Comparison of Motor Evoked Potentials Neuromonitoring Following Pre- and Postoperative Transcranial Magnetic Stimulation and Intraoperative Electrical Stimulation in Patients Undergoing Surgical Correction of Idiopathic Scoliosis

Abstract

The relationships between the results of pre- and intraoperative motor evoked potential recordings during neuromonitoring and whether idiopathic scoliosis (IS) surgical correction improves the spinal efferent transmission have not been specified in detail. This study aims to compare the results of surface-recorded electromyography (EMG), electroneurography (ENG, M, and F-waves), and especially motor evoked potential (MEP) recordings from tibialis anterior muscle (TA) bilaterally in 353 girls with right idiopathic scoliosis (types 1–3 according to Lenke classification). It has not yet been documented whether the results of MEP recordings induced by transcranial single magnetic stimulus (TMS, pre- and postoperatively) and trains of electrical stimuli (TES; intraoperatively in T0—before surgery, T1—after pedicle screws implantation, and T2—after scoliosis curvature distraction and derotation following two-rod implantation) can be compared for diagnostic verification of the improvement of spinal cord neural transmission. We attempted to determine whether the constant level of optimal anesthesia during certain surgical steps of scoliosis treatment affects the parameters of MEPs recorded during neuromonitoring procedures. No neurological deficits have been observed postoperatively. The values of amplitudes but not latencies in MEP recordings evoked with TMS in IS patients compared before and after surgery indicated a slight improvement in efferent neural transmission. The results of all neurophysiological studies in IS patients were significantly asymmetrical and recorded worse on the concave side, suggesting greater neurological motor deficits at p = 0.04. The surgeries brought significant improvement (p = 0.04) in the parameters of amplitudes of sEMG recordings; however, the consequences of abnormalities in the activity of TA motor units were still reflected. ENG study results showed the symptoms of the axonal-type injury in peroneal motor fibers improving only on the concave side at p = 0.04, in parallel with F-wave parameters, which suggests that derotation and distraction might result in restoring the proper relations of the lumbar ventral roots in the spinal central canal, resembling their decompression. There were no significant differences detected in the amplitudes or latencies of MEPs induced with TMS or TES when comparing the parameters recorded preoperatively and intraoperatively in T0. The amplitudes of TES-evoked MEPs increased gradually at p = 0.04 in the subsequent periods (T1 and T2) of observation. A reduction in MEP latency at p = 0.05 was observed only at the end of the IS surgery. Studies on the possible connections between the level of anesthesia fluctuations and the required TMS stimulus strength, as well as the MEP amplitude changes measured in T0–T2, revealed a lack of relationships. These might not be the factors influencing the efferent transmission in spinal pathways beside the surgical procedures. Pre- (TMS-evoked) and intraoperative (TES-evoked) recordings are reliable for evaluating the patient’s neurological status before and during surgical scoliosis correction procedures. An increase in MEP amplitude parameters recorded on both sides after scoliosis surgery proves the immediate improvement of the total efferent spinal cord transmission. Considering comparative pre- and postoperative sEMG and ENG recordings, it can be concluded that surgeries might directly result in additional lumbar ventral root decompression. We can conclude that MEP parameter changes are determined by the surgery procedures during neuromonitoring, not the anesthesia conditions if they are kept stable, which influences a decrease in the number of false-positive neuromonitoring warnings.

Clinical Neurophysiological Methods Verify Improvement in the Motor Neural Transmission in Patients with Surgically Treated Idiopathic Scoliosis in Long-Term Follow-up

“…The results of this study in patients surgically treated for idiopathic scoliosis confirmed the previous findings in [7], namely, that the transmission of efferent neural impulses in the spinal cord tracts and within the fibers of the peripheral nervous system slightly improves immediately after the surgical correction of scoliosis. Moreover, we ascertained the further normalization of the motor function together with the improvement of TA muscle motor unit recruitment half a year after the surgical treatment in IS patients, in which the mcsEMG parameter values are comparable to those of the normal condition.…”

“…All surgical procedures were applied under the control of X-ray C-arm and neuromonitoring navigations (Figure 2(Da,Dc)). Further details regarding the surgical procedures and intraoperative neurophysiological recordings are described elsewhere [7].…”

“…A sequence of four stimuli, with a single pulse with a 500 µs duration and an intensity of 105 mA on average, were applied via bipolar subcutaneous electrodes. According to the previous description, we used our experience with applying the surface electrodes for the MEP recordings of the TA and the muscles of other upper and lower extremities [7].…”

“…Disorders in the conduction of neural impulses within the spinal ventral roots may lead to the development of neuropathy in the peripheral nervous system and, finally, to neurogenic changes in the muscular system as symptoms of secondary changes originating from IS [4]. Clinical neurophysiology diagnostics have proven the high incidence of the mentioned abnormalities before treatment and the axonal-type injury symptoms in peroneal motor fibers, which postoperatively improved on the concave side of IS in parallel with the lumbar ventral root neural motor conduction [7]. Although these pathologies can be considered subclinical, surgical intervention restores the proper relations between the lumbar ventral roots in the central spinal canal and symptoms resembling their decompression.…”

“…Neurophysiological assessment has the most important intraoperative significance when neuromonitoring the conduction of neural impulses within the spinal cord pathways [25]; however, preoperatively, in patients with IS, it supports the clinical assessments when making decisions about surgical treatment [26]. Few studies in the field of clinical neurophysiology presenting postoperative recordings, especially of motor-evoked potentials, proved an immediate functional improvement in the efferent conduction of spinal pathways in IS patients [7]. This does not imply that preoperative monitoring techniques are inherently more sensitive than intraoperative ones; different assessments, both pre-and intraoperative ones, serve different purposes and may provide complementary insights into the neurological aspects of idiopathic scoliosis.…”