PAPER 43: BIOMECHANICS OF A NEW HYBRID EXTERNAL FIXATOR

Abstract

Introduction: To determine the stiffness characteristics of a new proposed hybrid fixator in comparison with more commonly used hybrid external fixators.

Methods: A prospective laboratory investigation was used to evaluate the null hypothesis that there are no differences in the mechanical stiffness between the new proposed hybrid fixator and the Ace-Fischer, DePuy-ACE, Warsaw, IN; Hoffmann II, Stryker Howmedica Osteonics, Rutherford, NJ; Synthes Hybrid, Synthes USA, Paoli, PA; EBI DynaFix®, EBI, Parsippany, NJ. Identical composite tibiae, after modeling OTA 41 – A 2.3 fracture, were fixed with the above fixators. Load-deformation behavior was compared between the different configurations under identical conditions of central-compression, medial compression-bending, posterior compression-bending, posterior-medial compression-bending and torsional loading. Stiffness values were calculated from the load deformation and the torque angle curves.

Results: The new proposed hybrid external fixator was stiffer than all the other fixators tested in all modes of testing, except for torsion. The Hoffman II, DePuyACE, EBI, and Synthes fixators were essentially equivalent in stiffness in all five modes of testing.

Conclusions: Decreasing the distance of the side bar to the center of the bone effectively shortens the length of the half-pins, which decreases their deflection during bending, and thus increases stiffness. We think that a better stiffness of new fixator than of others is due to a shorter distance between the bone surface and points of fixation of wires and half-pins. The proposed hybrid fixator corresponds to the contemporary requirements for external fixation: possibility to control the stiffness, easy to apply, comfortable for the patient (being light and simple).