Chapter 41 Internal Fracture Fixation Flashcards
Buttress plating vs bridging implant
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
Buttress/bridging plate:
Forces resisted?
What type of fractures are they used for?
Function?
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
How many twists are necessary to maintain tension in cerclage wire
Twist knot - 1 twist
Single loop - 1.5 twists
What are the initial tension and load to loosen numbers for cerclage wire
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
recommended IM pin size - when its the only intramedullary device
Should fill at least 70% of the medullary diameter
How to calculate AMI of a pin
Radius of the pin ^ 4th power
What are the advantages of an interlocking nail
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
How to calculate AMI of an ILN
Radius ^ 4th power
Calculate plate AMI
Thickness ^ 3rd power
AMI 3.5 bolt vs AMI 4.5 screw
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
AMI of 8mm ILN vs 3.5mm DCP plate
8mm ILN 6.8x > 3.5mm DCP plate
8mm ILN 3.5x > 3.5 BROAD DCP plate
How far should self tapping screws extend past the cortex
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
Locking compression plate function
Can be used as a conventional dynamic compression plate for rigid fixation or as a pure internal fixator with unicortical locking head screws
Purpose of neutralization plate
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.
Dynamic compression plate
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.
Bridge plating function
What is its main focus and characteristics
How does it promote healing
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)
Core diameter, screw head, and drill diameter of 3.5mm cortical screw
Drill 2.5mm
Shaft/core 2.4
screw head 6mm
Core diameter and drill diameter of 3.5mm locking screw
Drill 2.8
Shaft 2.9
Drill diameter and shaft diameter of 4.0mm cancellous screw
Drill 2.5
Shaft 2.0
How much can you compress a 2.7mm DCP plate
0.8mm per hole
How much can you compress 3.5mm and 4.0mm DCP plates
1mm per hole
How much can a screw be inclined in the longitudinal and transverse planes in a DCP plate
25 degrees inclination in the longitudinal plane
7 degrees inclination in the transverse plane
How much can a screw be inclined in the longitudinal and transverse planes in a LC-DCP plate
40 degrees inclination in the longitudinal plane
7 degrees inclination in the transverse plane
When using a universal drill guide which side is neutral and which do you use to load
Green - neutral
Gold - eccentric/load
What is fretting
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.
What is the passive layer of a plate
forms on the surface of stainless-steel implants protecting implant from corrosion.
In a plate-rod combo, can the plate be shorter than if using a plate alone
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. *
How much canal fill should there be when using plate-rod combo
35-40%
Advantages of rod in bridging plate-rod
IM pin added to bridging plate reduces the internal plate stress and increases fatigue life of the plate
Pin reduces strain on screw hole
