Failure of Intraoperative Monitoring to Detect Postoperative Neurologic Deficits: A 25-year Experience in 12,375 Spinal Surgeries.

STUDY DESIGN Retrospective. OBJECTIVE The purpose was to categorize and evaluate intraoperative monitoring (IOM) failure to detect neurologic deficits occurring during spinal surgery. SUMMARY OF BACKGROUND DATA The efficacy of spinal cord/nerve root monitoring regarding undetected neurologic deficits is examined in a large, single institution series involving all levels of the spinal column and all spinal surgical procedures. METHODS Multimodality IOM included somatosensory-evoked potentials (SSEPs), descending neurogenic-evoked potentials (DNEPs), transcranial motor-evoked potentials (MEPs), dermatomal somatosensory-evoked potentials (DSEPs), and spontaneous and triggered electromyography (spEMG, trgEMG). We reviewed 12,375 patients who underwent surgery for spinal pathology from 1985 to 2010. There were 7178 females (59.3%) and 5197 males (40.7%); 9633 (77.8%) primary surgeries and 2742 (22.2%) revisions. Procedures by spinal level were cervical 29.7% (3671), thoracic/thoracolumbar 45.4% (5624), and lumbosacral 24.9% (3080). Age at surgery was > 18 years - 72.7% (8993) and < 18 years - 27.3% (3382). RESULTS Forty-five of the 12,375 patients (0.36%) had false negative outcomes. False negative results by modality were as follows: spEMG (n = 22, 48.8%), trgEMG (n = 8, 17.7%), DSEP (n = 4, 8.8%), DNEP (n = 4, 8.8%), SSEP (n = 3, 6.6%), DSEP/spEMG (n = 3, 6.6%), and trgEMG/spEMG (n = 1, 2.2%). Thirty-seven patients had immediate postoperative deficits unidentified by IOM; 30 patients (81%) involved nerve root monitoring, four patients had spinal cord deficits, and three patients had peripheral sensory deficits. Eight patients had permanent neurologic deficits, six (0.048%) were nerve root and two (0.016%) were spinal cord in nature. CONCLUSION Despite correct application and usage, IOM data failed to identify 45 (0.36%) patients with false negative outcomes out of 12,375 surgical patients. Eight patients (0.064%) of these 45 patients had permanent neurologic deficits, six patients had nerve root deficits in nature and two patients had spinal cord deficits. Although admittedly small, this represents the risk of undetected neurologic deficits even when properly using IOM. Deficits are at a higher risk to remain unresolved when not detected by IOM. LEVEL OF EVIDENCE 4.