Background

Each year in the United States, approximately 150,000 to 170,000 people sustain spinal column fractures; most of these will be caused by trauma, and such injuries can lead to short- and long-term complications. Posttraumatic kyphosis is a possible complication of spinal column trauma despite advances in surgical technique and management of spinal fractures. Methods in the management and treatment of this adverse outcome of spinal column fractures involving the thoracic spine are discussed in this chapter.

Normal Sagittal Balance

Recognition of posttraumatic kyphosis requires knowledge of what is defined as “normal.” Normal sagittal balance and the contributions of each segment are illustrated in Figure 58-1 . A plumb line dropped from the center of the C7 vertebral body on a lateral three-foot standing radiograph should fall over the posterior-superior corner of S1. A plumb line that falls anterior to the posterior-superior sacrum is called a positive global sagittal balance; clinically, the patient is pitched forward, a mechanically unbalanced situation. In contrast, a plumb line that falls posterior to the posterior-superior corner is called a negative sagittal balance.

Normal sagittal alignment with contributions of segmental levels to overall thoracic kyphosis.

Measurement of overall thoracic kyphosis from lateral radiographs proximally is hindered because of overlap of the shoulders. As a result, measurements of thoracic kyphosis can often be measured from T4 to T12, rather than from T1 to T12, and this measurement from T4 to T12 varies from 20 to 50 degrees of kyphosis with a mean of 35 degrees. Each segment in the thoracic spine contributes to this overall kyphosis, beginning with T1–T2, which contributes 1 degree. Each subsequent thoracic segment contributes to increasing amounts of kyphosis up to the apex at T5–T6, which contributes 5 degrees. Segmental contribution of each following level then decreases gradually, until the T11–T12 segment is reached.

In contrast, the thoracolumbar region of T11–L2 is a transition zone between kyphosis and lordosis that measures zero degrees, or slight lordosis. This is followed by the lumbar region, measured from T12 to the superior end plate of S1, at 40 to 80 degrees of lordosis with a mean of 60 degrees—approximately double that of thoracic kyphosis in a balanced spine.

Impact of Spinal Column Trauma on Alignment

Spinal column trauma can lead to focal kyphosis, most commonly in the thoracic and thoracolumbar regions. The magnitude of the focal kyphosis is ideally measured from the superior end plate of the cephalad level and the inferior end plate of the caudal level. The overall sagittal balance may still be normal as a result of compensation from increased lordosis in the lumbar spine.

Overall, vertebral body fractures, such as compression fractures of the thoracic spine, tend to be static and nonprogressive. In contrast, injuries that involve disruption of the posterior ligamentous complex, such as in the case of severe burst fractures or flexion-distraction injuries, can lead to acute progressive kyphotic deformities if the injuries are not surgically stabilized. Kyphotic deformities can also present later, and reasons for late presentation include 1) pseudarthrosis, 2) hardware failure, 3) short-segment stabilization, 4) presence of a laminectomy, and 5) Charcot spine or neuropathic spinal arthropathy in cases of long-term follow-up of patients with spinal cord injury. Deep wound infection needs to be ruled out in the case of pseudarthrosis, and hardware failure can occur as a result of inadequate fixation, owing to such things as poor bone quality, a breached pedicle screw, or an insufficient number of screws. In addition, short-segment fixation has been associated with progressive kyphosis in the case of comminuted burst fractures. Progressive kyphosis can also occur in the setting of laminectomy performed for a fracture. Failure to correct the kyphotic alignment during a revision procedure will lead to increased biomechanical stress on the screws utilized for the revision procedure.

Presenting Symptoms of Thoracic Kyphosis

Patients with thoracic kyphosis may come to medical attention with pain, neurologic deficit, or both. Pain is often localized at the site of the deformity and is due to altered biomechanics from the increased kyphosis, which causes increased strain on the posterior soft tissues. Patients may also complain of pain at adjacent regions because of premature degeneration from increased biomechanical stress, and focal kyphosis greater than 30 degrees may be associated with increased pain. Surgical correction of posttraumatic deformity may or may not reduce pain.

Patients may also present with worsening or new neurologic deficits in posttraumatic thoracic kyphosis because of progression of kyphosis or formation of a symptomatic posttraumatic syrinx. Progression of the thoracic kyphosis can lead to the thoracic spinal cord being “draped and stretched” against the dorsal vertebral body wall. New or progressive deficits may also be due to increased instability, with mechanical stress being transferred directly to the thoracic spinal cord. Alternatively, posttraumatic symptomatic thoracic syringomyelia may also be a cause of late-worsening neurologic function, with estimated rates varying from 1% to 9% of thoracic cord injuries; this can be associated with persistent neural compression as a result of progressive kyphosis. Symptomatic posttraumatic syringomyelia can be treated with correction of the kyphotic deformity and relief of the neural compression, along with a combination of intradural procedures that involve untethering of the thoracic cord, either with arachnolysis and duraplasty or in combination with syringopleural shunting.