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Ross Small Animal Surgery > Fracture Repair > Flashcards

Fracture Repair Flashcards

1
Q

What is the difference between stress and strain?

A

Stress: external force applied to any cross sectional area (cause of strain)
Strain: deformation of a loaded material as compared to its original form, typically measured in length (effect of stress)

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2
Q

What are the 3 types of strain a bone can experience?

How might they combine?

A
  1. Tensile – force to pull, increasing length of an object (eg. slinky)
  2. Compressive – force to push, decreasing length of an object (eg. memory foam)
  3. Shear – lateral forces in opposite directions

Combination of tensile and compressive forces on opposite sides bending
Combination of compressive, tensile, and shear forces torsion

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3
Q

What is the difference between elastic and plastic deformation?

A

Elastic - reversible change in shape

Plastic - permanent change in shape

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4
Q

What is porosity and how does it relate to deformation of bone?

A

Ratio of volume of open space to volume of total bone

High porosity (eg. cancellous bone) - long elastic phase and lower yield point
Low porosity (eg. cortical bone) - steep and short plastic phase (brittle)
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5
Q

What is viscoelasticity?

A

increased speed of loading (stress application) increases material stiffness

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6
Q

What is anisotropicity?

A

elastic modulus is dependent on the direction of loading

eg. bone is stronger and stiffer in compression, and weakest when shear stress is applied

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7
Q

What is the yield point and the failure point on a stress-strain curve?

A

Yield point - material begins to deform plastically (switch from elastic to plastic)

Failure point - material cannot withstain any more strain and fails

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8
Q

What are the differences in severity between the open fracture grades?

A

Type I – wound smaller than 1cm in the area where bone is fractured (bone may or may not be showing)
o Typically created by bone fragment from inside that retracts back through skin
o Mild/moderate soft tissue contusion
o Likely would not change surgical plan, but would require preventative antibiotics

Type II – open wound >1cm in size
o Typically created by an external source (eg. bite wounds)
o Mild soft tissue trauma without extensive soft tissue damage
o No flaps or avulsions of soft tissues

Type III
o IIIA – adequate soft tissue for wound coverage, large ST laceration/flap
o IIIB – extensive ST loss, bone exposure, stripped periosteum (shiny layer gone)
o IIIC – arterial +/- nerve supply to distal limb compromised, requires microvascular anastomosis or amputation

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9
Q

What is the most common complication associated with open fractures?

A

Osteomyelitis/deep infection

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10
Q

What is the appropriate order of steps when assessing and initially treating an open fracture?

A
  1. Systemic stabilization
    o Cover wound with sterile dressing and evaluate better once patient is stable
    o Remember that nosocomial organisms are far more virulent than what’s already in there

Remember to wear gloves!

  1. Assess tissue damage, vascular and nerve supply
  2. Assess neurovascular status of distal limb (may be difficult if analgesics on board)
  3. Imaging
  4. Clip and clean wound –> collect culture –> start treatment with Cefazolin (pending culture results)
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11
Q

What is the antibiotic of choice when treating an open fracture (awaiting culture results)?

A

Cefazolin

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12
Q

What are the 5 components of describing a fracture?

A
  1. Bone and side
  2. Open vs closed
  3. Location on bone
    - epiphyseal
    - metaphyseal
    - diaphyseal
    - physeal (aka Salter harris)
    - articular
  4. Shape/configuration
    - transverse
    - oblique (short or long, >2.0x diameter of diaphysis)
    - spiral
    - comminuted (reducible or not)
  5. Displacement
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13
Q

What is the grading system for Salter Harris fractures?

A
  1. Physis (prison) - across
  2. Metaphysis (makes) - across and up
  3. Epiphysis (every) - across and down
  4. Both metaphysis and epiphysis (both) - straight up/down
  5. Crush (crazy)
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14
Q

What are the four goals of fracture fixation

A
  1. Restore length and alignment to promote normal bone healing and limb function
  2. Minimize motion at fracture ends
  3. Permit early ambulation with use of as many joints as possible during healing period
  4. Balance the forces that promote bone healing vs. those that promote bone resorption
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15
Q

What are the pros and cons of internal fixation?

A

Pros:
♣ Variety of fixation options to promote stable repair
♣ Can promote normal muscle/joint function during bone healing
♣ Typically fewer rechecks than with external coaptation (exception is external fixation)
♣ Nothing externally to monitor (internal fixation)

Cons:
♣ Expense to clinic and owner (lots of specialized equipment)
♣ Requires training for appropriate application
♣ May require second surgery for explantation

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16
Q

What are the pros and cons of external coaptation (casting)?

A

Pros:
♣ Limited supplies necessary for placement
♣ Need for highly specialized training is limited
♣ Avoids prolonged surgical procedure

Cons:
♣ Requires frequent rechecks and bandage changes
♣ Limited effective applications
♣ Risk of bandage morbidity preventing continued use
♣ Immobilized joints (one above and one below fracture)

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17
Q

What is Wolff’s law?

Why is it important in regards to fracture fixation?

A

Wolff’s law: bone remodels based on the forces that are applied (thickens in response to increased forces, weakens in response to decreased forces)

Weight bearing is important in order to stimulate bone regrowth
o Fixation must provide stability but cannot bear the majority of forces on the bone

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18
Q

What are the indications and contraindications for external coaptation?

A
  1. Fractures below the knee or elbow
    ♣ Should be minimally displaced and amenable to reduction transverse, simple, closed
  2. Non-articular fractures
  3. Fractures expected to heal rapidly (eg. greenstick fractures)

NOT appropriate for femoral / humeral fractures (cannot immobilize the joint above)
NOT appropriate for open fractures (EVER)

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19
Q

What is open anatomic reduction?

Where is it required and where is it contraindicated?

A

Primary bone healing (

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20
Q

What is biological osteosynthesis?

What are the two protocols for it?

A

Secondary healing
o Avoid disruption of fracture hematoma (minimal iatrogenic trauma)
o Less rigid fixation

Protocol 1 – open but do not touch
♣ Fracture is surgically approached and visualized
♣ Fracture ends are NOT manipulated during placement of implants

Protocol 2 – minimally invasive plate osteosynthesis (MIPO)
♣ Implants are placed through incisions distant to the fracture
♣ Intra-operative fluoroscopy is used to guide placement of implants
♣ Steep learning curve

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21
Q

Which plate types can be used to achieve compression of a fracture?

A

Dynamic compression plates

Limited contact DCPs

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22
Q

What types of fractures are amenable to being compressed without risking displacement or further bone damage?

A

Simple, non-comminuted fractures

Articular fractures

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23
Q

Why must conventional plates be perfectly contoured to the bone on which they are applied?

A

Friction between bone and plate creates stability

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24
Q

Why do locking plates not need to be contoured to the bone?

A

Threaded locking screw heads lock into threaded screw holes on plate

25
Q

What parameter determines the maximum size of screws to be placed in diaphyseal bone?

A

Screw diameter should not exceed 40% of bone diameter

26
Q

What is a lag screw?

A

A screw placed perpendicular across an oblique or sagittal fracture line to promote compression of the fracture ends

27
Q

What are the indications for placing a lag screw?

A

Certain articular fractures / oblique fractures

Goal is to achieve anatomic reduction

28
Q

How does a position screw differ from a lag screw?

A

Position screws are placed across a fracture line to hold two fragments in place, but NO compression across the fracture is achieved
Weaker repair

29
Q

Why are cancellous screws better for use in cancellous/metaphyseal bone?

A

Improved pull-out strength due to:

  1. larger outer diameter
  2. deeper thread
  3. larger pitch
30
Q

Which type of screw is the strongest under bending stress? Why?

A

Cortical

Highest core diameter

31
Q

On which side of the bone should plates be placed?

A

Tension side of the bone

32
Q

How much ‘screw purchase’ needs to be achieved for conventional vs. locking plates?

A

Conventional: 6 cortices above and below
Locking: 4 cortices above and below

33
Q

Describe compression mode of plate application

A

Used for transverse or short oblique fractures where anatomic reduction is desired
Requires a compression plate (DCP / LC-DCP) with eccentric screw placement

34
Q

Describe neutralization mode of plate application

A

Plate is used to supplement (stabilize) other primary repair (lag screws, cerclage wire, etc.)

35
Q

Describe buttress mode of plate application.

What makes buttress mode different than the other modes?

A

Used for longitudinal fractures (eg. metaphyseal) to prevent collapse of the adjacent articular surface
Plate acts as a wall to keep all the pieces together

*These fractures are prone to distraction rather than compression - most or all screw holes must be filled

36
Q

Describe bridging mode of plate application.

With what fracture type is bridging mode necessary?

A

Plate spans fractured area which cannot be anatomically reconstructed (*communutions).
Plate bears all the load at the level of the fracture

37
Q

What is an interlocking nail?

In what fracture type might it be used?

A

Internal fixation that combines benefits of an IM rod and a plate

Diaphyseal comminuted fractures

38
Q

What appendicular bone cannot be repaired with an interlocking nail?

A

Radius - d/t curvature, no IM devices can be placed

39
Q

What complications are associated with internal fracture fixation?
(Indications for removal)

A

Implant failure - loosening, breaking, migration
Osteomyelitis
Impingement of nerves - femoral IM pins
Osteopenia - secondary to implants that are too large
Delayed/non-union
Malunion

40
Q

Describe the 5 types of external fixator configurations

A

Type 1A - unilateral, uniplanar
Type 1B - unilateral, biplanar
Type 2A - bilateral, uniplanar with full pins only
Type 2B - bilater, uniplanar with full and half pins
Type 3 - bilateral, biplanar

41
Q

How far away from the skin must the clamps connecting the pins and rods be in an ex fix?

A

> 1cm

42
Q

What style of transfixation pins are the strongest and why?

A

Positive profile threaded

  • increased bone purchase compared to smooth pins
  • increased bending strength compared to negative profile
43
Q

How big or small must a transfixation pin be in comparison to bone?

A

Pin diameter

44
Q

How many transfixation pins are required per bone segment

A

> 2 (3 ideal)

45
Q

What spacing should be considered when placing transfixation pins?

A

1/2 bone diameter from the fracture and each other

46
Q

What is dynamization?

When and why is it used?

A

Planned decrease of stability

Used in later stages of fracture healing to put more stress/force on the bone (Wolff’s law)

47
Q

What types of fractures can be reduced with cerclage wire (in addition to other fixation methods)?

A

Long oblique / spiral fractures

48
Q

How many cerclage wires should be placed when reducing a fracture?

A

2 per fracture

49
Q

What spacing should be considered when placing cerclage wire?

A

> 0.5cm from fracture ends, spaced 0.5-1x bone diameter apart

50
Q

How should cerclage wire be placed in relation to the bone?

A

Perpendicular

51
Q

How much cerclage wire should be left when cutting?

A

2-3 twists, or a 5-10mm arm

52
Q

What are skewer pins and how are they used?

A

K-wires driven perpendicularly across the fracture in combination with cerclage wire (same idea as a lag screw)

Used in short oblique fractures

53
Q

How is a pin and tension band implant configuration used (general rules for application), how does it provide stability, and where is it indicated?

A
  1. Fragment reduced and secured with 2 K-wires perpendicular to fracture (parallel to each other)
  2. Wire passed through hole drilled below fracture (same distance as fracture to K-wire insertion) and wrapped in figure 8

Fixation is used to neutralize the pull of muscles/tendons on the fracture fragment

Indicated in avulsion fractures

54
Q

What types of bones are suited for repair with interfragmentary wiring?

A

Simple fractures of flat, non-weight bearing bones (mandible / maxilla)

55
Q

What forces are neutralized by IM pins?

A

Bending only

56
Q

What percentage of the intermedullary canal should be filled by an IM pin?

A

70% + cerclage wire

35-40% + plate

57
Q

What types of fractures are suited to repair with cross pinning?

A

Transverse fractures close to the joint (SH I and II)

58
Q

What types of fractures are suited to repair with divergent pin placement?

A

SH I fractures of proximal humerus or femoral head

Ross Small Animal Surgery (3 decks)

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