## 2 Materials and Methods  
### Participants and Study Protocol  
The data of 45 girls with IS treatment between 2019 and 2023 at the Wiktor Dega Orthopedic and Rehabilitation Hospital in Poznan, Poland, were selected for this study from the cohort of 372 patients. The principles of this selection are presented in Figure 1.  
Figure 1: Flow chart of this study with the selection criteria for scoliotic subjects and healthy controls. Abbreviations: mcsEMG—tibialis anterior muscle maximal contraction surface electromyography  
recording, ENG--peroneal nerve electroneurography recording, and MEP--tibialis anterior muscle motor evoked potential recording. The inclusion criteria were as follows: primary right thoracic and secondary left lumbar IS with Cobb angles in similar ranges based on the measurements from anterior-posterior and lateral X-rays, Lenke types 1-3 (mainly 2) of IS [27], the employment of the same technique for the patients' surgeries using the Nova Spine corrective instrumentation with a similar number of implanted transpecicular screws between 8 and 19 (13 on average), data acquisition from the same set of three diagnostic clinical neurophysiology tests performed preoperatively (T0), one week postoperatively (T1), and six months after surgery (T2) (Table 1). The IS patients were assessed with neurophysiological recordings three times. The tests included bilateral tibialis anterior (TA) muscle electromyography recordings during maximal contraction with surface electrodes (mcsEMG); peroneal nerve electroneurography (ENG) recorded in the extensor digitorum brevis (EXT) muscle following the electrical stimulation of motor fibers in the ankle; and motor-evoked potential (MEP) recordings in the tibialis anterior muscles following transcranial magnetic stimulation (TMS). The exclusion criteria were similar to the contraindications for diagnostic TMS and transcranial electrical stimulation utilized during the neuromonitoring procedures. They comprised having head trauma, epilepsy, or cardiac disease; using pacemakers or other implanted biomedical devices; and pregnancy [28]. There was no need to apply anesthetics, neither in the pre- nor postoperative observations. The patients were fully aware and cooperative. The reference values for the parameters of mcsEMG, ENG, and MEP neurophysiological recordings were obtained from a control group of 80 healthy volunteers. To ensure the data comparability between patients and controls, the demographics (gender, age, height, and weight) were preliminarily matched during the data mining. Significant differences in age, height, and weight between the patients and healthy volunteers in the control group were not observed (Table 1). The patients were surgically treated and clinically evaluated three times in the T0-T2 periods of observation by the same team of four experienced spine surgeons. Neurophysiological studies were performed by the same two neurophysiologists. The surgeons independently evaluated the anterior-posterior and lateral spinal X-rays and MRI, and the final results were arbitrarily determined in the final analysis. The manual muscle strength testing of the TA was performed using [PERSON]'s scale (0-5), which consists of six grades that assess the different levels of muscle strength (from 0--no visible voluntary contraction