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Within 100ms of a rea-end motor vehicle collision the car seat of the front vehicle pushes into the occupant’s torso. The torso or chest is accelerated forward with the seat, while the head remains stationary due to inertia. At about 150ms after the impact, the torso is fully accelerated by the car seat.
At the same time the lower neck is pulled forward by rapidly moving torso, a resulting opposite sharp extension force on the head making rotate backward, whether a head restraint is there or not. At 300ms after the impact is initiated, acceleration of the head and torso forward ahead of the car seat occurs, resulting in flexion of the spine.
When extension of the cervical spine occurs during whiplash: an abnormal acceleration/deceleration phenomenon, it is about an abnormally high axis of rotation and vertebra rotates without translation (backward transverse motion). The extension of backward acceleration of the head and neck during whiplash results in abnormal distraction separation of the anterior elements of the neck as well as abnormal patterns of compression posteriorly on the cervical spine disc and/or facets.
Anterior elements of the cervical spine or neck at risk are: esophagus, anterior longitudinal ligament, anterior cervical muscles, odontoid process and the intervertebral disc. Posterior elements at risk are: posterior longitudinal ligament, posterior cervical muscles, facets surfaces or capsules, and the intervertebral disc.
Posterior structures at risk are the spinous processes and zygopophyseal (facet) joints. When extension occurs around an elevated axis of rotation, the facet joints do not glide across their supporting surfaces. Instead the inferior articular processes are driven into the superior articular facets. This can result in compression fractures of the articular cartilage or subchondral bone and tears in the intra-articular meniscoids.
Under sudden and high distraction and compression tension these structures on either side of the cervical spine (front and back) fail in varying degrees, resulting in tears of the muscles, ligaments, discs of via avulsion of the disc from the vertebral body. If the force of the rear-end impact is great enough the odontoid process, which bears the weight of the head in extension and may fail by fracture.
When flexion of the cervical spine, the whole of the neck structures recoil forward generating compression forces to the anterior elements of the neck and tensile forces to the posterior elements. Because the vertebral body itself is designed to sustain compression loads, the vertebral bodies are unlikely to fail under the compression loads incurred during whiplash. However, under impaction in extreme flexion, the upper corners of the articular pillars may be susceptible to fracture. Gay RE, Levine R. Biomechanics of Whiplash. In: Malanga GA, Nadler SF eds. Whiplash. Philadephia: Hanley and Belfus, 2002: 38. (the mechanism of whiplash is much more complicated that the simple Hyperextension injury proposed by early investigators.)
As a sequel to a car accident, almost 70% of injured patients report immediate occurrence of symptoms of cervical spine pain, as well as shoulder and lumbar spine pain, as well as dizziness are common, paraesthesia and muscle weakness of upper extremities, as well as radicular deficiency are all unfavorable symptoms. Headache due to traumatic brain injury during as whiplash are the latest type of injury currently being documented in association with motor vehicle accidents.
The following symptoms may also be associated with motor vehicle accidents: brain trauma, anxiety, depression, sleeplessness, suboccipital neuralgia, neck pain [associated with muscle injury, cervical and or lumbar disc injuries or ligament injuries, shoulder pain, sciatica, vertigo and cognitive disturbances.