secondary injury to the cord may be directly related to the energy impact delivered at onset. A syrinx (fluid-filled cavity) may develop in some patients and lead to further neurologic deficits. Cystic cavities due to neuronal degeneration that occur ex vacuo and glial scarring from activated microglia and astrocytes can make it very difficult for damaged axons to regenerate. Even if neurites are able to regrow, oftentimes the myelin white matter surrounding them has been substantially damaged and oligodendrocyte remyelination attempts are often impaired.
TABLE 13.1 Differential Diagnosis of Acute Myelopathy
injury. Mobile parts of the spine (eg, cervical spine) and transition zones (eg, cervicothoracic and thoracolumbar) are at greatest risk for injury. Different mechanistic forces (ie, flexion, extension, distraction, compression) tend to be associated with specific injuries (Figure 13.1).
TABLE 13.2 Subaxial Spine Injury Classification (SLIC) Severity Score
This injury disrupts all the major stabilizers of the craniocervical junction: tectorial membrane, alar ligaments, apical ligament, transverse ligament, O-C1 joint, and often C1-C2 capsular ligaments. Atlanto-occipital dissociation is highly unstable, and oftentimes instantly fatal. Given the magnitude of force it takes for this dislocation to occur, there are often other associated injuries, for example, subarachnoid hemorrhage (SAH), epidural hematoma at the foramen magnum, and vertebral artery injury. Atlanto-occipital dislocation requires surgical stabilization with an O-C fusion.
TABLE 13.3 Anatomic Subclassifications of the Spine
pars interarticularis fractures. This is the injury that is most classically described with judicial hangings, leading to a distraction and extension injury. However, this fracture type can often be seen with axial loading combined with flexion-type injuries. There is risk of disruption of the posterior longitudinal ligament with C2 subluxation, and C2-C3 disk rupture as well. The need for surgical stabilization may depend on the amount of angulation and displacement, but most of these fractures are unstable. There are three different fracture types of the dens. Type 1 is
rare and consists of avulsion of the upper portion of the dens with an intact transverse ligament. It is often associated with a distraction-type injury. Because the ligament is intact, this injury is stable. Type 2 is the most common, and is a fracture of the dens at its base. About 10% of these patients may have rupture of the transverse ligament, which renders this injury unstable. Ligamentous injury will be seen best on MRI. Younger patients who have less displacement may be able to heal with a brace or halo; however, elderly individuals do not tolerate external bracing as well. Surgical stabilization consists typically of posterior C1-C2 fusion, but a small percentage may be amenable to stabilization anteriorly with an odontoid screw. A type 3 fracture of the dens involves extension into the C1-C2 joints bilaterally. The greater the surface area of the fractured bones, the more likely the injury is to heal with an external brace. Type 3 fractures are more stable.