Clinical Application of Neurologic
Levels
Herniated Cervical Disks
There are eight cervical nerves and only seven cervical vertebrae; thus, each
cervical nerve leaves the spine adjacent to its corresponding vertebral body
except C8, the first cervical nerve exits between the occiput and C1, the sixth
between C5 and C6, and the eighth between C7 and T1 (Fig. 1-37). A herniated
disk impinges upon the nerve root exiting above the disk and passing through
the nearby neural foramen and results in the involvement of one specific
neurologic level. For example, a herniated disk between C5 and C6 impinges
upon the C6 nerve root (Fig. 1-38). When a disk herniates into a nerve root, pain
radiates along the path of the nerve root being irritated.
FIGURE 1-37 Cervical vertebrae and nerve roots.
There is slightly more motion between C5 and C6 than between the other
cervical vertebrae (except for between the specialized articulations of the
occiput and C1, and C1 and C2) (Figs. 1-39 and 1-40). Greater motion causes a
greater potential for breakdown, and the incidence of herniated disks and
osteoarthritis is greater at C5-C6 than at any of the other cervical disk spaces.
The incidence of herniation increases at C6-C7 as the patient grows older; the
reasons for this are not yet known.
To involve the nerve root, the disks must herniate posteriorly. They do so
for two reasons: first, the annulus fibrosus is intact and strong anteriorly and
defective posteriorly; second, the anterior longitudinal ligament is anatomically
broader and stronger than the narrower posterior longitudinal ligament. Because
a disk usually herniates under pressure, it breaks through in the direction of least
resistance, posteriorly. Because of the rhomboidal shape of the posterior
longitudinal ligament, the disk also tends to herniate to one side or the other
(Fig. 1-41); it is less common to have a midline herniation, because the disk
would then have to penetrate the strongest portion of the ligament.
FIGURE 1-38 A herniated cervical disk.
FIGURE 1-39 Specialized articulation between the occiput and
C1 allowing for 50 percent of the flexion and extension in the
cervical spine.
FIGURE 1-40 Specialized articulation between C1 and C2
allowing for 50 percent of the rotation in the cervical spine.
Pain in one arm or the other is symptomatic of herniated cervical disks; the
pain usually radiates to the hand along the neurologic pathways of the involved
root, although, occasionally, the pain may be referred only as far as the shoulder.
Coughing, sneezing, or straining usually aggravates the pain and causes it to
radiate throughout the involved neurologic distribution in the extremity.
FIGURE 1-41 The anatomic basis for posterior cervical disk
herniation.
The symptoms and signs caused by a herniated disk vary depending on the
location of the herniation. If the herniation is lateral, as is most common, it may
impinge directly upon the nerve root, giving classical root-level neurologic
findings. However, if the disk herniates in the midline, the symptoms may be
evident in the leg and arm as well (Fig. 1-42). If the disk protrudes but does not
herniate, pain may be referred to the midline of the back in the area of the
superior medial portions of the scapulae (Fig. 1-43). Lateral protrusion may send
pain along the spinous border of the scapula (most commonly to the superior
medial angles), with radiation of pain down the arm, but usually without
neurologic findings.
Occasionally, there may be inconsistent findings of neurologic level
involvement during the examination. Sometimes the brachial plexus, which
usually includes the nerve roots C5-T1, will begin a level higher (prefixed) or a
level lower (postfixed), causing variations in the segmental innervation of the
muscles; the findings will reflect this inconsistency in the innervation of the
upper extremity. It is also possible that such major inconsistencies are due to
brachial plexus or peripheral nerve injuries.
FIGURE 1-42 Pattern of pain radiation with a midline herniated
cervical disk.
Specific Tests for Locating Herniated Cervical Disks
To establish the exact neurologic level of involvement secondary to a herniated
disk, use the neurologic evaluation technique described earlier in this chapter
(Figs. 1-44 to 1-48).
Table 1-1 summarizes the areas of neurologic level testing. In addition, it
demonstrates the clinical application of neurologic level testing to pathology in
the cervical spine, especially with regard to the evaluation of herniated disks.
Other ways of locating herniated disks are through the following:
1. The magnetic resonance imaging (MRI), which reveals the abnormal
protrusion of a herniated disk into the spinal cord, nerve root, or cauda equina
at the involved level.
2. Myelogram, which is a test where contrast dye is injected into the spine, after
which a computed tomography scan is performed to look for problems in the
spinal canal, including spinal cord, nerve roots, and other tissue. The test is
commonly reserved for patients who have previously had spine surgery or
who cannot have an MRI (Fig. 1-49).
3. The electromyogram (EMG), which accurately measures motor potentials.
Two weeks after injury to a nerve, abnormal spontaneous electrical discharges
appear in the resting muscle (fibrillation potentials and positive sharp waves).
These are evidence of a muscle denervation, which can result from herniated
disks, nerve root avulsions, or cord lesions. (They can also occur in plexus
and peripheral nerve lesions.) It is important that muscles representing each
neurologic level (myotome) be sampled for a complete evaluation (see Table
FIGURE 1-43 Pattern of pain radiation with a lateral protrusion
of a cervical disk.
FIGURE 1-44 A herniated disk between vertebrae C4 and C5
involves the C5 nerve root.
General Test for Herniated Cervical Disks
The Valsalva test is a generalized test that indicates only the presence of a
herniated disk. The tests of each neurologic level are more precise and can
pinpoint the exact level of involvement.
Valsalva Test: The Valsalva test increases the intrathecal pressure. If there is a
space-occupying lesion in the cervical canal, such as a herniated disk or a tumor,
the patient will develop pain in the cervical spine secondary to the increased
pressure. The pain may radiate to the neurologic distribution of the upper
extremity that corresponds to the pathologically involved neurologic level.
To perform the Valsalva test, have the patient bear down as if moving the
bowels while holding the breath. Then ask the patient if there is any increase in
pain either in the cervical spine or, by reflection, in the upper extremity (Fig. 1-
50). The Valsalva test is a subjective test that requires that the patient answer
your questions appropriately; if the patient is either unable or unwilling to
answer, the test is of little value.
Cervical Neck Sprain versus Herniated Disk
Patients frequently develop neck pain after automobile accidents that cause the
cervical spine to whip back and forth (whiplash) or twist (Fig. 1-51A, B). The
resulting injury may stretch an individual nerve root, cause a nerve root to
impinge upon an osteoarthritic spur, or produce a herniated disk. Patients with
neurologic involvement complain of neck pain referred to the medial border of
the scapula and radiating down the arm to varying degrees, as well as of
numbness and muscle weakness in the extremity. However, such an injury may
simply stretch the posterior or anterior neck muscles, causing a similar neck pain
with radiation to the shoulder and medial border of the scapula.
FIGURE 1-45 A herniated disk between vertebrae C5 and C6
involves the C6 nerve root. This is the most common level of
disk herniation in the cervical spine.
Differentiation between generalized soft-tissue injury without neurologic
involvement and injury with neurologic involvement can be made by testing the
integrity of the neurologic levels innervating the upper extremities. With each
patient visit, neurologic testing must be repeated, because an originally
quiescent lesion may later clinically manifest itself. Note that the converse is
also true: patients who are hospitalized for treatment of neurologic problems
may show improved muscle strength, return of a reflex, or return of normal
sensation to the involved dermatome.
Many patients continue to complain of cervical pain six months to a year
after injury without evidence of either neurologic or objective MRI findings of
pathology. The practitioner should have the confidence, despite patient pressure,
to continue conservative (nonoperative) therapy, knowing that the patient may
have a permanent soft-tissue injury not involving the anterior primary nerve
roots or the intervertebral cervical disks.
FIGURE 1-46 A herniated disk between vertebrae C6 and C7
involves the C7 nerve root.
The Uncinate Processes and Osteoarthritis
The uncinate processes are two ridges of bone that originate on the superior
lateral surface of the cervical vertebrae. They help to stabilize the individual
vertebra and participate in the formation of the neural foramen (Fig. 1-52).
Enlargements or osteoarthritis involving the uncinate process may encroach
upon the neural foramen and directly compress the exiting nerve root or limit the
amount of room in which it can move (Fig. 1-53).
The neural foramen and portion of the uncinate process encroaching upon it
can be seen on an x-ray (Fig. 1-54). Note that the nerve roots emerge at a 45°
angle from the cord and vertebral body, the same angle that exists between the
neural foramen and the vertebral body. An osteophyte from the uncinate process
has little clinical significance unless it is accompanied by symptoms. Clinical
problems may arise after an automobile accident, when a patient with a
narrowed neural foramen may place excessive strain on the nerve root lying in it
because of the extreme extension/flexion of the head and neck and the
subsequent reactive edema of the nerve root. Note that the narrowed foramen
frequently has the x-ray appearance of a figure 8, a configuration that does not
allow room for the posttraumatic swelling of the nerve and results in pain. Pain
and neurologic findings are naturally found in the involved neural distribution in
the upper extremity. For example, trauma affecting the C6 nerve root may result
in decreased sensation to the lateral forearm, muscle weakness to the wrist
extensors, and an absent brachioradialis reflex (Fig. 1-40). It is also possible,
however, that the only symptom referred is pain to the superior medial angle and
medial border of the scapula.
FIGURE 1-47 A herniated disk between vertebrae C7 and T1
involves the C8 nerve root.
Where there is more motion, there is a greater chance of breakdown, and
uncinate process enlargement secondary to osteoarthritis is most often found at
the C5-C6 bony level.
Spurling Test
The cervical spine compression test determines whether the patient’s pain is
increased when the cervical spine is compressed. Pain caused by narrowing of
the neural foramen, pressure on the facet joints, or muscle spasm may be
increased by compression. The compression test may also faithfully reproduce
pain referred down the upper extremity from the cervical spine; in doing so, it
may assist in locating the neurologic level of existing pathology.
FIGURE 1-48 A herniated disk between vertebrae T1 and T2
involves the T1 nerve root. A herniated disk in this area is
unusual.
To perform the compression test, have the patient turn their head to the
affected side and slightly extend their head. Press on the top of the patient’s head
while the patient is either sitting or lying down; discover whether there is any
corresponding increase in pain either in the cervical spine or down the extremity.
Note the exact distribution of this pain and whether it follows any previously
described dermatome (Fig. 1-55).
Nerve Root Avulsions
Cervical nerve roots are frequently avulsed from the cord during motorcycle
accidents. When a rider is thrown from his cycle, his head and neck are forced
laterally, and his shoulder is depressed by the impact with the ground, causing
the cervical nerve roots to stretch and finally avulse (Fig. 1-56). The C5 and C6
nerve roots are the roots most commonly avulsed.
Physical examination shows the obvious results: with the loss of the C5
root, there is total motor paralysis along the C5 myotome and sensory deficit
along the C5 dermatome. The deltoid muscle is paralyzed, sensation along the
upper lateral portion of the arm is hypesthetic or anesthetic, and the biceps reflex
(C5-C6) is diminished or absent. The MRI shows an avulsion, the origin of the
C5 nerve root between the C4 and C5 vertebrae. Such a lesion is not amenable
to surgical repair. The injury is permanent; no recovery is to be expected.
TABLE 1-1 UNDERSTANDING HERNIATED DISKS AND
OSTEOARTHRITIS OF THE CERVICAL SPINE
UNCINATE
ROOT DISKMUSCLES REFLEX
SENSATION
EMG
MYELOGRAM PROCESS
C5
C4- Deltoid
C5 Biceps
Biceps
Lateral arm
Axillary nerve
Fibrillation Bulge in spinal C5
or sharp cord C4-C5
waves in
deltoid,
biceps
C5- Biceps
C6 Wrist
Brachioradialis Lateral forearm
Fibrillation Bulge in spinal C6
C6
Musculocutaneous or sharp cord C5-C6
extensors
nerve
waves in
biceps
C7
C6- Triceps
C7 Wrist
flexors
Triceps
Middle finger
Fibrillation Bulge in spinal C7
or sharp cord C6-C7
waves in
Finger
triceps
extensors
C8
T1
C7- Hand
T1 intrinsics forearm
Medial
Fibrillation or
sharp waves in
intrinsic hand
Bulge in
spinal
cord C7-
T1
Finger
flexors
Medial
antebrachial-
cutaneous
nerve
muscles
T1- Hand
T2 intrinsics Medial
brachial-
Medial arm
Fibrillation or
sharp waves in
hand muscles
cutaneous
nerve
Most common level of herniation.
Deltoid, rhomboid, supraspinatus, and infraspinatus muscles.
Extensor carpi radialis longus and brevis.
Triceps, flexor carpi radialis, extensor digitorum longus.
Flexor digitorum muscles.
FIGURE 1-49 MRI: herniated disk at C5-C6.
FIGURE 1-50 The Valsalva test.
FIGURE 1-51A, B Whiplash injury to the cervical spine.
FIGURE 1-52 The anatomy of a cervical vertebra.
FIGURE 1-53 Osteoarthritis of the uncinate process.
FIGURE 1-54 Narrowed neural foramen secondary to
osteoarthritis of the uncinate process, C3-C4.
FIGURE 1-55 Compression test. (Hoppenfeld, S.: Physical
Examination of the Spine and Extremities. Norwalk, CT:
Appleton-Century-Crofts, 1976.)
Although C5 and C6 are the most commonly avulsed roots, the C8 and T1
may also be avulsed. If the cyclist strikes the ground with his shoulder
hyperabducted, the lowest roots of the brachial plexus are usually the ones
injured, whereas the C5 and C6 nerve roots remain intact.
FIGURE 1-56 Avulsion of the C5 nerve root following a
motorcycle accident
