Intervertebral disc: Difference between revisions
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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 (Figure 1). | 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 (Figure 1). | ||
[[Image:Spinal_column.jpg]] | |||
Figure 1: Segment of 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). | |||
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The IVD consists of three distinct components (Figure 2): <br>• a central nucleus pulposus (NP);<br>• a peripheral annulus fibrosus (AF);<br>• two vertebral endplates (VEPs). | The IVD consists of three distinct components (Figure 2): <br>• a central nucleus pulposus (NP);<br>• a peripheral annulus fibrosus (AF);<br>• two vertebral endplates (VEPs). | ||
[[Image:IVD.jpg]] | |||
Figure 2: Detailed structure of the IVD (adapted from Bogduk 2005)<br> | Figure 2: Detailed structure of the IVD (adapted from Bogduk 2005)<br> | ||
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The nucleus pulposus is a gel-like mass composed of water and proteoglycans held by randomly arranged fibres of collagen [1-3]. 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. | The nucleus pulposus is a gel-like mass composed of water and proteoglycans held by randomly arranged fibres of collagen [1-3]. 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. | ||
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'''Annulus Fibrosus''' | '''Annulus Fibrosus''' | ||
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The 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. | The 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. | ||
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'''Vertebral endplate''' | '''Vertebral endplate''' | ||
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The IVD is largely avascular, with no major arterial branches to the disc [1]. 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 [6-8]. | The IVD is largely avascular, with no major arterial branches to the disc [1]. 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 [6-8]. | ||
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'''Biomechanics''' | |||
<br> '''Weight bearing''' | |||
'''Weight bearing''' | |||
The disc is subjected to various loads, including compressive, tensile and shear stresses [9, 10]. During compressive loading, hydrostatic pressure develops within the NP, which thereby disperses the forces towards the endplates as well as the AF [1, 11, 12]. This mechanism slows the rate applied loads are transmitted to the adjacent vertebra, giving the disc its shock absorbing abilities [1]. | The disc is subjected to various loads, including compressive, tensile and shear stresses [9, 10]. During compressive loading, hydrostatic pressure develops within the NP, which thereby disperses the forces towards the endplates as well as the AF [1, 11, 12]. This mechanism slows the rate applied loads are transmitted to the adjacent vertebra, giving the disc its shock absorbing abilities [1]. | ||
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'''Movements''' | '''Movements''' | ||
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The disc is also involved in permitting movements between vertebral bodies, which include: <br>• axial compression / distraction;<br>• flexion / extension;<br>• axial rotation;<br>• lateral flexion. | The disc is also involved in permitting movements between vertebral bodies, which include: <br>• axial compression / distraction;<br>• flexion / extension;<br>• axial rotation;<br>• lateral flexion. | ||
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'''Nuclear migration''' | '''Nuclear migration''' | ||
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Asymmetric compressive loading disc can cause the NP to migrate in a direction opposite to the compression [13-16]. 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 [17]. 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 [17]. | Asymmetric compressive loading disc can cause the NP to migrate in a direction opposite to the compression [13-16]. 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 [17]. 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 [17]. | ||
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Figure 4: Direction of nuclear migration within the IVD during spinal movements (adapted from McKenzie 1981)<br> | |||
Figure 4: Direction of nuclear migration within the IVD during spinal movements (adapted from McKenzie 1981)<br> | |||
== Differential Diagnosis == | == Differential Diagnosis == | ||
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== Examination == | == Examination == | ||
Refer to [http://www.physio-pedia.com/Lumbar_Discogenic_Pain Lumbar discogenic pain].<br> | Refer to [http://www.physio-pedia.com/Lumbar_Discogenic_Pain Lumbar discogenic pain].<br> | ||
== Key Research == | == Key Research == | ||
Revision as of 10:58, 6 October 2014
Original Editors
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Definition/Description[edit | edit source]
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 (Figure 1).
Figure 1: Segment of 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[edit | edit source]
Morphology
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
The nucleus pulposus is a gel-like mass composed of water and proteoglycans held by randomly arranged fibres of collagen [1-3]. 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
The 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
The vertebral endplate is 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.
Innervation
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 [1]. 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 [6-8].
Biomechanics
Weight bearing
The disc is subjected to various loads, including compressive, tensile and shear stresses [9, 10]. During compressive loading, hydrostatic pressure develops within the NP, which thereby disperses the forces towards the endplates as well as the AF [1, 11, 12]. This mechanism slows the rate applied loads are transmitted to the adjacent vertebra, giving the disc its shock absorbing abilities [1].
Movements
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 [13-16]. 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 [17]. 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 [17].
Figure 4: Direction of nuclear migration within the IVD during spinal movements (adapted from McKenzie 1981)
Differential Diagnosis[edit | edit source]
Refer to Lumbar discogenic pain and Thoracic disc syndrome.
Diagnostic Procedures[edit | edit source]
Refer to Lumbar discogenic pain and Thoracic disc syndrome.
Outcome Measures[edit | edit source]
add links to outcome measures here (also see Outcome Measures Database)
Examination[edit | edit source]
Refer to Lumbar discogenic pain.
Key Research[edit | edit source]
Bogduk, N., Clinical anatomy of the lumbar spine and sacrum. 4th ed. 2005, New York: Churchill Livingstone.
Resources
[edit | edit source]
add appropriate resources here
Clinical Bottom Line[edit | edit source]
add text here
Recent Related Research (from Pubmed)[edit | edit source]
see tutorial on Adding PubMed Feed
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References[edit | edit source]
see adding references tutorial.
