Biomechanical advantage of lengthening of the femur with an external fixator over an intramedullary nail.

The present experimental study investigated biomechanical differences in methods of femoral lengthening using a monolateral external fixator only and using an external fixator over an intramedullary nail. Three materials, namely polyvinyl chloride rods, composite synthetic bone, and cadaver-bone, were tested using the MTS machine. We evaluated the differences of axial stiffness according to the presence of a nail or the numbers of half-pins (two or three half-pins) that were fixed at each side of osteotomy. The addition of a nail may increase the axial stiffness of the frame of monolateral external fixator for limb lengthening. Additionally, it is enough to distract the femur with fixing two half-pins at each side, when using the technique of lengthening over a nail.