One of the first things to remember is that the thoracic spine is comprised of 12 vertebrae. These vertebrae have similar characteristics of the other vertebrae: a vertebral body (disk to vertebral body height ratio is 1:5), pedicles directed posterior from the body, lamina that connect to form a spinous process, and facets (Neumann, 2010). The transverse processes are directed posterolaterally and the spinous processes fall inferiorly (depending on the region), so that they are at the level of the transverse processes below. This is an important consideration for palpation. T1-3 and T10-12 actually have their spinous processes at the same level as the transverse processes (Egan et al, 2011). The spinous processes of T4-T6 fall half a level below the transverse processes, while T7-9 spinous processes fall a full level below the transverse processes. The pedicles actually sit directly posterior from the vertebral body, making the vertebral canal narrower here compared to other parts of the spine. T4-9 is known as the critical zone because the vertebral canal is narrowest here; it also has reduced blood supply (Egan et al, 2011). T6 is a tension point; here motion of the spinal core versus canal converge in different directions. The superior and inferior facets in the thoracic region are oriented about 60 degrees from the horizontal plane and 20 degrees from the frontal plane with the inferior facets facing anteriorly, inferiorly, and slightly medially; the superior facets face posteriorly, superiorly, and slightly lateral. Something to consider is that there is no immediate change between cervical to thoracic vertebrae and thoracic to lumbar vertebrae. The superior thoracic vertebrae bare qualities similar to the cervical spine and the inferior thoracic vertebrae resemble the lumbar spine.
You cannot discuss the thoracic spine without considering the ribs as they attach in this region. There are 12 ribs (usually) in the body, just as there are 12 thoracic vertebrae. Ribs 1-7 are true ribs in that they attach directly to the sternum in the front of the body (Neumann, 2010). Ribs 8-12 are false ribs. Ribs 8-10 join in cartilage before attaching to the cartilage of the 7th rib. Ribs 11 and 12 are floating ribs and have no ventral attachments. Ribs 3-9 have demifacets on the thoracic vertebrae for attachment that span 2 vertebrae. Ribs 1, 11, and 12 have one facet on the corresponding vertebrae. The 2nd rib attaches to both T1 and T2 vertebrae. Additionally, ribs 1-10 have facet attachments at the costotransverse joints, while ribs 11-12 lack these as "floating ribs." Above T7, the rib portion of the costotransverse joints are concave, allowing for more rotation compared to the planar joints of the below T7 (Egan et al, 2011). The sympathetic chain lies on the anterior side of the rib heads next to the costovertebral joints.
As stated previously, the fact that the thoracic spine connects the cervical spine to the lumbar spine is reason alone that this anatomical area should be considered for treatment. Think about the impact of posture. In most patients that sit for prolonged periods with a forward head posture, the anterior shift of the center of gravity places an excessive flexion moment arm to the thoracic spine, furthering the already kyphotic thoracic spine. As with any tissue, prolonged stress and creep eventually leads to pain when the tensile stiffness is no longer sufficient and the patient experiences pain. Training postural muscles is key to encouraging a more neutral posture that does not stress the tissues excessively. Consider facet restrictions: Limited joint mobility in one location often leads to hypermobility and pain in other regions, either nearby or distant. A joint dysfunction can often lead to hypertonic/painful muscle tissue near the joint as well. We can treat these restrictions with manual therapy. Two conditions less commonly discussed but seen relatively often include rib dysfunction and neural tension. Rib impairments are typically considered after a blow to the side or pain with breathing, but that is not always the case (making it harder to identify). A partially subluxed or restricted rib can be quite painful and present as thoracic paraspinal pain or even stomach pain as the tip of a floating rib presses against the anterior tissue. A potential location for pathology and treatment of neural tension is the thoracic spine. Remember that the thoracic spine contains the critical zone where the vertebral canal is narrowest. The spinal cord can easily become compressed here leading to pain/neural tension along the path of a nerve. A nerve can become irritated anywhere in the body. With the thoracic restrictions, a manipulation to the mid-thoracic spine often improves pain and neural tension by improving mobility. Think of it as a reset button as it also may have an impact on the sympathetic nervous system.
Egan W, Burns S, Flynn T, and Ojha H. The Thoracic Spine and Rib Cage: Physical Therapy Patient Management Utilizing Current Evidence. Current Concepts of Orthopaedic Physical Therapy, 3rd Ed. La Crosse, WI. 2011.
Neumann, Donald. Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation. 2nd edition. St. Louis, MO: Mosby Elsevier, 2010. 322-323. Print.