Internal Fixation Flashcards
What were the initial conclusions on bone healing
- rigid internal compression fixation is ideal
- intact vasculature and bio mechanical stability are prerequisites for bone healing
what is the revised conclusion on bone healing
Fixation is based on the biology and personality of the fracture
What are the stages in bone healing?
Inflammation —> Regeneration/repair—> remodeling
Fracture & Hemorrhage —> hematoma necrosis —> soft callus to hard callus —> Haversian remodeling lamella (woven) primary bone
What components contribute to bio mechanical stability of a fracture
- intrinsic factors
- extrinsic factors
- mechanical forces of fixation
- techniques of fixation
What are the aspects of intrinsic factors
- fragment size
- bone quality
- fracture orientation (transverse, oblique, comminuted)
What are the extrinsic forces that contribute to fracture stability
- compression (axially mediated)
- bending
- torsion (side to side)
- shear
- weight bearing - osseous motion
- muscle/tendon movement
Based on fixation principles, what are the 2 ways of achieving stability
- stability by compression of fracture ends
- stability by inherent by splintage
What are the different types of stability by compression
- lag (by design or by technique)
- axial compression
- tension band
- compressions staples
What are some components of stability by splintage
- buttress and anti glide (load bearing)
- bridge plates
- neutralization (load sharing)
- intramedullary nailing
- blade plates
What is the importance of the head of the screw
Driving mechanism
What is the land of the screw
Underside of the head
What is the pitch of the screw
Distance between threads
What is the core of the screw
The minor diameter
What is the importance of increasing core diameter
Increase bending resistance
What is the screw thread
The major diameter
at is the importance of increase screw thread
Better purchase in cancellous bone
Hat is the shaft of the screw
The region devoid of threads
What is the run out of the screw
Where the shaft meets the threads
What is the weakest point of the screw
The run out
What are the 2 different types of screw tips
- non self drilling
- self drilling
What are the types of non self drilling screws
- round
- pointed
What are the types of self drilling screws
- fluted
In relation to a fracture line, how should you position the runout of the screw
Place runout as far as possible from the fracture line
What are the screw sizes in the mini fragment
- 1.5mm
- 2.0mm
- 2.7mm
What surgery would you typically use mini fragment screws
- forefoot surgery
- Talar neck dx
- cuboid dx
What are the sizes of screws in the small fragmen
- 3.5mm
- 4.0mm
What surgery would you typically use small fragment screws
- lisfranc fx’
- calcaneal fix
- ankle dx
What are the screw sizes in the large fragment
- 4.5 mm
- 6mm
What type of surgery would you typically use screws from the large fragment
- hindfoot fusion procedures
Why is the design of the screw threads important
Influences screw purchase into bone
What is the thread angle
Determines the rate at which screw advances into bone
What is a similarity between buttress and V thread
Equal pull out strength
What are the differences between buttress (asymmetrical thread) and V thread
Buttress maximizes bone volumes between threads and increases bending resistance
Which type of screws have smaller pitches
Cortical screws
What is the purpose of cortical screws having smaller pitch
Maximize contact in short segment (cortical thickness) dense and compact bone
What is the purpose of cancellous screws having larger pitch
Increase limited bone volume between threads to maximize contact
What are some disadvantages of a cannulated scree
- decreased thread to core ratio
- lower pullout strength
- reduced bending stiffness
What is a disadvantage of headed screws
Prominence
What is an advantage of headed screws
Larger contact surface area, increase contact area to improve compression
Does a headed screw have threads in the head and does the head advance into bone
No threads in head and head does not advance into bone
Do headless screws have threads in the head and does the head advance into the bone
Yes heads have thread and head advances into the bone
What is the lag effect
Compression along bone ends
What is entailed in lag effect by technique
- fully threaded screw
- gliding hole: larger overdrive the near cortex, but not past the fracture site
- smaller underdrill the near and far cortex
- head of screw must be in contact with near cortex, and not penetrate near cortex
- compression will be lost if not perpendicular to fracture or greater than 22 degrees to line orthogonal to fracture
What are the three different techniques of the lag effect
- standard
- small fragment
- compromise technique
What is the standard lag technique
Overdrill near cortex first, then underdrill near and far cortices
What is the small fragment lag technique
Underdrill near and far cortex first, then overdrill near cortex
What is the compromise technique of the lag effect
No overdrill
- uses a clamp
- compression captured by a positional screw
What are two categories of plate deigns
- locking versus non-locking
- stainless steel versus titanium
What are the plating by function categories
- neutralization
- bridge
- anti glide/buttress
- dynamic compression
In convention plating how is stability obtained
- screw torque (3-5N) squeezes plate onto bone
- bone to plate apposition
How is coefficient of friction generated
- squeezing plate onto the bone
In conventional plating, what is the load
Any axially mediated forces that would cause the plate to fail
What happens if coefficient of friction is greater than the load
Plate remains stable
What happens if the load is greater than the coefficient of friction
The plate fails
What are two important points for bone to plate apposition
- coefficient of friction»_space; load
- screw purchase dependent on quality of bone
What is the importance of conventional plating
- promote primary bone healing
What are locking screws
- plate screws with threads in the head
- “lock” into plates (head is recessed)
- does not compress plate into bone
Describe the angle of locking screws
Fixed angle
Locking screws act as ________ fixators. Why?
Internal fixators
-Screw lengths 10.15 times shorter than external fixators pins
What type of bone healing does locking screws promote
Secondary bone healing
What type of beams do locking screws have and how does this compare to other types of beams
- single beam
- 4 times stronger than load sharing beams where motion occurs between individual components
What are some pros of locked plating
- improved fixation in pathological and osteopenic bone
- reduction in scre loosening
- spares periosteral perfusion
- convert sheer stress to compressive stress at screw-bone interface
- confers relative stability to promote secondary bone healing
The strength of locking plates is dependent on:
Screw diameter
Plate thickness
Which type of plating, conventional or locking, have a higher failure threshold
Locking
Are neutralization plates for load bearing or load sharing
Load sharing
What types of loads are neutralization meant to resist
- bending
- rotational/torsional
- axial/shear
Is the antiglide plate load bearing or load sharing
Load bearin
Where is an antiglide plate placed in relation to a fraction
Over the apex of the fracture, the direction it wants to fail towards
What type of forces do antiglide plates counter
- shear forces looking to overcome the coefficient of friction
What does the antipglide plates do to shear forces
Converts it to compressive axial forces - biomechanically strong
What is buttress plating
A support structure built against a wall
What makes buttress plating different from antiglide plating
Buttress plating is antiglide plates used with intra and peri articulation fractures
Can load bypass the fracture in buttress plating
No
What is one importance of buttress plating
- helps maintain length and alignment
What is bridge plating
Plating spanning an area of comminution
What is dynamic compression plating
Plate generated compression
What is dynamic compression plating indicated for
- short transverse fractures
- short oblique
Where ideally are your screws in compression plating
- towards the further ends of the hole, not dead center in the screw hole
Why do you have to pre-bend/pre-stress the plate in compression plating
Because the screws causes the far cortex to gap open
Ie it prevents gapping of opposite cortex
What re examined if fused angle constructs
- staples
- blade plate -needs a good construct, don’t use in porotic bone
Although intrameduallary nailing acts like a splint, what do you have to be aware of
- no compression
- increase risk of mal Union
Which plating is intramedullary nailing most similar to
Bridge plate
What type of forces are intrameduallary nailing strong against
Bendin
What type of forces are intrameduallary nailing weak against
Axial rotation
One biological benefit of intramedullary nailing
Preserves periostea’s perfusion
What are some indications of intramedullary nailing
- concerns with soft tissue healing
- comminuted shaft fractures
- Charcot
- geriatric ankle/tibial fractures
- TibioTalarCalcaneal fusion
- TibioCalcaneal fusion
What type of nails are recommended for tibial canal
Long thick nails
What kind of torque and speed for cannulated drill over guidewire through Calcaneus and guidewire
Low torque, high speed
What kind of torque and speed for sequential reading of tibial canal over guidewire
High torque low speed
