The thoracic spine is a rigid segment. The additional support provided by its articulation with the rib cage imparts a stiffness to the thoracic spine 2.5 times that of the ligamentous spine alone. Relative to other regions of the vertebral column, a large force is necessary to overcome the intrinsic stability of the thoracic spine. While injury to the thoracic spine is less common than in other regions, when it does occur it is usually significant. The spinal canal is narrower than that found in either the cervical or lumbar spine. The large spinal cord diameter relative to canal diameter increases the risk of cord injury. When cord injuries occur, most are neurologically complete. Of additional importance is the association between fractures of the thoracic spine and severe pulmonary injuries, including mediastinal hemorrhage. Patients with blunt chest trauma and mediastinal widening should be evaluated for both aortic and thoracic spine injuries. 4
The spine is divided into alternating mobile and fixed segments. The thoracolumbar junction (T11-L2) is considered a transitional zone between the fixed thoracic and mobile lumbar regions. This distinction is important because the transitional zones sustain the greatest amount of stress during motion. These areas are most vulnerable to traumatic injuries. In addition to this change in bony anatomy, the thoracolumbar junction serves as the level of transition from the end of the spinal cord (about L1) to the nerve roots of the cauda equina. Relative to the thoracic spine, the width of the spinal canal is greater. Despite a large number of vertebral injuries at the thoracolumbar junction, most are associated with normal neurologic exams or incomplete neurologic findings.
Relative to the thoracic and thoracolumbar regions, the lower lumbar spine is the most mobile. Isolated fractures of the lower lumbar spine rarely result in complete neurologic injuries. When neurologic injuries occur, they are usually complete cauda equina lesions or isolated nerve root injuries.
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