[Monitoring of the spinal cord function using evoked spinal cord potentials]

Monitoring of the spinal cord function by evoked spinal cord potentials (ESP) has come to be used widely with the establishment of a safe technique using an epidural electrode and the great improvement in medical electronic devices. According to other investigations ESP has been recorded through an electrode placed in the posterior epidural space, it is well known that residual ESP can be actually recorded after transection of the posterior half of the spinal cord and that ESP shows no change after a small transection of the anterior column. If ESP originating from the anterior half of the spinal cord is recorded, it is very useful for monitoring during anterior decompression surgery for myelopathy such as ossification of the posterior longitudinal ligament and cervical spondylosis. The purpose of this report is to analyse ESP originating from the anterior half of the spinal cord experimentally and further investigate the ESP monitoring clinically. Sixty cats were used in this study. ESP recording principally consisted of stimulation to the spinal cord at the level of thoracic or lumbar region and recording of ESP with a monopolar electrode placed in the cervical epidural space. Changes in the ESP after transection and compression of the spinal cord were analysed. Anterior vertebrectomy and laminectomy at C2 and C6 were performed for the purpose of placing an electrode correctly and facilitating transection or compression of the spinal cord. Recording electrodes were placed on both the anterior and posterior surfaces of the dura mater at C2. As the result of this study, it is apparent that there exists the ESP originating from the anterior half of the spinal cord. Such ESPs are more accurately recorded through an anterior placed electrode rather than through that placed posteriorly.