Chronic double-level cauda equina compression. An experimental study on the dog cauda equina with analyses of nerve conduction velocity

STUDY DESIGN: Nerve conduction velocity was studied in the dog cauda equina subjected to chronic double-level compression. OBJECTIVES: To analyze the effects of chronic double-level cauda equina compression. SUMMARY OF BACKGROUND DATA: Double-level cauda equina compression produces more symptoms in patients and more changes in acute experimental set-ups than does single-level compression. However, there have been no controlled, experimental studies on chronic double-level compression. METHODS: A total of 20 dogs were anesthetized. Two balloons were placed under the lamina of the seventh lumbar vertebra and the first sacral vertebra, respectively. One week (10 mm Hg, n = 5; 0 mm Hg, n = 5) and 1 month (10 mm Hg, n = 5; 0 mm Hg, n = 5) after inflation with a viscous substance, nerve conduction velocity was studied by local electrical stimulation and recording of muscle action potentials in the tail muscles. RESULTS: Nerve conduction velocity was determined over the cranial balloon, the caudal balloon, and both balloons. The data were similar for all three recordings. After 1 week there was a significant reduction in nerve conduction velocity induced by 10 mm Hg, compared with that induced by 0 mm Hg, which showed normal conditions. However, after 1 month this initial reduction in nerve conduction velocity had recovered partially. The reduction was similar to that described for single-level compression in a previous study in which the same compression model was used. CONCLUSIONS: Unlike the acute situation, chronic double-level compression does not induce more changes than single-level compression after 1 week, although the recovery after 1 month of compression is less complete after double-level compression. This less complete recovery may be a result of an adaptation of the nerve tissue and the vascularization of the cauda equina nerve roots to the applied pressure.