Spine - 2026-08-15 - Journal Article
Triggered Electromyography for Assessment of Pedicle Screw Placement in Pediatric Spinal Deformity Surgery: Is It Useful?
Wolf JJ, Shobode M, McKeon J, Roebke A, Stokey P, Mansour A, Memon R, Tulchin-Francis K, Beebe A, Chambers R, Kadado A
Topics
Key Takeaway
In 235 AIS patients with 4,518 screws, 7.8% triggered low-threshold EMG alerts (≤8 mA), yet 79.2% were retained without neurologic consequence, and neuromonitoring alert rates were identical between LTS and non-LTS groups.
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Summary
This study evaluated whether triggered EMG thresholds ≤8 mA (LTS) predicted neurologic risk or guided screw revision in AIS posterior spinal fusion (2011–2020). Of 4,518 screws, 351 (7.8%) were LTS in 127 patients; LTS patients had more levels fused and screws placed but identical SSEP/TcMEP alert rates and postoperative neurologic deficit rates compared to non-LTS patients. Screw revision was more likely only when intraoperative re-probe confirmed cortical breach, and LTS clustered within ±2 levels of the apex, likely reflecting apical pedicle morphology.
Key Limitation
Absence of routine postoperative CT means the study cannot determine what proportion of retained LTS screws were actually malpositioned, preventing any correlation between threshold value and true breach severity.
Original Abstract
STUDY DESIGN
Retrospective cohort study.
OBJECTIVE
To evaluate the characteristics and outcomes of low threshold screws (LTS) identified through triggered electromyography (TEM) in adolescent idiopathic scoliosis (AIS) surgery and assess the utility of TEM as a safety adjunct in pediatric spinal deformity correction.
SUMMARY OF BACKGROUND DATA
TEM is used intraoperatively to assess pedicle screw placement by measuring electrical stimulation thresholds, with lower thresholds (≤8 mA) potentially indicating screw malposition or proximity to neural structures. However, the reliability and clinical relevance of LTS in pediatric deformity surgery remain unclear, with limited evidence guiding intraoperative decision-making.
METHODS
Patients with AIS undergoing posterior spinal fusion between 2011 and 2020 were retrospectively reviewed. Screws with stimulation thresholds ≤8 mA were classified as LTS. Demographic, radiographic, and intraoperative neuromonitoring data were collected, including Cobb angles, levels fused, number of screws placed, Lenke classification, neuromonitoring alerts (SSEP, TcMEP), and screw-related outcomes. Comparisons were made between cases with and without LTS to assess differences in surgical and neuromonitoring parameters.
RESULTS
Among 235 patients (4518 screws), 351 screws (7.8%) were identified as LTS in 127 patients. These patients had more levels fused [12 (10-13) vs. 10 (9-12), P <0.001] and screws placed [21 (18-23) vs. 18 (14-22), P <0.001]. Neuromonitoring alerts (SSEP, TcMEP) and rates of postoperative neurologic deficit were similar between groups. The LTS group had higher preoperative and postoperative Cobb angles, although percent correction was comparable. Most LTS (79.2%) were retained, with changes more likely when intraoperative breach was confirmed on re-probe. LTS were commonly within ±2 levels of the apex.
CONCLUSIONS
In the largest reported cohort of LTS in pediatric spinal deformity surgery, low stimulation thresholds did not correlate with increased neuromonitoring alerts or compromised surgical outcomes. TEM should be used as part of a multimodal strategy, incorporating imaging and direct assessment, rather than as a standalone tool to guide pedicle screw evaluation in AIS surgery.
LEVEL OF EVIDENCE
Level III-retrospective cohort study.