You may be referring to a procedure called intraoperative monitoring (IOM). It is used to monitor the patient for any possible neurologic damage during the operation.
Post-operative muscle weakness can occur after spine surgery. This only happens if there has been some damage to the spinal cord or spinal nerves. Paralysis is very rare and not as likely as muscle weakness.
IOM is a relatively safe way to monitor motor function of the muscles during spine surgery. Any warning sign of change in muscle function and the surgeon can take care of the problem right away. There are many different IOM methods used by neurosurgeons and orthopedic physicians.
All of these methods are fast, painless, and inexpensive. Recordings are taken before the procedure begins. This gives a baseline against which other readings are compared. Measures of electrical activity in the muscles give the surgeon real-time (immediate) feedback.
IOM is a safe and effective way to prevent or reduce nerve tissue damage during surgery. Side effects of this monitoring are minimal to none. Needles are placed through the skin, so there’s always a very small risk of skin infection. The skin is cleaned and disinfected before needle placement. This step helps reduce the chances of local infection.
All needles used are sterile. They are only used one time (for you) and then thrown away. Some patients report mild soreness where the needles were inserted. That’s about it. The method is very successful with very few possible side effects.