## 5 Discussion  
The proposed system has the potential to provide support in assessing posture after sports injuries, particularly in martial arts, such as karate, where posture is fundamental to performing the sport correctly [24, 25, 36], and to monitor martial arts athletes after injuries to support the restoration of their movements and position. The superposition of 3D bone models reconstructed from medical imaging develops a more physiologically relevant environment. A more meaningful and detailed visualization of the body structures might be beneficial for experts to improve their assessment. Moreover, the 3D bone models overlayed on the subject allow observing how the bone segment is positioned during the athlete's performance without adding markers that could be affected by soft tissue artifacts. The Unity application is not yet complete but shows adaptability to be used in sport application. Indeed, it emerges that the devices are adequate as a starting point in applying this type. HL2 and Azure Kinect represent valid substitutes for the gold standard systems of their categories, although not as much accurate. The long-term purpose of this hybrid system composed of HL2 and Azure Kinect is to support athletes in restoring their abilities after an injury, but it still needs some improvements. Currently, MR-based systems that support athletes' recovery are not available. The systems presented in the literature are focused on the improvement of an athlete's performance. In Table 4, we compare the system illustrated in this paper with existing ones in the literature. Studies proposing MR in orthopedics stop at the 3D reproduction of bones from DICOM and the possibility of interaction as an inanimate object in order to support experts in surgical planning [1, 2, 3, 4]. Several studies recognize the contribution of such innovative technologies in reducing errors in surgery [8, 9, 10, 11, 30, 31, 32]. To our knowledge, a similar approach to the one presented in this work has not been suggested, except from [6]. It is worth noticing that in the work of [6], Vicon was the proposed device, which although allowing for the best possible accuracy in bone positioning and articulation is not applicable in clinical reality. Conversely, this project provides a system that is sufficiently accurate without the need for specific knowledge, given the absence of markers [42, 43, 44]. Furthermore, the system can also be considered low-cost if the HL2 is replaced by a cheaper VR visor, even though the AR or MR is more beneficial for this type of application for the overlap \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Joints** & **Mean x (m)** & **Mean y (m)** & **Mean z (m)** \\ \hline right hip & 1.81 & 0.24 & 0.14 \\ left hip & 1.85 & 0.10 & 0.14 \\ left shoulder & 1.88 & 0.04 & 0.57 \\ left elbow & 1.93 & \(-\)0.05 & 0.38 \\ left wrist & 1.86 & \(-\)0.04 & 0.30 \\ pelvis & 1.83 & 0.17 & 0.14 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._ \begin{table}
\begin{tabular}{c c c} \hline \hline
**Condition** & **Computed** & **Standard** \\ \hline Right hip—right ankle joints & 0.059 m & Aligned along z-axis \\ Left knee—Left ankle joints & 0.063 m & Aligned along z-axis \\ Right foot/ankle axis—Left and Right feet axis & 68.83\({}^{\circ}\) & Angle \(<\) 90\({}^{\circ}\) \\ Left shoulder/elbow axis—Left elbow/wrist axis & 99.23\({}^{\circ}\) & Perpendicular (90\({}^{\circ}\)) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The table compares the angles computed from the data output of the system and the karate standards for the Shuto Uke on Neko Aishi Dachi. of the skeleton on the subject and lesser side effects, such as motion sickness. The system could also be considered applicable in a remote setting where the trainer is not present. In this situation, the overlay of bones on the subject is not applicable, which can occur if the examination is in the present. In this context, the video recorded by the HL2 camera might be visible to the trainer in real-time with the skeleton reconstruction.