FRACTURE SITE MOTION WITH ILIZAROV AND HYBRID EXTERNAL FIXATION

Objectives: To evaluate differences in fracture site motion by using d ifferent external fixators. Design: A wooden dowel was used to simulat e a long bone with a transverse diaphyseal fracture. Ilizarov, ''hybri d,'' and strut-augmented ''hybrid'' external fixation was used to stab ilize the ''fracture.'' The wooden dowel was subjected to separate axi al, four-point bending, and torsional loads. Fracture site motion in t he axial plane, off-axis motion (shear and bending), and rotation were measured. Setting: All mechanical testing was performed with a sevohy draulic test frame (MTS Systems, Minneapolis, MN, U.S.A.). Fracture si te motion was measured with an interfragment motion device developed i n this laboratory. Intervention: Comparison was made between a traditi onal fourring Ilizarov fixator, a ''hybrid'' fixator using rings and t hreaded pins attached by a unilateral aluminum bar, and a ''hybrid'' f ixator augmented with a V-shaped strut. Main Outcome Measurement: Load -deformation behavior in axial displacement, shear displacement, and b ending displacement were compared between the different configurations under identical conditions of axial loading, torsional loading, and f our-point bending. In torsional loading, rotational displacement was a lso measured. Results: The Ilizarov configuration allowed significantl y less offaxis fracture site motion in all loading modes than either ' 'hybrid'' configuration while still allowing axial compression of the fracture ends. Conclusions: In a completely unstable fracture with poo r bone apposition, the mechanical behavior of a four-ring Ilizarov ext ernal fixator is superior to the mechanical behavior of a unilateral ' 'hybrid'' frame.