Injury mechanisms of the cervical intervertebral disc during simulated whiplash.

STUDY
DESIGN: A kinematic analysis of cervical intervertebral disc deformation during simulated whiplash using the whole cervical spine with muscle force replication model was performed.
OBJECTIVES: To quantify anulus fibrosus fiber strain, disc shear strain, and axial disc deformation in the cervical spine during simulated whiplash. SUMMARY OF BACKGROUND DATA: Clinical studies have documented acute intervertebral disc injury and accelerated disc degeneration in whiplash patients, although there has been no biomechanical investigation of the disc injury mechanisms.
METHODS: A bench-top sled was used to simulate whiplash at 3.5, 5, 6.5, and 8 g using six specimens. The 30 degrees and 150 degrees fiber strains, disc shear strains, and axial disc deformations during whiplash were compared with the sagittal physiologic levels.
RESULTS: Increases over sagittal physiologic levels (P < 0.05) were first observed during the 3.5 g simulation. Peak fiber strain was greatest in the posterior 150 degrees fibers (running posterosuperiorly), reaching a maximum of 51.4% at C5-C6 during the 8 g simulation. Peak disc shear strain was also greatest at the posterior region of C5-C6, reaching a maximum of 1.0 radian due to posterior translation during the 8 g simulation. Axial deformation at the anterior disc region exceeded physiologic levels at 3.5 g and above, while axial deformation at the posterior region exceeded physiologic limits only at C5-C6 at 6.5 g and 8 g.
CONCLUSIONS: The cervical intervertebral discs may be at risk for injury during whiplash because of excessive 150 degrees fiber strain, disc shear strain, and anterior axial deformation.