|Types of external fixators|
An external fixator is a device (known as a "frame") that is positioned outside the body. It is used to connect pins and screws to the inside of the body through the skin and muscle soft tissues to the bone.
There are several types of external fixators :
Unilateral external fixators
Unilateral external fixators are set along one side of the limb. At the thigh, the fixator is set on the outer lateral side of the limb. At the leg, the fixator is set on the inner, internal, or medial side of the leg.
Devices currently in use include Orthofix®, Heidelber®, Judet®, Wagner®, and FSA®.
The main section of the external fixator is connected to the bone with screws or half-pins that are large in diameter (4 mm to 6 mm). Patient tolerance of the fixator is good.
V-shape external fixators are 2 unilateral external fixators set in triangulation.
Circular External Fixators
Compared with unilateral external fixators, circular external fixators allow better stability of bone fragments. Small pins or wires (1.5 mm to 2 mm diameter) are used under tension and eventually combined with screws or half-pins. However, circular fixators are less comfortable for the patient, which is often why unilateral fixators are preferred. Circular fixators allow complex lengthening with multiple axis correction, which is gradually obtained after the surgery.
The first external fixator was designed by Ilizarov, who standardized the methods and modern procedures for limb lengthening with external fixators. He used the concept of the bicycle wheel, in which circular strength is maintained by connection to a hub through tensioned wires. This reduces the weight of the wheel and provides good stability, provided the wires are tensioned evenly.