Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_6029_Библиотеки_им_академика_М_И_Перельмана.pdf
88
6 Specific Reconstruction Techniques of Upper Cervical Spine and Craniovertebral Junction
The MR flow void or MRA can show an anomalous
course of VA; however, the bone-vascular relationship
cannot be well appreciated on MR imaging. Therefore,
Theodore et al. [226] used CTA to better visualize the
VA course in FT in three patients. Clearly, it is not only
the course of the VA but also the VA-bone occupancy
ratio that are important to assess. Cacciola et al. [26]
studied ten cadavers and found that VA completely
filled up the bony groove only in 30% of specimens. In
the majority of specimens, there was a space between
the artery and bone filled by periostial tissue and
venous plexus. The mean VA occupancy within the
groove was 79% (range 34–100%). This very important fact was reproduced by Moftakhar et al. [162] as
mentioned earlier. They performed detailed CTA
measurements in 106 patients with stroke or trauma
presentations. Their motivation to do so was the fact
that the majority of previously mentioned dimensions
were obtained from cadaveric specimens or evaluations of only osseous VA groove on CT scans rather
than imaging the actual real size and location of VA
itself (Fig. 6.19).
The potential risk of neurovascular injury anterior
to the C1 or C2 body is similar to those described for
C1 lateral mass screws and pedicle screws if bicortical
screw purchase is preferred. Jeanneret and Magerl
[116] have seen temporary bilateral hypoglossal palsy,
which they were not able to explain. Nonetheless, they
ended up replacing one of the screws as it was 4 mm
longer than desired.
6.3.2.2 Surgical Technique
Friedrich Magerl [116, 152] suggested to place the
screw entry point on C2 caudal articular process 2 mm
laterally and 3 mm cranially from the internal edge of
C2-3 facet and to follow strictly parasagittal trajectory
to reach posterior or middle thirds on inferior C1 facet
surface. The target point on lateral fluoroscopy was the
anterior tubercle of atlas in a reduced position. He used
a 2.5 mm drill bit and always tapped the pilot hole for
a cortical fully threaded 3.5 mm screw. If lagging was
required, they over-drilled the proximal part of the
hole with a 3.5 mm drill bit. The first drill was always
left in place until the second pilot hole was drilled to
avoid eventual dislocation. He emphasized the importance of visibility of the upper isthmus edge up to the
atlantoaxial joint capsule and always used a bone
adjunct, usually in the form of Gallie’s graft or intraarticular bony chips to enable fusion. Magerl and his
followers have described most of the surgical tricks in
their initial descriptions although they were later attributed to other authors [83, 116]. For example, they have
initially described: the possibilities of manual atlantoaxial dislocation reductions, how to perform the
intraarticular bone fusion in cases of missing C1 posterior arch, how to achieve the correct sagittal working
angle by means of cranial C2 spinous process traction,
and/or creating caudal stab wounds for trocars.
Ongoing widespread use of Magerl’s technique led
to more frequent descriptions of complications. The
first VA injury caused by transisthmic screw was published by Sasso et al. [199]. Madawi et al. [151] has
described 8% of VA injuries without any mortality.
Wright and Lauryssen [240], in their retrospective survey analysis of 1,318 patients treated with transarticular screws, estimated the risk of VA injury 4.1% per
patient or 2.2% per screw inserted with a 0.2% per
patient incidence of subsequent neurological deficit
and 0.1% mortality. However, the actual incidence of
VA penetration might be higher because of a low survey response (25.1%). Gluf et al. [69] later reported
2.6% incidence of VA injury and a 0.5% mortality rate
as a result of transarticular screw fixation in 191
patients. Recently, the same group of authors published
their series enlarged by 78 additional patients (269
total) emphasizing that increased experience and more
careful radiological planning can dramatically decrease
the frequency of VA injuries [61]. In this largest published series worldwide, they evaluated the risk of VA
injury as 1.9% per patient and 1.2% per screw having
13.3% sides anatomically unable to accept the transarticular screw.
Conversely, there are large studies available describing no VA injury [86, 154]. In the meantime, there
were a lot of other studies describing the use of transarticular screw and its modification [36, 44, 69, 86,
116, 154].
6.3.2.3 Our Preference
So far there is no published study substantially modifying the originally and, in our opinion, genially
described technique by Magerl. The technical development since then only allowed performing this surgery
more precisely, less invasively, and using hardware
6.3 Axis as an Anchoring Structure
89
made of better materials. The crucial step forward was
the evolution of imaging techniques. The precise
knowledge of anatomy of the isthmus of pars interarticularis and VA course can substantially decrease the
frequency of complications if correct screw trajectory
is preplanned and if those who cannot accommodate
the screw are primarily excluded. The main drawback
of this technique is that the screw passage cannot be
controlled by naked eye and the sagittal angle is not
very comfortable and sometimes even not achievable.
Interestingly, there is an important difference
between VA injury risk established from cadaveric
anatomical studies or 2D CT reconstructions (up to
23% risky) and those where thin sliced CT with threedimensional reconstruction were used (6% of risky or
unacceptable).
The VA injury risk is very variable among the published studies [69, 86, 151]. This fact brings about a
suspicion that approximately one half of these events
are not only the technique but possibly more surgeon
related. We suspect that this failure can hypothetically
be caused by an incorrect angle of placement in sagittal
plane or wrong preoperative planning and/or decision
to use this technique on unsuitable patients and/or
sides. Many authors warn about the potential injury of
the spinal canal contents. It needs to be stressed that no
spinal cord injury has ever been described in the literature when placing pars or pedicle screws in C2. This
fact can be explained by the usual direct visualization
of isthmus. Also, the medial cortex can be exceptionally breached without a significant risk of dural/neural
injury. Such or even quadricortical (intra-canal) screw
purchase in the case of pedicle screw placement is an
important bailout technique in certain situations where
other methods fail or are not possible (destructive
arthropathy in rheumatoid arthritis patients). It is the
circular bone stock available for round-shaped screw
in the narrowest place of its trajectory that we find critical (Fig. 6.23). The SAS can only be measured on 3D
models in the plane perpendicular to its planned trajectory. The preoperative modeling can be done on the CT
workstation or with the help of navigational machine
and its software (Fig. 6.24). The SAS should be at least
5 mm in diameter to allow a safe passage of a 3.5 mm
screw while using the standard technique guided by
anatomical landmarks and fluoroscopic guidance. If a
Fig. 6.23 Space available for
long transisthmic screw
modeled on navigational
computer station. (a) Model
of 3.5 mm screw passage
through the isthmus depicting
critical SAS in coronal plane.
(b) Model of 3.5 mm screw
showing critical SAS in
parasagittal plane
Fig. 6.24 Correct transarticular screw trajectory plan prepared on navigational workstation. (a) 3D image. (b) Parasagital projec-
tion. (c) Tilted axial section
90
6 Specific Reconstruction Techniques of Upper Cervical Spine and Craniovertebral Junction
4 mm screw is to be used then the SAS must be at
least 6 mm. In cases where image guidance, real-time
CT or isofluoroscopy are used, the SAS diameter can
be 1 mm less. In cases where morphology makes the
screw placement impossible (worst case scenario),
it has to be recognized on preoperative planning and
other options need to be considered.
The screw trajectory can vary substantially. If the
aim of the screw is to fix C1 in reducible dislocations,
then it has to pass through the posterior half of C2
upper facet. In cases of irreducible anterior dislocation
or settling of the atlas, the screw trajectory has to primarily respect a safe passage through the C2 pars and
only secondarily consider if C1 anchorage is sufficient
or even possible. Targeting of anterior tubercle of the
atlas is never as important as achieving a safe C2 transisthmic trajectory. At least 5 mm of screw should pass
through the bone of C1 lateral mass to achieve a firm
anchorage. Change of trajectory due to dislocated C1
or high located VA groove can result in undesirable
deviation of the screw. Thus, for example, the hypervertical trajectory can penetrate the C0-1 joint and in
such a situation, an adequately shorter screw has to be
selected. Medial or lateral tilt can be acceptable if sufficient anchorage of C1 is possible and if the screw
does not leave the middle third of the lateral mass in
coronal plane. An intentional decrease in cranial angle
could potentially be the most dangerous. If such caudal
tilt is necessary, the screw entry point needs to be
adjusted more cranially; otherwise, the VA groove
would be violated (Fig. 6.25). Similarly, a more lateral
trajectory can increase the risk of VA tear if the pathway is not changed appropriately according to 3D
modeling. Too long a screw can injure the anterior retropharyngeal structures. Internal carotid artery, hypoglossal nerve, and the posterior pharyngeal wall can be
injured if the tip of bicortical screw is too lateral and
protrudes more than 5mm out of the vertebra.
More freedom exists if the C1 anchorage is not
intended to fix C1 but rather is a part of a longer construct. In such situations, a nearly pedicular trajectory
can be selected. Alternatively, a concomitant caudal tilt
of the screw with a more superior location of entry
point can be advantageous in bicortically or monocortically placed isthmic screws. With respect to the VA,
one has to pay attention not only to the shape and direction of pure bony canal or the groove of VA but also to
the actual artery itself as it occasionally occupies only
a part of the foramen/groove. This becomes obvious in
cases of arterial asymmetry due to hypoplastic VA as
seen on a CTA (Fig. 6.19). The other choice is to place
only a short pars screw as described below.
6.3.2.4 Our Surgical Technique
Patients treated for C1-2 instability are carefully and
often fiber-optically intubated and electrophysiological monitoring electrodes are attached in the initial
recumbent position if needed. Prone positioning is performed gradually holding the head in neutral position
sometimes secured with a hard collar or halo vest. The
Fig. 6.25 Schematic picture of possible trajectories of C1-2 tran-
sarticular screw demonstrating that changing of trajectory must
be accompanied by the change of screw entry point. (a) Tilting of
the screw in sagittal plane without change of entry point can lead
either to inadequate C1 lateral mass bone anchorage (cranial tilt)
or undesirable VA vicinity. (b) Synchronous change of trajectory
and screw entry point is much more relevant
6.3 Axis as an Anchoring Structure
91
operating surgeon is always responsible for this maneuver and most often he is the person holding the head
and directing others to rotate the patient. Three-point
head fixation (e.g., Mayfield clamp) can be advantageous to allow for reduction of atlantoaxial dislocation
as well as positioning the C2 vertebra appropriately for
isthmic screw placement (40°–50° tilt). This maneuver
flexes the head while keeping the cervical spine
straight. Lateral fluoroscopy is always used during
positioning of the patient and the planned trajectory
angle is tested with metal probe (Fig. 6.26).
Occasionally, barrel chest or fixed hyperlordosis do
not allow for the correct trajectory. This is crucial and
one must not be satisfied if an absolutely perfect angle
cannot be achieved. It is also necessary to figure out
the angle achieved by extended instruments (drill etc.)
as the dorsal chest can dictate how much upward angle
is possible. The other trick is the “landing Concorde”
position of cervicothoracic junction. The head and
UCS should be located higher than right cardiac atrium
to avoid excessive venous bleeding from potentially
injured plexuses around the C2 nerve root. It is necessary to emphasize repeatedly that the positioning of
the patient before incision has the same substantial
value for final success as a clean and anatomically
clear surgical approach. We should do everything possible to increase patient’s safety, and also our comfort
to be concentrated to the critical parts of the procedure.
As neurosurgeons, we feel that any unnecessary bleeding results in blurring of anatomical structures and we
therefore insist on meticulous hemostasis from the
beginning of the procedure. We use subcutaneous local
anesthetic with adrenaline (epinephrine) infiltration
and electrocautery to decrease bleeding from skin and
subcutaneous tissue. It is important to maintain midline on deeper dissection through the nuchal ligament
and the muscular fascia as this will prevent blood loss
and allow for subperiostial dissection of neck muscles
off the spinous processes and laminae. The C2 spinous
process is often bifid, readily palpable, and is the largest one in the UCS thus allowing orientation. The other
important point of orientation is the posterior tubercle
of atlas. When placing the long isthmic screw, we
expose the posterior arch of atlas, C2 laminae, C2/3
joint, and adequate part of occiput. If a simple C1-2
transarticular screw is to be placed with intra-articular
bone fusion only, the approach can be less invasive
with sparing of some of the muscles attached to the C2
spinous process. However, when atlantoaxial reduction and posterior midline graft fusion are required, the
exposure needs to be extended to see all previously
mentioned structures. When placing an isthmic screw,
we believe it is critical to expose the whole C2 pars
interarticularis and the cranial ridge of C2 isthmus.
The desired sagittal angle for drilling is very often
achievable only via a caudolateral stab wound incisions. The entry points most often located 2 mm laterally and 3 mm cranially from lower medial aspect of
lower C2 facet are predrilled with a high-speed drill to
avoid drifting of the drill. The trocar is introduced
through the caudal stab incision and long drill in appropriate sleeve is passed through to reach the entry point.
Lateral fluoroscopy is now brought into the field and
the sagittal angle checked. We usually draw a line on
the fluoroscopy display to extend the line of drilling
and thus better predict the target. Frequently, the
Fig. 6.26 Testing of
achievable trajectory angle
with metal probe on lateral
fluoroscopical view
preoperatively. (a) Screen
view. (b) Video print
92
6 Specific Reconstruction Techniques of Upper Cervical Spine and Craniovertebral Junction
anterior atlas tubercle is the endpoint of our drilling.
This is, however, not true in dislocated situations as
was emphasized earlier. Before the drilling begins, the
superomedial ridge of C2 isthmus is visualized with a
Penfield dissector, thus enabling the surgeon to directly
monitor the lateral wall of the spinal canal. Usually, a
parasagittal plane or slightly medial (up to 15°) trajectories are used. If known, the screw hole is pre-drilled
on the non-dominant side first. Otherwise, we usually
choose the right side first. The drilling is discontinued
when the end cortex (most often, anterior C1 lateral
mass) is penetrated. If no excessive bleeding is seen
after the drill removal the tap is introduced through the
same trocar sleeve and the hole is tapped. This is the
most dangerous part of the procedure. The tap is a very
sharp instrument and can injure the VA more easily
than the drill and the trajectory of the original drill hole
can be changed unintentionally. Because of the mentioned drawbacks, some authors do not recommend
use of a tap and continue with self-tapping screw.
Nevertheless, we believe that tapping can increase the
strength of screw anchorage and also avoids unintentional redirection as is possible with self-tapping screw.
A full-threaded or half-threaded screw is finally introduced via the same trocar. A specially developed selfretaining screw driver can be very helpful during the
trocar passage of the screw. All steps of the screw
placement are monitored by lateral fluoroscopy.
In our series of 100 transisthmic screws, we have
seen two VA injuries. It was always during tapping.
One has to consider this complication whenever significant venous bleeding is encountered out of the drill
hole. This can be a warning sign caused by injury of
venous plexuses surrounding the VA. If the VA is violated, pulsatile arterial bleeding may be seen out of the
drill hole. In such situations, a second attempt to pass
the screw would be ill-advised, in our opinion. The
transisthmic screw can also be introduced under image
guidance. One has to consider that only C2 vertebra is
registered. We only use image guidance in borderline
cases where we believe that transisthmic screw is necessary and where the SAS is between 4 and 5 mm.
6.3.3 Short C2 Pars Interarticularis Screw
The use of a short screw in the C2 pars interarticularis
to avoid the vertebral artery was suggested by Resnick
and Benzel, in 2001 [185]. They have chosen this
technique in a very obese woman with odontoid
pseudoarthrosis where the low angle of a transarticular
screw was impossible and patient’s obesity made fluoroscopy guidance difficult. They used an entry point
located 14 mm above the C2-3 facet line, approximately
in the center of the pars. A 20 mm screw was introduced
in a sagittal angle parallel to the spinous process.
Unfortunately, as other authors, they called this screw a
“pedicle” screw despite it being placed in the actual C2
pars in terms of anatomy. The construct was finished by
a rod connection to C1 lateral mass screws bilaterally.
Stokes et al. [213] described C2 “pedicle” screws placed
via the same entry point as Magerl’s screw in his series
of four patients (first 1999) treated by “Harms” technique. However, the trajectory was less cranial and more
medial. In fact, he placed short pars screws not reaching
the VA groove. Many other authors presented good
clinical and morphological results using the connection
between C1 lateral mass screws and short pars screws
while describing them as “pedicle” ones [41, 181].
6.3.3.1 Our Preference
The short screws placed monocortically in the pars
represent the least stable method of C2 fixation [47].
The only real advantage is a minimal risk of VA injury.
This technique can be used very seldom if all other
possibilities are not possible or fail. This can be of
importance, for example, in very obese patients where
achieving of required angles can be difficult.
6.3.4 Laminar C2 Screws
Wright [238, 239] was the first to describe the possibility of C2 laminar screw instead of a more technically
demanding and risky isthmic or pedicle fixations in
atlantoaxial stabilization techniques. He performed the
first surgery using crosslaminar C2 screw in 2002.
Independently the same method was described later by
Gorek et al. [77] who used unilateral laminar screw as
a salvage technique in cases where one side C2 pars/
pedicle was not large enough to accept a 3.5 mm screw.
As an alternative, for cases with deeply furrowed C2
spinous processes, Sciubba et al. [200] recently developed a technique where shorter, not crossing screws
6.3 Axis as an Anchoring Structure
93
are introduced into the laminae after removal of bifid
spinous process. Laminar screws currently represent a
viable alternative to the other techniques using C2 vertebra as an anchoring structure. Their stability was
tested by Nassos et al. [167] on cadaveric specimens
and compared to other methods of C2 fixation in occipitocervical constructs (pedicle and transarticular
screws). Although similar in its ability to limit motion,
laminar screws tended to be weaker in lateral bending.
Their long-term stability remains questionable.
Parker et al. [180] analyzed a cohort of 167 patients
treated with 152 C2 laminar and 161 pedicle screws in
C1-C3 fusions or subaxial long constructs. On postoperative CT scans, they documented lower frequency of
cortical breach with laminar screws (1.3%) than with
pedicle screws (7%) but both without any clinical sequelae. During at least 1 year follow-up, they confirmed
that, especially in the short UCS constructs, the crosslaminar screws remain stable. In longer subaxial constructs they found a higher frequency (6.1%) of laminar
screw revisions mostly due to pull out, hardware failure,
or pseudoarthrosis. Safety and feasibility of laminar C2
screws were also described by Sciubba et al. [200];
however, 12.5% of their patients required revision a few
months after surgery because of pseudoarthrosis and
screw pullout. Wang [232] also reported early hardware
failure in 6.6% of treated patients. Wright [239]
described 100% fusion in a 1-year follow-up in his
series of 20 patients treated for various pathologies with
different constructs using the C2 laminar screws. He did
not have any clinical complications but postoperative
CT revealed 15% of cortical breach of C2 laminae. Most
authors [105, 180] prefer a free-hand technique respecting anatomical landmarks with occasional help of fluoroscopy when placing laminar screws. Although, the
accuracy of laminar screws is generally very good, some
authors suggest more precise techniques. Nottmeier
[172] placed 4mm laminar screws in eight patients using
3D isofluoroscopy image-guided technique with excellent accuracy. Lu et al. [147] suggested the use of a
patient-specific navigational template attached to C2
spinous process. This template was created according to
a plastic model of C2 vertebra prepared before the procedure with the help of CAD and 3D CT image.
Recently, Dmitriev et al. [47] biomechanically tested 14
cadaveric specimens and found similar insertional
torque while placing the screws into C2 pedicle or lamina but significantly lower values were registered with
short monocortical isthmic screws. Interestingly, the
postfatigue pull-out strength was significantly better for
pedicle than for laminar or isthmic screws. The strength
of laminar screw pull-out resistance can be increased by
bicortical purchase as described by Jea et al. [114]. This
modification of Wright’s method is also safer because
the tip of the screw is visible at the distal end of its pathway. On the other hand, it is probably not possible in all
C2 arch variations.
6.3.4.1 Anatomical Background
C2 lamina is considered to be the largest in the upper
and middle cervical spine; nonetheless, a great variability in its diameter and length is documented by anatomical works [27, 232, 242]. The average laminar
angle to sagittal plane was 44.1° (range 37°–50°) when
measured on 38 dried cadaveric specimens (76 C2 laminae) by Wang [232]. The laminar length available for
a screw (including the width of spinous process) was,
on an average, 31.6 mm (range 27.0–37.0 mm). The
same author measured the cross-sectional diameter of
the C2 lamina. He found that, in its thinnest portion, the
average height of the lamina was 11.5 mm (range 9.0–
14.1 mm) and average thickness was 6.3 mm (range
3.6–9.1 mm). He thus found that 21% of laminae could
not accommodate a 3.5 mm screw (less than 5.5 mm
space available) if allowing for an extra circumferential
millimeter 42% of tested sides cannot accommodate a
4 mm screw (less than 6 mm space). Cassinelli et al.
[27] observed a similar C2 lamina thickness on 420
dried C2 vertebrae similar but found a gender difference with larger values obtained from male specimens.
They concluded that 70.5% of laminae had thickness
equal to or greater than 5 mm, 92.6% more than 4 mm,
and 96.7% more than 3.5 mm. The average length of
arches was lower than in previous series. Only 45.2%
of laminae were able to accept 25 mm screws and only
1.9% could accommodate 30 mm screws without entering the lateral mass (internal distance measured). As
others [203, 242], they found that caudal part of lamina
is thicker than cranial one and recommended to aim the
screw to lower laminar margin.
6.3.4.2 Surgical Technique
According to Wright’s recommendation [239], after a
subperiostal exposure of C2 spinous process and
94
6 Specific Reconstruction Techniques of Upper Cervical Spine and Craniovertebral Junction
laminae, a small cortical window is created on the right
side of rostral part of C2 spinous process at its junction
with the right lamina. The hand drill is used to drill the
pilot hole along the visible left-sided C2 lamina. The
trajectory should be kept slightly away from the spinal
canal than the downslope of the lamina. A ball probe
confirms the integrity of the intralaminar canal. A 30 ×
3.5 mm screw was placed and no tap mentioned. The
opposite screw is introduced in the same manner but
the entry point is located more caudally in order to
allow the screw intralaminar crossing. According to the
author, no fluoroscopy or navigation is necessary to
introduce 3.5 mm crosslaminar screws but a preoperative CT evaluation of laminae and their size is mandatory. To avoid canal content damage, the internal surface
of C2 lamina can be palpated in cases of angle or thickness uncertainty. Gorek [77] advised to tap the initial
part of screw hole located in the middle of the junction
of spinous process and lamina for unilateral screw purchase. The appropriate screw length with endpoint
located no further than the junction between pars and
lamina was determined by depth gauge. Jea et al. [114]
prefer the penetration of the distal cortex with a screw
tip by modification of the introductory angle.
6.3.4.3 Our Preference
Influenced by the mentioned anatomical works and our
own experience, we argue that prior to any C2 laminar
screw placement, a thin-sliced CT should be obtained
to determine the thickness of C2 laminae. It also allows
establishing the ratio between cortex and cancellous
intralaminar bone canal and the appropriate screw
length in order to avoid penetration of C2/3 joint
(Fig. 6.27). In our opinion, this technique is a useful
salvage procedure (Figs. 6.28 and 6.51). Laminar C2
screw technique can be helpful in cases of small pedicles or pars or erroneous attempt of pedicle or isthmus
cannulation resulting in weak bone or need for a different (now risky) trajectory.
It seems obvious that a correct transpedicular or
transisthmic screw technique with bicortical purchase
should provide stronger screw anchorage than a screw
placed in the cancellous bone cavity of C2 lamina.
A further potential and so far unknown risk is that
of a ventral laminar breach of the screw during daily
life overload. Fortunately, such complication with
clinical sequelae has not yet been described. An early
postoperative CT confirms proper screw position and
is highly recommended as plain radiographs will not
show any ventral cortical penetration [140].
When planning various types of fixation with axis
serving as anchoring structure, the preoperative CT
analysis should always include a study of possible
“salvage” options. Routine production of patient-specific templates will, probably, not be available to every
surgeon but the use of 3D isofloroscopes connected to
navigational systems seems to be the feature allowing
not only a precise screw placement but also an immediate check of their real-time position.
6.3.5 Odontoid Process Screw
This specific screw is used only for the treatment of
odontoid process fractures and not as a part of any segmental fixating construct. It was first used by Nakanishi
et al. from Japan in August 1978 [166] and independently Friedrich Magerl performed the same procedure
in January 1979 [87] in Switzerland for odontoid
pseudoarthrosis. He also suggested using this technique for the treatment of fractures. First documented
series of 12 fractures treated this way was published by
Böhler [20] with annotation that the idea came from
Magerl. The pioneers described the necessity of use of
two screws where the longer one is acting as a lag
screw and the shorter securing the rotational stability.
Numerous papers then described the success of this
method in the treatment of type II and shallow type III
odontoid fractures [2, 68, 128, 182, 220]. Later, especially North American authors, under influence of biomechanical works [79, 198] began to advocate single
screw fixation of odontoid fractures [117, 216]. Overall
fusion rate achieved by direct odontoid screw was
between 85% and 95%.
6.3.5.1 Anatomical Background
The approach trajectory is oblique to allow the screw
passage from anteroinferior edge of C2 vertebral body
to the tip of the odontoid process. There is approximately 14 mm of available space for a safe screw purchase in the midline of the base of C2 [131]. The
distance to the base of the odontoid is approximately
20 mm and the process itself is another 20 mm long, on
6.3 Axis as an Anchoring Structure
95
Fig. 6.27 Modeling of SAS for C2 intralaminar screw placement on navigational workstation documenting large SAS
an average. Thus, one can calculate that the length of
the lag screw should theoretically be between 36 and
The odontoid tip is covered by very dense cortical
bone, which has to be penetrated with a longer screw.
44 mm. The odontoid process diameter is approximately 10 mm at its base, just enough space for two
4 mm screws under normal conditions. Certainly, there
6.3.5.2 Surgical Technique
is large gender, race, and age variability, which has to
be taken into account and patient-specific individual
parameters have to be measured exactly (best on CT).
Odontoid fractures can be treated with a direct
screw compressive osteosynthesis only if reduced
96
Fig. 6.28 Crosslaminar
screw used as salvage
procedure on the side where
the transpedicular and
transisthmic screw introduction was not feasible. (a) Left
high riding VA visible on
coronal CT reconstruction.
(b) Left parasagittal
reconstruction showing
unfeasibility of transisthmic
screw. (c, d) Postoperative
axial CT scan showing left
C2 crosslaminar screw and
Magerl’s screw on the right
side
6 Specific Reconstruction Techniques of Upper Cervical Spine and Craniovertebral Junction
preoperatively. Therefore, patient positioning on the
table allows for oblique introductory angle without dislocation of the fracture and is, indeed, a critical step in
the surgical procedure. The screw angle can be a limiting factor in obese people, patients with fixed cervical
kyphosis, and those with a barrel chest. The obliquity
of this approach usually starting at the level of C5 and
steep cranial angle allows only for a fairly limited illumination. This fact led to further development of various self-retaining and tubular retractors [96, 204]. Also,
the screws come in a variety of shapes and materials:
full-threaded or partially threaded; double-threaded;
3.5 or 4 mm diameter; steel, titanium alloy or PLDLA,
and full or cannulated [2, 6, 9, 129]. Initially, the fullthreaded 3.5 mm stainless steel screws were used and
the proximal part of the pilot hole for the lag screw
was over-drilled with larger diameter drill to achieve
compression [20]. Later, cannulated screws guided by
a Kirschner wire were used with a short apical thread
and long smooth shaft [2]. The fixation itself started
with drilling followed by tapping and screw placement
performed under real-time double fluoroscopy.
6.3.5.3 Our Preference
There is no doubt, in our opinion, that direct compressive osteosynthesis of type II and shallow type III
odontoid fractures is the most physiological method
available with highest fusion rates if correctly indicated
and performed. Main advantage of the direct osteosynthesis is that no other motion segment is involved in the
fusion. It can be performed only if the fracture is
reduced and the introductory angle is possible.
6.3.5.4 Our Surgical Technique
In our experience it often took more time to position the
patient on transparent table correctly, than the surgery
itself. The patient’s head is fixed in halo ring (not necessary in every case) to enable free manipulation with continuous traction (Fig. 6.29). The patient is intubated
without changing of the spine position (under fluoroscopical control, fiberoptically, or awake), and his/her
mouth is held open with mouth distractor or simple roll
6.3 Axis as an Anchoring Structure
97
Fig. 6.29 Setup of two rectangular fluoroscopes. (a) Position of C-arms and the transparent surgical table. (b) Peroperative halo-
ring traction
of gauze. It is very difficult and very important to set
the C2 vertebra in sagittal plane correctly to achieve
acceptable angle for screw placement and not to dislocate
the fracture especially in posteriorly dislocated or
oblique fractures. Positioning maneuvers and the introductory angle are checked on lateral fluoroscopy using
an extended radiopaque marker (e.g., long K-wire)
(Fig. 6.30). Following that, a second fluoroscopic machine
is set up perpendicular to the first one to allow for a transoral view. It is usually adjusted in such a way as to visualize the tip and shaft of odontoid process and the base
of C2 simultaneously on both screens (Fig. 6.31). The
screens are always positioned in front of the operating
surgeon and the pictures turned to depict the same orientation as the patient position (Fig. 6.32). We never start
Fig. 6.30 Preoperative fluoroscopical testing of correct angle
achievability with metal probe
the procedure if the previously described harmony of
position and radiographic visibility is not achieved.
A right-sided horizontal incision is made just above
the C4-5 interspace and the anterior spine is exposed
through a standard, bloodless anterolateral approach.
The prevertebral fascia is sharply cut and oblique tunnel reaching the base of C2 is created by blunt dissection. The extent of exposure can be checked by lateral