## 5 Discussion
Their non-randomized comparative study showed that the AR system can provide significantly greater accuracy during distal femoral resection in TKA compared with the conventional intramedullary guide. Similarly, [PERSON] et al. [26], after the promising results obtained at preclinical level, aimed to extend their study to a clinical level to assess the technical efficacy of this AR technique. Indeed, it has the potential to quickly simplify the workflow of mechanical axis deviation measurement, by combining X-ray and video images into a single procedure while avoiding the exposure to ionizing radiation of patients and operators. However, considering the lack of available literature in clinical settings, further high-quality studies are probably necessary before we widely support the diffusion and application of AR systems in TKA. Interesting results have also been reported regarding RSA and TEA, even though these fields are yet to be fully explored and thoroughly understood. In particular, baseplate glenoid component positioning has been studied by several authors [35; 36; 37] in sawbones and cadaveric scapulae specimens to evaluate the potential benefits of AR technology, and these studies reported that baseplate navigation in RSA using AR through an HMD seems feasible, showing high accuracy and precision at preclinical level. However, the application of this novel technology in such fields is still in its infancy and various technical problems still need to be addressed before it can be widely used in clinical practice. Similarly, [PERSON] et al. [34] investigated the field of TEA stating that the AR technique can provide several advantages over the conventional surgical technique, with quick registration and easy application while being able to reproduce the preoperative placement plan onto the surgical field, potentially leading to more accurate component placement. Nevertheless, we still need valuable data to confirm these promising preliminary results in order to support the application of this technology in the clinical setting of TEA. In spite of the promising preliminary results, we must remember that, recently, many surgical techniques have been introduced hoping to achieve improved results in total joint arthroplasty including MIS, PSI, CAOS, and, lastly, robotics. However, after an initial interest they can easily follow [PERSON]'s description of the parabola of the rise and fall of surgical techniques [52], facing an exponential drop-off when the high costs of such innovative tools are not balanced by improved clinical outcomes. There were a variety of limitations to this study. First, we were limited by the quality and the type of the original studies, most of the studies related to the application of AR in TJA are preclinical (sawbones), leading to the impossibility to define a clear conclusion on the efficacy of this technology and effectively compare the results between the different studies. Second, we encountered a high heterogeneity among the studies available in the literature, including different devices used and different clinical and preclinical settings, undermining the possibility to systematically analyze them. Third, different outcomes were often used across the reported studies, limiting the possibility to directly compare them among each other and assess overall results, and provide clear conclusions and potential suggestions. Fourth, very few clinical studies are currently available, and they often analyze different outcomes and different AR devices; moreover, limited data are available from comparative studies between AR and conventional techniques, probably due to the limited diffusion of this novel instrumentation. Fifth, the devices used to provide AR were often different or related to pilot studies, limiting the possibility to provide a clear and objective conclusion on each of them. Finally, many of these studies were industry funded, leading to potential selection, performance, and publication bias; therefore, the authors suggest interpreting the reported results with caution. F.M.