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106 Procedure 12 | Cervical Spine: Lateral Mass Screw Fixation
S T E P 4 P EA R L S
• In extended and complex instrumented
fusions, additional stability can be
achieved by linking cross connectors to
the longitudinal rods.
• In patients with poor bone quality
unsuitable for placement of lateral
mass screws, sublaminar wires can be
secured to open cable connectors
attached to the rods for additional
fixation.
S T E P 4 P IT FA L L S
• Titanium rods should not be contoured
multiple times, because fatigue may
occur to the rod.
• A cross connector should be carefully
placed in a dorsal location following a
laminectomy to avoid posterior dural
impingement.
FIGURE 12-9
S T E P 4
I N S T RU M E N T A T I O N /
I M P L AN TAT IO N
• Polyaxial screw and rod system,
reduction tools
5 mm
FIGURE 12-10
Step 5: Placement of Screw Caps
n
Screw tightening (once the inner nut is placed in the polyaxial screw head)
should be performed in a gentle and systematic fashion to facilitate rod seating,
allow controlled manipulation of the spinal segments, and to avoid screw
torque, which may result in screw loosening (Figure 12-9).
n
Final nut tightening is performed utilizing the torque driver and antitorque
device to guarantee optimal tightening of the nuts and to avoid late rod
loosening.
Postoperative Care and Expected Outcomes
n
Depending on the length and extent of the entire surgical procedure, the pathol-
ogy, and bone quality, the required postoperative care may differ significantly
(Figure 12-10).
Procedure 12 | Cervical Spine: Lateral Mass Screw Fixation 107
n
Patients are routinely monitored in the hospital overnight.
n
A soft collar orthosis may be used in the setting of short segment reconstruc-
tions in degenerative disease. A hard collar is may be applied in the postoperative period for approximately 6 weeks, depending upon the pathology and
length of the instrumented construct. Rigid external fixation with a halo-vest
orthosis is rarely indicated, except in severe osteoporosis, questionable compliance, neoplasms, and certain traumatic lesions.
n
Deep or superficial wound infections should be addressed at an early stage.
Extensive infections may require hardware removal and rigid external
immobilization.
n
Postoperative neurologic deterioration resulting from hardware malpositioning
requires hardware revision or removal.
n
Failure of bony fusion may result in instrumentation failure, necessitating hard-
ware revision.
Evidence
Bayley E, Zia Z, Kerslake R, Klezl Z, Boszczyk BM. Lamina-guided lateral mass
screw placement in the sub-axial cervical spine. Eur Spine J 2010;19:660-4.
Results of this study indicate that using the subaxial cervical lamina as a
reference plane for the insertion of lateral mass screws in the cervical spine
decreases the likelihood of vertebral injury.
Deen GH, Birch BD, Wharen RE, Reimer R. Lateral mass screw-rod fixation of the
cervical spine: a prospective clinical series with 1-year follow-up. Spine J
2003;3:489-95.
These data indicate that posterior cervical stabilization with polyaxial screw–rod
fixation is a safe, straightforward technique that appears to offer some
advantages over existing methods of fixation.
Merrola AA, Castro BA, Alongi PR. Anatomic consideration for standard and
modified techniques of cervical lateral mass screw placement. Spine J
2002;2:430-5.
This study indicates that there are significant differences in potential
neurovascular injury, which are dependent on the technique used for screw
entry, the level instrumented, and the angle of screw trajectory in the
parasagittal plane.
Wang MY, Levi AD. Minimally invasive lateral mass screw fixation in the cervical
spine; initial clinical experience with long-term follow-up. Neurosurgery
2006;58:907-12.
The results of this study indicate that the minimally invasive approach preserves
the integrity of the components that provide stability to the cervical spine.
Xu R, Haman SP, Ebraheim NA, Yeasting RA. The anatomic relation of lateral mass
screws to the spinal nerves: a comparison of the Magerl, Anderson, and An
techniques. Spine 1999;24:2057-61.
The results of this study indicate that the potential risk of nerve root violation
is higher with the Magerl and Anderson techniques than with the An
technique.
P R O C ED U R E 1 3
Cervical Pedicle
Screw Fixation
Kuniyoshi Abumi, Manabu Ito, and Yoshihiro Hojo
Overview
n
Despite increasing acceptance of the use of pedicle screws in the lumbar and
thoracic spine, screw insertion into the cervical pedicle has been considered by
spine surgeons to be too risky for the neurovascular structures, except at C2
and C7. Leconte first reported C2 pedicle screw insertion for osteosynthesis of
the C2 hangman’s fracture. In the late 1980s, Goel and Laheri started to use
C2 pedicle screws for atlantoaxial plate fixation in combination with C1 lateral
mass screws. However, there had been no reports of pedicle screw fixation from
C3 to C6 until the 1994 report by Abumi and colleagues of pedicle screw fixation for traumatic lesions of the lower cervical spine. Biomechanical studies
revealed the superior stabilizing effect of pedicle screw fixation compared with
other internal fixation procedures used with the cervical spine, including lateral
mass screw fixation. In their recent experimental study, Johnston and colleagues
revealed the superior pullout strength of a cervical pedicle screw versus a lateral
mass screw after repetitive loading. Dunlop and colleagues demonstrated, by
an in-vitro biomechanical study, that cervical pedicle screw/rod constructs
support a greater axial load than lateral mass screw/rod constructs.
n
The pedicle screw fixation procedure allows rigid fixation that provides the high
correction capability needed to restore physiologic sagittal alignment of the
cervical spine, as well as sufficient correction of malalignment in the occipitoatolantoaxial region. In addition, the pedicle screw fixation procedure, which does
not require use of the lamina for stabilization, is quite valuable in patients who
undergo one-stage posterior cervical decompression and stabilization, and in
patients who undergo posterior reconstruction after previous posterior cervical
decompression. On the other hand, the risks of neurovascular complications
caused by inadequate screw placement into the cervical pedicle cannot be
completely obviated. Thorough knowledge of local anatomy, sufficient preoperative radiologic examinations, and the application of established surgical techniques are essential for this procedure.
Indications
n
Almost all the pathologic conditions requiring posterior stabilization of the
occipitocervical junction, cervical spine, or cervicothoracic junction.
n
Most middle and lower cervical injuries with posterior disruption, or anterior
and posterior disruption without a severely disrupted anterior column, can be
managed by posterior surgery using cervical pedicle screw fixation alone.
I N D I CAT I O NS P I T F A L L S
• Infectious disorders at the posterior
portion of the cervical spine are
contraindications for pedicle screw
fixation.
• Pedicles destroyed by injuries, tumors,
rheumatoid arthritis
• Marked osteoporosis
• Extremely small pedicles
• Pedicles of the vertebra associated with
major anomalies of the vertebral artery,
and so forth, are inadequate and risky
for screw insertion (Figures 13-1 and
13-2).
•
Figure 13-1 shows an abnormal
condition of the cervical pedicle.
Pedicles destroyed by injuries, tumors,
or marked osteoporosis; extremely small
pedicles; pedicles of the vertebrae
associated with major anomalies of
the vertebral artery, and so forth,
are inadequate and risky for screw
insertion. Figure 13-1, A shows a
fracture of the pedicle in a patient with
a lateral mass fracture. Figure 13-2, B
shows a pedicle of an extremely small
size in a patient with rheumatoid
arthritis.
•
Figure 13-2 shows a small size of the
pedicle of the axis. Figure 13-2, A
shows that the diameter of right side of
the pedicle of the axis is too small for
screw insertion by high-riding vertebral
artery bends into the lateral mass of
the axis (arrow). Figure 13-2, B shows
extremely small pedicles of the axis for
screw insertion.
Procedure 13 | Cervical Pedicle Screw Fixation 109
A
VA
B
FIGURE 13-1, A-B
A
FIGURE 13-2, A-B
B
110 Procedure 13 | Cervical Pedicle Screw Fixation
n
• Patients sometimes have extreme
unilateral dominance of the vertebral
artery. In this condition, the dominantside foramen transversarium enlarges,
and the ipsilateral side of the pedicle
decreases in size (Figure 13-3).
Retrogression of the pedicle is found
on the side of the dominant vertebral
artery. Figure 13-3, A shows that
patients sometimes show extreme
right-left dominance of the vertebral
artery. Figure 13-3, B shows that the
dominant side of the foramen
transversarium enlarges and that the
ipsilateral side of the pedicle decreases
in size (white arrow).
• For the patient with unilateral
obstruction of the vertebral artery by
injury, tumor, congenital anomaly,
and so forth, screw insertion on
the preserved artery side must be
conducted with great care, or screw
insertion should only be performed on
the obstructed side.
Cervical spinal instability caused by nontraumatic lesions, including meta-
static tumor, rheumatoid arthritis, destructive spondyloarthropathy, cervical
intervention for posterior decompression of the spinal cord or nerve root,
and so forth, are well managed by this procedure.
n
Cervical kyphosis caused by many causes, including postlaminectomy and post-
traumatic kyphosis, cervical spondylotic myelopathy associated with kyphosis,
and so forth, can be corrected sufficiently by this procedure.
n
A degenerative cervical spine with segmental instability requiring posterior
decompression also can be managed by simultaneous decompression and stabilization using pedicle screw fixation.
n
This procedure is beneficial for stabilization of the unstable motion segment
caused by extensive decompression of the nerve root or spinal cord, affecting
stability of the facet joint.
n
Salvage of pseudarthrosis of anterior fusion.
n
Fusion-level elongation for adjacent segment degeneration after anterior or
posterior fusion surgery.
A
B
FIGURE 13-3, A-B
Procedure 13 | Cervical Pedicle Screw Fixation 111
Examination/Imaging
n
Preoperative oblique-projection plain radiograph films are valuable for evalua-
tion of the pedicle size. In an oblique projection, the contralateral pedicle is seen
as an oval projected onto the vertebral body, showing the outer and inner
diameter of the pedicle. If the projection shows no inner diameter, the pedicle
does not have a medullary canal.
n
Computerized tomography (CT) evaluations (adjusted to the bone windows) are
essential to assess the pedicle morphometry and to determine pedicle size,
which allows surgeons to choose the appropriate pedicle screw diameter, length,
direction in the coronal plane, and screw insertion point. Reconstructive CT in
the oblique plane provides useful information about the size of the neural
foramen.
n
Preoperative evaluation of the morphology of the vertebral artery is important
in preventing serious complications involving the artery.
• Duan and colleagues demonstrated, in an imaging anatomic study, that the
incidence of abnormal course of the vertebral artery is high at the craniovertebral junction.
• The incidence of ischemic brain complications caused by unilateral obstruction
of the vertebral artery is low.
◆
However, if the dominant vertebral artery is injured, serious neurologic
complications can occur.
• CT and magnetic resonance imaging (MRI) provide information regarding
right-left dominance and anatomic variations of the vertebral artery. Magnetic
resonance angiography (MRA) must be conducted for patients with evidence
of the abnormalities or in whom these abnormalities are suspected.
Surgical Anatomy
n
According to previous studies by Panjabi and colleagues and by Karaikovic and
colleagues, the pedicle of the cervical spine in a normal population has a sufficient diameter to allow insertion of a screw with a diameter of 3.5 mm or
more.
• These authors defined this quantitatively by measuring the cadaveric cervical
spine. Both the outer width and outer height were largest at C2 and smallest
at C3, with subsequent increasing size if progressing to C7.
• Pedicles in some patients have a diameter that is too small to allow screw
insertion.
n
According to an anatomic study by Reinhold and colleagues, the average overall
angle between the sagittal plane and the longitudinal pedicle axis was 46
degrees, varying from 30 degrees to 62 degrees. The smallest angle was at C7,
the largest at C4. Their results were similar to previous studies by Karaikovic
and colleagues.
n
Pedicle screw insertion into a vertebra with an extremely large angle between
the pedicle axis and the sagittal plane may be possible but puts the vertebral
artery and the spinal cord at risk. Figure 13-4 shows an extremely large angle
between the pedicle axis and the sagittal plane. The left side of the foramen
transversarium is enlarged toward the vertebral body (Figure 13-4, A,
arrow
), and the angle between the pedicle axis (
black line
) and the sagittal
plane is extremely large because of deformation of the foramen. In a case of
C6 spondylolysis, the angle between the pedicle axis (Figure 13-4, B,
and the sagittal plane is extremely large. Screw insertion into the left side of
the pedicle is too risky for the vertebral artery and the spinal cord.
n
Karaikovic and colleagues defined the inner morphology of the cervical pedicles.
They revealed that the thinnest pedicle cortex was always the lateral cortex, and
some pedicles had no medullary canal (i.e., where solid cortical bone is expected:
0.9% for C2, 2.8% for C3 and C4, and 3.8% for C5 pedicles).
open
black line
)
112 Procedure 13 | Cervical Pedicle Screw Fixation
C5
A
FIGURE 13-4, A-B
70°
C6
60°
Lt
B
70°
Lt
A
FIGURE 13-5, A-C
B
C
n
The vertebral artery sometimes bends into the vertebral body forming the loop,
and screw insertion into the ipsilateral side of the pedicle may put the artery at
risk. Figure 13-5 shows loop formation of the vertebral artery.
n
MRA shows the medial loop of the left vertebral artery (Figure 13-5, A,
n
CT (Figure 13-5, B) and MRI (Figure 13-5, C ) images show that the vertebral
artery bends into the vertebral body, forming the loop (
arrows
). Screw insertion
arrow
into the left side of the pedicle is too risky for the artery.
).
Procedure 13 | Cervical Pedicle Screw Fixation 113
Anesthesiologist
Surgeon
Nurse
FIGURE 13-6
C-arm monitorAssistant surgeon
Positioning
n
The authors prefer to stand at the head of the patient, to ensure symmetric
insertion of the right and left screws, while the assistant for a right-handed
surgeon usually stands on the left side of the patient.
n
The C-arm display is placed on the left side of the patient near the patient’s
pelvis for easy viewing by the surgeon. The authors’ preferred operation room
setup for posterior cervical spinal procedures is shown in Figure 13-6.
n
The patient is placed prone on a Relton-Hall frame, using a horseshoe-type
headrest or a Mayfield headholder.
n
The shoulders are pulled caudally using heavy bandage for intraoperative lateral
fluoroscopic imaging of the lower cervical spine.
Portals/Exposures
n
A skin incision is made, usually longer than that required for a standard spinous
process wiring. The cephalad adjacent lamina of the most cephalad-fixed vertebra should entirely be exposed, taking care to protect the surrounding facet
joint capsule. The paravertebral muscles are dissected laterally to expose the
lateral margins of the articular masses for exact mediolateral determination of
the screw insertion point.
Procedure
Step 1: Manual Screw Placement
n
The cranial margin of the C2 lamina is the craniocaudal landmark for the screw
insertion point for C2. To confirm the screw insertion points in C2, a small
spatula can be inserted into the spinal canal along the cranial margin of the C2
lamina to the medial surface of the C2 pedicle. Figure 13-7 shows the pedicle
screw insertion point for C2. The cranial margin of the C2 lamina (white broken
line) is the landmark for the screw insertion point for C2 (asterisk). To confirm
the screw insertion points in C2, a small spatula can be inserted into the spinal
canal along the margin cortex of the C2 pars interarticularis to the medial
surface of the C2 pedicle. The black broken arrow indicates the screw direction
toward the C2 pedicle.
n
The angle for the C2 pedicle should be 15 to 25 degrees medial to the midline
in the transverse plane.
114 Procedure 13 | Cervical Pedicle Screw Fixation
FIGURE 13-7
15°-25°
C1
C2
VA
*
FIGURE 13-8
n
The screw insertion points for the C3 to C7 pedicles are slightly lateral to the
C2
C3
C4
C5
C6
center of the articular mass and close to the inferior margin of the inferior
articular process of the cranially adjacent vertebra. However, the shape and size
of the lateral mass are variable in each vertebra and in each patient.
n
The lateral margin of the articular mass of the cervical spine has a notch
approximately at the level of the pedicle. The pedicles are located approximately
below the lateral vertebral notch at C2, at the notch at C3 through C6, and at
or slightly above the notch at C7. Figure 13-8 shows the pedicle screw insertion
points for C3 to C7. Three-dimensional CT reconstruction shows the screw
insertion points for C3 to C7. The lateral margin of the articular mass of the
cervical spine has a notch approximately at the level of the pedicle (
white arrow
The pedicles are located approximately below the lateral vertebral notch at C2,
at C3 to C6, and at or slightly above the notch at C7. Screw insertion points
(
black crosses
) are 2 to 4 mm medial to the notch. The
white asterisk
the C2 pedicle screw insertion point.
• The screw insertion points for the C3 to C7 pedicles are slightly laterally to
the center of the articular mass and close to the inferior margin of the inferior
articular process of the cranially adjacent vertebra. Craniocaudal orientation
of the screw insertion point can be confirmed by a lateral image intensifier.
• The anatomic direction of the pedicle axis in the transverse plane varies from
a minimum for the C7 pedicle to a maximum for the C5 pedicle.
• Pedicle screw insertion with a large angle relative to the sagittal plane can
be difficult. Because of short length of cervical pedicle axis, however, the
screw can be inserted at a smaller angle than the angle of the anatomic axis.
• The authors usually insert screws at an angle of 25 degrees to 45 degrees
relative to the sagittal plane for the pedicles from C3 to C7.
).
shows
Procedure 13 | Cervical Pedicle Screw Fixation 115
C6
FIGURE 13-9
• By making the funnel-shaped hole bigger and deeper with a curette or highspeed burr, the surgeon can see the medial cortex of the posterior portion of
the pedicle and the pedicle cavity directly in most cases. This funnel-shaped
resection of the outer portion of the articular mass toward the entrance of
the pedicle cavity allows more freedom and potential angulation for positioning the screw. Figure 13-9 shows the starting point and direction of the cervical pedicle screw. The authors usually create a funnel-shaped hole at the
screw insertion point using a high-speed burr. The
two dashed black lines
indicate the anatomic axis of the pedicle. The semicircular shaded area
denotes the excised outer portion of the articular mass. Through funnelshaped resection of the articular mass toward the entrance of the pedicle
cavity using a high speed burr, the starting point of the screw approaches
the entrance of the pedicle cavity. Consequently, the surgeon obtains more
freedom with the screw insertion angle. The triangular area between the two
black lines indicates the possible screw insertion direction.
• In addition, the surgeon can see the pedicle cavity directly, in many cases, by
enlarging the insertion hole with a curette or high-speed burr.
• After creating the insertion hole, a small pedicle probe, tap, and screws are
inserted into the pedicle with the help of a lateral image intensifier, to confirm
the direction and insertion depth. The authors recommend confirming the
proper creation of the screw insertion path after probing and tapping, using
a pedicle sounder. Screw insertion is regulated using a C-arm. The
white lines
indicate the cranial and caudal margins of the pedicle (Figure
two dashed
13-10). The pedicle probe, tap, and screws must be advanced between the
two lines. Figure 13-10, A shows the making of a funnel-shaped hole. Figure
13-10, B shows the probing of the pedicle, and Figure 13-10, C shows the
tapping of the pedicle. Screw insertion is shown in Figure 13-10, D.
• Yukawa and colleagues demonstrated that the use of oblique projection fluoroscopy imaging increased the rate of proper screw insertion.
n
The thinnest pedicle cortex is always the lateral cortex. Therefore the surgeon
should keep this in mind while probing and tapping the pedicle and while
placing the screws.
n
The medial pedicle cortex must be used as a safe guide for the insertion of the
screw into the vertebral body through the pedicle isthmus.