Chapter 20 The Intervertebral Disk. Overview The IVD forms a symphysis or amphiarthrosis between two adjacent vertebrae The IVD forms a symphysis or amphiarthrosis.

Chapter 20Chapter 20

The Intervertebral DiskThe Intervertebral Disk

OverviewOverview

The IVD forms a symphysis or The IVD forms a symphysis or amphiarthrosis between two adjacent amphiarthrosis between two adjacent vertebraevertebrae

Represents the largest avascular Represents the largest avascular structure in the bodystructure in the body

In the human spinal column, the In the human spinal column, the combined heights of the IVD accounts combined heights of the IVD accounts for approximately 20-33% of the total for approximately 20-33% of the total length of the spinal columnlength of the spinal column

OverviewOverview

Intervertebral discs are able to Intervertebral discs are able to distribute compressive stress evenly distribute compressive stress evenly between adjacent vertebrae because between adjacent vertebrae because the NP and inner AF act like a the NP and inner AF act like a pressurized fluid, in which the pressure pressurized fluid, in which the pressure does not vary with location or directiondoes not vary with location or direction

The biomechanical studies of the IVD The biomechanical studies of the IVD seem to indicate that the disc acts to seem to indicate that the disc acts to provide flexibility at low loads, and provide flexibility at low loads, and stability at high loadsstability at high loads

AnatomyAnatomy

Lumbar DiskLumbar Disk– The lumbar disc is approximately cylindrical, its The lumbar disc is approximately cylindrical, its

shape being determined by the integrity of the shape being determined by the integrity of the annulus fibrosis (AF)annulus fibrosis (AF)

– The AF consists of approximately 10-12 (often as The AF consists of approximately 10-12 (often as many as 15-25) concentric sheets of many as 15-25) concentric sheets of predominantly type I collagen tissue bound predominantly type I collagen tissue bound together by proteoglycan geltogether by proteoglycan gel

The number of annular layers decreases with age, but The number of annular layers decreases with age, but there is a gradual thickening of the remaining layersthere is a gradual thickening of the remaining layers

The fibers of each successive sheet or lamella maintain The fibers of each successive sheet or lamella maintain the same inclination of 65º but in the opposite direction the same inclination of 65º but in the opposite direction to the preceding lamella, resulting in every second to the preceding lamella, resulting in every second sheet having the same orientationsheet having the same orientation

AnatomyAnatomy

Lumbar DiskLumbar Disk– Although the posterior aspect of the IVD is Although the posterior aspect of the IVD is

thinner, the collagen is more tightly packed than thinner, the collagen is more tightly packed than it is anteriorlyit is anteriorly

– Consequently, the posterior part of the annulus Consequently, the posterior part of the annulus will have thinner but stronger fibers, and it is will have thinner but stronger fibers, and it is capable of withstanding tension applied to this capable of withstanding tension applied to this area during flexion activities and postures which area during flexion activities and postures which occur more frequently than with extensionoccur more frequently than with extension

– However, due to the predominance of flexion However, due to the predominance of flexion activities in life, fatigue damage may occur in the activities in life, fatigue damage may occur in the posterior aspect of the disc, making it a common posterior aspect of the disc, making it a common site of injurysite of injury

AnatomyAnatomy

Lumbar DiskLumbar Disk– With the exception of early youth, With the exception of early youth,

there is no clear boundary between there is no clear boundary between the NP and AF, and it resembles a the NP and AF, and it resembles a transitional zonetransitional zone

– The biomechanical make up of the The biomechanical make up of the NP is similar to that of the AF, NP is similar to that of the AF, except that the NP contains mostly except that the NP contains mostly type II collagen, as opposed to type Itype II collagen, as opposed to type I

AnatomyAnatomy

Lumbar DiskLumbar Disk– Each vertebral end plate consists of a Each vertebral end plate consists of a

layer of hyaline and fibrocartilage about layer of hyaline and fibrocartilage about 0.6 to 1 millimeter thick, which covers the 0.6 to 1 millimeter thick, which covers the top or bottom aspects of the disc, and top or bottom aspects of the disc, and separates the disc from the adjacent separates the disc from the adjacent vertebral bodyvertebral body

– The two end plates of each disc, therefore, The two end plates of each disc, therefore, cover the NP in its entirety, but fail to cover the NP in its entirety, but fail to cover the entire extent of the AF cover the entire extent of the AF

AnatomyAnatomy

Lumbar DiskLumbar Disk– The outer half of the IVD, the The outer half of the IVD, the

posterior longitudinal ligament, and posterior longitudinal ligament, and the dura are innervated by the the dura are innervated by the sinuvertebral nerve, which is sinuvertebral nerve, which is considered to arise from the ventral considered to arise from the ventral ramus and the sympathetic trunkramus and the sympathetic trunk

BiomechanicsBiomechanics

Lumbar DiskLumbar Disk– Although the lumbar IVD appears destined Although the lumbar IVD appears destined

for tissue regression and destruction, it for tissue regression and destruction, it remains unclear why similar age-related remains unclear why similar age-related changes remain asymptomatic in one changes remain asymptomatic in one individual, yet may cause severe low back individual, yet may cause severe low back pain in otherspain in others

– The basic changes that influence the The basic changes that influence the responses of the disc to aging appear to be responses of the disc to aging appear to be biochemical, and may concern the collagen biochemical, and may concern the collagen content levels in the NP.content levels in the NP.

PathologyPathology

Lumbar diskLumbar disk– Three main types of lumbar disc herniation Three main types of lumbar disc herniation

are recognized:are recognized: Contained herniation (protrusion)Contained herniation (protrusion)

– With this type, the nuclear material bulges With this type, the nuclear material bulges outwards through the tear to strain, but not escape outwards through the tear to strain, but not escape from, the outer AF and/or the posterior longitudinal from, the outer AF and/or the posterior longitudinal ligament ligament

Extrusion (prolapse)Extrusion (prolapse)– The nuclear material remains attached to the disc, The nuclear material remains attached to the disc,

but escapes the AF and/or the posterior but escapes the AF and/or the posterior longitudinal ligament to bulge posterior-laterally longitudinal ligament to bulge posterior-laterally into the intervertebral canal into the intervertebral canal

PathologyPathology

Lumbar diskLumbar disk– SequestrationSequestration

The migrating nuclear material escapes The migrating nuclear material escapes contact with the disc entirely, and contact with the disc entirely, and becomes a free fragment in the becomes a free fragment in the intervertebral canal intervertebral canal

PathologyPathology

Nerve CompressionNerve Compression – Mechanical compression of the nerve root Mechanical compression of the nerve root

alone does not explain sciatic pain and alone does not explain sciatic pain and radiculopathyradiculopathy

– Recent models of lumbar radiculopathy Recent models of lumbar radiculopathy suggest that the underlying mechanisms are suggest that the underlying mechanisms are probably due, in part, to a local chemical probably due, in part, to a local chemical irritant such as proteoglycans released from a irritant such as proteoglycans released from a disc creating an inflammatory reaction, an disc creating an inflammatory reaction, an autoimmune reaction from exposure to disc autoimmune reaction from exposure to disc tissues, or an increased concentration of lactic tissues, or an increased concentration of lactic acid, and/or a lower pH around the nerve roots acid, and/or a lower pH around the nerve roots

PathologyPathology

Specific Lumbar Disc LesionsSpecific Lumbar Disc Lesions– At the L 1 and L 2 levels, the nerves At the L 1 and L 2 levels, the nerves

exit the intervertebral foramen above exit the intervertebral foramen above the disc. From L 2 downward, the the disc. From L 2 downward, the nerves leave the dura slightly more nerves leave the dura slightly more proximally than the foramen through proximally than the foramen through which they pass, and at a decreasing which they pass, and at a decreasing angle of obliquity, and an increasing angle of obliquity, and an increasing length within the spinal canal length within the spinal canal

PathologyPathology

High Lumbar Disc LesionsHigh Lumbar Disc Lesions– The high lumbar radiculopathy does The high lumbar radiculopathy does

not typically radiate pain down the not typically radiate pain down the back of the leg, but instead causes back of the leg, but instead causes an insidious onset of pain in the an insidious onset of pain in the groin or anterior thigh, which is groin or anterior thigh, which is often relieved in a flexed position often relieved in a flexed position and worsens with standingand worsens with standing

– The superficial cremasteric reflex is The superficial cremasteric reflex is also invariably present also invariably present

PathologyPathology

Third Lumbar Nerve RootThird Lumbar Nerve Root– The L 3 nerve root travels behind The L 3 nerve root travels behind

the inferior aspect of the vertebral the inferior aspect of the vertebral body and the L 3 discbody and the L 3 disc

– Clinical findings may include:Clinical findings may include: Symptoms in the mid lumbar, upper Symptoms in the mid lumbar, upper

buttock, whole anterior thigh and knee, buttock, whole anterior thigh and knee, medial knee, and just above the anklemedial knee, and just above the ankle

Slight weakness of iliopsoas, grosser Slight weakness of iliopsoas, grosser loss of quadricepsloss of quadriceps

PathologyPathology

Fourth Lumbar Nerve RootFourth Lumbar Nerve Root– About 40% of IVD impairments affect About 40% of IVD impairments affect

this level, about an equal amount as this level, about an equal amount as those that affect the L 5 root. those that affect the L 5 root.

– Clinical findings may include:Clinical findings may include: Symptoms located in the lumbar area or Symptoms located in the lumbar area or

iliac crest, inner buttock, outer thigh and iliac crest, inner buttock, outer thigh and leg, and over the foot to the great toeleg, and over the foot to the great toe

Weak dorsi-flexion Weak dorsi-flexion

PathologyPathology

Fifth lumbar nerve rootFifth lumbar nerve root– Frequently compressed by the L 4-5 Frequently compressed by the L 4-5

disc as well as the L5-S1 discdisc as well as the L5-S1 disc– Clinical findings may include:Clinical findings may include:

Pain in the sacroiliac area, lower Pain in the sacroiliac area, lower buttock, lateral thigh and leg, inner 3 buttock, lateral thigh and leg, inner 3 toes and medial sole of the foottoes and medial sole of the foot

Weakness of peroneal muscles, extensor Weakness of peroneal muscles, extensor hallucis and hip abductor muscles hallucis and hip abductor muscles

PathologyPathology

11stst, 2, 2ndnd and 3 and 3rdrd sacral nerve roots sacral nerve roots– Can be compressed by a fifth lumbar Can be compressed by a fifth lumbar

disc protrusiondisc protrusion– The clinical findings with a lesion at The clinical findings with a lesion at

the S1 level may include:the S1 level may include: Pain in the low back to buttocks to sole Pain in the low back to buttocks to sole

of foot and heelof foot and heel Weakness of the calf muscles, peronei, Weakness of the calf muscles, peronei,

and hamstringsand hamstrings

PathologyPathology

44thth sacral nerve root sacral nerve root– A lesion of this nerve root is always A lesion of this nerve root is always

a concern as a permanent palsy may a concern as a permanent palsy may lead to incontinence and impotence lead to incontinence and impotence

– Clinical findings may include:Clinical findings may include: Pain in the lower sacral, peroneal and Pain in the lower sacral, peroneal and

genital areasgenital areas Saddle paresthesiaSaddle paresthesia Bladder, bowel and/or genital Bladder, bowel and/or genital

dysfunctiondysfunction

PathologyPathology

Schmorl's nodeSchmorl's node– A herniation of disc substance A herniation of disc substance

through the cartilaginous vertebral through the cartilaginous vertebral end plate of the IVD into the body of end plate of the IVD into the body of the adjacent vertebra the adjacent vertebra

ExaminationExamination

The conventional physical examination The conventional physical examination for a suspected disc herniation consists for a suspected disc herniation consists of tests for strength and range of of tests for strength and range of motion, reflex, and sensory testing, and motion, reflex, and sensory testing, and dural mobility tests such as the SLR testdural mobility tests such as the SLR test

It must be remembered that no single It must be remembered that no single test in the physical examination has a test in the physical examination has a high diagnostic accuracy alone for disc high diagnostic accuracy alone for disc herniationherniation

AnatomyAnatomy

Cervical DiskCervical Disk– In the cervical spine, there are five discs, with In the cervical spine, there are five discs, with

the first disc located between C 2 and C 3the first disc located between C 2 and C 3– The cervical discs are named after the vertebra The cervical discs are named after the vertebra

above (the C 4 disc lies between C 4 and C 5)above (the C 4 disc lies between C 4 and C 5)– The IVD height to body height ratio (2:5) is The IVD height to body height ratio (2:5) is

greatest in the cervical spine, and the greatest in the cervical spine, and the intervertebral discs make up approximately 25% intervertebral discs make up approximately 25% of the superior-to-inferior height of the cervical of the superior-to-inferior height of the cervical spine spine

AnatomyAnatomy

Cervical DiskCervical Disk– Anteriorly, the cervical AF consists of Anteriorly, the cervical AF consists of

interwoven, alar fibers, whereas posteriorly, interwoven, alar fibers, whereas posteriorly, the AF lacks any oblique fibers, and consists the AF lacks any oblique fibers, and consists exclusively of vertically orientated fibersexclusively of vertically orientated fibers

– In no region of the cervical AF, do successive In no region of the cervical AF, do successive lamellae exhibit alternating orientationslamellae exhibit alternating orientations

– Protection against disc herniation is afforded Protection against disc herniation is afforded by the uncovertebral joints by the uncovertebral joints

AnatomyAnatomy

Cervical DiskCervical Disk– As in the lumbar spine, the cervical IVD As in the lumbar spine, the cervical IVD

functions as a closed but dynamic system, functions as a closed but dynamic system, distributing the changes in pressure equally to distributing the changes in pressure equally to all components of the container, i.e., the end all components of the container, i.e., the end plates and the AF, and across the surface of the plates and the AF, and across the surface of the vertebral bodyvertebral body

AnatomyAnatomy

Cervical DiskCervical Disk– It has been observed that in the first and second decades of life, It has been observed that in the first and second decades of life,

before complete ossification occurs, lateral tears occur in the before complete ossification occurs, lateral tears occur in the annulus fibrosus, most probably induced by motion of the cervical annulus fibrosus, most probably induced by motion of the cervical spine in the bipedal posturespine in the bipedal posture

– The tears in the lateral part of the disc tend to enlarge toward the The tears in the lateral part of the disc tend to enlarge toward the medial aspect of the intervertebral discmedial aspect of the intervertebral disc The development of such tears through both sides may result in a The development of such tears through both sides may result in a

complete transverse splitting of the disccomplete transverse splitting of the disc Such a process can be observed in the second and third decades of Such a process can be observed in the second and third decades of

life in the lower cervical spine when the intervertebral disc is split in the life in the lower cervical spine when the intervertebral disc is split in the middle into equal halvesmiddle into equal halves

With this aging process, the NP rapidly undergoes fibrosis such that, by With this aging process, the NP rapidly undergoes fibrosis such that, by the third decade, there is barely any nuclear material distinguishable the third decade, there is barely any nuclear material distinguishable

PathologyPathology

Cervical diskCervical disk– When considering cervical IVD, it is clear that When considering cervical IVD, it is clear that

the pathology affecting the cervical IVD is the pathology affecting the cervical IVD is different from that affecting the lumbar disc different from that affecting the lumbar disc

PathologyPathology

Cervical diskCervical disk– Almost everyone older than 40 years of age has Almost everyone older than 40 years of age has

evidence of cervical disc degenerationevidence of cervical disc degeneration– According to Töndury and Theiler, the NP According to Töndury and Theiler, the NP

usually dries out in the fourth and fifth decades usually dries out in the fourth and fifth decades of life and acute extrusion is not expected then of life and acute extrusion is not expected then

PathologyPathology

Cervical diskCervical disk– Anteriorly, compression of the nerve roots is Anteriorly, compression of the nerve roots is

likely caused by protruding discs and likely caused by protruding discs and osteophytes of the uncovertebral region, osteophytes of the uncovertebral region, whereas the superior articular process, the whereas the superior articular process, the ligamentum flavum, and the periradicular fibrous ligamentum flavum, and the periradicular fibrous tissues often affect the nerve posteriorly tissues often affect the nerve posteriorly

PathologyPathology

Cervical diskCervical disk– Considering the structure of the cervical AF, the Considering the structure of the cervical AF, the

possibilities that emerge for mechanisms of possibilities that emerge for mechanisms of discogenic pain are strain or tears of the discogenic pain are strain or tears of the anterior AF, particularly after hyperextension anterior AF, particularly after hyperextension trauma, and strain of the alar portions of the trauma, and strain of the alar portions of the posterior longitudinal ligament when stretched posterior longitudinal ligament when stretched by a bulging discby a bulging disc

PathologyPathology

Cervical diskCervical disk– In the lumbar disc, a prolapse is common. In the In the lumbar disc, a prolapse is common. In the

cervical spine, a straightforward prolapse is uncommon, cervical spine, a straightforward prolapse is uncommon, and a cervical disc herniation should not be considered and a cervical disc herniation should not be considered as a miniature version of lumbar disc herniationas a miniature version of lumbar disc herniation

– Acute disc herniations may result in compression of Acute disc herniations may result in compression of nerve roots. Cervical discs may become painful as part nerve roots. Cervical discs may become painful as part of the degenerative cascade, from repetitive of the degenerative cascade, from repetitive microtrauma, or from an excessive single load microtrauma, or from an excessive single load

PathologyPathology

Cervical diskCervical disk– The most common level of cervical nerve root The most common level of cervical nerve root

involvement has been reported at the seventh involvement has been reported at the seventh (C7, 60%) and sixth (C6, 25%), followed by the (C7, 60%) and sixth (C6, 25%), followed by the C4‑C5 disc C4‑C5 disc

ExaminationExamination

As with the lumbar spine, the conventional As with the lumbar spine, the conventional physical examination for a suspected physical examination for a suspected cervical disk herniation consists of tests for cervical disk herniation consists of tests for strength and range of motion, reflex, and strength and range of motion, reflex, and sensory testing, and dural mobility testssensory testing, and dural mobility tests

AnatomyAnatomy

Thoracic diskThoracic disk Thoracic disks have been poorly researched. They Thoracic disks have been poorly researched. They

are narrower and flatter than those in the cervical are narrower and flatter than those in the cervical and lumbar spine, and contribute approximately and lumbar spine, and contribute approximately one-sixth of the length of the thoracic columnone-sixth of the length of the thoracic column

Disk size in the thoracic region gradually increases Disk size in the thoracic region gradually increases from superior to inferiorfrom superior to inferior

The disk height to body height ratio is 1:5, The disk height to body height ratio is 1:5, compared to 2:5 in the cervical spine, and 1:3 in compared to 2:5 in the cervical spine, and 1:3 in the lumbar spine, making it the smallest ratio in the lumbar spine, making it the smallest ratio in the spine, and affording the least amount of motion the spine, and affording the least amount of motion

AnatomyAnatomy

Thoracic diskThoracic disk In the thoracic spine, the segmental In the thoracic spine, the segmental

nerve roots are situated mainly behind nerve roots are situated mainly behind the inferior-posterior aspect of the the inferior-posterior aspect of the upper vertebral body rather than upper vertebral body rather than behind the disk, which reduces the behind the disk, which reduces the possibility of root compression in possibility of root compression in impairments of the thoracic disk impairments of the thoracic disk

AnatomyAnatomy

Thoracic diskThoracic disk In contrast to the cervical and lumbar In contrast to the cervical and lumbar

regions, where the spinal canal is regions, where the spinal canal is triangular/oval in cross section and triangular/oval in cross section and offers a large lateral excursion to the offers a large lateral excursion to the nerve roots, the mid thoracic spinal nerve roots, the mid thoracic spinal canal is small and circular, becoming canal is small and circular, becoming triangular at the upper and lower levelstriangular at the upper and lower levels

At the levels of T 4 through to T 9 the At the levels of T 4 through to T 9 the canal is at its narrowest canal is at its narrowest

PathologyPathology

Thoracic diskThoracic disk Herniated disks have been found at every level of Herniated disks have been found at every level of

the thoracic spine, although they are more common the thoracic spine, although they are more common in the lower thoracic spinein the lower thoracic spine

The intra-spinal course of the upper thoracic nerve The intra-spinal course of the upper thoracic nerve root is almost horizontal (as in the cervical spine). root is almost horizontal (as in the cervical spine). Therefore, the nerve can only be compressed by its Therefore, the nerve can only be compressed by its corresponding disk. More inferiorly in the spine corresponding disk. More inferiorly in the spine though, the course of the nerve root becomes more though, the course of the nerve root becomes more oblique, and the lowest thoracic nerve roots can be oblique, and the lowest thoracic nerve roots can be compressed by disk impairments of two compressed by disk impairments of two consecutive levels (T 12 root by 11th or 12th disk) consecutive levels (T 12 root by 11th or 12th disk)

ExaminationExamination

Thoracic diskThoracic disk The clinical manifestations of thoracic The clinical manifestations of thoracic

disk herniation are extremely variable disk herniation are extremely variable and vague. This often results in long and vague. This often results in long delays between presentation and delays between presentation and diagnosis diagnosis