The impact of configuration of the Ilizarov fixator on its stiffness and the degree of loading of distraction rods

Abstract

Background: The mechanical parameters of the Ilizarov fixator are influenced by many factors related to its spatial configuration. The aim of this study was to experimentally evaluate the impact of the type of implant and the number of distraction rods on the uniformity of loading of distraction rods and stiffness coefficients of the Ilizarov fixator.

Methods: The tests were carried out on a physical model. The model was mounted in a universal loading station MTS 858 Mini Bionix. Forces in distraction rods are measured with the use of strain gauge force transducers. Displacements of bone fragments were measured by means of digital image correction.

Findings: In the case of a fixator with 3 distraction rods, configuration of implants has no statistically significant effect on the forces occurring in distraction rods. In the case of a fixator with 4 distraction rods, there are statistically significant differences in the forces in distraction rods. The highest transverse stiffness coefficients occurs in the system with 4 distraction rods and the configuration of 1K1S implants, while the smallest transverse stiffness coefficients occurs in the fixator with 4 distraction rods and the configuration of 0K1S implants.

Interpretation: Based on the results of experiments on the physical model, we observed an asymmetry in the distribution of forces transmitted through distraction rods. The configuration with 3 distraction rods provides more uniform distribution of forces in distraction rods and reduces the impact of the implant configuration on transverse stiffness coefficients. The use of a configurations with 4 rods may be advantageous when we want to obtain greater transverse stiffness coefficients of a system consisting of the fixator and fragments of the lengthened bone.

Keywords: Distraction rods; Ilizarov; Load distribution; Stiffness coefficients.