To avoid further damage to the sensory or motor function of the body, the surgeon uses intraoperative monitoring (IOM). But the methods available aren't fool proof even when two or more are used together. Sometimes this is because there is already so much pressure on the spinal cord or spinal nerves before the surgery.

In such cases, electrical impulses through the nerve pathways to the muscles have been blocked by the tumor. Monitoring the neurologic function during the operation then becomes very difficult. Most of the time, a baseline measure is possible. When it is present, the surgeon must work very carefully to avoid further injury.

In a small number of cases, permanent partial or complete paralysis does occur. This can happen even with IOM. Research is ongoing to find better ways to monitor the nerve tissue and prevent this from happening.