Production of chronic compression of the cauda equina in rats for use in studies of lumbar spinal canal stenosis

Study Design. The pathophysiology of lumbar spinal canal stenosis was analyzed with a new model in rats. Objectives. To produce chronic compression of the cauda equina in rats for analysis of the pathophysiology of lumbar spinal canal stenosis. Summary of Background Data. Models of compression to date have involved acute or subacute compression. A model of chronic compression has not been available. Methods. A stainless steel wire was fastened around the spine at L5 in 3-week-old rats, with a plate inserted against the ventral aspect of the vertebra to protect it from the wire. As the rats grew, the wire cut into the spinal canal. One year after the operation, canal stenosis was present without paralysis of the back limbs. Results. Stenosis seen in sagittal sections, as a percentage of the original width, was 51.6 +/- 6.2% (mean +/- standard deviation). In histologic analysis of the region near the wire, findings included axonal degeneration, demyelination, vacuolar degeneration of the nerve fibers, and narrowing of intradural blood vessels with a decrease in their number. Cephalad and caudad to the wire, congested intradural blood vessels, degenerative foci near these congested vessels, fibrosis around these foci, congested epidural vessels, and fibrosis around these vessels were observed. During electrophysiologic analysis (six rats with stenosis), the conduction velocity of the cauda equina was found to be delayed. Conclusions. The histologic and electrophysiologic findings in this animal model were similar to findings in human subjects, so rats prepared in this way should be useful for study of chronic compression of the cauda equina.