# Augmented Reality: Mapping Methods and Tools for Enhancing the Human Role in Healthcare HMI
## 3 Results
### Intraoperative Solution
#### 3.3.1 Lower and Upper Limbs  
With the development of technology, AR was adopted to support surgeons in challenging arthroplasty procedures, improving the outcome of this kind of surgery thanks to its peculiar advantages. The accurate prosthetic components' positioning is one of the core factors contributing to a fast recovery and lower risk of revision. [PERSON] et al. [81] developed an AR-based 3D computer navigation tool for hip resurfacing applied to femoral preparation. They used the HoloLens, a 3D camera, and robotic technology assistance to automatically track the pose of the target femur without the use of any marker. A comparison of the post-intervention perforation orientation with the pre-intervention plane in a phantom study gave an average error of approximately 2 mm. In the work of [PERSON] et al. [65], AR and 3D-printed technologies were combined to accomplish a challenging THA surgery on a 59-year-old man. The real-time automatic registration process involved an HMD through landmark recognition on the reference registration tool. In this way, the virtual models of the patient's hard and soft tissues were superimposed on the real anatomy; a customized surgery was achieved, while the operation time was not significantly increased. [PERSON] et al. [80] proposed an AR solution for intraoperative assistance of direct anterior approach THA, based on two C-arm X-ray images combined with 3D AR visualization to simplify planning-based impactor and cup placement. The developed methodology allows the intraoperative planning of the acetabular cup position relying on two fluoroscopic images acquired after a femoral head dislocation. Subsequently, it is possible to align the impactor color and depth information, namely a point cloud provided by the 3D camera, with the planned virtual cup-impactor displayed in the AR environment. The system was validated and compared with standard fluoroscopic guidance for acetabular component positioning using a radiopaque foam pelvis [47]. Compared to the fluoroscopic technique, the AR guidance system produced a more robust implantation of the acetabular component in both inclination and anteversion. In addition, the AR guidance system was easier and faster. Although the radiation dose involved was similar to the fluoroscopic technique, the surgical team could be not exposed to the radiation. [PERSON] et al. [57] presented an AR-based device for acetabular cup positioning. The so-called AR-HIP system uses the smartphone camera to overlay the acetabular cup po sitioning angle and functional pelvic floor image with real-world images of the surgical field. In the registration process, the surgeon is required to register two anatomical landmarks, namely the right and the left anterior superior iliac spines, in order to automatically determine the functional pelvic floor. In a randomized controlled trial [83], the group obtained that the absolute values of the difference between the detected angles and the postoperative radiographic measurement angle were significantly lower in the AR-based navigation system group than in the mechanical guidance group in terms of inclination, thus demonstrating that the AR-based navigation system provided better accuracy in terms of cup positioning angle than the conventional technique using mechanical guidance. In a retrospective study, the above-mentioned AR-Hip system was compared to the accelerometer-based portable navigation system, called HipAlign, consisting of a reference sensor and a disposable computer display unit [39]. With both the HipAlign and AR-Hip systems, it was always possible to know the angles of acetabular cup placement during THA, although the final acetabular cup placement depended on the surgeon's medical judgment in each patient. The most important finding of this study was that in the THA procedure with the patient in the lateral decobitus position, the AR-Hip system provided more accurate acetabular positioning than the HipAlign system. In Total Knee Arthroplasty (TKA), an AR-assisted system was developed by [PERSON] et al.