The mechanism of whiplash injuries remains less than completely understood, partly because obvious tissue damage detectable by radiography or MRI may not accompany the injury, according to researchers at Daping Hospital, Third Military Medical University, in Chongqing, China. To help explain whiplash injury mechanisms and gain a better understanding of cervical facet pain, the investigators undertook an extensive series of biomechanics studies that involved injury epidemiology, neck kinematics, facet capsule ligament mechanics, injury mechanisms, and injury criteria. The evidence they gathered includes the following:
•Whiplash injuries generally are thought to be a soft tissue injury of the neck; symptoms include neck pain and stiffness, shoulder weakness, dizziness, headache, and memory loss.
•Kinematic studies found potential for neck injury in 3 distinct stages: (1) flexural deformation of the neck is observed, along with a loss of cervical lordosis; (2) the cervical spine assumes an S-shaped curve as the lower vertebrae begin to extend and gradually cause the upper vertebrae to extend; and (3) the entire neck is extended because of the extension moments at both ends.
•With examination of strains across the facet joint as a mechanism of whiplash injury, experimental findings suggested a capsular strain threshold or a vertebral distraction threshold for whiplash-related injury, potentially producing neck pain.
•Injuries to the facet capsule region of the neck are a major source of postcrash pain. Three of the potential whiplash-associated injuries are related to strains within the facet capsule connected with events that occur early in the impact.
•Several injury criteria may correlate with the duration of symptoms in reconstructions of actual crashes.
These results form the biomechanical basis for a hypothesis that the facet joint capsule is a source of neck pain, the researchers noted. They added that the pain may result from large strains in the joint capsule causing pain receptors to fire.
