Wednesday, September 26, 2018 1:00 PM – 2:00 PM Navigation and Intraoperative Monitoring: 43. Direct nerve root stimulation: a novel approach to neuromonitoring for reduction of high grade spondylolisthesis

BACKGROUND CONTEXT Traditional methods of neuromonitoring for spinal deformity cases lack accuracy and reproducibility in monitoring for high grade spondylolisthesis. Free run electromyography (EMG) has not been shown to be accurate in detecting radicular injuries in lumbar degenerative surgeries. PURPOSE The purpose of this project is to introduce direct nerve stimulation as a novel alternative to nerve root monitoring in the reduction of high grade spondylolisthesis. METHODS Prospectively collected intraoperative neuromonitoring data including MEP, SSEP and free run EMG, was collected on pediatric patients undergoing posterior reductions for high grade L5 or S1 spondylolisthesis. A fourth modality using direct nerve root stimulation (DNS) of the L5 and S1 nerve roots was recorded by placing a stimulator directly on the exposed nerve root and recording threshold stimulus. Along with the other modalities, DNS was carried out prior to reduction, following all reduction maneuvers and prior to closure. RESULTS Five patients with high grade spondylolisthesis were analyzed, four with Grade IV and one with Grade V. All patients had positive bilateral straight leg raises. Four of 5 patients had intact preoperative lower extremity motor examinations, with one patient having left-sided 4/5 EHL weakness. Three patients did not have any neuromonitoring alerts during their surgical procedure. Their average change in threshold value from baseline to final stimulation in these cases for the L5 nerve root was 1.3 mA. Two patients had intraoperative alerts of MEPs, SSEPs and EMGs which resulted in greater nerve root stimulation threshold values at closing compared to baseline. One patient showed a three-fold increase in DNS threshold while a second patient had a 25-30-fold increase. In both cases, further nerve root exploration and decompression was performed. Both cases resulted in immediate postoperative neurologic deficits in bilateral ankle dorsiflexion. CONCLUSIONS After establishing a prereduction threshold of direct nerve stimulation, increases in DNS threshold were associated with postoperative neurologic deficits in cases of posterior reduction of high grade spondylolisthesis. DNS provided an accurate measure of nerve function in this series. Recognizing increases in DNS thresholds intraoperatively can alert the surgeon to potential real time nerve injuries. A larger multicenter series can help determine the utility of this technique. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.