Use of a flexible epidural stimulating electrode for intraoperative monitoring of spinal somatosensory evoked potentials.

The use of an epidural stimulating spinal electrode has been adapted for recording spinal somatosensory evoked potentials (SSEP) during spinal surgery. This technique utilizes a flexible, 1 mm diameter electrode with four platinum contacts that is easily slipped into the epidural space both rostral and caudal to the exposed surgical field. The flexibility of the electrode assembly ensures against dural penetration. Incoming somatosensory spinal evoked potentials recorded using the lumbosacral electrode are compared with the SSEP recorded above the surgical site (rostral electrode). The spinal SEPs were generally triphasic (thoracic) or polyphasic (lumbosacral) with an amplitude of 5 microV. This system has been used for intraoperative monitoring during 33 major spinal operations. Waveform morphology, as well as the latencies and amplitudes of the component peaks of the spinal SEPs remained relatively constant compared with the cortical SEPs.