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Musculoskeletal > SA MS 2: Fracture Biomechanics And Classification > Flashcards

SA MS 2: Fracture Biomechanics And Classification Flashcards

1
Q

Bones

A

Subjected to many forces (which are often combined) during normal function

When magnitude of these forces exceeds ultimate strength of the bone, fracture will occur

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2
Q

Forces that cause fractures

A

Bending, torsion, compression, tension

Same forces must be neutralized when repairing fracture
Geometry of the fracture and the location of the muscle groups attached to the fragment involved will determine which forces predominate in the fractured bone

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3
Q

Bending

A

Bending force acts to move the ends of the bone out of line with the bone’s long axis
—all fractures have some tendency to bend

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4
Q

Torsion

A

Tendency for a bone or its pieces to twist around the bone’s long axis

Produces rotation of the fragments

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5
Q

Compression

A

Acts along the long axis of the bone to move the ends of the bone toward each other

Often causes fragments to override

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6
Q

Shearing

A

Component of compression
Acts within bone or bone fragments
Essentially tendency of two pieces to slide past each other

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7
Q

Tension

A

Acts along longitudinal axis of the bone but pulls ends away from each other, producing distraction

  • -negative form of compression
  • -Causes avulsion fractures of the apophyses like the olecranon and the calcaneus
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8
Q

Shape of the bone

A

Has some influence on the fracture pattern that will result when excessive force is applied

Fracture pattern more dependent on the orientation of the forces that caused the fracture and the relative strength of the bone in each loading orientation

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9
Q

Compressive forces result in?

A

OBLIQUE FRACTURES!

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10
Q

Tensile forces result in?

A

TRANSVERSE FRACTURES

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11
Q

Why do compressive forces result in oblique fractures?

A

Bone, as as result of osteonal and collagen fiber arrangement, = dramatically weaker in shear than in compression

When loaded in compression, bone fails along lines of highest shear stress rather than compressive stress - lines tend to be at an angle of 30-45 degrees to the direction of the compressive force

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12
Q

Why do tensile forces result in transverse fractures?

A

Transverse fractures = approx perpendicular to the direction of loading
Fractures resulting from pure tensile forces = rare (most w/ bending)
–influenced by bone shape
–location and shape of physis in immature bone

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13
Q

Bending forces result in what type of fracture?

A

TRANSVERSE FRACTURES

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14
Q

Why do bending forces result in transverse fractures?

A

When bone subjected to bending force, convex side = under tension, concave side under compression
–Neutral axis lies somewhere toward the center of the bone
Because bone weaker in tension than compression, fracture begins on the tension surface and propagates toward the compressive surface

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15
Q

Bones loaded in bending and compression

A

Suffer combo of bending and compressive patterns

Often as the crack propagates from the tension to the compressive surface, it splits and deviates proximally and distally along the shear stress line, creating a butterfly fragment on the compressive side

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16
Q

Torsional forces result in which types of fractures?

A

SPIRAL FRACTURES!

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17
Q

How do torsional forces cause spiral fractures?

A

Initiated by the formation of a crack along the long axis of the bone

Crack then spirals - starts at one end of the longitudinal crack, through the bone along the 45 degree shear stress planes, until winds up back at the originating longitudinal crack, completing spiral with longitudinal fracture segment

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18
Q

Loading rate

A

Influences appearance and severity of fracture patterns
–ie whether a fracture is simple or highly comminuted depends not just on the magnitude of the specific force but also how fast the force is applied

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19
Q

Bone as viscoelastic material

A

Strength of bone depends on the rate at which it is loaded

  • -bone = stronger when loaded rapidly than when loaded slowly
  • -if force applied slowly, less of it can be absorbed before the bone deforms and breaks
  • -if force applied rapidly, more energy is absorbed before the bone finally breaks but when it does break, it shatters because has absorbed so much energy
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20
Q

Highly comminuted fractures

A

Product of relatively more energy absorption/faster loading than simple fractures are
Tend to be associated with a lot more concomitant ST damage

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21
Q

How classify fractures

A

-extent of ST injury
-degree of cortical disruption
-geometry
-location within the bone
-degree and direction of displacement
+/- underlying cause

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22
Q

ST disruption: closed

A

No wound connecting the bone to the outside world

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23
Q

ST disruption: open

A

There IS a wound connecting the bone to the outside world

- four types

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24
Q

ST disruption: open Type I

A

Open fracture
Small laceration (<1cm)
Clean

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25
Q

ST disruption: open Type II

A

Open fracture
Larger laceration (>1cm)
Mild ST trauma
No flaps/avulsions

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26
Q

ST disruption: open Type IIIa

A

Open fracture
Vast ST laceration or flaps or high energy trauma
ST available for wound coverage

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27
Q

ST disruption: open Type IIIb

A

Open fracture
Extensive ST injury loss
Bone exposure present
Periosteum stripped away from bone

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28
Q

ST disruption: open Type IIIc

A

Open fracture
Arterial supply to the distal limb damaged
+/- arterial repair required for limb to salvage

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29
Q

Extent of Cortical Disruption

A
  1. Greenstick
  2. Fissure
  3. Complete
  4. Depressed
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30
Q

Extent of Cortical Disruption: greenstick

A

Bending fracture
Cortex doesn’t break all the way through but the bone deforms relative to its longitudinal axis
–usually a fracture of young animals

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31
Q

Extent of Cortical Disruption: Fissure

A

Crack

Only involves one side of he bone (one cortex) and it’s usually longitudinally oriented

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32
Q

Extent of Cortical Disruption: Complete

A

Both cortices disrupted

Fracture goes all the way through the bone resulting in 2 separate fragments

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33
Q

Extent of Cortical Disruption: depressed

A

When a fracture segment is displaced into the cavity it once formed a wall of - sinuses, skulls

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34
Q

Geometry of fracture lines: transverse

A

Fracture perpendicular to the long axis of the bone

Rotation of fragments = big problem with this one

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35
Q

Geometry of fracture lines: oblique

A

Fracture occurs at an angle greater than 30 degrees to the long axis of the bone
–can be short or long
–long oblique fracture = one in which the length of the fracture line equals or exceeds twice the diameter of the bone at this point
Compression: major issue with this fracture type (fragments shear past each other)

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36
Q

Geometry of fracture lines: spiral

A

Fracture line curves around the diaphysis

Acts a lot like an oblique fracture

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37
Q

Geometry of fracture lines: comminuted

A 
More than 2 pieces 
Fractures have zero inherent stability
Types:
--butterfly
--highly comminuted 
--segmental 
--multiple
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38
Q

Comminuted: butterfly

A

Aka wedge –> wedge shaped chunk of bone broken off but the proximal and distal fragments still touch each other at some point

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39
Q

Highly comminuted

A

Bunch of pieces
Ex of a complex fracture
Pieces should share a common fracture line

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40
Q

Comminuted: segmental

A

Section interposed between the most proximal and the most distal fragments so they can’t touch
Pieces that do not share a common fracture line

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41
Q

Comminuted: multiple

A

Segmental fracture in which the interposed segment is in more than one piece
Ex of a complex fracture

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42
Q

Location within the bone: articular

A

Fracture involving joint surface

43
Q

Location within the bone: physeal

A

Fracture involving the growth plate

6 types

44
Q

Location within the bone: physeal SH Type I

A

Fractures run through physis

45
Q

Location within the bone: physeal SH Type II

A

Fractures run through physis and portion of metaphysis

46
Q

Location within the bone: physeal SH Type III

A

Fractures run through physis and epiphysis

Generally IA

47
Q

Location within the bone: physeal SH Type IV

A

IA, run through epiphysis, across the physis, and through the metaphysis

48
Q

Location within the bone: physeal SH Type V

A

Crushing of physis which is not visible radiographically but is evident several weeks later when physeal growth closes

49
Q

Location within the bone: physeal SH Type VI

A

Partial physeal closure resulting from damage to a portion of the physis

50
Q

Location within the bone: metaphyseal

A

Fracture involving the metaphysis

51
Q

Location within the bone: diaphyseal

A

Usually will specify whether fracture in the proximal, middle or distal third of the diaphysis

52
Q

Location within the bone: condylar, supracondylar, subtrochanteric

A

If there’s a part of the bone with a cool anatomic name, you correctly remember it, and the fracture involves it or is near to it, then show off a little

53
Q

Displacement: non-displaced

A

Bone fractured but pieces flying close in formation in their proper alignment
Suggests there is still an intact periosteal sleeve holding them together

54
Q

Displaced

A

Pieces not in usual alignment
Displacement described by referring to the distal fragment’s location relative to the proximal fragment
–Ex: if the distal piece is caudal and lateral to the proximal fragment, then you say the fracture has a CD-L displacement

55
Q

Causes

A
  1. Traumatic
  2. Pathologic
  3. Fatigue
  4. Iatrogenic
56
Q

Cause: Traumatic

A

Force may either be direct (blow from outside) or indirect (w/ bone fixed or planted in a certain position, such as when an animal’s own muscles break the bone)

57
Q

Cause Pathologic

A

Something wrong with the bone that weakens it to the point that otherwise normal, ordinary forces placed upon it will cause it to fracture

  • -osteopenia in humans
  • -neoplasia in animals
58
Q

Cause: Fatigue

A

Caused by repetition of forces that wouldn’t be sufficient too break the bone in a single application - racing greyhounds

59
Q

Iatrogenic

A

Create these by using screws that are a little too large when fix another fracture

60
Q

Why care about fracture classification and forces?

A

Type and location of fracture has very strong influence on how easily it will heal, how likely it is that nasty complications like IFX, quadriceps tie-down and OA will appear and what kind of repair is appropriate (or possible) to perform
–Goal: choose form of fracture fixation that effectively neutralizes forces that will be acting on your fracture once it has been reduced

61
Q

Casts and splints

A

Good for controlling bending

Help control rotation if fit well

62
Q

Wires

A

Help control tension (while producing compression themselves) but terrible at controlling all the other forces - should almost never be used by themselves

63
Q

Intramedullary pins

A

Control bending

64
Q

Three repair mechanisms that control all of the forces?

A
  1. Bone plates
  2. Interlocking nails
  3. External fixators
65
Q

Bone plates, external fixators, interlocking nails

A

Pretty good at controlling all of the forces providing you’ve chosen hardware that’s strong enough and in proper placement and configuration

66
Q

External Coapation: def

A

Immobilization of a body part with externally applied support

Ex: casts, splints, braces, bandages

67
Q

External Coapation: Forces neutralized

A

Bending forces - depends on how rigid a form of compaction you’ve chosen
Torsion - fair, depending on how form-fitting coapation is
DOES NOT CONTROL COMPRESSION AND TENSION

68
Q

External Coapation: +

A

Minimal disruption of blood supply (assuming applied correctly)
Minimal effect on physeal growth
Initial application often cheaper than sx repair
–frequent bandage changes and rechecked may make total cost comparable to sx

69
Q

External Coapation: -

A

Poor control over compressive and distractive forces
Less rigid stabilization than internal or external fixation
Alignment and reduction may be difficult to achieve in a closed fashion - generally only obtainable with incomplete or transverse fractures
Joints above and below must be immobilized
–jt immobilization can lead to jt stiffening and arthritic changes

70
Q

Internal Fixation

A 
Fracture repair by means of stabilization apparatus that is somehow directly attached to the bone 
--Can provide more rigid stabilization than external coaptation does 
Ex:
1. IM pins 
2. Cross pins 
3. Cerclage wire 
4. Tension bandage wiring 
5. Locked IM nail
6. Plates and screws 
7. External skeletal fixator
71
Q

Intramedullary (IM) Pins

A

Rods that stabilize broken bones by passing longitudinally within medullary canal, providing support very close to the neutral axis of the bone

72
Q

Intramedullary (IM) Pins: forces neutralized

A

BENDING ONLY

73
Q

Intramedullary (IM) Pins: +

A

Availability:
–cheap, readily available, don’t req fancy equip to place
Axial alignment:
–fracture fragments skewered along linear rod, good axial alignment easy to achieve
Bending control

74
Q

Intramedullary Pins: -

A

Only control bending
Anatomic repair req’d
Potential injury to surrounding structures from pin placement/migration
Inadequate for repair of certain bones - flat bones, radius*

75
Q

Cross Pins

A

Similar to IM pins

Placed so that they cross the two cortices as well as the fx line

76
Q

Cross Pins: forces neutralized

A

Mod effective for bending

Better than IM pins for torsion, compression

77
Q

When appropriate?

A

Most freq used for repairing physeal or very distal/prox physeal fractures

78
Q

Cerclage Wire

A

Added to other types of repair to:

  • -prevent propagation of fissure
  • -reconstruct fragments to aid in fx reduction
  • -hold fx in reduction while definitive repair applied
79
Q

Cerlage wire - forces neutralized

A

Help control torsion/compression when main form of repair is an IM pin
do NOT provide much bending control

80
Q

Tension Band Wiring

A

Involves placing 2 small, parallel pins perpendicular to fx line
Figure of 8 wire then passed through hole distal to fx, around the protruding ends of pin, and tightened

81
Q

Tension Band Wiring - Forces neutralized

A

Counteracts tensile forces

Converts them to compressive forces at a transverse fx site to favor direct bone union

82
Q

Locked IM Nail

A

Special rod placed within medullary canal –> fixed with screws that pass from outside the bone, through holes in the rod, and back out thru cortex of bone

83
Q

Locked IM Nail - Forces Neutralized

A

Very strong countering bending forces
Screws = quite strong against compression, tension, torsion
–prevent nail from migration

84
Q

Locked IM Nail +

A

Fixing comminuted fx w/o req anatomic reconstruct
Moderately less disruptive of blood supply
Not usually removed

85
Q

Locked IM Nail -

A

Used almost exclusively at femur, humerus, tibia

Cannot be applied to radis

86
Q

Plates and Screws

A

Bone plates = screwed directly onto the fx’d bone so that the screws transfer the forces of WB from the bone to the plate by increasing friction btw the 2

  • -better the friction btw plate and bone, stronger plate/bone/screw construct is
  • -Most plates need to be closely contoured to fit the bone
87
Q

Locking Plates

A

When screws not only lock into the bone but also the plate
Little internal external fixators
Very strong
Don’t need to be closely contoured to the bone –> can be less invasive

88
Q

Plates, Screws Forces Neutralized

A

ALL!
Screws alone control torsion and compression or tension
Very strong fx repair = IM pin + plate

89
Q

Screws, Plates +

A

Anatomic reconstruct not necessary
Plate sits directly against bone surface –> entirely buried, can be used in areas w/ lots of overlying muscle
Very little intervention by o - usually do not req removal

90
Q

Screws, Plates -

A

Req most bone exposure –> most disruptive to the blood supply
Screw placement dictated by location of preformed holes in the plate = difficult or impossible to capture very short prox or distal fragments w/ minimum # of screws necessary for stability
If IFX - plate must be removed once bone is healed.

91
Q

External Skeletal Fixator

A

Splints a bone by passing fixation pins from outside of the body and through both cortices of the bone in a more or less transverse fashion
–pins then attached to at least 1 external connecting bar
Can be combined w/ IM pin –> aids in alignment of fragments, controls bending

92
Q

External Skeletal Fixator Forces Neutralized

A

ALL!

93
Q

Main Goal for Tx of Any Fx

A

Early return of patient to full fxn

94
Q

Fx Fixation Should

A
  1. Restore limb alignment

2. Stabilize fracture

95
Q

What should you consider when planning fx repair?

A
  • Age of P
  • Wgt
  • Concurrent injuries
  • Overall health of animal
  • expected activity level/intended use of the animal
  • Ability of owner to provide post-op care
96
Q

Reconstruction

A

Permits load sharing btw implants and the bone

Protects implants from fatigue and early failure

97
Q

Biologic Environment

A

Young animals w/ active periosteum and metaphyseal fx - quick to heal in most situations
Comminuted high energy fractures may have impaired vascularity –> longer healing times anticipated
Geriatric or debilitated animals/animals with substantial ST injury will experience prolonged healing times = stable implants for longer period of time

98
Q

Indications for Anatomic Reconstruction

A
  1. Articular fx
  2. Simple fx
  3. Fx w/ 2 or 3 lrg segments
99
Q

Indications for Major Segment Alignment

A

Severely comminuted fx: tx w/ plates, plate-rod combos, locked IM nails, or external fixators

100
Q

Open Reduction

A

Allows for bone grafting and anatomical reconstruction of articular and comminuted fx

  • -prolongs sx time
  • -impairs blood supply
101
Q

Closed Reduction

A

Utilizes indirect reduction
–alignment of fragments by distraction of bone ends
Preserves blood supply/biology of fx
–Comes at cost of fx alignment
Best for minimally displaced or incomplete fx or for comminuted fx tx’d w/ external fixation

102
Q

Indications for Open Reduction

A
  1. Articular fx
  2. Simple displaced fx
  3. Communities fx tx’d by major segment alignment and cancellous bone grafting
103
Q

Indications for Closed Reduction

A
  1. Non-displaced or incomplete fx

2. Comminuted fx tx’d w/ external fixation

104
Q

Fx Planning Checklist

A 
Decide on appropriate fixation based on fx and patient assessment 
Plan fx reduction 
Plan fx fixation 
Select sx approach(es)
Check implant inventory 
Perform dx 
Critically eval post-op RADS

Musculoskeletal (10 decks)

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