Cervical Spine Instability, Flexion Extension X-rays
The cervical spine consists of the first seven vertebrae of the spinal column, C1-C7. When determining instability of the c-spine, flexion/extension x-ray views of the spine will need to be ordered. Flexion/extension x-ray views detect subtle ligamentous injuries that are not apparent on routine neutral static views. These specific x-rays are done in order to avoid missing an unstable injury in the cervical spine. It is one of the many tactics that improves understanding the extent and personality of the neck injury.
Other tactics include:
· Imaging of the C7-T1 junction
· Observing the occiput C1-C2 area
· Imaging the entire spine if there is a cervical spine injury (noncontiguous cervical spine injury can be as high as 15%)
Flexion/extension cervical spine x-rays may not be advisable if there is a head injury involved, especially if the patient is intoxicated, if there is a neurological deficit, or if the patient is unable to flex/extend due to pain. If the latter is the case, you can perform the x-ray a few days later when the spine is less tender.
Flexion/Extension Cervical Spine x-rays are done when the patient has no abnormal findings on x-rays and if the patient has pain (lateral, AP, and Odontoid views). The patient should do the flexion/extension by themselves under direct supervision. Performing an MRI is an alternative but, it has its own advantages and disadvantages.
The atlanto-dens interval (ADI) is the distance between the odontoid and the anterior arch of the axis. If the ADI is more than 3mm in adults, check for a transverse ligament injury. The space available for the cord (SAC) is the space between the odontoid and the posterior arch of the axis. An increased ADI indicates an unstable spine.
The sagittal cervical spine is separated into three planes: the Anterior Vertebral, the posterior vertebral, and spinolaminar. The normal cervical spine should represent smooth curves with no malalignment or displacement. In cervical spine injuries, displacement more than 3.5 mm signifies an unstable injury. In cervical spine injuries, angulation of more than 11 degrees of contiguous cervical vertebrae signifies an unstable injury.