Detection Of Impending Neurologic Injury During Surgery For Adolescent Idiopathic Scoliosis: A Comparison of Transcranial Motor and Somatosensory Evoked Potential Monitoring in 1121 Consecutive Cases

Methods: We reviewed the intraoperative monitoring records of 1121 consecutive patients (834 females, 287 males, mean Age=14.8 years) from four institutions monitored by a single, standardized multi-modality monitoring protocol during surgery for adolescent idiopathic scoliosis between 2000-2004. Significant neurophysiologic change (alert) was defined for SSEPs as an amplitude reduction of at least 50% from baseline, while that for tceMEPs was greater than or equal to a 65% amplitude loss either unilaterally or bilaterally.

Results: In total, 3.4% of patients (38/1121) met the definition of significant signal change (i.e. alert). Among these, 24% (9/38) were related to hypotension and corrected with blood pressure augmentation (average MAP at alert: 59mmHg). The remaining 29 alerts were related directly to a surgical maneuver. Of those 29, 16/29 (55%) had motor evoked amplitude changes of > 65% without any evidence of SSEP changes. Three events were related to segmental vessel clamping, and 90% (26/29) were related to instrumentation. Thirty-five percent (9/26) of patients with instrumentation-related alerts awoke with a motor or sensory deficit, all of which were detected by tceMEP, but 44% (4/9) of which were not detected by SSEP. On average, when SSEP changes were detected, they lagged behind tceMEP changes by 4.8 minutes (range: 0-10 minutes).

Conclusions: Overall, tceMEP monitoring was 100% sensitive and 100% specific in the detection of impending neurologic injury. SSEP monitoring, however, had a sensitivity of only 55.5% and specificity of 100%, and lagged behind tceMEP changes by 4.8 minutes on average. In this large, multicenter series, tceMEP was a more sensitive and rapid method of detecting an impending neurologic injury.

Hibbs Award Nominee for Best Clinical Paper