Intervertebral disc

Original Editors - Alexander Chan

Top Contributors - Alexander Chan 


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The intervertebral disc (IVD) is important in the normal functioning of the spine. It is a cushion of fibrocartilage and the principal joint between two vertebrae in the spinal column. There are 23 discs in the human spine: 6 in the cervical region (neck), 12 in the thoracic region (middle back), and 5 in the lumbar region (lower back).

Clinically Relevant Anatomy


The IVD consists of three distinct components (Figure 2):
• a central nucleus pulposus (NP);
• a peripheral annulus fibrosus (AF);
• two vertebral endplates (VEPs).


Figure 2: Detailed structure of the IVD (adapted from Bogduk 2005)

Nucleus Pulposus: a gel-like mass composed of water and proteoglycans held by randomly arranged fibres of collagen [1] [2] [3]. With it’s water-attracting properties, any attempt to deform the nucleus causes the applied pressure to be dispersed into various directions, similar to a person on a waterbed.

Annulus Fibrosus: consists of “lamellae” or concentric layers of collagen fibres [4]. The fibre orientation of each layer of lamellae alternate and therefore allow effective resistance of multidirectional movements.

Vertebral endplate: a plate of cartilage that acts as a barrier between the disc and the vertebral body. They cover the superior and inferior aspects of the annulus fibrosus and the nucleus pulposus.


The disc is innervated in the outer few millimetres of the annulus fibrosus [5].

Vascular supply and nutrition

The IVD is largely avascular, with no major arterial branches to the disc [6]. The outer annular layers are supplied by small branches from metaphysial arteries [1]. Due to the avascular nature of the disc, the nutrition is dependent on metabolite diffusion [7] [8] [9].


Weight bearing: The disc is subjected to various loads, including compressive, tensile and shear stresses [10] [11]. During compressive loading, hydrostatic pressure develops within the NP, which thereby disperses the forces towards the endplates as well as the AF [12] [13] [12]. This mechanism slows the rate applied loads are transmitted to the adjacent vertebra, giving the disc its shock absorbing abilities [14].

Movement: The disc is also involved in permitting movements between vertebral bodies, which include:
• axial compression / distraction;
• flexion / extension;
• axial rotation;
• lateral flexion.

Nuclear migration: Asymmetric compressive loading disc can cause the NP to migrate in a direction opposite to the compression [15] [14] [16] [17]. For example, during forward bending (or flexion) of the lumbar spine, the NP migrates posteriorly or backwards (Figure 4). Conversely, during backwards bending (or extension), the nucleus is squeezed anteriorly or forwards. This concept is known as the dynamic disc model [18]. Although NP migration has been shown to behave predictably in asymptomatic discs, a variable pattern of migration occurs in people with symptomatic and/or degenerative IVDs [18].


Figure 4: Direction of nuclear migration within the IVD during spinal movements (adapted from McKenzie 1981)



Lumbar Disc[20]

Diagnostic Category Characteristics
Normal - Morphologically normal (not inclusive of degenerative, developmental, or adaptive changes that could in some context be considered clinically normal)

- In adults, a bilocular appearance resulting from the development of a central horizontal band of fibrous tissue is a normal sign of maturation

Congenital/Developmental - congenitally abnormal

- changes in morphology as an adaptation to the abnormal growth of the spine (i.e. scoliosis or spondylolisthesis)

Degenerative/Trauma Annular Fissures/Tear - separation between annular fibres OR

- avulsion of fibres from their vertebral body insertions OR

- breaks through the fibres that extend radially/transversely/concentrically involving one or many layers of the annular lamellae

Degeneration - any or all real/apparent desiccation, fibrosis, narrowing of the disc space OR

- diffuse bulging of the annulus beyond the disc space OR

- extensive fissuring (i.e. numerous annular tears) OR

- mucinous degeneration of the annulus OR

- defects and sclerosis of the endplates OR

- osteophytes at the vertebral apophyses

- A disc with one or more of these changes can be further categorised into: 1. spondylosis deformans (normal aging process) 2. intervertebral osteochondrosis (pathologic process)

Herniation - defined as a localised displacement of disc material beyond the limits of the IVD space

- Protrusion: the base is greater than the edges of the disc material beyond the disc space

- Extrusion: the base is smaller than the edges of the disc material beyond the disc space

- 2 types of Extrusion: 1. Sequestration: displaced disc has lost continuity with parent disc 2. Migration: displacement of material away from site of extrusion with/without sequestration

- Contained: displaced portion is covered by outer annulus

- Uncontained: displaced portion has no covering

Inflammation/Infection - infection, infection-like inflammatory discitis, and inflammatory response to spondyloarthropathy
Morphologic Variant of Unknown Significance - abnormal morphology without enough data to warrant diagnostic categorisation

Differential Diagnosis

Refer to Lumbar discogenic pain and Thoracic disc syndrome.

Diagnostic Procedures

Refer to Lumbar discogenic pain and Thoracic disc syndrome.

Outcome Measures

See Outcome Measures Database


Refer to Lumbar discogenic pain.

Key Research

Bogduk, N., Clinical anatomy of the lumbar spine and sacrum. 4th ed. 2005, New York: Churchill Livingstone.


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