Redirecting a Low-Screw Threshold During PLIF with T-EMG Monitoring
November 22, 2025
Posterior lumbar interbody fusion (PLIF) is a proven surgical option for patients with debilitating lumbar spine conditions. By decompressing nerves, restoring disc height, and stabilizing the spine with cages and screws, PLIF can deliver meaningful relief and improved function. But precision is everything—particularly when placing hardware near sensitive neural structures.
This case highlights how intraoperative neuromonitoring (IONM) detected a dangerously low pedicle screw threshold, prompting immediate correction before permanent nerve injury could occur.
The Role of Neuromonitoring in Lumbar Fusion
Nerve injury is one of the most serious risks of lumbar fusion surgery. Pedicle screws, while essential for stability, sit just millimeters from spinal nerve roots. Even slight misplacement can cause postoperative weakness, sensory changes, or lasting pain.
That’s where triggered electromyography (T-EMG) proves invaluable. By measuring compound muscle action potentials (CMAPs) in response to electrical stimulation, T-EMG provides real-time feedback on screw proximity to neural tissue. Thresholds below 10mA may signal medial breach or dangerous nerve contact—giving surgeons the chance to act before harm is done.
Case Study: Patient Profile and Surgical Plan
A 62-year-old female presented with chronic low back pain and neurological symptoms impacting daily function. Her medical history included gastrointestinal and cardiac issues, irritable bowel syndrome, hypothyroidism, and hypertension, making surgical precision and safety even more critical.
The surgical plan included a posterior lumbar interbody fusion with intraoperative monitoring. Approved modalities included:
- Transcranial Motor Evoked Potentials (TcMEPs) to assess motor pathways
- Somatosensory Evoked Potentials (SSEPs) to monitor sensory conduction
- Electromyography (EMG) for continuous motor nerve activity
- Triggered EMG (T-EMG) for screw testing and nerve proximity feedback
- Train of Four (TOF) to evaluate neuromuscular blockade
Intraoperative Findings and Intervention
Baseline SSEPs proved difficult to reproduce consistently, but T-EMG soon delivered a critical alert: the left L4 pedicle screw elicited a CMAP at just 5mA, well below the safe 10mA threshold.
Recognizing the risk of medial breach, the monitoring technologist immediately notified the surgeon. The screw was withdrawn, redirected, and retested—this time yielding a safer 14mA threshold.
From that point forward, neuromonitoring remained stable:
- SSEPs and TcMEPs held within normal limits
- EMG showed no abnormal bursts or sustained activity
- TOF responses confirmed adequate neuromuscular monitoring
Why This Adjustment Mattered
A pedicle screw stimulating at just 5mA indicates a dangerous proximity to nerve roots. Left uncorrected, it could have caused:
- Postoperative sensory loss or motor weakness
- Chronic neuropathic pain
- Functional impairment or the need for revision surgery
Thanks to real-time monitoring and immediate surgical response, these outcomes were avoided.
Protecting Patients with Neuromonitoring
This case demonstrates the life-changing role of T-EMG in lumbar fusion:
- Immediate Risk Detection – Abnormal thresholds reveal potential hardware breach.
- Real-Time Correction – Surgeons can adjust placement before injury occurs.
- Optimized Outcomes – Preventing nerve damage preserves mobility and quality of life.
Making Neuromonitoring Standard in Fusion Surgery
In procedures where millimeters can mean the difference between recovery and disability, neuromonitoring isn’t optional—it’s essential. This case reinforces how vigilant use of T-EMG and multimodal monitoring can transform outcomes and protect patients when it matters most.
For more on how intraoperative neuromonitoring can enhance the safety and success of spinal procedures, contact our team at 888-344-2947.
