81 W S P I N A L

81
S P I N A L
D E G E N E R A T I V E
D I S O R D E R S
DUNCAN Q. MCBRIDE
W
eight bearing, flexion, extension, and rotatory
movements all can cause gradual degeneration of intervertebral discs and spinal facet joints. Dehydration,
degeneration, collapse, and herniation of intervertebral
discs can occur. This causes failure of the spine to bear
its normal axial load and can also cause compression
and irritation of neural elements. The result is pain
and neurologic dysfunction. The specific neurologic
deficits are related to the exact location and function of
the affected nerves. This chapter introduces the spectrum
of degenerative disorders that involve the human spinal
column.
CASE 1
CERVICAL SPONDYLITIC
MYELOPATHY
A 66-year-old female complained of the insidious onset of
neck pain radiating to her shoulders and arms, right
greater than left.
She was experiencing tingling, burning, and numbness
in her right thumb and index finger. She also noted progressive upper and lower extremity weakness to the extent
that she was unable to open a jar or turn a doorknob with
her hands. She complained that her gait had become stiff
and she was unable to run or to climb stairs without assistance. She denied difficulties with urination or anal sphincter control.
She had mild atrophy of the thenar and hypothenar
eminences, right greater than left. Her gait was slightly
spastic in nature. Her mental status, cranial nerves, and
cerebellar examinations were normal. She had 4+/5 weakness of the right biceps and brachioradialis muscles, and
5–/5 weakness of the wrist extensor on the right and the
triceps bilaterally. She also had 5–/5 weakness of the lower
extremities diffusely. There was hyperesthesia with tingling sensation on palpation in the index finger and thumb
on the right side and into the radial aspect of the forearm.
Pin/dull discrimination revealed error in the same distributions bilaterally, with diffuse errors in the trunk and the
lower extremities. Joint position sense was intact. Deep
tendon reflexes were absent at the biceps and brachioradialis. She had 2+ triceps reflexes and 3+ patellar and
Achilles reflexes. The plantar reflexes were extensor bilaterally, and there was mild clonus at the ankles.
Cervical spine radiographs showed the normal lordotic curve with osteophytic spurs at C4-C5 and C5-C6
with evidence of foraminal stenosis. An MRI scan demon587
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N E U R O S U R G E R Y
strated circumferential stenotic levels at C4-C5 and C5C6 due to disc herniation and osteophytes ventrally and
ligamentous hypertrophy dorsally (Fig. 81.1). The stenosis
at C5-C6 was quite severe with compression of the cervical spinal cord and lack of CSF signal at that level. There
was marked stenosis of the neural foramina bilaterally,
with greater narrowing on the right side. She was placed
in a cervical collar and given dexamethasone acetate. An
anterior cervical spinal decompression with discectomies
at C4-C5 and C5-C6 was done urgently. The C5 vertebral
body underwent corpectomy. The osteophyte and herniated disc segments were carefully elevated and removed.
The posterior longitudinal ligament was opened and the
dura allowed to relax forward into the defect created in
the bone. Foraminotomies were performed at C5-C6 with
careful excision of bony material from the neuroforamina.
The spine was fused using autologous iliac crest.
Postoperatively, she noted immediate improvement in
her pain syndrome in the upper extremities and neck. She
had residual numbness in the C5-C6 distribution, which
gradually resolved. Her abnormal gait and lower extremity
symptoms had begun to improve while on dexamethasone
and continued to improve over the course of several
months, such that she had a normal gait on long-term follow-up. At 6 weeks postoperatvely, she was able to discontinue the cervical collar orthosis. Cervical spine flexion/extension views demonstrated a good fusion of the bone
graft with C4, C5, and C6 moving as one solid unit.
CASE 2
LUMBAR DISC HERNIATION
A 31-year-old male was lifting a couch when he felt a
“pop” in his back. He suffered immediate severe lower
back pain and could not straighten up properly. Within an
hour, he began to note burning of the left leg from his buttock down to the dorsum of his foot. This pain was a
shooting, electrical sensation that was quite severe. Whenever he tried to stand, walk, or sit or whenever he coughed
or sneezed, he noted increased pain in the lower extremity. He spent 1 or 2 days in bed, which gave some relief;
however, he sought medical attention when pain relievers
and bed rest did not completely resolve his pain syndrome. He had not had difficulty urinating.
On physical examination, he was in marked distress
and unable to straighten, preferring to lie on the examination table. He had decreased light touch in the posterolateral aspect of his left thigh down into his calf and onto the
dorsum of his foot, including the lateral aspect onto the
plantar surface. He had normal power in his lower extremities except for his left extensor hallucis longus, which was
4/5. He was unable to stand on his toes on the left, and had
difficulty with heel standing. The deep tendon reflexes
were 2+ at the knees and the right ankle and absent at the
left ankle. The straight leg raising test produced severe
pain in the left leg at 30 degrees. The back was nontender
to palpation, and there was no paraspinous muscle spasm.
An MRI of the lumbar spine showed a large disc herniation with probable extrusion of disc fragment into the
spinal canal on the left side at L5–S1 (Fig. 81.2). The disk
caused entrapment of the L5 nerve root exiting at that
level as well as the traversing S1 root.
He underwent an L4-L5 hemilaminotomy on the left
with microscopic discectomy. A large free disc fragment
was found to be compressing the L5 and S1 nerve roots
and it was removed.
Postoperatively, he had immediate resolution of his severe pain. He rapidly recovered power in his toe and
ankle, although he had persistent absence of the deep tendon reflex at the left ankle on long-term follow-up.
D
GENERAL CONSIDERATIONS
egenerative disorders of the spine are quite common. Approximately 50% of individuals over 50 years of
age who are studied with lumbar or cervical magnetic resonance imaging (MRI) scans show degenerative changes.
Disc herniations can occur acutely with trauma, or insidiously with dehydration and degeneration of the disc and
gradual inability of the disc to carry its normal weight and
motion load. This causes the disc to lose its height and results in bony osteophyte formation, where bone edges
touch that previously did not. This abnormal friction
causes overgrowth of bony end-plates and results in bone
spur formation (spondylosis). Furthermore, abnormal motion and chronic degenerative changes in posterior facet
joints results in hypertrophy of the joint and the adjacent
ligamentum flavum. This commonly occurs in the lumbar
spine, resulting in progressive circumferential stenosis of
the spinal canal with advanced age. In the cervical spine,
this can be further aggravated by degeneration and hypertrophy of the uncovertebral joints that lie at the posterolateral aspects of the disc space bilaterally.
The principal manifestations of spinal degenerative
disease are pain and neurologic deficit. Patients with cervical spine disc herniation present with a syndrome of
neck, arm, and head pain, typically in the dermatomal pattern of the exiting nerve root. Frequently this pain is a severe burning, tingling numbness that awakens the patient
at night due to repeated minor trauma to the cervical
nerve root. Pain often is felt in the paraspinous muscle
area and at trigger points in the interscapular region and
occipital areas.
Cervical disc herniation or cervical spondylosis can
also cause neurologic deficit in the spinal cord (Case 1). In
these circumstances, patients will have long tract upper
motor neuron findings manifested below the level of cervical compression, as well as lower motor neuron periph-
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D E G E N E R A T I V E
D I S O R D E R S
A
B
FIGURE 81.1 (A) Saggital T2-weighted MRI of the cervical spine demonstrating degenerative discs
with spinal cord compression maximum at C4-C5 and C5-C6. Note increased signal intensity between
these discs indicative of cord edema. (B) Axial CT image through the C5-C6 disc illustrates spinal canal
stenosis and spinal cord compression.
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N E U R O S U R G E R Y
A
B
FIGURE 81.2 (A) Saggital T2-weighted MRI of the lumbar spine demonstrating degenerated herniated
disc at L5–S1 with nerve root entrapment. (B) Axial view through L5–S1 disc illustrates neural foramenal and nerve root compression on the right from the disc extrusion.
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D E G E N E R A T I V E
eral findings in the distribution of the nerve root at the
level of compression.
Lumbar spinal degeneration occurs by similar mechanisms. The highest percentage of cases occur below L4,
and neurologic signs are virtually always peripheral nerve
in nature. Patients with lumbar degenerative disease typically present with varying degrees of a combination of low
back pain and leg pain. Radiating leg pain in the distribution of affected nerve roots is often called sciatica. Because
low back pain is so common (60–80% incidence) the judicious use of conservative management, diagnostic testing,
and surgery is extremely important. Thus, operation is limited to those patients who fail conservative management.
The importance of psychosocial issues in the treatment of spinal degenerative disease cannot be overemphasized. All studies that have examined surgical outcome have demonstrated the effect of litigation. Other
forms of secondary gain should also be considered, including familial sympathy, drug seeking, and other psychosocial motivators.
K E Y
P O I N T S
• Disc herniations can occur acutely with trauma, or insidiously with dehydration and degeneration of the disc and gradual inability of the disc to carry its normal weight and motion
load; this causes the disc to lose height and results in bony osteophyte formation, where bone edges touch that previously
did not
• Principal manifestations of spinal degenerative disease are
pain and neurologic deficit
• Patients with cervical spine disc herniation present with
neck, arm, and head pain, typically in the dermatomal pattern
of the exiting nerve root; frequently pain is severe burning, tingling numbness that awakens patient at night due to repeated
minor trauma to cervical nerve root
• In circumstances of neurologic deficit of spinal cord, patients
will have long tract upper motor neuron findings manifested
below the level of cervical compression, as well as lower motor
neuron peripheral findings in the distribution of the nerve root
at the level of compression
• Highest percentage of cases occur below L4, and neurologic
signs are virtually always peripheral nerve in nature
• Radiating leg pain in the distribution of affected nerve roots
often called sciatica
T
D I S O R D E R S
head movements, and often the patient will feel more
comfortable with the head tilted away from the side of
maximum root compression. The patient may also complain of weakness and numbness in the hand or arm. Specific complaints depend on the level of compression and
the degree of neurologic compromise. In those with spinal
cord symptoms, the complaints include weakness or abnormal sensation in the legs as well as, potentially, bowel
and bladder sphincter disturbance. As in lumbar disease,
maneuvers that increase the degree of neural compression
cause increased symptoms. These include extreme flexion,
extension, or lateral rotation of the spine or Valsalva maneuvers that increase the intrathecal pressure. Thus, the
patient’s complaints might include increased pain on
coughing, sneezing, laughing, or defecation.
Symptoms from lumbar disc disease are similar. Those
with disease producing nerve root entrapment have leg
symptoms that far outweigh the low back complaints. The
patients have abnormal posture, tilting away from the side
of disc herniation. The pain can be so severe that they
cannot straighten completely or stand upright (Case 2).
Symptoms of lumbar stenosis, without acute disc herniation, differ considerably from those of the acute herniated disc with stenosis. Patients typically have an insidious
onset of pain rather than acute pain. The pain is exclusively
in the legs and is often bilateral. If back pain does exist, it is
typically a low-level dull ache in the uncomplicated stenosis patient. The hallmark feature of lumbar stenosis is onset
of leg pain on walking some distance that is relieved by
rest. Usually the patient will say they can walk a block or
two and then they have to sit down to relieve the burning
pain in the posterolateral aspects of their thighs and calves.
In cervical degenerative disease, a wide variety of physical findings may be present. These include pain and tenderness in the paracervical musculature and at trigger
points in the interscapular area. Limited range of motion
in the neck may also be present. A thorough motor examination of the upper and lower extremities is essential.
Motor testing results are given on a five-point scale (Table
81.1). Because the motor power scale is weighted toward
the weaker end, clinicians often will include the subcategories of 4+ and 5– power to indicate various degrees of
opposition to applied resistance (Case 2). As individual
muscle groups are tested, their bulk and tone should also
TABLE 81.1
Motor power scale
DIAGNOSIS
he chief complaint of a patient with cervical degenerative disease is likely to be neck, shoulder, arm, and possibly hand pain. The pain is frequently described as an
electrical shooting, pins-and-needles sensation in the
more distal regions of the nerve root and more of an ache
or stabbing pain in the neck. The pain is exacerbated by
5 9 1
0 No contraction
1 Palpable or visible contraction with no joint movement
2 Movement of joint only when gravity eliminated
3 Can overcome gravity but not added resistance
4 Can push against added resistance, but weakly
5 Normal strength
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N E U R O S U R G E R Y
be documented. The presence of atrophy should be clearly
defined. Sensory testing, including light touch, pin/dull discrimination and joint position sense, aid significantly in the
localization of both radicular and spinal cord problems.
The testing of deep tendon reflexes, Babinski response,
Hoffmann response, and clonus of the ankles is essential in
the diagnosis of upper and lower motor neuron problems.
Analysis of the patient’s gait and ability to stand on heels
and toes, and the Romberg test, further define the neurologic deficit that may be present (Table 81.2).
Lumbar degenerative disease examination of the low
back for scoliosis, percussion for deep tenderness, and palpation of paraspinous musculature, sacroiliac joint, and the
sciatic notch for tenderness is done. Range of motion of
the back, and examination of the hip, knee, and ankle
should be noted. The typical syndromes for the lumbar
and sacral roots are listed in Table 81.3. In herniation, a
tension test should be done by straight leg raising. The patient is placed on the back and the leg is elevated by holding the ankle. This puts significant stretch on the nerve
root that is compressed by the herniated disc. Absence of
straight leg raising or other tension test findings should
place significant doubt on the diagnosis of lumbar disc disease that is correctable by operative decompression. In patients with lumbar stenosis, all of the above mentioned root
syndromes and tension test findings, are likely to be completely absent. In these patients, careful examination of the
hip joint as well as the peripheral vascular pulses in the
legs are extremely important to differentiate other commonly occurring sources of similar pain. Additionally, abdominal and rectal examinations are indicated since there
are significant abdominal and retroperitoneal conditions
(abdominal aortic aneurysm) that may produce leg pain.
A large percentage of plain radiographs of the lumbar
spine fail to diagnose the pathology completely, and further
imaging is required. At present, MRI scanning is the imaging test of choice for initial evaluation of spinal disorders.
Neuronal elements are clearly seen on MRI, and often, disc
and bone pathology is adequately imaged by this technique.
Computed tomography (CT) scan is superior to MRI in
TABLE 81.2
LEVEL
Lumbar sacral spine levels
MOTOR
SENSORY
REFLEX
L1
Iliopsoas
Upper anterior thigh
Cremasteric
L2
Hip flexion,
leg adduction
Mid-anterior thigh
None
L3
Hip extension
Anterior thigh,
medial knee
None
L4
Quadriceps
femoris
Knee, medial calf
Patellar
L5
Ankle dorsiflexors,
toe dorsiflexors
(EHL)
Lateral thigh and
calf, dorsum foot
to great toe
None
S1
Ankle, toe
plantar flexors
Lateral calf, ankle
and foot, sole
Achilles
S2
Hamstrings
Posterior thigh
None
S3–4
Anal sphincter
Perianal
Anal wink
Abbreviation: EHL, extensor hallucis longus.
imaging of bony foramina and for disc versus osteophyte
differentiation. On occasion, patients require both MRI and
CT scanning to complement each other. The best preoperative test remains the myelogram with postmyelogram CT
scan. The myelogram, with intrathecal injection of water
soluble contrast material, clearly delineates individual nerve
roots as well as spinal cord anatomy. The cross-sectional CT
scan with the contrast dye in the thecal sac, gives a superior
image of the relationship of disc, bone, ligament, and nerve.
In patients with multilevel problems, those with both cervical and lumbar degenerative problems, and those with difficult-to-diagnosis pathology, the myelogram remains the ultimate preoperative imaging test.
K E Y
P O I N T S
• Pain exacerbated by head movements; often patient will feel
more comfortable with head tilted away from side of maximum
root compression
• Patient may also complain of weakness and numbness in
hand or arm
• Patients typically have insidious onset of pain rather than
acute pain, exclusively in legs and often bilateral
Cervical spine levels
SENSORY
TABLE 81.3
LEVEL
MOTOR
REFLEX
C1–3
Neck muscles
Posterior head and neck
None
C4
Diaphragm
Shoulder
Pectoral
C5
Deltoid
Lateral upper arm
(Biceps)
C6
Biceps, wrist
extensors
Radial forearm,
thumb, and index finger
Biceps,
brachioradialis
C7
Triceps, wrist
flexors
Long finger and
dorsal web of hand
Triceps
C8
Finger flexors
Ring, little fingers, and
ulnar forearm
None
• If back pain exists, typically low-level dull ache in uncomplicated stenosis patient; hallmark feature of lumbar stenosis is
onset of leg pain upon walking some distance that is relieved by
rest
D
DIFFERENTIAL DIAGNOSIS
egenerative disorders can present in a similar fashion to cervical spondylitic disease. These include acute disc
herniation, gradual disc collapse, osteophyte formation, cir-
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cumferential spinal stenosis, hypertrophied ligamentum
flavum, ossification of the posterior longitudinal ligament
(OPLL), and segmental instability. Rheumatoid arthritis and
ankylosing spondylitis must also be considered. Tumors of
the cervical spine, both intramedullary and extramedullary,
can cause nerve root symptoms and long track findings.
Central nervous system disorders such as multiple
sclerosis and peripheral nerve entrapment syndromes
commonly mimic cervical spine degenerative complaints.
Peripheral nerve compression syndromes include carpal
tunnel syndrome with entrapment of the median nerve in
the wrist, and cubital tunnel syndrome with entrapment of
the ulnar nerve at the elbow. The former is distinguished
from a C6 or C7 radiculopathy by the presence of normal
sensation in the radial nerve innervated portion of the dermatomes (volar aspect of the thumb, index, and long fingers). Tinel’s sign (electric shock sensation produced by
tapping over the nerve) may be found at the point of entrapment. Often, however, one must perform EMG (electromyograph)/NCV (nerve conduction velocity) testing to
distinguish between peripheral entrapment and cervical
radiculopathy.
Lumbar disc herniation or degenerative collapse, progressive lumbar stenosis with hypertrophy of the nerve
roots in the lateral gutters, and spondylosis with osteophyte formation are all degenerative spinal disorders. Additionally, spondylolisthesis, when a vertebra is out of anteroposterior alignment with its neighbor (subluxation),
can be degenerative, congenital, or traumatic. All these
disorders can cause nerve root entrapment with varying
degrees of associated low back pain. Retroperitoneal and
pelvic pathologies including renal stones and neoplasms,
can also mimic the lumbar pain syndrome. Back pain and
neurologic symptoms and signs in the legs are occasionally
caused by thoracic disc herniation.
Claudication is pain in the calf on exertion due to
poor arterial inflow. It can be distinguished from lumbar
neurogenic claudication by the quality of the pain, which
is usually a cramp or a tight sensation that progresses
from distal to proximal in vascular disease. This is unlike
the burning proximal to distal pain experienced by the
patient with lumbar stenosis. In addition, those with vascular claudication will obtain some relief when standing
up, whereas the patient with neurogenic claudication
usually needs to sit or lie down to get relief from pain in
the legs. Physical examination is very helpful in distinguishing these two disorders.
A
TREATMENT
ll patients with cervical radicular signs and symptoms, without myelopathy, are given a course of conservative management in an attempt to relieve their pain.
Those with profound motor weakness due to peripheral
D I S O R D E R S
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nerve entrapment who do not have myelopathy may be
the exception to this rule. Conservative management of
cervical spine disorders is immobilization with a cervical
collar. Cervical traction is another option for pain due to a
degenerative cervical spine. Application of axial traction in
the neutral to slightly flexed position may open the interspace at the disc level and allow the neural foramen some
relief of compression from either disc or osteophyte. Traction is applied intermittently during the day for as long as
the patient can tolerate. It is used in addition to a soft cervical collar, which should be worn at all other times, especially at night.
Anti-inflammatory agents, particularly nonsteroidal
drugs, are most often prescribed. Analgesics can be helpful,
but prolonged narcotic use should be avoided. Muscle relaxants are only indicated in patients with severe intermittent muscle spasm. Tricyclic antidepressants, particularly
amitriptyline, are often used with considerable success in
the nerve root entrapment syndromes. Immobilization and
traction may address the cause of the patient’s pain, while
other approaches merely treat the symptoms. With these
modalities, a significant percentage will obtain relief of their
symptoms. If significant neurologic findings are absent, the
patient should be treated in this manner for at least 6
weeks.
A conservative approach is indicated initially for all patients who present with the low back pain syndrome, with
or without pain radiating into the leg. The exceptions to
this rule are patients with acute cauda equina syndrome
and those with documented progressive motor loss. Similar to cervical pathology, the mainstay of treatment is immobilization. This is best achieved in the lumbar spine by
bed rest for at least 7–10 days.
Patients with cervical stenosis and myelopathy, or patients with traumatic soft disc herniations with myelopathy, should be operated on without a prolonged attempt at
conservative treatment. High dose steroids, either intravenous or oral, are indicated as a perioperative adjunct.
Additionally, those with radicular symptoms who do not
significantly improve with conservative management are
in need of operation. In those cases, the degree of the patient’s pain and neurologic deficit determines the urgency
of the elective operation.
There are varying surgical approaches for relief of cervical degenerative radiculopathy and myelopathy. All patients with cervical spine pathology require extremely
careful intubation, using an awake fiberoptic nasal technique with minimal head manipulation. In addition, they
must be positioned very carefully to ensure that there is
no exacerbation of cervical compression while anesthetized.
Those with myelopathy should be monitored with intraoperative electrophysiologic evoked potentials.
The typical approach in the presence of ventral cervical compression from a disc or osteophyte is an anterior
cervical discectomy. This is done through a small incision
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in the anterior aspect of the neck, with removal of the intervertebral disc in a piecemeal fashion.
Posterior cervical procedures include a focal laminectomy and foraminotomy for relief of unilateral radiculopathy due to a laterally placed disc or osteophyte. This small
operation is often highly effective in relieving compressive
symptoms of the root. Occasionally the ventral disc material can be removed as well. The major advantage of this
approach is that it does not require cervical fusion. A more
extensive bilateral laminectomy is indicated in patients
with myelopathy who have greater than two levels of compression, especially those with circumferential compression that includes narrowing of the canal posteriorly. Operation for a lumbar disc should be performed acutely in
those with cauda equina syndrome (loss of urinary control,
weakness, sensory loss) or progressive motor loss. In addition, when degenerative lumbar stenosis is present, a significant response to conservative management is unlikely.
Lumbar disc decompression should be performed only on
those with pain syndromes predominantly in the leg. In
addition, these patients must have failed a course of conservative management and be free of severe psychosocial
problems. For some, litigation revolving around the disc
herniation and its consequences is a relative contraindication to operation.
A new, less invasive approach is currently being advocated. This is known as endoscopic discectomy and is performed through a similar posterolateral approach; however, this instrumentation is placed into the neuroforamen.
With direct visualization of the disc and root through a microendoscope, the surgeon is able to remove disc material
both from the spinal canal and from the intervertebral disc
space. As this promising technique is quite new, determination of its safety and efficacy is yet to be made.
P
FOLLOW-UP
atients who are motivated and unencumbered by secondary gain issues, who have clear-cut pathology and
whose operation is successful, should have a very high
percentage of cure from their pain syndrome. In those
with myelopathy, the patient’s age and the duration and
severity of the myelopathy will determine the outcome.
Peripheral nerve injury generally has a favorable long
term recovery rate due to wallerian regeneration.
After anterior cervical approach and alignment of the
cervical spine, the position of the bone graft and the ultimate fusion of the graft must be assessed. These patients
are kept in a cervical collar until the graft is fused. When
this occurs at 6 weeks to 2 months postoperatively, the patient is taken out of the collar and flexion/extension lateral
cervical spine views are taken to ensure that the fused segment moves as one block. Those who have myelopathy or
a significant motor loss from radiculopathy are treated
postoperatively with physical and occupational therapy to
maximize their recovery.
Patients who have undergone simple lumbar laminectomy are generally mobilized to their feet on either the
first or the second postoperative day and go directly into a
physical therapy program to exercise their back and abdominal musculature, and assist them in ambulation. Postlaminectomy lumbar instability and recurrent disc herniations are both potential postoperative problems.
SUGGESTED READINGS
Chevrot A, Vallee C: Imaging of degenerative disk diseases. Curr
Opin Radiol 4:103, 1992
A very useful reference on current modalities of diagnostic
imaging.
Hardin JG, Halla JT: Cervical spine and radicular pain syndromes. Curr Opin Rheumatol 7:136, 1995
A good general review of radicular pain syndromes.
QUESTIONS
1. Lumbar degenerative disease most commonly presents
with?
A. Altered control of voiding.
B. Sciatica.
C. Neurogenic impotence.
D. Lower extremity spasticity.
2. Lumbar stenosis, in contradistinction to acute disc herniation?
A. Primarily has lower extremity complaints.
B. Has pain with ambulation not relieved by rest.
C. Has slower onset of symptoms.
D. Is associated with severe and constant back pain.
3. The imaging test of choice for the initial diagnosis of
spinal disorders is?
A. Myelography.
B. CT.
C. MRI.
D. Plain films of the spine.
(See p. 605 for answers.)