Spine (Phila Pa 1976). 2025 Oct 7. doi: 10.1097/BRS.0000000000005526. Online ahead of print.
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 (4,518 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 pre- and postoperative Cobb angles, though 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.
CONCLUSION: 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.
PMID:41056460 | DOI:10.1097/BRS.0000000000005526
