Thoracic Spine Fractures and Dislocations 

Thoracic spine fractures, especially those resulting from high energy, can be devastating, often resulting in permanent neurologic injury. Neurologic deficit is encountered in 10-25% of all spinal column injuries, irrespective of the level of injury. A deficit occurs in 15-20% of all thoracolumbar injuries. In the event of a complete neurologic injury, very few patients regain any useful motor function. Concomitant neurologic injury with spine fractures also adversely affects long-term survival. The 10-year survival rate for people younger than 29 years is 86%. This percentage drops precipitously to 50% for patients older than 29 years.

The images below display some examples of burst fractures, flexion distraction injury, and fracture dislocations.

Recent studies

In a study by Smith et al, nonreconstructed CT detected fractures of the thoracolumbar spine more accurately than plain radiographs and is recommended for the diagnosis of thoracolumbar spine fractures in acute trauma patients with altered mental status. According to the investigators, reconstructions do not need to be ordered unless an abnormality is found on the nonreconstructed CT scan that needs additional elucidation. In 59 patients, CT spine reconstructions identified 72 thoracolumbar fractures. Nonreconstructed CT scans of the abdomen and pelvis detected 58 fractures, and scans of the chest identified 16 fractures. CT of the chest, abdomen, and pelvis had a sensitivity of 89% and a specificity of 85% for detection of all fractures, compared with 37% and 76% for plain radiographs, respectively.^[1]

In a case-control study by Singh et al, cervical and lumbar spine injuries and rib fractures were found to be positively associated with thoracic spine fractures, whereas skull fractures and lower limb injuries were found to be negatively associated with thoracic spine injuries. As a result, according to the authors, special attention should be paid to the chance of thoracic spine injuries in patients with lumbar and cervical spine injuries and rib fractures.^[2]

Stadhouder et al compared nonoperative treatment methods for traumatic thoracic and lumbar compression fractures and burst fractures and found that, for compression fractures, the treatment of choice was the use of a brace along with physical therapy. For burst fractures, however, no significant differences were found between nonoperative therapies. The authors also noted that more than 20% of all patients had moderate or severe back pain at long-term follow-up.^[3]

For excellent patient education resources, visit eMedicine's Back, Ribs, Neck, and Head Center. Also, see eMedicine's patient education article Vertebral Compression Fracture.

Documented treatment of spine fractures dates back several thousands of years. Closed treatment and manipulation to correct the sustained deformity were typically used. In the early 20th century, most treatment consisted of immobilization in hyperextension.

Treatment of spine fractures did not begin to evolve from universally closed treatments to the surgical modalities that are in place today until the advent of current anesthesia and radiographic techniques. Internal fixation was first seen after World War II. Initially, it was in the form of spinous process plating. Harrington then introduced his posterior spinal instrumentation. From this, modern surgical techniques and instrumentation have developed. Although the spinal stability and alignment established with these newer techniques have dramatically improved, improvement in neurologic deficits sustained in these injuries has remained relatively unchanged over the years of spine fracture management.

Thoracic spine fractures, especially those resulting from high energy, often result in permanent neurologic injury.

Frequency

See Etiology. The male-to-female ratio is roughly 4:1.

The vast majority of spine fractures occur as a result of motor vehicle accidents (45%), falls (20%), sports (15%), acts of violence (15%), and miscellaneous activities (5%). The percentage secondary to acts of violence is higher in urban areas. For mechanisms of injury, see Clinical.

An extensive physical examination should be performed and neurologic status should be documented upon initial presentation. Concomitant injuries should be assessed, and the patient's overall physical condition should be optimized promptly.^[2] Once the patient is stabilized hemodynamically and other visceral injuries have been investigated and excluded, definitive treatment of the thoracic spine injury can be contemplated.^{[4, 5, 6]}

If neurologic deficit (spinal cord) is present and less than 8 hours have elapsed from the time of injury, begin treatment with high-dose methylprednisolone (5.4 mg/kg bolus followed by 30 mg/kg/h infusion for 23 h). Operative versus nonoperative treatment can be entertained based upon the clinical status of the patient and radiographic appearance of the fracture. The stability and location of the fracture and the underlying mechanism of injury all can play major roles in the decision whether to operate or treat conservatively.

Several distinct classification schemes are available to assess spinal stability.^[7] Holdsworth initially proposed the 2-column theory of spinal stability.^[8] In this model, the vertebra is divided into an anterior and posterior column. The anterior column consists of the vertebral body, intervertebral disc, anterior longitudinal ligament, and the posterior longitudinal ligament. The posterior column comprises the facets, neural arch, and interspinous ligaments. Disruption of one or more columns implies instability of the involved segment.

Denis expanded on this model, developing the most common model used for assessing spinal stability.^[9] In this model, the vertebra is divided into 3 columns: anterior, middle, and posterior. The anterior column comprises the anterior half of the vertebral body along with the anterior longitudinal ligament and the anterior portion of the annulus fibrosis. The middle column is made up of the posterior annulus fibrosus along with the posterior half of the vertebral body and the posterior longitudinal ligament. The posterior column consists of the posterior ligamentous complex and the posterior bony elements. When 2 of the 3 columns are disrupted, the fracture is considered unstable.^[9]

Classification schemes generally also encompass mechanisms of injury and their resultant fracture patterns. Several different mechanisms of injury can occur within the thoracic spine. Most commonly, a combination of 1 or 2 mechanisms accounts for the injury. These mechanisms include the following:

• Axial compression: This type of injury results in a purely compressive load. Endplate failure occurs, followed by vertebral body compression. With higher energy, a centripetal displacement occurs, resulting in what is commonly referred to as a burst fracture. In severe burst fractures, discs become fragmented and the posterior elements are disrupted. Radiographically, this mechanism can manifest as a widened interpedicular distance. The image below depicts a burst fracture. Thoracic spine fractures and dislocations. Burst fracture T12. Note the widened interpedicular distance.
• Flexion: This mechanism results in compression anteriorly. Disruption of posterior elements with flexion often results in instability of the involved area. If anterior compression exceeds 40-50%, the posterior ligamentous structures are often disrupted. Instability ultimately can result in progressive deformity and neurologic deficit if not appropriately stabilized.
• Lateral compression: This mechanism usually results in a stable injury unless disruption of posterior structures or associated axial compression occurs.
• Flexion-rotation: With a flexion-rotation injury, posterior ligamentous structures commonly fail. Oblique disruption of the anterior vertebral body and disc failure occur. This type of injury can result in what commonly is known as a slice fracture. With fractures of the facets and concomitant disruption of posterior elements, thoracic spine dislocation can occur.
• Shear: Shear injuries often result in severe ligamentous disruption and subsequent anterior, posterior, or lateral listhesis. Anterolisthesis is the most common of the 3, with complete spinal cord injury often being the unfortunate result. However, occasionally, concomitant fractures through the pars interarticularis result in autolaminectomy, with resultant neural sparing.
• Flexion distraction: This injury is more commonly referred to as the seatbelt injury. The axis of flexion is anterior to the vertebral column. Osseous, disc, and ligamentous structures are disrupted either alone or in combination. Combined osteoligamentous or purely ligamentous injuries can be present, and this injury occurs most commonly at the thoracolumbar junction. Bilateral facet dislocation can occur. The image below depicts a flexion distraction injury. Thoracic spine fractures and dislocations. Flexion distraction injury with facet dislocation.
• Extension: Tension is placed on the anterior longitudinal ligament, with compression occurring posteriorly. Facet, laminar, and spinous process fractures often occur. Most of these injuries are stable, provided that significant retrolisthesis does not occur.

In the Denis classification system, significant fractures are divided into the following groups: (1) primarily axial load injuries, including compression and burst fractures; (2) flexion-distraction injuries; and (3) fracture subluxation and/or dislocation. The image below depicts a fracture dislocation.

The mechanism of failure of the middle column further differentiates the various types of fractures. The middle column is spared in compression fractures, yielding a stable fracture. It fails in compression with burst fractures, distraction in seatbelt injuries, and shear and/or rotation injuries. Fracture dislocations yield unstable injuries.

The Denis classification system has been criticized due to its occasional inability to be used to adequately distinguish between stable and unstable fractures—for example the "stable" burst fracture. In addition, biomechanical studies have been performed that bring into question the importance of the middle column. McAfee recognized this and expanded upon the Denis classification scheme to further elucidate stable versus unstable fractures. His classification system emphasizes the posterior ligamentous complex as a major factor in fracture stability. While many classification systems exist, the Denis classification is probably the most frequently used.

Another shortcoming of structural or mechanistic classifications is that they often fail to take neurologic deficit into account. Significant neurologic injury implies instability irrespective of the fracture pattern in that the spine has failed in protecting the neural elements. In general, stable fracture patterns in a neurologically intact patient can be treated nonoperatively. Indications for surgery can vary and include significant neurologic deficit and fracture subluxations. Excessive deformity is also an indication, although defining this is difficult, and the effect of kyphosis on long-term results is uncertain. Kyphosis greater than 30º; may be associated with poorer long-term results, and kyphosis greater than 25º; is often mentioned as a relative indication for surgery.

The presence of other injuries also may affect the choice between operative and nonoperative treatment. The most predictable benefit of surgery is more rapid mobilization, which can be an important consideration in the patient who has experienced multiple traumatic injuries.

The primary goals of treatment for thoracic spine fractures include protecting the neural elements and preventing deformity and instability. Surgery often facilitates achieving these goals and often hastens the patient's rehabilitation. Hospital stays are often shorter with surgery. Surgery is particularly often beneficial in patients with multiple traumatic injuries. The ultimate decision to operate is based on many factors, including fracture morphology, and the choice is often complex (see Clinical). Surgical management should be strongly considered when neurologic deficit or significant deformity or instability is present. See Medical therapy for a discussion of indications for surgery in patients with specific thoracic spine injuries.

A thorough knowledge of thoracic spine anatomy is essential in the treatment of thoracic spine fractures. Twelve thoracic vertebrae exist. The normal thoracic spine has an inherent kyphotic curve ranging from 18-51°. The vertebral bodies are wedge-shaped, being larger posteriorly than anteriorly. The kyphosis of the thoracic spine results in a center of gravity anterior to the apical T7 vertebrae, resulting in compression anteriorly and tension posteriorly in the resting state.

Significantly less flexion capabilities exist in the thoracic spine relative to the cervical and lumbar spine. The C7-T1 articulation flexes approximately 9°, T1-T6 flexes 4°, and T6-7 to T12-L1 gradually increases to 5-12°. Less lateral bending occurs within the thoracic spine as well. Lateral bending is approximately 6° per level from T1-T10 and approximately 8° at the thoracolumbar junction. Axial rotation is 8° from T1-T8. This is largely due to the coronal orientation of the facets in the thoracic spine. The axial rotation of the lower thoracic spine and thoracolumbar junction is reduced to 2° below T10 due to the transition to more sagittally oriented facets than those seen in the lumbar spine.

The thoracolumbar junction is relatively susceptible to injury. Injuries in this region constitute 50% of all vertebral body fractures. The decrease in rib restraint is largely responsible for the susceptibility of this area to injury. Other factors include changes in stiffness in flexion and axial rotation and the changes in disc size and shape that occur at the transition between the thoracic and lumbar spine.

The terminal portion of the spinal cord, the conus medullaris, normally begins at the T11 level. It ends at the L1-2 disc space in males and slightly more proximally in females. The cauda equina emanates from this region and extends distally into the lumbosacral spine with each peripheral nerve root exiting at its corresponding neural foramen. The cauda equina is more resistant to injury and has greater potential for recovery than the spinal cord.

The diameter of the spinal canal is also of great significance in thoracic spine fractures. The canal diameter of the thoracic spine is narrower than that of the cervical and lumbar spine. At the T6 level, the long axis of the spinal canal is approximately 16 mm in diameter, whereas in the midcervical and midlumbar spine, the long axis is 23 mm and 26 mm, respectively. These dimensions have ramifications regarding the smaller amount of space available before cord compression is sustained in the event of a thoracic spine fracture. In addition, the smaller diameter may make fixation techniques such as sublaminar wire fixation more difficult and, thus, a less desirable method of stabilization.

The orientation and shape of the pedicles in the thoracic spine are different from those of their lumbar counterparts and can often preclude pedicle fixation. The pedicular isthmus width is smaller in the T-spine than in the lumbar spine. The transverse angle is approximately 27° medial inclination from posterior to anterior in the proximal thoracic spine, decreasing to 1° at T11 and to -4° at T12.

Relatively few contraindications exist to operative stabilization of unstable thoracic spine fractures. Patients who are unstable medically with thoracic spine fractures requiring operative intervention should not undergo surgical stabilization. Once the patient is in optimal medical condition, surgery should be undertaken. Operative intervention for thoracic spine fractures is also contraindicated in the presence of active infection.