## 2 Materials and Methods  
The methodology contained various steps, including requirements engineering, which was based on qualitative and quantitative aspects and an iterative prototyping process. The entire process utilized a user-centered design (UCD) approach [46], with therapists involved in the development. The therapists were questioned based on their expertise and availability. Formulating the sampling was found to be crucial [47]; therefore, the sampling was defined to match the following constraints: expertise with hand rehabilitation, experience in the field, no age restrictions, and availability. A few therapists were approached via e-mail based on internet research. In addition, another therapist known to one of the research team members was also included and helped find other possible participants (see Table 2 for an overview of the final participating therapists). The authors assume that there was no bias associated with acquiring the exercises and requirements for this serious game. An interview guideline was defined, and all therapists were interviewed, gathering feedback on possible requirements, information about wrist injuries, associated exercises, the overall process, and serious gaming/VR aspects (such as their experience). After defining the initial requirements and corresponding movement patterns used within current rehabilitation exercises, the game idea was developed. The outcome was a VR game utilizing the \"MetaQuest 2\" VR headset. This device was chosen because of its availability and because one of the authors had already used it in another context. After defining the game narrative and prerequisites, the movement patterns were mapped into in-game movements. Since not all identified patterns could be transferred, the focus was on the remaining ones. Subsequently, the prototype was developed. The overall setup included the \"MetaQuest\" head-mounted display (HMD) for the patients to wear. The game was tested on the \"MetaQuest 2\" and \"MetaQuest 3\" devices, which showed an equal gaming experience. The controllers are unnecessary because the game is controlled by hand movements (captured by the included cameras of the \"MetaQuest\" headset). By moving one or both hands, the avatar within the game is controlled, and interactions within the environment are performed. The movements used were defined by the necessary exercises identified by the therapists. The game was developed using the Unity game engine [48]. Within a game menu (by making a peace gesture), different settings can be accessed. The game can be saved, the tutorial can be conducted again, some background information can be retrieved, and more additional information about playtime can be displayed. Different exercises (movements) are currently included and mapped to individual actions within the game (see Figure 1 for an overview of the setup and architectural components). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**ID** & **Age** & **Gender** & **Type** & **Working Years** & **VR Experience** \\ \hline P01 & 55 & M & Physiotherapist & 33 & N \\ P02 & 37 & F & Physiotherapist & 15 & N \\ P03 & 38 & F & Occupational therapist & 9 & N \\ P04 & 26 & F & Occupational therapist & 3.5 & N \\ P05 & 60 & F & Occupational therapist & 36 & Y \\ P06 & 42 & M & Evaluation Testuser & N/A & Y \\ P07 & 30 & M & Evaluation Testuser & N/A & Y \\ P08 & 38 & M & Evaluation Testuser & N/A & N \\ P09 & 33 & M & Evaluation Testuser & N/A & N \\ P10 & 20 & F & Evaluation Testuser & N/A & N \\ P11 & 31 & M & Evaluation Testuser & N/A & Y \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Overview of all participants in the different phases. Succeeding the development phase, a short evaluation with a playtest was conducted to gain preliminary insights into design and usability aspects. Students and university members were recruited (utilizing a convenience sample) to participate. They had the opportunity to play the game and give feedback through two questionnaires immediately after a play session.