Screws and plates Flashcards
What forces do plates contol?
all the forces
plate–bending
screws–torsion, compression, tension
What is required for a bone plate to adequately control all of the forces acting on a fracture?
The screws holding it must engage 6 cortices in both the proximal and distal fragments
How does an IM pin help a bone plate?
it provides better control over cycling forces than the plate alone
How do locking plates differ from other bone plates?
they act like external fixators so their rules of application differ from those applicable to regular bone plates
What are nonlocking bone plates?
The bone plates are screwed into the fractured bone so scews transfer forces of weightbearing from bone to plate by increasing friction between bone and plate–thus want plate closely contoured to bone
What are locking bone plates?
the scews screw into the bone AND into the plate. “internal external fixators” Don’t need to be as closely applied to the bone. However, cannot place scews at an angle
What are locking bone plates?
the scews screw into the bone AND into the plate. “internal external fixators” Don’t need to be as closely applied to the bone. However, cannot place screws at an angle
What are forces neutralized by plates?
all forces
Why are screws not usually used by themselves?
they don’t control bending
What are advantages of plate fixation?
- reconstruction of fractured bone not necessary
- can be placed in areas of a lot of overlying muscle mass (femoral, humoral, pelvic fracture repairs)
- require little intervention once plated
- can compress fracture fragments to increase friction
What are the disadvantages of plate fixation?
- nonlocking plates require surgical approach almost as long as the plate (can sometimes tunnel to place locking plate)
- screw placement dictated by location of preformed holes in plate
- can be difficult to capture short proximal or distal fragments with the minimum 3 screws
- if infection present can be difficult to resolve completely without removing the plate–requires operation!
What are the advantages of pin-pate combinations?
- the IM pin adds significant bending control, the plate takes care of torsional and axial forces
- the pin can simplify fracture reduction for plate placement
What is the minimum number of cortices that is required to be engaged by a screw in each major fragment with the pin-plate combination?
3
What should the diameter of the pin be in a pin-plate combination?
50%
What should the diameter of the pin be in a pin-plate combination?
50%
Screws are sized based on what?
their outer diameter
What size hole do you drill to place a screw?
the size of the inner diameter. then cut threads to the outer diameter of the scew
What are interfragmentary scews?
screws that are placed across the fracture once it is in alignment. can make a counterskin to prevent them form interfering with the plate
What are the rules for counting cortexes?
- 2 vs 1 cortex
- if a scew passes through a hole or a fracture line then that cortex doesn’t count
- a screw may be in the cortex of one segment and the cortex of another
What are positional screws?
screws for which both cortices are drilled and tapped and the screw is placed (may have to clamp if is going across a fracture line)
What are lag scews?
the near cortex is overdrilled so the threads don’t engage here. As you tighten the screw, the screw head hits the near cortex and the head compresses the near cortex against the far one
What are variable pitch screws and pins?
they have different pitch so they compress the fracture
How are bone plates named?
by the size of screws their holes accommodate
How are bone plates named?
by the size of screws their holes accommodate
What are three types of holes in a screw for plate placement?
- locking
- round holes
- oval holes–allow fracture to be compressed
What is a neutralization plate?
it holds the fracture fragments in close formation so that some axial forces can be borne by reconstructed bone
What is a compression plate?
the fragments are squeezed together–transverse fracture
What is a tension band?
the plate is there to counter mostly tensile forces
What is a butress plate?
the fracture isn’t fully reconstructed and the plate must bear most or all of the forces of weightbearing until the bone heals
What side of a bone should a plate be placed on?
on the tension side of the bone–better to stress in the long direction than to bend it
What are fractures that are good to plate?
- diaphyseal fractures (long time)
- fractures in locations where external skeletal fixation is not a good choice (muscle!)
- fractures in animals that may not return for a recheck
What fractures are NOT good to plate?
- fractures with short proximal or distal fragments
2. fractures involving growth plates
