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The design specification for the human vertebral column is the provision of structural stability affording full mobility as well as protection of the spinal cord and axial neural tissues.1 While achieving these seemingly disparate objectives, the spine also contributes to the functional requirements of gait and to the maintenance of static weight-bearing postures (see Chap. 6).1
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At the component level, the basic building block of the spine is the vertebra. The vertebra serves as the weight-bearing unit of the vertebral column, and it is well designed for this purpose. Although a solid structure would provide the vertebral body with sufficient strength, especially for static loads, it would prove too heavy and would not have the necessary flexibility for dynamic load bearing.2 Instead, the vertebral body is constructed with a strong outer layer of cortical bone and a hollow cavity, the latter of which is reinforced by vertical and horizontal struts called trabeculae.
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The term vertebral column describes the entire set of vertebrae excluding the ribs, sternum, and pelvis (Fig. 22-1). The normal vertebral column is made up of 29 vertebrae (7 cervical, 12 thoracic, 5 lumbar, and 5 sacral) and four coccygeal segments. The adage that “function follows form” is very much applicable when studying the vertebral column. Although all vertebrae have similar characteristics, each has specific details that reflect its unique function (Table 22-1). The overall contour of the normal vertebral column in the coronal plane is straight. In contrast, the contour of the sagittal plane changes with development. At birth, a series of primary curves give a kyphotic posture to the whole spine. With development of the erect posture, secondary curves develop in the cervical and lumbar spines, producing a lordosis in these regions. The curves in the spinal column provide it with increased flexibility and shock-absorbing capabilities.2
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A motion segment in the vertebral column is ...