39 Neuraxial Block Anatomy

Neuraxial blocks—spinal, epidural, and caudal—are the most widely used regional blocks. The main reasons for their popularity are that neuraxial blocks have well-defined end points and the anesthesiologist can produce the blocks reliably with a single injection. The first step in being able to use neuraxial blocks effectively is to gain an understanding of neuraxial anatomy.

To understand the neuraxial anatomy it is necessary to develop a concept of the relationship between surface and bony anatomy pertinent to the neuraxial structures (Fig. 39-1). Beginning cephalad, the spinous process of the seventh cervical vertebra, the vertebral prominence, is the most prominent midline structure at the base of the neck. A line drawn between the lower borders of the scapula crosses the vertebral axis at approximately the spinous process of T7. The lower extent of the spinal cord, the conus medullaris, ends in the adult at approximately L1. (In the infant the conus medullaris may extend to L3.) The line between the iliac crests (Tuffier’s or the intercrestal line) most often crosses through the spinous process of L4. A line drawn between the posterior superior iliac spines identifies the level of the second sacral vertebra and the caudal extent of the dural sac containing cerebrospinal fluid (CSF).

Figure 39-1. Neuraxial anatomy: surface relationships.

The 33 vertebrae from C1 to the tip of the coccyx have a number of common features as well as differences that should be highlighted. Each vertebra contains a spinous process joined to the lamina, from which a transverse process extends laterally into both lamina and pedicle. The pedicle joins this posterior assembly to the vertebral body, which relates to the neighboring vertebral bodies through both superior and inferior facet joints (Fig. 39-2). Figure 39-3 outlines the general relationship of these structures at levels that correspond to common sites for cervical, thoracic, and lumbar punctures of the neuraxis.

Figure 39-2. Neuraxial anatomy: lumbar vertebra.

Figure 39-3. Neuraxial anatomy: vertebral column relationships.

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