Purpose: Few studies have analyzed spinal cord monitoring (SCM) during spine deformity surgery when neural axis abnormalities (NAA) are present. Our purpose was to compare the effectiveness of SCM between NAA and AIS patients.

Methods: This is a retrospective review of all patients from 1993–2002 with an isolated NAA who had SCM during spinal deformity surgery. These were compared to a randomly selected group of AIS patients during the same time period when techniques for somatosensory-evoked potentials (SSEP) and motor-evoked potential (MEP) monitoring remained the same.

Results: There were 41 NAA patients and 139 AIS patients. The age at surgery was similar (14.4 vs. 14.5 yrs), but there were more males (48.8 vs. 18.7%)* in the NAA group. For NAA patients, the most common abnormalities were syringomyelia (n=29) and tethered cord (n=5) for which 68% required neurosurgery. The preoperative curve magnitude was greater in the NAA group (65.9° vs 59.6°)* but there were no differences in surgical time (39.6 vs. 35.9 min/level) and estimated blood loss (99.4 vs. 82.0 cc/level) between the groups. There was a trend towards more surgical complications in the NAA group (7.3 vs. 3.6%). Good baseline values were achieved less often in the NAA group for SSEPs (85% vs 99%)* and MEPs (83% vs 100%)*. Significant deviations from baseline values were seen more often in the NAA group for SSEP (5.0% vs. 1.4%)* and MEP (4.0% vs. 2.5%)*. * (p< 0.05)

Conclusions: Obtaining baseline SCM values was more difficult and deviations from baseline were more common in the NAA patients when compared to AIS patients. However, SCM did not miss a neurologic injury and was found to be very useful and necessary during spine deformity surgery in the NAA population.