Principles of External Fixation

Indications

 

Acute / damage control

- compound injures

- periarticular injuries

- high energy injuries / let soft tissues settle

- multi-trauma (avoid second hit)

 

Chronic / definitive management

- mal /non union

- infection

- deformity

- LLD

 

Problems

 

Pin site infections

Malunion

Non union

 

Construction

 

Pins

 

Diameter

- < 1/3 diameter of bone

- 3, 4, 5 mm

 

Materials

- stainless steels

- titanium

- HA coated

 

Bars

 

Increased diameter

- increased strength and rigidity

 

Clamps

 

Modular, multidirectional

- pin to bar

- bar to bar

 

Frame types

- uniplanar

- biplanar

- circular

- hybrid (combination of planar + circular)

- joint spanning (non or articulated)

 

Increasing strength / stiffness

 

Increase pin diameter

Increase number of pins

Increase pin spread on same side of fracture

- near / far / near / far

 

Decrease distance of bar to bone

Increase number of bars

 

Note:  Increasing stiffness can lead to non union

- to increase union rates

- reduce stiffness

- i.e. reduce above factors

 

MRI issues

 

Non compatible

- local heating

- production of current

- costly disruption of MRI machine

- interference with pictures

 

Healing

 

1.  Rigid inter-fragmentary fixation

- intramembranous ossification

 

If a frame is too rigid

- osteopenic nonunion

- need to reduce rigidity

- may need bone graft

 

2.  Micro-motion / strain

- collagen formation and endochondral ossification

 

If a frame is too loose

- excessive callous

- hypertrophic non union

 

Types

 

Ankle External Fixation

 

Fracture blisters 1Fracture blisters 2

 

Ankle Ext Fix 1Ankle Ext Fix 2Ankle Ext Fix 3