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Kobylarz et al. Plast Aesthet Res 2023;10:2 https://dx.doi.org/10.20517/2347-9264.2022.38 Page 7 of 20

Figure 3. Spontaneous EMG recording demonstrating two large bursts of neurotonic activity in the orbicularis oris muscle during facial
nerve retraction.Amplitude is 20 µV per division. The sweep speed is 400 msec per division.

Figure 4. Spontaneous EMG recording demonstrating trains of neurotonic activity from several motor units in the orbicularis oculi and
multiple motor units in the orbicularis oris muscles during facial nerve retraction. Note the superimposed electrocardiogram artifact in
the trapezius muscle recording. Amplitude is 20 µV per division. The sweep speed is 400 msec per division.

without an initial large burst or train of neurotonic activity. In addition, manipulation and stimulation of
the distal nerve stump may still activate the muscle, leading the surgical team to erroneously conclude that
the motor nerve remains intact [18-20] .

It can be determined whether or not the change in EMG activity is related to a surgical action by temporal
and anatomic correlation. If there is no relation of the activated muscles to the timing and location, e.g.,
spinal nerve root or peripheral nerve, of the surgical manipulation, it is unlikely that there is a causative
relationship. For example, increased EMG activity in the abductor pollicis brevis muscle (C8, T1) cannot be
explained by surgical manipulation near the ipsilateral C5 spinal nerve root. Other potential causes of
neurotonic discharges include temperature changes related to local cool saline irrigation, heat from
electrocautery, or local osmotic changes. Determining mechanical versus non-mechanical causes is essential
since it is less common for the latter to result in neurotonic activity or neural damage. However, mechanical