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Research Papers

Analysis of the Effect of Ring Stiffness on the Mechanical Performance of a Two-Ring Ilizarov Fixator

[+] Author and Article Information
S. Olutunde Oyadiji

e-mail: s.o.oyadiji@manchester.ac.uk

Dynamic and Aeroelasticity Group,
School of Mechanical, Aerospace
and Civil Engineering,
The University of Manchester,
Manchester M60 1QD, UK

1Corresponding author.

Manuscript received November 14, 2011; final manuscript received September 12, 2013; published online December 6, 2013. Assoc. Editor: Vijay Goel.

J. Med. Devices 8(1), 011001 (Dec 06, 2013) (12 pages) Paper No: MED-11-1100; doi: 10.1115/1.4025907 History: Received November 14, 2011; Revised September 12, 2013

The two-ring Ilizarov fixator is superior, in terms of space and weight savings, to the traditional four-ring Ilizarov fixator. But the stiffness of the two-ring Ilizarov fixator is low. This weakness causes the two-ring Ilizarov fixator to be hardly used in corrective surgery. It has been shown that the configurations of the fixator, such as ring diameter and cross angle of the wires, can affect the stiffness of the fixator. In this study, the focus was on the effects of the properties of the ring, such as ring diameter, ring deformation, and ring material, on the stiffness of the two-ring Ilizarov fixator. The finite element analysis (FEA) technique was employed to model all the two-ring Ilizarov fixators using the ABAQUS FEA software. The following findings were achieved: (1) the radial deformation of the ring has an almost linear relationship with the vertical displacement of the bone especially when the radial deformation is larger, (2) the change in the stiffness of the two-ring Ilizarov fixator caused by the variation of the wire angle is due to the deformation of the ring, (3) the pretension on the wire is greatly reduced after it is attached to the ring, and (4) the influence of ring material on the stiffness of the two-ring Ilizarov fixator is less when the fixator wire angles are 90 deg-90 deg rather than 0 deg-0 deg. Based on these findings, in a real clinical application, the stiffness acting in a fixator-bone system during the course of a treatment and the stiffness of the growing bone can be deduced in a nonintrusive way.

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References

Figures

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Fig. 1

Two-ring Ilizarov fixators

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Fig. 2

Relationship between displacement and mesh size when using different element types (C3D20R, C3D20, and C3D8R)

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Fig. 3

Rotation of the wires

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Fig. 4

Displacement distribution for model ϕ150-0 deg-0 deg of ring diameter 150 mm and first and second level wire angles of 0 deg (a) in U1 direction and (b) in U2 direction

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Fig. 5

Displacement level for the ϕ150-0 deg-0 deg of ring diameter 150 mm and first and second level wire angles of 0 deg in U3 direction: (a) isometric view; (b) cut view

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Fig. 6

Displacement level for the ϕ150-30 deg-60 deg of ring diameter 150 mm and first and second level wire angles of 30 deg and 60 deg, respectively, (a) in U1 direction, (b) in U2 direction, and (c) in U3 direction

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Fig. 7

(a) Relationship between displacement and axial load and (b) stiffness characteristics of two-ring Ilizarov fixators of 150 mm ring diameter, and first and second level wire angles of 0 deg-0 deg, 0 deg-30 deg, 30 deg-30 deg, 30 deg-60 deg, 60 deg-90 deg, and 90 deg-90

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Fig. 8

Displacement of the wire under different load on the bone of model 240-0-0

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Fig. 9

Relationship between displacement and axial load of two-ring Ilizarov fixators with ring diameter of 150, 180, 200, 240 mm, (a) first and second level wire angles are 0 deg, and (b) first and second level wire angles are 90 deg

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Fig. 10

Stiffness characteristics of two-ring Ilizarov fixators with ring diameter of 150, 180, 200, 240 mm, (a) first and second level wire angles are 0 deg, and (b) first and second level wire angles are 90 deg

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Fig. 11

Displacement of the bone against the diameter of the ring for different models

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Fig. 12

Differences in fixator displacements per 10 mm increase of the ring diameter of each model

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Fig. 13

Radial displacement of ring on (a) first level; (b) on second level

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Fig. 14

Transverse displacement of the wire on (a) first level; (b) on second level

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Fig. 15

Deformation of frames (a) with the same wire angle on each ring (b) with different wire angle on each ring (scale factor 30)

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Fig. 16

Radial displacement of ring on first level against the wire angle on first level of model ϕ240-m deg-0 deg

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Fig. 17

Displacement and stiffness of two ring fixator for different wire angles of model ϕ240-m deg-0 deg under 1000 N axial load

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Fig. 18

Stress distribution and deformation of model 240-0-0; (a) stress distribution, (b) deformation of the ring (with a scale factor of 100), (c) detailed view on the connection of wire and ring, and (d) detailed deformation of the ring (with a scale factor of 100)

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Fig. 19

Stress on the wire on model 240-0-0

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Fig. 20

Relationship between wire and bone vertical displacement and ring radial deformation when the load on the bone increases from 100 N to 1000 N on model 240-0-0: (a) wire displacement, (b) bone displacement

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Fig. 21

(a) Single ring radial deformation, and (b) single wire vertical displacement on model ϕ240

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Fig. 22

Displacement of Ilizarov fixator with different materials

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Fig. 23

Displacement of Ilizarov fixator for generic values of Young's modulus: (a) overall view, (b) detailed view

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Fig. 24

Distribution of stress in two-ring Ilizarov fixators with ring diameter of 150 mm and first and second level wire angles of 0 deg, which are designated as models ϕ150-0 deg-0 deg: (a) without holes; (b) with holes

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