Internal Fixation of Spine Flashcards Preview

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Flashcards in Internal Fixation of Spine Deck (134):
1

What are the three main functions of the Spine?

Motion
Weight Transfer
Protection of Neural Elements

2

The vertebra is the _______, a rigid object that pivots

Level

3

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

Disc and facets

4

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

Muscles

5

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

Ligaments

6

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

Up

7

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

Two adjacent vertebral bodies and the intervening soft tissue

8

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

FSU/Motion Segment

9

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

Axial

10

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

Rotate, lateral bend, flexion, and extension

11

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

Frontal

12

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

Sagittal

13

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

Flexion, extension, rotation

14

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

80%

15

The spine is located _______ in the torso

Posteriorly

16

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

Curves

17

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

Bony cage

18

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

Ligaments

19

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

Nerves

20

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

Rubber bands

21

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

Cord

22

Define spinal instability

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

23

Two goals of spine surgery

Decompression
Restoration of stability

24

Define decompression

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

25

Define direct decompression

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

26

Define indirect decompression

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

27

Define restoration of stability

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

28

Define arthrodesis

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

29

What are the 5 steps for plate and screw constructs

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

30

What are two methods used to size a plate

Calipers, templates

31

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

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

32

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

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

33

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

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

34

What order should screw be inserted in a plate?

Alternating pattern to prevent tilting or lift off

35

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

Torque limiting driver

36

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

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

37

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

Drilling (with drill guide)
Probing (after perforation with awl)

38

When are holding sleeves especially important?

As incision get smaller with encroaching soft tissue

39

What are the 6 steps for an interbody fusion?

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

40

What is used to make an annulotomy?

Scalpel

41

What is used to separate disc material from endplate?

Periosteal elevator

42

What is used to pull out disc tissue?

Pituitary rongeur

43

What is used to scrape disc material from the bone?

Curette

44

What is used to remove bony osteophytes?

Kerrison rongeur

45

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

A rasp or high speed burr

46

Which allograft type should be thawed before implantation?

Frozen allograft

47

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

Freeze dried

48

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

Fracture

49

What are the 3 functions of a screw head?

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

50

What is the function of the screw shaft?

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

51

What are the two functions of the screw tip?

1. Can cut pathway for screw
2. Guides the screw into bone

52

What are the two main functions of a screw thread?

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

53

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

Pullout strength

54

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

1. Quality of bone
2. Thread design (more thread = better pullout strength)

55

The vertical distance between threads

Pitch

56

What two things does pitch affect?

1. Speed of insertion
2. Pullout strength

57

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

Pitch

58

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

Smaller pitch has more threads than greater pitch

59

The width of the shaft including the threads

Major diameter

60

The width of the shaft EXCLUDING the threads

Minor diameter

61

Describe the thread design on a cortical screw

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

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

Cortical

63

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

Cancellous

64

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

Larger

65

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

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

66

The threads on a cancellous screw are _______ and _______

Larger, sharp

67

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)

Dual core

68

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

Dual lead

69

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

Pullout strength

70

Partially threaded screws have two main advantages

Ability to lag
Tissue protection

71

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

Lag screw

72

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

Head

73

What prevents lagging in a plate construct?

Threads at plate to screw interface

74

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

Exposed, sharp

75

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

Drilling, tapping

76

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

Drilling or probing

77

What are the two different self-tapping screw designs?

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

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

Drilling or tapping

79

A self-drilling screw will always follow what?

The path of least resistance

80

Self-drilling screws have what type of tip?

A sharp, pointy tip

81

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

A hole using an awl

82

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

Load bearing

83

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

Stress shielding

84

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

Load sharing

85

Define modulus of elasticity

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

86

What is the ideal material for a spinal implant?

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

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

Bearing

88

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

Locking screw rigidly connected to plate
Blocking screw prevented from backing out of plate by secondary blocking mechanism

89

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)

Locking

90

What are the two common locking screw designs?

Conical locking screw
Expansionhead screw

91

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

Conical locking screw

92

How does a conical locking screw work?

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

How does an expansionhead locking screw work?

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

How does a blocking screw work?

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

How does a blocking clip work?

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

________ and _______ screws provide greater resistance to pullout

Convergent and divergent

97

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

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

98

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

Reorient

99

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

V-Thread
Buttress Thread
Square Thread

100

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

Easy crossthreading
Tend to exert force both outward in addition to downward

101

What does a buttress thread prevent?

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

102

What does a square thread provide more resistance to?

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

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

Buttress thread

104

What are three key considerations when selecting implant materials?

Elasticity
Effect on post-operative imaging
Biocompatibility

105

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

Can't assess fusion

106

Why are metal implants not ideal for MRI?

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

107

MR Safe implants are defined as implants that....

Pose no hazard

108

MR Condition implants are defined as implants that...

Pose no hazard under certain conditions

109

MR Unsafe implants are defined as implants that...

Pose a hazard

110

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

May not be MR Safe or Conditional

111

What is an imaging concern with MRI?

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

When bone grows in and around an implant providing additional fixation

Osseointegration

113

An alloy of iron with corrosion resistant properties

Stainless steel

114

SS modulus of elasticity is _______ than titanium

Higher

115

Implant grade _____ L stainless steel

316

116

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

Signal void, starburst effect

117

Stainless steel does not osseointegrate

True

118

Stainless steel has been implanted in humans for over _ decades

3 decades

119

Some patients may be allergic to ____ in stainless steel

Nickel

120

3 types of titanium used

Unalloyed
Commercially Pure
Alloyed with other metals

121

The modulus of elasticity of CP Ti is _____ than SS

Lower

122

What is the most common metal used in spinal implants?

CP Titanium

123

CP Ti creates ____ interference in MRI imaging than SS

Less

124

Titanium is exceedingly biocompatible, osseointegrates, and allergies are rare

True

125

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)

True

126

PEEK stands for...

Polyetheretherketone

127

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

True

128

PEEK does not osseointegrate and is instead...

Hydrophobic

129

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

Higher

130

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

Polymer

131

PMMA stands for...

Polymethylmethylacrylate

132

PMMA is a ____

Polymer

133

PMMA modulus of elasticity is _____

Very high

134

PMMA gives off what as it hardens

Heat