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116 Procedure 13 | Cervical Pedicle Screw Fixation
C5
A
C
FIGURE 13-10, A-D
B
D
n
Use of a drill bit
cannot
be recommended to penetrate the cortex of the lateral
mass or to make a hole for screw advancement. However, the neurocentral
junction in the cervical spine, which is near the base of the pedicle in the vertebral body, is sometimes hard to pass with the pedicle probe, because it is in
the thoracic and lumbar spine. In such cases, the junction can be perforated
with a Kirschner wire or with small-sized high-speed diamond burr to make the
path for the pedicle probe into the vertebral body.
n
The intended angle of screw insertion in the sagittal plane is parallel to the
upper end plate for the pedicles of C5 to C7, and it is slightly in the cephalad
direction for C2 to C4 (based on angulation in the sagittal plane). The C2 screw
usually is perpendicular to the anterior surface of the vertebral body.
S T E P 1
I N S T RU M E N T A T I O N /
I M P L AN TAT IO N
• Screw diameters vary from 3.5 to
4.5 mm for cervical pedicle screw
fixation. However, a screw with a
proper diameter must be chosen to
obtain sufficient bite of the screw
thread in the pedicle cortex. The length
of the screw is usually 20 to 24 mm for
C3 to C7. A screw length of 24 mm
or more is sometimes required to
penetrate the anterior cortex of the
vertebral body to increase the C2 screw
stability. A constrained type of locking
mechanism is essential for connecting
the screws and plates/rods, to obtain
the rigid stabilizing effect of this
procedure. Regarding the longitudinal
connectors of screws, a rod rather than
a plate is recommended for
multisegmental fixation.
Procedure 13 | Cervical Pedicle Screw Fixation 117
Computer-Assisted Screw Placement
n
Modern technology for computer navigation systems has been developing in
the field of cervical spine surgery.
n
Kim and colleagues and Ludwig and colleagues conducted a study to compare
current computer-assisted technology with the original fluoroscopy-based technique in the laboratory. They concluded that the use of a computer-assisted
image guidance system did not enhance the safety or accuracy of placing pedicle
screws. However, their computer-assisted system (StealthStation; Medtronic
Sofamor-Danek USA, Memphis, Tenn.) only navigated a screw guide tube at the
insertion point of the bone surface and did not guide the actual tip of the pedicle
probe, tap, or screw within the pedicle.
n
Kotani and colleagues developed a new computer-assisted guidance system for
cervical pedicle screw placement. The system facilitates obtaining real-time,
three-dimensional instrument/screw tip information at each step (probing,
tapping, and screw insertion into the vertebra) and is useful in improving the
safety and accuracy of pedicle screw placement in the cervical spine.
n
More recently, several authors have reported that intraoperative three-
dimensional fluoroscopy-based navigation improved the safety and accuracy of
the pedicle screw insertion in the cervical spine.
n
Rajasekaran and colleagues emphasized that the advantages conferred by
cervical pedicle screws into adults also can be extended to the pediatric
population.
n
Further modifications and developments in technology will increase safety and
refine surgical techniques.
Step 2
n
Before plate or rod application, a posterior decompression by laminoplasty or
laminectomy is recommended for a patient with a narrow spinal canal, to avoid
possible neurologic deterioration caused when the vertebral alignment is
changed after longitudinal connection of the screws.
n
The lateral masses and laminae must be decorticated, and bone chips obtained
from spinous processes and laminae must be placed.
n
In the final stage of instrumentation, inserted screws are connected with a plate
or rod.
• Simple plate fixation is preferred for one- or two-segment fixation. Monosegmental fixation is shown in Figure 13-11; the patient has cervical spondylotic
myelopathy associated with segmental instability at C3-4. Radiograph films
in the extension and flexion positions show segmental instability at C3-4 (see
Figure 13-11, A and B, respectively). MRI images and a CT scan (see Figure
13-11, C to E ) show a narrowed spinal canal and spinal cord compression.
Figure 13-11, in parts F and G, shows postoperative images of C3-4 single-
level pedicle screw/plate fixation. Axial CT scans (see Figure 13-11, G and I )
show the location of inserted screws.
n
The alignment of the screw head in the coronal plane may be off in multilevel
fixation. Therefore a rod with a screw rather than plate is recommended for
multilevel fixation across three segments.
118 Procedure 13 | Cervical Pedicle Screw Fixation
C6
C3
A
D
FIGURE 13-11, A-I
B
C
C3-4
E
Procedure 13 | Cervical Pedicle Screw Fixation 119
F
C3
H
FIGURE 13-11, cont'd
G
C4
I
120 Procedure 13 | Cervical Pedicle Screw Fixation
A
C
FIGURE 13-12, A-F
B
D
Step 3
n
The pedicle screw procedure is a strong tool for correction of the deformities in
the cervical spine.
n
Plates and rods are contoured in the sagittal plane, with the expected correction
of kyphotic deformity.
n
Correction of the kyphosis is performed by tightening the nuts or by rotating
the rods using rodholders (Figure 13-12). A preoperative myelogram (see Figure
13-12, A) shows postlaminectomy kyphosis. MRI images (see Figure 13-12, B
and C ) demonstrate dumbbell-type recurrent spinal cord tumor (schwannoma).
A postmyelogram CT (see Figure 13-12, D) shows that the tumor is expanding
from intracanal-extradural to the outside of the spinal canal. The patient sustained progressive spinal cord compression symptoms. The patient underwent
simultaneous posterior decompression by tumor extirpation and correction of
kyphosis (see Figure 13-12, E and
cervical spine can be shortened.
F
). Consequently, the posterior part of the
S T E P 3 P EA R L S
• The neural foramina in patients with
degenerative disorders are sometimes
stenotic preoperatively. There is the risk
of iatrogenic nerve root lesion because
of foraminal stenosis caused by
reduction of anterior translation or
correction of kyphosis.
• Reconstructive CT performed in the
oblique plane provides useful
information about the size of the
neural foramen.
• The use of a washer under the plate/
rod for the cranial vertebral screws is
helpful in situations where excessive
reduction would occur during screw
tightening.
• During the correction of kyphosis, the
surgeon must also avoid applying
excessive compression force at the
spinal segment having neural foraminal
stenosis because of degenerative
changes. A prophylactic foraminotomy
is recommended for the segments with
marked stenosis of the neural foramen.
Procedure 13 | Cervical Pedicle Screw Fixation 121
E
FIGURE 13-12, cont'd
F
S T E P 3 P IT FA L L S
• Surgeons must be careful to avoid
excessive shortening of the spine
because of the potential for developing
nerve root lesions by iatrogenic
foraminal stenosis.
C3-7: 31°
A
FIGURE 13-13, A-K
n
Cases of cervical scoliosis requiring surgical correction are uncommon. If neces-
B
Continued
sary, however, the deformity is correctable using this procedure by applying distraction force on the concave side (Figure 13-13). Preoperative images (see Figure
13-13, A and B) show 31 degrees of scoliosis after laminoplasty. The patient suf-
fered from severe radiculopathy of the left C5 and C6 caused by C4-5 and C5-6
foraminal stenosis. Preoperative CT scans (see Figure 13-13, C to F ) show proliferated degenerative changes of the left lateral mass. In Figure 13-13, G and H,
postoperative images show sufficient correction of scoliosis. Postoperative CT
images (see Figure 13-13, G to K ) show proper screw placement in each vertebra.
122 Procedure 13 | Cervical Pedicle Screw Fixation
C4
C4-5
C
D
C5
C5-6
E
G
FIGURE 13-13, cont'd
F
C3-7: 14°
H
Procedure 13 | Cervical Pedicle Screw Fixation 123
C4
I
C6
J
C5
K
FIGURE 13-13, cont'd
Postoperative Care and Expected Outcomes
n
Complications directly attributable to screw insertion
• There have been several published reports in English referring to results of
cervical pedicle screw fixation. In total, 306 patients underwent cervical
reconstructive surgery in those three reports.
◆
Two cases of vertebral artery injury and five cases of nerve root lesion
directly attributable to pedicle screw insertion were described in the three
reports.
◆
There were no cases of spinal cord injury caused by pedicle screw insertion
in any of the reports.
• Onishi and colleagues reported a case of a late complication of cerebral
infarction caused by a laterally perforated cervical pedicle screw.
• Based on the experience of Abumi and associates in 571 cases of cervical
pedicle screw fixation from 1990 to 2009, the rate of neurovascular complication was relatively low.
◆
In the authors’ series, there were five patients with neurovascular complica-
tions directly attributable to screw insertion into the cervical pedicles: two
with vertebral artery injury and three with radiculopathy by screw
insertion.
124 Procedure 13 | Cervical Pedicle Screw Fixation
◆
Intraoperative injury of the vertebral artery during the tapping of a frac-
tured pedicle occurred in one patient with an injury at C6-7. Bleeding
stopped immediately by packing bone wax into the insertion hole.
◆
Obstruction of the vertebral artery by a laterally dislodged screw occurred
in one patient who underwent occipitoatlantoaxial fixation.
• No further ischemic neurologic complications of the brain were observed
in these two cases.
◆
Radiculopathy caused by an inserted pedicle screw was identified in three
patients.
A C6 nerve root lesion caused by superiorly perforated C6 screw threads
•
resolved during the course of the follow-up without screw removal.
• Two C5 nerve root lesions associated with muscle weakness was caused
by an inferiorly perforated C4 screw, and recovered to normal strength
upon screw removal.
n
Complications not directly attributable to screw insertion
• Based on Abumi and colleague’s published results of 227 cases of cervical
pedicle screw fixation, late neurologic deficits after posterior correction
surgery occurred in 2.6% of cases.
◆
The neurologic deficits were associated with correction of cervical kyphosis
by posterior instrumentation.
◆
The neurologic deficits occurred in 20% of patients who underwent cor-
rection of cervical kyphosis.
◆
Possible causes of this complication are iatrogenic foraminal stenosis and/
or tethering of the nerve because of posterior shift of the spinal cord after
correction of kyphosis.
◆
As the correction angle increases, the incidence of this complication was
higher.
Prophylactic foraminotomy at C4-5 is recommended when foraminal
•
stenosis is present on preoperative CT images.
• Excessive correction, exceeding 9.7 degrees per segment in the middle
cervical spine, should not be conducted to prevent this complication.
• When this complication occurs, regardless of revision, decompression,
or observation, the majority of patients will improve on their own over
time.
Summary
n
Pedicle screw fixation is a strong procedure for reconstruction of the cervical
spine in various types of disorders. Furthermore, a screw inserted into the cervical pedicle screw can be a strong anchor for reconstruction of the craniocervical
junction and cervicothoracic spine. Surgeons must keep in mind that there must
be limitations of cervical pedicle screw placement based on anatomic variations
of the pedicle and vertebral artery. Complications associated with cervical
pedicle screw fixation cannot be completely obviated; however, they can be
minimized by sufficient preoperative imaging studies of the pedicles, thorough
knowledge of local anatomy, and strict control of screw placement during
surgery.
n
Cervical pedicle screw fixation may become a more definitive tool for reconstruc-
tion of the cervical spine in the future with progress in supplemental technology,
including computer navigation systems, monitoring procedures of the nerve, and
so forth.
Procedure 13 | Cervical Pedicle Screw Fixation 125
Evidence
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