CHRONIC DOUBLE-LEVEL CAUDA-EQUINA COMPRESSION - AN EXPERIMENTAL-STUDYON THE DOG CAUDA-EQUINA WITH ANALYSES OF NERVE-CONDUCTION VELOCITY

Study Design. Nerve conduction velocity was studied in the dog cauda e quina subjected to chronic double-level compression. Objectives. To an alyze the effects of chronic double-level cauda equina compression. Su mmary of Background Data. Double-level cauda equina compression produc es more symptoms in patients and more changes in acute experimental se t-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 place d 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) an d 1 month (10 mm Hg, n = 5; 0 mm Hg, n = 5) after inflation with a vis cous substance, nerve conduction velocity was studied by local electri cal stimulation and recording of muscle action potentials in the tail muscles. Results, Nerve conduction velocity was determined over the cr anial balloon, the caudal balloon, and both balloons. The data were si milar for all three recordings. After 1 week there was a significant r eduction in nerve conduction velocity induced by 10 mm Hg, compared wi th that induced by 0 mm Hg, which showed normal conditions. However, a fter 1 month this initial reduction in nerve conduction velocity had r ecovered partially. The reduction was similar to that described for si ngle-level compression in a previous study in which the same compressi on model was used. Conclusions. Unlike the acute situation, chronic do uble-level compression does not induce more changes than single-level compression after 1 week, although the recovery after 1 month of compr ession is less complete after double-level compression. This less comp lete recovery may be a result of an adaptation of the nerve tissue and the vascularization of the cauda equina nerve roots to the applied pr essure.