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Wheeless' Textbook of Orthopaedics

Wheeless' Textbook of Orthopaedics

C.R. Wheeless MD

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Wheeless' Textbook of Orthopaedics


Mechanical performance of Ilizarov circular external fixators in

comparison with other external fixators.

Podolsky A. Chao EY.

Clinical Orthopaedics & Related Research. [JC:dfy] (293):61-70, 1993 Aug.

The fundamental difference of the Ilizarov fixator is the type of pins

used for bone fixation, i.e., Kirschner wires 1.5 mm and 1.8 mm in

diameter, pretensioned from 50 to 130 kg before being affixed to the rings

that are connected and fixed by threaded rods. The mechanical

characteristics of external fixators may influence the biologic

environment at the fracture site and ultimately decide the outcome of a

surgical procedure. Thus, knowledge of the mechanical properties of the

Ilizarov fixator is essential to a surgeon using it in clinical practice.

The main objective of this study was to quantitate the mechanical behavior

of the standard Ilizarov fixator under different loading conditions and

fixator frame/wire configurations. The fixator was found to have a

nonlinear stiffness behavior under axial compression. The nonlinearity in

axial stiffness also varied with wire pretension. Such characteristics,

however, were not as pronounced under torsion and bending loads within the

test range studied. Besides the wire pretension, the most important factor

affecting the structural stiffness of the Ilizarov device was the diameter

of the wire. Offset bone position provided greater stiffness in loads up

to 45 kg in axial compression, in torsion up to 5 degrees of rotation, and

in the final loading range under bending. Fixators with wires crossing at

45 degrees had significantly greater stiffness in torsion as compared with

90 degrees crossing wires, but the opposite was true in axial compression.

Torsional stiffness increased significantly under coupled axial

compression applied through the bone ends. All four-point bending tests

demonstrated two distinct stiffness curves that were probably due to

slippage of the bone model on the wires. This information should help to

understand the mechanical behavior of the Ilizarov device and thereby

improve its clinical performance.



Mechanical performance of Ilizarov circular external fixators in

comparison with other external fixators.

Podolsky A. Chao EY.

Clinical Orthopaedics & Related Research. [JC:dfy] (293):61-70, 1993 Aug.

The fundamental difference of the Ilizarov fixator is the type of pins

used for bone fixation, i.e., Kirschner wires 1.5 mm and 1.8 mm in

diameter, pretensioned from 50 to 130 kg before being affixed to the rings

that are connected and fixed by threaded rods. The mechanical

characteristics of external fixators may influence the biologic

environment at the fracture site and ultimately decide the outcome of a

surgical procedure. Thus, knowledge of the mechanical properties of the

Ilizarov fixator is essential to a surgeon using it in clinical practice.

The main objective of this study was to quantitate the mechanical behavior

of the standard Ilizarov fixator under different loading conditions and

fixator frame/wire configurations. The fixator was found to have a

nonlinear stiffness behavior under axial compression. The nonlinearity in

axial stiffness also varied with wire pretension. Such characteristics,

however, were not as pronounced under torsion and bending loads within the

test range studied. Besides the wire pretension, the most important factor

affecting the structural stiffness of the Ilizarov device was the diameter

of the wire. Offset bone position provided greater stiffness in loads up

to 45 kg in axial compression, in torsion up to 5 degrees of rotation, and

in the final loading range under bending. Fixators with wires crossing at

45 degrees had significantly greater stiffness in torsion as compared with

90 degrees crossing wires, but the opposite was true in axial compression.

Torsional stiffness increased significantly under coupled axial

compression applied through the bone ends. All four-point bending tests

demonstrated two distinct stiffness curves that were probably due to

slippage of the bone model on the wires. This information should help to

understand the mechanical behavior of the Ilizarov device and thereby

improve its clinical performance.

 
 
 
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