Overview

Because of the biomechanical features of the region, the most common site of injury in the lower spine is the thoracolumbar junction. The thoracic spine is stabilized by the rib cage, which results in a transition point at T12–L1. The lumbar spine also transitions from the kyphotic thoracic spine to the lordotic lower lumbar spine, which increases the potential stress on the upper lumbar region. Fractures of the lower lumbar spine are less common because of the significant size of the vertebral bodies.

The most common cause of spinal cord injury in the United States is motor vehicle accidents, which account for about 40%, and the second most common is falls, which represent another 28%. Other causes include violence and sports-related injuries. Traumatic fractures of the lumbar spine can result in a spectrum of neurologic injuries, presenting with no symptoms at all or with complete bilateral lower extremity paraplegia with loss of bowel and bladder function. The extent of the injury—including the radiographic features, neurologic symptoms, and the acuity of the fracture—all contribute to the management of the fracture.

Classification of Lumbar Fractures

Fractures of the spine may be labeled as either stable or unstable. In 1970, Holdsworth introduced the two-column model that comprises an anterior and a posterior column. The anterior column is composed of the anterior longitudinal ligament (ALL), vertebral body, and posterior longitudinal ligament (PLL); the posterior column is composed of the laminae, transverse processes, spinous process, and interspinous ligament (ISL). Violation of both columns denotes instability.

In 1983, Denis proposed the three-column model, which comprises an anterior, middle, and posterior column. The anterior column is the ALL and anterior two thirds of the vertebral body and disk; the middle column is the PLL and posterior third of the vertebral body and disk. The posterior column includes the pedicles, laminae, spinous process, ISL, facets, and transverse processes. A fracture is considered unstable when two of the three columns have been violated.

Types of Fractures

A compression fracture usually involves an axial load, sometimes with a flexion component that causes violation of the anterior column. It may extend into the middle column but usually does not violate the posterior cortex of the vertebral body. These fractures are commonly managed nonoperatively and may or may not require external orthosis.

A burst fracture also usually involves an axial load with resultant compromise of the anterior and middle columns. These may be managed nonoperatively, or they may require surgical intervention for stabilization.

A Chance fracture is a complex fracture that involves a flexion component of injury in the anterior column with an associated distraction injury in the middle and posterior columns. The fracture may extend through the bony vertebral body or through the disk anteriorly and through the lamina or the facets posteriorly. Chance fractures are destabilizing injuries that usually require operative intervention.

A fracture-dislocation is a high-energy injury to the spine that involves not only violation of all three columns with associated ligamentous injury but also a translation or dislocation of the fractured parts. These fractures are most commonly associated with spinal cord or nerve root injury and therefore require operative stabilization.

Radiographic Evaluation of Fractures

Plain radiographs are less likely to be the modality used to initially evaluate a fracture, given the availability of computerized tomography (CT) in the setting of trauma. A set of anteroposterior (AP) and lateral radiographs gives the surgeon the opportunity to better assess a fracture with respect to the coronal and sagittal curvature of the spine. The posterior elements, including the pedicles and lamina, are more difficult to assess on plain radiographs. However, vertebral body abnormalities, such as compression fractures, may be readily noticed on plain radiographs, and consideration of the overall anatomic relationships in the spine can be obtained from three-foot standing or lateral/AP films. Neglecting to evaluate preoperative and postoperative alignment can lead to postoperative complications in the long term ( Figs. 39-1 and 39-2 ).

Plain anteroposterior radiograph of an L1 burst fracture, with fracture through the right pedicle.

Plain lateral radiograph of an L1 burst fracture.

CT is a better modality to evaluate the fine cuts of the fractures and the anatomic parts of the affected vertebrae. It also can help assess the extent to which retropulsion, listhesis, or violation of the pedicles and facets has occurred. The CT axial cuts are reconstructed to sagittal and coronal orientations to enable the surgeon to evaluate all three planes of the fracture ( Figs. 39-3 and 39-4 ).

Sagittal computed tomography of an L3 vertically oriented burst fracture with retropulsion of bony elements into the canal.

Axial computed tomography of L3 burst fracture with the fracture extending into the right pedicle.

Magnetic resonance imaging (MRI) is also frequently used to assess injury to the soft-tissue structures, such as the nerve roots, thecal sac, and ligaments. The T2-weighted fast spin-echo (TSE) and fluid-attenuated inversion recovery (FLAIR) images are used to assess vertebral body marrow edema. The gradient-echo T2-weighted sequence can best outline the vertebral body, ligamentous (ALL, PLL, ISL), and thecal sac anatomy. MRI is the most useful modality to examine the extent of the injury to the nerve roots (foraminal stenosis), ligamentous injury (ALL, PLL, ISL), and facet and disk joint violation. If an MRI were to show extensive ligamentous injury, the threshold for operative intervention might be lowered.

CT is better utilized to evaluate the bony fracture itself, including extent of canal compromise, violation of the vertebral elements, and often the mechanism of injury (compression, distraction, dislocation; Fig. 39-5 ).

Magnetic resonance imaging of the lumbar spine depicting an L3 burst fracture with some impingement on the thecal sac in the sagittal ( A ) and axial ( B ) planes.

Indications for Surgery

Evaluation for Surgical Approach

In trauma, several considerations weigh into the decision as to which surgical approach to use. A patient with a lower body mass index is easier in general for positioning prone, lateral, or anterior. Operative positioning can be affected by other injuries, such as an open abdomen from exploratory laparotomy, external fixation devices on upper and lower extremities, and pulmonary injuries from trauma.

Positioning patients for anterior approaches is easiest and safest in the setting of trauma with an unstable spine injury. However, anterior approaches are commonly used as adjuncts for stabilization rather than as the sole or primary approach. Posterior approaches involve prone positioning, usually on a Wilson frame or Jackson table.

Sometimes other injuries associated with the trauma make positioning challenging. Associated hip, pelvic, or long bone injuries to the upper or lower extremities may also add a confounding variable to positioning.

Patients who have undergone prior spine surgeries may require special consideration in operative preparation. Someone who has existing instrumentation might require removal of the hardware or extension of the construct. These factors all play an important role in the decision-making process for surgical approaches in the setting of management of spine trauma.