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6 Specific Reconstruction Techniques of Upper Cervical Spine and Craniovertebral Junction
and deviating from the recommended trajectory through
the C2 isthmus. Incorrect screw angle can often be a
result of inappropriate patient positioning, a short neck,
spine deformity, or hyperlordotic spine curve. Further,
atlas settling, absent C1 anterior tubercle after transoral
decompression or VA variability (in approximately
20% of patients) can lead to VA injury. On the other
hand, if atlantoaxial transarticular fixation is correctly
indicated and performed, it represents a very stable
fixation avoiding the need for hard external bracing and
providing high fusion rates. Certainly, in some countries, the lower cost of two screws when compared to
other methods may be an important factor.
C1 Lateral Mass – C2 Pedicle Screw and Rod Fixation (Goel, Harms)
Goel and Laheri performed the first C1-2 fusion in
1988 [72]. To achieve a wide exposure of the C1-2 joint
they amputated the C2 nerve root in all cases. Both the
C1 lateral mass and C2 pedicle screw were placed
monocortically over a steel plate regularly used for finger bone osteosynthesis (economic reasons – personal
communication) (Fig. 6.48). In some of their patients a
longer plate was used to allow for occipitocervical
fusion. Later, they analyzed a series of 160 patients
treated for various C1-2 instabilities by their method
[70]. They accepted a bicortical screw purchase as a
more stable option and described some of the pitfalls of
their method. In few cases, screw placement was impossible due to the encountered morphology. Eighteen
patients described specific sensory loss in C2 root area.
In four patients, they have seen profound arterial bleeding while drilling the pilot hole for C2 pedicle screw.
Although it was not confirmed angiographically as
Fig. 6.48 Screw and plate AA fixation according to Goel
there were no neurological sequelae, they concluded
that the bleeding was related to VA injury. They considered all constructs stable after 5 months of follow-up
and only one screw was broken after 18 months.
Postoperative CT was not routinely performed.
The same method, supplemented by joint distraction and placement of a hydroxyapatite or titanium
spacer was used in fixed atlantoaxial dislocation in 19
patients [71] to treat atlas settling or dislocation. Most
of the patients (18) were suffering from fixed dislocated odontoid pseudoarthrosis and/or os odontoideum. Construct stability was not biomechanically
tested and the authors had their patients wear a hard
cervical collar for 3 months. Harms and Melcher, who
advocated bicortical screw purchase, improved the
technology of previously described fixation [94]. They
developed polyaxial screws allowing top loaded rod
connection (Fig. 6.49). The longer C1 screws with a
smooth proximal shaft allowed sparing of the C2 nerve
root and indirect manipulation of the atlas (in case of
fracture distraction) and consequently in connection to
C2 pedicle screws to manipulate the atlantoaxial joint.
Their construct can easily be extended either cranially
if occipitocervical fusion is required or caudally to fix
the UCS to subaxial cervical spine.
Bone graft can be packed either directly into the
atlantoaxial joint or as a posterior onlay graft. The
above-described techniques enable significantly more
comfortable angles of screw placement; however, the
risk of VA injury is not eliminated. Increasing number
of publications documented successful use of Goel’s
technique. Stulik et al. [215] performed atlantoaxial
fusion with Harms instrumentation in 46 patients.
They used the system either for temporary or permanent fixation. Twenty four patients were evaluated retrospectively with at least a 12-month follow-up. Three
C2 screws (5.4%) were considered malpositioned on
the postoperative CT scan, with one breaching the
canal cortex and two encroaching the FT. They did not
have any clinical complications and documented 100%
fusion rate. Arayan et al. [14] retrospectively evaluated
102 patients treated with Harms fixation/fusion. In this
probably largest available series, most of the patients
(48 patients) were treated for instability caused by
odontoid pseudoarthrosis. The authors used navigational system in first third of treated patients and neuromonitoring in all of them. They always cut the C2
nerve root with only one case of neuropathic pain in
follow-up. They distracted the atlantoaxial joint when
6.4 Monosegmental Fusion Constructs
Fig. 6.49 (a) posterior (b) lateral view
109
needed using force transmitted through screws and in
38% of procedures introduced bilateral allograft spacer
intra-articularly. In 23% of patients, at least one side
was anatomically not suitable for C2 pedicle screw.
Therefore, pars screws were placed (probably, the short
ones) instead. The risk of VA injury in this study is
similar to that of Magerl. Two VA injuries were encountered but happened during subperiostal exposure of C1
due to atypical VA loop. The strength of the construct
was increased by regular use of crosslink. The followup revealed 98% fusion rate. The Goel-Harms technique was also successfully used in a limited number
of pediatric patients (6 patients, the youngest being 7
years old). Similar restrictions applied to children as
they do for adults [98]. The biomechanical stability of
Harms technique was tested in multiple studies and it
is similar to transarticular screw fixation if supplemented by posterior wiring [106, 132, 159].
Again, there are advantages as well as disadvan-
tages of the described technique:
Advantages of Goel-Harms technique
– Immediate stability, no external support needed
– The angle of C2 pedicle screw trajectory is easy to
achieve
– The screw placement is not dependent on relative
C1-2 position
– Reduction of atlantoaxial dislocation feasible dur-
ing procedure
– C1-2 joint is not damaged, temporary fixation is
possible
– Isolated C1 fracture compression practicable
– Laminae could be absent, no wiring necessary
– Prolonging of construct easy
– High fusion rate
Disadvantages of Goel-Harms technique
– VA injury risk underestimated and possibly as high
as 23% of patients
– Cannot be used if target structures are comminuted
or destructed
– Steep learning curve
– Cost (Harms fixator is much more expensive than
other techniques)
– Fluoroscopy mandatory
– High profile of the polyaxial construct
Our Preference
The Goel-Harms technique is a valuable tool in all types
of C1-2 instability providing excellent immediate immobilization. The specific advantages in comparison to
Magerl’s technique are of two kinds. First, the angle necessary for C2 pedicle screw placement is much easier to
achieve and secondly, in cases of dislocated or fractured
atlas, the vertebra can be manipulated independently.
We would like to emphasize, however, that there is no
evidence that this method has a lower risk of VA injury.
C1 Lateral Mass – C2 Crosslaminar Screw and Rod Fixation (Wright)
Due to limited stability of C1-2 wiring fixations more
rigid methods using C2 isthmic and/or pedicle screws
were developed. All those techniques required for a
110
6 Specific Reconstruction Techniques of Upper Cervical Spine and Craniovertebral Junction
screw to pass through an anatomically variable area
neighboring the C2 VA groove and thus posing a substantial risk to the artery. In order to avoid this technically demanding procedure, Wright [238] suggested to
place two crossing laminar screws and connect them to
C1 lateral mass screws with rods (Fig. 6.50).
The acute stability of C1 lateral mass – C2 laminar
screw fixation was biomechanically tested and compared to Harms construct and combination of laminar/
pedicle construct by Gorek et al. [77]. No statistically
significant differences in stiffness were found and, at
least in cadaver models, the laminar screw construct is
comparable to other atlantoaxial fixation techniques.
However, other authors demonstrated less rigidity with
laminar screw constructs when compared to pedicle
screw anchor, most pronounced during lateral bending
and rotation [32, 135]. Similar results were confirmed
by Dmitriev who studied construct stiffness after an
experimental odontoid process transection [47].
The position of laminar polyaxial screw heads does
not allow the use of sublaminar wire in C1-2 fixations.
The eventual bone graft has to be fashioned to stay
below the rods.
The other concern, in comparison to Harms technique, is the possibility to manipulate C1 on C2 with the
help of distraction/compression forceps when the screw
heads are near to the spinous process of C2. Although
never biomechanically proven, the proximity of the laminar screw heads to the medial axis and the curvilinear
rod needed to connect them can potentially be less resistant to lateral translation, bending, and rotational forces.
This can be of increased importance if unexpected
polyaxial screw head would not retain initial stability.
Advantages
– No risk of VA injury
– Less technically demanding
– Can be used if C2 pedicle or pars is not large enough
to accept a 3.5 mm screw
– Can be a salvage procedure in cases of C2 pedicle/
pars erroneous placement
– Decreased perioperative radiation exposure
– Direct visualization of the target structure (i.e., C2
laminae)
– Retained possibility to reduce the C1-C2 dislocation
– Independence on C1 position
– Easy angle of screw trajectory
– Immediate C1-2 construct stability compared to
other rigid techniques
– Good long-term stability of translaminar screws in
short C1-3 constructs
Disadvantages
– Cannot be used if C2 laminae are absent
– If the core diameter of lamina is less than 3.5 mm,
cortical breach can occur
– Potential risk of spinal cord injury
– Fixation of Gallie’s type graft can be difficult
– Not enough space to connect C2 to C3 lateral mass
screw
– Offset connectors or significant rod contouring
necessary
– Problematic long-term stability in long subaxial
constructs
Our Preference
In our department, we use Wright’s technique with
increasing frequency, mostly as a salvage procedure in
situations where a high-riding VA prevents a pedicle or
transarticular screw placement. This is usually only on
one side in the construct. So far only once, has this
situation occurred bilaterally (Fig. 6.51).
Fig. 6.50 Artist’s drawing of
C1 lateral mass – C2
crosslaminar AA fixation
according to Wright
6.4 Monosegmental Fusion Constructs
111
Fig. 6.51 Bilateral high riding VA in patient with odontoid
pseudoarthrosis not allowing any C2 postero-anterior (transisthmic, transpedicular) screw introduction treated by crosslaminar
screw C2 – massa lateralis C1 fixation acc. to Wright. (a) Frontal
Intralaminar Screws C1 – Short Pars C2 (Donnellan)
In rare cases, the posterior C1 arch can be defective
and the lateral mass eroded by inflammatory or degenerative process together with concomitant C2 high riding VA. This situation does not allow either placement
of transarticular or pedicle screw fixation in the axis
plane reconstruction. (b) Postoperative axial scan in the C2 arch
plane. (c) Plain postoperative laterogram. (d) CT in 3D posterior
crosslaminar C2 screw purchase and C1 lateral mass screw fixation supplemented with autologous graft
nor lateral mass fixation or wiring of the atlas.
Donnellan et al. [48] suggested to use a combination of
intralaminar C1 screws connected to short C2 pars
screws (Fig. 6.52). They have documented good results
and 100% fusion rate in three patients treated with this
technique. The method seems safe, avoiding all the
known risks of arterial injury but has not been biomechanically tested so far.
112
Fig. 6.52 Artistic drawing of
intralaminar C1 – short
isthmic C2 AA fixation
suggested by Donnellan
6 Specific Reconstruction Techniques of Upper Cervical Spine and Craniovertebral Junction
Our Preference
In our opinion, only rarely does a situation arise requiring the use of this construct. Nonetheless, it does represent a salvage option if more robust constructs are
impossible. We suppose that a construct connecting C1
and C1 laminar screws is another less stable, salvage
option of atlantoaxial fixation.
6.4.2 Anterior Monosegmental Fusion Constructs
6.4.2.1 Anterior Screw Fixation of C2-1
Lesoin et al. [141] were the first to perform anterior
transarticular C2-1 fusion in six patients with acute or
chronic posttraumatic C1-2 instability (Fig. 6.14).
They used right-sided high anterolateral approach to
place 25–35 mm long screws from C2 body perpendicularly through the joint reaching the C1 lateral
masses. However, their approach was quite extensive
and the head rotated 15° away from the exposed side.
Also, the indications were not in concordance with
current expert opinions. A similar technique, but performed from less invasive, oblique approach (like for
odontoid screw) with intraarticular curette decortications, was described by Sonntag and Dickman [45,
209]. The same group of authors later used a combination of odontoid screw and two anterior transarticular
screws as a salvage procedure to stabilize an 85-yearold man with combined atlas-axis fracture [11].
Analyzing dry specimens and embalmed cadavers,
anatomical guidelines for anterior atlantoaxial fixation
were suggested by Lu et al. [146]. Using the same
entry points as previous authors, they recommended to
place 15–25 mm long screws in lateral angle of 5°–25°
and posterior angle of 10°–25°. Vaccaro et al. [230]
performed bilateral high cervical approach, directly
decorticated the atlantoaxial joints and packed them
with bone graft and placed bilateral transarticular
screws. They used K-wires introduced under biplanar
fluoroscopy followed by tapping and cannulated screw
placement. Although, the usual lateral trajectory angle
of 30° is described, they actually used a 0° angle in
coronal plane and 25° posterior tilt in sagittal plane.
The screws were 26 mm long on both sides in their
case. The patient was placed in long-term, postoperative halo vest as the original indication for surgery was
a failed posterior Brooks’s fixation for odontoid
pseudoarthrosis. In 1999, Knöller et al. presented the
first larger series of patients (11) treated for odontoid
process pseudoarthrosis with only temporary anterior
transarticular fixation [127]. Another case of fixation
of combined unstable atlantoaxial fractures (odontoid
and C1) treated with anterior triple screw fixation was
published by Reindl et al. [184]. The initial concerns
about the short-term stability of anterior atlantoaxial
transarticular screw fixation techniques were disputed
by biomechanical work of Sen et al. [202]. They tested
posterior versus anterior transarticular fixation techniques in nine cadavers and did not find any significant
differences between these two techniques. However,
they discovered that if a cable fixed graft is added to
the posterior fixation, stability was significantly higher
especially in flexion and extension. They placed the
screw in lateral angle of 20° and posteriorly tilted in an
angle of 30°. The screws were introduced perpendicularly to the joint fissure in the middle third of articulation. The entry point was located in the groove created
by articulation process in the middle of C2 body.
Koller et al. suggested different trajectory for anterior transarticular screw fixation, having performed a
thorough anatomical analysis of fine CT scans with
3D reconstructions in 42 healthy individuals and
6.4 Monosegmental Fusion Constructs
113
comprehensive literature review [131]. They described
a safe zone of approximately 14 mm in the midsagittal base of C2 vertebral body. They proposed a precise
algorithm for safe screw placement from the base of
C2 through the body to the C1 lateral mass (Fig. 6.15).
The transcorporeal route logically enables the use of a
longer screw bone passage and therefore also a higher
construct stiffness. On the other hand, using the C2 pinafore does not allow triple screw introduction if odontoid screw is needed. Respecting their own anatomical
results, the authors successfully fused atlantoaxial
joint in seven patients concluding that the indication
for anterior can be the same as for posterior fusion and
thus anterior procedure can be recommended especially
if anatomical situation precludes the posterior one.
Advantages
– Less muscular damage
– Smaller risk of VA injury
– Relatively easy approach (no cavity opened)
– Trajectory angle is easy to achieve
– Possible combination with odontoid screw technique
– Comparable short-time stability to other screw
techniques
– Theoretical possibility to extend the screw trajec-
tory to fix the occipital condyle
occipital joint. The exact preoperative radiological analysis and perioperative biplanar fluoroscopy are
mandatory. In our opinion, the main disadvantage is
that only intra-articular surface can be used to potentiate the fusion but no additional graft can be added out of
it. Questionable long-term stability makes this method
more exceptional and useful in rare specific cases as it
is documented by the lack of published larger series of
patients.
6.4.2.3 Anterior Plate or Construct C1-2
Anterior atlantoaxial plate to stabilize the C1-2 after
transoral odontoidectomy was proposed by Harms
et al. [95]. The plate was fixed by two screws to the
anterior lateral C1 masses and by two other to the C2
vertebral body (Fig. 6.53). Fifth screw transfixed the
axis body at the base of the odontoid process. Their
technique was biomechanically tested by Kandziora
et al. [121] who found out that, only if supplemented
by posterior Brooks fusion, is this technique comparable in rigidity to Magerl’s procedure alone. Previous
biomechanical conclusion was confirmed by clinical
series of 15 patients treated for irreducible atlantoaxial
Disadvantages
– Limited amount of bone graft, only intraarticularly
– Long-term stability questionable
– Biplanar fluoroscopy necessary
– Decompression, if necessary, hardly possible
– Possible violation of spinal canal (too posterior
trajectory)
– Possible violation of atlanto-occipital joint (too long
screw)
6.4.2.2 Our Preference
The technique is very elegant in some atlantoaxial combination fractures where the anterior transarticular
screw technique can be combined with odontoid screw
or anterior C2/3 plate (Fig. 14.3, Chap. 14). Also, in
cases of failed posterior fusion or anatomical situation
not allowing posterior fixation, this method can serve as
a salvage procedure. The attention should be focused
not only to the angles of purchase but also to the length
of screws, not to unintentionally damage the atlanto-
Fig. 6.53 Anterior plate for transoral AA transoral fixation
designed by Harms
114
6 Specific Reconstruction Techniques of Upper Cervical Spine and Craniovertebral Junction
kyphosis [125]. Kerschbaumer et al. saw two cases of
screw loosening in their first three patients treated with
Harms plate as a standalone fixation and they, therefore, always supplemented the anterior plate with posterior Brooks’s fusion with good long-term results
[125]. Kandziora et al. [122] also criticized the design
of Harms plate and suggested a new one with locked
screws located in more condensed subarticular bone in
C2 near to the base of odontoid (subarticular atlantoaxial locking plate (SAALP)). They confirmed higher
biomechanical stability for their type of plate; however, clinical data for the new plate are not available. In
order to avoid the need for posterior stabilization,
another plate with locked screws and option to reduce
atlantoaxial kyphosis was designed by Yin et al. [247].
This is done with special forceps distracting the cranial
part of plate against temporarily inserted C2 body
screw ( transoral atlantoaxial reduction plate (TARP)).
They have successfully reduced and fixed 4 patients
with odontoid pseudoarthrosis and kyphotic deformity.
The demand to reconstruct anterior column with sparing of adjacent segment motion, resulted in design of
more complex constructs replacing the C2 vertebral
body in tumor surgery. Sar and Eralp [197] used a
custom-modified Harms cage fixed with screws in C1
and C2 to replace the C2 anterior body in a patient with
C2 sarcoma. For the same purpose, C2 body prosthesis
was developed and used by Jeszenszky et al. [118].
Advantages
– Direct anterior decompression
– Sophisticated plate can reach enough stability to
avoid posterior fixation
– Atlantoaxial release possible
– Atlantoaxial kyphotization can be reduced
– Atlantoaxial joint can be distracted
Disadvantages
– Risk of infection of intracavitary approach
– Wide exposure causing more damage of soft tissue
(approx. 4 cm)
– Possible screw loosening
– Risky revision (infection)
– If reduction fails, posterior compression cannot be
eliminated
6.4.2.4 Our Preference
A sophisticated locking plate with realignment ability
can really address the problem of IAAD. However, to
achieve this goal, anterior atlantoaxial release must be
possible. This is not always the case. In RA patients
and some developmental anomalies, the joint could be
severely deformed and it can be very difficult to circumferentially release it. If incompletely released, it
can be dangerous to use inappropriate force to reduce
it. The bone is often very weak and does not provide
strong support for intra-articular distraction instruments. C1 lateral masses can be so deformed and pronounced that any screw purchase is problematic. In our
opinion, if the reduction is not achievable with traction
prior to the surgery, its surgical reducibility can only be
realized during the procedure thus postponing the decision to use or not to use the plate to this moment. The
infection risk is higher than for standard transoral procedure because the time necessary for fixation prolongs
the surgery and also the lateral exposure necessary to
fix the plate to C1 is much larger implicating important
soft retropharyngeal tissue damage. In summary, anterior C1-2 plating can be advantageous if preoperatively
irreducible AAD can be released during the surgery.
Then, the most sophisticated locking plate should be
used. The complex constructs used to support anterior
column after tumor resection represent a different topic,
which will be described in tumor chapter.
6.4.3 Lateral Monosegmental Fusion
Lateral atlantoaxial fusion was first used by Barbour
from Australia to treat the odontoid fractures in 1971
[17]. As he mentioned, starting in 1956, he was probably the first who used stable screw fixation of C1-2.
He used a skin incision along the anterior border of
sternocleidomastoid and extended it behind the mandibular angle to reach the lateral position of C1 transverse process. He nibbled it partially away and asked
anesthesiologist to turn the head to neutral position and
introduced the screw from C1 lateral mass medially and
downward transarticularly to C2 (Fig. 6.54). The same
procedure was then performed from the opposite side.
He recommended placing iliac crest onlay grafts on the
lateral vertebral surface. Unfortunately, neither number of treated patients nor the follow-up data are presented in his original paper. Encouraged by Barbour’s
work but not satisfied with approach difficulties, Du
Toit modified the technique and successfully treated
a patient with odontoid fracture [49]. He learnt from
cadaveric dissections and used an angled skin incision
to cut off the proximal attachment of SCM to reach the
6.5 CVJ and UCS as a Part of Multisegmental Constructs
Fig. 6.54 Drawing of lateral down-slope transarticular C1-2
fixation performed from bilateral approach according to Barbour
and DuToit
transverse process of C1. Anterolateral aspect of atlas
and lateral joint fissure was reached strictly subperiostally. Then he denuded the joint and filled it with autologous morselized bone. The drilling was performed
caudally (25° below horizontal plane) and posteromedially with custom-made drill guide allowing maximal
10° of backward angle and had 24 mm depth stop. The
pilot hole was tapped and the joint transfixed with AO
navicular screws. To avoid eventual spinal canal penetration, he established 20° as a maximal posterior tilt
of drilling. Later, this group described four other cases
(os odontoideum and dens pseudoarthrosis) successfully treated with bilateral transarticular screw fusion
[205].
6.4.3.1 Our Preference
We see some important drawbacks to have this procedure in standard fusion armamentarium. First of all the
bilateral access is needed, the anatomy of the approach
is complicated with the accessory nerve, auricular
nerve, jugular vein but namely VA in dangerous positions. Second, there is not enough bony surface for
eventual bone graft insertion and one has to believe
that intra-articular fusion potential would be enough.
6.5 CVJ and UCS as a Part of
Multisegmental Constructs
CVJ and UCS instability are disorders caused by
various etiologies including trauma, inflammation,
developmental anomaly, tumors, degenerative disease,
115
and/or iatrogenic decompression. During stabilization
procedures, one should avoid undesirable fusion of
disease-free segments and attempt to fix only the
unstable spinal motion units. This is of utmost importance in CVJ, the most mobile area of the spine.
Generally, we can divide long constructs to those
involving the occiput (occipitocervical) and those
starting subaxially and ending at C2 or C1 (suboccipital constructs). The decision process always involves
striking a balance between the loss of range of motion
versus the required extent of construct anchorage.
Occipitocervical fusion is indicated when the CVJ,
namely occipitoatlantal segment, is unstable or it is
expected that further progression of pathological process can involve this joint (RA patients, tumors, etc.).
Any multisegmental fusion has to be supplemented
with bone grafts with or without addition of bone
growth accelerators. The exceptions from this rule are
those with secondary bone tumors with limited life
expectancy.
6.5.1 Occipitocervical Constructs
By definition, this technique always involves the
occipital bone. The fusion extends at least to C2, often
to subaxial vertebrae, and sometimes is performed as
skip framework starting at occiput skipping C1 and/or
C2 and ending usually in two or three level fixation to
subaxial lateral masses or pedicles. Performing any
procedure fixating the cervical spine to head the surgeon must adapt the craniospinal angle in sagittal
plane and respect the neutral rotational position [155].
This is to allow the patient neutral horizontal view
otherwise the dictated position in non physiological
flexion, extension, and/or rotation will lead to compensatory deformation of spine balance. In patients
with substantial sagittal profile derangement, we also
have to calculate the whole spine profile with potential
planning of corrective spinal osteotomy in other
regions. It is well known that hyperflexed cervical
spine can also cause swallowing and breathing difficulties [15].
Foerster was the first who described the occipitocervical fusion with the use of fibular strut graft, in
1927 [64]. Newman and Sweetman, in 1969, reported
a series of nine patients treated with occipitocervical
onlay autograft. They had only one pseudoarthrosis
but their patients were postoperatively treated with
6 weeks of tong traction and then placed in Minerva
116
6 Specific Reconstruction Techniques of Upper Cervical Spine and Craniovertebral Junction
jacket for another 6 weeks [169]. Freely lodged standalone grafts did not secure any stability and the fusion
rate can be also very low [62]. Therefore, wiring techniques were introduced to fix these grafts [78, 92, 110,
235]. Also, methylmethacrylate was used to enhance
the occipitocervical stabilization [25]. Later, Ransford
et al. introduced contoured Lugue rod again fixed with
wire to posterior elements as a more stable technique
[183]. This wire and frame application was further
modified using different metal rods or pins [10, 59,
113]. All the techniques using wires for fixation, however, had some drawbacks. The stability was not very
high and the external fixation with halo vest or Minerva
jacket had to be used, the posterior elements (occipital
bone, laminae) had to be intact, sublaminary introduced hardware can injure the underlying neural structures and their coverings [149, 171, 211, 221] and the
wires often have a tendency to abrade through the bone
[43]. Despite prolonged external immobilization, in
halo vest or Minerva cast, the wire fixation methods
have failure rates up to 30% [145, 190]. The previously
mentioned techniques most often used doubled holes
in the occipital calvarium to pass the wires through.
To increase the stability of so called “semi-rigid
techniques,” Grob et al. [81] described Y plate connecting the transarticular C1-2 screws with the occiput,
where two screws fixed it to midline. Comparing
cohort of patients treated with this technique with
another group of patients fixed with older graft wiring,
the same authors found pseudoarthrosis rate of 6% vs.
27%, respectively [85]. Grob was also the first who
performed the occipital midline screw placement as he
knew that there is the thickest bone available. This new
plate and screw “rigid” technique was confirmed as
good enough to provide up to 100% of fusion without
indispensability of hard external supports by Sasso
et al. using two AO plates fixed by screws to occiput
and to Magerl screws, caudally [199]. Promising
results of other authors gained popularity for plate and
screw occipitocervical fusion [175, 196, 207]. Screw
and plate techniques were also confirmed as much
more stable than all the other previous by many biomechanical studies thus allowing to fuse less segments
than before [7, 111, 173]. Their main concern is that
the plate, although contoured, has defined holes for
screws and thus determines their position often to less
than optimal location. The other problem is in lining of
the construct. This means that most of plates even if
bended are reaching lateral occipital regions where
there is limited thickness of the bone. Screw purchase
cannot be strong enough and bicortical introduction is
potentially dangerous. Pait et al. suggested the insideoutside technique to avoid the screw loosening, subdural injury, and allow lateral occipital purchase [175].
They performed a trephination out of finally planed
screw location and then cut a slit with craniotome ending at the desired position. The flat screw head is
passed to this position epidurally from trephination
hole and the nut is then used to fix it to the plate.
Nevertheless, this sophisticated technique could be
impossible in patients with very thin bone. Another
concern of plate and screw technique is higher frequency of screw breakage and pullout caused by stress
transmitted to hardware interfaces.
To overcome the problem, modular systems were
introduced [1, 170, 178]. Most of them have isolated
(non dependent) occipital plate with a variety of available screw positions. This plate is connected with malleable rod to the screws (mostly, polyaxial ones)
introduced in C1 lateral masses, C2 anchors, and/or to
subaxial spine screws. Currently, the instrumentation is
made up from Titanium alloy and the rods usually fortified or thickened in the place of craniovertebral bending. Although the variability of modular systems is
providing much more flexibility in surgical decision
there are still advocates of the use of the plate and screw
systems [170]. Their main argument is higher resistance
in lateral bending confirmed by biomechanical works
[7] and the ability to correct deformity according the
pre-shaped contour of the plate during tightening of the
screws. Nevertheless, the potential to correct a deformity is probably higher using the modular systems [1].
6.5.1.1 Our Preference
According to Grob [84], the ideal CVJ fixating system
should: fix only the target segment, not encroach into
the spinal canal, provide immediate reduction and stability, and be effective if laminae are absent. We would
like to add that currently there is also a desire to have a
system strong enough to provide long-term stability,
made up from biocompatible and MRI-friendly materials and modular – means easy to use. The modular facility is very important not only because it makes the
surgical work more comfortable but also it allows correct placement of anchoring elements (screws) without
any stress created either to hardware or the underlying
References
117
bone. The other demand is its low profile especially in
occipital region and connectivity to eventual continuing
caudal fusion constructs (RA patients).
In summary, there is a very rare indication for semirigid fixation of adult CVJ nowadays. On the other
hand, there is still a place for autologous grafts and
wires in very small children with surgically corrected
instabilities and deformities in our opinion. Their
potential for bony healing is very high as well their
adaptability to external hard brace wearing. The correctly longitudinally placed autograft (often, the rib)
can grow without limitations given by fixed hardware.
In some cases, temporary metal fixation can be considered as well.
Nowadays, we are not using the plates and screws.
The restraints of screw positioning determined by fixed
position of holes do not allow introducing the screws
correctly and the mechanical stress created after tightening of screws is too large. The consequent potential
screw breakage and/or loosening usually require revision and prolong the bone fusion. Also, the required
contouring of the plates to reach the acceptable angle in
craniovertebral transition (up to 80°) can lead to material microfractures and weakness. The midline occipital
screw anchorage, which is in our opinion the strongest
and safest, can be hardly achieved even with pre-bend
and medially angulated plates. The biomechanical
argument supporting the use of plates because of greater
stiffness can be overcome with the new developments
where the connecting rods are reinforced and the use of
strut grafts is a regular part of the constructs.
Modern modular systems allow independent placement of screws in the most suitable positions without any
stress (Figs. 19.23 and 19.29, Chap. 19). They allow multidirectional manipulation (reduction, distraction, rotation, etc.) with the help of supplemented forceps adapted
to be able to connect different screws. The grafts can be
placed easily because the constructs are more subtle and
not covering the acceptor side. The fusion rates and stability achieved are similar or even superior to previously
described modalities. As in other long constructs, the
final goal – bony fusion has to be achieved. This is of
utmost importance, especially in the dangerous UCS
region. Correct decortication of acceptor area and preferably autologous bone should be used in our opinion.
Despite all the potential complications accompanying the
autologous bone harvesting, its osteogenic, osteoinductive, and osteoconductive potential cannot be substituted
by any other material. Although the allograft, bone
substitute, or BMP can be added, autologous bone should
always form the majority of the graft content.
6.5.2 Suboccipital Constructs
Whenever possible, we prefer to exclude the occiput
out of the fusion. Atlanto-occipital joint is responsible
for up to 40% of cervical flexion and extension and
therefore should be spared. The same can be said about
the atlantoaxial connection responsible for 60% of cervical spine rotations.
It is clear that if a solid anchorage can be used then
it is not necessary to prolong the fixation to a desirable
length. For example, a C2 pedicle screw, if acceptable
as cranial construct end, is one of the most firm
anchorages available in cervical spine. On the other
hand, if short isthmic screw is chosen, then one can
hesitate about its strength and extend the fixation to
C1. The majority of suboccipital multisegmental
fusions are performed for complex, combined surgeries treating multilevel stenosis, deformity, tumors, or
infection [201].
6.5.3 Anterior Multisegmental Constructs
Large decompressions in the deformity cases and
mainly in tumors can lead to important loss of structures supporting anterior CVJ and UCS. In such cases,
posterior occipitocervical fusion can be considered as
insufficient and the anterior column is reconstructed
with custom-made titanium mesh cages fixed with or
without plates to different anatomical structures, anteriorly [187, 217].
References
1. Abumi, K., Takada, T., Shono, Y., et al.: Posterior occipitocer-
vical reconstruction using cervical pedicle screws and platerod systems. Spine (Phila Pa 1976) 24, 1425–1434 (1999)
2. Aebi, M., Etter, C., Coscia, M.: Fractures of the odontoid
process. Treatment with anterior screw fixation. Spine (Phila
Pa 1976) 14, 1065–1070 (1989)
3. Ai, F., Yin, Q., Wang, Z., et al.: Applied anatomy of transoral
atlantoaxial reduction plate internal fixation. Spine (Phila Pa
1976) 31, 128–132 (2006)