[Vertical and excentric stress in case of a defect on the fracture gap].

In order to compare the external fixator of the Arbeitsgemeinschaft für Osteosynthesefragen (AO) to different types of assembly of the Stuhler-Heise fixator (frame fixator, three-dimensional fixator, three-dimensional fixator with two screws of Schanz) with different spans (110, 140 and 190 mm), a vertical and excentric stress was exerted on a defect on the fracture gap. The comparable types of assembly of the AO fixator were lighter by 20% on an average. In two thirds of all assemblies, i.e. in 12 among 18 assemblies, the Stuhler-Heise device showed markedly better results of stability at the simulated fracture gap with respect to a vertical downward movement. In three assembly series there were identical results, in the other three series the AO device brought about better results. Under excentric stress, both fixator types showed considerable torsion movements from the horizontal line within the fracture gap. The differences between the two fixator systems found out for defects on the fracture gap will probably be significantly less important in case of compression osteosynthesis. This assumption will be verified by further examinations.