Use of electromagnetic fields in a spinal fusion. A rabbit model.
METHODS
The biomechanical and histologic characteristics of posterolateral spinal fusion in a rabbit model with and without the application of a pulsed electromagnetic field were analyzed in a prospective, randomized trial. In addition, fusion rate with and without a pulsed electromagnetic field in this model was assessed by biomechanical testing, radiographs, and manual palpation.


OBJECTIVE
To evaluate the influence of a pulsed electromagnetic field on the spinal fusion rate and biomechanical characteristics in a rabbit model.


BACKGROUND
Previous studies performed to assess the benefits of a pulsed electromagnetic field in spinal fusion have been complicated by the use of instrumentation, and the animal models used do not have a pseudarthrosis rate comparable to that seen in humans. In contrast, the posterolateral intertransverse process fusion in the rabbit is uncomplicated by the use of instrumentation and has been shown to have a pseudarthrosis rate similar to that found in humans (5-35%).


METHODS
Ten New Zealand white rabbits each were randomly assigned to undergo spinal fusion using either 1) autologous bone with electromagnetic fields, or 2) autologous bone without electromagnetic fields. A specially designed plastic constraint was used to focus the pulsed electromagnetic field over the rabbits' lumbar spine 4 hours per day. Animals were killed 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 electromagnetic field, but this decrease in the nonunion rate was not statistically significant given the number of animals per group. Biomechanical analysis of the fusion mass showed that a pulsed electromagnetic field resulted in statistically significant increases in stiffness (35%), area under the load-displacement curve (37%), and load to failure of the fusion mass (42%). Qualitative histologic assessment showed increased bone formation in those fusions exposed to a pulsed electromagnetic field.


CONCLUSIONS
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-displacement curve, and load to failure of the fusion mass. This investigation provides a basis for continued evaluation of biologic enhancement of spinal arthrodesis with the use of a pulsed electromagnetic field.
Glazer
P A
PA
Department of Orthopaedic Surgery, University of California, San Francisco, USA.
Heilmann
M R
MR
Lotz
J C
JC
Bradford
D S
DS
D000818:Animals; D004195:Disease Models, Animal; D004574:Electromagnetic Fields; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D008954:Models, Biological; D010012:Osteogenesis; D011446:Prospective Studies; D011542:Pseudarthrosis / Q000473:pathology; D011817:Rabbits; D011859:Radiography; D013123:Spinal Fusion / Q000379:methods*; D013314:Stress, Mechanical