The 12 vertebrae of the thoracic spine form a curve that is convex posteriorly (Fig. 12.1A). This sagittal plane curve is referred to as the thoracic kyphosis, which ranges from 20 to 50 degrees when assessed radiographically.1 The vertebrae composing the curve have a number of unique features. Spinous processes slope inferiorly from T1 to T10 and overlap from T5 to T8, whereas the spinous processes of T11 and T12 take on the horizontal orientation of the lumbar region’s spinous processes. The transverse processes from T1 to T10 are large, with thickened ends that support paired costal facets for articulation with the ribs. Paired demifacets (superior and inferior costovertebral facets), also for articulation with the ribs, are located on the posterolateral corners of the vertebral bodies from T2 to T9.
(A) A lateral view of the thoracic spine shows the spine's convex posterior sagittal plane curvature. The costal facets are visible on the enlarged ends of the transverse processes from T1 to T10 and the costovertebral facets can be seen on the lateral edges of the superior and inferior aspects of the vertebral bodies. The zygapophyseal joints are shown between the inferior articular facets of the superior vertebrae and the superior articular facets of the adjacent inferior vertebrae. (B) A superior view of a thoracic vertebra shows the articulations between the vertebra and the ribs: the left and right costovertebral joints, the costotransverse joints between the costal facets on the left and right transverse processes, and the costal tubercles on the corresponding ribs.
The intervertebral and zygapophyseal joints in the thoracic region have essentially the same structure as described for the cervical region, except that the superior articular zygapophyseal facets face posteriorly, somewhat laterally, and cranially. The superior articular facet surfaces are slightly convex, whereas the inferior articular facet surfaces are slightly concave. The inferior articular facets face anteriorly and slightly medially and caudally. In addition, the joint capsules are tighter than those in the cervical region.
The costovertebral joints are formed by slightly convex costal superior and inferior demifacets (costovertebral facets) on the head of a rib and corresponding demifacets on the vertebral bodies of a superior and an inferior vertebra (Fig. 12.1B). From T2 to T8, the costovertebral facets articulate with concave demifacets located on the inferior body of one vertebra and on the superior aspect of the adjacent inferior vertebral body. Some of the costovertebral facets also articulate with the interposed intervertebral disc, whereas the 1st, 11th, and 12th ribs articulate with only one vertebra. A thin, fibrous capsule, which is strengthened by radiate ligaments (see Fig. 12.1B) and the posterior longitudinal ligament, surround the costovertebral joints. An intra-articular ligament lies within the capsule and holds the head of the rib to the annulus pulposus.