| ABSTRACT | A
study was conducted to find out whether in a rear impact motor vehicle accident,
velocity changes in the impact vehicle of between 10 and 15 km/h can cause so
called "whiplash injuries";. An assessment of the actual injury mechanism
of such whiplash injuries and comparison of vehicle rear end collisions with amusement
park bumper car collisions was also carried out. The study was based on experimental
biochemical, kinematic, and clinical analysis with volunteers. In Europe between
DM 10 and 20 billion each year is paid out by insurance companies alone for whiplash
injuries, although various studies show that the biodynamic stresses arising in
the case of slight to moderate vehicle damage may not be high enough to cause
such injuries. Most of these experimental studies with cadavers, dummies, and
some with volunteers were performed with velocity changes below 10 km/h. About
65% of the insurance claims, however, take place in cases with velocity changes
of up to 15 km/h. Fourteen made volunteers (aged 28-47 years; average 33.2 years)
and five female volunteers (aged 26-37 years; average 32.8 years) participated
in 17 vehicle rear end collisions and 3 bumper car collisions. All cars were fitted
with normal European bumper systems. Before, 1 day after and 4-5 weeks after each
vehicle crash test and in two of the three bumper car crash tests a clinical examination,
a computerized motion analysis, and an MRI examination with Gd DTPA of the cervical
spine of the test persons were performed. During each crash test, in which the
test persons were completely screened off visually and acoustically, the muscle
tension of various neck muscles was recorded by surface electromyography (EMG).
The kinematic responses of the test persons and the forces occurring were measured
by accelerometers. The kinematic analyses were performed with movement markers
and a screening frequency of 700 Hz. To record the acceleration effects of the
target vehicle and the bullet vehicle, vehicle accident data recorders were installed
in both. The contact phase of the vehicle structures and the kinematics of the
test persons were also recorded using high speed cameras. The results showed that
the range of velocity change (vehicle collisions) was 8.7 - 14.2 km/h (average
11.4 km/h) and the range of mean acceleration of the target vehicle was 2.1-3.6
g (average 2.7 g). The range of velocity change (bumper car collisions) was 8.3
- 10.6 km/h (average 9.9 km/h) and the range of mean acceleration of the target
bumper car was 1.8 - 2.6 g (average 2.2 g). No injury signs were found at the
physical examinations, computerized motion analyses, or at the MRI examinations.
Only one of the male volunteers suffered a reduction of rotation of the cervical
spine to the left of 10 degrees for 10 weeks. The kinematic analysis very clearly
showed that the whiplash mechanism consists of translation/extension (high energy)
of the cervical spine with consecutive flexion (low energy) of the cervical spine:
hyperextension of the cervical spine during the vehicle crashes was not observed.
All the tests showed that the EMG signal of the neck muscles starts before the
head movement takes place. The stresses recorded in the vehicle collisions were
in the same range as those recorded in the bumper car crashes. From the extent
of the damage to the vehicles after a collision it is possible to determine the
level of the velocity change. The study concluded that, the "limit of harmlessness"
for stresses arising from rear end impacts with regard to the velocity changes
lies between 10 and 15 km/h. For everyday practice, photographs of the damage
to cars involved in a rear end impact are essential to determine this velocity
change. The stress occurring in vehicle rear end collisions can be compared to
the stress in bumper car collisions. |