Tag: EMG

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Low Posterior Electromyographic Threshold and Functional Outcomes After L4-5 Lateral Lumbar Interbody Fusion

Operative Neurosurgery 30:566–570, 2026

This single-institution retrospective study evaluates whether low posterior electromyography (EMG) stimulation thresholds during lateral L4-5 lumbar interbody fusion (LLIF) correlate with postoperative femoral nerve motor or sensory neurapraxia. Forty-two lateral-position single-level L4-5 LLIFs with neuromonitoring data showed no significant association between posterior EMG threshold or retractor time and transient postoperative anterior thigh numbness or weakness.

The cohort experienced transient sensory neurapraxia in 38% at six weeks that resolved by six months; only one patient had temporary motor neurapraxia. Limitations include small sample size, retrospective design, and short follow-up, leading authors to conclude no demonstrable link between posterior EMG threshold and plexus injury in this series.

Context: In L4-5 transpsoas LLIF, the retractor is placed near the lumbar plexus; directional EMG stimulation thresholds are used intraoperatively to estimate nerve proximity and potentially reduce injury risk.

Objective: Assessed whether posterior EMG stimulation threshold was associated with lumbar plexus injury/neurapraxia after single-level L4-5 LLIF performed in the lateral position.

Design/criteria: Retrospective, single-institution review of single-level L4-5 LLIF (Jan 2019–May 2022) with available neuromonitoring thresholds and retractor time; excluded cases with additional levels or missing monitoring data.

Cohort/intraop metrics: 42 patients (mean age 66 years); mean retractor time 12.4 minutes; mean posterior EMG threshold 10.4 mA.

Neurologic outcomes: Femoral motor neurapraxia occurred in 1 patient (2%); sensory neurapraxia (anterior thigh numbness) occurred in 16 patients (38%) at 6 weeks and resolved to 0% by 6 months.

Main finding: Posterior EMG threshold was not associated with postoperative motor neurapraxia or sensory neurapraxia at 6 weeks (including logistic regression showing OR 1.00; P=.98 for thigh numbness).

Other associations: No significant correlation between posterior EMG threshold and retractor time (Spearman ρ=0.11; P=.50) or postoperative ODI (ρ=0.17; P=.33).

Notable case/interpretation: The single motor neurapraxia case had 27-minute retractor time with posterior EMG 5 mA and recovered by 6 months; median retractor time in the cohort was low (10.8 minutes), limiting conclusions about longer retraction durations.

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Ability of electromyographic monitoring to determine the presence of malpositioned pedicle screws in the lumbosacral spine: analysis of 2450 consecutively placed screws

J Neurosurg Spine 15:130–135, 2011.DOI: 10.3171/2011.3.SPINE101

Pedicle screws provide efficient stabilization along all 3 columns of the spine, but they can be technically demanding to place, with malposition rates ranging from 5% to 10%. Intraoperative electromyographic (EMG) monitoring has the capacity to objectively identify a screw breaching the medial pedicle cortex that is in proximity to a nerve root. The purpose of this study is to describe and evaluate the authors’ 7-year institutional experience with intraoperative EMG monitoring during placement of lumbar pedicle screws and to determine the clinical utility of intraoperative EMG monitoring.

Methods. The authors retrospectively studied 2450 consecutive lumbar pedicle screws placed in 418 patients from June 2002 through June 2009. All screws were inserted using a free-hand technique and anatomical landmarks, stimulated at 10.0 mA, and evaluated with CT scanning within 48 hours postoperatively. Medial pedicle screw breach was defined as having greater than 25% of the screw diameter extend outside of the pedicle, as confirmed on CT scanning or intraoperatively by a positive EMG response indicating a medial breach. The sensitivity and specificity of intraoperative EMG monitoring in detecting the presence of a medial screw breach was evaluated based on the following definitions: 1) true positive (a positive response to EMG stimulation confirmed as a breach intraoperatively or on postoperative CT scans); 2) false positive (positive response to EMG stimulation confirmed as a correctly positioned screw on postoperative CT scans); 3) true negative (no response to EMG stimulation confirmed as a correctly positioned screw on postoperative CT scans); or 4) false negative (no response to EMG stimulation but confirmed as a breach on postoperative CT scans).

Results. One hundred fifteen pedicle screws (4.7%) showed positive stimulation during intraoperative EMG monitoring. At stimulation thresholds less than 5.0, 5.0–8.0, and > 8.0 mA, the specificity of a positive response was 99.9%, 97.9%, and 95.9%, respectively. The sensitivity of a positive response at these thresholds was only 43.4%, 69.6%, and 69.6%, respectively. At a threshold less than 5.0 mA, 91% of screws with a positive EMG response were confirmed as true medial breaches. However, at thresholds of 5.0–8.0 mA or greater than 8.0 mA, a positive EMG response was associated with 89% and 100% false positives (no breaches), respectively.

Conclusions. When using intraoperative EMG monitoring, a positive response at screw stimulation thresholds less than 5.0 mA was highly specific for a medial pedicle screw breach but was poorly sensitive. A positive response to stimulation thresholds greater 5.0 mA was associated with a very high rate of false positives. The authors’ experience suggests that pedicle screws showing positive stimulation below 5.0 mA warrants intraoperative investigation for malpositioning while responses at higher thresholds are less reliable at accurately representing a medial breach

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