Mechanical performance of hybrid Ilizarov frames containing full-threaded Schanz screws.

Modification of circular Ilizarov frames is necessary to overcome the difficulties in pin positioning due to unfavorable anatomic site or local soft-tissue conditions. Hybrid frame configurations consisting of half pins or full-threaded schanz screws are widely used in clinical practice. This study compared the mechanical performance of hybrid frames and a standard system. One standard and five modified hybrid systems were tested under axial compression, four-point bending, and torsional forces. Systems modified with full-threaded schanz screws showed a higher stiffness than half pin modifications and exhibited a similar mechanical performance of a standard system.

Comparison of mechanical performance among different frame configurations of the Ilizarov external fixator: experimental study.

The circular frame of the Ilizarov fixator can be modified to reflect anatomic variations and treatment aims. However, these modifications in the frame system cannot always achieve the mechanical performance of the standard frame system. A standard system has two rings in each bone fragment connected by four longitudinal bars on each side of the ring. In this study, the mechanical performances of one standard and eight modified frame systems were compared. Each system was loaded on a material testing machine, with calculation of axial compression, four-point bending, and torsion. As a result, systems that were modified with drop wires and Schanz screws 45 degrees oblique to the wires on the proximal ring provided a mechanical performance closer to the standard system than systems with other modifications.