AO Principles Flashcards
according to AO, what is the most common microbial agent causing the majority of orthopedic infections?
Staph intermedius
what three methods of planning fracture fixation will aid in implant selection?
direct overlay
intact contralateral bone
bone specimen of a similar size animal
what are the six basic modalities used to decrease pain, reduce inflammation, and stimulate normal healing?
local hypo and hyper thermia massage therapeutic exercise hydrotherapy ultrasound electrical stimulation
what is effleurage?
superficial or light stroking massage used to relax and acclimatize the animal
what is petrissage
deep kneeding and squeezing of muscle and surrounding soft tissues
what is cross fiber massage
a deep massage concentrated along the lines of restrictive scar tissue and is designed to promote ROM
what is tapotement
percussive massage manipulation with a cupped hand
what is screw purchase dependent on?
the implant-bone interface… therefore, the goal is to achieve as much contact area as possible
what is the maximum size diameter screw that should be used?
use a screw diameter that does not exceed 40% of the diameter of the bone
What drill do you use for a threaded hole for a 1.5 cortical screw?
1.1 mm
What drill do you use for a threaded hole for a 2.0 cortical screw?
1.5 mm
What drill do you use for a threaded hole for a 2.7 cortical screw?
2.0
What drill do you use for a threaded hole for a 3.5 cortical screw?
2.5 mm
What drill do you use for a threaded hole for a 4.0 cancellous screw?
2.5 mm bit
also does not have a glide hole size
What drill do you use for a threaded hole for a 4.5 cortical screw?
3.2 mm
What drill do you use for a threaded hole for a 5.5 cortical screw?
4.0
What drill do you use for a threaded hole for a 6.5 cancellous screw?
3.2 mm
use a 4.5 bit for the glide hole
why do we countersink lag screws?
it will increase the contact between the bone and screw head
when might a shaft screw in lag fashion be appropriate over a screw with threads the whole way?
a shaft screw will prevent the threads from becoming engaged in the glide hole on the near cortex. this can occur because an inclined screw will produce axial force and then the force will shift the screw head alone the bone surface towards the fracture - making it easier for the threads to engage the glide hole
which drill sleeve would you use for a DCP plate? For an LC-DCP?
use the standard drill sleeve for a DCP
use the universal drill sleeve for an LC-DCP
what is the greatest force that should be applied, dependent on screw size, to tighten a screw? in terms of fingers/hand
two finger tight for 2.0 mm screw
three finger tight for 2.7 mm screw
whole hand tight for 3.5 mm screw
why do we apply plate screws at each end of the plate, then close to the fracture, then the remaining plate holes?
to ensure axial alignment of the plate to the bone
what size screws do you use with a DCP 4.5 mm plate?
4.5 mm cortical or 6.5 mm cancellous
what size screws do you use with a 3.5 DCP plate?
- 5 mm cortical
4. 0 mm cancellous
In a DCP plate, how much compression is allowed per hole? Dependent on plate size
for DCPs 3.5 and 4.5, allows up to 1 mm compression
for DCP 2.7 allows 0.8 mm compression
For a DCP plate, how much inclination is possible in the longitudinal and transverse plane?
up to 25 degrees in the longitudinal plane
up to 7 degrees in the transverse plane
what does it mean for a screw to be eccentrically placed? Which color of the drill guide will allow for it?
this is done on the DCP plate to allow for axial compression
use the GOLD collar in the load position
the gold drill guide produces a hole 1.0 mm off center from the fracture
Which side of the drill guide do you use for a neutral screw?
green places it in neutral
technically, the hole is 0.1 mm off center so it still gives a tiny bit of compression
what are the advantages of the LC-DCP plate
decreased plate bone contact
even distribution of stiffness
ease of contouring
symmetrical evenly distributed plate holes
which drill guide should you use for the LC-DCP?
use the universal drill guide
you should also use the universal guide for a DCP in buttress/bridging fashion
Are the plate holes of the LC-DCP symmetrical? why or why not?
they are symmetrical because this allows for eccentric placement of a screw in either direction and therefore compression for segmental fractures
how much inclination in the longitudinal and transverse planes can an LC-DCP allow?
40 degrees longitudinally
7 degrees transversely
what sizes do veterinary cuttable plates come in? how long are they>
they come in a size that can take 1.5 and 2.0 mm as well as a size that accepts 2.0 and 2.7 mm
they are 300 mm long with 50 holes
can you stack cuttable plates?
yes - you can stack cuttable plates
you should use the plate with the smaller holes or shorter of the two placed superficially
what is unique about reconstruction plates?
they have deep notches that make them easier to bed and contour
they come in 2.7, 3.5, and 4.5
what function is a plate serving when combined with a lag screw through the plate?
it is acting as a neutralization plate that is protecting the interfragmentary compression achieved with the lag screw from all rotational, bending, and shearing forces
what is the function of a buttress plate? where along the bone is it likely to be used?
a buttress plate prevents collapse of a fracture - usually preventing collapse of the adjacent articular surface
to prevent sliding of the plate, the screw hole is placed opposite to the slope in the plate hole
what is the function of a bridging plate
acts as a splint to maintain the correct length of the bone - prevent axial deformity as the result of shear or bending forces
how does a rod aid a plate-rod construct
adding an IM pin will reduce the internal plate stress and increase the fatigue life of the plate
the IM pin also reduces the strain concentration at the screw hold to approximately the strain present at the solid center of a similar plate that is not supported by the IM pin
what are the elements of an LCP combination hole?
- one half of the hole has the design of the standard DCP/LC-DCP for conventional screws including lag screws
- the other half of the hole is conical and threaded so that it may accept the matching thread of the new locking screw head
what are the two ways an LCP can be applied?
as a conventional dynamic compression plate for rigid fixation
or as a pure internal fixator with unicortical locking head screws
describe elements of the UniLock system
- available as 2.0 and 2.4 mm - the 2.0 accepts all 2.0 screws. The 2.4 accepts 2.4 and 3.0 mm locking head screws, 2.4 mm non locking cortical screws, 2.7 mm emergency screw
- never seen anyone use this ever
describe elements of the clamp rod internal fixator
- comes in 2.0, 2.7, 3.5
- affordable and strong
- never even heard of this one
what are positive profile pins? what size do they come in?
a positive profile pin has a shaft diameter that is the same its whole length - this reduces the bending stress
they come in 1-6 mm
what diameter acrylic or epoxy bar is comparable to a 3.137 mm stainless steel bar?
19 mm acrylic or epoxy
what size pins should be chosen for an external fixator
pin diameter should be no more than 25% of the bone diameter
how far away should the pins in an external fixator be?
at least two pin diameters from the fragment edge
for interlocking nails with the screw or bolt not locked directly in the nail, where should you place the screw/bolt in relation to the fracture
because the screw or bolt does not lock directly into the nail, it is best if the hole is located as far away from the fracture site as possible
what is the range of sizes that IM (steinmann) pins come in?
2-5 mm in diameter
230-300 mm long
what is the range of sizes for a K wire?
0.8-2.0 mm in diameter
150 mm to 300 mm in length
what is the optimal size of IM pin?
about 70% of the bone diameter
if combining with a plate, 50% of the bone diameter
what is the range of size that orthopedic wire comes in
0.5 - 1.5 mm (24-16 gauge)
how far apart should cerclage wire be placed?
distances between half to the entire bone diameter
what is the initial tension and load to loosen for a twist cerclage?
70-100 N
260 N to loosen
what is the initial tension and load to loosen for a single loop cerclage?
150-200 N
260 N to loosen
what is the initial tension and load to loosen for a double loop cerclage?
300-500 N
666 N to loosen
what are the five factors in the pathogenesis of osteomyelitis
tissue ischemia bacterial inoculation bone necrosis and sequestration fracture instability foreign material implantation
but mainly tissue damage in the presence of bacterial contamination
what are the three components of any biolfim?
the offending microbe(s)
the microbe produced glycocalyx
host biomaterial interface
What makes bacteria resistant to antimicrobial agents when in a biofilm?
- the biofilm acts as a molecular filter - hard for antimicrobials to perfuse to the target
- the microbes enter a quiescent growth pattern in a biolfilm which means they arent reproducing and then the antimicrobials can’t act
- the biofilm microenvironment is harsh - low pH, high CO2, low PO2 and hydration - and most antimicrobials are then rendered ineffective
what is the most important predisposing factor for refracture following implant removal?
open screw holes
it makes them especially weak against torsional forces –> oblique fracture
what does the stiffness of an implant depend on?
the material itself as well as the design and dimensions of the device
Under similar bending condition and cross sections, titanium plates will deform twice as much as a steel plate. Why is that?
the steel has a higher (200 GPa) modulus of elasticity than titanium (100 GPa)
