Turned-head position is often associated with more severe whiplash symptoms. This has prompted a number of biomechanical studies using human cadaveric necks to test whether head position produces measurable changes in whiplash injury. These tests have been limited to certain flexion/extension moments and did not examine the effects of posterior shear and axial compression loading, according to researchers Sigmund et al. That leaves remaining questions of how different axial forces impact ligament loading. Sigmund et al. set out to investigate how a head-turned position interacts with multiaxial loading to alter injury to the facet capsule.
Using vertebral bodies donated form female cadavers, researchers created a simulation of a rear-end collision with turned-head position. They applied axial pretorques, axial compression preloads, and quasi-static shear load to the vertebral bodies to simulate the kinematics of whiplash injury. Three dimensional markers were placed on the vertebral bodies to help researchers measures strains on the ligaments during loading. The effects of the varying forces were calculated using repeated-measures analyses of variance. They discovered that:
- Axial rotation doubled maximum peak strain. In other words, a turned-head position doubled the strain placed on facet capsules. Peak capsule strain with pretorque was 17% ±6%.
- Axial pretorque influenced peak strain more than axial compression or posterior shear loading.
- The effect of having a head-turned position was similar to effects of partial ligament failure found in previous studies.
- Head rotations to the right produced strain on the right facet capsule. Peak strains were higher when pretorque force was applied towards the capsule rather than away (reaching 34% ±18% percent).
These findings confirm that turned-head posture increases strain placed on the facet capsules. This provides further explanation for the more severe symptoms experienced by whiplash patients whose heads were turned during the collision.
Siegmund G, Davis M, Quinn K, et al. Head-turned postures increase the risk of cervical facet capsule injury during whiplash. Spine 2007; 33(5): 1643-1649.