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

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.