Cadaveric Lumbar Spine Responses to Flexion with and without Anterior Shear Displacement · 2016-10-04 · WITH AND WITHOUT ANTERIOR SHEAR DISPLACEMENT Aditya Belwadi, King H. Yang

RESPONSE OF THE CADAVERIC LUMBAR SPINE TO FLEXION

WITH AND WITHOUT ANTERIOR SHEAR DISPLACEMENT

Aditya Belwadi, King H. Yang

Wayne State University, Detroit, MI

ABSTRACT

A custom-designed multi-axis spine machine was used to test cadaveric three-vertebra two-disc

motion segments until failure, 13 in combined flexion-anterior shear and six in flexion only loading.

The average shear force was 1.990.64 kN with a shear displacement of 15.615.03 mm; flexion

moment of 174.2758.21 N-m and flexion angle of 14.102.3 degrees at failure for the 13 specimens

loaded in combined anterior shear-flexion. For the six specimens loaded in flexion, failure moment

was 140.4318.4 N-m at a flexion angle of 12.72.29 degrees. This difference was not statistically

significant. Also, there were no significant differences in the failure flexion moment and compressive

force between those in combined and standalone condition. The average compressive forces at

failure were lower than the values needed to fracture a vertebra as reported in the literature review.

Keywords: SPINE, FORCE, BIOMECHANICS, AUTOMOBILES, ACCIDENTS.

KNEE AIRBAGS, DEPLOYABLE KNEE BOLSTERS, AND SEAT MOUNTED ANTI-

submarining airbags have been introduced to control the lower torso kinematics and reduce the

likelihood of posterior cruciate ligament (PCL) injury. Though these devices function against the

“Balanced Restraint” concept of occupant kinematics, they engage the lower torso early in a crash and

may prevent submarining. During a frontal crash, the knee airbag or deployable knee bolster works

in concert with the main airbag to reduce the risk of injury. While the knee airbag or deployable

knee bolster may greatly reduce the lower torso movement, it may cause a combined anterior shear

with flexion load to the lumbar spine in adult occupants not seen prior to the introduction of knee

airbag and deployable knee bolster. Only limited data has been reported in this loading mode.

There were several reported studies on the lumbar spine response and fracture tolerance under

different test conditions. A brief literature survey of these data on anterior shear, flexion,

compression, and combined loading studies is summarized in Table 1. In this table, a functional

spinal unit (FSU) consists of two adjacent vertebrae and the intervertebral disc. It is important to

note that in the literature FSU and motion segment (MS) were used interchangeably as two-vertebra

one-disc specimens. In this table and the rest of the current study, we used MS to indicate three-

vertebra two-disc specimen in contrast to two-segment FSU.

Table 1: Summary of literature review on published cadaveric lumbar spine tests

Loading condition Specimen Failure force/moment

or Non-failure stiffness Observed injury Reference

ANTERIOR SHEAR

Anterior shear by max. load

133 N 19 FSU 0.190 - 0.665 kN/mm None Lin et al. (1978)

Anterior shear by max. load 86N and 145 N

42 FSU 0.143 kN/mm (86 N); 0.146 kN/mm (145 N)

None Berkson et al. (1979)

Anterior shear by max. load

1.029 kN 14 FSU 0.097 kN/mm None Miller et al. (1986)

IRCOBI Conference – Bern (Switzerland) – September 2008 397

Loading condition Specimen Failure force/moment

or Non-failure stiffness Observed injury Reference

Anterior shear at 160 N 9 FSU 0.078±0.081 kN/mm None McGlashen et al.

(1987)

Combined compression & anterior shear at max 160N

13 FSU 0.119 kN/mm None Janevic et al. (1991)

Anterior shear at 0.5

and 50 mm/s 16 FSU

0.155±0.077 kN/mm for quasi-

static condition;

1.292±0.106 kN for unconstrained at 0.5 mm/s;

2.776±0.39 kN for constrained

at 0.5 mm/s. 1.767±0.46 kN for

unconstrained at 50 mm/s

2.894±0.144 kN for constrained at 50 mm/s

Facet capsules torn.

Ligament rupture.

Intervertebral disc failure.

Begeman et al.

(1994)

Anterior shear by max.

displacement 38.1 mm 10 T12-L5 0.038±0.010 kN/mm None

Demetropoulos

et al. (1998)

FLEXION

Flexion by max. load 95 N-m

14 FSU 5.5 N-m/deg None Miller et al. (1986)

Flexion-Compression 9 T3-L5 1 T12-L5

176.56±63.5 N-m 245 N-m (T12-L5)

Wedge and compression

fractures seen at levels

varying from T7-L1

Yoganandan et al. (1988b)

Flexion 18 FSU 72.8±18.1 N-m Ragged tear in the outer posterior anulus

Adams et al. (1994)

Flexion by 11.2 degrees at

loading/unloading at 1, 1/3,

0.1 Hz.

25 FSU

58.5±23.6 N-m (1 Hz);

56.5±23.0 N-m (1/3 Hz);

52.3±21.7 N-m (0.1 Hz)

None Adams et al. (1996)

Flexion 10 T12-L5 7±3 kN/mm None Demetropoulos et al. (1998)

COMPRESSION

Compression Vertebral body 2.63±0.97 kN Wedge compression fx Hansson et al.

(1980)

Compression 9 vertebrae 4.97±2.41 kN Wedge compression fx Myklebust et al.

(1983)

Compression 14 T12-Sacrum 2.1±1.4 kN Wedge compression fx Myklebust et al. (1983)

Compression 11 L1-L5 4.59±2.06 kN N/A Yoganandan et al.

(1988a)

Compression 63 vertebrae

(T12-L5)

4.28±0.34 kN Vertebral body fx Yoganandan et al.

(1988b)

Compression 27 FSU (T10-L5)

4.5±1.7 kN Not Reported Brinckman et al. (1989)

Compression (with pre-flexion)

16 FSU: Group

A (male age 22-

46)

10.2±1.71 kN End-plate fx most often

Hutton and Adams (1982) 17 FSU: Group

B (Male age

46+ or Female)

5.59±1.64 kN End-plate fx, or anterior vertebral fx

Compression 22 L2, 22 L3,

and 17 L4

5.56±2.7 kN Vertebral body fx Myers et al. (1994)

Compression Isolated Facet Joint

6.0 kN Capsule rupture Yang and King (1984)

Compression - max.

displacement of 6.35mm

10 T12-L5 0.52±0.28 kN/mm None Demetropoulos et

al. (1998)

ANTERIOR SHEAR-FLEXION

Anterior shear-flexion quasi-static loading

16 FSU †156±11 N-m/ 0.62±0.053 kN Overt rupture Osvalder et al. (1990)

Anterior shear-flexion

quasi-static loading 10 FSU †121±10 N-m/ 0.49±0.038 kN Permanent deformation

Neumann et al.

(1992)

Anterior shear-flexion

dynamic loading by a pendulum impact

10 FSU (5 g) †140±11 N-m/ 0.43±0.036 kN Posterior elements

disruption

Osvalder et al.

(1993) 7 FSU (12 g) †185±15 N-m/ 0.6±0.045 kN

* FSU (Functional Spinal Units): two adjacent vertebrae and the intervertebral disc,

† denotes reaction moment/shear force at failure. fx denotes “Fracture”

398 IRCOBI Conference – Bern (Switzerland) – September 2008

Almost all of the experimental studies reviewed were conducted under a single loading mode,

even though it was known that spinal degrees-of-freedom are coupled to one another (e.g. Panjabi et

al. 1992) and hence very difficult to achieve single mode loading. Xu et al. (2000) reported lumbar

spine loads, among other transducer data, for a three-point belt restrained Test-Device for Human

Occupant Restraint (THOR). Their results indicated that the lumbar spine was mainly loaded in a

combined anterior shear, flexion, and compression mode during frontal crashes with a peak anterior

shear force of 1.2 kN, flexion moment of 140 N-m, and compression of 2.4 kN. Similarly, the

lumbar spine of a Hybrid III also exhibited combined loading of anterior shear, flexion, and

compression due to frontal impact. To the best of our knowledge, the works of Osvalder et al. (1990

and 1993) and Neumann et al. (1992) were the only failure studies using combined anterior shear-

flexion loading conditions. Osvalder et al. (1990) tested lumbar FSU’s statically in combined flexion

and shear. The specimen was first potted in a lower steel cup attached to a fixed force transducer. A

weighted pulley system was used to control the motion of a vertical adjustable lever arm attached to

the upper steel cup. At failure, the average maximum horizontal displacement was 9.4±2.0 mm and

the average maximum flexion angle was 19.6±1.9o with the failure moment and force measured at the

load cell denoted in Table 1. Using the same experimental setup, Neumann et al. (1992) reported a

slightly smaller average horizontal displacement of 7.5±1.4 mm and a smaller average maximum

flexion angle of 15.8±0.9o at failure. In their dynamic test setup (Osvalder et al. 1993), a combined

flexion-shear load was transferred to the FSU through a padded pendulum. The tests were conducted

with two different load pulses: a moderate pulse with peak acceleration of 5 g’s, rise time of 30 ms

and a total duration of 150 ms and a severe pulse with peak acceleration of 12 g’s, a rise time of 15 ms

and a total duration of 250 ms. The load pulse variation was achieved by changing the pendulum

padding material and adjusting the drop height of the pendulum to vary the impact velocity. The

authors did not mention if multiple impacts were needed before achieving the desired load pulse.

Resulting maximum horizontal displacements were 6.1±1.0 mm under the moderate pulse and 8.1±1.1

mm under the severe pulse. The maximum flexion angles were 14.2±1.6o under the moderate pulse

and 19.1±1.3 under the severe pulse. The kinematics of flexion and shear loading in these studies

were not controlled. More critically, tension (instead of compression) is more likely to be generated

in a pendulum impact. This is opposite from what has been observed in frontal crashes where

compression is more dominant than tension (Xu et al. 2000).

Most studies in the literature used two-vertebra one-disc FSU’s. Yang and King (1984) argued

that realistic lumbar spine motion in all possible physiological degrees-of-freedom could not be

achieved by testing FSU’s that were constrained at the top and bottom vertebrae. In these test setups,

only the intervertebral disc between the adjacent vertebrae would be tested. They recommended the

use of three-segment motion segment (MS), which consisted of three vertebrae and two intervertebral

discs in between, to allow natural kinematics of the middle vertebra during loading.

Because the spine is subjected to combined anterior shear, flexion, and compression in frontal

impact as reported by Xu et al. (2000) and there is no injury tolerances reported for three-segment

motion segment subjected combined anterior shear, flexion, and compressive loading, the main

purposes of this study were to:

1) Investigate the injury mechanisms and tolerance of cadaveric lumbar MS’s (three-vertebra two-

disc specimens) during combined anterior-shear with flexion loading until failure.

2) Compare failure flexion moment between MS’s tested under combined anterior shear-flexion

loading and MS’s tested under flexion.

METHODS

Spine Testing Machine: A custom designed multi-axis spine testing machine, schematic diagram

shown in Figure 1, was used to perform all the tests. Two parallel linear vertical actuators, driven by


a pair of DC geared motors, were used to control the angular displacement (flexion or extension) and

vertical motion (tension or compression) of the loading platen. A third DC motor drove a threaded

rod, controlling the horizontal displacement (anterior or posterior shear) of the platen.

A 16-bit micro-controller programmed in MP Lab (Microchip Technology Inc, Arizona) with a

Windows HyperTerminal 5.1 (Microsoft Corporation, CA) interface was used to control the platen

motion. Rotary potentiometers attached to each motor provided data for feedback control and

determination of the displacement and angle of the platen. A closed-loop control program written in

Lab View 6.0 (National Instruments, Austin, Texas), was used to control motions of the loading

platen individually (for single mode loading) or simultaneously (for combined loading) based on

displacement feedback from three potentiometers. All tests were conducted at fixed actuator speeds

of +8 mm/s for the anterior vertical actuator, -8 mm/s for the posterior vertical actuator, and 4 mm/s

for the horizontal axis until failure. Because the distance between the two actuators was fixed at 254

mm, the machine is capable of a rotational deformation rate of 3.5°/s (0.061 rad/s), if the two vertical

actuators were moving in opposite directions; vertical deformation rate of 8 mm/s, if the two vertical

actuators were moving in the same direction and a horizontal displacement rate of 4 mm/s for anterior

and posterior shear.

Data Collection and Processing: The test device was instrumented with a 10 kN, six-axis load cell

(WSU-NMN-01, Denton, Rochester Hills, MI) to measure forces (Fx, Fy, Fz) and moments (Mx, My,

Mz), along with three potentiometers (SKU Wirewound, Clarostat International) to measure

displacements (Dx, Dzanterior, Dzposterior) of the loading platen. The angular displacement

(flexion/extension angle) was calculated from the two actuator displacements Dzanterior, Dzposterior, and

the fixed distance between them. All electronic data were collected at 1,000 Hz using a TDAS Pro

system (DTS Inc., Seal Beach, CA) and then exported to Microsoft Excel to calculate the maximum

load. Reaction forces and moments due to these applied displacements and rotations were measured

at the load cell and used for data analyses. Data was processed using Diadem 9.1 (National

Instruments, TX) and the statistical analysis was performed using SPSS 14 (SPSS Inc, IL).

Graphical plots were created using Origin Pro 7.5 (OriginLab Corporation, MA).

Figure 1: Schematic diagram of the spine testing machine with the specimen orientation


Specimens: Cadaveric lumbar spine specimens (T12-Sacrum) were obtained from bodies donated

through the Willed Body donation program at University of Michigan (UM), International Institute

for the Advancement of Medicine (IIAM), and the National Disease Resource Interchange (NDRI).

Pre-test X-rays were taken to exclude specimens with any pre-existing abnormal spinal conditions.

A dual energy X-ray absorptiometry (DEXA, QDR-1000 Plus, Hologic, Bedford, MA) machine was

used to determine the lumbar bone mineral density (BMD) for each specimen. Table 2 shows the

age, stature, weight, and BMD (in g/cm2) where MS’s were obtained. The measured average BMD

(0.920.1 g/cm2) was slightly higher than the average male population at 55 to 64 years (0.82 g/cm

2)

and 65 to 74 years (0.8 g/cm2) of age as reported by American Academy of Orthopaedic Surgeons

(1999). After the anthropometric measurements were completed, the specimens were wrapped in

saline soaked cloths, sealed and stored in plastic bags at -20 °C. Several basic anthropometries of the

specimens tested are listed in Appendix A.

Table 2: Relevant information on the cadavers used

No

.

Specimen No. Age

(yrs.)

Gender

(M/F)

Stature

(cms.)

Weight

(kgs.)

BMD (g/cm2)

1 UM31720 48 M 172 90.9 0.852

2 UM32015 75 M 173 75.9 1.010

3 UM32016 83 M 173 72.7 1.121

4 IIAM56601466 64 M 178 80.0 0.864

5 IIAM53101265 62 M 177 77.7 0.770

6 NDRI54002 69 M 185 77.3 1.051

7 NDRI 57167 72 M 177 88 0.881

8 NDRI 58780 60 M 171 123 0.912

9 NDRI 57139 88 M 168 83 0.923

10 NDRI 57308 33 M 188 127 0.901

11 UM32326 68 M 183 91 0.855

12 UM32380 78 F 173 73 0.919

Average 6615 - 176.56.1 88.318.3 0.920.1

Boundary Conditions and Initial Position of Motion Segments: The specimens were thawed at

room temperature 24 hours prior to testing. All musculature was removed while the ligaments were

kept intact. Each spine was dissected into two halves through the mid-line of the L3 vertebral body

to form two MS’s: Motion segment one (M1) consisted of the S1, L5, and L4 and motion segment

two (M2) consisted of L2, L1, and T12. A custom-made fixture was used for potting the inferior

vertebra (S1 for M1 and L2 for M2) into an aluminum pot using DynaCast (Kindt-Collins Co.,

Cleveland, OH). In an earlier study performed in-house, DynaCast was found to be better than

Bondo (Bondo Corporation, Atlanta, GA) and several other commonly used potting materials based

on its compressive strength, minimum temperature at set, setting time and workability (Belwadi, A.

2006). After DynaCast solidified, the pot along with the specimen imbedded in it was then inverted

and connected to the six-axis load cell located at the top of the spine testing machine. The MS was

allowed to set at its natural position under gravitational force. The loading platen was then translated

and rotated until the center of gravity of the lower vertebra (L4 for M1 and T12 for M2) was lined up

with the center of the lower pot and the superior edge of the endplate of the superior vertebra was

parallel to the top of lower pot before DynaCast was injected. This set of procedures was performed

to ensure that there was no preload as per Foster et al. (1977) and allowed the L5 or L1 vertebra with


intervertebral discs superior and inferior of it free to assume its natural load path. Four bone screws

were inserted into the top and bottom vertebrae of each MS to improve fixation inside the potting

material.

Motion Segment Tests: Each of the 19 motion segments was loaded to failure in combined

anterior shear-flexion or flexion. The load cell, which was rigidly attached to the testing frame, acted

to constrain the inferior end of the test specimen while linear and rotational displacements were

applied to flex and anteriorly shear the specimen at the superior end. All forces and flexion moment

were directly measured from the load cell without any coordinate transformation. Failure loads were

defined at the instant of the first significant drop in the time history curves of the bending moment

My, the shear force Fx, or the compression force Fz. After the failure test, the specimens were

examined by a board certified orthopedic surgeon for identification and classification of the fractures.

RESULTS

The shear forces, bending moments, and compressive forces, as well as flexion angles and shear

displacements at failure are summarized in Table 3. Note that the shear forces at failure (average

0.120.01 kN) for the flexion tests were relative small in magnitude. On the other hand, the

compressive force at failure (average 2.150.17 kN) was much higher than the shear force in flexion

tests, most probably due to the high compressive stiffness (see Table 1). Statistically, the differences

in these failure parameters obtained from L4-L5-S1 MS’s and T12-L1-L2 MS’s were not significant.

Consequently, all data were analyzed without consideration of which motion segment (M1 or M2) the

test result came from. Spine NDRI57139 (Test 10) had the lowest failure flexion moment (83.1 N-

m) for all specimens loaded in combined anterior shear-flexion while the same spine (Test 16) also

had the lowest failure flexion moment (117.2 N-m) among all specimens loaded in flexion. Not

surprising, the age of NDRI57139 was the highest among all spines tested. Also, cadaver

NDRI54002 had the highest failure tolerance values of 3.2 kN in shear and 226.1 N-m in flexion

moment for L4-L5-S1 and 3.1 kN for shear and 322.6 N-m in flexion for T12-L1-L2. This 69 year-

old 185 cm tall male had the largest vertebral body size among all specimens tested. Classifications

of these injuries are provided in Appendix B with representative images and fracture locations in

Appendix C. Combined anterior shear with flexion loading resulted in primarily anterior wedge

fractures (eight specimens) compared to five specimens subjected to anterior compression fractures

(Table B-1, Appendix B). On the other hand, flexion only loading resulted in primarily anterior

compression fractures (five out of six specimens). Such results indicated that the load path may be

specimen-dependent and the complex nature of combined loading.

The average failure moment for Tests 1 to 13 (loaded in combined anterior shear-flexion) was

174.27 N-m compared to 140.43 N-m for Tests 14 to 19 (loaded in flexion). This difference was not

significant (p = 1.374, α = 0.05). The average failure flexion angle for Tests 1 to 13 (loaded in

combined anterior shear-flexion) was 14.1 degrees compared to 12.7 degrees for Tests 14 to 19

(loaded in flexion only). This difference was not significant either (p=1.234, α = 0.05). In six

lumbar spines, one motion segment was tested in combined anterior shear-flexion (Tests 8 to 13)

while the other motion segment was tested in flexion (Tests 14 to 19). Using pair-t tests, it was

found that the differences in failure flexion moment and angles between these two loading modes

were not significant.


Table 3: The anterior shear force, shear displacement, flexion moment, flexion angle, and

compressive force at failure measured for all 19 MS’s

Test

No. Cad. No. MS

Measurements at Failure

Anterior

Shear

Force

Fx

(kN)

Anterior

Shear

Displacement

Dx

(mm)

Flexion

Moment

My

(N-m)

Flexion

Angle

(Deg)

Compressive

Force

Fz

(kN)

Combined anterior shear and flexion

1 UM31720 T12-L1-L2 1.4 9.7 161.6 18.7 2.1

2 UM32015 L4-L5-S1 1.6 10.3 185.8 12.7 1.8

3 IIAM56601466 T12-L1-L2 1.6 12.8 157.5 12.4 1.95

4 IIAM53101265 L4-L5-S1 1.8 11.6 196.8 11.8 1.77

5 IIAM53101265 T12-L1-L2 1.9 14.2 209.9 12.3 2.3

6 NDRI54002 L4-L5-S1 3.2 13.1 226.1 13.1 2.5

7 NDRI54002 T12-L1-L2 3.1 13.7 322.6 13.6 2.1

8 NDRI57167 L4-L5-S1 2.3 22.1 158.2 16.2 1.63

9 NDRI58780 L4-L5-S1 2.1 23.2 155.6 17.6 1.87

10 NDRI57139 L4-L5-S1 0.9 23.8 83.1 13.1 2.32

11 NDRI57308 T12-L1-L2 1.9 11.3 148.7 12.8 1.9

12 UM32326 T12-L1-L2 1.7 17.7 123.2 12.5 1.8

13 UM32380 T12-L1-L2 2.4 19.4 136.4 16.5 1.66

Average 1.990.64 15.615.03 174.2758.21 14.102.3 1.980.27

Flexion

14 NDRI57167 T12-L1-L2 0.14 0.0 121.7 11.3 2.33

15 NDRI58780 T12-L1-L2 0.12 0.0 155.1 10.1 2.21

16 NDRI57139 T12-L1-L2 0.125 0.0 117.2 10.6 2.1

17 NDRI57308 L4-L5-S1 0.11 0.0 139.7 14.1 1.95

18 UM32326 L4-L5-S1 0.13 0.0 164.3 15.4 1.94

19 UM32380 L4-L5-S1 0.10 0.0 144.6 14.7 1.98

Average 0.120.01 0.0 140.4318.4 12.72.29 2.150.17

DISCUSSION

During our combined loading of anterior shear and flexion, the average reactive compressive

force at the instant of failure was 1.98±0.27 kN. Similarly, the average compressive force due to

flexion loading was 2.150.17 kN. These values were significantly lower than those reported for

compression only studies, such as the 5.59±1.64 kN reported by Hutton and Adams (1982),

4.972.41 kN reported by Myklebust et al. (1983), 4.28±0.34 kN reported by Yoganandan et al.

(1988b), and 4.51.7 kN reported by Brinckmann et al. (1989). Thus, it can be assumed that while

compression may play a role, it may not be the main failure mechanism when spinal motion segments

are subjected to combined anterior shear-flexion loading.

The average flexion moment (174.2758.21 N-m) at failure for the combined anterior shear-

flexion loading was slightly higher than the 140.4318.4 N-m average failure moment obtained from

our flexion tests. However, the difference was not statistically significant and further investigations

of the six spines, in which one MS was loaded in combined anterior shear-flexion and the other MS


tested in flexion, showed no statistical difference between these two modes of testing. Thus,

simultaneously adding anterior shear to flexion at the rates employed in this study did not increase the

failure flexion moment. Our average failure flexion moment was in the same range as 176.56±63.5

N-m reported by Yoganandan et al. (1988b) who tested nine T3-L5 specimens in combined flexion

with compression to failure. Additionally, our failure flexion moment was similar to those reported

by Osvalder et al. (1990, 1993) and Neumann et al. (1992). Note that in these studies, a weight-

pulley or a pendulum system was used to load the two vertebrae FSU’s in combined shear-flexion.

As a result, reaction force was in the tensile direction. No other data were found related to failure

moment for flexion loading. However, it was difficult to believe that flexion moment was the only

injury mechanism because the flexion moment at failure varied widely with a range from 83.1 to

322.6 N-m.

The average failure shear force (1.990.64 kN) in this combined anterior shear-flexion study fell

within a similar range, but was higher than that reported by Begeman et al. (1994) for pure shear tests

in the unconstrained condition (1.292±0.106 kN) and lower than that for the constrained condition

(2.776±0.39 kN). However, it was difficult to compare directly the results of the current study to

those by Begeman et al. (1994), in which 2-segment FSU’s specimens were used compared to 3-

segment MS’s used in the current study. No other data were found in regard to fracture force due to

shear load only.

Most researchers have tested two-segment motion segments and this kind of setup usually

constrained the upper and lower vertebrae. As a result, the intervertebral disc sandwiched in between

cannot assume its physiological motions. The usage of three-vertebra two-disc motion segment in

this study allowed the natural movement of the vertebral body and the disc without being constrained,

allowing it to mimic real world kinematics.

Because the sample size used in this experimental study was relatively small, results should be

interpreted with care. There was no preload applied on any of the experimental specimens either.

The current study is also limited by the fact that the actuator speeds used did not reflect a physical

condition seen in typical car crash environments. More research is needed to improve these

shortcomings.

CONCLUSIONS

The characteristics of the lumbar motion segment under combined anterior shear-flexion

loading conditions have been investigated using a multi-actuator test system. Several conclusions

can be drawn from this study:

1. The average flexion moment at failure was 174.2758.21 N-m for the 13 three-vertebra two-

disc specimens loaded in combined anterior shear-flexion compared to 140.4318.4 N-m for

the six specimens loaded in flexion. The difference was not statistically significant.

2. Compressive force generated as a result of combined anterior shear-flexion loading was

1.980.27 kN while it averaged at 2.150.17 kN for flexion testing. The difference was not

statistically significant. The average compressive forces at failure were lower than the

values needed to fracture a vertebra in compression only tests as reported in the literature

review.

ACKNOWLEDGEMENT

The authors are extremely grateful to Dr. Jay Zhao, Mr. Gopal Narwani and Mr. Tadayuki Ato

from Takata Corporation, MI for their continuous support and funding for this project. The authors

also wish to thank Dr. Jacques Noel, M.D. (William Beaumont Hospital, MI) for his expertise in

inspection and classification of spinal fractures. The authors are also grateful to Mr. Joe Mazur

(BGM Corporation, MI) for his support in building the spine testing machine. We are also thankful

to Dr. Sriram Balasubramanian and Mr. Vipin Koppikar from the Departments of Biomedical and

Mechanical Engineering, respectively, at Wayne State University for their support in performing the

tests.


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Appendix A: Characteristic dimensions of the spines tested

Figure A-1: The width (a) and depth (b) of the superior edge of the vertebral body and height (c) of

the vertebral body measured to document the size of the spine specimen. Figure on the right shows the

characteristic height of a motion segment used in failure tests.

Table A-1: Dimensions of the width (a), depth (b), and height (c), in mm, of the vertebral

bodies tested

Cadaver

No.

T12 L1 L2 L3 L4 L5 S1

a b c a b c a b c a b c a b c a b c a b c

UM31720 34 31 15 33 32 13 36 33 18 35 31 19 40 38 19 42 43 22 45 44 27

UM32015 44 38 24 48 41 23 55 43 23 54 44 18 56 43 24 55 47 23 57 44 25

UM32016 39 34 25 41 37 22 42 44 25 44 43 24 49 51 19 47 48 20 49 51 21

IIAM56601466 39 38 22 40 39 21 44 48 20 47 46 18 49 47 19 49 48 21 50 45 23

IIAM53101265 32 29 12 32 28 13 31 33 12 35 32 16 36 31 18 41 38 23 44 38 21

NDRI54002 42 40 23 40 37 21 43 38 19 45 44 25 47 48 25 49 51 27 51 48 25

NDRI57167 37 34 23 36 37 25 39 43 27 42 47 25 45 52 21 47 45 19 51 52 21

NDRI58780 37 32 24 40 38 21 42 40 27 46 41 22 51 48 18 50 46 21 50 48 22

NDRI57139 36 31 22 39 28 23 39 31 24 41 46 21 47 48 17 41 43 23 46 48 22

NDRI57308 37 35 22 40 38 18 41 38 23 42 41 22 47 47 24 44 47 21 50 48 22

UM32326 35 32 21 37 38 19 44 41 22 45 40 25 46 48 17 46 47 22 48 43 23

UM32380 37 32 23 43 35 24 32 39 19 43 41 23 47 48 18 48 50 24 51 49 23


Table A-2: Height of motion segments tested

Test No. Cadaver No. Motion Segment Height (h, mm)

1 UM31720 T12-L1-L2 38

2 UM32015 L4-L5-S1 31

3 IIAM56601466 T12-L1-L2 33

4 IIAM53101265 L4-L5-S1 34

5 IIAM53101265 T12-L1-L2 39

6 NDRI54002 L4-L5-S1 36

7 NDRI54002 T12-L1-L2 37

8 NDRI57167 L4-L5-S1 35

9 NDRI58780 L4-L5-S1 38

10 NDRI57139 L4-L5-S1 31

11 NDRI57308 T12-L1-L2 36

12 UM32326 T12-L1-L2 40

13 UM32380 T12-L1-L2 35

14 NDRI57167 T12-L1-L2 37

15 NDRI58780 T12-L1-L2 35

16 NDRI57139 T12-L1-L2 34

17 NDRI57308 L4-L5-S1 37

18 UM32326 L4-L5-S1 35

19 UM32380 L4-L5-S1 38

Average 35.74±2.47

Appendix B: Classification of Fractures of the Cadaveric Lumbar Spine Motion Segments

Table B-1: Fracture location and classification

Test

No. Cadaver No.

Motion

Segment Fracture Location and Classification

Combined anterior shear and flexion

1 UM31720 T12-L1-L2 Anterior Wedge Fracture

2 UM32015 L4-L5-S1 Anterior Wedge Fracture

3 IIAM56601466 T12-L1-L2 Anterior Wedge Fracture

4 IIAM53101265 L4-L5-S1 Anterior Compression Fracture with intact posterior elements

5 IIAM53101265 T12-L1-L2 Anterior Wedge Fracture

6 NDRI54002 L4-L5-S1 Anterior Compression Fracture with intact posterior elements

7 NDRI54002 T12-L1-L2 Anterior Compression Fracture with disrupt posterior elements

8 NDRI57167 L4-L5-S1 Anterior Wedge Fracture



11 NDRI57308 T12-L1-L2 Anterior Compression Fracture with intact posterior elements

12 UM32326 T12-L1-L2 Anterior Wedge Fracture

13 UM32380 T12-L1-L2 Anterior Compression Fracture with intact posterior elements

Flexion

14 NDRI57167 T12-L1-L2 Anterior Compression Fracture with disrupt posterior elements

15 NDRI58780 T12-L1-L2 Anterior Compression Fracture with intact posterior elements

16 NDRI57139 T12-L1-L2 Anterior Wedge Fracture

17 NDRI57308 L4-L5-S1 Anterior Compression Fracture with intact posterior elements

18 UM32326 L4-L5-S1 Anterior Compression Fracture

19 UM32380 L4-L5-S1 Anterior Compression Fracture with intact posterior elements


Appendix C: Representative Images along with fracture location

Figure C-1: Specimen NDRI54002 (L4-L5-S1) - Anterior compression fracture with intact

posterior elements: X-ray

Figure C-2: Specimen UM31720 (T12-L1-L2) - Anterior wedge fracture: X-ray

ANTERIOR POSTERIOR

ANTERIOR POSTERIOR


Figure C-3: Specimen NDRI57167 (T12-L1-L2) - Anterior Compression Fracture with disrupt

posterior elements: X-ray

ANTERIOR POSTERIOR


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