Annulus fibrosus

Dr Kieran Kusel and Assoc Prof Frank Gaillard ◉ ◈ et al.

The annulus fibrosus (plural: annuli fibrosi) surrounds the nucleus pulposus and together they form the intervertebral disc.

Gross anatomy

The annulus comprises 15 to 20 collagenous (type I) laminae which run obliquely from the edge of one vertebra down to the edge of the vertebra below. The direction of the fibers alternates from lamina to lamina. The inner portion of the annulus is made of fibrocartilage which gradually blends with the nucleus pulposus.

Posterolaterally, the annulus is not only thinner but also has more disorganized collagen bundles, and a greater proportion of vertical fibers, contributing to it being the weakest part, and accounting for the high rate of disc herniation. Furthermore, the composition of particularly the annulus fibrosis varies by spinal level.

Within the posterior cervical discs, the annulus fibrosus is thinner and consists of a single set of longitudinally-oriented fibers, rather than the multilaminated structure seen in lumbar discs ³.

Related conditions

annulus fibrosus calcification

References

Anatomy: Spine

osteology
intervertebral disc
- annulus fibrosus
- nucleus pulposus
articulations
ligaments
musculature of the vertebral column
- muscles of the neck
- muscles of the back
  - suboccipital muscle group
    - rectus capitis posterior major muscle
    - rectus capitis posterior minor muscle
    - obliquus capitis superior muscle
    - obliquus capitis inferior muscle
  - splenius capitis muscle
  - splenius cervicis muscle
  - erector spinae group
  - transversospinalis group
  - quadratus lumborum
spinal meninges and spaces
spinal cord
- gross anatomy
- white matter tracts (white matter)
  - corticospinal tract
  - anterolateral columns
  - lateral columns
  - dorsal columns
    - fasiculus gracilis (column of Goll)
    - fasiculus cuneatus (column of Burdach)
- grey matter
- nerve root
  - conjoined nerve root
- central canal
- functional anatomy
  - thoracic autonomic outflow
  - sacral autonomic outflow
- spinal cord blood supply
  - arteries
    - vertebral artery
      - anterior spinal artery
        sulcal artery
      - posterior inferior cerebellar artery (PICA)
        posterior spinal arteries
    - segmental arteries
      - artery of Adamkiewicz
  - veins
    - spinal segmental veins
      - vertebral venous plexus
      - Batson venous plexus
sympathetic chain
- stellate ganglion

Article information

rID: 6113

System: Musculoskeletal, Spine

Section: Anatomy

Tag: intervertebral disc

Synonyms or Alternate Spellings:

Anulus fibrosus

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Cases and figures

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