THORACOLUMBAR SPINE TRAUMA
Most thoracic and lumbar fractures result from vertical compression or flexion-distraction injuries. These injuries frequently occur around the thoracolumbar junction (T11-L2), because it represents a transition from the stiffer thoracic to the more flexible lumbar spine. The upper thoracic region (T1-10) is more injury resistant because it is stabilized by the ribs, and the lower lumbar region (L3-5) has larger, stronger, and more injury-resistant vertebra.
Multiple classification systems exist for thoracolumbar trauma, but the three-column theory of Denis is among the simplest to conceptualize (see Plate 1-28). This concept divides the vertebral body into three columns: the anterior column extending from the anterior longitudinal ligament through the anterior two thirds of the vertebral body, the middle column containing the posterior third of the vertebral body and posterior longitudinal ligament; and the posterior column, which includes the posterior spinal elements (lamina, pedicles, spinous processes) and posterior ligamentous complex (supraspinous and interspinous ligaments, facet capsules, and ligamentum flavum). Injuries involving one column can frequently be treated nonoperatively, two-column injuries may require surgical management, and three-column injuries generally mandate surgical stabilization and fusion.
THREE-COLUMN CONCEPT OF SPINAL STABILITY AND COMPRESSION FRACTURES
Compression fractures result from failure of the anterior vertebral column when a flexion force is applied. This most commonly occurs at the thoracolumbar junction in elderly patients with osteoporosis. It is generally a stable fracture, and treatment is usually symptomatic with pain medication, restricted activity, and a thoracolumbar orthosis for comfort. The fracture typically becomes stable once the bone heals. Surgical treatment involves cement augmentation of the vertebral body to provide immediate stability and to minimize the risk of progressive kyphosis. Multiple compression fractures in patients with severe osteoporosis can cause a kyphotic, stooped posture (see Plate 1-28). In such cases, cement augmentation of the fractured vertebra should be considered.
Burst fractures involve failure of the anterior and middle columns of the spine from an axial load and are generally associated with higher-energy trauma than simple compression fractures. Because the posterior vertebral body (middle column) is fractured, bony fragments can retropulse into the spinal canal and may cause spinal cord or nerve root injury (see Plate 1-30). Suspected burst fractures should be evaluated by CT or MRI to evaluate the degree of spinal canal compromise and the integrity of the bony and ligamentous structures of the posterior column. Posterior column injury denotes a more severe fracture pattern (a “three-column” injury) that frequently requires surgery.
Treatment of burst fractures varies and has been the subject of some controversy. Stable burst fractures without neurologic injury can be treated with pain medication, activity restriction, and a thoracolumbar orthosis to relieve pain and promote bony healing. Relative indications for surgery include greater than 25 degrees of kyphosis, greater than 50% height loss of the vertebral body, or greater than 50% spinal canal compromise. A complete or incomplete neurologic injury and an injury to the posterior column (a three-column injury) constitute absolute indications for surgery. Surgery typically involves instrumented spinal fusion two levels above and two levels below the fractured vertebra. If there is a neurologic injury, then a decompression is also performed. Posterior-only procedures can be performed when there is no need for decompression of bony fragments within the spinal canal, such as when there is no neurologic injury. It can also be performed in patients requiring decompression with an acute fracture (<5 days after injury) because such fracture fragments are mobile and can usually be reduced by a combination of distraction and lordosis. Anterior procedures are appropriate for subacute injuries requiring decompression, in patients with a severe neurologic deficit and significant canal intrusion by fracture fragments, and in patients with severely comminuted vertebral body fractures with no anterior column support (see Plate 1-30).
A Chance fracture is typically a bony injury through the vertebra in the thoracolumbar spine. It is best visualized on the lateral radiograph or CT scan. The Chance fracture is also known as a “seat belt” fracture, because it frequently results from motor vehicle accidents in which the patient wears a lap belt without a shoulder belt. With sudden deceleration, the patient simultaneously experiences flexion anteriorly, with the lap belt acting as the pivot point, and distraction (tension) of the posterior column of the spine. As the distraction continues, a fracture propagates from posterior to anterior through the spine, involving all three columns (see
Plate 1-30). Although the fracture often reduces spontaneously, it is inherently unstable. Fractures must be treated surgically or immobilized in a thoracolumbar orthosis (with spinal stability verified with a standing radiograph in the brace). Occasionally, this flexion-distraction injury affects only the discoligamentous structures in the spine, resulting in a “soft tissue Chance” injury. In this variant of the injury, the transverse cleavage plain propagates through the posterior ligamentous complex (supraspinous and interspinous ligaments, ligamentum flavum, and facet capsules) and anteriorly through the intervertebral disc. Signs of this injury on the lateral radiograph include gapping at the facet joint and widening of the distance between spinous processes. This injury must be treated by spinal fusion because these discoligamentous structures will not spontaneously heal after being disrupted.
UNSTABLE INJURIES OF THE THORACOLUMBAR SPINE
The thoracolumbar junction is vulnerable to several different mechanisms of injury: flexion, rotation, axial loading, or any combination of those forces. Fracture- dislocations are relatively common in this region, where the less mobile thoracic spine meets the highly mobile segments of the lumbar spine. A fracture-dislocation of the thoracolumbar spine is severe and involves disruption of all three columns of the spine (see Plate 1-30). These fractures are inherently unstable and are associated with a high rate of neurologic injury. Treatment of these injuries typically involves instrumented spinal fusion and is directed at restoring stability to this area.
Traumatic sacral fractures can present as a solitary injury but often are observed in association with a pelvic ring or lumbosacral facet injuries in a patient with multiple injuries. The closer the fracture is to the midline (either involving the sacral neural foramina or central canal), the higher is the rate of neurologic injury. Most sacral fractures are stable and do not require surgery. In patients with neurologic injury and objective evidence of neurologic compression, however, surgical decompression and stabilization may be indicated.