2:32 Intraoperative monitoring during interbody fusion

Abstract Purpose of study: A reported 5% to 10% neurologic complication rate has been reported after interbody fusion (both anterior [ALIF] and posterior [PLIF]). Iatrogenic injuries during these procedures have been reported to occur in response to excessive nerve root retraction and thecal sac manipulation. Somatosensory evoked potential (SSEP) and spontaneous electromyographic (EMG) recordings may detect and potentially prevent nerve root and thecal sac injury during ALIF and PLIF procedures. We describe the feasibility and utility of recording SSEPs and spontaneous electromyography EMG during ALIF and PLIF procedures. Methods used: A total of 165 patients underwent surgical procedures involving decompression and stabilization of the lumbar spine using either ALIF (n=90) or PLIF (n=75) procedures. Pedicle screw fixation was used in 65 of the PLIF cases. Spinal procedures were performed by one team of surgeons, and standardized SSEP and EMG was performed sequentially on all patients undergoing interbody fusion procedures. Detection of nerve root compression, manipulation, stretching and/or permanent injury was based on changes from baseline EMG recordings. The severity of nerve root compromise was based on the type of spontaneous discharges that were recorded. of findings: In a total of 12 cases (all PLIF), spontaneous EMG activity was reported to the surgeon. In no cases were significant SSEP changes observed. Five patients awoke with new or an exacerbation of a preexisting neurological deficit. In those cases where EMG recording was performed, only two new transient neurological deficits were observed with cage placement. In both of these cases, multiple periods of sustained EMG activity were recorded during placement of instrumentation/retraction of nerve roots. Relationship between findings and existing knowledge: Thecal sac and nerve root injury may or may not be detected depending on the neurophysiologic modality that is being monitored. The present report demonstrates the increased sensitivity and specificity of combined neurophysiologic modality testing during instrumented procedures in predicting postoperative morbidity. The data in this report describe a powerful conjunction of simple tools that provide immediate “early-warning” feedback to the surgeon concerning the state of sensory and motor function during lumbar interbody fusion procedures. Overall significance of findings: Spontaneous EMG activity appears to be a sensitive indicator of nerve root retraction and predictor of potential iatrogenic nerve root compromise during PLIF procedures. Our data suggest that EMG recording during lumbar interbody fusion procedures is a sensitive and specific indicator of nerve root compromise. Multimodality monitoring, an assessment of both sensory and motor function, is the best approach for the prevention of iatrogenic injury incurred during decompression and complex fusion of the lumbosacral spine. Disclosures: Device or drug: interbody fusion cages. Status: approved. Device or drug: pedicle screws. Status: approved. Conflict of interest: William Welch, consultant, Sulzer Spine Tech.