[Fixateur interne: a comparative biomechanical study of various systems]

The three-dimensional stability provided by three spinal fixation devices of the type "fixateur interne" have been studied in an in vitro model using L2-L4 sections of the lumbar spine. Three-dimensional rotations and translations for the intact and instrumented spine under physiological loads in flexion/extension, lateral bending, and axial rotation were determined. To objectify the results, a dimensionless related stability parameter was introduced. The tested devices were: Dick (AO-Synthes), Kluger (Endotec), and SOCON (Aesculap). In addition a vertebrectomy L3 was performed to simulate a severe fracture model. Different screw diameters allowed for a direct comparison of two internal fixateur systems on identical specimens. In contrast to the intact spine, the instrumented spine reflects purely linear structural behaviour with a stabilization significant in flexion/extension and lateral bending and only moderate in axial rotation. Differences for various systems tested were found to be small. The results for the fracture model confirmed the efficiency of these internal fixation devices.