In anterior cervical spine surgery, a horizontal incision is made in the neck, the retractors are inserted, deflecting the trachea in an anterior direction. Then an X-ray is taken to confirm the position of the spine, which is then plated.
Explore This IssueSeptember 2009
The study involved 40 patients who had the operation performed, 25 of them from the left side and 15 of them from the right side. One surgeon did the right-sided procedures, and another did the left. The intraoperative nerve monitoring involved continuous free-run electromyography recorded from the recurrent laryngeal nerve. A technologist monitored visual and auditory information in the operating room.
A board-certified clinical neurophysiologist then analyzed the data independently, noting the number of signals lasting less than 10 seconds, those lasting 10 to 30 seconds, and those lasting more than 30 seconds.
The one case of paralysis that was found was from a right-sided surgery, but that was not statistically significant.
More interesting, researchers said, was the greater amount of signaling of the right true vocal fold with right-sided surgery than with the left.
Of the nine nerve integrity monitoring signals during the right-sided surgeries, four of them (44.4%) lasted longer than 30 seconds. That compared to one out of 24 signals (4.17%) during the left-sided surgeries that lasted longer than 30 seconds and two (8.33%) that lasted between 10 and 30 seconds.
The greater activity on the right side dovetailed with some prior research that found more susceptibility for injury on the right side.
In 1997 (Weisberg et al. Otolaryngol Head Neck Surg 1997;116:317-26), researchers who examined 10 cadavers found that because the left recurrent laryngeal nerve is redundant along its course, it was impossible to place any linear tension on it. But on the right nerve, which has minimal redundancy, researchers were to achieve a C4 stretch in three of the 10 and a C7 stretch in all 10 cadavers.
There is clear evidence that the right side is at greater risk of being stretched and, in our study, stimulated, Dr. Bellapianta said. However, this does not translate into a higher risk of being injured and that has yet to be proven.
Is Nerve Monitoring Necessary?
There is even lingering question over whether nerve monitoring during the surgery is even necessary. Dr. Bellapianta said that some research has indicated that it might be useful.
A 2007 study (Shindo et al. Arch Otolaryngol Head Neck Surg 2007;133:481-5), involving 684 patients undergoing a thyroidectomy with and without nerve monitoring, found a 5.8% injury rate in the monitored group and a 6.6% injury rate in the unmonitored group.