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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5259_Библиотеки_им_академика_М_И_Перельмана.pdf
Response (A) Fatigue failure describes the failure of a
material with repetitive loading at stress levels below the
ultimate tensile strength.
78. Which of the following describes a scenario wherein
spinal implants protect the spine from the transfer of
normal stresses of weight bearing?
a) Stress integration
b) Stress shielding
c) Snaking
d) Annealing
e) Toggling
Response (B) Stress Shielding refers to the situation
wherein spinal implants protect the spine from the transfer of
normal stresses of weight bearing. This can lead to stress
reduction osteoporosis [2].
79. Which of the following refers to the constant mor-
phological parameter for an individual describing
the relation between the sacral endplate and femoral
heads?
a) Pelvic tilt
b) Pelvic incidence
c) Sacral slope
d) Lumbar lordosis
e) Plumb line
Response (B) Pelvic incidence is a fixed pelvic parameter
defined as the angle between a line orthogonal to the supe-
rior S1 endplate and a line from the center of the S1 endplate
through the center of the femoral head.
80. Which law states that the stress is proportional to
the strain produced?
a) Doyle’s Law
b) Bernulli’s Law
c) Hooke’s Law
d) Wolff’s Law
e) Dalton’s theorem
Response (C) Hooke’s Law states that the stress is pro-
portional to the strain produced.
81. Pelvic Tilt is equal to which of the following?
a) Pelvic incidence – sacral slope
b) Pelvic Incidence + sacral slope
c) (Pelvic Incidence + sacral slope)/2
d) 2*(Pelvic Incidence + sacral slope)
e) 2(sacral slope) – Pelvic Incidence
Response (A) Pelvic tilt is equal to Pelvic Incidence –
sacral slope.
82. Musculoskeletal cells respond differently to loading
and oxygen levels. Which of the following is true
regarding this relationship?
a) Chondrocytes are most activated by low-loads
and low oxygen environments.
b) Osteobl asts are most stimulated to form bone
under low loads in low oxygen environments
c) Osteobl asts are stimulated to form bone under
high loads in high oxygen environments
d) Osteocl asts are stimulated to reabsorb bone under
high loads
e) Osteobl asts are stimulated to reabsorb bone under
high loads in high oxygen environments
Response (C) Chrondrocytes are stimulated to produce
collagen by high loads in low oxygen environments.
Osteoblasts are stimulated to form bone under high loads in
high oxygen environments. Osteoclasts are stimulated to
reabsorb bone under low loads.
83. Bone is anisotropic. Which of the following correctly
identifies the relative strength of bone in resisting
loading from different directi ons?
a) Bone is strongest in resisting compression and
weakest in resisting shear.
b) Bone is strongest in resisting shear and weakest
in resisting compression.
c) Bone is strongest in resisting tension and weakest
in resisting compression.
d) Bone is strongest in resisting shear and weakest
in resisting tension.
e) Bone exhibits equal strength in resisting com-
pression, shear, and tension.
Response (A) Bone’s elastic modulus depends on the
direction of loading. It is weakest in resisting shear, then
tension, then compression.
84. Which law states that an object replies to the sum-
mation of forces applied to it?
a) Newton ’ s First Law
b) Newton ’ s Second Law
250 L. A. Silveira et al.
c) Newton ’ s Third Law
d) Newton ’ s Fifth Law
e) Newton ’ s Sixth Law
Response (C) Newton’s Second Law states that an object
responds to the summation of forces applied to it [2].
85. A 42 year old woman undergoes upright lumbar
spine XRays which demonstrate a 60% anterolis-
thesis of her L5 vertebral body over her S1 vertebral
body? According to the Meyerding classification,
what grade is this spondylolisthesis?
a) 1
b) 2
c) 3
d) 4
e) 5
Response (C) An anterolisthesis of greater than 50% but
less than 75% qualifies as a grade 3 sponylolisthesis by the
Meyerding classification.
86. Which of the following terms describes the weak-
ened portion of a structure resulting from the focal
application of a stress that results in distortion?
a) Fatigue point
b) Motion segment
c) Stress Riser
d) Boundary zone
e) Runt center
Response (C) A stress riser describes the weakened portion
of a structure resulting from the focal application of a stress
that results in distortion.
87. The distance that a screw advances axially in one
turn is referred to as which of the following?
a) Lead
b) Rotational advancement
c) Drive increment
d) Drive interval
e) Spin distance
Response (A) The distance that a screw advances axially in
one turn is referred to as the lead.
88. The difference between the inner (minor) and outer
(major) diameter of the screw is a reflection of which
of following?
a) Thread depth
b) Thread pitch
c) Shaft length
d) Neck length
e) Screw head diameter
Response (A) The difference between the inner (minor)
and outer (major) diameter of the screw is a reflection of
thread depth.
89. If you push on the top center of a tin can, it indents.
If you push with the same force of the superior edge
of the tin can, it maintains its shape. This is an
example of which effect?
a) Outsider effect
b) Cylindrical coat effect
c) Boundary effect
d) Mantle effect
e) Core effect
Response (C) The boundary effect refers to the enhanced
buttressing of an axial load provided by the edge of a
materially heterogenous object. It applies to placing inter-
body grafts. It is preferable to place the graft such that they
are not exerting maximal force into the superior and inferior
centers of the vertebral bodies but toward the perimeter of
the superior and inferior vertebral bodies.
90. Stress is equal to which of the following?
a) Bending moment/ torque
b) Torque/bending moment
c) Load/torque
d) Bending moment/strength
e) Strength/bending moment
Response (D) Stress is equal to bending moment over
strength. Strength is proportional to the third power of the
inner diameter of a screw.
91. Which of the following is correct regarding the
relationship between pelvic incidence and lumbar
lordosis?
a) Those individuals with a low pelvic incidence
require less lumbar lordosis to have a balanced
spinal alignment.
b) Those individuals with a low pelvic incidence
require more lumbar lordosis to have a balanced
spinal alignment
11 Biomechanics of the Spine 251
c) Pelvic incidence is in no way related to lumbar
lordosis
d) Those individuals with a high level of lumber lor-
dosis and a high level of pelvic tilt will have a low
pelvic incidence
e) Individuals can adjust their pelvic incidence through
various postures to compensate for a high level of
lumbar lordosis
Response (A) Those individuals with a low pelvic inci-
dence require less lumbar lordosis to have a balanced spinal
alignment. For those individuals with a large pelvic inci-
dence, more lum bar lordosis is required to have a balanced
spinal alignment. Pelvic incidence is a fixed parameter that
cannot be altered by posture. Pelvic incidence reflects the
angle between a line drawn orthogonal to the S1 superior
endplate and a line drawn from the middle of the S1 superior
endplate through the center of the femoral head.
92. Full length upright X-rays are obtained on two
identical twins. The pelvic incidence for twin A is
calculated and determined to be 2 that of twin B?
Which of the following is true?
a) The lumbosacral shear stress is higher for twin B
than twin A
b) Twin B would be expected to have a higher risk of
progression of lumbosacral spondylolisthesis
c) The lumbosacral shear stress is higher for twin A
than twin B
d) The lumbosacral shear stress would be equal for the
two twins
e) Twin B would require a higher degree of lumbar
lordosis to maintain sagittal balance
Response (C) The lumbosacral shear stress is higher for
twin A than twin B given the higher degree of lumbar lor-
dosis and higher sacral slope associated with a higher pelvic
incidence. Given the higher shear stress experienced at the
lumbosacral region, individuals with a higher pelvic inci-
dence are at higher risk for progression of a lumbosacral
spondylolisthesis.
93. How is depth of screw penetration for pedicle screws
related to pullout strength?
a) There is no correlation between depth of screw
penetration and pullout strength
b) 80% depth of vertebral body screw penetration is
associated with increased pullout strength compared
to 50% depth of vertebral body penetration
c) Pedicle screw length is inversely proportional to
pullout strength
d) Pedicle screws which do not traverse the vertebral
body have greater pullout strength than those that do
e) Depth of penetration only impacts pullout strength
for unilateral pedicle screws
Response (B) Increased depth of screw penetration into the
vertebral body is associated with increased pullout strength.
80% depth of vertebral body penetration was found to
increase pullout strength by a factor of about 1 third com-
pared to 50% depth of vertebral body penetration [13].
94. Which of the following is true regarding pedicle
screws versus rib-pedicle screws placed in the tho-
racic spine?
a) For a fixed diameter screw, screws placed com-
pletely in the pedicle have a lower pullout strength
than a rib-pedicle screw at the same level
b) For a fixed diameter screw, screws placed com-
pletely in the pedicle have a higher pullout strength
than a rib-pedicle screw at the same level
c) For a fixed diameter screw, screws placed com-
pletely in the pedicle have the same pullout strength
as a rib-pedicle screw at the same level
d) Thoracic rib-pedicle screw pullout strength is
inversely related to screw outer diameter
e) Thoracic rib-pedicle screws with a 2 mm diameter
will exhibit a greater pullout strength than a thoracic
pedicle screw maintained completely in the pedicle
with a 3 mm diameter
Response (B) For a fixed diameter screw, screws placed
completely in the pedicle have a higher pullout strength than
a rib-pedicle screw at the same level. Rib-pedicle screws
have about 70% of the pullout strength compared to a screw
of the same size maintained completely within the pedicle.
However, rib-pedicle screws allow for use of a larger
diameter screws in the thoracic spine, where the pedicles are
often very narrow.
95. For short segment pedicle instrumentation in the
osteoporotic patient, which of the following correctly
describes the effect of placing supplemental offset
hooks?
a) Increases construct stiffness and decreases screw
bending moments
b) Decreases construct stiffness and increases screw
bending moments
252 L. A. Silveira et al.
c) Has no effect on construct stiffness
d) Decreases construct stiffness but decreases screw
bending moments
e) Increases construct stiffness and increases screw
bending moments
Response (A) For short segment pedicle instrumentation in
the osteoporotic patient, placing supplemental offset hooks
increases construct stiffness, absorbs some of the construct
strain, and decreases screw bending moments [14, 15].
96. Which of the following is true regarding tapping of
pedicle screws?
a) Insertional torque and pullout strength are lower for
screws placed without first tapping
b) Tapping the full length of the screw is associated
with a lower pullout strength than tapping 1 mm less
than the screw length
c) Tapping 1 mm shy of screw length is associated
with lower pullout strength than tapping to 0.5 mm
shy of screw length
d) Screw tapping does not effect pullout strength or
insertional torque
e) Screw tapping negatively effects insertional torque
but not pullout strength
Response (B) Tapping the full length of the screw is
associated with a lower pullout strength than tapping 1 mm
less than the screw length. Tapping prior to screw placement,
especially in osteoporotic bone, is associated with a
decreased pullout strength [16].
97. Placement of a crosslink in a short segment pedicle
fixation construct provides what advantage?
a) Increases torsional stiffness
b) Decreases torsional stiffness
c) Provides additional protection against rod notching
d) May induce rod notching
e) Provides a site for dural adheren ce to prevent CSF
leaking
Response (A) Placement of a crosslink in a short segment
pedicle fixation construct increases torsional stiffness by an
estimated 44% [17].
98. Which of the following correctly describes the trend
in thoracic pedicle width from cranial to caudal?
a) Middle thoracic level pedicles are wider than lower
thoracic or upper thoracic pedicles
b) Lower thoracic level pedicles are narrower than
lower thoracic or upper thoracic pedicles
c) Middle thoracic level pedicles are narrower than
lower thoracic or upper thoracic pedicles
d) Upper thoracic level pedicles are narrower than
lower middle or lower thoracic pedicles
e) Thoracic pedicles are approximately equal in width
from T1 through T11
Response (C) The thoracic pedicles become progressively
narrower from T1 to T6 then become progressively wider
from the mid to lower thoracic spine such that the mid
thoracic pedicles are typically the narrowest [18].
99. When attempting to salvage and replace a pedicle
screw in osteoporotic bone, which option most sig-
nificantly increases insertional torque?
a) Increases the length of the replacement screw
b) Decreasing the length of the replacement screw
c) Increasing the diameter of the replacement screw
d) Decreasing the diameter of the replacement screw
e) Placing shims in the osteoporotic bone
Response (C) Increasing the diameter of the replacement
screw most significantly increases the insertional torque,
which is not significantly affected by placing shims and is
minimally effected by placing a longer screw [19].
100. What is most common site for a pre-lordosed rod to
fracture?
a) Pre-lordosed rods are not subject to fracturing
b) Adjacent to the set screw
c) Mid way along the shaft of the rod
d) Nearest the cranial tip of the rod
e) Nearest the caudal tip of the rod
Response (B) Pre-lordosed rods tend fracture adjacent to a
set screw, whereas intra-operatively bent rods are more
likely to fracture at notching sites produced by bending.
101. Bone is anisotropic. From which direction is the
vertebral body strongest in resisting loading?
a) Bone is strongest in resisting compression.
b) Bone is strongest in resisting shear
c) Bone is strongest in resisting tension
d) Bone exhibits equal strength in resisting compres-
sion and tension.
e) Bone exhibits equal strength in resisting compres-
sion and shear
11 Biomechanics of the Spine 253
Response (A) Bone is strongest in resisting compression as
compared to tension or shear.
102. Which of the following terms is defined as a change
in length in response to a stress?
a) Torque
b) Moment arm
c) Strain
d) Acceleration
e) Deceleration
Response (C) Strain is defined as a change in length in
response to a stress. It is the ratio of deformation to the initial
length in the direction of the applied force.
103. If a rod is bent by a force such that it changes shape
and does not revert back to its init ial configuration,
in which portion of the stress–strain curve is it said
to be?
a) In the pre-elastic phase
b) Beyond the yield point but not yet to the point of
failure
c) Beyond the point of failure
d) Beyond the point of rupture
e) Just prior to the yield point but still in the elastic
phase
Response (B) If a rod is bent by a force such that it changes
shape and does not revert back to its initial configuration, it
is said to have surpassed its yield point and moved beyond
the elastic phase. However, it has not yet reached the point
of ultimate failure or rupture, as it has not fractured.
104. A muscular spine surgeon tightens a screw as hard
as he can. He then scrubs out of the case to briefly
answer a page. On re-scrubbing and returning to
the case, he finds he can now tighten the screw a bit
more. Which biomechanical prop erty of viscoelastic
materials is being illustrated?
a) Yielding
b) Stress relaxation
c) Toggle
d) Torque
e) Stretch
Response (B) The above scenario illustrates the phe-
nomenon of stress relaxation, wherein the stress required to
hold a material at constant deformation diminishes with time
and is said to relax.
105. Which term, applicable to the vertebral bodies,
refers to the properties of material dependent upon
direction of force applied to that material?
a) Isotropic
b) Anisotropic
c) Hypertrophic
d) Hypotrophic
e) Polyaxial
Response (B) Bone is anisotropic. The vertebral bodies are
specifically able to sustain loads of higher magnitude from
above and below than from the front, back, or sides. The
vertically oriented pattern of vertebral body trabeculae
reflects this.
106. Which of the following rods will have the shortest
fatigue life?
a) A titanium rod that has been bent multiple times
intra-operatively with a French rod bender but is not
attached to any horizontal connectors
b) A titanium rod that has been bent multiple times
intra-operatively with a French rod bender and is
attached to multiple horizontal connectors
c) A titanium rod that was pre-lordosed and annealed
attached to multiple horizontal connectors
d) A stainless steel rod that has been bent multiple
times intra-operatively with a French rod bender but
is not attached to any horizontal connectors
e) A stainless steel rod that has been bent multiple
times intra-operatively with a French rod bender
and is attached to multiple horizontal connectors
Response (B) Titanium has a shorter fatigue life than steel
and is more sensitive to notching from both intra-operative
bending and placement of connectors. Option B above
provides such a scenario where the shortest fatigue life
would be expected.
107. How is rod stiffness related to the distance between
two pedicle screw points of fixation?
a) Rod stiffness is directly proportional to the cubed
distance between two pedicle screw points of
fixation
b) Rod stiffness is proportional to the squared distance
between two pedicle screw points of fixation
c) Rod stiffness is inversely proportional to the
squared distance between two pedicle screw points
of fixation
d) Rod stiffness is inversely proportional to the cubed
distance between two pedicle screw points of fixation
254 L. A. Silveira et al.
e) Rod stiffness is inversely proportional to the dis-
tance between two pedicle screw points of fixation
Response (E) Rod stiffness is inversely proportional to the
distance between two pedicle screw points of fixation.
108. A 32 year old man involved in a motor vehicle
accident sustains an L2 burst fracture with pain
prohibiting ambulation. He undergoes an L1-3
posterior spinal fusion with pedicle screws placed
in the right L1, L2, and L3 pedicles. The fracture
morphology prohibits placing a left L2 pedicle
screw. How does the stiffness of the left rod con-
struct compare to that of the right rod construct?
a) Left rod construct is half as stiff
b) Left rod construct is 1/8th as stiff
c) Left rod construct is 1/4th as stiff
d) Left rod construct is 1/16th as stiff
e) Left rod construct is 2 stiffer than the right
Response (A) In the scenario described above, the left rod
construct is half as stiff, as there is two 2 the distance
between points of fixation compared to the right construct.
Rod stiffness is inversely proportional to the distance
between two pedicle screw points of fixation.
109. Which of the following is true regarding the role of
the pedicle and vertebral body with regard to pull-
out strength and resistance to cantilever bending for
pedicle screws?
a) The pedicle provides a greater portion pullout
strength and a greater degree of resistance to can-
tilever bending than the vertebral body
b) The pedicle provides a greater portion of pullout
strength but a lesser degree of resistance to can-
tilever bending than the vertebral body
c) The pedicle provides an equal portion pullout
strength to the vertebral body but a greater degree of
resistance to cantilever bending than the vertebral
body
d) The pedicle provides an equal portion of pullout
strength to the vertebral body but a lesser degree of
resistance to cantilever bending than the vertebral
body
e) The pedicle provides a lesser portion of pullout
strength to the vertebral body and a lesser degree of
resistance to cantilever bending than the vertebral
body
Response (A) The pedicle provides a greater portion pull-
out strength and a greater degree of resistance to cantilever
bending than the vertebral body.
110. Pullout strength of a screw is related to the shear
strength of the bone it penetrates. Which of the
following directly impacts the shear strength of
bone?
a) Bone mineral density
b) Blood pressure
c) Spinal level
d) Serum sodium
e) Serum potassium
Response (A) The shear strength of bone is a mechanical
property based on its composition. Increased bone mineral
density is associated with increased shear strength and
therefore increased pullout strength.
111. Pullout strength of a pedicle screw is a product of
what two components?
a) Area of bone encircled by threads and shear strength
of bone entered
b) Length of screw body and diameter of screw head
c) Diameter of screw neck and screw length
d) Diameter of Screw head and inner screw diameter
e) Outer screw diameter and length of screw
Response (A) Pullout stre ngth of a pedicle screw is a
product of the surface area of bone encircled by threads and
shear strength of bone entered. Force = shear strength
surface area.
112. Which of the following are true of dual thread
design screws?
a) They are designed to have a narrower pitch in
pedicle bone and wider pitch in cancellous bone,
decreasing insertional torqu e
b) They are designed to have a narrower pitch in
pedicle bone and wider pitch in cancellous bone,
increasing insertional torque
c) They are designed to have a wider pitch in pedicle
bone and narrower pitch in cancellous bone,
increasing pullout strength
d) They are designed to have a wider pitch in pedicle
bone and narrower pitch in cancellous bone,
increasing insertional torque
11 Biomechanics of the Spine 255
e) They are designed to have a wide pitch for the
proximal third of the screw shaft, a narrow pitch for
the middle third of the screw shaft, and a wide pitch
for the distal third of the screw shaft
Response (B) Dual thread screws are designed to have a
narrower pitch in pedicle bone and wider pitch in cancellous
bone, increasing insertional torque and theoretically
increasing pullout strength.
113. Which of the following is true regarding the width
and depth (ventral to dorsal length) of the vertebral
bodies?
a) Width and depth both increase cranial to caudal
from cervical to thoracic to the lumbar spine
b) Width increases cranial to caudal but vertebral body
depth de creases cranial to caudal
c) Width and depth both decrease from cranial to
caudal
d) Width decreased from the cervical to thoracic spine
but increases from the thoracic to lumbar spine
e) Width and depth increase from the cervical to tho-
racic spine but decrease from the thoracic to lumbar
spine
Response (A) Width and depth of the vertebral bodies both
increase cranial to caudal from cervical to thoracic to the
lumbar spine.
114. Which of the following spinal vertebral bodies
exhibits the highest compression strength?
a) C3
b) C7
c) T6
d) T10
e) L4
Response (E) The lumbar vertebral bodies are the largest
and exhibit the highest compression strength, with the lower
lumbar levels nearing a compression strength of nearly 8000
Newtons compared to a compressive strength near 2000
Newtons in the cervical spine [5].
115. The uncinate processes and the uncovertebral joints
which they form play an important role in coupling
and stabilizing which portion of the spine during
axial rotation?
a) C3-C7
b) T6-T12
c) C1-2
d) L5-S1
e) L1-L4
Response (A) The uncinated process projects from the
rostro-dorsal-lateral aspect of C3-C7. It is involved in cou-
pling within the subaxial c ervical spine and provides some
stabilization during axial rotation.
116. Which of the following correctly states the relation
of the instantan eous axis of rotation (IAR) to spinal
curvature?
a) The IAR is located more dorsally in a kyphotic
segment than in a vertically straight segment
b) The IAR is located more ventrally in a kyphotic
segment than in a vertically straight segment
c) The IAR is located more dorsally in a lordotic
segment than in a vertically straight segment
d) The IAR is not affected by sagittal spinal curvature
e) The IAR is located more ventrally in a kyphotic
segment than in a lordotic segment
Response (A) The location of the instantaneous axis of
rotation (IAR) is variable. When a ventral bending moment
is applied to the spine and a relative kyphosis is induced, the
IAR migrates dorsally as compared to the in a vertically
straight spinal segment. When a dorsal bending moment is
applied to the spine and a relative lordosis is induced, the
IAR mig rates ventrally.
117. Which of the following spinal levels is typically
associated with the narrowest portion of the spinal
canal in a healthy adult spinal column?
a) C1
b) C7
c) T10
d) L3
e) S1
Response (C) The spinal canal is typically narrowest in the
lower thoracic spine. As such, the thoracic spine is less for-
giving to compressive pathologies such as tumors invading
the canal or fractures with retropulsed bone. There is less
room to accommodate additional space occupying lesions.
118. If the instantaneous axis of rotation (IAR) for a
particular thoracic spinal level is located in the
center of the vertebral body, which of the following
spinal ligaments has the longest moment arm (L)?
a) The interspinous ligament
b) The ligamentum flavum
256 L. A. Silveira et al.
c) Capsular ligament
d) Anterior longitudinal ligament
e) Posterior longitudinal ligament
Response (A) If the IAR is located in the center of the
vertebral body, the interspinous ligament will have the
longest moment arm, as the distance from the IAR to the
interspinous ligament is greater than from the IAR to any
other named spinal ligament. In this case, the interspinous
ligament therefore has the longest lever arm.
119. Which of the following has the highest ratio of
cortical to cancellous bone?
a) Small pedicle
b) Small vertebral body
c) Large pedicle
d) Large vertebral body
e) The ratio is the same in pedicles and a respective
vertebral body for any given person
Response (A) The ratio of cortical to cancellous bone
affects load bearing. It is greater in the pedicles than in the
vertebral bodies, and it is greater in smaller pedicles than
large pedicles. Bone density correlates with screw pullout
resistance such that the pedicles provide more resistance to
pullout than the vertebral bodies.
120. How does normal, healthy cervical spine curvature
aid in preventing cervical disc degeneration?
a) Cervical spine lordosis allows for the facets to
participate in load sharing, taking some pressure off
the discs
b) Cervical spine lordosis relieves the facets of par-
ticipation in load sharing
c) Cervical spine kyphosis allows for the facets to
participate in load sharing, taking some pressure off
the discs
d) Cervical spine kyphosis relieves the facets of par-
ticipation in load sharing
e) Sagittal cervical spine curvature has no effect on the
progression of disc degeneration
Response (A) The healthy cervical spine has some degree
of lordosis. This relatively normal extension posture obli-
gates the dorsal cervical spine facet joints to partake in
compressive load sharing, thereby taking some excessive
pressure off of the intervertebral discs and deceleration their
degeneration relative to a kyphotic or straight cervical spine
curvature.
121. Which of the following materials has the greatest
resistance to corrosion?
a) Pure Titanium
b) Stainless steel
c) Cobalt-Chrome
d) Titanium-alloy
e) There is no difference in corrosion resistance
between different metals if they are placed in the
same biologic environments
Response (A) Titanium is much more resistant to corrosion
than stainless steel. Cobalt chrome and Titanium alloy have
intermediate resistances.
122. Which of the following terms is used to describe the
direct bonding of bone to an implant?
a) Shot peening
b) Corrosion
c) Osteoinduction
d) Osteoconduction
e) Osteointegration
Response (E) Osteointegration refers to the direct bonding
of bone to an implant. It is a property dependent upon the
surface material of a given implant and therefore bears some
consideration in selecting a material for spinal fixation
hardware [2].
123. Why is shot peening utilized in surface treatment of
metals?
a) To improve capacity for osseointegration
b) To enhance fatigue resistance
c) To improve osteoconduction
d) To improve osteoinduction
e) To increase insertional torque
Response (B) Shot peening is a metal surface treatment
used to enhance fatigue resistance of a given metal. It has no
effect on the other options listed [20].
124. Which of the following materials has the greatest
capacity for osteointegration?
a) Cobalt-chromium
b) Stainless steel
c) Titanium
d) Titanium has an equal capacity to stainles s steel
e) Each metal has approximately the same capacity for
osteointegration
11 Biomechanics of the Spine 257
Response (C) Of the listed metals, titanium has the highest
capacity for osteointegration, allowing for a smoother and
more evenly distributed loading between implant and bone
[2].
125. The axis about which the lumbosacral region rotates
in the sagittal plane is referred to as which of the
following?
a) Pelvic tilt point
b) Center of lordosis
c) Lumbosacral transition focus
d) Pelvic Incident
e) Lumbosacral pivot point
Response (E) The axis about which the lumbosacral region
rotates in the sagittal plane is referred to as the lumbosacral
pivot point. It is approximately located at the dorsal annulus
of the L5-S1 disc. It is significant in that it must be surpassed
either ventrally or caudally by a fixation device in order to
provide adequate stabilization of the spine with regards to
sagittal plane rotation.
126. Which of the following pelvic parameters is a fixed
variable?
a) Pelvic tilt
b) Pelvic retroversion
c) Pelvic Incidence
d) Neck extension
e) Knee bending
Response (C) Of the options listed, pelvic incidence is a
relatively fixed variable.
127. Which of the following is true regarding the apex of
lumbar lordosis?
a) The apex of lumbar lordosis is always located at
L5-S1
b) The apex of lumbar lordosis is always located at
L4-L5
c) The apex of lumbar lordosis shifts superiorly for a
person with a very high pelvic incidence compared
to a low pelvic incidence
d) The apex of lumbar lordosis shifts inferiorly for a
person with a very high pelvic incidence compared
to a low pelvic incidence
e) The apex of lumbar lordosis is always centered at
the L3 vertebral body
Response (C) The apex of lumbar lordosis shifts superiorly
for a person with a very high pelvic incidence compared to a
low pelvic incidence.
128. Which of the following zones on the physiologic
range of motion stress–strain curve can be increased
by stretching exercises?
a) Elastic zone
b) Neutral zone
c) Yield zone
d) Zone of failure
e) None of the zones on the physiologic range of
motion stress–strain curve can be increased by
stretching exercises
Response (B) The neutral zone is associated with sub-
stantial flexibility at low loads. It is a zone of relative
non-engagement within minimal ligamentous tension. This
zone can be incre ased to some degree by stretching
exercises.
129. A 32 year old morbidly obese male presents to clinic
complaining of severe midline back pain worse with
standing for prolonged periods. Why must the
downward force exerted by the dorsal spinal mus-
cles significantly surpass the downward force exer-
ted by the weight of this patient’s protuberant
abdomen?
a) The dorsal spinal muscles are located a significantly
shorter distance from the instantaneous axis of
rotation of the spine than the patient’s protuberant
abdomen
b) The dorsal spinal muscles are located a significantly
longer distance from the instantaneous axis of
rotation of the spine than the patient’s protuberant
abdomen
c) The dorsal spinal muscles exert an upward dorsal
force to counteract the ventral downward force
imparted by the patient’s protuberant abdomen
d) The dorsal spinal muscles always exert a fixed
downward force independent of the weight of the
patient’s protuberant abd omen
e) The dorsal spinal muscles need not exert any greater
downward force as a result of the ventral downward
force of the patient’s protuberant abdomen
Response (A) If the patient described is standing upright
and not in motion, a dorsal downward application of force
258 L. A. Silveira et al.
must be applied, in this case by the dorsal spinal muscles
that are located a short distance from the instantaneous axis
of rotation (IAR) of the spine compared to the patient’s
protuberant abdomen. Given that the dorsal and ventral
bending moments must be equal with respect to the IAR, the
dorsal spinal muscles must generate a greater down ward
force than the weight of the weight of the patient’s abdomen
because the dorsal spinal muscles have a shorter moment
arm compared to the patient’s abdomen. Bending moment is
equal to force x distance from IAR, or force x moment arm.
130. A 62-year-old woman undergoes a successful L1-S1
posterior fusion and decompression to address
multilevel stenosis and neurogenic claudication. She
returns to clinic 1 month later with worsened back
pain and posture. Her X-rays below (Fig. 11.3), in
tandem with her symptomatic presentation, are
suggestive of which entity?
a) Proximal facet widening
b) Thoracic bone demineralization
c) Proximal junctional kyphosis
d) Scheuermann's Kyphosis
e) Rod bending
Response (A) The above clinical case illustrates the phe-
nomenon of proximal junctional kyphosis, a common
radiographic finding after a long spinal fusion. Constructs
ending at spinal transition zon es such as the cervicothoracic
junction and thoracolumbar junction are particularly sus-
ceptible to resulting in a proximal junctional kyphosis given
the increased stress experienced at the levels just superior or
inferior to the fusion construct amplified by a transition in
spinal alignment.
131. Sacral Slope is equal to which of the following?
a) Pelvic incidence − pelvic tilt
b) Pelvic Incidence + pelvic tilt
c) (Pelvic Incidence + pelvic tilt)/2
d) 2*(Pelvic Incidence + pelvic tilt)
e) 2(pelvic tilt) − Pelvic Incidence
Response (A) Sacral slope is equal to Pelvic Incidence—
pelvic tilt.
132. The weakened portion of a rod that results from
intraoperative focal bending and contouring is
referred to as which of the following?
a) Culprit focus
b) Stress riser
c) Yielding zone
d) Strain target
e) Soft spot
Response (B) The weakened portion of a rod that results
from intraoperative focal bending and contouring is referred
to as a stress riser.
133. Which of the following materials has the lowest
incidence of biofilm attachment and formation?
a) Titanium
b) Cobalt-Chromium
c) Stainless steel
d) Titanium alloy
e) No difference
Fig. 11.3 Standing lateral scoliosis XR of patient with L1-S1
posterolateral arthrodesis
11 Biomechanics of the Spine 259