Positional disappearance of motor evoked potentials is much more likely to occur in non-idiopathic scoliosis

"Real-Time Neuromonitoring" Increases the Safety and Non-Invasiveness and Shortens the Duration of Idiopathic Scoliosis Surgery

Introduction: A practical solution to the incidental unreliability of intraoperative neuromonitoring (IONM) may be the simultaneous neurophysiological recording and control of the surgical field through a camera (the concept of "Real-time" IONM). During "Real-time" IONM, the surgeon is immediately warned about the possibility of damage to the neural structures during, but not after, standard idiopathic scoliosis (IS) corrective surgery procedures (the concept of "Surgeon-neurophysiologist" interactive, verbal IONM). This study aimed to compare the advantages, utilities, reliabilities, and time consumption of the two IONM scenarios. Methods: Studies were performed in two similar groups of patients undergoing surgery primarily due to Lenke 2 idiopathic scoliosis (N = 120), when both IONM approaches were applied. Neurophysiological evaluations of the spinal transmission were performed pre- (T0), intra- (before (T1) and after (T2) surgery), and postoperatively (T3), as well as once in healthy volunteers (control, N = 60). Non-invasive and innovative recordings of the motor evoked potentials (MEPs) bilaterally from the peroneal (PER) nerve and tibialis anterior (TA) muscle were performed with surface electrodes as a result of transcranial magnetic stimulation (TMS) or electrical stimulation (TES) at T0-T3. Results: In both groups, the MEP amplitudes and latencies recorded from the PER nerve were approximately 67% lower and 3.1 ms shorter than those recorded from the TA muscle. The MEP recording parameters differed similarly at T0-T3 compared to the control group. In all patients, the MEP parameters induced by TMS (T0) and TES (T1) did not differ. The MEP amplitude parameters recorded from the TA and PER at T1 and T2 indicated a bilateral improvement in the neural spinal conduction due to the surgical intervention. The TMS-induced MEP amplitude at T3 further increased bilaterally. In both IONM groups, an average 51.8 BIS level of anesthesia did not affect the variability in the MEP amplitude, especially in the PER recordings when the applied TES strength was 98.2 mA. The number of fluctuations in the MEP parameters was closely related to the number of warnings from the neurophysiologist during the transpedicular screw implantation, corrective rod implantation, and distraction, derotation, and compression procedures, and it was higher in the "Surgeon-neurophysiologist" IONM group. The average duration of surgery was shorter by approximately one hour in the "Real-time" IONM group. The number of two-way communications between the surgeon and the neurophysiologist and vice versa in the "Real-time" IONM group decreased by approximately half. Conclusions: This study proves the superiority of using "Real-time" IONM over the standard "Surgeon-neurophysiologist" IONM procedure in increasing the safety and non-invasiveness, shortening the time, and lowering the costs of the surgical treatment of IS patients. The modifications of the MEP nerve-conduction-recording technology with surface electrodes from nerves enable precise and reliable information on the pediatric patient's neurological condition at every stage of the applied surgical procedures, even under conditions of slight fluctuations in anesthesia.

The role of intraoperative extensor digitorum brevis muscle MEPs in spinal surgery

PURPOSE

Intraoperative muscle motor evoked potentials (m-MEPs) are widely used in spinal surgery with the aim of identifying a damage to spinal cord at a reversible stage. Generally, lower limb m-MEPs are recorded from abductor hallucis [AH] and the tibialis anterior [TA]. The purpose of this work is to study an unselected population by recording the m-MEPs from TA, AH and extensor digitorum brevis (EDB), with the aim of identifying the most adjustable and stable muscles responses intraoperatively.

METHODS

Transcranially electrically induced m-MEPs were intraoperative recorded in a total of 107 surgical procedures. m-MEPs were recorded by a needle electrode placed in the muscle from TA, AH and EDB muscles in the lower extremities.

RESULTS

Overall monitorability (i.e., at least 1 Lower Limb m-MEP recordable) was 100/107 (93.5%). In the remaining 100 surgeries in 3 cases, the only muscle that could be recorded at baseline was one AH, and in other 2 the EDB. Persistence (i.e., the recordability of m-MEP from baseline to the end of surgery) was 88.7% for TA, 89.8% for AH and 93.8% for EDB.

CONCLUSION

In our series, EDB m-MEPs have demonstrated a recordability superior to TA and a stability similar to AH. The explanations may be different and range from changes in the excitability of the cortical motor neuron to the different sensitivity to ischemia of the spinal motor neuron. EDB can be used alternatively or can be added to TA and AH as a target muscle of the lower limb in spinal surgery.

Temporary Flexible Rods for Correction of Severe Pediatric Spinal Deformity

Surgical correction of large, rigid scoliotic and kyphotic curves carries an increased risk of perioperative complications, such as neurological injury and excessive blood loss, compared with correction of less severe curves. Titanium temporary flexible rods (TFRs), designed for pediatric long bone fracture fixation, may be helpful as adjuncts to achieve gradual, stepwise intraoperative correction of severe pediatric spinal deformities. A retrospective review was conducted of spinal fusion cases for pediatric scoliosis or kyphosis at our institution that used TFRs as a correction technique from 2007 to 2019. Patients underwent posterior spinal fusion with predominantly pedicle screw instrumentation. Intraoperatively, a non-contoured titanium elastic nail was temporarily positioned in the screws unilaterally to achieve partial correction while the contralateral side was instrumented. Then, the TFR was removed and replaced with a permanent rod. Thirty-four patients with severe spinal deformities underwent posterior spinal fusion. Seventeen had scoliosis (mean major Cobb angle, 89.3°) and 17 had kyphosis (mean T5-T12 kyphosis, 73.8°). Idiopathic deformity was the most common etiology; neuromuscular, syndromic, and postsurgical causes contributed to the remainder of cases. All patients had Ponte osteotomies. Four patients (11.8%) had neuromonitoring alerts, 1 of which was related to insertion of the TFR; all were reversible. For patients with scoliosis, the mean postoperative Cobb angle measured 40.2° (53.6% correction). For patients with kyphosis, the mean postoperative T5-T12 angle measured 43.3° (30.4° of correction). TFRs appear to be helpful adjuncts for correction of severe pediatric spinal deformities, facilitating gradual intraoperative correction in a single-stage operation. Neuromonitoring alerts are common but reversible. [Orthopedics. 2023;46(4):234-241.].