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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_6019_Библиотеки_им_академика_М_И_Перельмана.pdf
Lumbosacral and Pelvic Fixation Techniques
Osama N. Kashlan, Kevin S. Chen,
and Frank La Marca
Introduction
The lumbosacral region is important for the
alignment and movement of the lumbar spine,
with the L5–S1 segment shown to provide the
greatest amount of flexion/extension in the lumbar spine [1–3]. Due to the considerable motion
at that segment, long-segment fusions to the
sacrum have high pseudarthrosis rates at L5–S1.
Also this may explain the difficulty in achieving
bony fusion at the lumbosacral segment. In addition, the high rate of instrumentation failure at
the lumbosacral junction is related to pseudoarthrosis, poor bone quality of the sacrum, the complex anatomy, and the substantial biomechanical
forces at the lumbosacral junction [
Pelvic fixation was developed and is used to
help solve this problem. The first use of pelvic
fixation was described in the 1980s with development of the Galveston technique [
technique, pelvic anchors were inserted at the
posterior superior iliac spine (PSIS) between the
O.N. Kashlan, MD • K.S. Chen, MD
F. La Marca, MD (*)
Department of Neurosurgery, University of Michigan,
1500 E. Medical Center Drive, Room 3552 TCx,
Ann Arbor, MI 48109-5338, USA
okashlan@med.umich.edu;
e-mail:
kechen@med.umich.edu
Frank.LaMarca@allegiancehealth.org
;
4].
5, 6]. In this
30
inner and outer tables of the pelvis (Fig. 30.1).
The Galveston technique was a major advancement in addressing the problem of lumbosacral
pseudarthrosis and set the stage for development
of the modern pelvic fixation techniques
described elsewhere in this chapter [4].
Anatomy
The sacrum and ilium constitute the posterior
aspect of the pelvic ring and articulate through
the sacroiliac joint (Fig. 30.2). Although not
fused, this joint is composed of an irregular yet
complementary bony cartilaginous surface that
interlocks the ilium to the sacrum. The sacroiliac
joint is stabilized by the anterior sacroiliac ligament and the posterior sacroiliac ligament
(Fig. 30.3). Other ligaments that serve as reinforcements include the iliolumbar ligament
which links the L4 and L5 transverse processes to
the iliac crest, the sacrospinous ligament which
connects the ischial spine to the lateral edge of
the sacrum, and the sacrotuberous ligament
which connects the whole lateral edge of the
sacrum and PSIS to the ischial tuberosity [7]. The
posterior sacroiliac ligament is commonly
encountered during surgical preparation of the
iliac crest for a bone harvest or iliac screw placement. Ligaments of the sacropelvis are also
important in transmission of axial loads through
© Springer International Publishing AG 2017
L.T. Holly, P.A. Anderson (eds.), Essentials of Spinal Stabilization,
DOI 10.1007/978-3-319-59713-3_30
401
402
O.N. Kashlan et al.
the first sacral segment and through the iliac
wings to the acetabulum bilaterally by permitting
a certain degree of shock force absorbance [
8, 9].
In addition to having knowledge of the anatomy, it is also important for a surgeon instrumenting the pelvis to be familiar with how to correlate
radiographs to anatomic landmarks. Lateral fluoroscopy is the most common view utilized in our
practice as shown in Fig.
Fig. 30.1 Galveston rods, one of the first successful techniques for pelvic fixation, visualized via posterior
approach
30.4A. The most impor-
tant landmarks to note in this view are the greater
sciatic notch, the femoral heads with the associated acetabulum, and the anterior inferior iliac
spine. The greater sciatic notch contains the sciatic nerve and superior gluteal artery. The pelvic
inlet view is a fluoroscopic trajectory parallel to
the sacrum and is important in visualizing the
main pelvic ring (Fig. 30.4B). The pelvic outlet
view is a fluoroscopic trajectory perpendicular to
the sacrum and can be used in visualizing the
sacral foramina (Fig. 30.4C). Obturator oblique
imaging of the pelvis, also named as obturator
outlet views, can be used to visualize the “teardrop” of the ilium. The teardrop signifies the safe
zone within the iliac bony cortices in which fixation can be placed (Fig. 30.5).
Indications and Patient Selection
There are no absolute indications for when to
instrument the pelvis or whether to stop at the
sacrum when performing a long-segment construct. Until there is more robust data in the literature, most of this decision-making is left to surgeon
preference and comfort level. The benefits of pelvic fixation include securing distal fixation, protecting sacral screws, adding pelvic derotation, and
protecting/overriding the sacroiliac joint.
Disadvantages include the extra surgical time it
Fig. 30.2 Illustration of
the articulation between
sacrum and ilium
30 Lumbosacral and Pelvic Fixation Techniques
403
takes to place the pelvic hardware, the technical
difficulty in placement via a minimally invasive
approach, the added risk of greater sciatic notch
violation of important neurovascular structures
within, and the possible high profile of the hardware causing pain and ultimately requiring
removal.
Even with the lack of absolute indications, the
relative indications for pelvic fixation [1, 4, 5,
10–13] include:
Fig. 30.3 Important ligaments of the sacrum including
the anterior sacroiliac ligament, posterior sacroiliac ligament (not shown), and iliolumbar ligament
• High-grade spondylolisthesis (Meyerding
Grade 3 or higher)
• Unstable sacral fractures
• Sacral tumors requiring sacrectomy
• Long construct with proximal end around or
past thoracolumbar junction
• Osteoporosis and/or poor sacral fixation
• Lumbar deformity and pelvic obliquity correction, especially in children with neuromuscular deformity
• Three-column osteotomy at the lumbosacral
junction
• Sacral insufficiency fractures
Sacral insufficiency fractures can also be an
indication for lumbopelvic fixation [1, 14, 15].
These fractures occur in osteoporotic patients, in
patients with metabolic derangements, and in
patients with a history of lumbosacral fixation.
From all the etiologies listed, the most common
indication is management of long constructs in
adult deformity patients [1].
There is controversy over what constitutes a
long construct. A recent review article defines a
long arthrodesis requiring pelvic fixation as one
involving five or more levels [5, 16]. Another
biomechanical study showed that constructs
extending above L3 should have the sacral screws
protected by pelvic instrumentation [5, 17]. With
the lack of guidelines, the final decision rests
with the surgeon and should depend on specific
patient characteristics, including patient body
Fig. 30.4 Important pelvic landmarks on lateral fluoroscopy (A), pelvic inlet view (B), and pelvic outlet view (C)
on a patient undergoing a minimally invasive sacroiliac
fusion (technique not discussed in this chapter). Structures
labeled are femoral heads (a), greater sciatic notch (b),
sacrum (c), L5 (d), anterior inferior iliac spine (e), sacroiliac join (f), main pelvic ring (g), obturator foramen (h),
and sacral foramen (i)
404
Fig. 30.5 Obturator outlet view of a salvage procedure to
replace a misplaced iliac bolt. The misplaced iliac bolt laterally breaches the “teardrop.” The Lenke probe visualized demonstrates adequate trajectory within confines of
“teardrop” for placement of a new iliac screw
mass index (BMI), nutritional status, bone mineral density, and medical comorbidities.
Relative contraindications to placement of
pelvic instrumentation include patients with poor
anatomy or previous surgery precluding safe
placement of hardware [1]. A history of an iliac
bone harvest does not inhibit the ability to place
pelvic fixation; however, it is important to determine if an iliac crest bone harvest was performed,
as this will affect tactile feedback during placement of hardware as discussed later in this
chapter.
Preoperative Considerations
As described above, an important preoperative
decision is whether pelvic fixation is definitely
needed at the end of a construct or not. This decision should be based on multiple factors including patient bone quality, BMI, medical
comorbidities, and goals of surgery. In our practice, we are more likely to plan placement of pelvic instrumentation in patients requiring a long
construct that also have a history of osteoporosis,
smoking, high BMI, and diabetes, or in patients
with sacral tumors requiring a sacrectomy. In
O.N. Kashlan et al.
contrast, in patients with terminal cancer with
involvement of the lower lumbar spine requiring
a corpectomy, we are more likely to limit instrumentation to the sacrum, as the patient’s lifespan
likely is shorter than the time it would take for
pseudarthrosis at the lumbosacral segment to
occur. In this situation, placement of pelvic fixation can have risks that outweigh any potential
benefits. In reality, the decision to place pelvic
instrumentation is made intraoperatively after
evaluating the quality of sacral fixation. Specific
preoperative considerations for each type of
instrumentation that can be used are discussed
below. In some cases, such as after iliac crest
bone grafting, pelvis CT is useful to plan surgical
technique and to assess adequacy of bone stock.
Sacral Instrumentation
S1 Pedicle Screw The S1 pedicles are wide with
less cortical bone to allow for screw purchase.
Therefore, S1 screws at the end of long constructs
can be prone to failure [1]. In terms of pedicle
screw length, the average length of an S1 pedicle
is 46.9 mm in women and 49.7 mm in men [4,
18]. Tricortical fixation with S1 screws breaching
anteriorly through the promontory improves biomechanical stability and should be the goal [1,
19]. However, even with that improved strength,
long fusions ending at the sacrum can have failure rates as high as 44% [
S2 Pedicle Screw
used in our practice. They are technically
demanding due to a narrow safe zone and have
not been shown to increase construct stiffness [1,
22, 23]. Because the S2 pedicles are dorsal to the
biomechanical pivot point, they offer very little
additional strength for resisting pullout and flexion forces [
4, 23, 24].
S1 Alar Screw Alar screws, which are screws
that start at S1 and are aimed laterally into the
ala, also have a narrow safe zone and have not
been shown to significantly reduce pseudarthrosis rates clinically [1, 23]. In fact, despite being
resistant to higher pullout forces, long fusion to
4, 20, 21].
S2 pedicle screws are not
30 Lumbosacral and Pelvic Fixation Techniques
405
the sacrum using these techniques has been associated with poor clinical results in addition to
high pseudarthrosis rates [4, 20, 23].
Dual S1 Pedicle/S1 Alar Screws There are
devices available that allow for insertion of both
an S1 pedicle screw and an S1 alar screw, which
allows for triangulation of these two screws.
These devices allow for greater construct stability when compared to an S1 pedicle screw in isolation [25]. However, these devices also have
disadvantages, including increased muscle dissection, decreased bone surface available for
fusion, and mechanical inferiority to iliac screws
[4, 26].
Pelvic Instrumentation
Iliac Screw (Iliac Bolt) Iliac screws (also called
iliac bolts) have an attractive biomechanical profile when compared to sacral screws for two reasons: they are divergent from the proximal
fixation points in the coronal plane, and they are
longer screws enabling placement anterior to the
axis of pelvic rotation [1]. Both attributes make
them better able to prevent pseudarthrosis and
hardware failure at the distal end of the construct.
In our practice, bilateral screws are placed whenever feasible. Unilateral iliac screw fixation has
the potential to improve clinical outcomes without compromising biomechanical stability, but
long-term studies are needed to determine equivalence between unilateral and bilateral iliac screw
pseudarthrosis rates [
S2 Alar-Iliac (S2AI) Screw
has the benefit over traditional iliac screws in that
it minimizes the prominent screws present when
the PSIS is used as a starting point and also makes
it easier to attach these screws to the rest of the
construct (Fig.
point being more in line with the pedicle screws
used in the rest of the construct. Not having to
use an offset connector theoretically takes away
the additional point where loosening of the construct may occur. The S2AI screw is also noted to
have greater cortical purchase than the traditional
1, 27].
The S2AI screw
30.6). This is due to their starting
iliac screw as it crosses over the cortical bone at
the sacroiliac joint [
28]. The drawback of this
technique is that this screw traverses the sacroiliac joint. In a study of 51 adult patients with S2AI
screws, there was no evidence of sacroiliac joint
arthritis or fusion at 2 years or 5 years radiographically [5]. However, the effect of this trajectory on sacroiliac joint arthritis and sacroiliac
pain continues to be debated.
Galveston Technique
The Galveston technique
has a low pseudarthrosis rate but is associated
with a high incidence of loosening secondary to
micromotion at the rod tips within the ilium,
despite achieving a fusion at the lumbosacral
junction [4]. When loosening occurs, there is the
potential for pain and the need for implant
removal [4]. This technique has been replaced by
the use of iliac screws (whose pullout strength
has been shown to be three times greater) and
S2AI screws [4, 29].
Other fixation techniques that are used rarely
or mostly have historic significance include the
sacral sublaminar wires and hooks, the iliosacral
screws, the Jackson intrasacral rods, and the
Kostuik transiliac bar [4, 5]. These techniques
will not be discussed in this chapter.
Comparison of Iliac Screws to S2AI
Screws
There are mixed results regarding which
method (sacral screws vs. S2AI screws) has a
lower complication rate. Sponseller et al. found a
statistically significant improvement in pelvic
obliquity but no difference in postoperative complications, including infection, dehiscence, and
hardware loosening, in pediatric patients [30].
However, a more recent study retrospectively
reviewed the pelvic fixation techniques used in
120 consecutive cases of adult and pediatric
deformity and showed that there is a clear difference between the two techniques [31]. The S2AI
pelvic fixation technique was associated with a
statistically significant decrease in implant loosening, acute wound infections, delayed wound
problems, need for revision surgery, and the incidence of persistent posterior pelvic pain
>3 months after surgery [31]. The reason for the
decrease in infections was theorized to be lack of
406
Fig. 30.6 Anteroposterior views of S2AI screws (left) versus iliac screws (right)
O.N. Kashlan et al.
the need for tissue dissection over the PSIS, as is
required during an iliac screw placement.
However, more prospective studies are needed
before determining if there is a difference in
complication rate of either method.
Surgical Technique
Sacral Instrumentation
The S1 screw starting point is inferior and slightly
lateral to the midpoint of the L5–S1 facet joint. A
pilot hole is drilled at that position. Utilizing fluoroscopy or CT image guidance, a trajectory
pointing toward the sacral promontory is undertaken. A Lenke probe is advanced by hand until
the promontory point of the anterior sacral cortical bone is reached. At that point, a mallet is used
to break through the cortical bone. A pedicle
screw sized to reach slightly anterior to this point
is placed. Tapping of the far cortex is useful to
prevent screw stripping during insertion if it does
not penetrate the pilot hole. S1 screws can be
placed via a minimally invasive approach. A
novel proposed method to place lumbosacral
screws in a medial-to-lateral trajectory has been
shown to be a safe alternative to the usual lateral-
to- medial trajectory described above [
32]. The
potential benefits of these cortical bone trajectory
pedicle screws include less lateral muscle dissection, decreased potential for pain, and reduced
chance of a medial breach resulting in nerve root
injury.
Pelvic Instrumentation
Iliac Screw In our practice, a separate fascial
opening is utilized which is more lateral to the
midline fascial opening used in the placement of
lumbosacral pedicle screws. The starting point for
an iliac screw is found by exposing the PSIS. In an
attempt to deeply insert the screw head to decrease
the chance of prominent hardware causing discomfort to the patient, the entry point is below
(ventral to) the PSIS along the medial aspect of the
ilium just above the sacrum. After the muscle/ligamentous attachments are cleared, the starting point
is marked with a burr or rongeur. The trajectory is
from the PSIS to the anterior inferior iliac spine
and is highly variable, but typically angled 20–45
degrees caudal and 30–45 degrees lateral [
Utilizing an iliac probe and gently advancing by
hand allow for the trajectory to stay between the
inner and outer tables of the ilium. The screw
1, 5].
30 Lumbosacral and Pelvic Fixation Techniques
407
should be positioned just above the sciatic notch.
Obturator outlet views that show the “teardrop” of
the ilium and position of the probe or screw within
the teardrop can be helpful.
In cases where two ipsilateral iliac screws are
necessary, care must be taken when passing the
first screw so as to leave enough room for the second screw. Either fluoroscopy or CT guidance
can be used to place these screws. A lateral radiographic view can be utilized to guide the screw
approximately 1 cm above the greater sciatic
notch in the supra-acetabular region where the
thickest part of the ilium allows for optimum
screw purchase [1]. Screws of up to 100 mm in
length can be used with this technique. Obturator
oblique views and iliac oblique views can also be
utilized to better visualize the thick column of the
bone just above the greater sciatic notch, also
known as the “teardrop” and the greater sciatic
notch, respectively [1]. Iliac screws can also be
placed in a minimally invasive manner [33, 34].
S2AI Screw
The S2AI screw technique involves
fixation along a pathway between the second
sacral segment and the anterior inferior iliac
spine [5]. The starting point for S2AI screws is
2–4 mm lateral and 2–8 mm inferior to the S1
foramen. This point aligns on the dorsal aspect of
the sacral ala, at the midpoint of a line that connects the lateral aspect of the S1 and S2 dorsal
foramina. The screw trajectory is directed toward
the anterior inferior iliac spine [
1, 4, 5]. Feeling
the greater trochanter is a palpable landmark for
this trajectory [
5]. After a starting point is found
and a pilot hole formed using a drill or awl, a 2.5mm drill is pointed 40 degrees lateral and 20–30
degrees caudal [4]. Using anteroposterior fluoroscopy to visualize the pelvis and sciatic notch,
the drill is advanced slightly past the sacroiliac
joint. The path of the drill should be within
20 mm proximal to the greater sciatic notch and
aimed toward the anteroinferior iliac spine [
4].
Past the sacroiliac joint, a 3.2-mm drill is used to
protect against breaking the smaller drill bit in
the ilium [4]. At this point, obtaining an obturator
oblique fluoroscopy view with a 30-degree caudal and 30-degree lateral beam visualizing the
“teardrop” can help avoid a cortical breach [4, 5].
The most common screw size is 9 × 90 mm [5].
S2AI screw insertion can be also performed via a
minimally invasive approach, or utilizing image
guidance [35].
Galveston Technique The Galveston technique
allows for incorporation of the ilium via insertion
of rods between the inner and outer tables of cortical bone. The transverse portions of the rods are
inserted submuscularly and enter the ilium at the
PSIS [4]. The rods are oriented 30–35 degrees
caudally and 20–25 degrees laterally [4]. The rods
cross the sacroiliac joint and contouring can be
difficult [4, 36]. This technique is used much less
frequently than the iliac screw or the S2AI screw.
Illustrative Case
History
A 62-year-old male with no significant history
presented with progressive difficulty with balance, sexual dysfunction, and bladder dysfunction over the course of a year. He also had pain
involving his left buttock and hip radiating down
the posterior aspect of his thigh and calf and stopping at his ankle. The patient noted difficulty
with ankle plantar flexion over the past 2 years.
Physical Exam
On physical examination, the patient had full
strength throughout. His reflexes were normal
and symmetric. His sensory examination was
normal.
Radiographical Imaging
CT scan demonstrated a large destructive lesion
involving the lower lumbar and upper sacral
spine on the left (Fig.
MRI shows the amount of involvement of the
sacrum and spinal canal (Fig. 30.8); the significant
extension of this mass into the pelvis is not
shown.
30.7). Sagittal T2-weighted
408
Fig. 30.7 Coronal CT of lumbosacral spine demonstrating a destructive bony lesion at the lower lumbar and
upper sacral spine. Pathology was consistent with
neurofibroma
Treatment
CT-guided biopsy of the mass was consistent with
neurofibroma. The patient was then offered surgical debulking of the mass for symptom control.
Because of the bony destruction seen at L5 and the
sacrum, the decision was made preoperatively to
place iliac screws to achieve fusion across the lumbosacral junction. In the operating room, the patient
was positioned prone and a midline incision utilized. Subperiosteal dissection was carried out with
exposure of the posterior elements from L3 to the
midsacrum. After bilateral L4 pedicle screws were
inserted, attention was then directed to placement
of iliac screws. Using suprafascial dissection, the
PSIS was digitally palpated. The fascia was opened
and the PSIS exposed. Using an osteotome, a bony
O.N. Kashlan et al.
Fig. 30.8 Sagittal T2-weighted MRI demonstrating
extension of the destructive mass into spinal canal. Not
shown is extension into left hemipelvis
defect was created. Under direct and fluoroscopic
visualization, the Lenke probe was passed along
the trajectory to cannulate the iliac wing. The trajectory was probed and found to be without bony
breach. Iliac bolts of the appropriate length and
diameter were placed. Dissecting superiorly from
the primary iliac bolt, entry points were selected.
Under direct and fluoroscopic visualization, a drill
was used to create pilot holes. The Lenke probe
was then passed in an appropriate trajectory to create solid bone on palpation. Double iliac bolts of
the appropriate length and diameter were inserted.
L4 through S1 laminectomies were performed, and
the lesion, which was partially extradural and partially intradural, was debulked. Adequate arthrodesis was performed. Autograft and allograft
materials were used to spur bony fusion.
Outcome
The patient did well postoperatively with
improvement in his left-sided radicular symptoms. His postoperative radiographs demonstrated normal sagittal balance, restoration of
lumbar lordosis, and adequate hardware placement (Fig.
30.9).
30 Lumbosacral and Pelvic Fixation Techniques
Fig. 30.9 Sagittal standing postoperative radiograph
demonstrating L4-ilium fusion with no sign of hardware
malposition or failure
409
requiring contouring in two planes to link the
iliac screw and the S1 screw [33]. As such, an
option for consideration would be to not place
an S1 screw when pelvic fixation is enough to
sustain functional demand and maintain hardware integrity until bone fusion occurs [33].
• During placement of S2AI screws, difficulty
advancing through the cancellous bone of the
ilium is commonly caused by abutting the lateral cortex of the ilium [5]. To overcome this
issue, start more lateral with a more vertical
trajectory, closely abutting the notch [5].
• Loosening of iliac screws and S2AI screws is
not an uncommon phenomenon. As long as a
patient is not having pain due to prominent
hardware and there is no evidence of pseudarthrosis across the lumbosacral junction, these
patients should be followed with serial imaging rather than taken for reoperation.
Complications and Strategies for Avoidance
Technical Pearls
• In cases where both an S1 pedicle screw and
an iliac bolt are to be used, having the starting point of the iliac screw more inferior
than the sacral screw is crucial in order to
make connection to the rod easier. In our
practice, a medial-lateral connector is used.
However, if this is not desired, then a more
dramatic lordotic bend in the rod combined
with leaving the S1 screw head slightly
more lateral and prominent can help with
this connection [1].
• When a minimally invasive approach is undertaken to place an iliac screw, contouring the
rod and connecting the iliac screw to the proximal hardware present a challenge. To solve
this problem, a hyperacute lordotic bend of
30–40 degrees at the distal 2–3 cm of the rod
enables easier connection [33]. This connection is even more difficult in the presence of
an S1 screw due to the shorter rod segment
Prominent Implants
A common complication associated with iliac
screws is prominent, painful implants, with a
prevalence of up to 20% postoperatively [1, 26,
35]. Another study showed that 22% of patients
needed to have the screws removed at 2 years [4,
37]. The strategy to avoid this complication
includes starting the iliac screw deep to the PSIS
and removing enough bone at the entry site for
the screw head to sit comfortably without protruding above the outer margin of the iliac crest.
Alternatively, if patient anatomy does not allow
for placement of a non-prominent iliac screw, an
S2AI screw can be utilized instead. Having nonprominent implants can also theoretically help
with wound healing as it takes pressure off the
incision. This fact is especially important in
trauma cases where wound healing can be an
issue. Options to utilize in high-risk wounds
include negative-pressure wound therapy and
vancomycin powder.
410
O.N. Kashlan et al.
Potential Need for Interbody Fusion
In adult deformity patients, there is an 11% major
failure rate when pelvic fixation is used, including rod breakage between L4 and S1, failure of
S1 screws, and prominent iliac screws requiring
removal [
fixation is achieving a fusion at the lumbosacral
junction. However, if a bony fusion does not
occur in a timely manner, fixation failure is bound
to happen, either from implant breakage or loosening [4]. As such, many authors advocate anterior column support through interbody cage
placement at L4–L5 and/or L5–S1, as this greatly
improves solid fusion [4, 38–40]. However, this
point is controversial, as some studies did not
demonstrate any change in pseudarthrosis rates
with interbody cage placement when pelvic fixation and/or recombinant human bone morphogenetic protein is used [28, 41]. Even though not
proven to be of benefit, this should be considered
in long fusion constructs that extend to the upper
thoracic spine to remove some of the stresses
from posterior implants and allow for early bony
fusion [4].
1]. The most important goal in pelvic
cancellous bone in the ilium will be altered drastically. In these instances, both cancellous and
cortical bones are hard, and a breach into the
greater sciatic notch is more likely.
Problems with Rod Fracture
Even though newer titanium alloy metals along
with the use of cobalt chrome or stainless steel
have reduced the chance of rod fracture, it has not
been eliminated entirely. In cases of rod failure, a
4-rod technique can be used where differing
insertion angles of pedicle screws allow for
placement of two rods on each side of the construct [42]. In this method, only a subset of pedicle screws on each side are joined by one rod,
while another joins the rest. This is repeated on
the other side. Another alternate method of placing four rods is by utilizing a side-to-side connector with all pedicle screws being joined by one of
the rods on each side.
Pelvic Screw Fracture
Greater Sciatic Notch Breach
During placement of pelvic instrumentation,
there is potential for injury to the sciatic nerve or
superior gluteal artery if the sciatic notch is
breached. To protect against this complication, it
is of utmost importance to follow the cancellous
bone as the iliac probe is advanced by hand. If a
cortical rim is felt, redirection of the probe should
be entertained. Fluoroscopy or image guidance
can be used to decrease the risk of breaching the
greater sciatic notch. More importantly, this complication can be avoided by familiarization with
sacropelvic anatomy, which can be accomplished
with the use of cadavers [
where a patient has a history of an iliac bone graft
harvest, it is important to utilize the different fluoroscopic views or place the screw with CT guidance as the tactile feedback from feeling for the
4]. Moreover, in cases
In a review of 51 adults treated for spinal deformity with S2AI screws and a minimum 5-year
follow-up, there were 6 broken screws in 4
patients [5]. In a similar study of 80 children with
a minimum follow-up of 2 years, 9 patients had
fractured S2AI screws, and 3 had pseudarthrosis
at L5–S1 requiring revision surgery [5]. None of
the adult patients were symptomatic and therefore required no revision [
groups that fractured were 7 mm or less in diameter with the exception of 38-mm screws that
broke in the pediatric population [5]. Therefore,
it is advised to use at least 8-mm screws when
utilizing this technique [
onstrated that adult patients with S2AI screws
underwent fewer unplanned reoperations for
symptomatic instrumentation failure, wound
breakdown, or removal of pelvic fixation because
of painful prominence than those who received
iliac screws [28].
5]. All screws in both
5]. Another group dem-