Intra-operative nerve monitoring refers to the evaluation of function of the nerves and spinal cord during spine surgery. This provides your surgeon with immediate feedback on the status of the spinal cord and can be used to prevent any injury to the nervous tissue during the surgery. It improves the chances of a favorable outcome during complex surgical procedures of the spine.
The various types of intra-operative nerve monitoring procedures include:
Somatosensory Evoked Potentials (SSEPs): Sensation is measured by the placement of electrodes in the area or limb that could be affected by the surgery. Electrodes may also be placed on the skull corresponding to the location of the brain where the impulse generated from the limb is received. A machine is used to monitor the response in the brain to stimulation of the limb with an electric current. Monitoring the sensory portion of the nerve is done using this procedure. However, injury to an individual nerve root may not be detected using SSEPs.
Electromyography (EMG): Motor function is assessed by the placement of electrodes into muscle groups corresponding to the surgical site. The electrical activity is then monitored in the muscle during the procedure. A significant change in the electrical activity is an indication of impending nerve injury.
Use of SSEPs and EMG monitoring during spine surgery ensures a higher safety level. Other nerve monitoring procedures include spinal cord mapping, facial nerve monitoring, dermatomal evoked potentials, brainstem auditory evoked potential, transcranial electrical stimulation, motor evoked potentials, urinary and rectal sphincter electromyography.
Intra-operative nerve monitoring may be used in spinal surgeries performed for:
- Spinal cord injury
- Placement of hardware
- Vertebral disc injury
- Spinal cord stimulator placement
- Spine fractures
After the induction of anesthesia, electrodes are placed in the muscles that may be affected by the surgery, for example with lumbar spine surgery the electrodes may be placed in the legs and for neck surgery the electrodes may be placed in the arms. The nerve monitoring is usually done by a technician present during the entire procedure. Any slight damage to the nerves during the surgery will be picked up by the electrodes and your surgeon will be able to take corrective action to ensure there is no permanent injury to the nerves. If pedicle screws are being placed, the surgeon can use a handheld probe to provide electrical stimulation to the screw and depending on the response, the surgeon will be able to judge if the screw placement is correct.
There is no added risk to the spine surgery with the use of intra-operative nerve monitoring other than a very small chance of skin infection due to placement of the electrodes. Overall, intraoperative nerve monitoring greatly reduces the risks and complications of spine surgery.