AO Basics

Question 1

What are the four main principles of fracture management?

Answer 1

Anatomic reduction
Stable fixation
Preservation of blood supply/soft tissues
Early active mobilisation

Question 2

2 methods of bone healing?

Answer 2

1o- Absolute stability- <2%, no callus formation, cutting cones lead

2o- callus formation, relative stability- 2-10%, haematoma, soft callus, hard callus, remodelling

Question 3

How can you achieve absolute stability?

Answer 3

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

Question 4

Describe how to perform a lag screw to achieve absolute stability?

Answer 4

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

Question 5

What is Perren’s strain theory?

Answer 5

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

Question 6

What is Wolf’s Law?

Answer 6

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

Question 7

Features of the screw?

Answer 7

Device for converting rotational movement into linear movement

Head, pitch (distance between each thread), core and thread diameter

Question 8

Categories of screws?

Answer 8

Cortical vs cancellous
Partially vs fully threaded
Locking and non locking
Cannulated vs solid
Self tapping

Question 9

Purpose of locking screw?

Answer 9

Threaded head which engages into the place creating a fixed angle construct- internal external fixation

Question 10

Function of a washer?

Answer 10

To prevent sinking of screw into bone by distributing pressure + increases contact with bone

Question 11

Why do you countersink?

Answer 11

To increase surface area of the screw- dissipates stress

Question 12

Different types of plates?

Answer 12

Dynamic compression plates
LC DCP- limited contact dynamic compression plater
LCP- locking compression plate
Recon plate
Anatomical plate
Tubular pates

Question 13

How to perform dynamic compression plating?

Answer 13

Eccentric drilling + pre bending of the plate can lead to compression of the bone at the fracture site

Question 14

What is the working length?

Answer 14

The distance between the 2 fixation points closest to the fracture site. Decreasing working length leads to increased stiffness and stability.

Question 15

Difference between load bearing and loading sharing?

Answer 15

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

Question 16

What is the tip apex distance?

Answer 16

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

Question 17

How do you increase the stability of an Ex-Fix device?

Answer 17

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

Question 18

Describe the tension band principle?

Answer 18

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.

Question 19

How to manage a fracture related infection?

Answer 19

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

Question 20

How to debride an open fracture?

Answer 20

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