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Orthopaedic materials > Plates > Flashcards

Plates Flashcards

1
Q

Types of non-locking plates?

A
  • Dynamic Compresison Plate (DCP)
  • Limited-contact DCP
  • veterinary cuttable plate
  • reconstruction plate
  • acetabular plate
  • L and T-plates
  • lengthening plate
  • osteotomy plate
  • athrodesis plate
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2
Q

How does a compression plate work?

A

Oval hole -> when a hole is drilled eccentrically away from the fracture, the bone fragment moves horizontally towards the fracture site as the scerw is tightened

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3
Q

How does neutralization mode work?

A

Fracture is reconstructed and the plate help protect the reconstruction by resisting being forces

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4
Q

Bridging mode?

A

plate is applied across a non-reconstructed fracture and is required to resist all the load-bearing forces

Additional fixation often required

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5
Q

Buttress mode?

A

Plate is used to hold collapsed juxta-articular fragments in position after they have been reduced

Rarely used

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6
Q

Non-locking plates rely on what forces?

A

Non-locking plates rely on frictional forces between the plate and bone to transfer the load. Friction is created b the screw lagging the plate to the bone -> plate has to be accurately contoured to the bone

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7
Q

Do you need to contour a DCP plate?

A

YES

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8
Q

What kind of compression is achieved by dynamic compression plates?

A

Static

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9
Q

How can you place the screws in a DCP plate?

A

Neutral - no compression
Load - compression

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10
Q

With DCP plates, how many screw holes should be filled? how far from fracture line?

A

All if possible!

But not possible –> 6 cortices ideally

4-5mm from fracture line

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11
Q

Which side of the bone should the plate be positioned to?

A

Tension side

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12
Q

What does pre-stressing a DCP plate mean?

A

When applying DCP to compression of a fracture, pre-stressing means slightly over-contouring the plate so there is a small gap between the bone over the fracture -> produces compression at the trans-cortex and the plate is compressed against the bone

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13
Q

Whats the risk of overcompressing a DCP plate?

A

fissures

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14
Q

How much compresison does a 3,5mm DCP plate achieve?

A

1mm ?? Står 4mm annanstans..

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15
Q

Which screws do you place first if you are to place a DCP plate to a fracture with compression?

A

Nearest fracture - compression
Further screws in neutral, move away from fracture, place on each side of fracture alternating

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16
Q

Why must you control screw tightness again after a few min?

A

bone relaxes -> screw loosens

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17
Q

What is the maximum compression screws and compression you can achieve?

A

max 4 screws (2 on each side of fracture)
max 4mm compression

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18
Q

What plates can be cut and/or stacked?

A

VCP - veterinary cutting plates

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19
Q

At what angles can you angle screws with DCP plates?

A

25 degrees longitudinally, 7 degrees transversely

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20
Q

At what angles can you angle LC-DCP plates?

A

40 degrees

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21
Q

What are the major differences between LC-DCP and DCP plates?

A

LC-DCP has grooves underneath -> more even stiffness profile
LC-DCP slightly less stiff
LC-DCP allows greater degree of angling of screws (25 vs 40)
LC-DCP can compress in both directions, DCP can only compress towards the centre of the plate

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22
Q

Reconstruction plates - properties?

A

Made of steel
can be contoured in 3 planes
Low stiffness and strength

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23
Q

Arthrodesis plates?

A

Hybrid plates - larger screws proximally, smaller distally

24
Q

The stability of non-locking plates relies on what factors?

A
  • bone properties
    plate material and geometry
  • plate-bone interface
  • screw-bone interface
  • number of screws, screw material and torque
  • compression between fragments (for compression mode)
  • placement on bone relative to loading
25
Q

Where can we place the plates on the bones?

A
26
Q

What are the advantages of locking plates?

A
  • elimination of screw toggling (entire plate and screw construct acts as a single unit)
  • improved periosteal vascularity (no need to compress plate onto bone
  • simpler plate contouring (internal fixator, no accurate bone hugging contouring)
  • monocortical screw fixation
27
Q

Disadvantages of locking plates?

A
  • fixed screw angles (some have polyaxial screws)
  • increased costs
  • pre-contoured plates cannot be used to reduce fracture
28
Q

What philosphy are locking plates designed with?

A

Biological osteosynthesis (biological reduction)

29
Q

What philosophy are locking plates designed with?

A

Biological osteosynthesis (biological reduction)

30
Q

The stability of locking plate is dependent on?

A
  • plate material and geometry
  • number of screws, screw material, screw core diameter and torque
  • placement of bone relative to loading

And to a much lesser degree:
- bone properties
- plate-bone interface
- screw-bone interface
- compression between fragments

31
Q

What is an LCP plate? How does it work? What is important in screw placement of LCP plates?

A

Locking compression plate
Combination hole - can be placed as locking screw or compression screw/neutral screw
Must place compressing screws prior to locking -> if not, locking screws locks fragment in place and you cannot achieve compression

32
Q

SOP plates - properties?

A

String of pearls
Are locking
Can be used with standard cortical screws
contoured in three planes
Relatively stiff and strong

33
Q

Disadvantage of SOP plates?

A

cortical screws have a smaller core diameter than locking-> weaker -> risk to fail at screw-plate interface

34
Q

ALPS plate properties?

A

Advanced locking plate system
Non-locking or locking screws in all holes
bending in 2 directions
Neutral or compressing (at 90 degree angle)

35
Q

Polyaxial locking plates - properties?

A

Locking plate with can be angled at 10 degrees from perpendicular in any direction

36
Q

What are the disadvantages of double plating - orthogonal or bilateral?

A

increased surgical exposure
Increased cost of implants

37
Q

What are the four A’s of fracture repair?

A
  1. Alignement
  2. Apposition
  3. Apparatus
  4. Activity
38
Q

What are the 4 A’s of fracture repair?

A

1) Alignement
2) Apposition
3) Apparatus
4) Activity

39
Q

4 A’s - Alignement?

A

Alignment
- assess entire bone and in particular the joint above and below
- evaluate limb in terms of angular and torsional alignment relative to normal
- goal is to return and maintain limb in normal alignment

40
Q

4 A’s - Apposition?

A

Apposition
- evaluate realignment of fracture fragments for apposition
- desired amount of apposition is dependent upon fixation method
- Maintenace of apposition is important during follow-up evaluation

41
Q

4 A’s - Apparatus?

A

Apparatus
- Assess appropriateness of implants chosen and state of implants
- Evaluate each individual implant for evidence of current or impending failure

42
Q

4 A’s - Activity?

A

Activity
- Assess biological activity of bone in response to fixation (i.e. callus formation)
- Evaluate fracture site for evidence of lysis and periosteal new bone formation
- Evaluation requires knowledge of the patient’s age, time since repair and consideration of factors such as infection or other wounds/injuries

43
Q

Size of instrument related to plate size?

A

Number of plate relates to the size of thread screw -> i.e. 2.0 plate with 2.0 screws (and 1,5 drillbit for cortical)

44
Q

For cats, which plate sizes do we usually use?

A

1.5 or 2.0 or 2.4 (or 2.7)

45
Q

For dogs, which plate sizes do we usually use?

A

2.7 or 3.5 (or 4.5)

46
Q

What size of gap can a DCP plate close?

A

2.7 DCP will close a gap of 3,2mm
3.5 DCP will close a gap of 4mm
4.5 DCP will close a gap of 4mm

47
Q

What should be the width of DCP plate related to bone size?

A

about 50-75%

48
Q

Indications for use of a neutralisation plate?

A
  • long oblique fractures
  • spiral fractures
  • comminutes fractures that can be accurately reconstructed using lag screws or cerclage wire
49
Q

Function of bridging plate?

A

maintain bone length and angular relationships between joints

50
Q

What plates do not contain holes in the middle and why?

A

limb lengthening plates, to increase strength of plate in this region

As often spanned across comminuted fractures

51
Q

What is the ideal length of a plate?

A

2/3rd to the full lentgh of the bone

52
Q

What can happen with too strong plate/screws?

A

Osteoporosis, soft tissue damage

53
Q

At what percentage related to the bone does the holding power of the screw diminish?

A

When it reaches 40% of the bone

54
Q

When is plate removal indicated?

A
  • loose, broken or bent
  • thermal conductor
  • stress protection or compromized vasculature -> osteoporosis
  • plate crosses a growth plate
  • irritation (lick granuloma)
  • infection
  • impede performance in performing animals
  • when has healed, and plate is redundant (min 5 months postop)
55
Q

How much does an IM pin reduce stress on the plate when combined?

A

50% or more

Orthopaedic materials (7 decks)

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