USE OF ELECTROMAGNETIC-FIELDS IN A SPINAL-FUSION - A RABBIT MODEL

Study Design. The biomechanical and histologic characteristics of post erolateral spinal fusion in a rabbit : model with and without the appl ication of a pulsed electromagnetic field were analyzed in a prospecti ve, randomized trial. In addition, fusion rate with and with-out a pul sed electromagnetic field in this model was assessed by biomechanical testing, radiographs,and manual palpation. Objectives. To evaluate the influence of a pulsed electromagnetic field on the spinal fusion rate and bio-mechanical characteristics in a rabbit model. Summary of Back ground Data. Previous studies performed to assess the benefits of a pu lsed electromagnetic field in spinal fusion have been complicated by t he use of instrumentation, and the animal models used do not have a ps eudarthrosis rate comparable to that seen in humans. In contrast, the posterolateral inter:transverse process fusion in the rabbit is uncomp licated by the use of instrumentation and has been shown to have a pse udarthrosis rate similar to that found in humans (5-35%). Methods. Ten New Zealand white rabbits each were :randomly assigned to undergo spi nal fusion using either 1) autologous bone with electromagnetic fields , or 2) autologous bone without electromagnetic fields. A specially de signed plastic constraint was used to focus the pulsed electromagnetic field over the rabbits' lumbar spine 4 hours per day. Animals were ki lled at 6 weeks for biomechanical and histologic testing. Results. The rate of pseudarthrosis, as evaluated radiographically and manually in a blinded fashion, decreased from 40% to 20% with the pulsed electrom agnetic field, but this decrease in the nonunion rate was not statisti cally significant given the number of animals per group. Biomechanical analysis of the fusion mass showed that a pulsed electromagnetic fiel d resulted in statistically significant increases in stiffness (35%), area under the load-displacement curve (37%), and load to failure of t he fusion mass (42%). Qualitative histologic assessment showed increas ed bone formation in those fusions exposed to a pulsed electromagnetic field. This study demonstrates the reproducibility of a rabbit fusion model, and the ability of a pulsed electromagnetic field to induce a statistically significant increase in stiffness, area under the load-d isplacement curve, and load to failure of the fusion mass. The investi gation provides a basis for continued evaluation of biologic enhanceme nt of spinal arthrodesis with the use of a pulsed electromagnetic fiel d.