The Vertebrae Column
The vertebral column consists of 33 bony vertebrae grouped into five regions. Each vertebra is joined to the one above and the one below by cartilaginous intervertebral discs, articular facets and ligaments. These give the vertebral column stability and mobility.
- The cervical spine has seven cervical vertebrae and has a curve that is concave posteriorly
- The thoracic spine is made up of 12 vertebrae, which articulate with the ribs. It is concave anteriorly
- The lumbar spine has five vertebrae. It has a curve called the lumbar lordosis, which is concave posteriorly
- The sacrum is composed of five fused vertebrae
- The coccyx is made up of three to five fused vertebrae and is the remnants of a tail
The vertebral column has two primary curves (concave anteriorly), which are in the thoracic and sacral regions, and two secondary or compensatory curves (concave posteriorly), which are in the cervical and lumbar regions.
Babies are born with only one C-shaped curve of the spine, called the primary curvature. In the thoracic and sacral regions this curve persists into adulthood owing to the shape of the vertebrae themselves. The secondary curves are postural and develop in the cervical and lumbar regions when, as infants, sufficient muscle strength is developed to hold the head up and to walk.
Although there are variations in the anatomy of vertebrae in different regions, all the vertebrae (with the exception of the first cervical vertebra (C1)) have three features in common
- A vertebral body
- A vertebral or neural arch consisting of:
- A vertebral foramen
Each neural arch supports seven processes allowing for the attachment of muscles and ligaments:
- A spinous process
- The spinous process projects posteriorly and can usually be palpated through the skin
- Two transverse processes
- The two transverse processes project laterally, one on each side, where the lamina meets the pedicle
- Four articular processes
- Each lamina gives rise to a superior articular process and an inferior articular process. The two inferior articular processes of any vertebra articulate with the two superior articular processes of the vertebra below, by means of facets; these form the facet joints
- The orientation of the facet joints varies between the different vertebrae, and determines the degree and direction of movement allowed in each region of the spine
The pedicles of a typical vertebra are notched above and below. The notches of two adjacent vertebrae form, one on either side, an intervertebral foramen, through which the ventral root of a spinal nerve exits the vertebral canal.
Boundaries of an invertebral foramen
- Superiorly: Inferior vertebral notch on the pedicle of the vertebra above
- Inferiorly: Superior vertebral notch on the pedicle of the vertebra below
- Anteriorly: Posterolateral aspect of the bodies of the two adjacent vertebrae and the associated intervertebral disc
- Posteriorly: Superior and inferior articular processes of the adjacent vertebrae forming a facet joint with its capsule
Between each vertebral body is an intervertebral disc, a cartilaginous structure that provides articulation between adjacent vertebral bodies
Each disc has two parts:
- An annular ligament or annulus fibrosus on the outside, a dense, strong, fibrocartilaginous ring comprising the outer one-third of the disc
- A nucleus pulposus on the inside, an avascular semi-fluid core of gelatinous proteoglycans
Attachments of the intervertebral discs:
- Hyaline cartilage: A thin layer of hyaline cartilage covers the superior and inferior surfaces of each vertebral body, to which each disc is adherent
- Longitudinal ligaments: The discs are attached to the anterior longitudinal ligament in front (Fig 3) and the posterior longitudinal ligament behind
If the nucleus pulposus herniates through the fibrous tissue surrounding it, it can put pressure on an individual nerve root or the spinal cord. This is a disc prolapse, or in layman’s terms, a ‘slipped disc’.
Intervertebral disc degeneration leading to prolapse is most common at the top and bottom of the lumbar region.