Chapter 42: External Skeletal Fixation Flashcards
Name 5 advantages of ESF (external skeletal fixation)
- More biological repair vs. internal fixation
- Less soft tissue disruption
- Less expensive / less specific equipment needed
- Placed with minimal periosteal contact - less damage to periosteum
- Minimal to no exposure of fracture site
- Used with open wounds, able to treat wounds and fracture at same time
- Use in irregular anatomic contour areas - mandible, vertebral column, small bones or juxta-articular fractures
- Accessible and easily adjustable
What are (5) disadvantages to ESF?
- Percutaneous nature
- Increased infection rates v. internal fixation
- External and eccentric - so large bending forces acting on fixation pins
- Patient morbidity risks - pin loosening, pin tract inflammation, infection, fixation failure increases with time
- Patient tolerance and owner compliance
Is an Ellis pin a negative or positive threaded pin?
Negative
What are 3 advantages of positive profile pins?
Greater axial pull out
increased pin stiffness
greater fatigue life compared to smooth pins
Duraface has a what % increase in fixation stiffness and ultimate pin strength compared to the same size positive-profile pin?
55% stiffness / 54% ultimate pin strength
Name the three ESF clamp systems?
SK Clamp (Imex)
TITAN (Securos)
U-Clamp (Securos)
A type II ESF can also be called what?
Bilateral uniplanar
Addition of a horizontal articulation to a type Ib ESF does what?
Greater resistance to shear force
Increases bending, torsional and axial stiffness of the construct
Diameter of the acrylic column should be how many times the diameter of the bone?
Diameter of the acrylic bar should be how many times that of a comparable stainless steel connecting bar to reach similar stiffness?
Diameter of the acrylic column should be 2-2.5x the diameter of bone.
Diameter of an acrylic bar should be 3-4 times that of comparable stainless steel.
Acrylic is better suited to smaller diameters, if over 25mm in diameter it may be subject to what?
Vaporization - consequence of heat produced within the larger diameter acrylic columns, resulting in voids in the material.
Epoxy resin creates a bond ___ times stronger than MMA with smooth pins?
How much stronger (%) is a knurled pin interface vs a smooth pin -epoxy?
4 times stronger than MMA
Knurled = 40% stronger than smooth.
Bending the pin over in an epoxy resin frame can help do what?
increase pin purchase and pin pull-out strength
In regards to 1.6mm wire in a circular ESF, when tensioned it is as strong as a ____mm pin?
4mm
The level of the hinge (if present) in a circular ESF for distraction osteogenesis/ALD correction corresponds to the what?
CORA - The motor is positioned along and opposite to the vector of deformity and the rings of the frame are angled to match the angulation of bone such that when deformity is corrected, rings will be parallel to each other
Name a disadvantage of fine wires for circular ESF and name a way around this?
Have little resistance to bone sliding or translating, along the length of the wire - Olive wires are K wires that have a stopper or olive - on the shaft near its midpoint - the wire is driven so that the olive rets against the cortical bone surface, allowing pressure to be exerted on the cortex in the direction of the wire
Rate for distraction osteogenesis?
1mm/day after initial latency for hematoma formation- Bone is regenerated in distraction gap in a process that is histoiologically similar to that observed in an active physis
Period of latency for distraction osteogenesis is what?
3- 5 days for hematoma formation - after which the fracture is distracted slowly
In circular ESF do smaller or larger rings provide greater resistance to axial compression?
Smaller rings
Extended periods of transarticular ESF (>4weeks) can lead to what?
Arthrosis secondary to joint ahesions
Soft tissue contracture
Degenerative articular changes
Resulting in loss of motion, muscle mass and limb use
Name 3 ESF types for transarticular ESF?
- Rigid ESF
- Hinged ESF
- Flexible ESF
On which bone can you use a type 3 ESF?
Tibia (ONLY bone that can take all types)
Name the safe corridor locations (green) for the humerus, radius/ulna, femur and tibia?
Humerus - Cranioproximal at greater tubercle, and also distal at medial and lateral epicondyles
Radius/unla - Lateral to medial in center of olecranon, distomedial radius, medially on mid to distal radius
Femur - lateral greater trochanter, distal middle of condyle medial to lateral
Tibia - Medial, not most cranioproximal aspect of TT or most distal aspect of tibia
Which pins are placed first?
Two far pins, then two near pins, then interposition pins placed
What % of bone diameter away from joint and away from fracture should you place your ESF pins?
75% from joint and 50% from fracture
The stiffness of a pin is related to what?
Stiffness of a pin is inversely proportional to exposed length of pin to 3rd power - shorter pin = shorter working length, increases stiffness of construct
How can you increase stiffness of a pin?
- decrease working length (reduce bone to clamp - exposed pin)
- Dvergent pins - up to 35° - increases axial stiffness and cr-cd bending strength of frame
- Closer connecting bar is to bone
- Increasing no. of pins per fragment up to a point (4)
The most common source of weakness or failure of an ESF is?
Pin to bone interface
Pin size for ESF?
Threaded portion should be 20-30% of bone diameter
What is the insertion speed for ESF pins?
<300rpm
What is the recommendation not to exceed for working length between skin surface and clamp?
No more than 1cm from surface of skin
Name 4 ways of increasing the strength of the pin bone interface junction and pin pull out strength?
Pin size - threaded portion 20-30% of bone diameter
Pin type - threaded, duraface better
Pin insertion force - appropriate
Pin insertion speed <300rpm
Pin placement - centrally in widest part of bone
Pre-drilling with a drill bit 0.1mm smaller than pin shaft
Name 4 ways to decrease the load and bending force per pin?
Adequate pin number - 3-4 per fragment
Decrease the pin working length - place clamp with bolt toward patient and no more than 1cm from surface of skin
Pin configuration and frame stiffness - far-near-near-far pin placement, consider multiplanar frames and consider augmentation (articulations, diagonals, IM pins)
You should not exceed x% of the bone diameter for pin selection due to >y% predisposing to cortical fractures through the pin hole
X - 25%
Y - 30%
Advantages of negative profile pins over positive profile pins?
Greater shaft diameter relative to bone-hole diameter
Benefits when using in areas of small fragment size, obese animals with high BCS, greater ST covered area requiring greater working length of pins
AMI of a pin?
Radius to the fourth power
Central placement of pin within the bone is beneficial because?
- Avoids iatrogenic bone fracture
- Maximises bone purchase
Benefits of predrilling using a drill bit <0.1mm of the core diameter of the pin being placed?
- Decreases thermal damage and mechanical damage during pin insertion
Why no hand insertion of ESF pins?
Wobbly hand = microfractures and large irregular pin tract and precipitating pin loosening
Frame destabilisation - staged partial disassembly to optimise bone healing as healing progresses - what is the timing recommended for - young dogs, adult dogs and older dogs and cats
Young dogs - 4-6 weeks
Adult dogs - 6 weeks
Older dogs and cats - 8-10 weeks
How far should pins be from a physis?
at least 1cm or 3 pin diameters from a physis to avoid inadvertent physeal disruption
what does SPIDER stand for?
Secured Pin Intramedullary Dorsal Epoxy Resin
What is the critical length over which will lead to clinical nonunion for the feline tibia?
1.5 x diameter of bone for feline tibia
Most common complication of ESFs?
Pin tract infection - minor does not tent to result in pin loosening but major does
Name other complications of ESFs?
Pin tract infections, construct complications - loosening or breakage, premature loosening, ST injury
Is an LCP stiffer than a ESF type 2 in ML bending?
Yes and also axial compression
