Triggered electromyography for placement of thoracic pedicle screws: is it reliable?

Abstract

Reliable electromyography (EMG) thresholds for detecting medial breaches in the thoracic spine are lacking, and there is a paucity of reports evaluating this modality in patients with adolescent idiopathic scoliosis (AIS). This retrospective analysis evaluates the ability of triggered EMG to detect medial breaches with thoracic pedicle screws in patients with AIS. We reviewed 50 patients (937 pedicle screws) undergoing posterior spinal fusion (PSF) with intraoperative EMG testing. Postoperative CT scans were used for breach identification, and EMG values were analyzed. There were 47 medial breaches noted with a mean threshold stimulus of 10.2 mA (milliamperes). Only 8/47 breaches stimulated at 2-6 mA. Thirteen of the forty-seven screws tested at an EMG value ≤6 mA and/or a decrease of ≥65% compared with intraosseously placed screws. The sensitivity and positive predictive value for EMG was 0.28 and 0.21. A subanalysis of T10-T12 screws identified six of seven medial breaches. Using guidelines from the current literature, EMG does not appear to be reliable in detecting medial breaches from T2 to T9 but may have some utility from T10 to T12.

Neuromonitoring with pulse-train stimulation for implantation of thoracic pedicle screws: a blinded and randomized clinical study. Part 1. Methods and alarm criteria

“…8) that were roughly comparable to or better than those from other studies. 55,60 Not only did this allow us to corroborate findings from these other studies, but we effectively had a baseline against which we could compare findings from our novel approach. Having now done this and shown that monitoring leg EMG activity is far more reliable for predicting medially malpositioned screws, we see no advantage to continuing to monitor intercostal or abdominal muscle groups going forward and have stopped this practice.…”

“…It is not clear whether stimuli were delivered to the pedicle track via a ball-tipped probe, but screw stimulation was definitely used in that study. 60 With a reported sensitivity of only 0.28 to medial defects of 2 mm or more in magnitude, 60 it is hard to argue with the conclusions of that study.…”

“…16,38,55,60 The authors of one of these studies wrote: "EMG does not appear to be a reliable means for detection of medial cortical breaches when placing pedicle screws in the thoracic spine of patients with AIS [adolescent idiopathic scoliosis]." 60 That study used single-pulse stimulation, with intercostal and abdominal muscles as targets. It is not clear whether stimuli were delivered to the pedicle track via a ball-tipped probe, but screw stimulation was definitely used in that study.…”

“…Using target muscles including intercostals and abdominals, some groups have reported acceptable results, 15,16,33,37,53,54,56,64 whereas others found the technique lacked sensitivity and abandoned its use. 16,38,55,60 There are two reasons why the original lumbosacralbased method of monitoring pedicle screw placement may not work as well for pedicle screws placed in the thoracic spine. First, nearly all groups directly stimulate the screw after placement, whereas the original descriptions of this technique emphasized the need to stimulate the pedicle track with a ball-tipped probe before placing the screw.…”

Valor predictivo de la estimulación eléctrica de los tornillos pediculares torácicos en la mal posición medial de los mismos en la instrumentación de cirugía de columna

“…A pesar de que la electromiografía (EMG) con tren de impulsos es una técnica aceptada para la correcta monitorización de la instrumentación transpedicular en la columna lumbar 10 , sigue existiendo controversia sobre su fiabilidad a nivel del segmento torácico 1 , si bien otros autores, como Rodríguez-Olaverri 2 , han demostrado su utilidad en la instrumentación de niveles torácicos altos.…”