The anatomy and sonoanatomy of the vertebral column vary between the cervical, thoracic, lumbar, and sacral spine, but the key anatomical landmarks are common to both landmark, two-dimensional (2D) and three-dimensional (3D) ultrasound-guided procedures. The bones of the vertebral column are well visualized in ultrasound imaging, but the ligaments and neural elements are less well seen.

The anatomical features of lumbar vertebrae can usually be well defined using ultrasound. The vertebral body supports the vertebral arch, which is made of the two pedicles and two laminae (Fig. 50.1 and 50.2). The posterior surface of the vertebral body and the vertebral arch enclose the vertebral foramen. Within the vertebral foramen are the targets for anesthetic interventions, the epidural and intrathecal spaces (Fig. 50.3). The processes supported by the vertebral arch form imporTant anatomical landmarks for imaging. The spinous processes mark the midline, and the articular processes mark the lateral limit of the lamina. Further lateral to the articular processes are the transverse processes, which are imporTant landmarks for paravertebral anesthesia (Fig. 50.3).

The identification of the vertebral anatomy forms the basis of a proposed systematic approach to the 2D examination (Table 50.1).¹ The examination begins laterally from the transverse processes and moves medially over the articular processes and laminae. The level for insertion is then determined by counting up from the sacrum or 12th rib. This approach is used to mark a needle insertion point and determine an angle of needle approach for neuraxial anesthesia, the so-called scan and mark approach.

The sequence of views acquired is less imporTant than the application of a systematic and efficient examination.

Between spinous processes of adjacent vertebrae run the thick cord of the supraspinous ligament and the membranous interspinous ligaments. During midline landmark-guided neuraxial procedures, the needle is passed through these ligaments into the ligamentum flavum, which runs between the laminae of adjacent vertebrae. Ultrasound imaging through these structures is usually poor because of their density, so neuraxial ultrasound is generally performed in a paramedian location with the probe directed obliquely toward the midline.

Identifying the space between the laminae of adjacent vertebrae using ultrasound is imporTant in identifying a suitable approach for needle insertion. The presence of a space between laminae can be confirmed by visualization of deeper structures. This “acoustic window” to deeper structures increases confidence that a needle can successfully be inserted between



the laminae. The posterior border of the vertebral body and intervertebral discs, which are covered by the posterior longitudinal ligament, are the deepest structures that can be seen between the laminae. (Fig. 50.3). The spinal cord or cauda equina can be seen in some patients, particularly children, through the vertebral foramen