Intra‐operative Neurophysiological Monitoring in Patients Undergoing Posterior Spinal Correction Surgery with Pre‐operative Neurological Deficit: Its Feasibility and High‐risk Factors for Failed Monitoring

OBJECTIVE: Considering spinal deformity patients with pre‐operative neurological deficit were associated with more intra‐operative iatrogenic neurological complications than those without, intra‐operative neurophysiological monitoring (IONM) has been used for detecting possible iatrogenic injury timely. However, the IONM waveforms are often unreliable. To analyze the performance of intra‐operative neurophysiological monitoring (IONM) including somatosensory evoked potentials (SEP) and motor evoked potentials (MEP) in patients with pre‐operative neurological deficit undergoing posterior spinal correction surgery, and to identify the high‐risk factors for failed IONM. METHODS: Patients with pre‐operative neurological deficit undergoing posterior spinal correction surgery between October 2017 and January 2022 were retrospectively reviewed. The presence or absence of SEP and MEP of target muscles were separately recorded. The P37/N50 latency and amplitude of SEP, and the MEP amplitude were measured. Any IONM alerts were also recorded. The IONM performance was compared among patients with different etiologies, levels responsible for neurological deficit, and strength of IONM‐target muscles. Patients' demographics were analyzed using the descriptive statistics and were presented with mean ± standard deviation. Comparison analysis was performed using χ (2)‐test and statistically significant difference was defined as p < 0.05. RESULTS: A total of 270 patients (147 males, 123 females) with an average age of 48.4 ± 36.7 years were involved. The SEP records were available in 371 (68.7%) lower extremities while MEP records were available in 418 (77.4%). SEP alerts were reported in 31 lower extremities and MEP alerts in 22, and new neurological deficit at post‐operation was observed in 11. The etiologies of neuromuscular and syndromic indicated relatively lower success rates of IONM, which were 44.1% and 40.5% for SEP, and 58.8% and 59.5% for MEP (p < 0.001). In addition, patients with pre‐operative neurological deficit caused by cervical spine and muscle strength lower than grade 4 suffered from higher risk of failed IONM waveforms (p < 0.001). CONCLUSION: Patients with pre‐operative neurological deficit suffered from a higher incidence of failed IONM results. The high‐risk for failed IONM waveforms included the neuromuscular and syndromic etiologies, neurological deficit caused by cervical spine, muscle strength lower than grade 4 in patients with pre‐operative neurological deficit undergoing posterior spinal correction surgery.