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<50% reduction in amplitude in tcMEP
17%
189/1127
A 40% decrease in SSEP amplitude
30%
335/1127
Low frequency signal on free running EMG
7%
81/1127
A greater than 100 volt increase in threshold with tcMEP
33%
376/1127
A 12 mA threshold on pedicle screw stimulated EMG
12%
135/1127
Select Answer to see Preferred Response
A greater than 100 V increase in the threshold for transcranial motor evoked potential (tcMEP) is associated with an early spinal cord injury. Intraoperative neuromonitoring allows the detection of spinal cord injuries during procedures. Leads are placed in various anatomic regions and monitor the patency of action potentials from the cerebral cortex to the peripheral nervous system. Transcranial motor evoked potential is the most sensitive and specific method of detecting a spinal cord injury. A >50% decrease in amplitude or a greater than 100 V increase in threshold are associated with potential spinal cord injuries and necessitate further intraoperative evaluation. Stecker reviewed intraoperative neuromonitoring in spine surgery. The author reported tcMEP is the most sensitive and specificity for early detection of spinal cord injury but is most effective when used in multimodal monitoring regimens. The author concluded neuromonitoring has limitations that must be understood to effectively troubleshoot monitoring issues intraoperative and navigate intraoperative neurologic changes. Laratta et al. reviewed intraoperative neuromonitoring in spinal deformity surgery. They reported preoperative neurologic deficit, fusion >5 levels, resection of 2 or more vertebrae, and preoperative kyphosis as risk factors for neurologic complication rates. They reported intraoperative neuromonitoring is effective and improves safety in spinal deformity surgery. Incorrect answers Answer 1: A >50% reduction in tcMEP amplitude is associated with a potential spinal cord injury. Answer 2: A >50% decrease in somatosensory evoked potentials is associated with a potential spinal cord injury. Answer 3: Short high-frequency bursts are associated with nerve root injuries. Answer 5: Multiple studies have reported varying pedicle screw stimulation thresholds, but generally <5 mA is considered a breached pedicle and ~2 mA suggestive of the screw in contact with a nerve root. It is recommended that pedicle screws that stimulate <8 mA should be investigated by palpation.
2.6
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