92


PART II THE VERTEBRAL COLUMN


Note to Students: It is recommended that you review the pretest questions before reading the chapter to better understand the critical elements of the text. As you complete each section, stop and answer the corresponding questions to test your comprehension. The pretest does not cover all the material in each chapter and should not be used as a sole means of self-assessment of knowledge.


The spine provides both mobility for functional move- ment of the human body and stability required for verti- cal support of the torso. The spine transmits and absorbs forces between the upper and lower extremities while pro- tecting the spinal cord. The anterior portion of the spinal column consists of the vertebral bodies and intervertebral discs, weight-bearing surfaces that provide shock absorp- tion and mobility in various directions. The posterior section of the spinal column protects the spinal cord; guides and limits motion; and, through elongation of muscles over the bony segments, increases the mechani- cal advantage of the muscles. This chapter fi rst outlines the general characteristics and structures of the bony, joint, and ligamentous structures of the spine. It then discusses characteristics specifi c to the various regions of the spine and then describes the skeletal muscles of the spine and their function.


SPINAL STRUCTURES


The spine consists of 33 vertebrae and 23 intervertebral discs. There are 7 cervical, 12 thoracic, 5 lumbar, 5 fused sacral, and 4 fused coccygeal vertebrae. Vertebrae are numbered and referred to by the letter representing the specifi c region in which they are located and the number of their order within that region. For example, the second cervical vertebra is identifi ed as C2, and the fi fth lumbar vertebra is identifi ed as L5 (Fig. 5.1). The structures that make up the spine have many similarities, but there are regional differences. The examination of the spine begins with structures that tend to be similar throughout the spine before focusing on differences associated with each individual region.


SPINAL CURVES


In utero and at birth, a newborn displays a single spinal curve. This single curve, which is convex posteriorly and concave anteriorly, is a kyphotic curve and is classifi ed as a primary curve. As the infant begins to lift the head against gravity while in a prone position, a secondary lor- dotic curve develops in the cervical spine. This second- ary curve is convex anteriorly and concave posteriorly. Development continues as the infant gains the ability to assume and maintain a quadruped position for crawling, producing a lumbar lordotic curve (Fig. 5.2A). In an adult, there are four curves—cervical lordosis, thoracic


Figure 5.1 Vertebral regions of the spine. The spine consists of five regions: cervical, thoracic, lumbar, sacral, and coccygeal. (From Roy S, Wolf SL, Scalzitti DA. The Rehabilitation Specialist’s Handbook, 4th ed. Philadelphia, PA: F. A. Davis Company, 2013: p. 46, with permission.)


kyphosis, lumbar lordosis, and sacrococcygeal kyphosis (Fig. 5.2B). These curves assist the spine by resisting compressive loads when placed under stress. The curved spine, in contrast to a straight column, can fl ex and bend in response to the forces acting on it.


VERTEBRAE Bony Structures


Most of the vertebrae—the bony units of the spine— consist of an anterior vertebral body that is the weight- bearing structure of the bone and a posterior neural arch (Fig. 5.3). The vertebral foramen is a large opening posterior to the vertebral body that functions as a canal through which the spinal cord passes down the length of the vertebral column. The vertebral body is connected to the posterior portion of the vertebrae by the neural arch, which can be further separated into a bony pedicle, one on each side, and the posterior elements. The pedicles trans- mit forces generated by trunk muscles and by positions


1 2


3 4 5


6 7 1 2 3 4


5 6


7 8 9 10 11


12 1


2 3


4 5


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