This interesting article has an "Etiology" section that neatly summarizes whiplash biomechanics:
"Neck pain among car occupants may follow an impact from any direction, though rear-end impacts cause it almost twice as often as frontal collisions. An 8-mile/h rear-end collision with a 2-g (2 times the gravitational force of earth) acceleration of the vehicle may result in a 5-g acceleration of the head, and experiments using volunteers have shown that a 10-mile/h rear-end collision generates a 9-g acceleration of the neck and 23 g of the frontal cortex. Sprains of the neck occur in 10-60% of car occupants after an accident. Those wearing seatbelts have more neck sprains than those not wearing them. Head restraints reduce the incidence of whiplash injuries in rear-end impacts by 10% in cars with adjustable head restraints and by 17% in cars with fixed restraints."
The authors go on to evaluate the different imaging techniques, with particular focus on the strengths and weaknesses of each:
- Plain radiographs: "Plain radiography is the first imaging technique that should be used in patients who sustained a whiplash injury. This is not only to evaluate possible traumatic lesions, but also to have a reference image of the cervical spine at the time of the trauma. This way secondary lesions, such as degenerative disease, can be objectively assessed when they are recognized some time after the trauma." The authors also warn that, "Plain radiographs have a low sensitivity for identifying traumatic cervical spine lesions. In a large series of patients2 with cervical injuries, the combination of cross-table lateral (CTL), AP and OM-views missed 61% of all fractures, 36% of subluxations and dislocations and falsely identified 23% of the patients, half of whom had unstable cervical injuries, as having normal cervical spines. Therefore, trauma victims with plain films positive for cervical injury, or negative for cervical injury but with a high clinical suspicion of injury, should undergo CT or MRI for a more definitive evaluation of the cervical spine."
- CT scans: "CT is indicated in all acute trauma patients when there is no optimal visualization of the cervical spine on plain film, when unexplained focal neck pain or a neurologic deficit exists with a negative plain film, when there is unexplained pre-vertebral soft tissue swelling or whenever the plain film is abnormal...CT is also able to show soft-tissue abnormalities such as disk herniation, soft tissue hematoma and sometimes ligamentous rupture. CT however has definite limitations in evaluating cervical trauma. Increases in intervertebral distances, abnormal angulations, subluxations and dislocations are less well visualized in comparison with plain radiography or tomography. In one study3 CT only detected 54% of dislocations and subluxations in trauma victims."
- "MRI findings in whiplash injuries are very diverse and are different depending on the time interval between imaging and the accident.
- "In the chronic phase, more than 1 year after the original trauma, findings are mostly non-specific and include degenerative disk disease, disk protrusion and herniations. Only a minority of patients show bony or ligamentous lesions."
- "In the subacute phase, within 4 months of the whiplash trauma, more characteristic findings such as separations of the disk from the vertebral end plate and ligamentous lesions are reported. The anterior longitudinal ligament (ALL) is more often injured than the posterior longitudinal ligament (PLL) or interspinous ligament..."
- "In the acute phase, within 15 days after the original trauma, no specific findings are made."
- "Indications for MRI after whiplash injury include myelopathy, radiculopathy, progressive neurologic deficit, spinal cord injury and an unexpected level of signs above the level of radiographically seen injury...MRI should probably also be used in all patients with whiplash injury who have persistent complaints or significant findings at any other investigation, since these patients have a worse prognosis and may exhibit significant MRI findings."
- Van Goetham JWM, Biltjes IGGM, van den Hauwe L, et al. Whiplash injuries: is there a role for imaging? European Journal of Radiology 1996;22:30-37.
- Woodring JH, Lee C. Limitations of cervical radiography in the evaluation of acute cervical trauma. Journal of Trauma 1993;34:32-39.
- Woodring JH, Lee C. The role and limitations of computed tomography scanning in the evaluation of cervical trauma. Journal of Trauma 1992;33:698-708.