863 Finite element modelling of the Ilizarov external fixation system M Watson1,2, K J Mathias1, N Maffulli3, D W L Hukins4, and D E T Shepherd4* 1 Department of Bio-Medical Physics and Bio-Engineering, University of Aberdeen, Fosterhill, Aberdeen, UK 2 Finsbury Orthopaedics, Leatherhead, Surrey, UK 3 Department of Orthopaedic and Trauma Surgery, Keele University School of Medicine, Hartshill, Stoke on Trent, UK 4 Department of Mechanical Engineering, School of Engineering, The University of Birmingham, Edgbaston, Birmingham, UK The manuscript was received on 9 August 2006 and was accepted after revision for publication on 18 June 2007. DOI: 10.1243/09544119JEIM225 Abstract: This study describes a computational method for predicting the mechanical response of any configuration of the Ilizarov external fixation system. Mechanical testing of each of the individual components (ring, threaded rod, and wire) of the Ilizarov system was used to determine the stiffness of each component. Finite element (FE) analysis was then used to model each of the individual components. Each model was tuned to match the mechanical testing. A modular FE modelling system, using a master input file, was then developed where the tuned FE models of the individual components could be generated, positioned, and inter- connected to replicate a range of fixator configurations. The results showed that the stiffness predications from the FE modelling of the fixator configurations were consistently 10 per cent higher than the stiffness values obtained from the mechanical testing. The FE modelling system can be used to predict the characteristic response of the fixator configurations and clearly shows the relative changes in that response for variations in the number of components used. Keywords: external fixation, finite element modelling, Ilizarov system, mechanical testing 1 INTRODUCTION as well as the number of wires, rings, and threaded rods that are used to produce a particular fixator assembly [7]. The fixator stiffness is, therefore, The Ilizarov [1] external fixation system is commonly used for fracture fixation and limb lengthening. critical to bone healing. Computational modelling can investigate the stiff- A fixator assembly consists of wires, rings, and threaded rods that can be assembled in various con- ness of different fixator assembles without the need for experimental testing. Finite element (FE) modelling figurations for use in different treatments. The rings are connected by threaded rods. Wires are placed has previously been used to study the wire and ring components [7, 8–11], but only one previous attempt through the bone and are bolted to one side of the ring. Using a tensioning device, the wires are then has been made to use FE modelling to investigate the whole Ilizarov external fixator system, but this tensioned to between 500 and 1300 N before they are bolted to the other side of the ring [1–3]. was just limited to the ankle [12]. In this study, an FE model of the Ilizarov fixation device was created During patient activity, there will be a degree of movement between the bone fragments and, within to assess the feasibility of using this method as an aid to preclinical planning. The objectives of the certain limits, this motion can be beneficial to the healing process [4–6]. The movement of the bone at study were as follows: a fracture site is influenced by the fixator stiffness, (a) to characterize the behaviour of each individual which mainly depends on the tension of the wires, component of the Ilizarov fixation system using * Corresponding author: Department of Mechanical Engineering, mechanical testing; (b) to generate FE models of each individual School of Engineering, The University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK. email: d.e.shepherd@bham.ac.uk component; JEIM225 © IMechE 2007 Proc. IMechE Vol. 221 Part H: J. Engineering in Medicine