Principles of internal fixation: plates and screws (Johnson) Flashcards
Principles of internal fixation
anatomic reduction
Stabilize
Cortical screw
Core diameter larger than outer diameter
Lower thread pitch
Advantages of cortical screw
Thick core, size matters
less breakage
Disadvantage of cortical
Pulls out too quick
When would you use cortical screws
Diaphyseal
most common
When would you use cancellous screws
Metaphyseal
Advantage of locking screw over cortical
Threaded head is ribbed for pleasure, resists bending
Thicker core diameter
Implant screws
Used with plates
Traditional implant screw
compress plate to bone surface
Locking implant screw
the head threads into the plate
Does not compress the plate to the bone
Position screw
Aid in initial reduction
Hold fragment in reduction
No compression
Comminuted fractures
Design of lag screw
Partially threaded screw
Threads engage far, cortex creates compression
Dynamic compression plate
Compression across fracture
Full contact between plate and periosteum
Limited contact dynamic compression plate (LC-DCP)
Reduces contact w/ bone
increases blood supply
Reduces stress riser at screw holes
Locking compression plate
Screws in shear
No compression
No screw loosening
Neutralization plate
Protects interfragmentary stabilization via lag screw/cerclage/hemicerclage from bending, shear and torsional loading
Bridging plate
Splint to maintain limb length and joint alignment
prevent bending or shear
For traditional plate repair, minimum number of cortices on each side of fracture
6
Screw size compared to bone diameter
30%
