Intraoperative neurophysiological monitoring in spinal surgery

Table 1 Summary of advantages and disadvantages of each monitoring technique

	Advantages	Disadvantages
SCEP	Easy to record using very simple hardware	The electrode used to deliver stimulation to the spinal cord should be located in the epidural space and the recording electrode in the intrathecal space
	Provides real-time information because its potentials are large enough without averaging	The malposition of the electrode can occur
		Previous scarring can sometimes impair electrode placement
SEP	Broadly available	Does not directly monitor corticospinal tract. Only assess the functional integrity of spinal cord dorsal columns. In the case of anterior spinal artery syndrome, postoperative paraplegia despite intraoperative SEP preservation has been reported
	Easy to implement	When approaching the intramedullary tumor during the initial dorsal myelotomy, SEPs can completely disappear
	Has no contraindications	SEP recording requires signal averaging, which results in a time delay until data interpretation can generate a response to the surgeon. Therefore, an injury can be irreversible before it is even detected
	Can be combined with other monitoring techniques
	Allows continuous monitoring throughout case
	Excellent specificity (approaching 100%)
Neurogenic	Fast and easy to implement	Their specificity remains relative because they correspond to the joined activation of motor and sensory pathways
MEP	Resistant to most anesthetics	Require curarization
	Sensitive in detecting a lesion	The terminal medullary cone is not monitored
	In case of alert, the lesional level can be determined by displacing the stimulation electrode along the intervertebral spaces
D waves	Very rapid acquisition	The recording electrode is in the surgical field and its use by the surgeon can produce artifacts
	D waves are specific of motor pathways	Laterality cannot be distinguished
	They can establish a lesional level by displacing the spinal electrode along the intervertebral spaces	D waves cannot be used in small children, generally under 4 yr of age (incomplete maturation of motor path-ways)
	D waves have prognostic value	Cannot be recorded below the level of T12 because there are not enough corticospinal tract fibers
	Correlates most accurately with long-term motor function following	Previous scarring can sometimes impair electrode placement
	intramedullary spinal cord tumor resection
Muscle MEP	Do not require an averaging. Thus immediate feedback can be available	Require at least partially functional motor pathways
	Preserved sensitivity and sensitivity even after posterior myelotomy	Incompatible with prolonged curarization
		Exceptional adverse effects have been described: tongue or lip laceration, mandibular fracture, cardiac arrhythmia, epileptic seizures, scalp burn and intraoperative awareness
		Often difficult to carry out on patients under the age of 6 yr because of incomplete maturation of motor pathways
Pedicle screw testing	Rapid and easy technique	Sensitive to a large number of anesthetics
	Can be combined with new surgical instruments used during screw placement	Can be distorted by curarization
	High sensitivity for medial pedicle breach	Less sensitive for thoracic pedicle screws than for lumbar pedicle screw
	Useful in minimally invasive surgery where anatomical landmarks may be challenging to visualize	Optimal alarm criteria not firmly established
		Does not directly assess for neurological injury, only provides information regarding pedicle integrity

SCEP: Spinal cord evoked potentials; MEP: Motor evoked potential; SEP: Somatosensory evoked potentials.