## 3 Hand Orthosis Development
### Diverse Designs of Hand Orthoses  
This sub-section provides an overview of several existing hand orthosis designs, highlighting their purposes, design principles, and the specific needs they address (Table 1). By examining these examples, readers will gain a first insight into the diverse approaches and solutions in the field of hand orthotic devices. Each example is accompanied by a figure with a reference to manufacturer product information, a detailed description of its application, and the underlying design considerations, illustrating the functionality and thought process behind these medical devices. \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt}} \hline \hline
**Orthosis Application** & **Design Explanation** \\ \hline  & Thermoplastic, customized rigid structure on the ventral side of a forearm and a hand. Cyclro fasteners make it easier to put on and take off the splint independently. The recess around the MCP joint of the thumb and fingers 2–5 allows movement of a large part of the thumb and finger movements, but the orthosis restricts the overall mobility of the wrist. Stability is achieved by fixation over a half-length of the forearm. \\ \hline  & Pre-fabricated splint which immobilizes the thumb up to the end joint. The rigid grid structure enables better ventilation, while padding improves wearer comfort. \\ \hline  & Minimalistic design based on three support points with a small area covered by the orthosis. It allows sliding of the orthosis on the finger. \\ \hline  & Minimalist design that requires no additional fasteners thanks to wrapping around the hand. The bars between the fingers place the fingers in a physiological position. \\ \hline  & A chain mechanism, mounted on the dorsal side of the fingers, uses rubber bands to support finger extension without producing axial force on the finger joints. The wrist joint allows for wrist flexion and extension. This type of joint can be used to limit the RoM of the hand joint. The torsion spring in this joint can be activated to support extension, and deactivated when donning the orthosis. The position of the wrist joint can be adjusted using slotted holes placed on the forearm part. \\ \hline  & \\ \hline  & \\ \hline \hline  & \\ \end{tabular}
\end{table} 
Table 1: Examples of different commercial and customized hand orthoses with a description of their application and explanation of different aspects of the design. Implementing all the requirements for hand orthoses can be challenging and is often not possible. A common simplification involves restricting the movement of the wrist and metacarpophalangeal (MCP) joints to a single plane. Splinting is particularly demanding, as it must cater to a wide variety of needs and conditions, often requiring careful compromises. Especially for patients with severe impairments, achieving the perfect balance between functionality, comfort, and aesthetic appeal can be difficult. In recent years, advancements in 3D printing technology have opened new possibilities for the design and customization of hand orthoses. This approach offers the potential to create more personalized and adaptable solutions, addressing the unique needs of each patient with greater precision.