierce, M.S. 1
Duane Steffey, Ph.D. 3
Andrew Ostarello, M.S. 3
1

Exponent Failure Analysis Associates
Phoenix, Arizona
2
Harrington Department of Bioengineering
Arizona State University
Tempe, Arizona
3
Exponent Failure Analysis Associates
Menlo Park, California
ABSTRACT
The increased utilization of three-point restraint systems has
greatly reduced the incidence of spinal injuries in motor vehicle
accidents. Nevertheless, several studies which rely upon the
National Automotive Sampling System (NASS) have documented
lower thoracic and upper lumbar fractures in restrained occupants
involved in frontal collisions of moderate severities. Although it has
been postulated that the injury mechanism may be related to the
occupant being out-of-position or sitting in an unusual posture,
conclusions with regard to the precise mechanism of injury are
difficult due to the lack of information contained in the NASS
database. In addition, previous studies have not reported statistical
significance of these injuries. In this study, we combined statistical
analysis of frontal collisions in the NASS database with the analysis
of data acquired from sled and crash tests, which utilized
anthropomorphic test devices (ATDs), in order to evaluate the
incidence and potential injury mechanisms underlying thoracic and
lumbar spine fractures in moderate frontal impacts. In the first
portion of the study, we performed a statistical analysis of the NASS
database to estimate the incidence rate of spinal fracture. This was
complemented with measurements and analysis of lumbar spine load
data derived from frontal sled and crash tests. Analysis of the NASS
database demonstrated that thoracolumbar spinal injuries are rare

50th ANNUAL PROCEEDINGS
ASSOCIATION FOR THE ADVANCEMENT OF AUTOMOTIVE MEDICINE
October 16-18, 2006

when an occupant is restrained by a lap and shoulder belt, and are
often accompanied by abdominal injury. The spinal loads measured
during frontal impacts with restrained and nominally positioned
ATDs were found to be well below injury thresholds. Our results
also suggest that the potential for isolated fracture is increased when
the geometry of occupant-to-restraint interaction is compromised, as
occurs when an occupant submarines the lap belt.
INTRODUCTION
It is widely accepted that three-point restraint systems greatly
reduce the number and severity of injuries in frontal collisions.
However, case studies derived from entries in the NASS database
and other crash injury databases (Huelke et al., 1995) have identified
a number of cases where lap and shoulder belt restrained occupants
sustained thoracic and lumbar spine fracture or dislocation in frontal
collisions of moderate severity. Similar findings have been reported
by Ball et al. (2000), who conducted a retrospective chart review at a
regional spinal cord injury center and identified a number of cases
where three-point restrained occupants sustained thoracolumbar
fracture in frontal impacts. While the latter study did not involve an
assessment of collision severity, the majority of the injuries involved
a lower thoracic or upper lumbar burst fracture. Additionally,
Miniaci and McLaren (1989) provided a collection of 4 case reports,
wherein lap-shoulder belted occupants sustained an anterolateral
wedge compression fracture of a thoracolumbar vertebra with lateral
compression occurring on the side opposite the restrained shoulder.
What is unclear from the case reports described above is the
prevalence of thoracolumbar injury in three-point restrained
occupants in frontal impacts, and the collision severities at which
such injuries occur.
In this study, we combined statistical analysis of the NASS
database with the analysis of data acquired from sled and crash tests
in order to evaluate the incidence of thoracolumbar spine injuries
amongst three-point restrained occupants in frontal impacts.
Previous authors (Miniaci and McLaren, 1989, Huelke et al. 1995;
Ball et al. 2000) reported incidents of thoracolumbar injuries
occurring in cases where occupants were restrained only by threepoint belts. Considering the prevalence of airbags in the modern
vehicle fleet, we also conducted a NASS analysis of occupants
restrained by three point belts supplemented by airbags.
In the first portion of the study, frontal collision cases were
identified from the 1995 to 2004 NASS database where occupants
sustained thoracic and/or lumbar AIS 2+ and 3+ injuries while

126

restrained: (a) by a three-point belt (no airbag), or (b) by a threepoint belt and deployed airbag. The incidence rate of these injuries
was quantified, and accompanying abdominal injuries were
identified. In the second portion of the study, experimental data
from automobile crash and sled testing performed at Exponent was
analyzed in order to quantify the loads present in the lower spine
during frontal automobile collisions. The Hybrid III 50th-percentilemale ATD, which is widely accepted for use in frontal crash tests,
was utilized in this testing.
METHODS
NASS DATABASE – NASS was developed in 1979 by the
National Center for Statistics and Analysis (NCSA), part of the
National Highway Traffic Safety Administration (NHTSA), as an
investigative tool to aid in the reduction of motor vehicle crashes,
injuries, and deaths on U.S. highways.
NASS is composed of the Crashworthiness Data System
(CDS) and the General Estimates System (GES), both of which
acquire data from police accident reports in randomly selected
counties and cities comprising a representative segment of the
United States. The CDS data specifically focuses on passenger
vehicle crashes and the investigation of injury mechanisms, and
contains detailed data on thousands of automobile crashes of varying
severity. CDS researchers input data on approximately 5000
passenger vehicle crashes per year, and over 140,000 crashes have
been included into the CDS system since its inception. CDS
researchers obtain scene and accident data, inspect vehicles,
document vehicle damage, estimate vehicle Delta-Vs, interview
vehicle occupants, review occupants’ medical records, and classify
the nature and severity of occupants’ injuries. All of these variables
are coded and entered into the NASS CDS database (NASS, 2005).
Since it is not practical for researchers to investigate all
automobile accidents, NASS uses an unequal probability selection
procedure to obtain a sample of accidents to be included in the
database. A simple random sample of all accidents would not
provide effective statistics since it would result in a large percentage
of low speed crashes with few injuries, since these types of crashes
make up a large portion of all crashes. Instead, a weighting factor is
assigned to crashes, which increase or decrease the probability of
selection for inclusion in the NASS CDS database. All accidents
reported in the NASS CDS database have an associated weighting
factor, which can be used for statistical analysis. By using this

127

sampling methodology the NASS CDS database is able to provide
effective data across a wide range of accident severities and types.
The NASS CDS database uses the Abbreviated Injury Scale
(AIS) coding system [AAAM, 1998] to classify all occupant injuries,
and can record up to 10 injury entries for each occupant. Per AIS,
all injuries are classified into nine body regions: head, face, neck,
thorax, abdomen, spine, upper extremity, lower extremity, and
unspecified. The injuries are further classified by severity, ranging
in scale from 1 (minor) to 6 (currently untreatable).
The NASS CDS database from 1995-2004 was initially
queried for all frontal collisions that were not preceded or followed
by an additional harmful event (i.e., a vehicle-to-vehicle collision,
vehicle-to-object collision, rollover, etc.). Frontal collisions were
defined as a collision where the principal direction of force (PDOF)
ranged between –30º and +30º. This frontal collision subset was
then surveyed for front seat occupants, restrained by a lap and
shoulder belt, who sustained thoracic and/or lumbar spine injuries.
This query searched specifically for all AIS codes referencing injury
to the thoracic or lumbar spine with a score of 2 or higher, excluding
skin lacerations and lumbar nerve root injuries. The same frontal
collision subset was also surveyed for front seat occupants restrained
by three-point belts and deployed airbags.
The risk of injury to the occupant was assessed using the AIS
injury classifications, and was evaluated in terms of an occupant
sustaining at least moderate (AIS 2+) or serious (AIS 3+) injury.
CRASH TEST DATA – A total of eight vehicle-to-vehicle
and sled tests, producing rearward occupant compartment Delta-Vs
up to 22.9 kph, were performed. For all tests, a Hybrid III 50thpercentile-male ATD was used. The ATD had a stature of 1.7m, a
weight of 78 kg, and was equipped with a seated pelvis. The sled
and vehicle-to-vehicle crash tests involved ATDs restrained by lap
and shoulder belts only (no airbags were deployed.) For all tests, the
ATD instrumentation included a 3-channel lumbar load cell capable
of measuring forces in the x and z direction as well as the moment
about the y-axis. Lap and shoulder belt loads were also measured.
The tests were documented using high-speed and real-time video,
and still photographs.
Vehicle-To-Vehicle Tests – Six crash tests were performed
in two configurations using similar 1983 Nissan Pulsar NXs
(Figure 1, Table 1). Four of the six crash tests were performed with
a full contact front-to-rear impact configuration, with the
longitudinal centerlines of the bullet and target vehicles aligned.
This configuration was run at bullet vehicle speeds of 9, 16, 24, and
33 kph. An angled contact front-to-rear impact configuration was

128

utilized for the two remaining crash tests, with the target vehicle
rotated 10 degrees counterclockwise from the aligned position. The
angled configuration tests were conducted at bullet vehicle speeds of
6 and 16 kph. For all tests, the target vehicle was at rest prior to
impact.
Each vehicle was instrumented with two triaxial
accelerometers mounted on the rocker panel at the left and right Bpillars. The Hybrid III 50th-percentile male ATD was positioned in
the driver’s seat of the vehicle and secured with the available threepoint restraint.
In each test the available three-point restraint system was
properly utilized. The lap belt was routed over the ATD’s rigid
pelvis area, and the shoulder belt was routed across the chest and
over the left shoulder.
Table 1 Summary of vehicle-to-vehicle crash tests.
Bullet Vehicle

Impact Speed (kph) Delta-V (kph)
8.8
6.4
16.3
10.4
23.7
14.4
32.8
18.7
5.8
5.6
16.3
9.9

Impact Configuration
Full-Contact
Full-Contact
Full-Contact
Full-Contact
Angled-Contact
Angled-Contact

Figure 1 Photograph illustrating pre-impact positioning of ATD in vehicle-tovehicle tests.

129

Sled Tests – Two additional sled tests were performed using
a Seattle Safety sled with a wire-bending decelerator (Table 2). Sled
deceleration was recorded for all tests. A late-model production seat
was mounted to the sled top plate, as shown in Figure 2. A
Hybrid III 50th-percentile male ATD was positioned in the seat and
secured with a three-point restraint that was mounted in accordance
with restraint geometry measured in an exemplar vehicle.
Table 2 Summary of sled tests.
Delta-V (kph)

Peak Sled Accel. (g)

13.6
22.9

8.2
14.1

Figure 2 Photograph demonstrating the occupant, seat, and restraint
configurations used in sled tests.

130

RESULTS

Cumulative Percent of Frontal Impacts

NASS DATABASE – The data from the 1995-2004 NASS
CDS database consisted of 9262 front seat occupants involved in
frontal collisions who were restrained by three-point belts (no
airbags) and 4887 occupants restrained with three-points belts and
deployed airbags Analysis of the distribution of impact severities
(Figure 3) indicates that 80% of these impacts occurred at Delta-Vs
below 37 kph. Tables 3 and 4 report statistics for occupants
restrained by: (a) three-point belts only, and (b) three-point belts and
airbags, respectively (Unrestrained and lap-belt only restraint
conditions, as well as unknown impact severities were not included).
Of the three-point restrained occupants, 82 sustained AIS
2+ thoracolumbar injury, and 13 sustained AIS 3+. Using the
weighted data, the percentage of restrained occupants sustaining AIS
2+ and AIS 3+ injuries was computed across all severities (Figures 4
and 5). Since most modern vehicles are equipped with airbags, data
for three-point restrained with airbag deployment (Table 4) was also
plotted on Figures 4 and 5. As shown, injury rates for moderate
(AIS 2+) thoracolumbar injury is less than 0.6% for severities up to
50 kph, but increases to 10.3% and 11.3%, respectively for threepoint restrained and three-point restrained with airbag deployment at
Delta-Vs greater than 60 kph. AIS 3+ thoracic and lumbar spine
injury rates generally increased with increasing collision severity,
but were less than 1% for both three-point restrained occupants and
three-point restrained occupants with airbag deployment at all
Delta-V levels.
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
0

20

40

60

80

100

120

Delta V (kph)

Figure 3 Cumulative percent of weighted front seat occupants involved in frontal
collisions, sorted by Delta-V.

131

Table 3 Occupants restrained by three-point belts (no airbag) with AIS 2+ and
AIS 3+ thoracic and/or lumbar spine injuries.

DeltaV (kph)

Number
of 3-point
belted
Occupants
in Frontal
Collisions

Weighted
Number
of 3-point
belted
Occupants
in Frontal
Collisions

Three-Point Belted Occupants with Lumbar and/or Thoracic Injuries

Number
Occupants
with AIS 2+

Weighted
Number
Occupants
with AIS 2+

Weighted
Percent of
Occupants
with AIS 2+

Number
Occupants
with AIS 3+

Weighted
Number
Occupants
with AIS 3+

Weighted
Percent of
Occupants
with AIS 3+

0-20

3778

2,865,921

6

3485

0.12%

1

0

0%

20-30

2986

1,476,383

20

1748

0.12%

4

323

0.02%

30-40

1382

379,602

12

932

0.25%

2

106

0.03%

40-50

617

101,675

11

549

0.54%

2

101

0.10%

50-60

273

40,857

11

813

1.99%

2

59

0.15%

>60

226

14,469

22

1488

10.28%

2

89

0.62%

Table 4 Occupants restrained by three-point belts and airbags with AIS 2+ and
AIS 3+ thoracic and/or lumbar spine injuries.

DeltaV (kph)

Number
of 3-point
belted
Occupants
in Frontal
Collisions

Weighted
Number
of 3-point
belted
Occupants
in Frontal
Collisions

Three-Point Belted Occupants with Lumbar and/or Thoracic Injuries

Number
Occupants
with AIS 2+

Weighted
Number
Occupants
with AIS 2+

Weighted
Percent of
Occupants
with AIS 2+

Number
Occupants
with AIS 3+

Weighted
Number
Occupants
with AIS 3+

Weighted
Percent of
Occupants
with AIS 3+

0-20

1754

1130105

3

2974

0.26%

1

0

0.00%

20-30

1695

663607

10

927

0.14%

1

242

0.04%

30-40

803

184768

6

331

0.18%

0

0

0.00%

40-50

358

46281

3

85

0.18%

1

37

0.08%

50-60

156

12441

6

663

5.33%

1

9

0.08%

>60

121

8718

11

985

11.30%

0

0

0.00%

132

AIS 2+

Percentage (%)

20%

3-Point Belted
3-Point Belted and Airbag

15%
10%
5%
0%
0-20

20-30

30-40

40-50

50-60

>60

Delta V (kph)

Figure 4 Percentage of three-point belted occupants with moderate or greater (AIS
2+) thoracic and/or lumbar spine injuries as a function of collision severity,
separated by the presence or absence of a deployed airbag.

AIS 3+
3-Point Belted
3-Point Belted and Airbag

Percentage (%)

5%
4%
3%
2%
1%
0%
0-20

20-30

30-40

40-50

50-60

>60

Delta V (kph)

Figure 5 Percentage of three-point belted occupants with serious or greater (AIS
3+) thoracic and/or lumbar spine injuries as a function of collision severity,
separated by the presence or absence of a deployed airbag.

133

Additional analysis was performed to evaluate the percentage
of occupants restrained by the three-point belts (no airbag) who
sustained moderated or greater (AIS 2+) thoracolumbar injury and
also sustained moderate or greater abdominal injury (Figure 6).
Overall, 35% of occupants with moderate or greater thoracolumbar
injury also sustained moderate or greater abdominal injuries. For
Delta-Vs in the range of 20-30 kph and over 60 kph, this percentage
was over 50%.

AIS 2+ Abdominal Injuries

Percentage (%)

60%
50%
40%
30%
20%
10%
0%
0-20

20-30

30-40

40-50

50-60

>60

Delta V (kph)

Figure 6 Percentage of three-point belted (no airbag) occupants who also
sustained AIS 2+ abdominal injuries (of those with AIS 2+ thoracic and lumbar
spinal injuries).

CRASH TEST DATA – The data plotted in Figures 7 and 8
is a compilation of the lumbar load cell data from the sled and crash
tests. As shown in these summary figures, the peak lumbar
compression loads exhibited a maximum value of 882 N at 13.6 kph,
and then leveled off with further increases in impact severity.
Lumbar flexion moment, on the other hand, exhibited a linear
increase (R2 = 0.8) with increasing collision severity.

134

4000
3500

Lumbar Compression (N)

3000
2500
2000
1500
1000
500
0
0

5

10

15

20

25

Delta V (kph)

Figure 7 Maximum lumbar compression loads measured during frontal vehicle-tovehicle and sled impacts.
300

Lumbar Flexion Moment (Nm)

250

200

150

100

R2 = 0.80

50

0
0

5

10

15

20

25

Delta V (kph)

Figure 8 Maximum lumbar flexion moment measured during frontal vehicle-tovehicle and sled impacts.

135

DISCUSSION
Previous studies (Ball et al., 2000; Huelke et al., 1995) have
identified incidents of three-point restrained occupants sustaining
thoracolumbar spine injuries in frontal collisions. In this study, a
survey of the 1995-2004 NASS database also revealed incidents of
thoracolumbar injuries in three-point belted occupants involved in
frontal collisions; however, statistical analysis showed the rate of
this occurrence to be quite low. At Delta-Vs of less than 50 kph,
moderate or greater (AIS 2+) thoracolumbar spinal injuries occurred
less than 0.6% of the time for both three-point restrained occupants
and three-point restrained occupants with airbag deployment. Only
at higher Delta-Vs was the incidence rate significant. At Delta-Vs of
greater than 60 kph, the incidence rate increased to 10.3% for threepoint restrained occupants and 11.3% for three-point restrained
occupants with airbag deployment. Serious or greater (AIS 3+)
injuries were exceedingly rare in collisions with Delta-Vs of less
than 60 kph, as illustrated in Figure 5. For three-point restrained
occupants, the rate of AIS 3+ injuries was less than 1% at all
Delta-V levels, regardless of whether or not the three-point restraint
was supplemented by airbag deployment.
Schmidt et al. (1975) and Kallieris et al. (1991) performed
numerous frontal impact tests at 30 to 50 kph and 30 to 60 kph,
respectively, which provide some insight into the increased
incidence of moderate thoracic injuries (AIS 2) at Delta-Vs above
50 kph and particularly above 60 kph. In these tests, restrained
cadaver occupants sustained injuries to the cervical and thoracic
spine from the C1 to T4 levels; lower thoracic and lumbar injuries
were not evaluated. Kallieris et al. (1991) reported the highest
incidence of injury was at T1 and T2, with 46% of the vertebral
column injuries classified as moderate or greater severity (AIS 2+).
Unfortunately, the authors did not break down results by severity of
impact.
Begeman et al. (1973) conducted a series of moderate
severity sled tests using cadavers wherein strains were measured in
the thoracolumbar spine, and vertical compressive forces acting
along the spine were documented. In all, 40 runs were performed on
3 cadavers, with each cadaver sustaining wedging or compression
fractures of the thoracolumbar spine. These investigators postulated
that in frontal collisions, the curvature of the spine may result in high
compressive loads in the thoracic and lumbar region. However,
these tests were run with a non-automotive seat and double shoulder
belts, which were horizontal as they passed over the shoulder. The
non-conventional seats and belt configuration may have caused a

136

wedging of the cadaver spine, resulting in higher than usual loads
during these tests.
In contrast, our study used standard automobile seats and
replicated true automobile restraint geometries. Experimental data
from this series of automobile crash and sled tests at Delta-Vs
ranging from 5.6 to 22.9 kph was analyzed. The maximum
compressive load observed across the range of severities
investigated was 882 N. For comparison, Willen et al. (1984)
evaluated the strength of the L1 vertebrae under dynamic loading
conditions, and identified a load level for fracture of 6000 to
10,000 N. These tolerance values are consistent with lumbar
compressive strengths as collated from the literature by Jager and
Luttman (1992), who indicated a mean compressive tolerance at age
40 of 6700 N for males and 4700 N females. The loads observed in
our test series are also well below the 3400 N compression limit
which is referenced by NIOSH in setting a Recommended Weight
Limit for safe occupational lifting (Waters et al., 1993).
Furthermore, biomechanical modeling studies, such as Chaffin and
Page (1994), have demonstrated that loads well above 3400 N can be
tolerated during lifting activities without injury.
As outlined previously, several authors have presented case
studies where occupants have sustained injuries concentrated at the
lower thoracic and upper lumbar spine. Although the Hybrid III
ATD provides a single point load measurement at approximately the
L-4 level, we anticipate this fairly captures the nature and magnitude
of loading in the lumbar spine and provides a bound for the
magnitude of loads in the lower thoracic spine. While this crash test
series is limited to just two different productions of seats and lapshoulder restraint geometries, it demonstrates that significant axial
compression of the lower spine is not expected to occur in low-tomoderate severity frontal impacts for a properly restrained occupant,
a position which is decisively confirmed by field data. Figure 7
indicates that the compressive lumbar loads do not continue their
upward trend at the higher severities evaluated. It is postulated that
increased forward torso motion and phase differences between the
pelvic and torso restraint, associated with higher severities results in
less compression in the lumbar spine.
Maximum flexion moments in the lumbar spine increased
approximately linearly with increasing impact severity in this test
series (Figure 8). However, even at the highest impact severities
evaluated, the peak lumbar flexion moments were less than those
that can be generated in the lower back during static and dynamic bimanual lifting (approximately 300 Nm, Jager and Luttmann, 1992).

137

Nevertheless, our study of the NASS database did reveal a
number of cases where thoracolumbar injuries were sustained at
moderate Delta-Vs. Analysis of the NASS data revealed a
correlation between abdominal injuries and thoracolumbar injuries
for three-point belted occupants. Figure 6 illustrates that as many as
51% of occupants with thoracolumbar injuries sustained moderate or
greater (AIS 2+) abdominal injuries. For collision severities of
20 kph or greater, overall approximately 35% of the occupants
sustained AIS 2+ abdominal injuries. These results are similar to
Ball et al. (2000), who did a retrospective case study of 37 patients
with thoracolumbar injuries involved in frontal impacts. He found
that 27% of patients required a laparotomy, indicating abdominal
injury, but he did not correlate his results to collision severity.
The relationship between abdominal injuries and
thoracolumbar injuries is important because it may provide an
indication that the lap belt loaded the abdomen rather than
interacting with the bony pelvic region. Injury potential is increased
when the restraint geometry is compromised, which suggests that
these thoracolumbar injuries may be related to belt misuse. It is
interesting that only a small percentage of abdominal injuries were
seen below 20 kph. Belt loads at this collision severity may not have
been high enough to cause AIS 2+ abdomen injuries even if worn
improperly.
CONCLUSIONS
Analysis of the NASS database indicates that AIS 2+
thoracolumbar injuries are rare during minor and moderate frontal
collision severities when an occupant is restrained by a lap and
shoulder belt with or without airbag deployment. The analysis
shows that AIS 3+ injuries are exceedingly rare, demonstrating that
these injuries represent an anomaly rather than the norm. NASS
data further indicates that a large percentage of three-point restrained
occupants sustained AIS 2+ abdominal injuries along with
thoracolumbar spinal injuries, indicating that the occupant-torestraint interaction was likely compromised. Frontal impact testing
performed with properly restrained and nominally positioned ATDs
revealed lumbar loads well below injury thresholds, and on par with
those that can be generated during common lifting activities. The
findings of this study indicate that thoracic and lumbar fractures are
rare during minor and moderate frontal collisions when occupants
are properly restrained with a three-point belt (no airbag) or with a
three-point belt supplemented with an airbag.

138

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