[Theoretical and experimental studies on the technology of external bone fracture stabilization]

The stability of the external fixation unit largely depends on the optimal utilization of the possible geometrical arrangement. In view of the vast variety range of variants existing for the construction of external fixation units, it seems to be essential to present the influences of various parameters for instance the distances between Steinmann-pins and Schanz-screws. For various typical constructions with external fixation units the stability and load limit are disclosed by means of calculations and experiment. Discussions serve to find out how the inclination and shifting in the fraction area can be minimalized by fixing the Steinmann-pins and Schanz-screws at a suitable point. The solidity of the frame and of the fixation of the pins and Schanz-screws are compared between the Hoffmann frame and the AO-frame. A simple formula is presented, which serves to detect the compressive force resulting from the elastic bending of the Steinmann-pins, which can be read from an x-ray for example. It is being demonstrated that interfragmentary compression can increase stability ten-fold. The load limit of the combination of Steinmann-pins, Schanz-screws and bones proves that this combination is liable to be overloaded in the case of unsuitable arrangement of the fixation unit. This is then likely to result in a loosening of the screws and pins through direct destruction of the bones in this area. Thus, it has been possible to find out the ideal arrangement of Steinmann-pins and Schanz-screws for the respective kinds of fractures and locations where they occur, as well as optimal means of fixing the frame. Guidelines have been elaborated, which guarantee an optimal functioning stability of the external fixation unit if they are exactly observed and if the operation technique is without fault. Drawing direct conclusions from absolute movements and directions in the fraction area which have been detected by means of calculations and experiment, make it possible to carry out further scientific investigations with regard to the problem concerning the necessary extent of the rigidity of an osteosynthesis.