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

Abstract

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 worldwide 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. Cite this article: EFORT Open Rev 2020;5:9-16. DOI: 10.1302/2058-5241.5.180032.

Keywords: intraoperative neuromonitoring; medicolegal issue; motor potentials; neurological deficit; safety; spinal deformity.

Fig. 1

Normal and altered somatosensory-evoked potentials (SSEPs): SSEP loss on left lower limb, concomitant to transcranial electric motor-evoked potential (TceMEP) loss (see Fig. 2.); blue line – baseline SSEP, purple line – SSEP during osteotomy; upper lines represent cortical, lower lines cervical responses; latency 27% (29.5 to 40.3 msec) of cervical response after stimulation of posterior tibial nerve; reduction of amplitude in left lower limb 76% (0.46 to 0.11) – red circles; rest of figure represents normal SSEPs.

Fig. 2

Normal and altered motor-evoked potentials (MEPs): upper lines represent response of tibialis anterior, lower lines of abductor hallucis muscles; no response in both left lower limb muscles on the left side, normal response on the right side.

Fig. 3

Free-running and triggered electromyography (EMG); two purple lines on the left side show free-running EMG recorded in the upper and lower parts of the rectus abdominis muscle; right side – adequate response in left inferior rectus abdominis muscle after triggering of T10 left pedicle, indicating that there is no breach of pedicle.