Plates Flashcards
Types of non-locking plates?
- Dynamic Compresison Plate (DCP)
- Limited-contact DCP
- veterinary cuttable plate
- reconstruction plate
- acetabular plate
- L and T-plates
- lengthening plate
- osteotomy plate
- athrodesis plate
How does a compression plate work?
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
How does neutralization mode work?
Fracture is reconstructed and the plate help protect the reconstruction by resisting being forces
Bridging mode?
plate is applied across a non-reconstructed fracture and is required to resist all the load-bearing forces
Additional fixation often required
Buttress mode?
Plate is used to hold collapsed juxta-articular fragments in position after they have been reduced
Rarely used
Non-locking plates rely on what forces?
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
Do you need to contour a DCP plate?
YES
What kind of compression is achieved by dynamic compression plates?
Static
How can you place the screws in a DCP plate?
Neutral - no compression
Load - compression
With DCP plates, how many screw holes should be filled? how far from fracture line?
All if possible!
But not possible –> 6 cortices ideally
4-5mm from fracture line
Which side of the bone should the plate be positioned to?
Tension side
What does pre-stressing a DCP plate mean?
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
Whats the risk of overcompressing a DCP plate?
fissures
How much compresison does a 3,5mm DCP plate achieve?
1mm ?? Står 4mm annanstans..
Which screws do you place first if you are to place a DCP plate to a fracture with compression?
Nearest fracture - compression
Further screws in neutral, move away from fracture, place on each side of fracture alternating
Why must you control screw tightness again after a few min?
bone relaxes -> screw loosens
What is the maximum compression screws and compression you can achieve?
max 4 screws (2 on each side of fracture)
max 4mm compression
What plates can be cut and/or stacked?
VCP - veterinary cutting plates
At what angles can you angle screws with DCP plates?
25 degrees longitudinally, 7 degrees transversely
At what angles can you angle LC-DCP plates?
40 degrees
What are the major differences between LC-DCP and DCP plates?
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
Reconstruction plates - properties?
Made of steel
can be contoured in 3 planes
Low stiffness and strength
Arthrodesis plates?
Hybrid plates - larger screws proximally, smaller distally
The stability of non-locking plates relies on what factors?
- 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
Where can we place the plates on the bones?
What are the advantages of locking plates?
- 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
Disadvantages of locking plates?
- fixed screw angles (some have polyaxial screws)
- increased costs
- pre-contoured plates cannot be used to reduce fracture
What philosphy are locking plates designed with?
Biological osteosynthesis (biological reduction)
What philosophy are locking plates designed with?
Biological osteosynthesis (biological reduction)
The stability of locking plate is dependent on?
- 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
What is an LCP plate? How does it work? What is important in screw placement of LCP plates?
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
SOP plates - properties?
String of pearls
Are locking
Can be used with standard cortical screws
contoured in three planes
Relatively stiff and strong
Disadvantage of SOP plates?
cortical screws have a smaller core diameter than locking-> weaker -> risk to fail at screw-plate interface
ALPS plate properties?
Advanced locking plate system
Non-locking or locking screws in all holes
bending in 2 directions
Neutral or compressing (at 90 degree angle)
Polyaxial locking plates - properties?
Locking plate with can be angled at 10 degrees from perpendicular in any direction
What are the disadvantages of double plating - orthogonal or bilateral?
increased surgical exposure
Increased cost of implants
What are the four A’s of fracture repair?
- Alignement
- Apposition
- Apparatus
- Activity
What are the 4 A’s of fracture repair?
1) Alignement
2) Apposition
3) Apparatus
4) Activity
4 A’s - Alignement?
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
4 A’s - Apposition?
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
4 A’s - Apparatus?
Apparatus
- Assess appropriateness of implants chosen and state of implants
- Evaluate each individual implant for evidence of current or impending failure
4 A’s - Activity?
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
Size of instrument related to plate size?
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)
For cats, which plate sizes do we usually use?
1.5 or 2.0 or 2.4 (or 2.7)
For dogs, which plate sizes do we usually use?
2.7 or 3.5 (or 4.5)
What size of gap can a DCP plate close?
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
What should be the width of DCP plate related to bone size?
about 50-75%
Indications for use of a neutralisation plate?
- long oblique fractures
- spiral fractures
- comminutes fractures that can be accurately reconstructed using lag screws or cerclage wire
Function of bridging plate?
maintain bone length and angular relationships between joints
What plates do not contain holes in the middle and why?
limb lengthening plates, to increase strength of plate in this region
As often spanned across comminuted fractures
What is the ideal length of a plate?
2/3rd to the full lentgh of the bone
What can happen with too strong plate/screws?
Osteoporosis, soft tissue damage
At what percentage related to the bone does the holding power of the screw diminish?
When it reaches 40% of the bone
When is plate removal indicated?
- 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)
How much does an IM pin reduce stress on the plate when combined?
50% or more
