A COMPARISON OF STRESS-INDUCED POROSITY DUE TO CONVENTIONAL AND A MODIFIED SPINAL FIXATION DEVICE

A hypothesis that device-related osteopenia can be reduced by decreasi ng the rigidity of a fixation device was tested through a canine study . Polymer washers were interposed between the integral nut and plate o f the variable spinal plating (VSP) system to reduce its rigidity. A s olid fusion was observed 6 months postoperatively in all of the animal s using VSP or modified systems. The stabilized segment using both sys tems showed similar load-displacement behaviors immediately after surg ery and 6 months postoperatively. Although not significant, 5.6 and 1. 8% decreases in volumetric density of mineralized bone were found in t he stabilized segments due to VSP and modified systems, respectively. The modified system also increased bone growth around screws. The new concept of using polymer washers, to decrease rigidity of the fixation device over time. may reduce device-related osteopenia.