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STUDY DESIGN: A bench-top trauma
sled was used to apply four intensities of whiplash trauma to human cadaveric
cervical spine specimens and to measure resulting intervertebral rotations
using high-speed cinematography.
OBJECTIVES: To determine the
cervical spine levels most prone to injury from whiplash trauma and to hypothesize
a mechanism for such injury.
SUMMARY OF BACKGROUND DATA:
Whiplash injuries traditionally have been ascribed to hyperextension of
the head, but other mechanisms such as hypertranslation also have been suggested.
METHODS: Six occiput to T1 (or
C7) fresh cadaveric human spines were studied. Physiologic flexion and extension
motions were recorded with an Optotrak motion analysis system by loading
up to 1.0 Nm. Specimens then were secured in a trauma sled, and a surrogate
head was attached. Flags fixed to the head and individual vertebrae were
monitored with high-speed cinematography (500 frames/sec). Data were collected
for 12 traumas in four classes defined by the maximum sled acceleration.
The trauma classes were 2.5 g, 4.5 g, 6.5 g, and 8.5 g. Significance was
defined at P < 0.01.
RESULTS: In the whiplash traumas,
the peak intervertebral rotations of C6-C7 and C7-T1 significantly exceeded
the maximum physiologic extension for all trauma classes studied. The maximum
extension of these lower levels occurred significantly before full neck
extension. In fact, the upper cervical levels were consistently in flexion
at the time of maximum lower level extension.
CONCLUSIONS: In whiplash, the
neck forms an S-shaped curvature, with lower level hyperextension and upper
level flexion. This was identified as the injury stage for the lower cervical
levels. A subsequent C-shaped curvature with extension of the entire cervical
spine produced less lower level extension.
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