[Prognostic value of evoked potentials of the spinal cord in surgical treatment of lumbar intervertebral disk prolapse].

Spinal potentials were evoked stimulating the peripheral nerves of lower extremities in healthy people and in patients with manifestations of lumbar disc prolapse. The patients were studied before and early after the operation. In healthy subjects the velocity of impulse conduction was nearly identical when both extremities were compared. In the patients the test before the operation revealed a significant prolongation of the latency of the potentials on the side of the damaged nerve root. After the operation a significant difference between the healthy and the affected side was still present early after the operation but it was significantly smaller than before the operation since the conduction velocity was improved on the side of the operation. The study of spinal evoked potentials makes possible recognition of disturbed function of nerve roots, and after the operation the rate of changes of potential latency is an important prognostic sign.