Vertebral Column

The human spine, or vertebral column, is the most important anatomical and functional axis of the human body. It consists of 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae and is limited cranially by the skull and caudally by the sacrum. The vertebral column is the foundation for the trunk, provides an attachment for muscles and ligaments, and protects the spinal cord and nerve roots.

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Overview

Definition

The vertebral column is the primary axis of the skeleton:

  • Supports the trunk
  • Provides an attachment for ligaments and muscles that move the body
  • Protects the spinal cord and nerve roots

The vertebral column consists of 33 vertebrae placed in series and connected by intervertebral discs and ligaments.

Regions of the vertebral column

Five different groups of vertebrae:

  • Cervical
  • Thoracic
  • Lumbar
  • Sacral
  • Coccygeal
Vertebral column, anterior view

Vertebral column, anterior view

Image by BioDigital, edited by Lecturio

Number of vertebrae per segment:

  • Cervical: 7
  • Thoracic: 12
  • Lumbar: 5
  • Sacral: 5
  • Coccygeal: 4 (ranges from 3–5, below sacrum)
Vertebral column, posterior view

Vertebral column, posterior view

Image by BioDigital, edited by Lecturio
Table: Vertebral column regions and their primary characteristics
VertebraeCharacteristics
Cervical
  • 7 cervical vertebrae
  • Lordotic curve
  • Most mobile region
  • C1 (atlas) and C2 (axis) are specialized:
    • C1: ring-shaped, with no vertebral body; articulates with skull; 50% of cervical flexion occurs here
    • Atlanto-occipital joint: skull to C1 (flexion: “yes”)
    • C1–C2 articulation: 50% of cervical rotation occurs here
    • Atlanto-axial joint: C1 to C2 (rotation: “no”)
  • C1: ring-shaped, no body, 2 prominent lateral masses, an anterior and posterior arch, and posterior tubercle instead of spinous bifid processes
  • C2 has a large vertebral body containing the odontoid process (dens) and articulates with the atlas, forming the atlanto-axial joint
  • C7 has a palpable spinous process.
  • Uncovertebral joints (joints of Luschka): frequent site of degeneration in the cervical spine
  • Facet joints: diarthrodial synovial joints (zygapophyseal joints), allow gliding movements of the cervical spine
  • Transverse foramen: foramen (opening) in each transverse process, pass-through opening for the vertebral artery traveling superiorly to the brain
Thoracic
  • 12 thoracic vertebrae
  • Kyphotic curve
  • Least amount of flexion/extension of regions of the spine
  • Narrow spinal canal
  • Costal facets:
    • 6 facets per thoracic vertebra
    • Facets articulate with the ribs
  • Spinous processes are long and are directed posteroinferiorly.
  • T1, T11, and T12 are “atypical ribs,” with variation of the costal facets.
Lumbar
  • 5 lumbar vertebrae
  • Highly flexible yet very strong
  • Large vertebral bodies, designed to bear weight
  • Vertebral foramen is triangular.
  • Lumbar spine is often divided into the anterior, middle, and posterior columns when discussing spinal fractures.
  • Short/horizontal spinous processes
  • Facet joints (zygapophyseal joints): synovial joints between the superior and inferior articular processes, permit gliding movements
  • Lumbar intervertebral discs form primary connection between vertebrae.
  • Multiple vertebral ligaments help maintain stability and limit range of motion (ROM).
Sacrum
  • Bony structure consisting of 5 coalesced vertebrae
  • Posterior aspect of pelvis; terminal portion of the vertebral canal
  • 3 sacral crests or prominent bony ridges:
    • Median: fused spinous processes
    • Intermediate: fused articular processes
    • Lateral: fused transverse processes
Coccyx
  • Bony structure consisting of 3–5 coalesced vertebrae
  • Articulates with inferior sacrum

Curvatures of the vertebral column

  • Primary (develop before birth):
    • Thoracic and sacral
    • Kyphosis: forward rounding of thoracic spine
  • Secondary (develop after birth):
    • Cervical and lumbar
    • Lordosis: inward curvature of lumbar spine
Table: Vertebral column segmentation and curvatures
Spinal segmentVertebraeCurvature
CervicalC1–C7Lordosis
ThoracicT1–T12Kyphosis
LumbarL1–L5Lordosis
SacralS1–S5 (fused)Kyphosis
Coccygeal3–5 (fused)

Spinal canal

  • The vertebrae form the spinal canal, which houses the spinal cord and spinal nerves.
  • Intervertebral foramen (or neural foramen): foramen for the spinal nerves exiting between 2 spinal vertebrae
Articulated Vertebrae Spinal cord

Spinal cord traveling through the vertebral foramen with nerve roots (in yellow) exiting through the intervertebral foramina

Image: “Articulated Vertebrae” by Phil Schatz. License: CC BY 4.0, edited by Lecturio.

Vertebrae

Vertebrae protect the spinal column.

Two adjacent vertebrae are often referred to as a motion segment or functional unit of the spine (e.g., C6 and C7).

Components of the vertebrae

  • Body:
    • Anterior portion of vertebra
    • Weight-bearing function
    • Lined with hyaline cartilage superiorly and inferiorly
  • Vertebral arch:
    • Lateral and posterior portion of vertebra
    • Encloses the vertebral canal
    • Vertebral arch consists of the following components:
      • Pedicles 
      • Laminae 
      • Processes: transverse (lateral), articular, and spinous (posterior)
Superior view (left) and Anterior view (right) of a lumbar vertebra-01
Components of vertebrae
Image by BioDigital, edited by Lecturio

Vertebral foramen

  • Large central opening in vertebrae that collectively form the spinal canal 
  • Contains the spinal cord, nerve roots, and blood vessels

Intervertebral foramen (neural foramen)

  • Boundaries include the superior and inferior notches of the vertebrae.
  • Spinal nerves exit here.
  • Contents: spinal nerve root, dorsal root ganglion, segmental arteries/veins, fat
  • Cervical spine:
    • C1–C7 nerve roots exit superiorly to the pedicles of C1–C7.
    • C8 nerve root exits inferiorly to the pedicles of C7.
  • Thoracic and sacral nerve roots exit inferiorly to their corresponding vertebrae.
  • May become stenotic with injury or degenerative changes

Atlas and axis

  • C1 and C2 are specially named because of their unique functions.
  • Atlas (C1):
    • Supports the entire skull
    • Does not possess a vertebral body
    • Primary function is to allow head to nod up and down.
  • Axis (C2):
    • Possesses a bony projection called the dens (also known as odontoid process):
      • Serves as a pivot point to allow head to rotate side to side
      • Commonly fractured during high-impact injuries
    • Has a bifid spinous process

Sacrum and coccyx

  • Sacrum
    • Consists of 5 fused vertebrae below the lumbar vertebrae
    • Represents the terminal portion of the vertebral canal
    • Articulates with the ilium (hip bone) to form the pelvic girdle
  • Coccyx
    • Consists of 3–5 fused vertebrae
    • Articulates with the inferior sacrum
Posterior (left), anterior (center), and lateral (right) views of the Sacrum

3 views of the sacrum:
The coccyx extends from the inferior portion of the sacrum.

Image by BioDigital, edited by Lecturio

Intervertebral Discs, Ligaments, and Joints of the Spine

Intervertebral discs

Intervertebral discs form the primary connection between vertebrae.

  • 25 discs (7 cervical, 12 thoracic, 5 lumbar, 1 sacral) account for 25%–30% of the length of the spine.
  • Provide shock-absorbing protection within the spine
  • 3 major components:
    • Annulus fibrosis:
      • Ring-shaped fibrous connective tissue around the nucleus pulposus
      • Multilayered alignment of predominantly collagen fibers → remarkable strength.
      • Adhere dorsally to the posterior longitudinal ligament
    • Nucleus pulposus:
      • Center of the intervertebral disc
      • Mucoid or gel-like structure
      • Responsible for much of the strength and flexibility of the spine
      • 70%–80% water when young, the remainder composed of collagen fibers and proteoglycans; % of water decreases with aging
      • Receives nutrition through diffusion
    • Cartilaginous end plates anchor the discs to the adjacent vertebrae.
Views showing the components of the intervertebral disc

Views showing the components of the intervertebral disc

Image: “Disc intervertebral” by Jmarchn. License: CC BY-SA 3.0

Ligaments of the vertebral column

The ligaments of the vertebral column are essential for stability of the spine:

  • Ligaments are composed of sheets of fibrous connective tissue.
  • Prevent excessive motion (e.g., hyperextension of the spine)
Table: Ligaments of the vertebral column
LigamentCharacteristicsFunctions
Anterior longitudinal ligament
  • From the sacrum to the occiput
  • Attaches to the anterior portion of the vertebral bodies and intervertebral discs
  • Primary ligament limiting extension
  • Maintains stability between vertebral bodies
Posterior longitudinal ligament
  • Attaches to the posterior portion of the vertebral bodies and intervertebral discs
  • Narrower than the anterior longitudinal ligament
  • Resists hyperflexion
  • Helps stabilize the vertebral column during flexion
  • Resists hyperflexion
Ligamentum flavum
  • Elastic tissue that attaches to the laminae
  • Flavum = yellow
Stabilizes the vertebral arch joint during flexion
Interspinous ligament
  • Attaches to the spinous processes
  • Connects to the supraspinous (dorsal) and flava (ventral) ligaments
Stabilizes, controls, and limits flexion, lateral flexion, and rotation
Supraspinous ligament
  • Attaches to the spinous processes of the adjacent vertebral bodies of C7 to the sacrum
  • Merges superiorly with the nuchal ligament
Stabilizes, controls, and limits flexion, lateral flexion, and rotation
Intertransverse ligamentConnects the transverse processes of adjacent cervical, thoracic, and lumbar vertebraeLimits both flexion and lateral flexion
Nuchal ligament
  • Strong, posterior ligament that attaches the external occipital protuberance and atlas to spinous processes of the cervical vertebrae
  • Ends at C7
Limits flexion of the cervical spine
Ligaments of the spine

Ligaments of the vertebral column

Image by Lecturio. License: CC BY-NC-SA 4.0

Joints of the spine

Joints of the spine consist of intervertebral discs and facet joints:

  • The vertebral bodies articulate with each other via the intervertebral discs.
  • The facet joints (zygapophyseal joints) consist of cartilage-covered surfaces with a joint capsule. Each vertebra has 2 sets of facet joints (facing superiorly and inferiorly).

Clinical Relevance

  • Herniated disc or herniated nucleus pulposus: Herniated nucleus pulposus occurs when the nucleus pulposus prolapses or herniates through a tear in the surrounding annulus fibrosus. This herniation results in pain from irritation and injury to adjacent nerve roots and surrounding tissue. Herniated discs occur most commonly in the cervical or lumbar spine. Physical therapy is the 1st-line treatment for a disc herniation.
  • Degenerative disc disease: Intervertebral discs undergo age- and trauma-related changes. The proteoglycan and water concentrations decrease in the disc, which decreases the height of the disc and leads to anatomical and biomechanical changes. These changes typically lead to low back pain, which is primarily managed through the use of nonsteroidal antiinflammatory drugs.
  • Spinal stenosis: occurs from narrowing of the spinal canal. Spinal stenosis is described as central and/or lateral stenosis, based on the location. Depending on the position and severity, the spinal nerves, spinal cord, or blood vessels may be affected by the compression. Classically, pain from spinal stenosis improves when leaning forward.
  • Cervical spondylosis: Stenosis of the cervical canal secondary to degenerative changes to the cervical spine leads to cervical spondylosis, which may lead to cervical myelopathy when there is encroachment on the cervical spinal cord.
  • Abnormal curvature of the spine:
    • Scoliosis: lateral curvature of the spine; usually an idiopathic process
    • Kyphosis: excessive thoracic curvature; can occur congenitally or be due to a traumatic event. Kyphosis is also referred to as a “hunchback” deformity.
    • Lordosis: excessive curvature of the lumbar spine

References

  • Desai, C. Reddy, V. Agarwal, A. (2020). Anatomy, back, vertebral column. StatPearls. Retrieved June 27, 2021, from https://www.ncbi.nlm.nih.gov/books/NBK525969/
  • Drake, R.L., Vogl, A.W., Mitchell, A.W.M. (2014). Gray’s Anatomy for Students, 3rd ed. Philadelphia:  Churchill Livingstone.
  • Mahadevan, V. (2018). Anatomy of the vertebral column. Surgery (Oxford) 36:327–332.

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