Measurement of internal fixation device support in experimentally produced fractures of the dorsolumbar spine

A reproducible flexion injury was induced in ten fresh cadaver spine preparations via four-point loading with continuous recording of load-deformation characteristics and additional monitoring by high speed photography. Each spine was then stabilized with Weiss springs, Harrington distraction rods and Harrington compression rods, and tested in a same manner.13 The elastic modulus of each instrumented spine system was compared to the preinjured state and to each of the devices tested. Fixation with Harrington compression rods had the highest elastic modulus, ie, was the most stiff, of the devices tested, yet failed with the least amount of displacement. Instrumentation with Weiss springs had the lowest elastic modulus, however, and was noted to best maintain continuity with displacement. Harrington distraction rods were intermediate in both modalities. This study demonstrated that no one internal fixation device was applicable to all flexion injuries involving the dorsolumbar spine. Each of the three devices tested was more applicable in selected injuries. None of the devices appeared successful in restoring the original stiffness of the preinjured spine.