AO fixation Flashcards
thread diameter : 2.0
core 1.3
thread diameter 2.7
core 1.9 ( use 2.0 drill bit)
thread diameter 3.5
core: 2.4
thread diameter 4.0
core: 1.9
What is the distinguishing charachteristic between cortical vs cancellous screws?
Pitch
who invented scarf?
Dr Myer
Fixation sequence?
underdrill overdrill countersink Measure Tap Screw
No underdrill
No lag
For underdrill the hole is of a diameter ——-than the core ( minor) diameter.
slightly larger
another name for Overdrill
Glide hole
overdrill drill only to
osteotomy or even less
These kinds of screws don’t need over drill?
Partially threaded
why countersink?
- Prevent screw head irritation to ST
- Prevent stress riser
- prevent head ( land) from spinning on the cortex
When measuring using barrel gauge add — to your final measurement ?
2 mm
why do you tap?
create Threads for the screw
What size tap do you use for a 2.7 mm screw
same size 2.7 mm
what do you do when the head of the screw contacts the bone but you are not getting compression yet?
do 2 finger thightness - use thumb and finger to tighten it down
what is PCDO?post calc displacement osteotomy
usually done for flat foot- ( make an ostetomy in the calc) put screw in post aspect of calc and go upward
what are you worried about with cannulated screws?
thermal necrosis
why do screws fail
- poor technique
- Micromotion at the site
- Axial pullout
- Bending forces
- Torque
conventional plates are for
Bicortical fixation
What physical force holds the plate to the bone
Friction
What steps are omitted from application process in conventional plating?
Overdrill and countersink
What type of screws are used in conventional plating?
cortical screws
Prebending allows
- Concentric loading of the bone –> distribute forces more equally along the insertion of the plate
- prevents Gapping of the far cortex
Load screw allow for
movement usually about 1mm on either side of the fracture
which screws can be utilized as a load screw?
The closest screw on either side of the fracture
what is the goal of biologic osteosynthesis
preservation of blood supply, periosteum, and endosteum via minimally invasive plating techniques
Also bone healing occures with bone callus formation.
what is stress shielding?
The rigid plate carrying much of the load ( force transmission)
What type of loading do you need to improve bone healing?
Axial loading
what desighn changes have been made to plates to prevent cancellization of the cortex?
Locking plate
Fixed angle osteosynthesis?
The locking plate is not tightly placed against the bone buy instead is locked into the plate a few mms above the bone surface
Indication fr the use of lokcing plate?
osteopenic bone
communited fracture
inability to attain anatomicity during fracture reduction
Apperence of callus is bad or good
GOOD - A sign of prompt and positive reaction
sign of secondary bone healing
