Mechanical Properties of External Fixator according to Its Arrangement and Structure

Han, Hong Jun; Lee, Byung Chang; Kim, Yeung Jin; Jin, Byung Soo; Lee, Gun Hyee

Abstract

PURPOSE: To obtain the accurate knowledge of the fundamental mechanical properties of the external fixator affected by variations in arrangements and structures. We used newly developed external fixator, Anyfix, universal testing machine and plastic padding bone model which had similar structural properties to human tibia. The measured performance for seven different configurations of external fixators was its ability to control the motion of the bone fragment at the fracture site. Based on a unit of applied load, the corresponding displacement measured at the fracture site was used to described the stiffness of the fixation device for each load. Three stiffness moduli can be determined as axial stiffness, anterior posterior bending stiffness and lateral bending stiffness.
RESULTS
In basic configuration, all three stiffnesses for unilateral two plane external fixator showed marked increase than those for unilateral one plane model. Axial compression stiffness and bending stiffness were increased when ring component were located far from the fracture site. In modified configuration, all three stiffnesses were increased when the number of pin was increased and small sized ring was used.
CONCLUSION
The stiffness of the external fixator can be substantially increased by using unilateral two plane, locating the ring at far portion from the fracture site, using a small sized ring and increasing the number of pins.