Intraoperative Monitoring of Segmental Spinal Nerve Root Function with Free-Run and Electrically-Triggered Electromyography and Spinal Cord Function with Reflexes and F-Responses

Abstract

Orthodromic ascending somatosensory evoked potentials and antidromic descending neurogenic somatosensory evoked potentials monitor spinal cord sensory function. Transcranial motor stimulation monitors spinal cord motor function but only activates 4-5% of the motor units innervating a muscle. Therefore, 95-96% of the motor spinal cord systems activating the motor units are not monitored. To provide more comprehensive monitoring, 11 techniques have been developed to monitor motor nerve root and spinal cord motor function. These techniques include: 1. neuromuscular junction monitoring, 2. recording free-run electromyography (EMG) for monitoring segmental spinal nerve root function, 3. electrical stimulation to help determine the correct placement of pedicle screws, 4. electrical impedance testing to help determine the correct placement of pedicle screws, 5. electrical stimulation of motor spinal nerve roots, 6. electrical stimulation to help determine the correct placement of iliosacral screws, 7. recording H-reflexes, 8. recording F-responses, 9. recording the sacral reflex, 10. recording intralimb and interlimb reflexes and 11. recording monosynaptic and polysynaptic reflexes during dorsal root rhizotomy. This paper is the position statement of the American Society of Neurophysiological Monitoring. It is the practice guideline for the intraoperative use of these 11 techniques. This statement is based on information presented at scientific meetings, published in the current scientific and clinical literature, and presented in previously-published guidelines and position statements of various clinical societies. These 11 techniques when used in conjunction with somatosensory and transcranial motor evoked potentials provide a multiple-systems approach to spinal cord and nerve root monitoring. The techniques reviewed in this paper may be helpful to those wishing to incorporate these techniques into their monitoring program.