Intraoperative evoked potentials in patients with ossification of posterior longitudinal ligament

Preoperative somatosensory evoked potentials (preSEPs) are used to evaluate the severity of myelopathy, and intraoperative neurophysiological monitoring (IONM) is used to reduce iatrogenic damage during operations. However, the correlation between preSEPs and IONM on postoperative neurologic deterioration (PND) in ossification of the posterior longitudinal ligament (OPLL) has not been studied. Thus, under the hypothesis that the patients with deteriorated preSEPs would be more likely to have significant changes in intraoperative SEPs (ioSEPs), and that this would be correlated with PND, we investigated the prognostic value of preSEPs on IONM and PND. This retrospective study included 265 patients who underwent preSEPs and IONM between January 2015 and July 2019. Muscle strength, the sensory scale of the Japanese Orthopaedic Association score examined within 3 days preoperatively, and at 48 h and 4 weeks postoperatively, was analysed. PreSEPs and intraoperative SEPs (ioSEPs) were recorded by stimulating the median and tibial nerves. Intraoperative motor evoked potentials (ioMEPs) were elicited by transcranial electrical stimulation over the motor cortex. PreSEPs latency prolongation of the median and tibial nerves showed significant correlations with ioSEPs. PMD at 48 h or 4 weeks after surgery correlated with ioSEPs and ioMEPs amplitudes. Postoperative sensory deterioration (PSD) at 48 h or 4 weeks after surgery correlated with latency prolongation of ioSEPs. There was a positive correlation between amount of blood loss and maximum percentage of ioSEPs latency prolongation and a negative correlation with PMD at 48 h and 4 weeks postoperatively. PreSEPs predict significant changes in ioSEPs. Furthermore, bleeding control is important to reduce PMD in OPLL.