# Augmented Reality: Mapping Methods and Tools for Enhancing the Human Role in Healthcare HMI
## 4 Discussion
### Implications for Future Research  
The main purpose of our study is to assess, in the vast panorama of surgical applications of augmented reality in orthopedics, what were the major gaps that research has not been able to fill yet. This was performed by analyzing 62 articles that met our selection criteria imposed in the systematic search and paying particular attention to the methods and tools used in each AR-based solution and to related problems that the authors reported. Consequently, the first major practical contribution of the present research is that it provides a collection, categorized by use-case, tools involved, and surgical procedure supported, of some of the most recent developments of AR technologies in the orthopedic field. This information is of paramount importance considering that the pace at which AR is developing and growing in all fields is unstoppable, and it is increasingly important to collect and sort existing studies to provide practical guidance to researchers and end-users. The second important implication, directly related to the first, comes from the analysis of our results, giving the possibility of identifying the open issues in order to explore how these can be solved in the near future. Technicalities that authors encountered in the development of these systems can hinder or slow down the development of such solutions in the field of orthopedics, thus it is important to know a priori what they are so that one can focus the research on bridging those gaps. The analysis of the collected results raises several opportunities for future research, both in terms of software and hardware development and concept validation. First, configuring AR as a powerful visualization technology, a researcher has to design AR-based solutions in which the geometric entities, the scale of objects, and the spatial relationships between real and virtual objects can be easily perceived. The development of AR-based applications must be, from the design phase, end-user oriented, i.e., it must include intuitive and easy-to-use human-machine interfaces, so as not to hinder the workflow of the medical team and increase the realism of the surgical simulation. A good design of the user interface and the realization of perceptual stimuli that are as realistic as possible can minimize the physical and cognitive discomfort of the user, decreasing the effort needed to perform the activity. In fact, the cognitive aspect regarding the use of AR is often underestimated, and although qualitative assessments have already been made on the mental effort required by AR applications, this is still not a very common practice. In these studies [37; 41; 46; 62; 68; 77; 84], although the overall feedback was positive, contrasting judgments about the self-assessment of one's performance emerged. The lack of knowledge about AR technology [28], along with a slow learning curve of AR-based procedures [83], could be responsible for these contrasting feedbacks. In order to maximize surgical performance, it becomes important to organize training phases for the use of AR and gestural and voice interactions, to increase medical team awareness of the functionalities of each application. This will provide all the necessary tools to make the most of AR's potential, and thus allow physicians to perform their activities with the necessary confidence and readiness. Secondly, registration and tracking represent one of the main components of AR-based applications. What emerges from this review is that, at the moment, the major limitation to the introduction of AR in daily clinical practice and surgical workflow lies in the lack of reliable tracking and registration systems. As discussed in Section 4.2, although several approaches were used, still none of them seems to be completely able to guarantee accurate and stable navigation, resulting in poorly positioned virtual models and unreliable spatial relationships between virtual and real objects.