Vertebral Column

Written by: Shatha Mallah, M.D.

Keywords: Vertebral column, spine, vertebrae, intervertebral discs, cervical, thoracic, lumbar, sacrum, coccyx, spinal cord, vertebral foramen, lordosis, kyphosis, scoliosis.

Overview

The vertebral column, also known as the spine or backbone, is a central structure of the human skeleton. It consists of 33 vertebrae that are divided into different regions: cervical, thoracic, lumbar, sacral, and coccygeal (Figure1). The vertebral column provides structural support for the body, houses and protects the spinal cord, and enables flexible movement of the trunk and neck. It also serves as the point of attachment for the ribs and muscles of the back and neck. The intervertebral discs between the vertebrae act as shock absorbers, while the curvature of the spine helps distribute weight and maintain balance.

Figure 1. Regions of the vertebral column. 

By Original: Arcadian Vector: Pixelsquid - Own work based on: Illu vertebral column.jpg:, Public Domain, https://commons.wikimedia.org/w/index.php?curid=97322815

Functions of the Vertebral Column

• Protection and support. 

• Body movements, from walking to bending.

• Conduit for the spinal cord, which transmits neural signals to the rest of the body.

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Structure of a Vertebra

Each vertebra consists of:

1. Body (Centrum):

   • The large, weight-bearing part of the vertebra. It is the main structure that bears the load of the body (Figure 2).

Figure 2. Superior view of the vertebra.

By Jmarchn - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=45613314

2. Vertebral Arch:

   • Surrounds the vertebral foramen (the space through which the spinal cord passes). The arch is made up of the pedicles and laminae (Figure 3).

Figure 3. Anatomy of the vertebra. Note that the laminae connect the pedicles to the transverse processes, and the pedicles connect the vertebral arch (transverse processes) to the body of the vertebra. Each vertebra has two pedicles and two laminae. Together they make the vertebral arch. 

3. Spinous Process:

   • A bony projection that can be felt through the skin, it serves as an attachment point for muscles and ligaments. Each vertebra has a single posteroinferiorly pointed spinous process (Figure 4).

Figure 4. Multiple views of vertebra. Note red circles around spinous processes. 

4. Transverse Processes:

   • Two bony projections on either side of the vertebra, which also serve as attachment points for muscles and ligaments. They extend posterolaterally from the vertebral body (Figure 5).

Figure 5. Multiple views of vertebra. Note blue circles around transverse processes. 

5. Articular Processes:

   • Superior articular processes: Project from the region where the pedicles join the laminae and articulate with the inferior articular processes of the vertebra above (Figure 6).

   • Inferior articular processes: Also project from the region where the pedicles join the laminae and articulate with the superior articular processes of the vertebra below (Figure 6).

Figure 6. Side view of the typical vertebra. Note the articulating inferior articular process of the above vertebra with the superior articular process of the below vertebra.

6. Intervertebral Discs:

   • Located between the bodies of adjacent vertebrae, these fibrocartilaginous structures act as shock absorbers, preventing vertebrae from rubbing against each other. The discs consist of an outer fibrous ring (annulus fibrosus) and a gel-like center (nucleus pulposus) (Figure7).

Figure 7. Superior view of intervertebral disc structure.

Structure of the Vertebra Column:

The vertebral column is composed of:

1. Cervical Region (Neck):

   • Composed of 7 cervical vertebrae (C1–C7), this region supports the head and allows for neck movement. The first cervical vertebra, called the atlas (C1), supports the skull (Figure 8), while the second vertebra, called the axis (C2), allows rotation of the head (Figure9).

   • The cervical vertebral body is especial in that it is shorter in height and square shaped when viewed from above and has a concave superior surface and a convex inferior surface (Figure 10).

   • Each transverse process is perforated by a round foramen transversarium through which the vertebral arteries travel to the brain (Figure 10).

   • The spinous process is short and bifid (except C1 - no spinous process and C7- longer spinous process and may not bifurcate) (figure 10)

   • The vertebral foramen is triangular (Figure 10).

Figure 8. The atlas (C1) lacks a vertebral body and composed of two lateral masses interconnected by an anterior arch and a posterior arch. Each lateral mass connects above to an occipital condyle of the skull via its superior articular facet and below with the superior articular process of vertebra CII (the axis). The atlanto-occipital joint allows the head to flex and extend up and down on the vertebral column.

Figure 9. Atlanto-axial joint. The posterior surface of the anterior arch of the atlas features an articular facet for the dens, which projects upward from the vertebral body of the axis (C2). The dens is secured in place by a robust transverse ligament of the atlas, located behind it, which extends between the oval attachment facets on the medial surfaces of the atlas's lateral masses. The atlanto-axial joint facilitates head rotation to the right and left.

Figure 10. Typical cervical vertebrae with triangular foramen, bifid spinous process, and foramen transversarium in each transverse process. 

2. Thoracic Region (Upper Back):

   • Composed of 12 thoracic vertebrae (T1–T12), this region connects with the ribs to form the rib cage, protecting vital organs like the heart and lungs. Thoracic vertebrae are less mobile than cervical vertebrae, providing stability to the chest. 

   • Each thoracic vertebra has two demi facets (one superior and one inferior) on either side of its vertebral body. These demi facets articulate with the heads of two different ribs, and the vertebral body is heart shaped (Figure 11).

   • On the transverse processes of the thoracic vertebrae, there is a transverse costal facet that articulates with the shaft of a single rib (Figure 11). For example, the head of Rib 2 articulates with the inferior demi facet of thoracic vertebra T1 and the superior demi facet of T2. The shaft of Rib 2 articulates with the costal facets of T2.

   • In contrast to the cervical vertebrae, the vertebral foramen of thoracic vertebrae is circular (Figure11).

Figure 11. Typical thoracic vertebrae with circular foramen and costal facets for rib articulation.

By Henry Vandyke Carter - Henry Gray (1918) Anatomy of the Human Body (See "Book" section below)Bartleby.com: Gray's Anatomy, Plate 82, Public Domain, https://commons.wikimedia.org/w/index.php?curid=792299

3. Lumbar Region (Lower Back):

   • Composed of 5 lumbar vertebrae (L1–L5), this region is responsible for bearing most of the body's weight. 

   • Lumbar vertebra have large kidney-shaped bodies, to support body weight (figure 12). 

   • The transverse processes are generally thin and long (figure 12).

   • The vertebral foramen is triangular in shape and larger than in the thoracic vertebrae.

Figure 12. Typical thoracic vertebrae with large vertebral bodies.

By Henry Vandyke Carter - Henry Gray (1918) Anatomy of the Human Body (See "Book" section below)Bartleby.com: Gray's Anatomy, Plate 93, Public Domain, https://commons.wikimedia.org/w/index.php?curid=207801

4. Sacral Region (Pelvic Area):

   • Composed of 5 fused sacral vertebrae (S1–S5), the sacrum forms the base of the vertebral column and connects to the hip bones (ilium) to form the pelvis. Facets are located on the lateral wall of the sacrum for articulation with the ilium at the sacroiliac joints. The posterior surface of the sacrum has four pairs of posterior sacral foramina, and the anterior surface has four pairs of anterior sacral foramina which serve as conduit for the posterior and anterior rami of spinal nerves (S1-S4) (Figure 13). 

Figure 13. The sacrum and sacroiliac joint superior view. 

By Mikael Häggström - File:Gray242.png, CC0, https://commons.wikimedia.org/w/index.php?curid=14606906

5. Coccygeal Region (Tailbone):

   • Composed of 4 fused coccygeal vertebrae (Co1–Co4). It is a small bone which articulates with the apex of the sacrum. It doesn’t have a vertebral canal or vertebral arches.

Curvatures of the Vertebral Column

The vertebral column exhibits natural curvatures that enhance its strength and flexibility:

• Cervical Lordosis: A gentle forward curve in the neck region, developed when an infant starts holding its head up.

• Thoracic Kyphosis: A natural outward curve in the upper back, which helps maintain balance.

• Lumbar Lordosis: A forward curve in the lower back that allows for the proper distribution of weight when standing or walking.

• Sacral Kyphosis: A backward curve in the sacral region that helps stabilize the pelvis.

Joints and Ligaments

The movable vertebrae connect with each other through joints between their bodies and articular facets:

• The superior articular facets (left and right) connect with the vertebra above.

• The inferior articular facets (left and right) connect with the vertebra below.

• The vertebral bodies are connected through intervertebral discs. The joints between vertebral bodies are cartilaginous, designed to bear weight. These joints are covered by hyaline cartilage and linked by the intervertebral discs (Figures 6, 7).

Two ligaments support the vertebral body joints (Figure14):

• The anterior longitudinal ligament, which is thick and prevents the spine from bending too far backward (hyperextension).

• The posterior longitudinal ligament, which is weaker and limits excessive forward bending (hyperflexion).

Figure 14. Ligaments of the spinal cord: anterior and posterior longitudinal ligaments, ligamentum flavum, interspinal and supraspinal ligaments. 

By Henry Vandyke Carter - Henry Gray (1918) Anatomy of the Human Body (See "Book" section below)Bartleby.com: Gray's Anatomy, Plate 301, Public Domain, https://commons.wikimedia.org/w/index.php?curid=423008 

The joints between the articular facets, called facet joints, allow small gliding movements between the vertebrae. They are reinforced by several ligaments:

• Ligamentum flavum: connects the laminae of adjacent vertebrae (Figure 14).

• Interspinous and supraspinous ligaments: connect the spinous processes of adjacent vertebrae. The interspinous ligaments connect between processes, while the supraspinous ligaments attach at the tips (Figure 14).

• Intertransverse ligaments: connect the transverse processes.

The Spinal Cord and Nerves

The spinal cord, which runs through the vertebral foramen, is a major component of the central nervous system. It is responsible for transmitting neural signals from the brain to the rest of the body and vice versa. Spinal nerves branch off the spinal cord at each level of the vertebral column, passing through the intervertebral foramina (gaps between adjacent vertebrae). These nerves provide motor and sensory functions to the body. 

Intervertebral foramina are formed on each side between adjacent parts of vertebrae and associated intervertebral discs. An intervertebral foramen is formed by the inferior vertebral notch on the pedicle of the vertebra above and the superior vertebral notch on the pedicle of the vertebra below (Figure 15).

Figure 15. The spinal cord and nerves. 

By Jmarchn - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=45612499

Clinical Relevance

1. Spinal Injuries:

   • Fractures of the vertebral column, especially in the cervical and lumbar regions, can result in spinal cord damage, leading to conditions such as paralysis (quadriplegia or paraplegia).

2. Intervertebral Disc Herniation:

   • A herniated disc occurs when the nucleus pulposus protrudes through the annulus fibrosus, pressing on nearby spinal nerves. This can cause symptoms such as back pain, numbness, and tingling, typically in the lumbar or cervical regions (Figure 16).

Figure 16. Posterolateral herniation of the intervertebral disc compressing on the spinal nerve root. 

3. Spina Bifida

   It’s a birth defect where the vertebral arches (the bony structures of the spine) fail to close completely during embryologic development, leaving a gap that can affect the spinal cord and surrounding nerves. There are three main types of spina bifida (Figure 17)

   
   

   • Spina Bifida Occulta:

     The mildest and most common form. The defect is hidden under the skin.

     
     

   • Meningocele:

     A more severe form where the meninges (the protective membranes surrounding the spinal cord) protrude through the gap in the spine, forming a sac.

     
     

   • Myelomeningocele:

     The most severe form of spina bifida. Both the meninges and the spinal cord protrude through the gap in the vertebrae, forming a sac. 

Figure 17. Types of spina bifida. 

4. Spinal Stenosis:

   • Spinal stenosis refers to the narrowing of the spinal canal, which can compress the spinal cord and nerves, leading to symptoms such as pain, numbness, and weakness, particularly in the lower back and legs.
     

5. Abnormal Spinal Curvature (Scoliosis, Kyphosis and Lordosis):

   • Scoliosis is a lateral curvature of the spine, often diagnosed in childhood or adolescence. Severe cases may require bracing or surgical intervention to prevent further deformity and improve posture (Figure18).
     

   • Excessive kyphosis (hunchback) or lordosis (swayback), can result from aging, muscle weakness, or postural problems. These conditions may cause pain and discomfort, and they may require physical therapy or corrective surgery (Figure18).

Figure 18. Spinal deformity types.