[The LS-8 lever fixator: repositioning and fixation aids for dislocations and dislocation fractures of the lumbar spine and the thoracolumbar transition. Part I. Biomechanical considerations and surgical technique].

We are reporting a lever-type internal fixateur, the LS-8 system, which can be used for reduction and stable fixation of fractures and fracture-dislocations of the thoraco-lumbar and lumbar spine. The LS-8 system is different from all previous systems: it combines the advantages of the spinal fixateur interne and conventional plate fixation, while largely avoiding their disadvantages, such as the fixed position of the screw hole and the mechanical overloading of the fixing points, as in the previous hook-type systems. In order to minimize these drawbacks, we have added a plate of variable length to our system, creating a fulcrum that prevents overloading. This means that the reinforced 8 mm diameter screws function as lever arms around this fulcrum, conducting and counterbalancing the active forces. As a result, the loading capacity of our system has been greatly improved. Since the LS-8 "lever fixateur" is a reinforced system, it is no longer necessary to use any plaster or brace fixation. We should like to illustrate the advantages and the capability of the LS-8 system by presenting one of our cases.