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Spinal Anatomy > Internal Fixation of Spine > Flashcards

Internal Fixation of Spine Flashcards

1
Q

What are the three main functions of the Spine?

A

Motion
Weight Transfer
Protection of Neural Elements

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2
Q

The vertebra is the _______, a rigid object that pivots

A

Level

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3
Q

What is the fulcrum of the spine, allowing the vertebra to move?

A

Disc and facets

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4
Q

What activates the spine, attaching to the vertebra via the spinous process or TP, pulling on the bone to create movement?

A

Muscles

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5
Q

What are the spine’s restraints, preventing the spine from exceeding its normal range of motion?

A

Ligaments

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6
Q

To tilt your head down, the muscles pull __ on the spinous processes in the back of your neck

A

Up

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7
Q

What makes up a functional spinal unit (FSU) or motion segment?

A

Two adjacent vertebral bodies and the intervening soft tissue

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8
Q

What is the smallest unit of the spine that behaves biomechanically like the entire spine?

A

FSU/Motion Segment

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9
Q

In the cervical spine, the facets are oriented in the ____ plane

A

Axial

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10
Q

Being oriented in the axial plane allows the cervical spine to ____, lateral bend, _____, and _______

A

Rotate, lateral bend, flexion, and extension

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11
Q

In the thoracic spine the facets are oriented in the ____ plane

A

Frontal

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12
Q

In the lumbar spine, the facets are oriented in the _____ plane

A

Sagittal

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13
Q

Since the facets are in the sagittal plane, the lumbar spine can achieve ____ and ____ with some lateral bending but minimal ________

A

Flexion, extension, rotation

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14
Q

In a healthy spine, __% of compressive loads are transferred through the anterior column (VBs and discs)

A

80%

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15
Q

The spine is located _______ in the torso

A

Posteriorly

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16
Q

The _______ in the spine give it flexibility to bend and absorb shock

A

Curves

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17
Q

The vertebrae form a ____ _____ around the spinal cord and spinal nerves

A

Bony cage

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18
Q

During both trauma and normal, physiologic movement, the _______ play a large role in protecting these neural structures

A

Ligaments

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19
Q

The spinal ligaments connect vertebra to vertebra and prevent extreme motion that could stretch or damage _______

A

Nerves

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20
Q

Ligaments are like _____ _____, they only create resistance when they are stretched beyond their resting length and provide no resistance to compression

A

Rubber bands

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21
Q

Without the ligaments to hold the vertebrae in position, even gentle movements could cause damage to the _____

A

Cord

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22
Q

Define spinal instability

A

Loss of the ability of the spine under physiologic loads to maintain its pattern of displacement leading to increased risk of neurological deficit, deformity, or incapacitating pain

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23
Q

Two goals of spine surgery

A

Decompression

Restoration of stability

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24
Q

Define decompression

A

The removal of any material causing undue pressure on the neural elements

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25
Q

Define direct decompression

A

Physically removing the tissue that is exerting pressure onto a neural element

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26
Q

Define indirect decompression

A

Involves increasing the space for the neural structures by increasing or restoring the height of the disc space

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27
Q

Define restoration of stability

A

The application of stabilizing implants to provide immediate mechanical stability and preserve neurological function, while allowing the patient to have an early return to function

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28
Q

Define arthrodesis

A

The body’s own bony fusion which will provide long-term stability to the spine

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29
Q

What are the 5 steps for plate and screw constructs

A
  1. Size the plate
  2. Position and provisionally stabilize the plate
  3. Create a pathway for the screws
  4. Insert the screws
  5. Performing final tightening
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30
Q

What are two methods used to size a plate

A

Calipers, templates

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31
Q

What are two key instruments used in positioning and provisionally stabilizing a plate

A

Plate holding forceps, temporary fixation pins (ideally place in diagonal plate holes)

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32
Q

What are two main techniques for creating a screw pathway when plating?

A

Drill (requires both a drill and drill guide, a tap may also be necessary to cut path for thread depending on type of screw)

Awl which ensures starting point of screw is in center of the plate hole by creating an opening in cortical bone

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33
Q

When inserting a screw in a plate, what instrument is used?

A

A screwdriver with or without a holding sleeve depending on type of screw

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34
Q

What order should screw be inserted in a plate?

A

Alternating pattern to prevent tilting or lift off

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35
Q

What is an instrument that is occasionally used for final tightening a plate?

A

Torque limiting driver

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36
Q

What are the 4 steps for implanting a screw and rod construct?

A
  1. Create a pathway
  2. Insert the screw
  3. Connect the screw to a rod
  4. Perform final tightening
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37
Q

What are the two most common methods for creating a pathway for a screw in a screw and rod construct?

A

Drilling (with drill guide)

Probing (after perforation with awl)

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38
Q

When are holding sleeves especially important?

A

As incision get smaller with encroaching soft tissue

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39
Q

What are the 6 steps for an interbody fusion?

A
  1. Access the disc
  2. Remove the disc
  3. Create an osteogenic environment
  4. Trial
  5. Prepare spacer
  6. Implantation
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40
Q

What is used to make an annulotomy?

A

Scalpel

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41
Q

What is used to separate disc material from endplate?

A

Periosteal elevator

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42
Q

What is used to pull out disc tissue?

A

Pituitary rongeur

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43
Q

What is used to scrape disc material from the bone?

A

Curette

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44
Q

What is used to remove bony osteophytes?

A

Kerrison rongeur

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45
Q

What is used to create osteogenic environment (cartilage remove from endplates and blood flowing to region)?

A

A rasp or high speed burr

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46
Q

Which allograft type should be thawed before implantation?

A

Frozen allograft

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47
Q

Which allograft type should be rehydrated in saline prior to implantation?

A

Freeze dried

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48
Q

What can happen if you don’t thaw or rehydrate an allograft?

A

Fracture

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49
Q

What are the 3 functions of a screw head?

A
  1. Acts as stop to prevent screw from traveling entirely through bone
  2. Holds or lags a plate securely against bone
  3. Contains drive mechanism that engages with screwdriver
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50
Q

What is the function of the screw shaft?

A

When inserted into bone, threads prevent the screw from pulling out

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51
Q

What are the two functions of the screw tip?

A
  1. Can cut pathway for screw

2. Guides the screw into bone

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52
Q

What are the two main functions of a screw thread?

A
  1. Upon rotation, they exert force to insert a screw into bone
  2. They increase the force required to remove a screw from the bone
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53
Q

The measurement of the force that is required to pull a screw from the material in which it is embedded

A

Pullout strength

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54
Q

What are the two main factors that influence screw pullout strength?

A
  1. Quality of bone

2. Thread design (more thread = better pullout strength)

55
Q

The vertical distance between threads

A

Pitch

56
Q

What two things does pitch affect?

A
  1. Speed of insertion

2. Pullout strength

57
Q

The distance the screw travels through the bone per 360 degree rotation

A

Pitch

58
Q

Screws with a ______ pitch have more thread revolutions than the same length screw with a _______ pitch

A

Smaller pitch has more threads than greater pitch

59
Q

The width of the shaft including the threads

A

Major diameter

60
Q

The width of the shaft EXCLUDING the threads

A

Minor diameter

61
Q

Describe the thread design on a cortical screw

A

The threads on a cortical screw are short and flat to exert forces outward and increase compressive force between the screw and the bone

62
Q

The goal for achieving purchase in _______ bone is to create compressive forces between the screw and bone

A

Cortical

63
Q

The goal for achieving purchase in ________ bone is to maximize the surface area of the screw in contact with the bone

A

Cancellous

64
Q

A cortical screw’s minor diameter is slightly ______ than the hole prepared for it

A

Larger

65
Q

A cancellous screw’s minor diameter is the _____ diameter as the minor diameter of the screw

A

Same size - a large core would simply push the cancellous bone away rather than creating compressive force

66
Q

The threads on a cancellous screw are _______ and _______

A

Larger, sharp

67
Q

These screws incorporate both cortical and cancellous screw attributes in the same screw (constant major diameter while minor transitions from wider at head to narrower at tip)

A

Dual core

68
Q

This screw has two threads traveling down the shaft of the screw simultaneously

A

Dual lead

69
Q

A dual lead screw yields twice the insertion speed of a single lead without sacrificing what?

A

Pullout strength

70
Q

Partially threaded screws have two main advantages

A

Ability to lag

Tissue protection

71
Q

A type of screw used to pull two pieces of bone together

A

Lag screw

72
Q

In a lag screw, the unthreaded portion is near the _____. As the threaded portion engages the distant fragment and advances, the threads of the screw pull the distant fragment toward the near fragment and the gap descreases

A

Head

73
Q

What prevents lagging in a plate construct?

A

Threads at plate to screw interface

74
Q

If a screw is not fully inserted into bone, ______ threads can be a problem since close contact between soft tissue and ______ threads can irritate or damage soft tissues

A

Exposed, sharp

75
Q

A standard screw has a tip that requires ______ a pilot hole for the screw and then ________ the hole before inserting the screw

A

Drilling, tapping

76
Q

A self-tapping screw has a tip that requires ______ or _______ to insert the screw but not tapping

A

Drilling or probing

77
Q

What are the two different self-tapping screw designs?

A

One design uses a flute cut into the tip of the screw to begin cutting the thread pattern

In another design the thread continues to the tip of the screw as the core tapers allowing the threads to bite in and begin to cut without a flute

78
Q

A self-drilling screw has a tip that can be inserted directly into the bone without ____ or _____

A

Drilling or tapping

79
Q

A self-drilling screw will always follow what?

A

The path of least resistance

80
Q

Self-drilling screws have what type of tip?

A

A sharp, pointy tip

81
Q

If trajectory or screw angle is important, what must be prepared for a self-drilling screw?

A

A hole using an awl

82
Q

If a construct is too rigid, or ____ _____ it will bear all of the load and shield the fusion site from feeling force

A

Load bearing

83
Q

When a construct shields the fusion site from feeling force, this is known as what?

A

Stress shielding

84
Q

Allowing the fusion site to feel load but protecting it from damaging forces

A

Load sharing

85
Q

Define modulus of elasticity

A

A measure of the stiffness of a material or how much the material flexes when a force is applied

86
Q

What is the ideal material for a spinal implant?

A

One in which the modulus of elasticity is close to that of bone so that the construct approximates a natural state for the body

87
Q

The stiffer a material is, the more likely it is to be load _____

A

Bearing

88
Q

What are the two ways that a screw remains locked to a plate?

A

Locking screw rigidly connected to plate

Blocking screw prevented from backing out of plate by secondary blocking mechanism

89
Q

A ________ screw is rigidly connected to a plate and the two implants interlock to prevent any movement at the screw-to-plate interface (maximizes pullout strength)

A

Locking

90
Q

What are the two common locking screw designs?

A

Conical locking screw

Expansionhead screw

91
Q

A locking screw that is cone shaped and threaded (the plate hole is similarly threaded)

A

Conical locking screw

92
Q

How does a conical locking screw work?

A

As the threads on the screw and plate engage, they pull the screw deeper into the plate and the conical shape of the screwhead creates a “wedge effect” increasing friction between the screw and plate

93
Q

How does an expansionhead locking screw work?

A

The larger expansionhead screw is inserted through the plate and into the bone - the smaller locking screw is then inserted into the expansionhead screw. The locking screw expands the head of the expansionhead screw so that it interlocks with the plate and creates a rigid construct.

94
Q

How does a blocking screw work?

A

A blocking screw is prevented from backing out of the plate by a secondary blocking mechanism however the blocking mechanism may not prevent motion at the plate to screw interface

95
Q

How does a blocking clip work?

A

A clip embedded inside a plate expands and snaps into a groove in the screwhead when the screw is inserted through the plate. This prevents the screw from backing out of the plate.

96
Q

________ and _______ screws provide greater resistance to pullout

A

Convergent and divergent

97
Q

Why do convergent and divergent screws provide greater resistance to pullout?

A

All of the bone tissue between the screws and plate must be overcome

98
Q

When screws are not locked to the plate, screw orientation does not have as much impact on pullout strength because the screws can ________

A

Reorient

99
Q

What are the three different thread profiles commonly found in locking caps

A

V-Thread
Buttress Thread
Square Thread

100
Q

A V-shape is not ideal for locking caps for what two reasons?

A

Easy crossthreading

Tend to exert force both outward in addition to downward

101
Q

What does a buttress thread prevent?

A

The right triangle threads prevent the thread from exerting outward force that could splay the screwhead

102
Q

What does a square thread provide more resistance to?

A

Cross-threading - they lack the sharp points that can cut into the opposing implant’s metal and are more likely to follow machined path

103
Q

What is more likely to exert outward force and cause splay, square or buttress thread?

A

Buttress thread

104
Q

What are three key considerations when selecting implant materials?

A

Elasticity
Effect on post-operative imaging
Biocompatibility

105
Q

Why are metal implants not ideal for CT/X-Ray?

A

Can’t assess fusion

106
Q

Why are metal implants not ideal for MRI?

A

MRI uses powerful magnets that can cause movement or heating in metal implants

107
Q

MR Safe implants are defined as implants that….

A

Pose no hazard

108
Q

MR Condition implants are defined as implants that…

A

Pose no hazard under certain conditions

109
Q

MR Unsafe implants are defined as implants that…

A

Pose a hazard

110
Q

Why is it never acceptable to leave instrument or instrument fragment in patient?

A

May not be MR Safe or Conditional

111
Q

What is an imaging concern with MRI?

A

Artifact causing signal loss (black spots) or image distortion around the implant making it difficult to asses the region surrounding for fusion or pathology

112
Q

When bone grows in and around an implant providing additional fixation

A

Osseointegration

113
Q

An alloy of iron with corrosion resistant properties

A

Stainless steel

114
Q

SS modulus of elasticity is _______ than titanium

A

Higher

115
Q

Implant grade _____ L stainless steel

A

316

116
Q

Stainless steel may create a _____ _____ or _____ effect in MRI images

A

Signal void, starburst effect

117
Q

Stainless steel does not osseointegrate

A

True

118
Q

Stainless steel has been implanted in humans for over _ decades

A

3 decades

119
Q

Some patients may be allergic to ____ in stainless steel

A

Nickel

120
Q

3 types of titanium used

A

Unalloyed
Commercially Pure
Alloyed with other metals

121
Q

The modulus of elasticity of CP Ti is _____ than SS

A

Lower

122
Q

What is the most common metal used in spinal implants?

A

CP Titanium

123
Q

CP Ti creates ____ interference in MRI imaging than SS

A

Less

124
Q

Titanium is exceedingly biocompatible, osseointegrates, and allergies are rare

A

True

125
Q

Titanium alloys are similar to CP TI in terms of elasticity, imaging, biocomp but may have greater tensile strength (max amount of strain before breaking)

A

True

126
Q

PEEK stands for…

A

Polyetheretherketone

127
Q

PEEK modulus of elasticity falls between that of cortical and cancellous bone

A

True

128
Q

PEEK does not osseointegrate and is instead…

A

Hydrophobic

129
Q

Cobalt chromium have a ______ modulus of elasticity than that of SS

A

Higher

130
Q

Ultra-high molecular weight polyethylene (UHMW) is a ______

A

Polymer

131
Q

PMMA stands for…

A

Polymethylmethylacrylate

132
Q

PMMA is a ____

A

Polymer

133
Q

PMMA modulus of elasticity is _____

A

Very high

134
Q

PMMA gives off what as it hardens

A

Heat

Spinal Anatomy (12 decks)

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