C h a p t e r 3 6
Disorders of Neuromuscular Function
895
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.
L4 vertebra
L4 spinal
nerve
L5 vertebra
L5 spinal
nerve
S1
S2
S3
S4
S5
Coccygeal
nerve
Herniation of nucleus
pulposus of L4/L5 disk
sparing L4 spinal nerve
but compressing L5 and
other nerves passing to
lower levels
Posterior
longitudinal
ligament
Vertebral canal
Herniation of
nucleus pulposus
Nucleus
pulposus
Nucleus
pulposus
Annulus
fibrosus
Annulus
fibrosus
Compressed spinal
nerve root
Herniation of
nucleus pulposus
Spinal canal
Defect in annulus fibrosus
Superior
articular
facets
Spinous process
Transverse
process
A
B
C
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.)
