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96 Procedure 11 | Posterior C1-C2 Fusion: Harms and Magerl Techniques
n
The K-wire is removed and screw placement can be confirmed with C-arm fluo-
roscopic imaging.
n
Steps 5 to 7 are repeated for the contralateral C1-2 transarticular screw.
S T E P 9
I N S T RU M E N T A T I O N /
I M P L AN TAT IO N
• High-speed burr
• Kerrison rongeur
S T E P 1 0
I N S T RU M E N T A T I O N /
I M P L AN TAT IO N
• Leksell rongeur
• Kerrison rongeur
S T E P 1 1
I N S T RU M E N T A T I O N /
I M P L AN TAT IO N
• Heavy needle driver
• Wire cutters
Step 9
n
The future areas of contact of the posterior arches of C1 and C2 with the strut
graft are decorticated with the high-speed burr. The inferior cortical margin of
the posterior arch of C1 and superior cortical margin of the posterior arch and
spinous process of C2 are decorticated with the burr.
n
A notch is made on the inferior margin of the spinolaminar junctions of C2 with
an angled Kerrison rongeur for future seating of the sublaminar wire.
Step 10
n
Using a Leksell rongeur, the tricortical strut graft is converted into a bicortical
graft by removing the rounded cortical edge.
n
The graft is placed between the posterior arches of C1 and C2 for final sizing
and to approximate the midline of the graft. The Leksell rongeur is used to make
any final modifications for optimal sizing of the graft.
n
A Kerrison rongeur is used to notch the midline on the inferior aspect of the
graft to accommodate the spinous process of C2 for a secure fit.
Step 11
n
The graft is placed back in between the atlas and axis with the notch of the
graft sitting on the spinous process of the axis for a secure fit.
n
The C1 sublaminar loop of wire is passed below and secured in the notch made
on the undersurface of the C2 spinous process (Figure 11-22).
n
The free ends of wire are wrapped around the bone graft and secured. A heavy
needle driver is used to twist the free ends of wire together and tighten them
snugly around the graft.
n
Any excess wire is cut with wire cutters and removed. The cut ends of wire are
carefully laid flush against the strut graft.
S T E P 1 2
I N S T RU M E N T A T I O N /
I M P L AN TAT IO N
• High-speed burr
Step 12
n
The posterior cortical surfaces of the C1 posterior arch, C2 lamina, and strut
graft are decorticated with the high-speed burr.
n
The bone dust and shavings from the burr are left in the operative field, and
the cancellous bone graft is placed over the posterior decorticated surfaces of
C1, C2, and strut graft.
FIGURE 11-22
Procedure 11 | Posterior C1-C2 Fusion: Harms and Magerl Techniques 97
Step 13
n
The wound is closed securely in a layered fashion, obliterating any dead space.
n
Steri-Strips are placed perpendicular to the incision and covered by sterile 4 ×
4 gauze and a clear Tegaderm dressing.
n
Final AP and lateral cervical radiographs are obtained to assess placement of
the hardware and alignment of the atlantoaxial region (Figure 11-23).
n
A rigid cervical collar (i.e., Philadelphia or Miami-J) is secured in place.
n
The patient is removed from the Mayfield headholder. The surgeon stands
at the head of the operating table and is responsible for stabilizing the neck
when the patient is repositioned onto the hospital bed in the supine position.
FIGURE 11-23
98 Procedure 11 | Posterior C1-C2 Fusion: Harms and Magerl Techniques
P O S T OP E R AT IV E P I T F A L L S
• Screw malposition can result in:
• Inadequate purchase, resulting in a
potentially unstable construct. Rigid
external immobilization in a halo vest
for 10 to 12 weeks should provide
enough atlantoaxial stability to
achieve fusion if instability is present.
• Dural tear and CSF leak. The authors
advocate the primary repair of all
dural tears, as well as placement
of Gelfoam over the repair.
• Violation of the foramen
transversarium can result in
vertebral artery rupture, dissection,
pseudoaneurysm, or occlusion. Even
without direct violation of the arterial
wall, the screw threads can contact
the artery and result in injury because
of normal pulsatile flow. If this
is discovered intraoperatively or
postoperatively, the screw should be
left in place to tamponade bleeding,
and then vascular studies should be
obtained.
• Intraoperative vertebral artery injury is
the most feared complication that
can cause serious clinical sequelae,
including brainstem stroke. If this
occurs, the screw should be removed
immediately, and the site should be
packed with pieces of Gelfoam large
enough not to be a source of emboli.
Bone wax can also be used to help
tamponade the bleeding. A direct
microvascular repair by a vascular
surgeon, after the surrounding bone
is skeletonized, is also an option.
Irrespective of the method used
to tamponade the bleeding, a
postoperative angiogram should be
obtained to evaluate the vertebral
artery.
Postoperative Care and Expected Outcomes
n
The patient should be taken to the recovery room or the surgical intensive care
unit (SICU) for postoperative recovery.
n
Supine and upright lateral cervical radiographs should be obtained in the cervi-
cal collar to assess stability on postoperative day one. If atlantoaxial stability
has been obtained, the patient can be mobilized.
n
On postoperative day 1, or when medically stable, the patient can be transferred
to a standard surgical floor.
n
A postoperative CT scan can be obtained if there is any question concerning
screw placement.
n
The patient can be discharged from the hospital when medically stable.
n
Rigid cervical collar immobilization is used for approximately 8 to 12 weeks
postoperatively.
n
Routine outpatient static lateral radiographs can be obtained 4 weeks postop-
eratively to ascertain stability. Radiographs can be obtained at 4-week intervals
to assess stability and fusion. Supervised dynamic lateral flexion and extension
radiographs can be obtained at the end of the 8- to 12-week period to further
assess atlantoaxial stability. If stability is obtained, the cervical collar can be
weaned from use.
n
Additionally, a CT scan can be obtained 3 to 6 months postoperatively to assess
fusion and fracture healing.
n
Fusion can be achieved in nearly 100% of cases, although 16.7% of patients
may experience complications (Finn and Apfelbaum, 2010).
Evidence
Cavalcanti D, Agrawal A, Garcia-Gonzalez U, et al. Anterolateral C1-C2
transarticular fixation for atlantoaxial arthrodesis: landmarks, working area, and
angles of approach. Operative Neurosurg 2010;67:38-42.
Five cadaver necks were dissected bilaterally to study anatomic landmarks, and
then 10 CT scans were analyzed to quantify working area and optimal angles of
approach. The C2 transverse process was a landmark for dissecting posterior to
the carotid sheath, and gray ramus communicans from the superior cervical
ganglion to the C2 nerve was a landmark for locating the C2 pars. The mean
working area was 71.2 mm2, and the ideal angle for screw placement was
22.9 degrees medial to the sagittal plane and 25.3 degrees posterior to the
coronal plane.
Currier B, Maus T, Eck J, et al. Relationship of the internal carotid artery to the
anterior aspect of the C1 vertebra. Spine 2008;33:635-9.
The authors retrospectively reviewed 50 head and neck CT scans, performed
with contrast, to study the relationship between the anterior aspect of the C1
vertebra and the internal carotid artery. The mean shortest distance between
the artery and C1 was 2.88 mm on the left and 2.89 mm on the right. The
lumen of the artery was medial to the foramen transversarium in 84% of cases.
The authors conclude that the proximity of C1 to the internal carotid artery
poses moderate risk in 46% of cases and high risk in 12% of cases on at least
one side. They therefore recommend preoperative contrast imaging in all cases
in which a screw is to be placed in C1. If the artery is in close proximity to the
anterior border of C1, unicortical fixation or a different fusion technique should
be considered.
Cyr S, Currier B, Eck J, et al. Fixation strength of unicortical versus bicoritcal C1-C2
transarticular screws. Spine J 2008;8:661-5.
The internal carotid artery and hypoglossal nerve lie in close proximity to the
anterior aspect of C1. The authors performed a biomechanical study of pullout
strength in 15 cadaver specimens. They found no statistically significant
difference in pullout strength between unicortical and bicortical C1-2
transarticular screws. In cases with adequate bone stock, the authors
recommend unicortical screws to avoid neurovascular injury.
Procedure 11 | Posterior C1-C2 Fusion: Harms and Magerl Techniques 99
Finn M, Apfelbaum R. Atlantoaxial transarticular screw fixation: update on
techniques and outcomes in 269 patients. Neurosurgery 2010;66A:184-92.
The authors retrospectively reviewed 269 patients who underwent transarticular
screw fixation for a mean follow-up of 15.7 months. Fusion was achieved in
99% of cases. Complications occurred in 16.7% of cases (including five vertebral
artery injuries, one of which was bilateral and fatal). The technique could not
be applied in 13.3% of cases because of anatomic constraints.
Harms J, Melcher R. Posterior C1-C2 fusion with polyaxial screw and rod fixation.
Spine 2001;26:2467-71.
The authors describe bilateral insertion of 3.5-mm polyaxial screws into the
lateral masses of C1 and the pars of C2, followed by reduction (if needed)
and fixation with 3-mm rods. Unlike transarticular screw and posterior wiring
techniques, this does not rely on an intact posterior arch, decreases the risk
of vertebral artery injury, and can be used to correct fixed C1-2 subluxation.
Because the facet joint surfaces remain intact, the patient can regain motion
after removal of hardware if indicated. The authors describe successful fusion
of 37 patients without neural or vascular injury.
Henriques T, Cunningham B, Olerud C, et al. Biomechanical comparison of five
different atlantoaxial posterior fixation techniques. Spine 2000;25:2877-83.
Eight cadaver spines were loaded in 3 degrees of freedom after instrumentation
with bilateral transarticular screws (1), posterior wiring (2), both (2), or control
(3). The authors found that three-point fixation (bilateral transarticular screws
in combination with posterior wiring) provides superior durability when
biomechanically loaded.
Jeanneret B, Magerl F. Primary posterior fusion C1/2 in odontoid fractures:
indications, techniques, and results of transarticular screw fixation. J Spinal
Disord 1992;5:464-75.
The authors present 12 acute odontoid fractures that were fixed with
transarticular screws. At follow-up, all were united and had maintained
reduction. The authors discuss the unstable fracture patterns that are more
appropriately treated with posterior fixation rather than anterior screw
fixation.
Jun BY. Anatomic study for ideal and safe posterior C1-C2 transarticular screw
fixation. Spine 1998;23:1703-7.
Reconstructed CT scans of 64 normal cervical spines were digitally implanted
with transarticular screws in multiple trajectories and analyzed with navigation
software. One patient had inadequate space available for the screw because of
the location of the transverse foramen and vertebral artery, and four others
had nearly insufficient space. Lateral fluoroscopy is imperative for safe screw
insertion.
Madawi A, Solanki G, Casey AT, et al. Variation of the groove in the axis vertebra
for the vertebral artery: implications for instrumentation. J Bone Joint Surg Br
1997;79:820-3.
The groove for the vertebral artery in C2 was investigated for 50 dry cadaver
specimens. The authors found that 11 specimens had either a pedicle width or
lateral mass height of less than 2 mm, which would put the vertebral artery at
risk or provide inadequate bone stock for transarticular C1-C2 fixation. The
authors contend that fine-cut CT scans are crucial for preoperative planning.
Magerl F, and Seemann P-S. Stable posterior fusion of the atlas and axis by
transarticular screw fixation. In: Kehr P, Weidner A, editors. Cervical Spine I.
New York: Springer Wien; 1986, p. 322-7.
Seal C, Zarro C, Gelb D, et al. C1 lateral mass anatomy: proper placement of
lateral mass screws. J Spinal Disord Tech 2009;22:516-23.
The authors dissected 15 cadaver spines to study C1 anatomy with caliper
measurements followed by CT scans. Additional specimens were instrumented,
and guidelines were established for C1 screw fixation. Fifty clinical cases were
retrospectively reviewed. The authors concluded that 10 degrees medial and 22
degrees cephalad was the preferred trajectory for C1 screw fixation.
Tan M, Wang H, Wang Y, et al. Morphometric evaluation of screw fixation in atlas
via posterior arch and lateral mass. Spine 2003;28:888-95.
Fifty atlas specimens were studied with calipers, protractors, and CT to
determine the optimal size and trajectory for transarticular screw fixation, and
parameters were applied to 5 patients without incident. The longest trajectory
distance of the screw path was about 30 mm. The outer thickness at the
thinnest part of groove was 4.58 mm, and it was found to be less than 4 mm
in four cases (8%). The entry point is 18 to 20 mm lateral to the midline and
2 mm superior to the inferior border of posterior arch. The direction of screw
placement is perpendicular to the coronal plane and about 5 degrees cephalad
to the transverse plane.
100 Procedure 11 | Posterior C1-C2 Fusion: Harms and Magerl Techniques
Wait S, Ponce F, Colle K, et al. Importance of the C1 anterior tubercle depth
and lateral mass geometry when placing C1 lateral mass screws. Neurosurgery
2009;65:952-7.
The authors reviewed 100 consecutive cervical CT scans. The mean depth of
the C1 tubercle was 6.9 mm (range 2.7 to 11.2 mm). Preoperative planning
and lateral fluoroscopy are essential to guide the depth of C1 lateral screw
placement.
Weidner A, Wahler M, Chiu T, Ullrich C. Modification of C1-C2 transarticular screw
fixation by image-guided surgery. Spine 2000;25:2668-74.
CT scan data for 37 prospectively assigned patients was uploaded into a surgical
planning computer program that generated an optimal screw trajectory. The
surgical field was matched to the virtual computer field, and C2 was drilled
according to plan. The historical control group included retrospective analysis of
78 patients who had a similar surgery performed under fluoroscopic guidance.
Image-guided surgery reduced, but did not eliminate, the risk of screw
misplacement. Surgical time was not increased.
Yoshida M, Feo M, Fujibayashi S, Nakamura T. Comparison of the anatomical risk
for vertebral artery injury associated with the C2-pars interarticularis screw and
atlantoaxial transarticular screw. Spine 2006;31:E513-7.
Three-dimensional reconstructed CT scans of 62 consecutive patients with
cervical lesions were retrospectively evaluated to compare the maximum
possible diameter of the atlantoaxial transarticular screw and C2-pars screw
trajectories. Both techniques had a similar anatomic risk for vertebral artery
injury.
Young JP, Young PH, Ackermann MJ, et al. The ponticulus posticus: implications
for screw insertion into the first cervical lateral mass. J Bone Joint Surg Am
2005;87:2495-8.
The ponticulus posticus is an osseous anomaly of the atlas. Through a
retrospective review of 464 lateral radiographs of the neck, the authors found a
prevalence of 15.5%. Surgeons should avoid using the ponticulus posticus as a
starting point for lateral mass screws in order to protect the vertebral artery.
P R O C ED U R E 1 2
Cervical Spine: Lateral
Mass Screw Fixation
Kern Singh, Jonathan A. Hoskins, Vamshi Yelavarthi, and
Alexander R. Vaccaro
I N D I CAT I O NS P E A R L S
• Beware of patients with aberrant bony
anatomy making screw placement
difficult, such as those with erosive
rheumatoid arthritis or osteoarthritis, or
ectatic coursing of the vertebral artery.
I N D I CAT I O NS
C O N T RO V E R S IE S
• In severe osteopenia/osteoporosis,
lateral mass fixation may be
inadequate. It may be supplemented
with posterior wiring if posterior
elements are present and/or with
pedicle screw fixation if the anatomy
allows.
T R E A T M E N T OP T I O N S
• Posterior wiring
• Posterior hook fixation
• Posterior cervical pedicle screw fixation
Indications
n
Acute and chronic instability
• Posterior element fractures
• Posterior ligamentous injuries
• Postlaminectomy instability
n
Destruction of bony anatomy secondary to neoplasm
n
Stabilization after multisegment anterior decompression and fusion (long
anterior fusions for tumor, infection, ankylosing spondylitis, diffuse cervical
spondylosis)
n
Stabilization after failed cervical arthroplasty
n
Pseudarthrosis following anterior cervical fusion
Examination/Imaging
n
Fine-cut (2-mm) computed tomography with two-dimensional reconstruction
allows assessment of the lateral mass quality in the lower cervical spine.
n
T2-weighted sagittal magnetic resonance imaging may allow identification of
neural compression and determination of the vascular anatomy (Figure 12-1).
FIGURE 12-1
102 Procedure 12 | Cervical Spine: Lateral Mass Screw Fixation
Vertebral arteries
Spinal cord
FIGURE 12-2
Surgical Anatomy (Figure 12-2)
n
Nerve root injury may occur if the screw trajectory is incorrect, if the screw
penetration is too deep (bicortical screw purchase), or if there is significant past
pointing of the drill.
n
Vertebral artery injury is an exceedingly rare complication that may occur if the
trajectory is medial and the screw penetration is too deep.
n
If brisk, pulsatile arterial bleeding is encountered from the drill hole, hemostasis
should be obtained using bone wax, thrombogenic agents, and, potentially,
P O S I TI O N I N G PE A R L S
• A slightly reverse Trendelenburg
position allows venous drainage and
less bleeding during surgery.
P O S I TI O N I N G PI T FA L L S
• Extreme flexion or extension of the
head should be avoided to prevent
fusion of the neck in a nonanatomic
position.
P O S I TI O N I N G EQ U I P M EN T
• Mayfield tongs
• Lateral plain radiography to visualize
cervical alignment
placement of a screw in the hole. Postoperative angiography should be obtained
to determine the status of the injured vertebral artery.
Positioning
n
Mayfield tongs are applied, rigidly fixing the head to the table in the prone
position (Figures 12-3 and 12-4).
n
The neck is slightly extended. If this compromises spinal canal patency to a
detrimental degree, lordosis may be obtained following decompression by
having an unscrubbed assistant readjust the head holder to improve cervical
lordosis.
n
The arms and elbows are placed adjacent to the torso and are well padded to
prevent pressure ulcers.
n
The shoulders are gently pulled caudad by adhesive tape.
n
The knees are flexed to prevent distal migration of patient.
Portals/Exposures
P O S I TI O N I N G
C O N T RO V E R S IE S
• Placing instrumentation without
appreciating cervical alignment may
lead to loss of horizontal gaze, or the
need for compensatory mechanisms
to maintain horizontal gaze, in the
postoperative period.
n
A midline vertical skin incision can be made (as necessary) extending from the
occipital protuberance past the spinous process of the seventh cervical vertebra
(typically the most superficially prominent vertebra).
n
The nuchal ligament is divided in the midline and incised as far as the tips of
the spinous processes.
n
The deep muscle layer is stripped off the spinous processes close to the bone
with the aid of electrocautery (Figure 12-5, A and B).
n
Subperiosteal dissection is carried to the lateral boundary of the articular masses.
Vertebral body
Spinal
nerve root
Dorsal root
ganglion
Lateral mass
P O RTA L S / E X P O S U R ES
P E A R LS
• The bifid nature of the spinous
processes may result in dissection into
the paraspinal musculature, affecting
the superficial plexus of veins.
• Care should be taken not to violate
the facet joint capsules until the target
vertebrae have been radiographically
confirmed.
P O RTA L S / E X P O S U R ES
P I T F A L L S
• Exposures performed too far
ventrolaterally to the facet joints may
result in increased bleeding and nerve
root injury.
P O RTA L S / E X P O S U R ES
E Q U I PM E N T
• Bovie electrocautery
• Cobb elevator
Procedure 12 | Cervical Spine: Lateral Mass Screw Fixation 103
FIGURE 12-3
P O RTA L S / E X P O S U R ES
E Q U I PM E N T
• The use of minimal incision portals may
decrease postoperative neck discomfort
and accelerate rehabilitation.
Occiput
Vertebral artery
Spinous process
FIGURE 12-4
Vertebral artery
A
FIGURE 12-5, A-B
Center of
lateral mass
B
104 Procedure 12 | Cervical Spine: Lateral Mass Screw Fixation
Vertebral
artery
foramen
Vertebral body
A
FIGURE 12-6, A-B
S T E P 1 P EA R L S
• A lateral radiographic or fluoroscopic
image is mandatory for confirming the
correct levels of instrumentation.
• Meticulous removal of soft tissue from
the articular masses will allow clear
delineation of the anatomic landmarks.
S T E P 1 P IT FA L L S
• Lack of preinstrumentation localizing
radiography may lead to wrong-level
surgery.
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
• 2-mm round-tip burr, drill, or Kirschner
wire
10° superior
25°-30° lateral
Lateral mass
25°-30° lateral
Vertebral
artery
foramen
Vertebral body
10°
Center of
lateral mass
aim 10° lateral
Lateral mass
10° lateral
B
Procedure
Step 1: Determining the Entry Point
n
The entry point for screw insertion is located 1 mm medial to the midpoint of
the lateral mass. The direction of the screw is 15 degrees cephalad and 30
degrees lateral for C3-6 (Figure 12-6, A).
Step 2: Drilling the Screw Hole
n
Holes are drilled with a 2.4-mm drill bit using the drill guide.
n
The drill depth can be increased in 2-mm increments.
n
A depth gauge is used to confirm the appropriate screw length.
Step 3: Tapping and Screw Insertion
n
The tap size may equal the outer screw diameter or be slightly undersized.
A self-tapping screw may avoid the need for additional tapping.
n
An appropriate-size screw is then placed in the same trajectory as the tap
(Figure 12-7).
Step 4: Rod Insertion
n
The determined length of rod is cut using the rod cutter (Figure 12-8, A) and
bent utilizing the rod bender (Figure 12-8, B).
n
Contouring of the rod is performed in gentle, limited steps until the desired
shape is achieved (Figure 12-8, C ).
S T E P 1 C ON T R O V ER S I E S
• The Roy-Camille technique may be used
for screw entry point (see Figure 12-6,
B). The starting point for the screw
insertion is located at the midpoint of
the lateral mass. The screw is directed
10 degrees lateral with no cranialcaudal inclination. This technique may
lead to cephalad articular joint violation.
S T E P 2 P EA R L S
• If the spinous process obstructs
application of the drill in the correct
direction, it may be trimmed with a
burr or rongeur.
• A small Penfield elevator can be placed
in the joint space to keep the drill
aligned in the sagittal plane parallel to
the facet joint.
Procedure 12 | Cervical Spine: Lateral Mass Screw Fixation 105
S T E P 2 P IT FA L L S
• Past pointing of the drill may result in
nerve root irritation.
• Improper drill trajectory may result in
injury to the spinal cord or vertebral
artery.
• Drill trajectories in the sagittal plane
that are too low may violate the facet
joint.
• Drill trajectories that are too medial
may encroach upon the vertebral artery.
S T E P 2
I N S T RU M E N T A T I O N /
I M P L AN TAT IO N
• Power or hand drill
S T E P 3 P EA R L S
• To ensure optimal screw anchorage in
the lateral masses, bicortical screw
placement is recommended.
• To avoid nerve root irritation when
performing bicortical screw placement,
screw length should be selected 2 mm
shorter than measured.
FIGURE 12-7
A
B
S T E P 3
I N S T RU M E N T A T I O N /
I M P L AN TAT IO N
• Tap
• Polyaxial screws
C
FIGURE 12-8, A-C