There are typically 12 thoracic vertebrae, however, as with the coccyx, sacrum and lumbar spine, there can be variation here. According to Glass et al (2002) approximately 5% to 8% of people only have 11 pairs of ribs and 11 thoracic vertebrae. Yan et al (2018) reported that 6% of people have 11 thoracic vertebrae.
The thoracic vertebrae have thin discs compared to the lumbar region and longer spinous processes. The thoracic facets are generally oriented in the frontal plane. Kapandji (2010) states that the shape and the orientation of the superior and inferior facets typically allow for 20° of lateral flexion and 35° of rotation in the thoracic spine. For extension and flexion, the author groups the thoracic and lumbar spine together and states that 60° and 105° are the typical ranges of movement respectively. It is important to note that there is no consensus among researchers regarding the typical range of movement at various levels of the vertebral column, but the figures can serve to show that each section is designed to move differently.
Masharawi et al (2004) state that asymmetry in facet orientation is a normal characteristic in the thoracic spine and report that right thoracic facets are more vertically and frontally oriented than the left ones. They suggest that flexion or extension in the thoracic facets will be coupled with right lateral flexion, ending with a rotational movement.
References:
Glass, R., Norton, K., Mitre, S. and Kang, E. (2002) ‘Pediatric ribs: a spectrum of abnormalities.’ Radiographics 22, 1, 87–104.
Kapandji, I. (2010) The Physiology of the Joints. 6 th ed. London: Churchill Livingstone.
Yan, Y., Li, Q., Wu, C., Pan, X. et al. (2018) ‘Rate of presence of 11 thoracic vertebrae and 6 lumbar vertebrae in asymptomatic Chinese adult volunteers.’ J Orthop Surg Res 13, 124.
Masharawi, Y., Rothschild, B., Dar, G., Peleg, S. et al. (2004) ‘Facet orientation in the thoracolumbar spine: three-dimensional anatomic and biomechanical analysis.’ Spine 29, 16, 1755-63.
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