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Page 2 of 20 Kobylarz et al. Plast Aesthet Res 2023;10:2 https://dx.doi.org/10.20517/2347-9264.2022.38

Keywords: Intraoperative neurophysiologic monitoring (IONM), electromyography (EMG), peripheral nerves,
spinal nerve roots, brachial plexus, pedicle screws, radiculopathy, brachial plexopathy, mononeuropathy

INTRODUCTION
Undergoing surgery introduces significant inherent risks to patients, particularly those risks involving the
[1]
nervous system . Surgical manipulation, including stretching, compression, heating from
electrocauterization, and constriction or clamping of local blood vessels causing local ischemia, can pose
risks to local neural structures, potentially resulting in irreversible neurologic injury. Since the surgeon’s
visual inspection of the operative field provides limited information, pre-operative electrodiagnostic studies
and intraoperative neurophysiologic monitoring (IONM) can significantly improve surgical outcomes. Pre-
operative electrodiagnostic studies allow for more precise diagnosis and localization of nerve injury by
[2-6]
providing information about the duration, severity, and outcomes . Intraoperative neurophysiologic
studies provide real-time functional data that allows intervention to eliminate or minimize intraoperative
injury . IONM also provides the opportunity to test segments of nerve inaccessible to surface testing and,
[7]
therefore, the ability to supplement the pre-operative electrodiagnostic data.

The physiologic elements of pre-operative testing include nerve conduction studies paired with
electromyography. IONM includes free-running electromyography, stimulated electromyography, and
intraoperative direct nerve stimulation. In this review, we will briefly describe these techniques in the
context of three essential types of nerve injury: (1) radiculopathy; (2) brachial plexopathy; and
(3) mononeuropathy (specifically ulnar neuropathy at the elbow). For each of these pathologic processes, we
will review the advantages and potential pitfalls surgeons should be aware of when relying on these data to
make diagnostic and therapeutic decisions. While these studies improve outcomes, recognition and
awareness of situations in which data can be misleading are vital. The success of pre-operative and
intraoperative electrodiagnostic studies depends on the interaction and communication between the
neurophysiologist and surgeon. The neurophysiologist must have a sufficient understanding of the surgery,
just as the surgeon must appreciate electrophysiologic procedures and the significance of the findings that
may occur pre-operatively and intraoperatively.

NEUROPHYSIOLOGIC TECHNIQUES
Pre-operative diagnostic nerve conduction studies and electromyography
Pre-operative electrodiagnostic testing should be considered to allow a better understanding of the nature
and extent of the nerve injury to facilitate surgical planning. Outpatient electrodiagnostic studies include
two complementary techniques, nerve conduction studies, and needle electromyography; these techniques
provide distinct types of data regarding pathophysiologic changes at different levels of the peripheral
neuraxis.

Nerve conduction studies
Nerve conduction studies (NCS) are performed using peripheral nerve stimulation to record an evoked
sensory or motor potential. This is achieved by applying a brief electrical pulse to the skin overlying the
nerve where it becomes superficial. A motor, sensory or mixed potential is obtained by recording electrodes
on the skin over a muscle, cutaneous sensory, or mixed nerve [2,3,8] . The result is a recorded compound
muscle (CMAP) or sensory nerve action potential (SNAP), the former representing a summated potential
derived from muscle fibers and the latter a summated response from nerve fibers [Figure 1]. The amplitude
of the response reflects the electrical activity of all the individual muscle or nerve fiber action potentials; a
reduced amplitude is, therefore, indicative of axonal loss of nerve or muscle fibers. In the case of the CMAP,