A MODEL FOR CHRONIC NERVE ROOT COMPRESSION STUDIES - PRESENTATION OF A PORCINE MODEL FOR CONTROLLED, SLOW-ONSET COMPRESSION WITH ANALYSES OF ANATOMIC ASPECTS, COMPRESSION ONSET RATE, AND MORPHOLOGIC AND NEUROPHYSIOLOGIC EFFECTS

Study Design. Compression onset rate, anatomic aspects, and morphologi c and neurophysiologic effects in spinal nerve roots were studied in a nerve root compression model in pigs. Objectives. To analyze the comp ression onset rate by measuring the gradual reduction of the inner dia meter of the constrictor, the motor nerve conduction velocity by elect romyography, the morphologic changes by light microscopy, and the gros s and vascular anatomy by dissection and ink injections, respectively, in a model for experimental chronic nerve root compression. Summary o f Background Data. Chronic nerve root compression is recognized to be related to back pain com syndromes, including sciatica. Various aspect s of morphologic and physiologic changes have been studied previously in models for acute compression and chronic nerve root irritation, but a controlled, graded chronic nerve root compression model has not bee n described. Methods. An ameroid constrictor was applied around a spin al nerve root just cranial to the dorsal root ganglion. The inner diam eter of this constrictor gradually becomes reduced. After 1 week or 4 weeks, electromyographic measurements were performed, and tissue sampl es were harvested for histologic analyses. The gross and vascular anat omy of the pigs' spinal nerve roots were studied by dissection and ink injections. Results. There was a statistically significant decrease i n the nerve conduction velocity in compressed compared with noncompres sed spinal nerve roots after 1 week and after 4 weeks. The ameroid con strictors induced nerve fiber damage, endoneural hyperemia, bleeding, and inflammation at the compression zone. There was often a severe red uction in the number of myelinated fibers after 4 weeks. Conclusion. A model for controlled, chronic, partial using a gradual compression-on set nerve root injury using constrictor is presented. This model allow s for induction of a controlled graded chronic nerve root injury and c an a be used for research on basic pathophysiologic mechanisms and on the effects of various interventions on nerve root injury development.