[On Dwyer's scoliosis operation using memory alloy wire (author's transl)].

In Dwyer's spinal column correction a titanium cable is stretched from vertebra to vertebra by a special clamp and secured to each vertebra with screws and clips. It is suggested to replace the titanium wire with wire consisting of the memory alloy NiTi. This will permit the prestretched wire to be tensioned by heating it to 60 deg C after it has been fixed at its ends in the vertebrae. The functional principle of the NiTi memory wire was demonstrated in an experiment carried out on a plastic model. This consists of 8 plastic vertebrae with 30 mm sides which are connected by interposed wedge-shaped soft rubber discs, giving the model a curved shape. Memory wire prestretched by 7% is led through eylets on the convex side and fixed at the ends. On being heated (electrically in this experiment for the sake of simplicity), the wire shortens, righting the model so that it assumes a straight shape. The authors also describe in detail the manufacture of the alloy, i.e. the melting and shaping operations, as well as the properties of the material, that is, the stress-strain and strain-temperature relationships and the transformation temperatures, as well as mechanical problems.