Comparative biomechanics of hybrid external fixation

Objective: To compare the elastic stiffness, in several loading modes, of commercially available hybrid external fixation systems. Design: Laboratory investigation using a Polyvinylchloride pipe periarticular tibia fracture model. Setting: Simulated periarticular fractures were created in an in vitro tibia fracture model. Instrumented specimens and intact controls were elastically tested in a biomaterials testing system. Intervention: Groups of simulated periarticular tibia fractures were stabilized with one of six different hybrid external fixator designs. Main Outcome Measurements: Elastic stiffness of each specimen was measured in compression, torsion, flexion bending, extension bending, and varus/valgus bending. Results: Fixators with multiple levels of fixation in the periarticular fragment, regardless of design, were stiffer than those with one level. Specifically, the EBI Ring Connector fixator was stiffer than all others in all modes of testing. The Ace, Synthes, Smith & Nephew Richards, and Howmedica fixators were mechanically similar. The Zimmer Torus fixator was the least stiff fixator tested. Conclusions: Fixators with multiple levels of fixation in the periarticular fragment, regardless of design, were stiffer than those with one level. The choice of which hybrid external fixator to use should be made based not only on stiffness but also on ease of clinical application, patient comfort, customer support from the manufacturer, and cost. Clinical investigation of the efficacy of each of these devices is warranted.