Spinal Cord Monitoring in Patients with Spinal Deformity and Neural Axis Abnormalities: A Comparison to AIS Patients

Summary: A retrospective review of 41 patients with neural axis abnormalities and 139 patients with AIS were reviewed to analyze the efficacy of spinal cord monitoring during spine deformity surgery. Good baseline values for SSEP and MEP were less and significant deviations were more for the NAA group compared to the AIS group and the false positive rate was higher resulting in a greater likelihood to use the wake up test.

Purpose: Few studies have analyzed spinal cord monitoring (SCM) during spine deformity surgery in patients with neural axis abnormalities (NAA).

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

Results: There were 40 patients in the NAA group and 139 patients in the AIS group. The average ages were similar (14.0 vs 14.1 yrs), with more males (48.8 vs. 18.7%) in the NAA group.(P<0 .05) For the NAA group, abnormalities included syringomyelia (n="2)" tethered cord spinal tumor and diastematomyelia for which neurosurgical intervention occurred in 68.3%. The preoperative curve magnitude was greater group (65.9º vs 59.6º)(P<0.05) but surgical time (39.6 vs. 35.9 min/level), estimated blood loss (99.4 82.0cc/level) were similar. Good baseline values achieved less often SSEPs (85.0% 100%) MEPs (81.8% 97.3%).(P<0.05) Significant deviations from seen more SSEP (5.0% 0%) MEP (18.2% 2.7%).(P<0.05) incidence of "false positives" (10.0% 2.2%) wake-up test used vs1.4%). There no false negatives either group.

Conclusions: Spinal cord monitoring in patients who have isolated neural axis abnormalities can be more difficult to obtain, results in a higher incidence of false positives but does not miss neurologic injury. Preoperative planning to consult patients that a wake-up test may be necessary is warranted in these patients.