The surgical steps of the neuromonitoring-assisted and cement-augmented pedicle screw fixation are detailed below.

All patients underwent a single-level percutaneous cannulated PMMA cement-augmented pedicle screw fixation, using the Longitude® System (Medtronic®) (Fig. 1). After the induction of general anesthesia and before patient positioning on the surgical table, needles for neuromonitoring were placed according to the electrode placement instructions that were provided with the NIM-Eclipse System. Based on the vertebral levels to be treated, the electrical activity of the rectus abdominis, vastus lateralis, quadriceps femoris, medial gastrocnemius, and extensor hallucis longus (both sides) was monitored. Two transcranial needles were also inserted subcutaneously in the scalp, for motor evoked potential (MEP) recording. Each electrode was connected to the workstation, and baseline electromyography (EMG) was recorded. We calculated that the entire electrode positioning and connecting procedures lasted about 10 min. The patient was placed in the prone position, maintaining the physiological alignment of the spinal curves, on a radiolucent table. In this step it is crucial both to try to achieve an initial reduction of the kyphosis and to ensure that the subcutaneous needles are not displaced by the positioning maneuvers. After patient positioning, EMG recording was restarted. The comparison with the first EMG recording allowed us to detect all variations in electrical activity arising from the position on the table. Firstly, the vertebral pedicles where the percutaneous screws had to be implanted were detected with anteroposterior (AP) fluoroscopic scanning. This allowed us to mark, on the skin surface, the entry point of the percutaneous device, considering that it is preferable to use an inlet positioned laterally to the outer margins of the pedicles, to promote a convergent trajectory of the screws. A 12-mm linear skin incision was performed and the dorsolumbar fascia was sectioned. A Jamshidi needle, adequately modified, was then connected to the stimulating system and introduced through each skin incision for pedicle hole preparation (Fig. 1a). We used the needle as a pedicle probe, tracing the best and safest direction for the screw. Usually, when possible, we preferred a more lateral pedicular entry point to allow a convergent trajectory, in order to place the tips of the screws in close proximity to the median line. This seemed to improve the resistance of the implanted systems and to prevent pullout. During this phase, monitoring is useful to detect any changes in EMG activity. If EMG abnormalities are recorded, the trajectory must be modified. Subsequently a Kirschner wire (K-wire) was introduced through the needle. The K-wire reached the vertebral body and was maintained in place in order to guide the introduction of progressive tubular retractors used to facilitate the introduction of the screw. Finally, under fluoroscopic guidance, the cannulated screw was placed and the K-wire removed. Once the screw was positioned, a special ball-tip probe was inserted through the cannula, for a final test. The probe is provided with two buttons to access the functions of the workstation. The device also allows the performance of so-called screw integrity test stimulation, which combines automatic electrical stimulation and EMG response analysis to speed-test pedicle screw placement. The surgeon can control this test directly from the operative field, contacting and stimulating the screw with the probe (Fig. 1b). The test begins by stimulating at the start intensity (usually 3 mA). For each increase in stimulus intensity, the EMG response is measured and compared with default response criteria, and the response either passes or fails based on the pass/fail criteria. A stimulation threshold greater than 15 mA indicates adequate screw positioning. A good response on this test predicts the absence of electric current leakage from the bone structures and this means that the pedicle is intact. A summary of the responses of all screws tested was recorded on the workstation, then printed and stored in the clinical folder. When all the transpedicular screws had been implanted, PMMA cement was injected through the cannulated screws (Fig. 1c). We introduced about 1.5 ml of PMMA cement for each screw under fluoroscopic guidance. During cement introduction, the EMG trace was carefully monitored to promptly detect any variation arising from this procedure. The last surgical step consisted of positioning and fixing the rods. The Longitude® System provides a free-hand inserter and reduction screw extenders that are designed to allow a stabilizing rod to be passed through a small incision over the higher treated level (Fig. 1d). After the last fluoroscopic control, the rods were locked and fixed to the screws after an adequate compression, in order to guarantee reduction of the fracture and the correct alignment of the spine (Fig. 2).