Validation of a finite element model of the Kirschner-Ehmer external skeletal fixation system

Objective-To determine the validity of finite element analysis (FEA) as a m eans of examining biomechanical properties of the Kirschner-Ehmer external skeletal fixation system, Sample Population-10 paired tibiae harvested from skelstally mature dogs we ighing between 30 and 38 kg immediately following euthanasia for reasons un related to musculoskeletal disease. Procedure-A gap fracture was created in each bone: fragments were stabilize d with 3 frame configurations (type I, type II, and type III), using enhanc ed-profile threaded pins. Each bone-frame construct was tested, using a mat erials testing machine in 3 modes of testing: axial compression (AC), medio lateral (ML) bending, and craniocaudal (CC) bending, for a total of 9 tests /bone. The elastic limit of the constructs was not exceeded during testing. Mean stiffness value were determined from load-displacement curves. A fini te element model of each construct was created, using three-dimensional ela stic beam elements, and stiffness values were calculated, using FEA. Correl ations between experimental and FEA data then were determined. Results-Significant differences in stiffness were seen among ail 3 construc ts in CC bending and AC, with stiffness increasing with construct complexit y No significant difference in ML bending stiffness was seen between type-i i and type-ill constructs; however, both were significantly stiffer than th e type-I constructs. The experimental and FEA stiffness data were strongly correlated (AC, r = 0.994; ML bending, r = 0.998; CC bending, r = 0.985). Conclusions and Clinical Relevance-Strong correlations among experimental a nd FEA data indicate that FEA is a valid method of comparing stiffness of K irschner-Ehmer external skeletal fixation constructs.