Screws and plates

Question 1

What forces do plates contol?

Answer 1

all the forces
plate–bending
screws–torsion, compression, tension

Question 2

What is required for a bone plate to adequately control all of the forces acting on a fracture?

Answer 2

The screws holding it must engage 6 cortices in both the proximal and distal fragments

Question 3

How does an IM pin help a bone plate?

Answer 3

it provides better control over cycling forces than the plate alone

Question 4

How do locking plates differ from other bone plates?

Answer 4

they act like external fixators so their rules of application differ from those applicable to regular bone plates

Question 5

What are nonlocking bone plates?

Answer 5

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

Question 6

What are locking bone plates?

Answer 6

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

Question 7

What are locking bone plates?

Answer 7

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

Question 8

What are forces neutralized by plates?

Answer 8

all forces

Question 9

Why are screws not usually used by themselves?

Answer 9

they don’t control bending

Question 10

What are advantages of plate fixation?

Answer 10

1. reconstruction of fractured bone not necessary
2. can be placed in areas of a lot of overlying muscle mass (femoral, humoral, pelvic fracture repairs)
3. require little intervention once plated
4. can compress fracture fragments to increase friction

Question 11

What are the disadvantages of plate fixation?

Answer 11

1. nonlocking plates require surgical approach almost as long as the plate (can sometimes tunnel to place locking plate)
2. screw placement dictated by location of preformed holes in plate
3. can be difficult to capture short proximal or distal fragments with the minimum 3 screws
4. if infection present can be difficult to resolve completely without removing the plate–requires operation!

Question 12

What are the advantages of pin-pate combinations?

Answer 12

1. the IM pin adds significant bending control, the plate takes care of torsional and axial forces
2. the pin can simplify fracture reduction for plate placement

Question 13

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?

Answer 13

3

Question 14

What should the diameter of the pin be in a pin-plate combination?

Answer 14

50%

Question 15

What should the diameter of the pin be in a pin-plate combination?

Answer 15

50%

Question 16

Screws are sized based on what?

Answer 16

their outer diameter

Question 17

What size hole do you drill to place a screw?

Answer 17

the size of the inner diameter. then cut threads to the outer diameter of the scew

Question 18

What are interfragmentary scews?

Answer 18

screws that are placed across the fracture once it is in alignment. can make a counterskin to prevent them form interfering with the plate

Question 19

What are the rules for counting cortexes?

Answer 19

1. 2 vs 1 cortex
2. if a scew passes through a hole or a fracture line then that cortex doesn’t count
3. a screw may be in the cortex of one segment and the cortex of another

Question 20

What are positional screws?

Answer 20

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)

Question 21

What are lag scews?

Answer 21

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

Question 22

What are variable pitch screws and pins?

Answer 22

they have different pitch so they compress the fracture

Question 23

How are bone plates named?

Answer 23

by the size of screws their holes accommodate

Question 24

How are bone plates named?

Answer 24

by the size of screws their holes accommodate

Question 25

What are three types of holes in a screw for plate placement?

Answer 25

1. locking
2. round holes
3. oval holes–allow fracture to be compressed

Question 26

What is a neutralization plate?

Answer 26

it holds the fracture fragments in close formation so that some axial forces can be borne by reconstructed bone

Question 27

What is a compression plate?

Answer 27

the fragments are squeezed together–transverse fracture

Question 28

What is a tension band?

Answer 28

the plate is there to counter mostly tensile forces

Question 29

What is a butress plate?

Answer 29

the fracture isn’t fully reconstructed and the plate must bear most or all of the forces of weightbearing until the bone heals

Question 30

What side of a bone should a plate be placed on?

Answer 30

on the tension side of the bone–better to stress in the long direction than to bend it

Question 31

What are fractures that are good to plate?

Answer 31

1. diaphyseal fractures (long time)
2. fractures in locations where external skeletal fixation is not a good choice (muscle!)
3. fractures in animals that may not return for a recheck

Question 32

What fractures are NOT good to plate?

Answer 32

1. fractures with short proximal or distal fragments

2. fractures involving growth plates