# Augmented Reality: Mapping Methods and Tools for Enhancing the Human Role in Healthcare HMI
## 3 Results
### Intraoperative Solution
#### 3.3.2 Spine Surgery
As an alternative to the microscope, also HMD devices implementing AR were studied in spine surgery procedures, particularly for percutaneous interventions such as pedicle screw placement, injections into facet joints, and kyphoplasty. In the study of [PERSON] et al. [70], an effective AR-based method for navigation and position during pedicle puncture in percutaneous kyphoplasty surgery was developed. Microsoft HoloLens, in combination with fluoroscopic C-arm images, was used to support orthopedics during surgery to obtain accurate, real-time guidance in the intravertebral vacuum cleft area. The use of HMD has reduced the operation time and the number of C-arm fluoroscopies acquired and has increased the accuracy and efficacy of the intervention. [PERSON] et al. [73] used Microsoft HoloLens to visualize a virtual model of the target rod. To navigate the bending of the rod implant ex situ, they estimate the 3D positions of the pedicle screw heads using a pointing device with an image-based marker, allowing the surgeon to shorten the length of the rod to the desired shape, bend it, and iteratively compare it with the target shape displayed by HoloLens. With this procedure, they were able to reduce re-bending maneuvers and operating time and decrease the risk of infection. Instead of using a pointer-based approach, [PERSON] et al. [43] proposed a markerless approach for surgical navigation to bend rod implants, achieving a similar average localization error of pedicle screw heads compared to the approach of [PERSON] et al. [73]. Their approach combines AR with Machine Learning so that, without touching the instrumented anatomy, a virtual model of the optimal rod shape on the device is generated and displayed. This method allows detection of the 3D positions of the implanted screw heads at interactive rates, without the need for manual acquisition and registration of the anatomy. Although rod bending navigation has demonstrated clinical and biomechanical advantages with respect to the conventional method, it has not yet been fully adopted in spinal surgery. In an in vitro study using a customized phantom, an optical see-through HMD was successfully tested by [PERSON] et al. [78] for kyphoplasty. Augmented visualization was achieved by placing the display in a specific location in the environment to obtain a \"world-anchored\" view. In phantom studies, such a registration approach is always possible, because a clear outline is easily seen, and the AR display can always be adjusted. The real world, on the other hand, always presents less controlled conditions, for which it is necessary to develop more robust approaches, based, for example, on intraoperative imaging. The study by [PERSON] et al. [64] assessed whether the use of Microsoft HoloLens for percutaneous needle navigation to simulate pedicle screw placement was suitable. The HMD-AR technology projects rebuilt 3D and 2D CT images onto a phantom of the lumbar spine, wrapped in an opaque silicone block, without the use of fluoroscopy or an intraoperative CT arm. The OpenSight (Novarad) application was used to integrate these visual data into Microsoft HoloLens, allowing the superimposition of virtual trajectory guides and CT images on the phantom in 3D and 2D. For intraoperative registration, commercial software was used, allowing the possibility for the user to manually refine the registration process. A limit for this study is the registration process because the need for intraoperative CT and a simple and large object to detect (e.g., a silicone phantom) makes it almost inapplicable in real surgical conditions. The work of [PERSON] et al. [72] provides a further workflow demonstration of the AR technology in spine surgery. The work consisted of projecting holographic images of the spine visualized with OpenSight onto Microsoft HoloLens on prone positioned cadavers. Surface anatomy was exploited to align the hologram, including previously planned trajectories for pedicle screw insertion, with the cadaver.