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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_6013_Библиотеки_им_академика_М_И_Перельмана.pdf
Procedure 24 | Complete Vertebral Resection for Primary Spinal Tumors 237
FIGURE 24-9
Postoperative Care and Expected Outcomes
n
Insert deep drains and apply suction for 2 to 3 days.
n
Keep the patient in the intensive care unit (ICU) for 24 hours if there is significant
blood loss or hypotension.
n
The patient should be fitted for and wear a thoracolumbosacral orthosis for 2
to 3 months.
Evidence
Boriani S, Weinstein JN, Biagini R. Primary bone tumors of the spine: terminology
and surgical staging. Spine 1997;22:1036-44.
This review article describes the Weinstein-Boriani-Biagnini (WBB) Surgical
Staging System for primary spinal tumors. The WBB system provides a consistent
method for classifying and planning the resection of tumors involving the
unique three-dimensional anatomy of the vertebra.
Kawahara N, Tomita K, Baba H, et al. Cadaveric vascular anatomy for total en bloc
spondylectomy in malignant vertebral tumors. Spine 1996;21:1401-7.
This cadaveric study characterized the vascular anatomy around the spine.
The thoracic aorta is in direct contact with the anterior vertebral column.
Furthermore, variability in the segmental arteries has been reported. Therefore
familiarity with the vascular anatomy around the involved level as well as
careful dissection is critical when performing complete vertebral resection.
Nambu K, Kawahara N, Kobayashi T, et al. Interruption of the bilateral
segmental arteries at several levels: influence on vertebral blood flow. Spine
2004;29(14):1530-4.
This Level I study, using a dog model, demonstrated that embolization of
bilateral segmental arteries at the affected level, as well as the levels cephalad
and caudal, reduces blood flow to the involved vertebra by 75% without
influencing spinal cord evoked potentials. Therefore preoperative embolization
may be a safe and effective means of decreasing intraoperative hemorrhage.
Tomita K, Kawahara N, Baba H, et al. Total en bloc spondylectomy: a new surgical
technique for primary malignant vertebral tumors. Spine 1997;22(3):324-33.
This Level IV study describes the surgical technique of complete vertebral
resection used by Tomita and colleagues. The study reports the results of this
technique in seven patients. Primary spinal tumors are relatively rare; therefore
higher quality evidence is unavailable.
Van Dijk M, Cuesta MA, Wuisman PIJM. Thoracoscopically assisted total en bloc
spondylectomy: two case reports. Surgical Endosc 2000;14:849-52.
This Level IV study describes thoracoscopically assisted ventral release and
anterior column reconstruction as a safer alternative to traditional thoracotomy.
The small number of subjects limits the quality of this study.
P R O C ED U R E 2 5
Sacropelvic Fixation
Khaled Kebaish and Mostafa H. El Dafrawy
I N D I CAT I O NS P I T F A L L S
• Variable anatomy of the sacrum and
pelvis may add challenge to the
procedure.
• The sacrum has poor bone quality, mainly
cancellous and often osteoporotic.
• The sacropelvis functions as a unit; this
segment must transmit the full weight of
the body from the spine to one or both
femoral heads. It must do this in a static
environment, such as sitting or standing,
and in a dynamic environment, such as
walking and running.
• Large loads going through this
segment, creating cantilever pullout
forces, are the primary reasons for
construct failure.
I N D I CAT I O NS
C O N T RO V E R S IE S
• Long fusion has been described by
some authors as four levels extending
to L2, while others define a long fusion
as one that crosses the thoracolumbar
junction.
• The long lever arm generated by
incorporating more segments into the
fusion requires additional fixation points
to achieve a rigid construct at the
lumbosacral junction.
• High risk of pseudarthrosis (9% to
41%), instrumentation failure (3% to
44%), and loss of lumbar lordosis (20%
to 49%) are associated with fusion
down to the sacrum.
• Terminating a long fusion at L5 might
lead to subsequent degeneration of the
L5-S1 disk and might impact sagittal
balance.
• Degeneration of the sacroiliac (SI) joint,
although so far not clinically significant,
might be a concern in patients with
implants violating the sacroiliac
articulation (iliac and S2AI screws).
Indications
n
Long spinal fusion to the sacrum
• Rigid sacropelvic fixation serves as the foundation for thoracolumbar reconstructions that extend to the sacrum. It is often used in the treatment of
complex lumbosacral spinal conditions.
n
Neuromuscular (NM) scoliosis
• The orthopedic spine literature supports pelvic fixation as the current standard
of care of neuromuscular scoliosis correction. Conditions include Duchenne
muscular dystrophy, spinal muscle atrophy, limb-girdle muscular dystrophy,
myelomeningocele, and spinal cord injury. Indications for surgical treatment
include unstable sitting posture, caused by coronal and/or sagittal imbalances
and pelvic obliquity. Other indications for surgery
scoliosis and compromising respiratory function.
n
Degenerative spinal deformities
• Spinal deformities involving the lumbosacral junction requiring corrective
osteotomies are the most common indication for pelvic fixation. Oblique
takeoff of L5, adult degenerative scoliosis, revision decompression surgery,
and postlaminectomy flat back syndromes represent the majority of these
cases. Along with advanced degeneration of the L5-S1 motion segment,
these conditions cause lumbosacral instability, exerting huge biomechanical
stresses on the construct; thus extending the fusion to the pelvis is a prerequisite to achieve and maintain the correction.
n
Spondylolisthesis (high grade)
• During reduction of grade 3 and 4 isthmic spondylolisthesis of the lumbosacral junction, strong consideration should be given to protect the sacral S1
screws both with interbody cages and pelvic fixation screws.
n
Sacrectomy
• Partial or complete sacrectomy in treatment of secondary and primary sacral
tumors, including chordoma, chondrosarcoma, and some giant cell tumors,
causes severe destabilization of the lumbopelvic region. Reconstruction
requires restoring the continuity of the pelvic ring and spinal column integrity
with a mechanical construct that can transfer loads from the spine to the
pelvis.
n
Trauma
• Fractures of the lower lumbar vertebra and sacral fractures with spinopelvic
dissociation
include
progressive kypho-
Procedure 25 | Sacropelvic Fixation 241
Biochemical Considerations
n
The lumbosacral junction is a transition from a highly mobile segment to a stiff
segment, resulting in great stress concentrations when the biomechanics of this
segment are altered by instrumentation and fusion. Forces include axial loading
of up to 3 times body weight in activities of daily living; substantial shear,
especially with a more vertical S1 end-plate alignment; flexion/extension
moments; and torsion.
n
The following three concepts
of lumbosacral fixation and its relevance to the stiffness of the cephalad
construct.
n
Lumbosacral pivot point (McCord et al, 1992)
• Based on an ex vivo biomechanical model, McCord defined the pivot point
for the flexural lever arm near the middle osseoligamentous column at the
L5-S1 disk. Figure 25-1 shows the McCord pivot point in schematic sagittal
and transverse sections in relation to S1, S2, and iliac screws.
• Stiffness increases as the implant extends anterior to this point.
are crucial in understanding the biomechanics
FIGURE 25-1
Iliac
S1
Pivot point
S2
L2
L3
L4
L5
S1
Iliac
S2
242 Procedure 25 | Sacropelvic Fixation
Zone
3
Zone 1
Zone 2
A
Pivot point
Zone 1
S1
Alar
FIGURE 25-3
Iliac
S2
Zone 3
B
FIGURE 25-2, A-B
Zone 2
n
Zones of sacropelvic fixation
• O’Brien and colleagues (2004) identified three distinct zones of the sacropelvic region. Fixation strength improves progressively from zone 1 to 3.
Figure 25-2, A shows a schematic coronal section of the zones of sacropelvic
fixation as defined by O’Brien. Figure 25-2, B shows a schematic sagittal
section of different sacropelvic fixation techniques in relation to the three
zones of O’Brien and the McCord pivot point).
◆
Zone 1: S1 vertebral body and the cephalad margins of the sacral alae
◆
Zone 2: the inferior margins of the sacral alae, S2, and the area extending
to the tip of the coccyx
◆
Zone 3: both iliac bones
n
Triangulation of the screws
• Pedicular screws triangulation had been shown to significantly enhance load
pullout. Directing the pedicle screws medially ensures maximum amount of
triangulation, which increases stability at the bone–metal interface. With
triangulation of screws, the strength of fixation is determined by the amount
of bone within the area between the two screws (Figure 25-3).
FIGURE 25-4
Procedure 25 | Sacropelvic Fixation 243
FIGURE 25-5
T R E A T M E N T OP T I O N S
• S1 pedicular screws
• Sacral alar screws
• Iliosacral screws
• Galveston rods
• Iliac screws
• Transilial bar
• S2 alar iliac screws
Examination/Imaging
n
Pelvic obliquity and sacral inclination should be noted, especially in cerebral
palsy patients.
n
Obtain spot lateral and true anteroposterior films of sacrum.
n
It is useful to visualize the sacral promontory, superior articular process (SAP),
sacral foramina, and the first to third sacral segments.
n
For long spinal fusion to the pelvis, radiographic evaluation should include long-
cassette, erect posteroanterior and lateral views to determine balance.
n
In patients with dural ectasia, variable anatomy or revision cases, attention
should be paid to the proximity of the abnormality to the entry point of the
screws to avoid injury of the neural elements.
n
Obtain a dual emission x-ray absorptiometry (DEXA) scan, especially in females
greater than 50 years of age, because bone density correlates with screw pullout
forces.
n
Intraoperative teardrop view of the pelvis allows safe placement of iliac and
sacroiliac screws in the bony canal between the posterior superior iliac spine
(PSIS) and anterior inferior iliac spine (AIIS). Figure 25-4 shows an intraoperative
radiograph showing a teardrop view with the guidewire within an all-osseous
channel between the PSIS and AIIS.
n
An intraoperative teardrop view is obtained by a combined obturator oblique–
outlet view, with an approximately compound 45-degree anterior and 45-degree
cephalad angulation of the beam. Figure 25-5 is a schematic representation of
the position of the pelvis while obtaining a teardrop view with superimposed
shadows of the PSIS and AIIS and iliac rim above the sciatic notch.
244 Procedure 25 | Sacropelvic Fixation
Facet of
Lumbosacral
superior
articular
process
Articular
surface
Sacral
foramina
Sacral
cornu
FIGURE 25-6
Superior
articular
process
Sacral
promontory
Sacral canal
Sacral tuberosity
Spinous process
Lateral sacral
crest
Median sacral
crest
Intermediate
sacral crest
Coccygeal
cornu
articular surface
Sacral ala
Sacral
Transverse
ridges
Apex of
sacrum
Coccyx
foramina
FIGURE 25-7
Surgical Anatomy
n
Anatomy of posterior sacrum (Figure 25-6) and ventral sacrum (Figure 25-7).
n
Important anatomic features include the following:
• Medial border of sacral pedicle
• S1 nerve root
• Superior articular process (SAP)
• Median sacral crest
• Superior sacral notch
• S1 dorsal foramina
• S2 sacral foramina
• Lateral sacral crest
• Transverse sacral tubercles
X X
FIGURE 25-8
Procedure 25 | Sacropelvic Fixation 245
P O S I TI O N I N G PE A R L S
• Iliac crests should be symmetrically
positioned horizontal to the floor.
• Preparation and draping should be
lateral and distal enough to allow
access to the PSIS.
P O S I TI O N I N G PI T FA L L S
• Inappropriate positioning may change
pelvic obliquity and sacral tilt.
• Nothing should block the imaging of
the pelvic area.
Positioning
n
Positioning is according to the procedure being done; the vast majority of
patients are positioned prone. Lumbar lordosis is maintained by pads placed
to support the chest, iliac crests, and thighs. The abdomen is left hanging free,
decreasing intraabdominal pressure. This decreases epidural bleeding.
Portals/Exposures
n
The standard posterior midline approach is used as in fusion to the sacrum.
Depending on the adopted technique of sacropelvic fixation, additional exposure might be necessary.
n
With S2AI screws, expose the S2 foramen.
n
With iliac screws, a separate fascial incision might be used over the PSIS.
Procedure A: S1 Pedicle Screws
n
S1 pedicular screws can either be placed unicortical, bicortical, or tricortical. S1
screws should always be supplemented by distal fixation or an interbody fusion,
because they are rarely used alone for fusion to the pelvis.
n
Unicortical fixation is not recommended because of the cancellous nature of the
sacrum and a short capacious S1 pedicle. The screw can easily toggle, leading
to loss of fixation and pullout.
n
Bicortical fixation has been the standard for many years. The classic trajectory
has been parallel to the end plate of S1, with appropriate medial convergence
to avoid the common iliac vessels.
n
Tricortical fixation by directing the screw toward the medial sacral promontory
allows purchase of the dorsal cortex, the anterior cortex, and the superior endplate cortex. This trajectory doubles the insertional torque of the bicortical
screws inserted parallel to the S1 end plate.
n
Technique
• The starting point is just lateral to the base of the superior articular process.
The starting point can be made with an awl or burr (Figure 25-8).
246 Procedure 25 | Sacropelvic Fixation
FIGURE 25-9
FIGURE 25-10
P R O C ED U R E A P E AR L S
• The tricortical technique provides three
potential points of fixation.
• The technique allows the surgeon to
place longer screws into the sacrum
than either the unicortical or bicortical
technique.
• This technique permits the standard
medial angulation, thereby allowing
triangulation of the pedicle screws in
the coronal and sagittal plane,
increasing screw pullout strength.
• Using the large pedicle finder (Figure
25-9) is preferred over a small one
or a drill because it allows more
medialization of the S1 screw and,
therefore, better triangulation.
P R O C ED U R E A P I TF A L L S
• Forward trajectory will only allow a
shorter screw and may place the iliac
vessels and L5 nerve root at risk.
FIGURE 25-11
• To establish screw direction, a slightly curved large pedicle finder (gearshift–
type) is used to sound the cancellous bone (Figure 25-9). The path of the
screw should be directed anteromedially, approximately 30 to 40 degrees and
superiorly toward the anterior tip of the sacral promontory. This is usually 15
degrees cephalad in the frontal plane or 5 to 10 degrees superior in the
horizontal plane, depending on sacral inclination. The direction is toward the
anterior tip of the promontory (Figures 25-10 and 25-11).
• The range of screw length is approximately 40 to 50 mm.
X X
Procedure 25 | Sacropelvic Fixation 247
A
C
FIGURE 25-12, A-C
P R O C ED U R E B P E AR L S
• Biomechanical studies show improved
fixation of sacral ala screws in
conjunction with S1 pedicle screws as
compared with S1 screws alone.
• The screws are connected to the same
rod as the S1 screws.
P R O C ED U R E B P I TF A L L S
• Sacral ala fixation is directed into
low-density cancellous bone.
• Bicortical technique is not
recommended, because the L5 nerve
roots cross the sacral ala bilaterally, and
the common iliac vessels are located
directly on the anterior surface.
• Angulation of more than 20 degrees
laterally puts the L5 root at risk for
anterior cortex penetration.
• The L4 root is at risk as it crosses over
the lateral one third of the anterior ala,
with screw angulation more than 30
degrees laterally.
B
Procedure B: Sacral Alar Screws
n
This typically involves unicortical fixation into the cancellous bone of the ala.
The screws are directed laterally in the ala. The internal iliac vessels, lumbosacral
trunk, and sacroiliac joints can be injured if these screws penetrate the anterior
cortex. Alar screws are currently used by some as supplemental fixation.
n
Technique
• The starting point is 5 mm cephalad to the S1 foramen and halfway between
the distal aspect of the superior articular process and the S1 foramen (Figure
25-12, A).
• For the screw direction, the screw is angled laterally between 30 and 40
degrees and caudally 25 degrees (Figure 25-12, B). The more inferior the
screw starting point, the less caudal the screw angulation.
• The screw length averages 35 mm.
Procedure C: Iliosacral Screws
n
Iliosacral screws are placed through the outer table of the ilium, through the SI
joint, and into the lateral sacrum. This bone channel has been well described
and is regularly used in pelvic trauma. The cortical purchase at the inner and
outer tables of the ilium and the entrance point to the sacrum provides greater
stability to pullout. Iliosacral screws have biomechanical advantage over S1 fixation and alar screw fixation, but the development of easier and safer techniques
has made their use less common.
248 Procedure 25 | Sacropelvic Fixation
P R O C ED U R E D P E AR L S
• Most commonly used in NM scoliosis
• Implant is relatively inexpensive
P R O C ED U R E D P I TF A L L S
• Difficult contouring
• High incidence of loosening and painful
instrumentation requiring removal
P R O C ED U R E E P E AR L S
• The iliac screws should be long enough
to end anterior to the pivot point, thus
allowing the force acting on them to
change from inline pullout to cantilever
bending.
• Partial excision of the PSIS allows the
head of the screws to lie deeper within
the ilium, preventing prominence.
• Iliac screws are directed toward the
cortical bone of the sciatic notch, which
is the strongest in the ilium.
Procedure D: Galveston Rods
n
In the 1980s, Allen and Ferguson (1982) introduced the Galveston technique to
incorporate the ilium into the base of the fusion construct. Their instrumentation
consisted of contoured smooth rods that were inserted from the posterior
superior iliac spine, extending into each ilium between the inner and outer
tables. The rods can be attached to the proximal levels by sublaminar wires and,
more recently, by pedicle screws and hooks (Figure 25-13).
n
Technique
• The starting point is the posterior superior iliac spine.
• The rod orientation is approximately 30 to 35 degrees caudal and 20 to 25
degrees lateral, directed to the region above the sciatic notch.
Procedure E: Iliac Screws (Iliac Bolts)
n
Iliac screws were developed as an evolution of the Galveston technique. Iliac
screws offer greater resistance to pullout secondary to the cancellous threads.
Iliac screws may be partially or fully threaded and are connected to the longitudinal rods with special connectors. This is one of the most widely used techniques, when long fusions to the pelvis are performed. The modularity makes it
possible to put more than one screw into the ilium, and screws can also be
placed even in the face of a previous bone graft harvest. Figure 25-14 shows
a schematic representation of lumbosacral fixation with S1 pedicular screws and
two iliac screws.
FIGURE 25-13
FIGURE 25-14