Intraoperative Monitoring of the Nerves

This technique is used during complex surgical procedures, especially those that involve manipulation of the spinal cord. IOM allows a neurotechnologist to monitor the health of the nervous system in real time during surgery. This greatly reduces the risk of surgery-related nerve damage.



Spine procedures are major surgical operations that carry certain risks with them. Fortunately, the benefits of these procedures usually far outweigh the risks, as patients are relieved of intense pain and other troubling symptoms. Although rare, some of the risks of these procedures may include injury to the spinal cord, damage to nerves and paralysis. To reduce these risks for the patient, surgeons today employ intraoperative monitoring.

Intraoperative monitoring (IOM) of the nerves allows surgeons to oversee and keep tabs on the functioning of the nerves throughout a surgical procedure. This involves the use of advanced technological devices that have become the standard of care when neurosurgery and spinal surgery are necessary. Using a range of techniques to evaluate the muscle response or electrical activity from multiple muscles as a reaction to nerve stimulation, these machines obtain vital information from a patient's central nervous system through the entirety of a surgery. The IOM systems are designed to alert the surgeon through sound or a visual cue that nerve function may be compromised. This can help decrease the chances of irreversible nerve damage occurring.

Monitoring can be established to prevent injury to the brain, spinal cord, cranial nerves and peripheral nerves throughout the body while undergoing surgery. When certain delicate procedures are being performed on the spine or spinal cord, brain or an area rich with nerves, IOM is very valuable. In these situations, neurological function can be compromised and this complication can lead to a permanent loss of ability in some part of the body. IOM can greatly assist the surgeon by providing notification that sensitive tissue is being affected so another approach may be taken or the procedure can be stopped before serious damage takes place.

Surgeons often use IOM for procedures including those to treat:

  • Spinal cord conditions
  • Scoliosis
  • Spinal disorders that require the implantation of hardware
  • Certain forms of decompression or discectomy
  • Vertebrectomy
  • Corpectomy
  • Total disc replacement

IOM is employed to lower the risk of postoperative problems including muscle weakness, paralysis, loss of sensation, hearing or vision loss and other forms of impairment due to neurological damage. The use of IOM is valuable in precluding many potential complications during spinal surgeries. Once the surgeon is notified in real time by the device of imminent damage or the very beginnings of damage to nerve tissue, correction can take place to avoid loss of function. This results in safer, more effective spinal surgery procedures.

There are a variety of methods employed for IOM, depending on the type of surgery and several other factors. Two of the most commonly used IOM techniques for spinal surgery are:

  • Somatosensory evoked potentials (SSEPs), which are used to analyze the conduction of impulses through the spinal cord. Electrodes are positioned on parts of the body that might be neurologically affected as a procedure progresses. The electrical activity taking place is recorded on the IOM device.
  • Electromyography (EMG), which evaluates the health of the muscles and the nerves that control them by measuring muscle electrical activity. Thin needle electrodes are inserted through the skin and into the muscle, where they detect and report on electrical activity.

IOM systems represent a tremendous improvement over earlier methods of protecting nerve function during complicated surgeries. Prior to this advancement, neurosurgeons would have to use a wake-up test or a clonus test during a procedure to test the nerves that could potentially be affected. When a wake-up test was conducted, the patient would be provided with an anesthetic that wore off quickly. Once conscious again, the patient was asked to move certain parts of the body to test motor function. However, if a problem was discovered, it was sometimes too late to correct, resulting in permanent damage.

The clonus test involved the surgeon stretching the patient's ankle during the surgery while the patient was still under anesthesia. An abnormal reaction, demonstrating neurological dysfunction, would be repeated contractions of the muscles in the area in a rhythmic movement. Again, this test would often not alert the surgeon to a problem until it might be too late to correct.

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