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Recon > Internal Fixation > Flashcards

Internal Fixation Flashcards

1
Q

What were the initial conclusions on bone healing

A
  • rigid internal compression fixation is ideal
  • intact vasculature and bio mechanical stability are prerequisites for bone healing
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2
Q

what is the revised conclusion on bone healing

A

Fixation is based on the biology and personality of the fracture

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3
Q

What are the stages in bone healing?

A

Inflammation —> Regeneration/repair—> remodeling

Fracture & Hemorrhage —> hematoma necrosis —> soft callus to hard callus —> Haversian remodeling lamella (woven) primary bone

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4
Q

What components contribute to bio mechanical stability of a fracture

A
  • intrinsic factors
  • extrinsic factors
  • mechanical forces of fixation
  • techniques of fixation
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5
Q

What are the aspects of intrinsic factors

A
  • fragment size
  • bone quality
  • fracture orientation (transverse, oblique, comminuted)
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6
Q

What are the extrinsic forces that contribute to fracture stability

A
  • compression (axially mediated)
  • bending
  • torsion (side to side)
  • shear
  • weight bearing - osseous motion
  • muscle/tendon movement
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7
Q

Based on fixation principles, what are the 2 ways of achieving stability

A
  • stability by compression of fracture ends
  • stability by inherent by splintage
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8
Q

What are the different types of stability by compression

A
  • lag (by design or by technique)
  • axial compression
  • tension band
  • compressions staples
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9
Q

What are some components of stability by splintage

A
  • buttress and anti glide (load bearing)
  • bridge plates
  • neutralization (load sharing)
  • intramedullary nailing
  • blade plates
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10
Q

What is the importance of the head of the screw

A

Driving mechanism

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11
Q

What is the land of the screw

A

Underside of the head

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12
Q

What is the pitch of the screw

A

Distance between threads

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13
Q

What is the core of the screw

A

The minor diameter

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14
Q

What is the importance of increasing core diameter

A

Increase bending resistance

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15
Q

What is the screw thread

A

The major diameter

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16
Q

at is the importance of increase screw thread

A

Better purchase in cancellous bone

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17
Q

Hat is the shaft of the screw

A

The region devoid of threads

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18
Q

What is the run out of the screw

A

Where the shaft meets the threads

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19
Q

What is the weakest point of the screw

A

The run out

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20
Q

What are the 2 different types of screw tips

A
  • non self drilling
  • self drilling
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21
Q

What are the types of non self drilling screws

A
  • round
  • pointed
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22
Q

What are the types of self drilling screws

A
  • fluted
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23
Q

In relation to a fracture line, how should you position the runout of the screw

A

Place runout as far as possible from the fracture line

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24
Q

What are the screw sizes in the mini fragment

A
  • 1.5mm
  • 2.0mm
  • 2.7mm
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25
Q

What surgery would you typically use mini fragment screws

A
  • forefoot surgery
  • Talar neck dx
  • cuboid dx
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26
Q

What are the sizes of screws in the small fragmen

A
  • 3.5mm
  • 4.0mm
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27
Q

What surgery would you typically use small fragment screws

A
  • lisfranc fx’
  • calcaneal fix
  • ankle dx
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28
Q

What are the screw sizes in the large fragment

A
  • 4.5 mm
  • 6mm
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29
Q

What type of surgery would you typically use screws from the large fragment

A
  • hindfoot fusion procedures
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30
Q

Why is the design of the screw threads important

A

Influences screw purchase into bone

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31
Q

What is the thread angle

A

Determines the rate at which screw advances into bone

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32
Q

What is a similarity between buttress and V thread

A

Equal pull out strength

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33
Q

What are the differences between buttress (asymmetrical thread) and V thread

A

Buttress maximizes bone volumes between threads and increases bending resistance

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34
Q

Which type of screws have smaller pitches

A

Cortical screws

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35
Q

What is the purpose of cortical screws having smaller pitch

A

Maximize contact in short segment (cortical thickness) dense and compact bone

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36
Q

What is the purpose of cancellous screws having larger pitch

A

Increase limited bone volume between threads to maximize contact

37
Q

What are some disadvantages of a cannulated scree

A
  • decreased thread to core ratio
  • lower pullout strength
  • reduced bending stiffness
38
Q

What is a disadvantage of headed screws

A

Prominence

39
Q

What is an advantage of headed screws

A

Larger contact surface area, increase contact area to improve compression

40
Q

Does a headed screw have threads in the head and does the head advance into bone

A

No threads in head and head does not advance into bone

41
Q

Do headless screws have threads in the head and does the head advance into the bone

A

Yes heads have thread and head advances into the bone

42
Q

What is the lag effect

A

Compression along bone ends

43
Q

What is entailed in lag effect by technique

A
  • fully threaded screw
  • gliding hole: larger overdrive the near cortex, but not past the fracture site
  • smaller underdrill the near and far cortex
  • head of screw must be in contact with near cortex, and not penetrate near cortex
  • compression will be lost if not perpendicular to fracture or greater than 22 degrees to line orthogonal to fracture
44
Q

What are the three different techniques of the lag effect

A
  • standard
  • small fragment
  • compromise technique
45
Q

What is the standard lag technique

A

Overdrill near cortex first, then underdrill near and far cortices

46
Q

What is the small fragment lag technique

A

Underdrill near and far cortex first, then overdrill near cortex

47
Q

What is the compromise technique of the lag effect

A

No overdrill
- uses a clamp
- compression captured by a positional screw

48
Q

What are two categories of plate deigns

A
  • locking versus non-locking
  • stainless steel versus titanium
49
Q

What are the plating by function categories

A
  • neutralization
  • bridge
  • anti glide/buttress
  • dynamic compression
50
Q

In convention plating how is stability obtained

A
  • screw torque (3-5N) squeezes plate onto bone
  • bone to plate apposition
51
Q

How is coefficient of friction generated

A
  • squeezing plate onto the bone
52
Q

In conventional plating, what is the load

A

Any axially mediated forces that would cause the plate to fail

53
Q

What happens if coefficient of friction is greater than the load

A

Plate remains stable

54
Q

What happens if the load is greater than the coefficient of friction

A

The plate fails

55
Q

What are two important points for bone to plate apposition

A
  • coefficient of friction&raquo_space; load
  • screw purchase dependent on quality of bone
56
Q

What is the importance of conventional plating

A
  • promote primary bone healing
57
Q

What are locking screws

A
  • plate screws with threads in the head
  • “lock” into plates (head is recessed)
  • does not compress plate into bone
58
Q

Describe the angle of locking screws

A

Fixed angle

59
Q

Locking screws act as ________ fixators. Why?

A

Internal fixators
-Screw lengths 10.15 times shorter than external fixators pins

60
Q

What type of bone healing does locking screws promote

A

Secondary bone healing

61
Q

What type of beams do locking screws have and how does this compare to other types of beams

A
  • single beam
  • 4 times stronger than load sharing beams where motion occurs between individual components
62
Q

What are some pros of locked plating

A
  • improved fixation in pathological and osteopenic bone
  • reduction in scre loosening
  • spares periosteral perfusion
  • convert sheer stress to compressive stress at screw-bone interface
  • confers relative stability to promote secondary bone healing
63
Q

The strength of locking plates is dependent on:

A

Screw diameter
Plate thickness

64
Q

Which type of plating, conventional or locking, have a higher failure threshold

A

Locking

65
Q

Are neutralization plates for load bearing or load sharing

A

Load sharing

66
Q

What types of loads are neutralization meant to resist

A
  • bending
  • rotational/torsional
  • axial/shear
67
Q

Is the antiglide plate load bearing or load sharing

A

Load bearin

68
Q

Where is an antiglide plate placed in relation to a fraction

A

Over the apex of the fracture, the direction it wants to fail towards

69
Q

What type of forces do antiglide plates counter

A
  • shear forces looking to overcome the coefficient of friction
70
Q

What does the antipglide plates do to shear forces

A

Converts it to compressive axial forces - biomechanically strong

71
Q

What is buttress plating

A

A support structure built against a wall

72
Q

What makes buttress plating different from antiglide plating

A

Buttress plating is antiglide plates used with intra and peri articulation fractures

73
Q

Can load bypass the fracture in buttress plating

A

No

74
Q

What is one importance of buttress plating

A
  • helps maintain length and alignment
75
Q

What is bridge plating

A

Plating spanning an area of comminution

76
Q

What is dynamic compression plating

A

Plate generated compression

77
Q

What is dynamic compression plating indicated for

A
  • short transverse fractures
  • short oblique
78
Q

Where ideally are your screws in compression plating

A
  • towards the further ends of the hole, not dead center in the screw hole
79
Q

Why do you have to pre-bend/pre-stress the plate in compression plating

A

Because the screws causes the far cortex to gap open
Ie it prevents gapping of opposite cortex

80
Q

What re examined if fused angle constructs

A
  • staples
  • blade plate -needs a good construct, don’t use in porotic bone
81
Q

Although intrameduallary nailing acts like a splint, what do you have to be aware of

A
  • no compression
  • increase risk of mal Union
82
Q

Which plating is intramedullary nailing most similar to

A

Bridge plate

83
Q

What type of forces are intrameduallary nailing strong against

A

Bendin

84
Q

What type of forces are intrameduallary nailing weak against

A

Axial rotation

85
Q

One biological benefit of intramedullary nailing

A

Preserves periostea’s perfusion

86
Q

What are some indications of intramedullary nailing

A
  • concerns with soft tissue healing
  • comminuted shaft fractures
  • Charcot
  • geriatric ankle/tibial fractures
  • TibioTalarCalcaneal fusion
  • TibioCalcaneal fusion
87
Q

What type of nails are recommended for tibial canal

A

Long thick nails

88
Q

What kind of torque and speed for cannulated drill over guidewire through Calcaneus and guidewire

A

Low torque, high speed

89
Q

What kind of torque and speed for sequential reading of tibial canal over guidewire

A

High torque low speed

Recon (10 decks)

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