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86 Procedure 11 | Posterior C1-C2 Fusion: Harms and Magerl Techniques
FIGURE 11-12
S T E P 2 P EA R L S
• Intraoperative landmarks, the
preoperative thin-cut (1-mm) axial CT
scan, and lateral and open-mouth
fluoroscopic imaging can all aid in the
accurate placement of the C1 lateral
mass and C2 pars interarticularis
screws.
• Alternative procedures for patients with
unilateral vertebral artery anomalies
at C2
• Polyaxial screw placement at C1 and
C3 on the side of the anomalous
vertebral artery.
• Polyaxial screw placement at C1,
C2, and C3 on the side with normal
anatomy. Perform a posterior fusion
from C1 to C3.
• If an anomalous vertebral artery
exists, you can also place a crossedintralaminar C2 screw if the lamina is
wide enough on CT, as an alternative
point of fixation.
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
• Penfield elevators
• Blunt pedicle probe
• High-speed burr
• Pneumatic drill and 2-mm drill bit
FIGURE 11-13
Step 2
n
At C2, a no. 4 Penfield is used to define the medial border of the C2 pars. The
starting point for the C2 pars interarticularis screw is in the superior and medial
quadrant of the C2 pars. The entry point for placement of the C2 pars screw is
marked with the 2-mm high-speed burr (Figure 11-12).
n
The starting hole and drill bit trajectory can be confirmed under C-arm guidance
with open-mouth and lateral views.
n
A pilot hole is made using a 2-mm drill bit in a 20- to 30-degree convergent
and cephalad trajectory, using the superior and medial aspect of the C2 pars
as a guide. The integrity of the walls of the pilot drill hole is confirmed with a
blunt pedicle probe.
n
A depth gauge can be used to confirm the measurement obtained from the
preoperative CT scan of the appropriate length screw and can be checked on
lateral fluoroscopic radiograph.
n
The drill hole is tapped, and the 3.5-mm polyaxial screw is placed into the C2
pars (Wait et al, 2009) (Figure 11-13).
n
Step 1 is repeated for the contralateral C2 pars.
Step 3
n
If reduction of C1 is necessary, the patient’s head can be repositioned before
fixation of the rods to the screws. When performed, the reduction is visualized
under fluoroscopy.
FIGURE 11-14
S T E P 3 P EA R L S
• C1-2 reduction can be accomplished by
direct manipulation of the C1 and C2
screws. The authors’ recommendation is
to obtain a reduction preoperatively, if
possible while the patient is awake, to
assess neurologic status. Alternatively,
reduction can be performed after the
patient is positioned prone on the
operating table before preparation and
draping.
S T E P 4 P EA R L S
• With this technique, one can avoid
damage to the C1-2 facet joints, and
the rods and screws can be used as
temporary fracture fixation without
definitive fusion (i.e., type II and III
odontoid fractures) (Harms and
Melcher, 2001). Eventual removal of
the hardware can allow the patient to
regain atlantoaxial motion after fracture
healing has occurred.
• The integrity of the posterior arch of
C1 is not necessary for stable fixation.
• Patients with rheumatoid arthritis
often have instability adjacent to the
atlantoaxial region requiring a more
extensive fusion. This technique can be
incorporated as part of fusions to the
occiput and/or the subaxial spine.
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
Procedure 11 | Posterior C1-C2 Fusion: Harms and Magerl Techniques 87
FIGURE 11-15
Step 4
n
The interconnecting rods are measured and secured with locking nuts (Figure
11-14).
n
Distraction or compression of the construct can be accomplished at this time.
n
The locking nuts are tightened with a torque wrench (Figure 11-15).
Step 5
n
For definitive fusion, posterior iliac crest bone graft is harvested. The posterior
superior iliac crest is palpated, and an 8-cm line centered over the crest is
marked with a sterile marking pen. A 10-blade scalpel is used to incise the skin.
Self-retaining retractors are inserted.
n
Bovie electrocautery is used to dissect the subcutaneous tissue down to the
junction of the lumbodorsal and gluteus maximus fascia.
n
The posterior superior iliac crest is palpated, and the fascia is initially reflected
using Bovie electrocautery. A subperiosteal dissection is performed using a Cobb
elevator at the superior and lateral margins of the crest. Osteotomes are used
to make a cortical window in the crest that is reflected medially. The window is
made within 8 cm of the posterior superior iliac crest to avoid injury to the
superior cluneal nerves.
n
Small gouges are used to harvest cancellous bone graft through the cortical
window.
n
The graft is placed in a sterile cup mixed with the patient’s blood and covered.
n
Hemostasis is obtained with bone wax. The wound is irrigated and the graft site
is packed with Marcaine-soaked Gelfoam, and the cortical window is closed.
n
The retractors are removed and the incision is closed in layers.
88 Procedure 11 | Posterior C1-C2 Fusion: Harms and Magerl Techniques
S T E P 5
I N S T RU M E N T A T I O N /
I M P L AN TAT IO N
• Cobb elevators
• Osteotomes
• Gouges
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 cerebrospinal fluid
(CSF) leak. The authors advocate
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 on
postoperative imaging, the screw
Step 6
n
The cervical operative field is irrigated with antibiotic solution, and the irrigation
fluid is suctioned from the field.
n
If definitive fusion is being performed, the posterior surfaces of C1 and C2 are
decorticated with the high-speed burr. Alternatively, decortication of the posterior aspects of C1 and C2 can be performed before insertion of the screws
and rods.
n
The cancellous bone graft is placed over the decorticated surfaces of C1
and C2.
n
The C1-2 joint surfaces can also be decorticated and packed with bone graft
for an intraarticular fusion.
n
Alternatively, a piece of iliac crest bone graft can be fashioned and secured
between the C1 ring and C2 spinous process.
Step 7
n
Final AP and lateral cervical radiographs are obtained to assess placement of
the hardware and alignment of the atlantoaxial region.
n
The wound is closed securely in a layered fashion obliterating any dead space.
n
A subfascial drain is placed if thought to be needed by the surgeon.
n
Steri-Strips are placed perpendicular to the incision and covered by sterile
4 × 4 gauze and a clear Tegaderm dressing.
n
A rigid cervical collar (i.e., Philadelphia or Miami J) is secured in place.
n
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. The patient is removed from the Mayfield headholder
(Figure 11-16).
FIGURE 11-16
Procedure 11 | Posterior C1-C2 Fusion: Harms and Magerl Techniques 89
should be surgically removed to
decrease the risk of vertebral artery
injury.
• Intraoperative vertebral artery injury
is the feared complication that
can cause serious clinical sequela,
including brainstem stroke. If this
occurs, the screw can be left in place
to tamponade bleeding, and then
vascular studies should be obtained.
• A direct microvascular repair by
a vascular surgeon after the
surrounding bone is skeletonized or
after endovascular repair are also
options. Irrespective of the method
used to tamponade the bleeding, a
postoperative angiogram should be
obtained to evaluate the vertebral
artery.
• Potential risk for internal carotid
artery injury with bicortical screw
fixation (Currier et al, 2008) anterior
to the ring of C1.
I N D I CAT I O NS P E A R L S
• Biomechanically superior to posterior
wiring techniques (Henriques et al,
2000)
• Postoperative halo-vest immobilization
not usually required
I N D I CAT I O NS P I T F A L L S
• Potential vertebral artery injury
• Technically demanding
• Maximum biomechanical stability
achieved when combined with posterior
wiring for three-point fixation
(Henriques et al, 2000)
• Requires intact posterior arches of C1
and C2
• Sublaminar wires increases risk of
neurologic injury
• Contraindicated for
• Comminuted fractures or erosive
lesions of the lateral mass of C1
• Bilateral anomalous vertebral artery
pathways through the C1 lateral
mass
• Inadequate reduction and alignment
of the atlantoaxial complex
• Relative contraindication
• A unilateral anomalous vertebral
artery pathway through the lateral
mass of C1 or C2 on one side, with
a concomitant contralateral dominant
vertebral artery. If injury occurs to
the dominant artery with screw
placement, blood supply to the
brainstem and the cervicomedullary
junction can be compromised.
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 1. If atlantoaxial stability has
been obtained, the patient can be mobilized (see Figure 11-16).
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 postoperatively.
n
Routine outpatient static lateral and supervised dynamic lateral flexion and
extension radiographs can be obtained at approximately 4 weeks to ascertain
stability. If stability is obtained, the cervical collar can be weaned from use.
Radiographs are obtained at 4- to 6-week intervals to assess stability and fusion.
n
Additionally, a CT scan can be obtained 3 to 6 months postoperatively to assess
fusion and fracture healing.
Technique B: C1-2 Transarticular Facet Screws (Magerl Technique)
Indications
n
Atlantoaxial instability resulting from
• Fractures of the odontoid (type II and III) (Jeanneret and Magerl, 1992)
• Adjacent fractures of C1 and C2
• Rotatory subluxation
• Rheumatoid arthritis
• Os odontoideum
• Postodontoidectomy without basilar invagination
• Congenital malformation (e.g., Klippel-Feil)
• Malignancy
n
Nonunions
• Odontoid nonunion (type II and III)
• Failed posterior C1-C2 fusion
n
C1-2 osteoarthritis
Examination and Imaging
n
Complete neurologic and musculoskeletal examination
n
Preoperative imaging should include plain radiographs (see Figure 11-3, A), CT
(see Figure 11-3, B), CT angiography, and MRI (see Figure 11-3, C ) of the cervical spine.
• Radiographs should include AP, lateral, and open mouth to evaluate the
alignment of C1 and C2. Supervised dynamic lateral flexion and extension
views helps determine the reducibility of atlantoaxial subluxation when
present.
• A CT scan with axial, sagittal, and coronal thin-cut (1-mm) reconstruction
images through the upper cervical spine is an important part of preoperative
planning. A CT can provide anatomic detail of the lateral mass of C1, and
the C2 facet for optimal placement of transarticular facet screws. It delineates
the position of the foramen transversarium through which the vertebral artery
runs. Additionally, it allows for the evaluation of adequate bone stock of the
atlas for sufficient fixation of the screws.
90 Procedure 11 | Posterior C1-C2 Fusion: Harms and Magerl Techniques
E X A M IN AT I ON / I M A GI N G
P E A R LS
• Unless specifically indicated, the authors
do not routinely use MRA to evaluate
the vertebral artery anatomy because
of its inability to define the spatial
relationship between the artery and
surrounding bony architecture.
T R E A T M E N T OP T I O N S
• Techniques for posterior C1-C2 fusion
include
• C1-2 transarticular facet screws
(Magerl technique) with and without
bone graft and sublaminar wiring
• Posterior C1-2 polyaxial screw and
rod fixation (Harms technique)
• C2 translaminar screw
• Gallie “bone block” graft placed
posteriorly between the arches of C1
and C2 secured with sublaminar wire
• Brooks “wedge” bone graft secured
to the posterior lamina with
sublaminar wire
• Halifax interlaminar clamp
• Approximately 20% of patients requiring atlantoaxial fusion show anatomic
variations in the path of the vertebral artery and osseous anatomy, which
would preclude screw placement (Jun, 1998; Madawi et al, 1997). In addition
to evaluating vertebral artery dominance, CT angiography can delineate the
course of the vertebral artery through the foramen transversarium and its
spatial relationship to the surrounding bony architecture. This can help determine if a screw can be placed safely with minimal risk to the vertebral artery.
• MRI permits visualization of any soft tissue injuries including the transverse
atlantal ligament, as well as visualization of the spinal cord.
◆
MRI can help identify injury to the transverse atlantal ligament with con-
comitant odontoid fracture, which may help dictate anterior versus posterior operative approach. Even with union, anterior odontoid screw fixation
alone will not restore atlantoaxial stability secondary to ligamentous
disruption.
◆
When present in rheumatoid patients, identification of pannus posterior to
the odontoid can give a more accurate measurement for the space available for the cord.
n
Noninvasive magnetic resonance angiography (MRA) can be utilized to evaluate
vertebral artery injury, patency, and/or dominance.
Surgical Anatomy
n
The cephalad orientation of the C1-2 transarticular screw and the final position
of the neck necessary for adequate atlantoaxial alignment may require percutaneous placement of the transarticular facet screws (Figure 11-17).
n
The ponticulus posticus or congenital arcuate foramen is a common bony
anomaly of the atlas (Young et al, 2005). It is a bony arch on the cephalad
aspect of the C1 lamina that contains the vertebral artery. If present, it can easily
be confused with the lamina of C1 and must be identified during the posterior
dissection to prevent vertebral artery injury.
n
The gray ramus communicans of the C2 nerve is a reliable landmark for locating
the entry point for a screw on the C2 pars (Cavalcanti et al, 2010).
FIGURE 11-17
P O S I TI O N I N G PE A R L S
• In very osteopenic bone, inverse
(negative) radiologic images can be
utilized for better bony visualization.
P O S I TI O N I N G PE A R L S
• It is imperative that you confirm that
the C1-2 joint is reduced or capable
of reduction preoperatively; otherwise
the accurate placement of the
transarticular screws can be difficult
and dangerous.
P O S I TI O N I N G EQ U I P M EN T
• C-arm fluoroscopic radiograph should
be positioned at the head of the
operating table.
• Mayfield headholder
• Four-poster frame
Procedure 11 | Posterior C1-C2 Fusion: Harms and Magerl Techniques 91
Positioning
n
After an awake fiberoptic nasotracheal intubation is performed, a nasogastric
tube is inserted for intraoperative gastric drainage.
n
If the patient is immobilized in a halo vest, a rigid Philadelphia collar is placed
on the patient before halo-vest removal. In coordination with anesthesia, the
surgeon stands at the head of the hospital bed and stabilizes the patient’s neck.
The patient is cautiously repositioned in the prone position on the operating
table with the torso on bolsters or a four-poster frame. The halo ring can be
attached to the Mayfield adapter. If the halo ring is removed, the patient is
placed in Mayfield tongs before prone positioning. After repositioning the
patient prone, the Mayfield tongs are fixed to the operating table using a Mayfield headholder with the neck in a neutral position.
n
All bony prominences are well padded, and the patient’s arms are secured by
their side using a folded sheet that is tucked beneath them.
n
Using fluoroscopic C-arm, proper alignment of the atlantoaxial bony structures
is confirmed with the radiograph centered at C1-2. The lateral fluoroscopic
image must not be oblique at C1-2; otherwise incorrect screw trajectory can
result.
n
If necessary, adjustments can be made while the patient is in the Mayfield
headholder to obtain reduction and should be confirmed on fluoroscopic radiograph. If possible, extreme positions of the neck should be avoided.
n
Somatosensory evoked potential and transcranial motor evoked potential moni-
toring are neurophysiologic spinal cord monitoring methods that can be utilized
intraoperatively. Baseline readings can be obtained before and after placing the
patient in the prone position.
Portals/Exposures
n
An electric razor is used to remove all hair from the patient’s occipital, suboc-
cipital, and neck regions. If transarticular screw fixation with bone graft and
sublaminar wiring is being performed, the posterior iliac crest is also shaved for
bone graft harvesting.
n
The skin surfaces of the neck and posterior iliac crest are prepared and draped
in sterile fashion.
n
Using the inion of the occiput cranially, and the protuberance of the vertebral
prominens caudally, the midline is identified and marked from the occiput to
C3-4 with a sterile marker.
n
The subcutaneous skin of the planned skin incision can be infiltrated with 0.5%
lidocaine containing epinephrine diluted 1:100,000.
n
A 10-blade scalpel is used to sharply incise the skin in the midline from the
occiput to C3-4.
n
Bovie electrocautery is used for the subcutaneous dissection down to and
through the underlying ligamentum nuchae. Midline dissection of the nuchal
ligament provides a relatively avascular dissection and decreases the risk of
injury to the greater and third occipital nerves. Self-retaining retractors are
inserted for adequate visualization.
n
At the cephalad end of the incision, a 1.5-cm fascial cuff of trapezius, along the
nuchal ridge, can be elevated to facilitate lateral exposure of C1-2, but this is
not usually necessary. Subperiosteal dissection of the paraspinous muscular
insertions from the suboccipital bone is completed.
92 Procedure 11 | Posterior C1-C2 Fusion: Harms and Magerl Techniques
n
P O RTA L S / E X P O S U R ES
P E A R LS
• The C2 spinous process is an easily
identifiable landmark. The C2 spinous
process sits more posterior relative to
the arch of C1 and can be used to
orient your dissection.
• If present, the ponticulus posticus or
congenital arcuate foramen can easily
be confused with the lamina of C1. It
must be identified during the posterior
dissection to prevent vertebral artery
injury.
• The lateral dissection should not be
carried past the lateral border of the
C1-2 articulation, to avoid iatrogenic
injury of the vertebral artery.
The midline tubercle of the arch of C1 and the larger spinous process of C2 are
used as palpable landmarks during dissection. Starting at the midline, the periosteum of C1 and the tip of the spinous processes of C2 and C3 are incised
sharply.
n
Careful subperiosteal dissection is continued from C3 to C1, starting in
the midline and proceeding laterally. Periosteal elevators can facilitate the subperiosteal dissection of the paraspinous muscles as they are swept laterally. C2
and C3 are exposed laterally with care not to disturb the C2-3 facet capsules.
n
The C1-2 joint can be exposed with dissection over the superior surface of the
C2 pars. The capsule of the C1-2 facet is reflected from caudal to cephalad,
using caution not to injure the C2 nerve and surrounding vessels. Significant
venous bleeding can be encountered with dissection around the venous plexus
of the C2 nerve. This can effectively be controlled with bipolar electrocautery,
thrombin-soaked Gelfoam, and cotton pledgets.
n
To decrease the risk of injuring the vertebral artery on the cephalic surface of
the C1 lamina, identify the lamina and follow the caudal edge of the posterior
arch during exposure of C1.
n
P O RTA L S / E X P O S U R ES
P I T F A L L S
• When palpating the bony landmarks
for dissection, take care to avoid
translocation of the atlas and its
potentially serious consequences.
The dissection is complete with exposure of the suboccipital rim of the foramen
magnum.
Procedure
Step 1
n
If posterior bone graft and sublaminar wiring are going to be utilized with
transarticular screw fixation, bone graft harvesting and passage of the C1 sublaminar wire should be completed before the insertion of the transarticular
S T E P 1 P EA R L S
• Stabilization of the C1-2 segment with
transarticular screws can make the
passage of the sublaminar wire more
difficult and dangerous. Therefore it is
the authors’ preference to pass the
sublaminar wire before screw fixation.
• The C1 sublaminar wire can aid in
reduction of the atlantoaxial segment,
thus facilitating placement of the
transarticular screws.
screws.
n
After the dissection, the C1-2 posterior arch interspace and graft size is approxi-
mated. A moist sponge is placed in the wound to prevent tissue desiccation
while harvesting the bone graft.
n
The posterior superior iliac crest is palpated, and an 8-cm line centered over the
posterior superior iliac crest is marked with a sterile marking pen. A 10-blade
scalpel is used to incise the skin. Self-retaining retractors are inserted.
n
Bovie electrocautery is used to dissect the subcutaneous tissue down to the
junction of the lumbodorsal and gluteus maximus fascia.
n
The posterior superior iliac crest is palpated, and the fascia is initially reflected
using Bovie electrocautery. A subperiosteal dissection is performed using a Cobb
elevator at the superior and lateral margins of the crest. Osteotomes and an
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
• Cobb elevators
• Osteotomes
• Oscillating saw
• Gouges
• Curettes
oscillating saw are used to obtain a tricortical strut graft within 8 cm of the
posterior superior iliac crest to avoid injury to the superior cluneal nerves.
n
A 1.5 × 4 cm tricortical strut graft is obtained. Small gouges/curettes are used
to then harvest additional cancellous bone graft.
n
Hemostasis is obtained with bone wax. The wound is irrigated, and the graft
site is packed with thrombin-soaked Gelfoam. The retractors are removed, the
wound is irrigated, and the incision is closed in layers.
n
Any soft tissue on the graft is removed with a small Cobb or curette. The graft
is placed in a sterile cup mixed with the patient’s blood and covered.
Procedure 11 | Posterior C1-C2 Fusion: Harms and Magerl Techniques 93
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
• Straight and curved microcurettes
• Woodson dissector
• Kerrison rongeurs
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
• Penfield elevators
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
• 16- or 18-gauge double-looped wire
• A wire-passer or 00-silk suture
Step 2
n
To prepare for the passage of the sublaminar wire, the ligamentum flavum on
the underlying surfaces of the posterior arches of C1 and C2 is elevated off the
superior and inferior surfaces of the lamina using a microcurette.
n
A Woodson dissector can be used to carefully free any adherent portions of
dura.
n
A 2-mm Kerrison rongeur is used to remove the ligamentum. Venous plexus
bleeding deep to the ligamentum can be controlled with bipolar electrocautery,
thrombin-soaked Gelfoam, and pledget packing.
Step 3
n
A no. 4 Penfield elevator is used to define the medial border of the C2 pars.
Care must be taken not to violate the dura with the Penfield. The Penfield can
be used to protect the C2 nerve root and venous plexus with gentle rostral
retraction. The removal of any ligamentum flavum adjacent to the C2 lamina
will improve visualization of the C2 pars and atlantoaxial joint and help with
orientation for transarticular screw placement.
n
Step 3 is repeated for the contralateral C2 pars.
Step 4
n
Using the Gallie technique, a C1 sublaminar wire is passed before the placement
of the transarticular screws. A smooth arch is bent into the end of 16- or
18-gauge double-looped wire and conformed to approximate both the length
and thickness of the C1 lamina.
n
The wire is carefully passed beneath the C1 lamina. This maneuver can be
facilitated by the use of 00-silk suture or a wire-passer. Using both hands, the
wire is pulled beneath the C1 lamina. One hand pulls and advances the sublaminar wire, while the other hand provides constant gentle tension on the other
decreasing the risk of impinging the wire upon the cord.
Step 5
n
Atlantoaxial alignment is necessary for accurate placement of C1-2 transarticu-
lar screws. This is confirmed using lateral C-arm fluoroscopy (see Figure 11-17).
n
If necessary, anterior atlantoaxial subluxation can be manually realigned intra-
operatively with gentle traction on the C1 sublaminar wire and pressure on
the axis.
n
Posterior atlantoaxial subluxation can be realigned with flexion repositioning of
the head in the Mayfield tongs. Alternatively, posterior atlantoaxial subluxation
can be reduced with the placement of the bone block graft between C1 and
C2. After placement, the graft can be manually manipulated against the posterior arch of C1 to obtain reduction. Reduction can be maintained after the C1
sublaminar wire is secured around the spinous process of C2 and the bone block
graft.
n
The cephalad angle of the C1-2 transarticular screw can make placement dif-
ficult. To facilitate screw placement the axis can be gently displaced rostrally
toward the occiput. This presents the C2 pars at a better angle for accurate
placement of the transarticular screws.
n
The position of the neck can also influence the trajectory necessary to obtain
optimal placement of the transarticular screws. Percutaneous placement of the
C1-2 facet screws may be necessary if intraoperative atlantoaxial alignment
precludes the placement of the screws through the wound created by the posterior cervical dissection.
94 Procedure 11 | Posterior C1-C2 Fusion: Harms and Magerl Techniques
S T E P 6
I N S T RU M E N T A T I O N /
I M P L AN TAT IO N
• Pointer tunneler
• Soft tissue protection sheath
S T E P 7 P EA R L S
• To decrease the risk of vertebral artery
injury, the K-wire must not be directed
laterally, and must follow the medial
wall of the C2 pars.
• Intraoperative bony landmarks, the
preoperative thin-cut (1-mm) axial CT
scan, and AP and lateral fluoroscopic
imaging can all aid in the accurate
placement of the K-wires and C1-2
transarticular screws (Weidner et al,
2000).
• Screw fixation with a cannulated
3.5-mm screw system is the authors’
preferred method for transarticular
screw placement.
Step 6
n
If the trajectory requires a percutaneous approach, a stab incision is made with
a 15-blade scalpel through the skin into the paraspinal region of T2-3.
n
A pointer tunneler is placed into the soft tissue protection sheath and inserted
through the stab incision made at T2-3. The soft tissue protection sheath has a
large handle that can be used to manipulate and guide your trajectory through
the soft tissues.
n
In the approximate trajectory necessary for transarticular screw placement, a
tunnel can carefully be made through the soft tissues of the neck with the
instruments exiting at the inferior aspect of the occipitocervical wound.
n
The tip of the tissue sheath is placed against the inferior articular process of
C2, and the pointed tunneler is removed from the tissue sheath.
Step 7
n
The K-wire drill guide is inserted into the soft tissue sheath. A 1.2-mm diameter
K-wire is then inserted into the drill guide and secured to a reversible pneumatic
drill.
n
If the percutaneous technique is not required, the K-wire drill guide can be
inserted directly into the soft tissue sheath and placed in the C2 fossa.
n
The starting point for screw entry is in the C2 fossa, 2 to 3 mm lateral to the
junction of the lamina and lateral mass (Figures 11-18 and 11-19).
n
C-arm fluoroscopy is used to identify all bony atlantoaxial structures and guide
the trajectory of the 1.2-mm K-wire. The K-wire is aimed toward the superior
border of the lateral mass of C1, just lateral to the C2 pars interarticularis, and
parallel to the medial border of the C2 pars interarticularis.
n
The K-wire is advanced through the pars interarticularis of C2, along the central
axis of the C2 pedicle in a 0- to 10-degree convergent trajectory in the AP plane.
FIGURE 11-18
FIGURE 11-19
S T E P 7
I N S T RU M E N T A T I O N /
I M P L AN TAT IO N
• 1.2 × 50 mm K-wires
• K-wire drill guide
• Reversible pneumatic drill
• Penfield elevators
S T E P 8
I N S T RU M E N T A T I O N /
I M P L AN TAT IO N
• 1.2 × 50 mm K-wire
• Cannulated drill bit
• Ruler
• Cannulated tap
• Cannulated fully threaded 3.5-mm
cortical screws (Figure 11-21)
Procedure 11 | Posterior C1-C2 Fusion: Harms and Magerl Techniques 95
n
A no. 4 Penfield can be used to protect the C2 nerve root and venous plexus
with gentle rostral retraction. This allows visualization of the K-wire as it passes
across the posterior edge of the atlantoaxial facet joint into the lateral mass of
C1. The tip of the K-wire should engage the anterosuperior margin of the C1
lateral mass.
n
C-arm fluoroscopy is used to confirm K-wire placement.
Step 8
n
A cannulated drill bit is placed and drilled over the K-wire under C-arm fluo-
roscopy. Care must be taken as the drill is advanced over the K-wire. Because
there is a risk of bending the tip of the K-wire as it crosses the C1-2 facet joint
and penetrates the C1 cortical surface, impingement of the K-wire in the cannulated drill can occur. This can result in subsequent advancement of the K-wire
into the posterior oropharyngeal fossa.
n
The drill guide is removed from the tissue sheath and a second K-wire of identi-
cal length is placed in the tissue sheath until it rests on the posterior surface
of C2 adjacent to the other K-wire. The difference in length of the K-wires
determines the length of the screw, and it is measured with a ruler.
n
The near cortex is tapped with a cannulated tap through the tissue sheath.
n
A cannulated fully threaded 3.5-mm cortical screw of appropriate length (usually
40 to 45 mm) is inserted with a cannulated screwdriver over the K-wire under
fluoroscopic visualization. The anterior cortex of the C1 lateral mass should
be purchased with the screw. Unicortical screws may be considered to avoid
neurovascular injury in cases with satisfactory bone quality (Cyr et al, 2008)
(Figure 11-20).
FIGURE 11-20
FIGURE 11-21