The essentials of this article
  • How does it work?
  • What does it monitor?
  • What happens when there is a signal change?
  • Does it actually prevent complications?
  • Beyond safety: preventing dysphagia and other subtle injuries

One of the questions patients ask most often before surgery is: how do you make sure you don't damage a nerve? The honest answer involves a technology most patients have never heard of but that their surgeon relies on throughout the entire operation: intraoperative neurophysiological monitoring (IONM). It is, in essence, a real-time surveillance system for your spinal cord and nerves. At CICOVE we use it in 100% of our surgical cases — not because regulation requires it, but because we consider it a non-negotiable standard of patient safety.

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Before surgery begins, while you are already under anesthesia, a neurophysiologist places small electrodes at specific points on your body — scalp, arms, legs, hands, feet. These electrodes record the electrical signals traveling through your nervous system. Throughout the surgery, the neurophysiologist continuously stimulates and records these pathways, watching for any change in amplitude, latency, or signal morphology. If something changes, the surgeon is alerted in real time — often within seconds — and can adjust the surgical maneuver before permanent damage occurs.

Modern IONM uses multiple modalities simultaneously, each watching a different part of the nervous system:

IONM modalities
  • SSEPs (somatosensory evoked potentials) — monitor the sensory pathways. Electrical stimulation is applied to peripheral nerves (wrists, ankles) and the response is recorded at the brain. This tells the surgeon whether the spinal cord's sensory tracts are intact.
  • MEPs (motor evoked potentials) — monitor the motor pathways. Stimulation is applied at the brain (transcranial) and the response is recorded at the muscles. The most direct test of whether the motor tracts — the ones controlling movement — are safe.
  • Free-running EMG — listens for spontaneous nerve root activity. If a nerve root is being irritated or stretched during the operation, it fires electrically — and the EMG picks it up immediately.
  • Triggered EMG — the surgeon stimulates a pedicle screw after placing it. If the screw is correctly within bone, a high threshold is needed to generate a response. If it breached the wall and is near a nerve, the threshold drops. This confirms screw position in real time.
Why multimodal monitoring matters
A prospective study of 2,728 spine surgery patients found that using multiple IONM modalities together (SSEPs + MEPs + EMG) significantly improved detection of neurological events compared to any single modality alone. Combined monitoring catches what a single channel might miss.
Sutter M et al., Eur Spine J 2019 · ref. 1

This is where IONM earns its value. When the neurophysiologist detects a significant change — a drop in amplitude, an increase in latency, or new EMG activity — the operating room responds immediately:

Response to a signal change
Alert

The neurophysiologist immediately informs the surgeon and anesthesiologist. The maneuver in progress is paused.

Systematic check

The team rules out technical and anesthetic causes (electrode displacement, drop in blood pressure, anesthetic depth). If the change is real, the surgeon reverses the last maneuver, repositions the instrument, relieves traction, or adjusts the implant.

Recovery

Signals are checked again. In most cases, if the intervention is timely, signals recover — meaning the nerve was stressed but not injured. Surgery continues with a modified approach.

This is the question that matters, and the evidence is substantial:

Systematic review and meta-analysis
A systematic review and meta-analysis published in Spine found that IONM is associated with reduced rates of new neurological deficits during spine surgery. The evidence supports its use across cervical and lumbar procedures, with particular value in cases involving spinal cord compression or instrumentation near neural structures.
Daniel JW et al., Spine 2018 · ref. 2
In degenerative cervical surgery specifically
A 2025 meta-analysis focused on IONM in degenerative cervical surgery confirmed its positive impact on neurological outcomes. The authors concluded that multimodal monitoring should be considered for cervical procedures where the spinal cord is at risk.
El Choueiri J et al., Neurosurg Rev 2025 · ref. 3

IONM isn't just for catastrophic events like paralysis. Recent applications include monitoring for recurrent laryngeal nerve injury during anterior cervical surgery — a complication that causes hoarseness or swallowing difficulty. A prospective clinical trial demonstrated that IONM can help prevent dysphagia (difficulty swallowing) after anterior cervical procedures by alerting the surgeon to excessive retraction of the esophagus and recurrent laryngeal nerve.

This is a question the field is actively debating. Some authors have argued that triple IONM (SSEPs + MEPs + EMG) should be considered standard of care for high-risk procedures such as cervical surgery for ossification of the posterior longitudinal ligament (OPLL). The general consensus is moving in that direction: while IONM is not yet universally mandatory, its use is expanding, and the published evidence overwhelmingly supports that it adds a measurable margin of safety.

A question worth asking your surgeon

If you're considering spine surgery, ask: "Will you use intraoperative neurophysiological monitoring during my procedure?" If the answer is no, ask why. Not every case is high risk, but the conversation itself tells you something about how your surgeon thinks about safety.

At CICOVE, IONM is not reserved for high-risk cases or used selectively. We use it in 100% of our spine surgeries — cervical and lumbar, first-time and revision, simple decompressions and complex instrumented fusions. The cost is included in the surgical package because we consider it part of the operation, not an add-on.

The logic is simple: even in procedures considered 'low risk,' the spinal cord and nerve roots are millimeters from the instruments. Having real-time confirmation that the nervous system remains intact throughout the entire operation is a margin of safety we are not willing to give up — for any patient, in any case.

The technology behind the safety you deserve

IONM doesn't replace surgical skill — it empowers it. A skilled surgeon with monitoring is safer than the same surgeon without it, because no human hand can feel a signal change happening inside a nerve. Technology can. Your surgeon's hands do the work; monitoring makes sure the nervous system is doing fine at every step.

Thank you for reading. If you're considering spine surgery, this is one of the things worth knowing before your consultation.

Dr. Rodrigo Ávila Cervantes
Spine Neurosurgeon · FAANS · FCNS · CICOVE Director