## 4 Discussion  
This study found no significant difference in the triggered threshold between the conventional probe and the newly developed magnetic probe that can be attached to a screwdriver, thus preventing real-time screw malpositioning and making it hassle-free, practical, and equally safe. The reason that there was no difference in the triggered threshold is that the wire part through which the current of the two probes flows is the same as shown in Figure 2, and the tip of the conventional probe is placed on the part where the magnetic probe can be attached as shown in Figure 1c. [PERSON] et al. demonstrated a pedicle screw threshold test (PSTT) in an experimental study using constant voltage stimulation in a porcine model. Triggered electromyography, has the advantage of allowing immediate assessment of the condition of the pedicle during surgery unlike other electrophysiological tests such as somatosensory evoked potentials and motor evoked potentials [9; 10; 17]. Moreover, triggered electromyography is sensitive to individual nerve root injury, making it easy to examine multiple sites concurrently [9; 17]. Several studies also suggest that t-EMG could help prevent pedicle screw malpositioning [18; 19; 20]. A meta-analysis study revealed that PSTT showed a weak diagnostic accuracy for pedicle screw malpositioning of the lumbar and thoracic spines [19]. However, when the triggered threshold during lumbar pedicle screw fixation was less than 8 mA, the diag  
Figure 6: Comparison of triggered threshold according to the use of conventional stimulator and novel magnetic stimulator. Group A (intact pedicle wall), Group B (broken pedicle wall). (**a–c**) Overall, (**a**) total (\(n=40\)), (**b**) Group A (\(n=20\)), (**c**) Group B (\(n=20\)), (**d–f**) 4 th lumbar vertebrae, (**d**) total (\(n=20\)), (**e**) Group A (\(n=10\)), (**f**) Group B (\(n=10\)), (**g–i**) Right side, (**g**) total (\(n=20\)), (**h**) Group A (\(n=10\)), (**i**) Group B (\(n=10\)). nostic odds ratios for sensitivity and specificity were high, indicating that PSTT is suitable for predicting screw malpositioning during lumbar pedicle screw placement, which is consistent with our results [19]. In order to perform a t-EMG during lumbar pedicle screw placement, a probe that transmits a current stimulus to the pedicle screw is required. To overcome the shortcomings of conventional probes, we developed a novel magnetic nerve stimulating probe for spine surgery. This probe can be attached to all magnetic metallic surgical instruments (Figure 1). There was no significant difference in the triggered threshold of the conventional nerve stimulating probe and the novel magnetic nerve stimulating probe when both the pedicle walls were intact nor when the pedicle wall was breached during pedicle screw placement in the porcine model. We demonstrated that our novel nerve stimulating probe attached to a pedicle screwdriver could provide adequate information about the breaching of the wall and the proximity of the screw to the neural structures during pedicle screw placement. The results of our study were consistent with those of several earlier studies on trigger thresholds. According to a study published by [PERSON] et al., a pedicle screw with a threshold of 8 mA or more could be considered capable of being correctly inserted into the pedicle [11]. For a screw with a threshold of less than 8 mA, pedicle screw malpositioning could be suspected. Furthermore, they reported that when the threshold is less than 4 mA, the screw is inserted through the pedicle wall defect, and there is strong likelihood that the dura or nerve roots may be close to the screw [11]. As a result of our experiment, the threshold median value was more than 10 mA when the pedicle wall was intact, and the threshold median value was less than 3 mA when the pedicle wall was broken. Thus, our results are consistent with the previous studies [11; 19].