Surgical Neurophysiology & Neuromonitoring Group ℠


Posts Tagged ‘Pedicle Screw Stimulation

New Intraoperative Neuromonitoring Technique for Implantation of Thoracic Pedicle Screws

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“In this study, a 10-mA threshold had an 88% chance of detecting a clinically relevant medial breach (2 or more millimeters) by an implanted screw and a 15-mA threshold increased that chance to 100% accuracy”

Thoracic PedicleResearchers from Syracuse, New York, report a new, highly accurate, neuromonitoring method that can be used during thoracic spine surgery to prevent malpositioning of pedicle screws such that they enter the spinal canal and possibly cause postoperative neurological impairment. Findings of this prospective, blinded, and randomized study are reported and discussed in two companion papers published today online, ahead of print, in the Journal of Neurosurgery: Spine by Blair Calancie, Ph.D., and colleagues.

Read more: New Intraoperative Neuromonitoring Technique for Implantation of Thoracic Pedicle Screws

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Reliability of Triggered EMG for Prediction of Safety during Pedicle Screw Placement in Adolescent Idiopathic Scoliosis Surgery

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Study Design

We performed a prospective study to evaluate the reliability of using triggered electromyography (EMG) for predicting pedicle wall breakthrough during the placement of pedicle screw in adolescent idiopathic scoliosis surgery.


We wanted to correlate pedicle wall breakthrough with the triggered EMG threshold of stimulation and the postoperative computed tomography (CT) findings.

Overview of Literature

Pedicle wall breakthrough has been reported to be difficult to evaluate by radiographs. Triggered EMG had been found to be a more sensitive test to detect this breakthrough.


Seven patients who underwent the insertion of 103 pedicle screws were evaluated. The triggered EMG activity was recorded from several muscles depending on the level of screw placement. The postoperative CT scans were read by a spine surgeon who was a senior fellow in orthopedics, and a musculoskeletal radiologist.


The mean age at surgery was 12.6 years (range, 11 to 17 years). The preoperative mean Cobb angle was 54.7° (range, 45 to 65°). There were 80 thoracic screws and 23 lumbar screws. All the screws had stimulation thresholds of ≥ 6 mA, except 3 screws with the stimulation threshold of < 6 mA. Ten screws (9.7%) showed violation of the pedicle wall on the postoperative CT scans. Five screws penetrated medially and another five penetrated laterally. No postoperative neurologic complications were noted in any of the seven patients.


Measuring the stimulation threshold of triggered EMG helps to assess the pedicle screw placement. Pedicle screws that had stimulation threshold of ≥ 6 mA were safe, with 90.3% reliability, as was assessed on the postoperative CT scans.

Full article PDF view and download:Reliability of Triggered EMG for Prediction of Safety during Pedicle Screw Placement in Adolescent Idiopathic Scoliosis Surgery

Keywords: Adolescent idiopathic scoliosis, Pedicle screw, Triggered electromyography


Asian Spine J. 2011 March; 5(1): 51–58.
Published online 2011 March 2. doi:  10.4184/asj.2011.5.1.51 PMCID: PMC3047898
Reliability of Triggered EMG for Prediction of Safety during Pedicle Screw Placement in Adolescent Idiopathic Scoliosis Surgery
Woo-Kie Min, Hyun-Joo Lee, Won -Ju Jeong, Chang-Wug Oh, Jae-Sung Bae, Hwan-Seong Cho, In-Ho Jeon, Chang-Hyun Cho, and Byung-Chul Park
Copyright © 2011 by Korean Society of Spine Surgery
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited

Triggered EMG – Stimulation of coated pedicle screws in IONM – What is YOUR threshold value?

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We all encounter instrumentation products from various manufacturers in our daily practice. Many different metals and coatings are used in an endless array of screws coming to the market almost daily. How do we determine the correct threshold? Are we carrying a list with values applicable to each product or are we guessing a safe value? Who is testing these products to determine its suitability for intraoperative neurophysiological monitoring? In product development, are the needs of IOM even considered? What are your thoughts?

Please consider the following research and presentation made available courtesy of Alpha Diagnostics, Santa Monica, CA

Please visit for more information.

Timothy T Davis, Ajay Vatave, James Patla, Johannes Bernbeck, Hyun W. Bae, Rick B. Delamarter

View this document on Scribd

Pedicle screws with high electrical resistance: a potential source of error with stimulus-evoked EMG.

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Abstract only. Read Article at LWWonline (Subscription required)

Anderson DG, Wierzbowski LR,Schwartz DM, Hilibrand AS, Vaccaro AR, Albert TJ

Department of Orthopaedic Surgery, University of Virginia, School of Medicine, Charlottesville, Virginia 22903, USA.
Spine [2002, 27(14):1577-81]

Type:  Journal Article

DOI: 10.1097/00007632-200207150-00018


STUDY DESIGN: Clinically relevant aspects of pedicle screws were subjected to electrical resistance testing.

OBJECTIVES: To catalog commonly used pedicle screws in terms of electrical resistance, and to determine whether polyaxial-type pedicle screws have the potential to create a high-resistance circuit during stimulus-evoked electromyographic testing.

SUMMARY OF BACKGROUND DATA: Although stimulus-evoked electromyography is commonly used to confirm the accuracy of pedicle screw placement, no studies have documented the electrical resistance of commonly used pedicle screws.

METHODS: Resistance measurements were obtained from eight pedicle screw varieties (5 screws of each type) across the screw shank and between the shank and regions of the screw that would be clinically accessible to stimulus-evoked electromyographic testing with a screw implanted in a pedicle. To determine measurement variability, resistance was measured three times at each site and with the crown of the polyaxial-type screw in three random positions.

RESULTS: Resistance across the screw shank ranged from 0 to 36.4 ohms, whereas resistance across the length of the monoaxial-type screws ranged from 0.1 to 31.8 ohms. Resistance between the hexagonal port and shank of polyaxial-type screws ranged from 0 to 25 ohms. In contrast, resistance between the mobile crown and shank of polyaxial-type screws varied widely, ranging from 0.1 ohms to an open circuit (no electrical conduction). Polyaxial-type screws demonstrated an open circuit in 28 of 75 measurements (37%) and a high-resistance circuit (exceeding 1000 ohms) in 5 of 75 measurements (7%).

CONCLUSIONS: Polyaxial-type pedicle screws have the potential for high electrical resistance between the mobile crown and shank, and therefore may fail to demonstrate an electromyographic response during stimulus-evoked electromyographic testing in the setting of a pedicle breech. To avoid false-negative stimulus-evoked electromyographic testing, the cathode stimulator probe should be applied to the hexagonal port or directly to the screw shank, and not to the mobile crown.

Read Article at LWWonline (Subscription required)

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