Neurogenic mixed evoked potential monitoring during scoliosis surgery: a 149-case retrospective analysis

Introduction We report a retrospective analysis of spinal cord monitoring with neurogeni c mixed evoked potentials (NMEPs) combined with somatosensory evoked potent ials (SSEPs) in 149 patients undergoing surgery for spinal deformity. Material and methods 149 patients (104 females and 45 males), mean age 28 yrs (13-72 yrs) were s tudied. NMEPs were elicited by electrical spinal cord stimulation in the ro stral part of the surgical field, via two needle electrodes set in the epid ural space and in the interspinous ligament above. They were recorded from the sciatic nerve at the knee and the sural nerve at the ankle. SSEPs were recorded from the scalp after stimulation of the posterior tibial nerve at the ankle. A decrease in amplitude of more than 50 p. 100 and/or an increas e in latency of more than 10 p. 100 were defined as significant warning cri teria. Results No false-negative result was observed. NMEP modifications did not reach cri tical value in 143 cases. In 6 cases, significant changes were observed. Mo ving the stimulation electrodes along the spinal cord allowed spinal lesion localization and helped the surgeon to perform the adapted maneuver, clear ly avoiding the occurrence of postoperative neurological defect in 5 of the 6 cases. Conclusion NMEP monitoring is a sensitive and specific method useful for detecting an impending lesion of the spinal cord. NMEPs are also helpful in localizing t he spinal level of the lesion. They represent a primary choice tool for neu romonitoring during scoliosis surgery.