A Finite Element Study of the Ilizarov External Fixator

Finite element models were constructed to represent two different Ilizarov External Fixator configurations in order to determine the effect of corticotomy location on the stresses at the hip and knee joints. The models of the fixator systems were attached to a finite element model of a human femur. Figure 3, which was constructed using an automated program developed to create the model from digitized data obtained from CAT scans of a cadaveric femur. The models were constructed using the I-DEAS VI software in three main phases; the two fixator configurations, the human femur, and the muscle groups. The first fixator configuration modeled, Figure 1, used for a proximal corticotomy location, was made up of 67 beam elements and 369 thin shell elements. The second fixator configuration, Figure 2, used for a distal corticotomy location, had again, 67 beam elements but only 155 thin shell elements, because of the smaller partial ring used. The femur model, Figure 3, consisted of 1,698 brick elements, 112 wedge elements and 8 tetrahedral elements, for a total of 1,818 solid elements, with orthotropic material properties of cortical bone. The Kirschner wires and half pins were modeled as beam elements passing through the solid elements where they connect to the bone model. The muscles were modeled as rod elements connected to the bone models, femur and partial tibia and pelvic bones, Figure 4, at their insertions and origins. The properties of the muscles differed based on their physiologic cross sectional areas.