Multimodal intraoperative neuromonitoring in scoliosis surgery: A two-year prospective analysis in a single centre

The present study is a prospective analysis of neuromonitoring [somatosensory evoked potentials (SSEP) and transcranial motor evoked potentials (TcMEP)] in consecutive scoliosis surgeries done at a tertiary care spine centre.

Prospective analysis was performed on 52 consecutive patients undergoing scoliosis correction from 2013 to 2015. SSEPs were obtained by stimulating the median and tibial nerves with stimulus intensity level 20-25 mA. TcMEPs were recorded bilaterally from abductor pollicis brevis, biceps, and deltoid for the upper limb, and from tibialis anterior, quadriceps, gastrocnemius, and abductor hallucis for the lower limb. Stimulation was given in the form of a high voltage (300-400 V) stimulus. An "alert" was defined as reduction in the amplitude of at least 50% for SSEP and at least 65% for TcMEP compared to the baseline recordings and an increase in the latency by more than 10%.

The mean age of the patients was 14.6 years (7-33 years). Thirty-nine of the patients were females and 13 were males. Baseline values in neuromuscular scoliosis were low compared to adolescent idiopathic scoliosis (AIS). There were no false negative incidents. False positive cases were due to low blood pressure and malfunctioning of the leads.

Use of upper limb leads could help in identifying malposition or malfunctioning of leads to eliminate false positive results. Combined multimodal intraoperative monitoring helps in increasing the safety in scoliosis corrective surgeries with a high sensitivity and specificity. Baseline values in neuromuscular scoliosis patients are possibly lower than idiopathic scoliosis patients. Intraoperative variations must be interpreted with caution.