## 1 Introduction  
Pedicle screws are essential for posterior fusion operations in lumbar degenerative diseases such as spinal stenosis and lumbar degenerative kyphosis [1, 2]. However, instrumentation of pedicle screws is a relatively unsafe procedure and may cause complications such as dural tears, nerve root injury, and vascular injury [3, 4, 5]. In particular, care should be taken while inserting the pedicle screw since damage to the spinal cord or nerve root is most likely irreversible and could be fatal. Surgical expertise allows pedicle screw instrumentation to be executed uneventfully, but in the hands of inexperienced surgeons, it may result in a high incidence of neurological complications (0.8-6.1%) due to screw malpositioning and pedicle breakage [6]. As safety is the topmost priority for both surgeons and patients, various surveillance devices, including image guidance systems and electromyographic tests for use during the actual surgery, are increasing in demand, and the interest in research in the field of spine surgery is on the rise. The most widely used surveillance devices during spinal surgery are image guidance systems, namely the dual-planar 2-D fluoroscopy and intraoperative 3-D scan [7, 8]. However, the disadvantage of these imaging devices is that they do not offer real-time and direct monitoring of the procedure for nerve damage while the pedicle screws are being inserted. Therefore, in order to minimize the chances of complications and produce the optimal outcome for the patient, intraoperative fluoroscopy alone is inadequate and intraoperative neurophysiologic monitoring (ION) should be performed routinely.  
Since 1992, when [PERSON] et al. introduced and proposed triggered electromyography (t-EMG) as a real-time ION technique during pedicle screw instrumentation, t-EMG has become increasingly popular for detecting intraoperative neural injuries in the field of spinal surgery [9, 10]. A study by [PERSON] et al. demonstrated that a breach of the pedicle wall determines a significant difference in the threshold stimulus intensity through porcine experimental model research and prospective human study [11]. Additionally, several studies have proven that triggered EMG is useful for determining whether or not a pedicle screw has been inserted accurately [12, 13, 14].  
In order to conduct ION during spinal surgery, nerve stimulating probes are required. A conventional probe has the disadvantage that it lacks the ability to detect intraoperative neural injury instantly. In addition, conventional probes and surgical instruments cannot be used simultaneously, and it is an inconvenience to replace the surgical instruments whenever ION is needed. To overcome these drawbacks of conventional probes, we develop novel magnetic nerve stimulating probes. The advantage of these probes is that the results of EMG can be known in real-time during the operation, which allows the immediate surgical application. In addition, they are convenient as they can be attached to all surgical instruments using magnetism.  
Moreover, the probe developed by us has already demonstrated its efficacy and safety in thyroid and ear surgery, respectively [15, 16]. Thus, we decided to use this newly developed probe in spinal surgeries where immediate recognition of nerve injury is vital. Therefore, we aimed to investigate and compare the efficacy of the novel magnetic stimulating probe and the conventional probe for ION during lumbar pedicle screw placement using a porcine model.