Internal Fixation Flashcards
What are the 4 AO principles?
- anatomical reduction
- stable internal fixation
- preservation of blood supply
- early active pain-free mobilization
where does most of the blood supply to the bone come from?
endosteal or medullary vessels (found in inner 2/3 to 3/4 of cortcial bone)
which type of bone healing bypasses callus formation?
direct osseous repair
how is absolute stability achieved?
using compression plates or screws
- ideal for articular fx
- needs less than 2% of strain
how is relative stability achieved?
using intermedullary nailing, ex-fix, locking plates
*needs 2-10% of strain
what is strain?
deformation of a material when a given force is applied
how is strain decreased?
increased gap length
decreased motion
how does titanium compare to stainless steel?
titanium is more flexible, which means it can break easier but there is not as much allergic reactivity to it compared to stainless steel (which contains nickel)
which metal would you use for someone who is allergic to nickel?
titanium
avoid stainless steel
which is the least dense of surgically implantable materials? most dense?
titanium- least dense = flexible
(then stainless steel)
cobalt chromium- most dense
which metal is the material of choice for joint implants?
cobalt chromium
what is the un-threaded part of the screw called?
shaft
what is the threaded part of the screw called?
shank
what is the term for the place where the shaft and shank meets? what is the significance of this place?
runout- it is the weakest part of the screw
compare the size of the pitch between cortical and cancellous screws.
cortical screws have a smaller pitch for grasping cortical bone.
cancellous screws have larger pitches.
what is a pitch?
distance between threads on a screw
which type of screws are usually partially threaded?
cancellous screws
compared to cortical screws which are fully threaded
describe the lag by technique screw. what is the order according to AO techniue?
- overdrill (or glide hole)
- underdrill (or guide hole or thread hole)
- countersink
- measure
- tap (if necessary)
when would you use a lag screw “by technique”?
when inserting a cortical screw
how does the lag screw “by design” compare to the lag screw “by technique”?
one less step- don’t need to do the overdrill
how far do you drill for a lag screw by technique?
need to insert 1mm past far cortex to increase “pull out strength”
how far do you drill for a lag screw by design?
do not want to pierce far cortex because they are cancellous screws
what type of fragment set is this? 3.5 and 4.0mm screws? and when would you use this size
small frag set
*good for midfoot work
what type of fragment set is this? 1.5, 2.0, 2,7mm screws? and when would you use this size?
- 5, 2.0, 2.7 mm screws
* good for forefoot work, metatarsal necks
what type of fragment set is this- 4.5, 6.5 mm screws?
large fragment set
*good for tibia or calcaneus
what size drill bit would you use to make a thread hole for a 1.5 mm screw?
1.1
what size drill bit would you use to make a thread hole for a 2.0 mm screw?
1.5
what size drill bit would you use to make a thread hole for a 2.7 mm screw?
2.0
what size drill bit would you use to make a thread hole for a 3.5 or 4.0mm screw?
2.5
what size drill bit would you use to make a thread hole for a 4.5 mm or 6.5 mm screw?
3.2
what type of screw would you use where screw head prominence may be problematic?
herbert screw (aka whipple screw) Ex. fusing the STJ
When would you use K-wires?
stabilize hammer toe procedures or osteotomies
When would you use Steinman pins?
- stabilize larger osteotomies or fusion (calcaneus or ankle)
- can be used as a metatarsal intramedullary nail
- across growth plates
when is cerclage/ monofilament wire used?
- comminuted metatarsal fx
- transverse osteotomies
- tension band wiring
- last resort type thing
when would you use tension band wiring?
fragments that may be too small or difficult to put a screw through or when there is a soft tissue attachment pulling against you
what kinds of forces do staples resist (and what do they not resist)?
resist distraction but generally not shear or bending forces
what are some ways to achieve compression with plates?
- eccentric drilling
- prebending
- tension device
- tension band
when doing eccentric drilling to achieve compression, where do you put the first screw?
on stable side of the fx (then place second screw on the unstable side of teh fx)
when prebending a plate to achieve compression, where do you put the screws first?
put the 2 screws centrally then move your way outwards to avoid gapping
when applying the tension band principle to achieve compression, on which side do you screw the screws?
put the screw on the side of teh fracture where you have tensile forces
what is teh drawback of dynamic compression plates?
there is a lot of contact of the bone to the metal plate that it can cause osteonecrosis under plate. (so then limited contact DCP were created)
what is the drawback of LC-DCP?
very thick and prominent
advtg is that it limits vascular trauma
what is the function of a neutralization plate?
helps protect inter-frag screw by preventing rotational forces
what type of plate would you use in a spiral fibula fx?
neutralization plate
what type of plate would you use in a transverse fx?
compression plate
what type of plate would you use in a tibial plateau or plafond fx? or calcaneal fx?
buttress plate
what is a buttress plate?
stabilizes fx by being anchored to the main stable fragment, not necessarily the fragment it is supporting
what type of plate would you use to fixate 2 main fragments followed by a graft placement?
bridge plate
how is a locking plate different from a traditional plate?
it has threaded holes for extra stability
what are the rules of stabilization?
- screw fixation
- plate stability
- vassals rule
- two screws are better than one
what is the rule for screw fixation when it comes to stabilizing a fx?
the length of fx should be at least twice the diameter of the bone involved
what is the rule of cortices for a metatarsal plate?
4 cortices: 2 screws on both sides of the fx
what is the rule of cortices for ankle plates?
need 6-8 cortices: 3-4 screws on both sides
what is vassals rule?
reduce the primary fx and secondary fx will spontaneously reduce
what is teh ‘2 screws are better than 1” rule?
2 points of fixation to resist rotatory forces
what is a MIPO (minimally invasive plate osteosynthesis) plate?
percutaneous plate usually used in tibia or teh femur that is anatomically pre-contoured and is a locking plate
*used to protect fx biology (minimally disruptive to soft tissue and periosteum)
what are potential complications of internal fixation use?
- prominent painful hardware
- hardware breakage
- hardware backing out
- malunion
- nickel allergy
- sterile abscess or reaction
- infection
