Lecture 13 2/13/25 Flashcards
How are plate sizes determined?
based on the size of the screw that will fit in the plate
What are the two screw types, based on the type of bone they are used in?
-cancellous: used in cancellous bone with wider, deeper tracts
-cortical: used in cortical bone with tighter, shallower tracts
What are the characteristics of a position screw?
-does not compress fracture
-drilled hole is uniform size the entire way through bone
-screw threads interacts with bone the entire length
What are the characteristics of a lag screw?
-screw head compresses fracture
-drilled hole is larger where the screw enters and narrower where the screw ends
-screw threads only engage with bone where the drill site is narrower; larger drill site is the width of the screw
How should plate size be chosen?
choose the biggest plate possible to provide the most strength
What are the plate types?
-DCP/LC DCP
-locking plates
What is the main feature of a locking plate?
plate has threads that allows the screw to screw into the plate as well as the bone
What are the steps of inserting a bone screw?
-drill
-countersink (lag screw only)
-measure
-tap
-screw
What are the key concepts to applying a bone plate?
-select appropriate plate size
-select a plate that spans the bone length for diaphyseal fractures
-accurately contour the plate
-place a minimum of three screws/secure six cortices above and below the fracture
-use a longer/stronger plate as a bridging plate or augment with an IM pin for unstable fractures
What allows for stability of the conventional bone plate?
friction between the plate and the bone
What happens when the patient load on a conventional plate is less than the frictional force between the plate and the bone?
the construct is stable and can withstand patient loading
What happens when the patient load on a conventional plate is greater than the frictional force between the plate and the bone?
the construct is unstable and patient loading can cause it to move
What is the purpose of plate contouring for a conventional plate?
increase the area of contact between the plate and the periosteum
Why is friction not needed between the bone and plate when using locking plates and locking screws?
there is friction between the screw and the plate
What is the model of failure for conventional plates/screws?
load can cause screws to move out one at a time; no defect in the drilled holes of the screws
What is the model of failure for locking plates/screws?
load causes screws/plate to move all together; can cause defects defects in the bone due to movement
What are the plate functions?
-compression
-neutralization
-bridging
Which plate functions provide absolute stability?
-compression plate
-protection/neutralization plate
Which plate function provides relative stability?
bridging plate
What are the steps of compression via DCP plate?
-screw is eccentrically placed/away from the fracture site
-screw tightening leads to fracture compression
What are the functions of a protection/neutralization plate?
-protects interfragmentary lag screw
-resists torsion, bending, and shearing forces
-provides absolute stability to promote direct bone healing
What are the characteristics of a bridging plate?
-used in multifragmentary fractures
-bridges the site to restore length. rotation, and angulation
-provides relative stability; bone heals via callus
Why is it important to minimize the size of the gap left between bone fragments?
a smaller gap will have the least amount of movement when load is applied to the bone
