## 4 Discussion  
In the modern spine surgical field, the development of MISS is important. Combined with tubular decompression and percutaneous instrumentation, MISS features a small wound, less blood loss, less post-operative pain, quick recovery, and a short hospital stay. It has been proven to be efficient in surgery of degenerative lumbar spondylosis, spondylolisthesis, and short segment scoliosis [11; 12; 13; 14; 15; 16]. However, percutaneous screw instrumentation is an experience-demanding technique, and it relies greatly on image guidance. The traditional method uses biplanar fluoroscopy for guidance. Compared to open surgery, fluoroscopy-guided percutaneous screw instrumentation has a steep learning curve that causes beginners to encounter some difficulties. Firstly, the surgeon must be remarkably familiar with the anatomical structure so that he or she can use 2D images (anteroposterior and lateral fluoroscopy) to reconstruct a 3D image in their mind. If the patient has experienced severe degeneration, it is difficult to find the proper entry point and trajectory. Secondly, surgeons must change their line of sight frequently from the surgical field to a remote screen, which inevitably leads to attention shifts and hand movements. It is an unintuitive way to perform the surgery. Hand-eye coordination is crucial to the success of instrumentation. Recently, anatomical identification experienced great improvement by introducing a computer navigation system. However, the problem of sightline change persisted. This problem has not been solved yet, even using state-of-the-art robots. With head-mounted goggles, AR could provide an immersive experience through the direct retinal projection of a 3D spine image onto the patient. Meanwhile, the 2D navigation images are also projected onto the AR goggles. The AR goggles could provide the necessary information so that surgeons could stay focused on the surgical field without changing their line of sight. Thus, the AR-assisted instrumentation procedure is an intuitive way to perform surgery, and the whole process is like open pedicle screw placement. This method could effectively reduce surgical time and improve the accuracy of screw placement. AR-assisted pedicle screw instrumentation is a novel technology. Until now, there are several systems launched and waiting for final FDA approval. The published data are scarce on this technology. [PERSON] et al. reported on two cadaveric reports describing AR technology. Although the authors documented the technology as AR, they did not use head-mounted equipment. Instead, they overlaid the navigation data onto a remote screen, which was similar to the current computer navigation system. The first cadaveric study documented the insertion of 47 pedicle screws with an accuracy of 85% [17]. The second report described the placement of 18 pedicle screws with an accuracy of 89% [6]. [PERSON] et al. also published two cadaveric reports using the same AR technology. The first report documented a 94.6% success rate from 120 pedicle screws' placement [9]. \begin{table}
\begin{tabular}{c c c} \hline \hline  & \multicolumn{3}{c}{**Screw Side**} \\ \cline{2-3}  & **Lt** & **Rt** \\ \hline T6 & 3 (M) & 0 \\ T7 & 3 (M) & 0 \\ T8 & 3 (M) & 0 \\ T9 & 0 & 0 \\ T10 & 0 & 0 \\ T11 & 0 & 0 \\ T12 & 0 & 0 \\ L1 & 3 (I/O) & 3 (I/O) \\ L2 & 3 (I/O) & 3 (I/O) \\ L3 & 3 (I/O) & 0 \\ L4 & 0 & 0 \\ L5 & 0 & 0 \\ \hline Overall accuracy & & 87.5\% \\ \hline \hline \end{tabular}  
* M: medial breach; I/O in-out-in trajectory.  
\end{table} 
Table 1: Screw insertion accuracy according to Gertzbein–Robbins grade. In the second report, the authors inserted 113 instruments, including 93 pedicle screws and 20 Jamshidi needles. Their overall accuracy was 99.1% [8]. [PERSON] et al. published two AR-assisted pedicle screw studies using different AR systems. In the first study, they described a cadaveric study using the OpenSight AR system (Novarad, American Fork, UT, USA) and Hololens AR glasses (Microsoft, Redmond, WA, USA).