Background: Vertebral artery injuries are often not diagnosed because they are asymptomatic. But there is information that up to 19% of all patients who incur trauma to the lower cervical spine have vertebral artery injuries. This incidence increase in flexion-distraction injuries. It is unclear as to the individual contribution of various force loads and resultant deformity on the etiology of these injuries.

Purpose: To evaluate the degree of vertebral artery deformation and potential injury in staged flexion-distraction deformities of the cervical spine. Study design: Thirtyfive fresh frozen cervical spine specimens underwent vertebral artery cannulization and angiography to determine the static influence of the four stages of subaxial flexion-distraction injuries as described by Allen et al. on the vertebral artery patency.

Methods: Each specimen was examined radiographically so as to exclude any preexisting cervical deformities. A cannula was inserted into the isolated cranial and caudal stumps of the vertebral arteries and perfused with contrast agent. A fluoro image intensifier recorded deformation in dye fluid passage in the four stages of flexion-distraction injuries.

Results: No significant deformation in vertebral artery flow was noted in the flexion-distraction stage I injuries within the physiological range of cervical flexion. Flexion-distraction type II and III injuries demonstrated considerable impairment to vertebral artery dye flow in proportion to the degree of vertebral deformity. Manipulating the dislocated vertebral segments into a localized lordosis further impaired vertebral vessel patency. Coexisting rupture of the vertebral radicular vessel was a constant finding in stage II and III injuries. Longitudinal stretch deformities of the vertebral artery were limited primarily to the injured vertebral segments. Stage IV injuries resulted in irreversible disruption of vertebral dye flow.

Conclusion: The static deformity of flexion-distraction stage II to IV subaxial cervical injuries results in significant objective compression of the vertebral vasculature, what seems to have consequences in treatment and establishing the diagnosis.