Internal Fracture Fixation (1 of 4) Flashcards
What are the 2 general types of fracture fixation?
Non-surgical
Surgical
What is an example of a non-surgical fx fixation?
External coaptation
What are 2 examples of surgical fx fixation?
External skeletal fixator (ESF)
Internal fracture fixation
What are the 4 main goals of fx fixation?
Restore length and alignment
Minimize motion at fx ends
Permit early ambulation and use of as many joints as possible during healing
Balance forces that promote healing with those that promote resorption
What does “alignment” mean with regards to fx fixation?
Means alignment of the limb, not the fracture fragments
Why is it important to minimize motion at the fx ends?
Rubbing causes bone to wear away
What is Wolff’s law?
Bone remodels based on the forces applied
- Thickens in response to increased force
- Weakens in response to decreased forces
What are 4 pros of internal fixation?
Variety of options
Promotes normal muscle/joint fxn
Fewer re-checks
Nothing externally to monitor
What are 3 cons of internal fixation?
Expense
Needs surgeon training
May need second surgery to remove
What are 3 pros to external coaptation?
Limited supplies needed
Specialized training is limited
Avoids a prolonged surgical procedure
What are 4 cons to external coaptation?
Frequent re-checks and bandage changes
Only for very specific fxs
Risk of bandage morbidity preventing continued use
Immobilized joints
What are 2 main indications for external coaptation?
Fx below the knee or elbow
Fx expected to heal rapidly
In addition to being below the knee or elbow, what are 4 more specific indications for the fx to be eligible for external coaptation?
Minimally displaced and amenable to reduction
Transverse, simple, closed
Greenstick
Non-articular
What are some things that may hinder fracture healing?
Metabolic dz
Steroids
Immunosuppressants
What are the two approaches for internal fixation?
Open anatomic reduction/reconstruction (surgical approach)
Biological osteosynthesis
What are 3 qualities of the open anatomic reduction/reconstruction approach?
Primary bone healing (
What are 3 qualities of the biological osteosynthesis approach?
Avoids disruption of fx hematoma
Less rigid fixation
Secondary healing
What is the desire when using biological osteosynthesis approach?
Restore length, alignment and provide support to allow bone to heal
What type of fx is open anatomic reconstruction required for?
Articular fractures
What type of fx is open anatomic reconstruction most appropriate for?
Repair of transverse, oblique, segmental and minimally comminuted fractures
What are the two kinds of biological osteosynthesis?
“Open but do not touch”
“Minimally invasive osteosynthesis”
What is “open but do not touch” biological osteosynthesis?
Fx is surgically approached and visualized and the ends are not manipulated
How is the fracture fixed with “open but do not touch” biological osteosynthesis?
Fx is reduced via traction of bone away from the fracture with minimal disturbance of the hematoma.
What is “minimally invasive osteosynthesis”?
Implants are placed through incisions distant to the fx, fracture is NOT approached
What is the goal of biological osteosynthesis?
To return limb alignment and length to normal without disruption of the fx
What are 4 considerations when selecting an implant?
Fx type and location
Bone affected
Patient factors
Surgeon preference
What are some patient factors you should consider?
Age
Comorbidities
Environment
Size/weight of patient
What is the difference between the implant needs of an older dog vs. a younger dog?
Old dogs need something that will be stable longer d/t prolonged healing.
Young dogs need something that will be less stable because they heal fast.
Why do you want a less stable implant for a younger dog?
Because if it’s too stable, Wolff’s Law will result in bone resorption.
What is a primary implant?
It provides rigid support/stability during healing
What are 3 examples of a primary implant?
Bone plates
Interlocking nails
External skeletal fixators
What is a secondary implant?
Devices used to help maintain reduction, or strength of the bone while applying the primary implant.
What are 3 examples of a secondary implant?
Kirschner wires (K-wire)
Cerclage wire
Interfragmentary screws
What 2 materials can you find plates in?
Stainless steel
Titanium
Which plate material is most common?
Stainless steel
Which plate material is stiff and fails by bending?
Stainless steel
Which plate material is more fatigue resistant?
Titanium
Which plate material is less reactive/more biocompatible?
Titanium
Which plate material is more expensive?
Titanium
What are the 5 most common types of plate?
Dynamic compression plate (DCP) Limited contact dynamic compression plate (LC-DCP) Veterinary cuttable plates Lengthening plates Reconstruction plates
What is special about the screw holes in a DCP?
They allow screw placement that promotes compression of the fx ends
What shape are the screw holes in a DCP and why?
They’re oval to allow for angulation
What is important to remember about placing a DCP?
Must be right up against the bone or else fixation won’t be as strong.
Describe the plate surfaces on the DCP.
They’re all flat
What is different about the shape of the LC-DCP compared to the DCP?
LC-DCP has a contoured underside to allow stress to be more evenly distribute across the plate
What is a major difference between the LC-DCP and the DCP?
LC-DCP has less contact with the bone for less disruption of periosteal vascularity.
Describe a veterinary cuttable plate.
More screw holes
Good for smaller bones
No compression
Does a semi-tubular plate provide compression?
No
What is a lengthening plate used for?
Highly comminuted fx
Does a lengthening plate provide compression?
No
What is a major weakness in lengthening plates?
Love to bend right in the middle
What is special about a reconstruction plate?
Can be contoured in all 3 directinos
What is a reconstruction plate used for?
Fx of curved bones
What is a locking plate (LCP)
A “fixed angle implant” that has threaded locking screw heads.
Think of it like an internal external fixator
What makes the LCP better than the DCP?
Because the screws lock into the plate, it removes need for plate-bone contact, and instead the stability comes from the screw in the bone and locked to the plate
Do you need to contour an LCP?
No
What patients are the LCPs good for?
Old animals and/or really comminuted fractures that will take longer to heal.
Can you use an LCP in a puppy?
NO! Wolff’s Law
What are 2 benefits to the LCP compared to the DCP?
LCP needs a greater amount of force to cause implant failure
Pull-out of screws only happens under significantly higher forces
What are 3 types of bone that an LCP would be better for.
Osteoporotic bone
Soft bone
Comminuted fx
What are LCPs excellent for?
MIPO (Minimally Invasive Plate Osteosynthesis)
What is a cortical screw used for?
Diaphyseal bone (dense cortical bone)
What is a cancellous screw used for?
Softer bone like metaphyseal or epiphyseal bone
What is a locking screw used for?
When you’re using a locking plate.
NOTE: Wouldn’t really use them otherwise because they’re expensive.
What type of thread pattern can you use as a lag screw?
Partially threaded
What are 4 steps you need to take if you’re not using a slef-tapping screw?
Drill, measure, tap, screw
What is a cannulated screw, and what is it used for?
Center is hollow.
Used for minimally invasive procedures
When would you used screws?
Can be used with a primary implant, or as a secondary implant
What is the goal when using screws?
To get as much contact with bone, with a sufficiently stable implant of minimal size
What diameter should your screw be?
Not exceeding% of the bone diameter in diaphyseal bone
What does the screw size refer to?
Outer diameter vs. core diameter
What does the core diameter of the screw determine?
The bending strength
What does outer diameter of the screw determine?
Pull out strength
What are 3 characteristics of a cancellous screw?
Increased outer diameter to core diameter ratio
Deeper thread
Larger pitch (gives better purchase in softer bone)
What are 3 characteristics of cortical screws?
Decreased outer diameter to core diameter
More shallow thread
Decreased pitch
How can you tell if a screw is self-tapping?
Will have a fluted tip
What type of screw has the largest core diameter?
Locking screws
T/F: Locking screws are also self-tapping.
True
In a DCP, how do the screws work with the plate?
Generates friction between bone and plate necessary for stability of fixation
Loading limb results in shared forces between bone and plate
In a LCP, how do the screws work with the plate?
Screws lock into the plate converting shear and bending stress into comprehensive forces at the bone-screw interface
How do you place a lag screw?
Drill a glide hole in the near cortex (threads not engaging here) PERPENDICULAR to the fx, far cortex is drilled to the core for the screw. This creates compression when the screw is tightened.
How should a lag screw be places relative to a fracture?
PERPENDICULAR
NOTE: Never place a screw through a fx unless it is a lag or positional screw. Otherwise, angle away from the fx.
What is a position screw?
Holds a fragment in place
Does a position screw provide compression?
No
How strong is a position screw compared to a lag screw?
Weaker
Can you place lag screws through conventional plate holes?
Yes
Can you place positional screws through conventional plate holes?
Yep!
What side of the bone is the plate applied to?
The tension side
What do you need to do to a conventional plate before you apply it?
Precisely contour it to the shape of the bone
For a stable repair with a conventional plate, how many screws do you need?
Need purchase of at least 6 cortices above and below the fracture
What is so nice about locking plates?
Minimal to no contouring
For a stable repair with a locking plate, how many screws do you need?
Need purchase of at least 4 cortices above and below the fracture
If not placing a lag or positional screw, what should you do regarding screws near the fracture.
Should never be placed through fx, instead angle screws away from fx at least 5mm
On what does a plate’s function depend?
How it is placed on the bone in relation to the fx.
What are the 4 different modes we can use with a plate to repair a fracture?
Compression
Neutralization
Buttress
Bridging
What is compression mode?
When plates are used to achieve compression across the fx ends
What 2 types of fx is compression mode used for?
Transverse
Short oblique
How is compression achieved in compression mode?
Eccentrically loaded screws
Where is most of the load carried in compression mode?
Mostly the bone
Why do we like compression mode?
Because it may promote primary bone healing
What is neutralization mode?
Plates are used in addition to primarily placed lag or positional screws
Why do we use neutralization mode?
The plate acts to protect/neutralize the shearing, bending and rotational forces
What is buttress mode?
Plate used in metaphyseal fractures to prevent collapse of the adjacent articular surface
What does buttress mode frequently incorporate?
Lag screws
Where is the load carried in buttress mode?
The plate is subject to full loading (plate supports cortex and resists displacement)
What should be done when using buttress mode?
Most or all screw holes should be filled
What is bridging mode?
Where the plate spans the fractured area which cannot be anatomically reconstructed
Where is the load carried in bridging mode?
All the weight is carried on the plate at the level of the fracture.
In bridging mode there is micro-motion at the fracture site, why can this be a good thing?
This is a good thing because it promotes secondary bone healing
What size plate would you use for bridging mode?
A longer plate with fewer screws
NOTE: Ideally, plate goes from top of bone to the bottom
What mode is used in biological osteosynthesis/MIPO (Minimally Invasive Plate Osteosynthesis)?
Bridging mode
What is elastic plate osteosynthesis?
A form of bridging mode that is ONLY appropriate for skeletally immature animals (
How do you apply elastic plate osteosynthesis?
Long, thin elastic implants with minimal screws placed divergently
What are 3 qualities of elastic plate osteosynthesis?
Spans the entire bone length and is not contoured
Deforms with axial loading within it’s elastic limit
Spares the bone-screw interface from shear force
What is an interlocking nail?
Internal fixation that combines the benefits of an intermedullary rod and a plate
What is an interlocking nail used for?
To treat a diaphyseal comminuted fracture
What can you NOT use an interlocking nail for?
Radius fracture, the curve of the bone prevents you from placing ANY intermedullary device
What are 4 risks of internal fixation?
Implant failure
Osteomyelitis
Impingement of nerves
Osteopenia
What are 3 types of possible implant failure?
Loosening
Breakage
Migration
What kind of pins do you commonly see nerve impingement with?
Femoral IM pins
When might you see osteopenia?
When the implants are too strong
