Intraoperative neuromonitoring in spine deformity surgery: modalities, advantages, limitations, medicolegal issues surgeons' views

In spine deformity surgery, iatrogenic neurologic injuries might occur due to the mechanical force applied to the spinal cord from implants, instruments, and bony structures, or due to ischemic changes from vessel ligation during exposure and cord distraction/compression during corrective manoeuvres. Prompt reaction within the reversible phase (reducing of compressive/distractive forces) usually restores functionality of the spinal cord, but if those forces continue to persist, a permanent neurological deficit might be expected. With monitoring of sensory pathways (dorsal column-medial lemniscus) by somatosensory-evoked potentials (SSEPs), such events are detected with a sensitivity of up to 92%, and a specificity of up to 100%. The monitoring of motor pathways by transcranial electric motor-evoked potentials (TceMEPs) has a sensitivity and a specificity of up to 100%, but it requires avoidance of halogenated anaesthetics and neuromuscular blockades. Different modalities of intraoperative neuromonitoring (IONM: SSEP, TceMEP, or combined) can be performed by the neurophysiologist, the technician or the surgeon. Combined SSEP/TceMEP performed by the neurophysiologist in the operating room is the preferable method of IONM, but it might be impractical or unaffordable in many institutions. Still, many spine deformity surgeries worldwide are performed without any type of IONM. Medicolegal aspects of IONM are different world-wide and in many cases some vagueness remains. The type of IONM that a spinal surgeon employs should be reliable, affordable, practical, and recognized by the medicolegal guidelines.