Porth's Essentials of Pathophysiology, 4e

895

Disorders of Neuromuscular Function

C h a p t e r 3 6

Vertebral canal

Posterior longitudinal ligament

L4 vertebra

Herniation of nucleus pulposus of L4/L5 disk sparing L4 spinal nerve but compressing L5 and other nerves passing to lower levels

Herniation of nucleus pulposus

L4 spinal nerve L5 vertebra

Nucleus pulposus

Annulus fibrosus

L5 spinal nerve

A

Spinous process

S1

Spinal canal

Compressed spinal nerve root

S2

Superior articular facets

S3

Transverse process

S4

Herniation of nucleus pulposus

S5 Coccygeal nerve

C

Defect in annulus fibrosus

Nucleus pulposus

Annulus fibrosus

B

FIGURE 36-9. Herniated intervertebral disk. (A) Longitudinal section. (B) Cross-section. (C) Location of L4 to L5 and S1 to S5 spinal nerves, with site of L4/L5 herniation of nucleus pulposus indicated. (Modified from Moore KL, Dalley AF. Clinically Oriented Anatomy. 5th ed. Philadelphia, PA: Lippincott Williams &Wilkins; 2006:503.)

Conditioning exercises of the trunk muscles, particu- larly the back extensors, are often recommended. Intervertebral Disk Disorders. The intervertebral disk is considered the most critical component of the load- bearing structures of the spinal column. It consists of a soft, gelatinous center called the nucleus pulposus, which is encircled by a strong ring of fibrocartilage called the annulus fibrosus. 29 The structural components of the disk make it capable of absorbing shock and changing shape while allowing movement. With dysfunction, the nucleus pulposus can be squeezed out of place and her- niate through the annulus fibrosus, a condition referred to as a herniated or slipped disk (see Fig. 36-9B). The intervertebral disk can become dysfunctional because of trauma, the effects of aging, or degenerative disorders of the spine. Protrusion of the nucleus pulpo- sus usually occurs posteriorly and toward the interverte- bral foramen and its contained spinal nerve root, where the annulus fibrosus is relatively thin and poorly sup- ported by either the posterior or anterior ligaments 28,29 (see Fig. 36-9A). Trauma results from activities such as lifting while in the flexed position, slipping, falling on the buttocks or back, or suppressing a sneeze. With aging, the gelatinous center of the disk dries out and loses much of its elasticity.

The level at which a herniated disk occurs is impor- tant (see Fig. 36-9C). The cervical and lumbar regions are the most flexible areas of the spine and are most often involved in disk herniations. Usually, herniation occurs at the lower levels of the lumbar spine, where the mass being supported and the bending of the verte- bral column are greatest. When the injury occurs in the lumbar area, only the nerve fibers of the cauda equina are involved. Because these elongated dorsal and ven- tral roots contain endoneurial tubes of connective tis- sue, regeneration of the nerve fibers is likely. However, months may be required for full recovery to occur because of the distance to the innervated muscle or skin of the lower limbs. The signs and symptoms of a herniated disk are local- ized to the area of the body innervated by the spinal nerve roots and include both motor and sensory mani- festations (Fig. 36-10). Pain is the first and most com- mon symptom of a herniated disk. The nerve roots of L4, L5, S1, S2, and S3 give rise to a syndrome of back pain, sometimes referred to as sciatica , which spreads down the back of the leg and over the sole of the foot. The pain is usually intensified with coughing, sneezing, straining, stooping, standing, and the jarring motions that occur during walking or riding. Slight motor weakness may occur, although major weakness is rare.