Figure 1 - The spine in profile.

 

The spine has the important function of supporting the man standing, in a erect posture, by constituting the main axis of the human body, receiving the most weight and projecting its cargo in the lower limbs.

The spine comprises the whole bone wrap - the vertebrae, separated by a fibrocartilaginous tissue - the intervertebral discs, ligaments and muscles that protect a very delicated tissue - the spinal cord through which nerve impulses from the brain to the trunk and limbs.

From the spinal cord leave the nerve roots and the nerves that carry information to the muscles, skin and internal organs. Diseases that affect the column can affect the spinal cord, nerve roots and nerves, and many of its symptoms are explained by this fact. The opposite is also possible, with diseases of the spinal cord and nerve roots causing deformities in the column. In both situations it is necessary specialized evaluation.

The spine has seven cervical vertebrae (C1-C7), twelve thoracic (T1-T12), five lumbar (L1-L5), five fused sacral bone in the sacrum (S1-S5) and five coccygeal waste. Between the vertebrae in the cervical, dorsal and lumbar, intervertebral discs are a total of twenty-three.

Figure 2 - The spine showing its three major curves

Normally, the spine has three bends. In the cervical (A) and lumbar regions (C) occur the so-called lordosis - Previous convex curvature, and in the thoracic region (B) occurs kyphosis - the one with anterior concavity.

It can be noticed that the size of the vertebral body increases as the load weight increases. Thus, the cervical vertebrae that support the head and the neck are smaller than the lower vertebrae that support the upper body.

There are five types of vertebrae classified according to location: cervical, thoracic, lumbar, sacral and coccygeal. In general, dorsal and lumbar cervical vertebrae have anatomical features in common. These elements are the vertebral body and the arch formed by the pedicle laminae and by transverse spinal processes.

Figure 3 - Design of the intervertebral disc and vertebral body seen from above (axial).

Figure 4 - Detail of the column, showing two lumbar vertebrae separated by intervertebral disc, in flexion and extension, revealing the movement allowed.

The vertebral body is the most anterior component of the column, presenting an appearance of a flat cylinder with a flat upper and lower surface called vertebral plateau. The intervertebral discs are found between these flat faces, which are discoid portions of fibrocartilaginous tissue and provide a link between the vertebral bodies.

The structure of the discs usually has a degenerative change in early adulthood and it is the major cause of back pain. This structure consists of an annulus fibrosus that surrounds a jelly-like substance called the nucleus pulposus. The annulus fibrosus may present weakening and lead to the called herniated intervertebral disc, resulting in compression of nerve roots, causing pain and neurological deficits.

The vertebrae also have a posterior bone-shaped arch component. This arch united with the vertebral body encloses the vertebral canal, which pass the spinal cord and nerve roots. With the juxtaposition of the vertebrae to form the spine, the vertebral foramen originate the exit place of the nerve roots.

Figure 5 - Design of the lumbar vertebra showing the posterior arch, formed by the lamina and bone eminences.

The posterior arch is formed by the lamina and bone eminences. The lateral eminences are called transverse processes and the medial eminence is called the spinous process. The spinous processes are visible on inspection of the dorsal region and can be easily palpated in most cases.

Connecting the lamina to the body is a bridge of bone called the pedicle, among which are the vertebral foramina or conjugation. The laminae leave the superior and inferior articular processes, transverse processes and spinous process. In addition to the intervertebral discs, the vertebrae, throughout the spine, are united by several ligaments which are inserted into the vertebral bodies in the apophyses and the laminae. There are also ligaments that attach the skull to the first cervical vertebrae and the sacrum and lower lumbar vertebrae to the pelvic bones.

 

		The major ligaments of the spine are:: Anterior longitudinal ligament; Posterior longitudinal ligament; Yellow ligament / Ligamentum flavum; Supraspinous ligament; Interspinous ligament.
Figure 6 - Design of the lumbosacral column, showing the anterior and posterior stabilizing ligaments and the exit of the nerve roots through the intervertebral holes, the sacrum and coccyx.

Figure 7 - Cervical Vertebra

Differences between the vertebrae

There are differences between the vertebrae of different levels. The cervical vertebrae have smaller bodies and, in their transverse processes, there is a foramen which passes the vertebral artery that runs to the posterior portion of the brain. The spinous processes of the cervical region have two eminences called tubercles. The foramen of the transverse process, where is the vertebral artery, only occurs in the cervical vertebrae.

Figure 8 - Thoracic Vertebra

In the thoracic region the vertebrae, besides articulating with its neighboring vertebrae, they also have articular surfaces for the ribs. This joint is very important for the formation of the rib cage. The joints of the facet joints with the ribs characterize the thoracic vertebrae.

Figure 9 - Lumbar Vertebra

The vertebral bodies get larger as you move down to meet the sacrum bone. In the lumbar region the spinous processes have a more horizontal orientation in relation to the levels above where they have a downward slope.

Atypical Vertebrae

Atlas and Axis

Figure 10 - Atlas

In addition to the typical vertebrae it is possible to meet special situations. The first two cervical vertebra have different characteristics. The first vertebra, called Atlas, holds the head. In its shape there are two lateral bony masses connected by an anterior and posterior bony arch. It is linked to the occipital bone through two condylar joints. The joints are located in the lateral masses. This joint is limited, because of the little movement that can be obtained from it.

The other atypical cervical vertebra is called Axis, because it has a bony eminence that acts as an axis. This process is called the odontoid and is connected to the Atlas through a joint like a pivot or trochoid. The odontoid process is affirmed by the Atlas in its anterior portion by firmly ligaments, the alar ligaments and trapezoids. Both C1 and C2 have the foramina in the transverse processes to the vertebral arteries.

Figure 11 - Axis

The particularity of this type of joint is that it allows large movements of head rotation by the presence of this central axis bone. In addition to the portion of the odontoid, the second vertebra (axis) has a similar format to the other cervical vertebrae. It is common in column traumatisms that occurs the separation, by fracture, of the odontoid bone of the body axis. This situation can be serious when it causes displacement and compression of the spinal cord.

Sacrum and Coccyx

In the sacral region, the vertebrae also have atypical characteristics. Usually, five sacral vertebrae are fused into a large and compact bone called the sacrum. This bone still has a spinal canal in its interior (sacrum canal), but the vertebral bodies and laminae are fused.

Figure 12 – Sacrum and coccyx

The sacrum is shaped with a curve of anterior concavity and contributes to the formation of the posterior limit of the pelvic cavity. There is a sharp angle that the spine undergoes at the junction between the last lumbar vertebra and the sacrum, called the promontory.

In the pelvic and dorsal sides there are four pairs of foramina. At the lower end of the outer face there is a hole in the shape of inverted "V", which is called the sacral hiatus at the end of the vertebral canal.

Similarly, four or five coccygeal vertebrae are fused in a small residual bone in man, without the formation of a center canal, called the coccyx.