External Skeletal Fixation (ESF)

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Basic Construct

An external fixator comprises a smooth pin, clamps and small pins that penetrate the bone at an angle.

Fig 1

Strong Construct

The use of multiple connecting bars, clamps and pins in different planes gives a very strong frame. This would generally be used in fractures with significant fragmentation that needs a strong scaffold. These frames are generally weakened by removal of components over time until the fracture heals.

Fig 2

Weak Construct

The Connecting bar is narrow and is very far from the centre of the bone.

Fig 3

External Fixators are essentially "Extramedullary Pins". In this method a smooth round pin is positioned outside of the skin and connected to the bone using small pins attached to the main bar with clamps (fig 1). 

External Fixators are weaker at resisting bending than Intramedullary Pins because they are further from the centre of the bone. They are excellent at resisting rotation and moderately good at resisting collapse of the fracture (this will depend on the number of clamped pins and the distance from the bone to the clamp.

Healing with External Fixation depends on the strength of the construct. If the frame is too strong it will slow healing, if it is too weak it may fail and/or prevent healing. The strength of a fixator can be influenced by:

1. Distance from centre of bone to the connecting bar.

2. Thickness and Number of External Bars.

3. Number of Clamps.

4. Diameter and design of the small pins penetrating the bone.

These factors are shown in figures 2 and 3.

The main problems seen with ESFs are associated with the interface between the pin and the skin the interface between the pin and the bone. The first is associated with discharge and infection (Fig 4) and the second with pin loosening (Fig 5).

External Fixation is generally used in extremity injuries such as Radial and Tibial Fractures or to bridge Hock Dislocations. This is because these bones have less muscle cover and thus the pins do not penetrate and Skewer the muscle to the bone. It is possible however to use specific constructs in the Femur and the Humerus to reduce this risk.

External Fixators can also be used to augment an intramedullary pin, reducing the risk of rotation (fig 6).

Torrington Orthopaedics, IES House, Mission Street, Brighouse, West Yorkshire, HD6 1NQ
Telephone 0844 880 8051 Fax 01484 404771
Contact me: andy@torvet.co.uk