External skeletal fixation: choosing a system based on biomechanical stability

Due to the increased popularity of external fixators for treating long-bone fractures, many devices are being introduced to the market. The choice of a particular fixation device depends on the anticipated loading conditions or the demands the fixator might encounter during the healing process. This study compares the biomechanical stability (rigidity, yield-load, failure-load) and load to produce 1 mm of fracture-gap displacement of various half-frames of five systems tested in axial compression, torsion, and both anterior-posterior and medial-lateral bending; the slippage tolerances of various interfaces of the universal joints or clamps were also analyzed. The frames were mounted on acrylic rods, with a midshaft transverse saw-cut, displaced by 10 mm, and set to standardized dimensions and tightened at set torques. In terms of stability, the Brooker and Hoffman systems are, in general, less stable than the RxFx, AO, and Orthofix fixators. The single half-frames of all systems, except the Orthofix, were particularly weak, and the double and stacked half-frames of each system were more stable.