Spinal Anatomy

The vertebral column is situated in the median line, as the posterior part of the trunk. It (backbone) consists of a series of 26 individual irregular bones called vertebrae, separated by fibrocartilaginous intervertebral discs and are secured to each other by interlocking processes and binding ligaments. There are 7 cervical, 12 thoracic, 5 lumbar, 5 fused sacral, and 4-5 fused coccygeal vertebrae (1-8). The vertebrae in the upper three regions of the column are known as true or movable vertebrae. Vertebrae enclose and protect the spinal cord, support the head and upper extremities while permitting freedom of movement, articulate with the rib cage, and provide for the attachment of various muscles and visceral organs (5,9,10). The fibrocartilaginous intervertebral discs lend flexibility to the vertebral column and absorb vertical shock. This structural arrangement permits limited movement between adjacent vertebrae but extensive movement for the vertebral column. The lateral opening windows between the vertebrae are called intervertebral foramina that allow passage of spinal nerves (10,11). The vertebral column contains several important anatomical curves. Viewed laterally, the cervical, thoracic, lumbar curves are designated by the type of vertebrae they include (Figure 1). The cervical curve begins from apex of the odontoid process, continues to the middle of the second thoracic vertebra. The thoracic curve begins from middle of the 2nd vertebra and continues to the middle of the 12th thoracic vertebra. The lumbar curve begins at the middle of the last thoracic vertebra, ends at the sacrovertebral angle. The pelvic curve (sacral curve) is formed by the shape of the sacrum and coccyx. The curves play an important functional role in increasing the strength and maintaining the balance of the upper part of the body. These spinal curves also make possible a bipedal stance. The four vertebral curves are not present in an infant. First, the cervical curve begins to develop at about 3-4 months. The lumbar curve develops as a child begins to walk. The vertebral canal follows the different curves of the column (3,5,6,10-12).