Background
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.
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.
For patient education resources, see Vertebral Compression Fracture.
Anatomy
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° to 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°, T1-6 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 for T1-10 and approximately 8° at the thoracolumbar junction.
Axial rotation is 8° from T1 to 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 because of 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 thoracic 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.
Etiology
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. The male-to-female ratio is roughly 4:1. For mechanisms of injury, see Presentation.
Prognosis
The results are favorable for correction of deformity, maintenance of reduction, healing, and fusion rates. Overall clinical outcome is generally good, depending on the patient's final neurologic function. Return of neurologic function, however, is variable, with little significant recovery seen in complete injuries irrespective of treatment.
Machino et al conducted a case-control clinical study to assess the usefulness and safety of transforaminal thoracic interbody fusion (TTIF) in the treatment of lower thoracic spine fracture dislocations and to compare its efficacy with that of posteroanterior combined surgery. [1] They concluded that TTIF was able to achieve posterior rigid fixation with instrumentation and anterior column reconstruction by interbody fusion and that it allowed early postoperative ambulation without respiratory problems.
Ma et al investigated possible contributors to lateral spinal angulation after surgical fixation of thoracolumbar fractures via an anterior approach. [2] On the basis of responses to Short Form (SF)-36, the Oswestry Disability Index, the Japanese Orthopaedic Association Back Pain Evaluation Questionnaire, and the Visual Analogue Scale, all of which the patients completed during their final follow-up visit, the investigators concluded that postoperative lateral angulation does not correlate with low back pain, quality of life, or preoperative lateral angulation.
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Thoracic spine fractures and dislocations. Burst fracture T12. Note the widened interpedicular distance.
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Thoracic spine fractures and dislocations. Flexion distraction injury with facet dislocation.
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Thoracic spine fractures and dislocations. Fracture dislocation T2-T3.
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Thoracic spine fractures and dislocations. Preoperative axial CT image of burst fracture with partial neurologic deficit.
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Thoracic spine fractures and dislocations. Burst fracture with partial neurologic deficit after stabilization with medial resection of right pedicle to allow access to anterior fragment.
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Thoracic spine fractures and dislocations. Pedicle screw fixation of a T12 burst fracture.
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Thoracic spine fractures and dislocations. Anteroposterior (AP) radiograph of T12 burst fracture treated with cage strut and anterior instrumentation.
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Thoracic spine fractures and dislocations. Lateral radiograph of T12 burst fracture treated with cage strut and anterior stabilization.
