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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5259_Библиотеки_им_академика_М_И_Перельмана.pdf
distal tip was placed too anteriorly, which vessel would be at
the greatest risk of injury or rupture?
A. Inferior vena cava.
B. Segmental artery.
C. Abdominal aorta.
D. Iliolumbar vein.
Response (A) The patient would be placed with the right
side of their body down, with the surgical ap proach occur-
ring from the left. An anterior cage placement would have
the greatest probability of injuring the vessel on the con-
tralateral side, which would be the inferior vena cava. The
iliolumbar vein and segmental arteries are more lateral and
would not have a risk of damage from the distal tip of the
interbody.
Question 10
When doing a posterior lumbar interbody fusion (PLIF) for
treating disc pathology, which of the following parts of the
vertebral bone must be removed to place the interbody cage
safely?
A. Lamina.
B. Facet joint.
C. Both A and B.
D. Neither A nor B.
Response (A) At least a part of the lamina MUST be
removed to place an interbody through the PLIF approach.
The interbody cage can safely be placed while keeping the
facet joint intact [8].
Question 11
Regarding dynamic stabilization of the spine, all of the
following are true,
EXCEPT:
A. It is a concept of placing anchors into the spine con-
nected with a flexible longitudinal member (e.g. rod).
B. The goal of this type of implant is to eliminate the
motion.
C. This type of implant will produce less stress on the
adjacent spinal segments and may prevent
adjacent-level degenerative changes.
D. Without concurrent spinal arthrodesis, these implants
may loosen or fail prematurely and require revision
surgery.
Response (B) The goal of this type of implant is to con-
strain but not eliminate motion. The other answers are cor-
rect [9].
Question 12
Regarding anterior spinal instrumentation, which one of the
following is true?
A. Restoration of spinal alignment is not required before
plate application.
B. Even with significant coronal or sagittal plane defor-
mity, the plating system can be placed.
C. In short-segment spinal problems, anterior plating sys-
tems permit corrective forces to be applied directly to
spinal segments, thereby restoring spinal alignment.
D. The anterior plating system can be used alone for
tumors, burst fractures, and degenerative spinal disor-
ders requi ring anterior fusion over one or two levels.
Response (C) Restoration of spinal alignment is mandatory
before plate application. Technical difficulties for the ante-
rior plating system arise because restoration of spinal
alignment is required before plate application, especially in
the presence of significant spinal deformity. Tumors, burst
fractures, and degenerative spinal disorders requiring ante-
rior fusion over one or two levels are indications for using an
anterior plating system however this is in conjunction with
decompression of cord or nerves as well as it is recom-
mended to posteriorly supplement it [10].
Question 13
Regarding spinal implants, all of the following are true,
EXCEPT:
A. Short-term stabilization of the spine is provided by
spinal implants, while long-term stabilization of the
spine is traditionally provided by fusion.
B. Autograft bone (e.g. fibula) can be used as an inter-
column implant to promote fusion.
C. Polymethylmethacrylate [PMMA] cannot be used as a
spacer to reconstruct an anterior spinal column defect.
D. Disc spacer can be used to maintain segmental mobility,
stability, and disc space height without fusion.
Response (C) Certain intracolumn implants (e.g. poly-
methylmethacrylate [PMMA]) are intended to function as
an anterior column spacer despite lack of potential for
3 Instrumentation 57
biologic incorporation; PMMA is used as a spacer to
reconstruct an anterior spinal column defect; anterior spinal
reconstruction of metastatic vertebral body lesions in
patients with a finite lifespan; or reconstruction of osteo-
porotic c ompression fractures. Vertebroplasty and kypho-
plasty procedures involve the injection of PMMA into the
vertebral bodies to alleviate pain secondary to acute and
subacute fractures.
Question 14
Regarding C2 screws, which one of the following is false?
A. C2 pedicle screw trajectory is more medial and superior
than the pars screw.
B. C2 pedicle screw has greater risk of injury to a high
riding vertebral artery.
C. A longer screw may be achieved using a C2 pedicle
screw than C2 pars screw.
D. C2 pars screw can be safely placed with bi-cortical
screw purchase.
Response (D) A C2 pars screw is typically a unicortical
screw that stops short of the transverse foramen to prevent
potential injury to the vertebral artery. The C2 pedicle is
located medial to the pars and is more superiorly oriented.
High riding vertebral artery and narrow C2 pedicle are two
anatomical variations that increase risk of vertebral artery
injury in placement of cervical pedicle screws [11, 12].
Question 15
Regarding C1–C2 screws, which one of the following is
true?
A. In case of vertebral artery anoma lies, transarticular
screw is less preferred.
B. Transarticular screws are more versatile than C1–C2
screw-rod systems.
C. Preoperative reduction of the C1–C2 joints is manda-
tory before the placement of the C1–C2 screw-rod
system.
D. Posterior wire/cable techniques or rod-clamps should be
complementary in every case.
Response (A)C1–C2 screw rod systems can be used in
cases where transarticular screws are contraindicated (e.g.,
vertebral artery anomalies, severe kyphosis). Screw rod
systems are more versatile and allowing for different screw
placement (laminar, pars, pedicle etc.) when compared to
transarticular screws. C1–C2 joints can be reduced
intraoperatively. Preoperative reduction is not a prerequisite
nor is it always possible. Posterior wire/cable techniques or
rod-clamps are not complementary in every case and can be
used alone when other techniques are not feasible [13].
Question 16
Regarding subaxial cervical spine instrumentation, all of the
followings are true,
EXCEPT:
A. C3–6 pedicle screw placement is not widely practiced
owing to the relatively high risk of vertebral artery
injury.
B. Compared to posterior wiring or cable fixation, cervical
lateral mass fixation significantly increases rotation and
extension stability.
C. Loss of wire fixation due to bony pullout or wire failure
is the most common complication associated with
wire/cable techniques.
D. Rigid external postoperative cervical immobilization
should be done with screw fixation techniques.
Response (D) Rigid postoperative external cervical immo-
bilization is not mandatory with screw fixation techniques.
Screw fixation techniques are an internal brace making addi-
tional rigid external cervical immobilization unnecessary [14].
Question 17
Which one of the following regarding L5–S1 fixation is
true?
A. 60% of axial load is transmitted through the anterior
spinal column, and the remaining 40% is transmitted
through the posterior column.
B. The oblique orientation of the L5–S1 disc results in
decreased shear forces across this level.
C. The sacrum is composed of cancellous bone and pos-
sesses multiple sites for screw fixation.
D. Long-segment fusion constructs (e.g. T10–S1) have a
higher failure rate than short-segment constructs (e.g.
L4–S1).
Response (D) Pseudarthrosis rate increases as the number
of levels undergoing fusion increases. Increasing the number
of instrumented levels proximal to the sacrum increases the
lever arm exerted by the proximal spine on the distal sacral
implants. The other options are incorrect because 80% of
axial load is transmitted through the anterior spinal column,
and the remaining 20% is trans mitted through the posterior
column. The oblique orientation of the L5–S1 disc results in
58 A. Khan et al.
increased shear forces across this level. The sacrum is
composed of cancellous bone and possesses limited sites for
screw fixation [15].
Question 18
All of the following structures are at risk when a screw is
placed through the anterior cortex of the sacrum,
EXCEPT:
A. Straight Ventral S1 screw placed without medial
angulation, the S1 nerve root is at risk of injury as it
crosses the anterior sacrum.
B. Screws placed laterally at the S1 level have greater
potential of injuring the lumbosacral trunk or the
internal iliac vein.
C. Laterally directed screws at the S2 level can injure the
colon.
D. Medially directed S1 screws directed parallel to the
upper S1 endplate or toward the sacralpromontory may
cause injury to the middle sacral artery and vein.
Response (A) Straight Ventral S1 screw placed without
medial angulation, the L5 nerve root is at risk of injury
where it crosses the anterior sacrum, not the S1 nerve root.
All other answers are correct [16].
Question 19
Which of the following is not a contraindication for anterior
odontoid screw fixation?
A. Type 3 odontoid fracture.
B. Barrel-shaped chest.
C. Long oblique fracture line that positioned from
anterior-caudal to posterior-cranial.
D. Combined 5-mm overhang of the lateral masses of C1
on C2.
E. Disruption of the transverse atlantal ligament.
Response (D) Odontoid screw fixation is useful for patients
with widely displaced type II odontoid fracture nonunions,
fractures (6 mm or more), or patients who are unable to wear
a halo brace. There are a variety of contraindications to
odontoid screw fixation, including fractures that extend
deeply into the body of the dens (type III), severe osteo-
porosis, irreducible fractures, large chest, short neck, oblique
fracture line that positioned from anterior-caudal to
posterior-cranial, and fixed cervical flexion deformities. The
most significant absolute contraindication is disruption of
traverse ligament (defined by the sum of the overhang of C1
lateral mass on C2 exceeds 7 mm) because C1-2 stability
cannot be restored by odontoid screw, even if the dens is
fixated solidly [17].
Question 20
The following necessitates an occipitocervical fusion
EXCEPT:
A. Congenital absence of complete Cl arch.
B. Basilar invagination.
C. Congenital anomalies of occipitocervical joints.
D. Type II odontoid fracture.
Response (D) Type II odontoid fractures can be treated by
an odontoid screw if the TAL is still intact. It is a problem of
the atlantoaxial joint and does not necessitate fusion to the
occiput. All other answers are indications for occipital cer-
vical fusion [18].
Question 21
In the transoral approach, the patient must be able to open
the mouth at least
A. 25 mm.
B. 35 mm.
C. 45 mm.
D. 20 mm.
Response (A) The patient needs to be able to open his
mouth at least 25 mm; if not, then other approaches such as
trans-nasal or trans-labio-mandibular should be considered.
Question 22
In the transoral approach, which anatomical structure can the
surgeon palpate to identify the midline?
A. The odontoid process.
B. The arch of C1.
C. The C1 tubercle.
D. None of the above.
Response (C) The C1 tubercle can be palpated throu gh the
posterior pharynx to locate the midline and for craniocaudal
orientations (see Fig. 3.1)[19].
3 Instrumentation 59
Question 23
Absolute contraindication of odontoid screw include all of
the foll owing
EXCEPT:
A. Rule of Spence > 7 mm.
B. Type 3 fracture when the fracture line is through the
body portion of the body of C2.
C. Fracture line in oblique orientation to frontal plane.
D. If the fracture is greater than six months old.
Response (D) The age o f fracture is controversial; fusion
rates in fractures more than 18 months old were 25%
fractures, while fractures less than six months old have
90% fusion rates. The Rule of Spence > 7 mm suggests an
TAL disruption which is unstable. This would not be
appropriately treated and stabilized with an odontoid screw
because of the instability at the C1–C2 joint. An oblique
fracture line from posterosuperior to anteroinferior that
would parallel screw trajectory is another contr aindication
to anterior fixation. A shallow Type 3 fracture is unstable,
Type II like fracture, and may be treated with an odontoid
screw, unlike one with a fracture deeper through the C2
vertebral body.
Question 24
When considering entry point for C3–6 lateral mass screws,
which one is correct?
A. In the An method, the screw is placed 1 mm medial to
the midpoint and a trajectory of 15° in the cephalad
direction and 30° in the lateral direction.
Fig. 3.1 Artist’s rendering of
transoral approach. The C1
tubercule can be palpated along
the posterior pharynx and used to
locate midline (Jeszenszky et al.
[19])
60 A. Khan et al.
B. In the Magerl method, the screw is placed 2 mm medial
to the midpoint and 2 mm cranial to the midpoint in the
crania-caudal direction with a trajectory of 20–25° lat-
eral and parallel to the facet joint.
C. In the Roy-Camille method, the screw is placed at the
midpoint in the mediolateral direction and craniocaudal
direction with a trajectory of 0–10° lateral and 0°
craniocaudal.
D. All of the above.
Response (D) All of the above are methods for lateral mass
screw placement.
Question 25
During anterior lumbar interbody fusion (ALIF) procedure at
LS-51 level, which artery has to be sacrificed?
A. Median sacral artery.
B. Artery of Adamkiewicz.
C. Paraspinal artery.
D. Posterior sacral artery.
Response (A) The median sacral artery runs inferiorly in
the midline over the anterior aspect of the vertebral body of
the lumbar vertebrae and sacrum towards the apex of the
coccyx and has to be sacrificed while doing an ALIF for the
operative corridor.
Question 26
A twenty-six-year-old patient presented with right upper
limb brachialgia. MRI showed a C4–5, C5–6, and C6–7
cervical disc prolapse. An anterior cervical discectomy and
fusion was planned using a zero profile interbody device.
Which of the following is wrong about the zero profile
devices?
A. Often easier to place adjacent to a previously placed
anterior plate.
B. Often avoid blades that are not parallel to the long axis
of the spine.
C. Posterior migration of the cage is reduced once the
screws are placed.
D. Biomechanical stability is inferior to that with a plate.
Response (D) The zero profile interbody devices offer
equivalent biomechanical stability as plates. The four screw
devices is as stable as three screw devices [20].
Question 27
Complications after lateral lumbar interbody fusion (LLIF)
include:
A. Thigh numbness.
B. Retrograde ejaculation.
C. Weakness in thigh extension.
D. All of the above.
Response (A) In the transpsoas LLIF, injury to the lumbar
plexus may cause thigh numbness. Direct damage to the
psoas muscle that may also cause weakness in the thigh
flexion. Anterior dissection of the superior hypogastric
sympathetic plexus can result in retrograde ejaculation
which is seen more in anterior lumbar interbody fusion.
Question 28
Twenty-five-year-old male patient presented after a fall from
standing found to have an acute type II odontoid fracture.
Good spinal alignment is maintained and the patient is
neurologically intact. However, an MRI reveals disruption of
the transverse ligament. Which of the following is the most
appropriate treatment?
A. C-collar immobilization.
B. Occiput to C2 posterior fusion.
C. Odontoid screw placement.
D. Posterior C1–C2 instrumented fusion.
Response (D) Type II odontoid fractures have a high rate
of nonunion, and therefore, surgical intervention is usually
recommended. Odontoid screw placement and posterior C1 –
C2 fusion are two acceptable options, but disruption of the
transverse ligament is a contraindication of the odontoid
screw.
Question 29
45-year-old male patient with a history of rheumatoid
arthritis presented with C2 pannus. The patient was planned
for transoral odontiodectomy. All the following are recom-
mended postoperative orders
EXCEPT:
A. Intravenous hyperalimentation.
B. Nasogastric feeding.
C. Early removal of the endotr acheal tube.
D. Halo-vest immobilization.
3 Instrumentation 61
Response (C) Intubation should be maintained until the
swelling subsides. Initial removal of an endotracheal tube over
a tube changer facilitates reintubation. If needed, nasogastric
feeding or intravenous hyperalimentation are used initially to
avoid disruption of the mucosal closure. If immediate stabi-
lization is not possible, then it is recommended to halo-vest
immobilize the patient until stabilization is completed.
Question 30
Which suture type has been demonstrated to have
evidence-based superiority at creating water-tight closure
when repairing a spinal cord durotomy?
A. 5-0 surgilon.
B. 3-0 vicryl.
C. 6-0 prolene.
D. 4-0 neurolon.
E. 4-0 monocryl.
Response (C) A study by Dafford et al. compared CSF
flow leaks following durotomy repair when completed using
either 6-0 prolene or 5-0 surgilon. There was a statistically
significant decrease in flow rate when the prolene sutures
were used. The suturing technique (interrupted vs. continu-
ous locking) was not found to have a significa nt role in the
dural healing rate [21].
Question 31
Which of the following is not considered a benefitofanterior
plating during anterior cervical discectomy and fusion (ACDF)?
A. Improved fusion rates for multilevel ACDFs.
B. Increased graft stability.
C. Decreased risk of dysphagia.
D. Decreased kyphosis.
E. Reduction in graft dislodgement.
Response (C) All answers except answer C are beneficial
for using anterior plating during an ACDF. Though still
somewhat controversial, several studies have demonstrated
decreased incidence of dysphagia following ACDF when
zero-profile cages are used [22].
Question 32
When using the Magerl technique for sub-axial cervical
lateral mass screw placement, what is the direction and
degree of angulation taken for screw placement?
A. 40–60° of lateral angulation.
B. 25–30° of medial angulation.
C. 40–60° of medial angulation.
D. 25–30° of lateral angulation.
E. 10° of lateral angulation.
Response (D) The Magerl technique is often used to guide
lateral mass screw placement in the sub-axial cervical spine.
In this technique, the lateral mass is divided into four
quadrants. The entry point is 1–2 mm superior and medial to
the mid-point of the quadrants. The screw is angled 25–30°
laterally and 40–60° in the cranial direction (parallel to the
facet joint).
Question 33
Which of the following corresponds with the correct
description of the Roy-Camille technique for placement of
lateral mass screws?
A. The screw insertion site is 2 mm medial and 1–2mm
cranial to the center of the lateral mass, and the orien-
tation of the screw is aimed 20–30° laterally and par-
allel to the adjacent facet.
B. The screw insertion site is 1 mm medial to the mid point
of the lateral mass and the midpoint of the mass in the
craniocaudal axis, and the orientation of the screw is
aimed 30° laterally and 15° cephalad with the cortical
surface.
C. The screw insertion site is located at the midpoint of the
mediolateral and craniocaudal axes of the lateral mass,
and the orientation of the screw is aimed perpendicu-
larly to the posterior vertebral plane and 10° lateral to
the sagittal plane.
D. The screw insertion site is located at the mid–facet line
where the superior facet joins the transverse process,
and the orientation of the screw is aimed 5–10° medi-
ally and 10–20° caudally.
Response (C) In the Roy-Camille technique, the screw is
inserted at the midpoint of the mediolateral and craniocaudal
axes of the lateral mass, aiming 0–10° laterally and 0° in the
craniocaudal axis. Choice A is the Magerl technique.
Choice B is the An technique. Choice D is used for the
placement of a thoracic spine pedicle screw [23].
Question 34
What are the three landmarks used to guide the placement of
pedicle screws in the lumbar spine?
62 A. Khan et al.
A. Transverse process, superior articulating facet, and pars
interaricularis.
B. Transverse process, inferior articulating facet, and pars
interaricularis.
C. Transverse process, mamillary process, and lamina.
D. Transverse process, mamillary process, and pars
interarticularis.
E. Spinous process, mamillary process and pars
interarticularis.
Response (D) It is suggested pedicle screws be placed at
the point at which the mamillary process, transverse process,
and pars interarticularis join.
Question 35
Where is the entry point for a C1–2 transarticular screw?
A. 3 mm medial to the junction of the C2 lamina and
inferior articulating process; 3 mm superior to the
caudal border of the inferior articulating process.
B. 3 mm lateral to the junction of the C2 lamina and
inferior articulating process; 3 mm inferior to the caudal
border of the inferior articulating process.
C. 3 mm medial to the junct ion of the C2 lamina and
inferior articulating process; 3 mm inferior to the caudal
border of the inferior articulating process.
D. 3 mm lateral to the junction of the C2 lamina and
inferior articulating process; 3 mm superior to the
caudal border of the inferior articulating process.
E. 3 mm lateral to the junction of the C2 lamina and
inferior articulating process; 3 mm inferior to the caudal
border of the superior articulating process.
Response (D) The entry location for C1–2 transarticular
screws is 3 mm lateral to the junction of the C2 lamina and
the inferior articulating process. In terms of the
cranial/caudal direction, the entry point is 3 mm superior to
the caudal border of the inferior articulating process of C2.
Typically, the screw is placed straight into the bone through
5° of medial angulation has been suggested as well.
Question 36
Pedicle violation during screw placement in which anatomic
planes is most likely to result in neurologic injury?
A. Inferior-medial.
B. Inferior-lateral.
C. Superior-lateral.
D. Superior-medial.
E. Anterolateral.
Response (A) Anatomic studies using human cadavers
have demonstrated that the distance to the nerve root adja-
cent to the pedicle is shortest in the inferior and medial
planes (0.8–2.8 mm and 0.9–2.1 mm, respectively). Based
upon these dimensions, damage to a nerve root due to vio-
lation of the pedicle is most likely to occur if the screw
violates the pedicle in the inferomedial direction [24].
Question 37
Which of the following statements regarding polyether-
ether-ketone (PEEK) cages is false?
A. PEEK is a hydrophobic polym er which in theory limits
its contact with bone.
B. PEEK is radiolucent.
C. PEEK has been reported to have decreased rates of
endplate subsidence owing to an elastic modulus that is
similar to that of bone.
D. PEEK cages have demon strated decreased hardware
failure rates when used in stand-alone cages to treat
spondylolisthesis.
E. PEEK spacers have been shown to have higher stress
forces within bone grafts compared to titanium
implants.
Response (D) All of the above answers are true statements
about PEEK except statement D. In fact, studies have
demonstrated that when stand-alone PEEK cages are used to
treat spondylolisthesis, they are associated with an increased
rate of hardware failure. One study done by Lastfogel et al.
[25] demonstrated three patients who underwent anterior
lumbar interbody fusion using stand-alone PEEK cages,
which were complicated with anterior sacral fractures.
Question 38
Cervical pedicles with a width less than which of the fol-
lowing are considered unsafe for cervical pedicl e screw
fixation?
A. 5.5 mm.
B. 5 mm.
C. 4.5 mm.
D. 4.0 mm.
E. 3.5 mm.
3 Instrumentation 63
Response (E) If the cervical pedicle width is less than
3.5 mm, it is suggested that cervical pedicle screws not be
placed at that level and can be replaced by lateral mass
screw.
Question 39
Which of the following choices best explains the concept of
stress shielding in terms of spinal instrumentation of cervical
spine?
A. The implantation of a prosthesi s removes the normal
physiologic stress on the bone, thus decreasing
osteoblastic activity.
B. Implantation of anterior cervical cages decreases the
stress on the anterior column, thus preventing
pseudoarthrosis.
C. The innate property of implanted hardware to resist
biomechanical stress.
D. The use of nanoparticle coating on implanted hardware
to shiel d the implant from the immune system.
E. Dynamic anterior cervical plates are superior to static
cervical plates because they shield the graft from
biomechanical forces thus decreasing the screw pullout
rate.
Response (A) Stress shielding is a concept first identified to
be important in orthopedic literature in terms of bone instru-
mentation. Bone formation is stimulated by biomechanical
stress on the bone, and implantation of a prosthesis removes
this stress by acting as a force sump. Unfortunately, this has
been found to result in focal osteopenia. This has proved to be
a major issue in the setting of tibial fractures. However, in
terms of spinal instrumentation, this concept has been
important in developing dynamic cervical plating systems. In
theory, static plates are too rigid and allow micromotions
within the operative level. These micromotions are thought to
induce stress on the bone touching the graft and promote
osteogenic fusion. Dynamic plates have been shown to allow
for this; however, much of the benefit is theoretical, with few
studies demonstrating a significant difference in pseu-
doarthrosis rates between the two plate types.
Question 40
What is the location for the placement of transarticular
screws in the thoracic spine?
A. Cranial to the transverse process.
B. Inferior and lateral border of the facet joint.
C. Inferior and medial border of the facet joint.
D. Superior and lateral border of the facet joint.
E. Superior and medial border of the facet joint.
Response (E) Transarticular screws may need to be placed
in cases of abhorrent anatomy or pedicle fractures in the setting
of trauma. The correct location for placement of transarticular
screws in the thoracic spine is found at the intersection of the
following lines: a horizontal line at the superior border of the
facet joint and a vertical line at the medial border of the facet
joint. The screw trajectory is 20° lateral in the coronal plane
and 45° downwards in the sagittal plane [26].
Question 41
Which of the following is not considered a potential
biomechanical benefit of cervical pedicle screws compared
to lateral mass screws?
A. Higher pullout resistance.
B. Increased stiffness when undergoing lateral bending.
C. Increased resistance to axial rotation.
D. Increased stiffness when used in a construct spanning
two unstable levels.
E. Greater construct stability when used at C7.
Response (C) Although cervical pedicle screws are
thought to offer increased resistance to lateral bending after
cyclic loading (fatigue testing), they do not offer increased
resistance to axial rotation when compared to lateral mass
screws [27].
Question 42
A 49-year-old male presents to the clinic with a 3-year
history of bilateral lower extremity radicular symptoms and
buttock pain. He had tried multiple conservative treatments,
including epidural steroid injections and physical therapy,
but none of them provided him with adequate symptom
relief. Which of the following neurological complications is
more likely to occur if this patient undergoes posterolateral
fusion at the L5–S1 level?
A. Weakness to knee extension.
B. Decreased patellar reflexes.
C. Weakness to big toe dorsiflexion.
D. Loss of bowel/bladder control.
E. Decreased Achilles re
flexes.
Response (C)L5–S1 posterolateral fusion is indicated for
low-grade spondylolisthesis that failed non-operative treat-
ment. However, this surgery places L5 nerve roots at risk for
64 A. Khan et al.
injury, which can manifest as a weakness to big toe
dorsiflexion. Weakness to knee extension and decreased
patellar reflexes are caused by L4 nerve injury. Loss of
bowel/bladder control and decreased Achill es reflexes would
result from S1 nerve injury [28].
Question 43
When performing anterior cervical discectomy and fusion
(ACDF), what is the benefit of slightly oversizing the graft?
A. Directly reduces pullout strength of the construct.
B. Prevents subsidence of the graft into the endplate.
C. Prevents fatiguing of the implant.
D. Improves incorporation of the graft with the surro und-
ing bone.
E. Avoids fibrous healing.
Response (D) According to Wolff’s law, compressive
loads increase the success of a bone graft incorporating with
the surrounding bone. As such, sizing grafts slightly larger
than the discectomy defect and using distraction to enlarge
the disc space temporally is often used in order to achieve a
larger compressive load.
Question 44
What is the preferred location for occipital plates and
screws?
A. Superior to the superior nuchal line along midline ridge
above the external occipital protuberance.
B. Inferior to the superior nuchal line along midline ridge
below the external occipital protuberance.
C. Inferior to the inferior nuchal line along midline ridge
below the external occipital protuberance.
D. Inferior to the superior nuchal line lateral to the midline
ridge below the external occipital protuberance.
E. Superior to the superior nuchal line lateral to the mid-
line ridge below the external occipital protuberance.
Response (B) Occipital plating and its associated screws
are best placed inferior to the superior nuchal line along the
midline ridge below the external occipital protuberance. At
this location, bone is thick, allowing for good screw pur-
chase, and overlying soft tissue is thick, decreasing the
likelihood of hardware eroding through the skin. Addition-
ally, the transverse sinus is superior to the nuchal line;
therefore, this structure is avoided when the aforementioned
location is used.
Question 46
Which fracture line orientations is/are considered amendable
to odontoid screw fixation?
A. Horizontal.
B. Anterior–superior to posteroinferior.
C. Anteroinferior to posterosuperior.
D. A and B.
E. All of the above.
Response (D) Horizontally-oriented fractures and fractures
oriented in an anterosuperior to posteroinferior direction are
considered to be amendable to odontoid screw fixation. In
particular, diagonal fractures oriented in an anterosuperior to
posteroinferior fashion are considered excellent candidates
for this technique as the screw will enter perpendicular to the
fracture line promoting the edges to come together. Con-
versely, fractures with an orientation from anteroinferior to
posterosuperior are contraindicated as the screw will enter
parallel to the fracture line, which may promote anterior
translation of the odontoid.
Question 46
When placing thoracic translaminar screws, which of the
following answer choices regarding entry point or trajectory
are correct?
A. Entry at the junct ion of the contralateral lamina and
spinous process.
B. Trajectory should approximate the intersection of the
ipsilateral transverse process and superior articulating
process.
C. Trajectory should approximate the intersection of the
ipsilateral transverse process and inferior articulating
process.
D. A and B.
E. A and C.
Response (D
) In the upper thoracic spine, pedicle diameter
is sometimes unfavorable for pedicle screw placement. In
this case, laminar screws can be used. The entry point is at
the junction of the contralateral lamina and spinous process.
The screw is aimed along the angle of the ipsilateral lamina,
3 Instrumentation 65
with a target trajectory approximating the intersection of the
ipsilateral transverse process and superior articulating
process.
Question 47
Which of the following is not considered an advantage of
cortical trajectory screws compared to traditional pedicle
screws?
A. Minimal lateral muscular dissection is required given
the medi al starting point of the screws.
B. Screws are directed away from the neural elements.
C. Has been shown to have increased insertional torque
compared to traditional pedicle screws.
D. Has the equivalent safety when placed at S1.
E. Can be placed at the same level as previously placed
pedicle screws to aid in fixation.
Response (D) All of the above statements except D are
correct. The cortical trajectory is not applicable at S1. The
cortical trajectory screws are theorized to have increased
pullout strength and load-bearing properties compared to
pedicle screws due to their placement in cortical bone,
large-scale studies have not consistently demonstrated
higher fusion rates. However, preliminary biomechanical
and small-scale in-vivo studies are promising and have
shown that cortical trajectory screws are at least equivalent
to pedicle screws in their resistance to pullout and their
screw-rod construct stability. It has also been shown to have
less screw loosening and pullout in patients with diagnosed
osteopenia and osteoporosis when compared to traditional
pedicle screw insertion.
Question 48
Where is the entry point for a cortical trajectory screw?
A. The junction of the inferior articulating proces s and
transverse process.
B. The center of the pars interarticularis at the level of the
inferomedial border of the pedicle.
C. The junction of the transverse process and the superior
articulating process.
D. The center of the pars interarticularis at the level of the
superomedial border of the pedicle.
E. The junction of the lamina and the base of the spinous
process.
Response (B) Cortical trajectory screws are placed at the
center of the pars interarticularis at the level of the inferior
border of the transverse process or inferomedial border of
the pedicle. The screws are angled superiorly and laterally.
Question 49
Which of the following results from using stiffer instru-
mentation in spinal arthrodesis?
A. Increased risk for pseudarthrosis.
B. Increased vascularization.
C. Decreased elasticity modulus.
D. Decreased bone mineral density.
Response (B) Rigid spinal instrumentation, which allows
for stronger fusion mass to form, is associated with signifi-
cantly greater amounts of fusion mass and transverse pro-
cesses vascularization. In the proces s of osteogenesis, early
vascularization is essential in providing nutrition to the
surviving cells of the peripheral portions of the graft. As a
result, bone mineral density is high at the fusion mass level
but decreases with increasing distance from the fusion level
[29].
Question 50
Comparing C1 lateral mass—C2 pedicle screw fixation to
posterior C1–C2 transarticular screw placement, which of
the foll owing is true?
A. C1 lateral mass—C2 pedicle screw fixation has a higher
risk for vertebral artery injury and C2 neuralgia than
C1–C2 transarticular screw placement.
B. C1–C2 transarticular screw placement has a higher risk
for vertebral artery injury and C2 neuralgia than C1
lateral mass—C2 pedicle screw fixation.
C. C1 lateral mass—C2 pedicle screw fixation has a higher
risk for vertebral artery injury but a lower chance of C2
neuralgia than C1–C2 transarticular screw placement.
D. C1–C2 transarticular screw placement has a higher risk
for vertebral artery injury, but a lower chance of C2
neuralgia than C1 lateral mass—C2 pedicle screw
fixation.
E. Both C1 lateral mass— C2 pedicle screw fixation and
C1–C2 transarticular screw placement have an equal
amount of risk for vertebral artery injury and C2
neuralgia.
Response (D) Atlantoaxial stabilization with C1 lateral
mass—C2 pedicle screws provide comparable stability to
C1–C2 transarticular screw. One advantage of C1 lateral
mass—C2 pedicle screw fixation is reduced risk of vertebral
66 A. Khan et al.