traumatic spinal cord transection is uncommon . in a study of 62 patients with spinal cord injuring who underwent magnetic resonance imaging ( mri ) , 7 had cord transections ( 1 ) .
in contrast to children in who closed spinal cord trauma may occur in the absence of skeletal injury , most cord injuries in adults are associated with major musculoskeletal injuries , such as vertebral fractures and/or dislocations ( 2 - 6 ) . in the subaxial cervical spine , hyperextension injuries without facet dislocations are well known as central cord syndromes , but cervical cord transection has not been described in the literature ( 7 - 10 ) .
we report a patient with a cervical cord transection in the absence of a vertebral dislocation secondary to air bag deployment without the use of a seat belt and discuss the mechanism of this type of injury .
a 33-yr - old male was admitted through the emergency room with neck pain , and loss of sensation and inability to move all four extremities .
he had crashed his car into the post of a traffic signal , was not wearing a seat belt , and the front air bag deployed . on neurologic examination , the patient had flaccid paralysis of all four extremities , a sensory level at c4 , no sphincter control or rectal tone , an absent anal wink , no sacral sparing , and a positive bulbocavernosus reflex .
he was fully alert with mild hypotension ( systolic arterial pressure < 100 mm hg ) .
plain radiographic evaluation of his cervical spine showed c5 , c6 wedge compression fractures and minimal c5 retrolisthesis on c6 ( fig .
a computed tomographic ( ct ) scan also demonstrated c5 , c6 vertebral body vertical fractures with laminar fractures , and a c3 spinous process fracture ( fig .
the fractured c5 lamina was depressed into the spinal canal through the lamina - facet junctions .
a mri revealed a linear area of abnormal signal intensity running horizontally through the spinal cord at the c5 - 6 disc space level , which was thought to represent a spinal cord transaction ( fig .
the patient had no brain , thoracic , or abdominal abnormalities on plain films and ct scans .
the patient underwent surgery via a posterior approach 5 days after his injury . a c5 laminectomy with a posterior fusion and lateral mass screw fixation at the c4-c7 levels
4 ) . during this procedure , disruption of the c4 - 5 supraspinous and interspinous ligaments were noted , but the facet joint capsules were intact at the c4-c7 levels in the operative field .
he was transferred to the rehabilitation department 1 month post - operatively and no neurologic improvement had been observed 4 months after the injury .
there have been no reports of traumatic spinal cord transections in adults other than fracture - dislocation injuries in the subaxial spine . although berlot et al . ( 11 ) described a delayed post - traumatic cervical cord transection in a spinal cord injury without radiologic abnormalities ( sciwora ) , the initial mri revealed only focal swelling of the spinal cord and several patch areas of cord contusions ; indeed , an initial incomplete lesion may have progressed to transection in the absence of fixation .
our patient 's injury appeared to have occurred when his torso overrode the air bag , which resulted in acute hyperextension of the cervical spine .
this potential mechanism has been shown in crash simulations using human cadavers and dummies positioned opposite airbags when unbelted ( 12 ) .
but in such simulations , the velocities were between 32 and 48 km / hr .
the velocity in our patient was more than 60 km / hr , so a more extreme hyperextension injury may have occurred . during the episode of hyperextension , rupture of the anterior longitudinal ligament and
the disc caused marked backward displacement of the c5 vertebral body against the cord ( 13 ) .
also , our patient had a c5 laminar fracture , which may have exacerbated the hyperextension and posterior displacement .
although there was no facet disruption , this circumstance could result in a c5/6 spinal cord transection . because the spine returned to its normal position by the elastic recoil of the vertebral muscles when the head is in the neutral position or in flexion ( 14 ) , subtle c5 retrolisthesis on c6
. the above mechanism of injury could explain the cord transection and injuries involving the posterior vertebral column .
however , c5 , c6 vertebral body fractures are unresolved . according to allen 's classification of subaxial cervical fractures and dislocations ( 15 ) ,
our patent 's injury was a distractive extension stage 2 lesion . in this type of injury , however , there was no co - existing vertical fracture centrum .
therefore , we propose the hypothesis that during the initial short moment of the collision , the airbag was just in contact with the torso , but not with the face of the patient . as a result ,
compressive flexion force interacted at the cervical spine , resulting in c5 , c6 vertebral body fractures .
5 . the course of treatment in this patient is of less interest than the proposed mechanism of injury .
distractive extension stage 2 lesions must be surgically stabilized , usually with an anterior approach . however , in the presence of cord involvement by laminar fragments with preservation of lordotic sagittal alignment , a posterior approach is also useful ( 16 ) . in this case report
four months after the operation , no cervical instability was observed while the patient ambulated in a wheelchair . although there is a constant search for ways and means to enhance recovery of spinal cord injury , this patient 's prognosis is very poor . according to data of the model spinal cord injury systems ( 17 )
, 94.4% of patients with neurological complete spinal cord injuries remained so at the 5-yr post - injury evaluation .
nevertheless , kirshblum et al . reported approximately 20% showed some improvement in motor power and neurologic level of injury from year 1 to year 5 ( 18 ) .
therefore medical rehabilitation service should be provided sufficiently and continuously for the sake of this patient 's recovery .
although this report describes just a single case of spinal cord transection by motor vehicle accident , it emphasizes the importance of proper use of seat belts especially in the circumstance of airbag deployment .
the authors ' proposed hyperflexion - hyperextension mechanism can result in significant neurologic deficits , but subtle radiographic abnormalities might be seen on plain films .
so clinicians in emergency centers should have the possibility of cord transection in the acutely injured patient in mind because it is important for both prognostic and therapeutic reasons .
 a patient is presented with a cervical spinal cord transection which occurred after a motor vehicle accident in which the air bag deployed and the seat belt was not in use . 
 the patient had complete quadriplegia below the c5 level and his imaging study showed cervical cord transection at the level of the c5/6 disc space with c5 , c6 vertebral bodies and laminar fractures . 
 he underwent a c5 laminectomy and a c4 - 7 posterior fusion with lateral mass screw fixation . 
 previous reports have described central cord syndromes occurring in hyperextension injuries , but in adults , acute spinal cord transections have only developed after fracture - dislocations of the spine . a case involving a post - traumatic spinal cord transection without any evidence of radiologic facet dislocations is reported . 
 also , we propose a combined hyperflexion - hyperextension mechanism to explain this type of injury . 
INTRODUCTION
CASE REPORT
DISCUSSION