Dalley, 10th Edition

109

Vertebral Column

Herniation of Nucleus Pulposus (Herniation of IV Disc)

does not receive support from either the posterior or the an terior longitudinal ligaments (Fig. B2.11B). A posterolateral herniated IV disc is more likely to be symptomatic because of the proximity of the spinal nerve roots. The nucleus pulp osus itself is insensitive. The localized back pain of a herni ated disc, which is usually acute pain , results from pressure on the longitudinal ligaments and periphery of the anulus brosus and from local in ammation caused by chemical ir ritation by substances from the ruptured nucleus pulposus. Chronic pain resulting from compression of the spinal nerve roots by the herniated disc is usually referred radiating pain , perceived as coming from the area (dermatome) supplied by that nerve. Because the IV discs are largest in the lum bar and lumbosacral regions, where movements are conse quently greater, posterolateral herniations of the nucleus pulposus are most common here. Approximately 95% of lumbar disc protrusions occur at the L4–L5 or L5–S1 levels. The marked decrease in the radiographic intervertebral space (i.e., in disc height) that may occur as a result of acute herniation of a nucleus pulpo sus may also result in narrowing of the IV foramina, per haps exacerbating the compression of the spinal nerve roots, especially if hypertrophy of the surrounding bone has also occurred. Because the nucleus becomes increasingly dehy drated and brous, or even granular or solid with aging, a diagnosis of acute herniation in advanced years is regarded

Herniation (protrusion) of the gelatinous nucleus pulposus into or through the anulus brosus is a well-recognized cause of lower back pain (LBP) and lower limb pain (Fig. B2.11). However, there are many other causes of LBP; furthermore, herniations are often coincidental ndings in asymptomatic individuals. The IV discs in young persons are strong—usually so strong that the vertebrae often fracture during a fall before the discs rupture. Furthermore, the water content of their nuclei pulposi is high (approaching 90%), giving them great turgor (fullness). However, violent hyper exion of the verte bral column may rupture an IV disc and fracture the adja cent vertebral bodies. Flexion of the vertebral column produces compression anteriorly and stretching or tension posteriorly, squeezing the nucleus pulposus further posteriorly toward the thinnest part of the anulus brosus. If the anulus brosus has degen erated, the nucleus pulposus may herniate into the vertebral canal and compress the spinal cord or the nerve roots of the cauda equina (Fig. B2.11). A herniated IV disc is inappropri ately called a “slipped disc” by some people. Herniations of the nucleus pulposus usually extend pos terolaterally, where the anulus brosus is relatively thin and

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Cauda equina in lumbar cistern of subarachnoid space Herniation of nucleus pulposus of L4/L5 disc sparing L4 spinal nerve but

Vertebral canal

L4 vertebra

Posterior longitudinal ligament

Herniation of nucleus pulposus Nucleus pulposus

L4 spinal nerve

L5 vertebra

L5 spinal nerve

compressing L5 and other nerves

Anulus fibrosus

passing to lower levels

L5

S1

S1

S2

Median section

(A) Herniated nucleus pulposus

S3

Median MRI

Intervertebral (IV) disc

Anterior longitudinal ligament

Anulus fibrosus

Nucleus pulposus Copyright © 2027 Wolters Kluwer. Unauthorized reproduction of the article is prohibited. S4

Posterior longitudinal ligament

S5

Herniation into IV foramen (spinal n. compression)

Herniation into spinal canal (cauda equina compression)

X

X

Coccygeal nerve

Posterior view

(C) Compression of spinal nerve roots by a posterolateral herniation of nucleus pulposus of IV disc

Cauda equina

Sites with greatest potential for anulus defect (anulus thinnest and lacking longitudinal ligament support)

X

Facet joint Dural sac

Transverse section

Axial MRI

(B) Herniated nucleus pulposus

FIGURE B2.11. Herniation of nucleus pulposus. A–C. Demonstration of hernia affecting dural sac and cauda equina in median ( A ), transverse ( B ), and posterior ( C ) views. ( Pink arrows in MRIs indicate herniations of nuclei IV discs.)