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Page 2 of 5 Nakamura et al. Mini-invasive Surg 2019;3:29 I http://dx.doi.org/10.20517/2574-1225.2019.28

INTRODUCTION
Transforaminal percutaneous endoscopic lumbar discectomy (TF-PELD) is usually performed on an
outpatient basis under local anesthesia (LA). The procedure is neurologically safe and avoids injury to the
[1-6]
exiting nerve root (ENR) since the patient is conscious and able to notify the surgeon of any pain .

However, some patients cannot tolerate intraoperative pain and may acquire intravenous analgesia, sedative
agents, or conversion to epidural or general anesthesia (GA) on another day.

PELD under GA is considered neurologically safe since the patient is unconscious. Recently, the efficacy
of free-run electromyography (f-EMG) has been reported in neurosurgery and spine surgery [7-12] , but not
for PELD. Therefore, the aim of this study was to evaluate the efficacy of f-EMG monitoring during PELD
under GA.

METHODS
Anesthesia
Propofol and remifentanil hydrochloride-based GA were administered. A muscle relaxant (rocuronium
bromide) was only used at the initial stage for intubation, and sugammadex sodium was used for reversal
of neuromuscular blockade. The stimulation pattern (i.e., train-of-four) was confirmed as more than 90%
before starting of f-EMG monitoring.

F-EMG
Continuous f-EMG activity was recorded using a NVM5® monitoring system (NuVasive Inc., San Diego,
CA, USA) with surface electrode patches placed at 6 positions (i.e., the bilateral vastus mediaris, tibialis
anterior, and gastrocnemius). Before affixing the patches, the skin was scraped with sandpaper to ensure
impedance was less than 10 kΩ. The threshold of electrical impact was set at 80 μV. All instances of f-EMG
activity were immediately reported to the surgeon.

Neurotonic, burst, and train waves that occurred in response to a surgical maneuver to the affected nerve
were considered to be abnormal. A small amplitude, low frequency, and isolated discharge were not
[10]
considered pathologic . Any of these instances automatically sounded an alarm to notify the surgeon.

Surgical procedure
TF-PELD
With the patient in the prone position on a radiolucent table, an 8-mm incision was made to the entry
points of the skin at about 9-11 cm lateral to the midline and then an 18-gauge needle was inserted into
the annulus fibrosus. Discography with 2 mL of liquid indigo carmine contrast agent (1:1) was performed
using the same needle. A guide wire and sleeve were inserted for endoscopy with a VERTEBRIS lumbar-
thoracic® instrument (Richard Wolf GmbH, Knittlingen, Germany). A bipolar radio-frequency electrode
system (Elliquence, Baldwin, NY, USA) was used for hemostasis and a high-speed Primado 2® drill with a
super slim hand piece 200® (NSK-Nakanishi medical, Tochigi, Japan) was used for foraminoplasty.

IL-PELD
With the patient in the prone position on a radiolucent table, an 8-mm incision was made to the entry
points of the skin at about 1 cm lateral to the midline. Once the entry point and the direction of the
sleeve were confirmed by image intensifier, a 8-mmsleeve was inserted. A VERTEBRIS lumbar-thoracic®
instrument was used for endoscopy and a bipolar radio-frequency electrode system was also used for
hemostasis. The ligamentum flavum was resected piece-by-piece using a micro punch. A high-speed
Primado 2® drill was used for laminotomy and medial facetectomy. Partial laminotomy was necessary in
almost all cases, particularly at L4-L5, to remove the laminae and ligamentum flavum and confirm the