[Investigation about the stability of a fixateur-externe using a new screw nail (author's transl)].

Since former investigations showed that the 4.5 mm Steinmann-nails hitherto were the weakest part of fixateur-externe systems, we developed a screw nail with a shank thickness of 7 mm and a thread identical to that of the cortical screw developed by the Arbeitsgemeinschaft für Osteosynthese (Workshop Society for Osteosynthesis). By conducting experiments with a metal alloy (square tube made of aluminium) in cadaver bones, the bending stress of a frame assembly R and of a three-dimensional assembly with 2 Schanz-screws Z2S was examined with 4.5 mm Steinmann-nails as well as with screw nails. The systems mounted with the new screw nails bent considerably less than the other systems. The improvement in stability achieved by screw nails is relatively more significant for the external frame fixator and in cases of a defect at the fracture gap than for the three dimensional fixateur externe with 2 Schanz-screws and in case of a compression at the fracture gap.