AO Basics Flashcards
(20 cards)
What are the four main principles of fracture management?
Anatomic reduction
Stable fixation
Preservation of blood supply/soft tissues
Early active mobilisation
2 methods of bone healing?
1o- Absolute stability- <2%, no callus formation, cutting cones lead
2o- callus formation, relative stability- 2-10%, haematoma, soft callus, hard callus, remodelling
How can you achieve absolute stability?
Absolute stability means anatomic reduction and interfragmentary compression with absence of fracture micromotion under physiological load.
Relative stability means functional reduction (correction of alignment, rotation and length) in addition to motion control of the fractured fragments under physiological load
Lag screw +/- neutralisation
Buttress plate
Compression plating
Tension band wiring
Describe how to perform a lag screw to achieve absolute stability?
Oblique, simple fractures
Perpendicular to fracture site
Guide hole- 3.5mm- diameter of screw thread
Drill far cortex- 2.5mm
Countersink
Measure
Tap?
Insert screw until you get interframentary compression
Do not over do it
Then neutralisation plate- prevents rotational instability
What is Perren’s strain theory?
Strain affects the type of tissue laid down
<2% strain leads to lamellar bone
2-5%= hard cllus
5-10%= cartilage
10-100%= granulation tissue
What is Wolf’s Law?
Bone will remodel according to the loads under which it is placed.
Site of bone loading will lay down additional bone to site of decreased bone loading will become less dense.
Compression vs tension side
Features of the screw?
Device for converting rotational movement into linear movement
Head, pitch (distance between each thread), core and thread diameter
Categories of screws?
Cortical vs cancellous
Partially vs fully threaded
Locking and non locking
Cannulated vs solid
Self tapping
Purpose of locking screw?
Threaded head which engages into the place creating a fixed angle construct- internal external fixation
Function of a washer?
To prevent sinking of screw into bone by distributing pressure + increases contact with bone
Why do you countersink?
To increase surface area of the screw- dissipates stress
Different types of plates?
Dynamic compression plates
LC DCP- limited contact dynamic compression plater
LCP- locking compression plate
Recon plate
Anatomical plate
Tubular pates
How to perform dynamic compression plating?
Eccentric drilling + pre bending of the plate can lead to compression of the bone at the fracture site
What is the working length?
The distance between the 2 fixation points closest to the fracture site. Decreasing working length leads to increased stiffness and stability.
Difference between load bearing and loading sharing?
Load bearing is when there is no bony contact so the plate takes all the weight.
Load sharing is when the bone and the plate share the force- better for the plate and for fracture healing
What is the tip apex distance?
Baumgaertner et al. 1995
Sum of the distance between tip of screw and apex of femoral head on AP and Lateral
<25mm to reduce cut out risk
How do you increase the stability of an Ex-Fix device?
Larger pins
Contact ends of the fracture- load sharing
Additional pins
Decrease bone to rod distance
Pins in difference planes
Rods in different planes
Pre drilling leading to incresed axial load and less bone necrosis
Describe the tension band principle?
A tension band converts tensile force into compression force at the opposite cortex. This is achieved by applying a device eccentrically, on the convex side of a curved bone.
How to manage a fracture related infection?
Early or acute FRI:
Treat sepsis
No Abx if well
Late FRI:
MDT approach
Orthoplastics approach
Approach:
Bloods + cultures, xrays- osteomyelitis/loosening, photos
Early deep sampling- surgical vs radiological
USS for collection aspiration
Surgical debridement 5 deep MCS + 2 histo
Abx free period- 2 week in non acute infections, discuss with micro
Key questions
Has union occured?
Micro involvement
Which bug?
MDT led
How to debride an open fracture?
Excise wound edges and extend in line with fasciotomy lines- BOAST guidelines
Systematic approach debride each layer
Clockwise
Skin, fat, fascia, muscle, bone
Assess muscle for consistency, capillary bleeding, colour and contractility
If in doubt get rid
Preserve Arteries and Nerves
Bone tug test
Deliver the bone ends
Washout with 6L saline
