Which curvatures are convex anterior

The sacral cornu are bony prominences on each side of the hiatus that are easily palpated in small children and serve as landmarks for a caudal epidural block. For more information, see Caudal Anesthesia. The vertebral column is stabilized by a series of ligaments. The anterior and posterior longitudinal ligaments run along the anterior and posterior surfaces of the vertebral bodies, respectively, reinforcing the vertebral column. The supraspinous ligament, a heavy band that runs along the tips of the spinous processes, becomes thinner in the lumbar region Figure 5.

This ligament continues as the ligamentum nuchae above T7 and attaches to the occipital external protuberance at the base of the skull. The interspinous ligament is a narrow web of tissue that attaches between spinous processes; anteriorly it fuses with the ligamentum flavum and posteriorly with the supraspinous ligament Figure 5. The ligamentum flavum is a dense, homogenous structure, composed mostly of elastin which connects the lamina of adjacent vertebrae, Figure 5.

The lateral edges of the ligamentum flavum surround facet joints anteriorly, reinforcing their joint capsule. When a needle is advanced toward the epidural space, there is an easily perceptible increase in resistance when the ligamentum flavum is encountered. More importantly for the practice of neuraxial anesthesia, a perceptible, sudden loss of resistance is encountered when the tip of the needle passes through the ligamentum and enters the epidural space.

Importantly, this midline fusion may be absent to a variable degree depending on the vertebral level. These fusion gaps allow for veins to connect to vertebral venous plexuses. Of note, the fusion gaps are more prevalent at cervical and thoracic levels.

In theory, a midline gap poses a risk of failure to recognize a loss of resistance at the cervical and high thoracic levels when using the midline approach, resulting in an inadvertent dural puncture. The ligamentum flavum is thinnest in the cervical and upper thoracic regions and thickest in the lower thoracic and lumbar regions. As a result, resistance to needle advancement is easier to appreciate when a needle is introduced at a lower level eg, lumbar.

At the L2—L3 interspace, the ligamentum flavum is 3- to 5-mm thick. At this level, the distance from the ligamentum to the spinal meninges is 4—6 mm.

Consequently, a midline insertion of an epidural needle at this level is least likely to result in an inadvertent meningeal puncture with epidural anesthesia-analgesia. The lateral wall of the vertebral canal has gaps between consecutive pedicles known as intervertebral foramina Figure 1A. Because the pedicles attach more cephalad of the middle of the vertebral body, the intervertebral foramina are centered opposite the lower half of the vertebral body, with the vertebral disk at the caudal end of the foramen.

As a consequence, the borders of the intervertebral foramina are the pedicle at the cephalad and caudal ends, the vertebral body cephalad and the disk caudally on the anterior aspect, a portion of the next vertebral body most inferiorly, and posteriorly the lamina, facet joint, and ligamentum flavum.

The spinal cord is an extension of the medulla oblongata. It has three covering membranes: the dura, arachnoid, and pia maters Figure 6A. These membranes concentrically divide the vertebral canal into three distinct compartments: the epidural, subdural, and subarachnoid spaces. The subdural compartment is formed by flat neuroepithelial cells that have long interlacing branches.

These cells are in close contact with the inner dural layers. This space can be expanded by shearing the neuroepithelial cell layer connections with the collagen fibers of the dura mater. This expansion of the subdural space can be caused mechanically by injecting air or a liquid such as contrast media or local anesthetics, which, by applying pressure in the space, separates the cell layers. The subarachnoid space is traversed by threads of connective tissue extending from the arachnoid mater to the pia mater.

It contains the spinal cord, dorsal and ventral nerve roots, and cerebrospinal fluid CSF. The subarachnoid space ends at the S2 vertebral level. There are eight cervical neural segments. The eighth segmental nerve emerges between the seventh cervical and first thoracic vertebrae, whereas the remaining cervical nerves emerge above their same-numbered vertebrae. Thoracic, lumbar, and sacral nerves emerge from the vertebral column below the same-numbered bony segment1 Figure 6A.

Anterior and posterior spinal nerve roots arise from rootlets along the spinal cord. The roots of the upper and lower extremity plexuses brachial and lumbosacral are significantly larger compared to other levels. The dural sac is continuous from the foramen magnum to the sacral region, where it spreads distally to cover the filum terminale. In children, the dural sac terminates lower, and in some adults, the sac termination can be as high as L5.

The vertebral canal contains the dural sac, which adheres superiorly to the foramen magnum, to the posterior longitudinal ligament anteriorly, the ligamentum flavum and laminae posteriorly, and the pedicles laterally.

The spinal cord tapers and ends as the conus medullaris at the level of the L1—L2 intervertebral disk Figure 7A. The filum terminale, a fibrous extension of the spinal cord, extends caudally to the coccyx. Each pedicle forms one of the lateral sides of the vertebral arch. The pedicles are anchored to the posterior side of the vertebral body. Each lamina forms part of the posterior roof of the vertebral arch.

The large opening between the vertebral arch and body is the vertebral foramen , which contains the spinal cord. In the intact vertebral column, the vertebral foramina of all of the vertebrae align to form the vertebral spinal canal , which serves as the bony protection and passageway for the spinal cord down the back.

When the vertebrae are aligned together in the vertebral column, notches in the margins of the pedicles of adjacent vertebrae together form an intervertebral foramen , the opening through which a spinal nerve exits from the vertebral column Figure 7. Seven processes arise from the vertebral arch. Each paired transverse process projects laterally and arises from the junction point between the pedicle and lamina. The single spinous process vertebral spine projects posteriorly at the midline of the back.

The vertebral spines can easily be felt as a series of bumps just under the skin down the middle of the back. The transverse and spinous processes serve as important muscle attachment sites.

A superior articular process extends or faces upward, and an inferior articular process faces or projects downward on each side of a vertebrae. The paired superior articular processes of one vertebra join with the corresponding paired inferior articular processes from the next higher vertebra. These junctions form slightly moveable joints between the adjacent vertebrae.

The shape and orientation of the articular processes vary in different regions of the vertebral column and play a major role in determining the type and range of motion available in each region. In addition to the general characteristics of a typical vertebra described above, vertebrae also display characteristic size and structural features that vary between the different vertebral column regions.

Thus, cervical vertebrae are smaller than lumbar vertebrae due to differences in the proportion of body weight that each supports. Thoracic vertebrae have sites for rib attachment, and the vertebrae that give rise to the sacrum and coccyx have fused together into single bones. Typical cervical vertebrae , such as C4 or C5, have several characteristic features that differentiate them from thoracic or lumbar vertebrae Figure 7. Cervical vertebrae have a small body, reflecting the fact that they carry the least amount of body weight.

Cervical vertebrae usually have a bifid Y-shaped spinous process. The spinous processes of the C3—C6 vertebrae are short, but the spine of C7 is much longer. You can find these vertebrae by running your finger down the midline of the posterior neck until you encounter the prominent C7 spine located at the base of the neck. The transverse processes of the cervical vertebrae are sharply curved U-shaped to allow for passage of the cervical spinal nerves. Each transverse process also has an opening called the transverse foramen.

An important artery that supplies the brain ascends up the neck by passing through these openings. The superior and inferior articular processes of the cervical vertebrae are flattened and largely face upward or downward, respectively.

The first and second cervical vertebrae are further modified, giving each a distinctive appearance. The first cervical C1 vertebra is also called the atlas , because this is the vertebra that supports the skull on top of the vertebral column in Greek mythology, Atlas was the god who supported the heavens on his shoulders. The C1 vertebra does not have a body or spinous process.

Instead, it is ring-shaped, consisting of an anterior arch and a posterior arch. The transverse processes of the atlas are longer and extend more laterally than do the transverse processes of any other cervical vertebrae. The superior articular processes face upward and are deeply curved for articulation with the occipital condyles on the base of the skull.

The inferior articular processes are flat and face downward to join with the superior articular processes of the C2 vertebra. The second cervical C2 vertebra is called the axis , because it serves as the axis for rotation when turning the head toward the right or left.

The axis resembles typical cervical vertebrae in most respects, but is easily distinguished by the dens odontoid process , a bony projection that extends upward from the vertebral body.

The dens joins with the inner aspect of the anterior arch of the atlas, where it is held in place by transverse ligament. The bodies of the thoracic vertebrae are larger than those of cervical vertebrae Figure 7. The characteristic feature for a typical midthoracic vertebra is the spinous process, which is long and has a pronounced downward angle that causes it to overlap the next inferior vertebra. The superior articular processes of thoracic vertebrae face anteriorly and the inferior processes face posteriorly.

These orientations are important determinants for the type and range of movements available to the thoracic region of the vertebral column. Thoracic vertebrae have several additional articulation sites, each of which is called a facet , where a rib is attached. These are for articulation with the head end of a rib. An additional facet is located on the transverse process for articulation with the tubercle of a rib.

Lumbar vertebrae carry the greatest amount of body weight and are thus characterized by the large size and thickness of the vertebral body Figure 7. They have short transverse processes and a short, blunt spinous process that projects posteriorly.

The articular processes are large, with the superior process facing backward and the inferior facing forward. The sacrum is a triangular-shaped bone that is thick and wide across its superior base where it is weight bearing and then tapers down to an inferior, non-weight bearing apex Figure 7.

It is formed by the fusion of five sacral vertebrae, a process that does not begin until after the age of On the anterior surface of the older adult sacrum, the lines of vertebral fusion can be seen as four transverse ridges. Similarly, the fused transverse processes of the sacral vertebrae form the lateral sacral crest. The sacral promontory is the anterior lip of the superior base of the sacrum.

Lateral to this is the roughened auricular surface, which joins with the ilium portion of the hipbone to form the immobile sacroiliac joints of the pelvis. Passing inferiorly through the sacrum is a bony tunnel called the sacral canal , which terminates at the sacral hiatus near the inferior tip of the sacrum. Each of these openings is called a posterior dorsal sacral foramen or anterior ventral sacral foramen.

These openings allow for the anterior and posterior branches of the sacral spinal nerves to exit the sacrum. The superior articular process of the sacrum , one of which is found on either side of the superior opening of the sacral canal, articulates with the inferior articular processes from the L5 vertebra.

The coccyx, or tailbone, is derived from the fusion of four very small coccygeal vertebrae see Figure 7. It articulates with the inferior tip of the sacrum. It is not weight bearing in the standing position, but may receive some body weight when sitting. When viewed from the front, the healthy spine is straight.

Viewed from the side, the mature spine has four distinct curves. These normal spinal curves are described as being either kyphotic or lordotic. A kyphotic curve is a convex curve in the spine i. The curves in the thoracic and sacral spine are kyphotic. A lordotic curve is concave i. George A. Frey focuses his medical practice on the treatment of all complex spine problems affecting the cervical, thoracic, and lumbar regions in adult and pediatric patients.