Chapter 41 Internal Fracture Fixation

Question 1

Buttress plating vs bridging implant

Answer 1

Bridging Implant: rigidly fixed to the proximal and distal major fragments and can bear the entire load. – usually used in comminuted fractures
Buttress implant: Same but relates to implants near the joint

Question 2

Buttress/bridging plate:
Forces resisted?
What type of fractures are they used for?
Function?

Answer 2

Resists all the forces
Used for fractures that can’t be anatomically reconstructed – Healing by biological osteosynthesis – secondary bone healing
Function of a bridging plate: to carry all the weight and prevent axial deformity as a result of shear and bending

Question 3

How many twists are necessary to maintain tension in cerclage wire

Answer 3

Twist knot - 1 twist
Single loop - 1.5 twists

Question 4

What are the initial tension and load to loosen numbers for cerclage wire

Answer 4

Twist: 70-100 load to loosen 260 N
Single loop: 150-200 load to loosen 260 N
Double loop: 300-500 load to loosen 666 N

Question 5

recommended IM pin size - when its the only intramedullary device

Answer 5

Should fill at least 70% of the medullary diameter

Question 6

How to calculate AMI of a pin

Answer 6

Radius of the pin ^ 4th power

Question 7

What are the advantages of an interlocking nail

Answer 7

Nails placed near neutral axis of bone – therefore subjected to compressive forces rather than bending (plates undergo bending forces during axial compression)
Larger area moment of inertia therefore, more resistant to bending and stiffer compared to plates
Locking mechanism provides stability in torsion and compression
IM location of nail eliminates risk of construct failure via screw pull out

Question 8

How to calculate AMI of an ILN

Answer 8

Radius ^ 4th power

Question 9

Calculate plate AMI

Answer 9

Thickness ^ 3rd power

Question 10

AMI 3.5 bolt vs AMI 4.5 screw

Answer 10

AMI 3.5 bolt = 7.4 - core diameter 3.5
AMI 4.5 screw = 4.0 - core diameter 3.0
All bolts core diameter are the same as their bolt size

Question 11

AMI of 8mm ILN vs 3.5mm DCP plate

Answer 11

8mm ILN 6.8x > 3.5mm DCP plate
8mm ILN 3.5x > 3.5 BROAD DCP plate

Question 12

How far should self tapping screws extend past the cortex

Answer 12

Screw must be advanced so that the cutting flutes pass completely through the far cortex to achieve holding power similar to a tapped screw = 2mm beyond the transcortex

Question 13

Locking compression plate function

Answer 13

Can be used as a conventional dynamic compression plate for rigid fixation or as a pure internal fixator with unicortical locking head screws

Question 14

Purpose of neutralization plate

Answer 14

Protects the interfragmentary compression achieved with the lag screw (or cerclage) from all rotational, bending, and shearing forces. Physiologic loads are carried largely by the plate and to a lesser extent by the reconstructed diaphysis.

Question 15

Dynamic compression plate

Answer 15

The DCP has a hole design allowing for axial compression by eccentric screw insertion. The same plate may function in different modes: compression, neutralization, bridging, or buttress.

Question 16

Bridge plating function

What is its main focus and characteristics
How does it promote healing

Answer 16

Focus on biological osteosynthesis by preserving blood supply.

Less stiff. Allows for more motion between fragments which promotes secondary bone healing.

Characterized by high plate bridging ratio (plate-to-bone length ratio), a low plate screw density (number of screws to number of plate holes ratio), and a low plate span ratio (plate-to-fracture length ratio)

Question 17

Core diameter, screw head, and drill diameter of 3.5mm cortical screw

Answer 17

Drill 2.5mm
Shaft/core 2.4
screw head 6mm

Question 18

Core diameter and drill diameter of 3.5mm locking screw

Answer 18

Drill 2.8
Shaft 2.9

Question 19

Drill diameter and shaft diameter of 4.0mm cancellous screw

Answer 19

Drill 2.5
Shaft 2.0

Question 20

How much can you compress a 2.7mm DCP plate

Answer 20

0.8mm per hole

Question 21

How much can you compress 3.5mm and 4.0mm DCP plates

Answer 21

1mm per hole

Question 22

How much can a screw be inclined in the longitudinal and transverse planes in a DCP plate

Answer 22

25 degrees inclination in the longitudinal plane
7 degrees inclination in the transverse plane

Question 23

How much can a screw be inclined in the longitudinal and transverse planes in a LC-DCP plate

Answer 23

40 degrees inclination in the longitudinal plane
7 degrees inclination in the transverse plane

Question 24

When using a universal drill guide which side is neutral and which do you use to load

Answer 24

Green - neutral
Gold - eccentric/load

Question 25

What is fretting

Answer 25

When screw head is moving in relation to the plate hole or in relation to a nail, the passive layer is repeatedly destroyed and there is “fretting” and local corrosion of the area of contact.

Question 26

What is the passive layer of a plate

Answer 26

forms on the surface of stainless-steel implants protecting implant from corrosion.

Question 27

In a plate-rod combo, can the plate be shorter than if using a plate alone

Answer 27

iii. Because most bones flare toward the metaphyses, it is usually possible to place bicortical screws closer to the ends of the bone. For this reason, the length of the plate is greater than might be used normally. *

Question 28

How much canal fill should there be when using plate-rod combo

Answer 28

35-40%

Question 29

Advantages of rod in bridging plate-rod

Answer 29

IM pin added to bridging plate reduces the internal plate stress and increases fatigue life of the plate
Pin reduces strain on screw hole