The differences in the regional characteristics of the thoracic spine result in a variety of developmental and postural deformities, fracture types, and joint dysfunctions. The cervicothoracic and thoracolumbar transitional regions are prone to specific mechanical problems, because these areas represent the junctions between the flexible cervical and lumbar spines with the less flexible thoracic spine.
Radiographically, almost all features of the thoracic spine are accountable on the anteroposterior (AP) and lateral views. The sternum and ribs are assessed on their own separate radiographic evaluations. They are included in this chapter as associated articulations often involved in injury, disease, and developmental abnormalities related to the thoracic spine.
The bones of the thorax include the 12 thoracic vertebrae, 24 ribs, and the sternum. The thorax forms a protective cage to house the heart, lungs, and upper abdominal viscera. The articulations of the thorax allow for flexibility to accommodate the actions of respiration and trunk mobility. Additionally, the thorax provides stability for movements of the neck and upper extremities.
Thoracic vertebrae are positioned in a convex posterior (kyphotic) curve spanning from 20 to 40 degrees of arc in the sagittal plane (Fig. 9-1). Mild lateral curves <10 degrees are commonly noted and are believed to be related to hand dominance. The upper thoracic vertebrae, T1–T4, exhibit some of the characteristics of cervical vertebrae, and the lower thoracic vertebrae, T9–T12, exhibit some of the characteristics of lumbar vertebrae. These transitional vertebrae are often referred to as components of the cervicothoracic and thoracolumbar regions, respectively. The vertebrae considered to be typical thoracic vertebrae are T5–T8.
Contrast-enhanced CT study of the body, obtained in one exam in less than 17 seconds. On the left is a three-dimensional reformatted image display showing the skeleton and organs. In the middle is a two-dimensional sagittal reformatted image displayed in a mediastinal window, meaning that both contrast-enhanced soft tissues and bone are displayed. On the right is an image that looks like a conventional radiograph but is a sagittal reformation of the osseous spine. (Image courtesy of Toshiba Medical Systems, Europe.)
Thoracic vertebrae have shield-shaped vertebral bodies; paired superior and inferior costal demifacets on the posterolateral surfaces of the bodies; round vertebral foramina and stout pedicles; short, thick laminae that partially overlap adjacent laminae in a shingle effect; long and downwardly inclined spinous processes; and long and posterolaterally inclined transverse processes with costal facets at the tips (Figs. 9-2 and 9-3). The paired superior and inferior articular processes form zygapophysial joints (facet joints) with adjacent vertebrae. Typical thoracic facet joints are oriented vertically in the frontal plane, although the upper thoracic facets gradually approach the angled coronal cervical facet orientation, and the lower thoracic facets gradually approach the sagittal lumbar facet orientation. Twelve pairs of spinal nerves exit the intervertebral foramina formed by coadjacent pedicles.
Typical thoracic vertebra, superior view.
Typical thoracic vertebrae, lateral view.