The benefits and utility of routine neuromonitoring with motor and somatosensory evoked potentials during lumbar spine surgery remain unclear. This study assesses measures of performance and utility of transcranial motor evoked potentials (MEPs) during lumbar pedicle subtraction osteotomy (PSO).
This is a retrospective study of a single-surgeon cohort of consecutive adult spinal deformity (ASD) patients who underwent lumbar PSO from 2006 to 2016. A blinded neurophysiologist reviewed individual cases for MEP changes. Multivariate analysis was performed to determine whether changes correlated with neurological deficits. Measures of performance were calculated.
A total of 242 lumbar PSO cases were included. MEP changes occurred in 38 (15.7%) cases; the changes were transient in 21 cases (55.3%) and permanent in 17 (44.7%). Of the patients with permanent changes, 9 (52.9%) had no recovery and 8 (47.1%) had partial recovery of MEP signals. Changes occurred at a mean time of 8.8 minutes following PSO closure (range: during closure to 55 minutes after closure). The mean percentage of MEP signal loss was 72.9%. The overall complication rate was 25.2%, and the incidence of new neurological deficits was 4.1%. On multivariate analysis, MEP signal loss of at least 50% was not associated with complication (p = 0.495) or able to predict postoperative neurological deficits (p = 0.429). Of the 38 cases in which MEP changes were observed, the observation represented a true-positive finding in only 3 cases. Postoperative neurological deficits without MEP changes occurred in 7 cases. Calculated measures of performance were as follows: sensitivity 30.0%, specificity 84.9%, positive predictive value 7.9%, and negative predictive value 96.6%. Regarding the specific characteristics of the MEP changes, only a signal loss of 80% or greater was significantly associated with a higher rate of neurological deficit (23.0% vs 0.0% for loss of less than 80%, p = 0.021); changes of less than 80% were not associated with postoperative deficits.
Neuromonitoring has a low positive predictive value and low sensitivity for detecting new neurological deficits. Even when neuromonitoring is unchanged, patients can still have new neurological deficits. The utility of transcranial MEP monitoring for lumbar PSO remains unclear but there may be advantages to its use.
Correspondence Darryl Lau: University of California, San Francisco, CA. firstname.lastname@example.org.
INCLUDE WHEN CITING Published online May 31, 2019; DOI: 10.3171/2019.3.SPINE181409.
Disclosures Dr. Smith reports consultant relationships with K2M, AlloSource, Cerapedics, Zimmer Biomet, and NuVasive; support from DePuy Synthes for the study described as well as for other clinical or research efforts; fellowship funding from NREF and AOSpine; and royalties from Zimmer Biomet. Dr. Shaffrey reports consultant relationships with Medtronic and NuVasive; direct stock ownership in NuVasive; patent holder relationships with Medtronic, NuVasive, and Zimmer Biomet; and support of non–study-related clinical or research efforts from ISSG Foundation. Dr. Ames reports consultant relationships with DePuy Synthes, Medtronic, Stryker, Medicrea, K2M, and Zimmer Biomet; receipt of royalties from Stryker, Zimmer Biomet Spine; DePuy Synthes, NuVasive, Next Orthosurgical, K2M, and Medicrea; research support from Titan Spine, DePuy Synthes, and ISSG; membership on the editorial board of Operative Neurosurgery; grant funding from SRS; membership on the executive committee of ISSG; and directorship of Global Spine Analytics.
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