Upper Thoracic Spine Fracture Dislocation in a Motorcyclist

Abstract

A 23-year-old woman suffered multiple injuries after a high-speed motorcycle crash. Initial supine anteroposterior chest radiograph showed a widened mediastinum. This finding led to a computed tomography (CT) angiogram that revealed a normal aorta, but disclosed upper thoracic spine fractures and paraspinal hematoma. Subsequent dedicated thoracic spine CT demonstrated comminuted fractures of T4-T6, anterior wedging of the T4 vertebral body, transverse process fractures at T4 and T5, and expulsion of bony fragments into the right paraspinous tissues with resultant paraspinal hematoma. These findings are consistent with fracture-dislocation injury due to severe shearing forces. There was no retropulsion of bony fragments into the spinal canal and spinal cord injury was not present. Additional CT findings included spinous process fractures of C6-T1. Fractures of the upper thoracic vertebrae require considerable force due to the stiffness and structural support provided by the anterior and posterior longitudinal ligaments, ligamentum flavum, and articulations with the ribs. Fracture dislocations are usually the result of shearing or rotational forces combined with significant flexion and axial loading. 1 As in this case, upper thoracic fracture dislocations are usually seen in motorcyclists and occur at the level of T4-T6. 2 Characteristic findings include anterior or lateral displacement of vertebral fragments above the level of injury and anterior wedging below the level of injury. Fractures of ribs and transverse processes are common associated findings due to the shearing forces. Fracture dislocations can be distinguished from burst fractures by the linear “windswept” appearance of bony fragments on CT scan, rather than a horizontal pattern of displacement. 3 This appearance is well demonstrated with coronal reformations from multidetection CT scanning (Fig 1). Fractures of the upper thoracic spine are also associated with other noncontiguous spinal fractures, often of the thoracolumbar or upper cervical spine, as in this case, necessitating a careful search for fractures when upper thoracic spine fractures are identified. 3 Spinal cord injury is common with upper thoracic spine fractures, with reported incidence of complete paraplegia in 80% of patients. A narrow spinal canal and limited vascular supply in the upper thoracic region contribute to neurologic injury in addition to the shear forces that cause vertebral fractures and retropulsion of bony fragments into the spinal canal. Upper thoracic spinal fracture dislocations without cord injury, as in this case, comprise a small minority of patients. 3 In the trauma setting, a widened mediastinum usually raises suspicion of traumatic aortic injury. Thoracic spine fractures are also a recognized cause of mediastinal widening, secondary to paraspinous hematoma or displaced bony fragments. Dennis and Rogers reported mediastinal widening in 69% of a series of patients with upper thoracic or lower cervical spine fractures. Among these patients, only 51% of fractures were identified on initial chest radiograph. 4 Motorcycle accidents tend to result in severe injuries and upper thoracic spine injury may not be readily apparent if the patient has concomitant cerebral, cervical, or major extremity trauma. An abnormal mediastinal contour on chest radiograph combined with the knowledge of mechanism of injury should prompt careful evaluation of the upper