Chronic compression model of the cauda equina: Histological and electrophysiological study

Histological and electrophysiological changes of the cauda equina caused by chronic compression with silicone film were assessed in the lumbar spine of adult cats. Twenty cats underwent laminectomy of the sixth lumbar vertebra. The animals were divided into four groups (n=5 each). In three groups, the dura was covered with silicone film. The fourth group (sham-operated) served as controls. Histological and electrophysiological studies, using spinal cord evoked potentials (SpEPs) with high frequency stimulation (HFS) were performed after periods of 4, 12, and 24 weeks. Controls were examined at 12 weeks. Dilatation of the endoneurial microvessels was noted in two of five cats in the 4-week group and in all animals in the 12- and 24-week groups. The nerve fibers of the control animals and the naimals in the 4-week group were normal. In the 12-week group, a decrease in the number of large myelinated fibers and an increase in the number of small myelinated fibers was seen in the dorsal and ventral nerve roots. Electrophysiologically, there was no significant difference in SpEPs before and after the silicone film coverage. Recovery of the peak latency was significantly delayed after HFS in the 24-week group. This model is considered to be useful in studying the pathophysiology of chronically compressed cauda equina.