Applied anatomy of the thorax and abdomen

The thoracic spine has a primary dorsal convexity (Fig. 1) associated with intrauterine life – a phylogenetic kyphosis – whereas the cervical and lumbar spine have a compensatory lordosis. The 12 thoracic vertebrae are intermediate in size between those in the cervical and lumbar regions. They are composed of a vertebral body – a cylindrical ventral mass of bone – continuing posteriorly into a vertebral arch (Fig. 2). The typical thoracic vertebral body is heart-shaped in cross-section and has on each of its lateral aspects a superior and inferior costal facet for articulations with the ribs (costovertebral joints). The arch is constructed out of two pedicles and two short laminae, the latter uniting posteriorly to form the spinous process. Laminae and spinous processes lie obliquely covering each other like the tiles of a roof, so protecting the posterior cord posteriorly. The pedicles carry the articular and transverse processes. The posterior aspect of the vertebral body and the arch enclose the vertebral foramen. The spinal cord at the thoracic level is rounder and smaller than at the cervical level, and in consequence the vertebral foramina are also smaller. Where the pedicles and laminae unite the transverse process is found, slightly posterior to the articular process, pedicle and intervertebral foramen. There is also an oval facet for the ribs on all the transverse processes, except for T11 and T12, to which ribs are not attached. The spinous processes at mid-thorax are long and very steeply inclined: each transverse process is at a level one and a half vertebrae higher than the tip of the corresponding spinous process. In the upper and lower thorax, the spinous processes are less inclined; here, the corresponding transverse process is located approximately one level higher. The oval intervertebral foramina are located behind the vertebral bodies and between the pedicles of the adjacent vertebrae and contain the segmental nerve roots. In the thoracic spine, these are situated mainly behind the inferoposterior aspect of the upper vertebral body and not just behind the disc. This makes a nerve root compression by a posterolateral displacement less likely at the thoracic level, whereas at the lumbar level nerve root compressions by posterolateral disc protrusions are quite common (Fig. 3, see Standring, Fig. 42.27). The location of the intervertebral foramen depends on the level. In the upper and lower thoracic area, it is level with the tip of the spinous process of the vertebra above, i.e. level above. At mid-thorax there is a difference of about 12 levels.