Rheumatoid arthritis (RA) causes a progressive loss of hand mobility, severely affecting patients' occupational independence and daily activities in Mexico. In advanced stages, conventional therapies and commercial orthoses are often insufficient, costly, or poorly adaptable for restoring complex grasping and fine manipulation functions. To address this problem, a customized thermoplastic polyurethane (TPU) hand orthosis with a monomaterial functional gradient was developed, allowing mechanical properties (stiffness, flexibility, and texture) to vary across different anatomical regions without changing the base material. The design was based on a systematic state-of-the-art review using the SALSA (Search, Appraisal, Synthesis, and Analysis) framework, including 20 indexed articles published between 2016 and 2026. User-Centered Design (UCD) principles were integrated with computational validation through Finite Element Analysis (FEA) in SolidWorks. Simulation results demonstrated that the optimized geometry reduced Von Mises equivalent stresses in critical regions of the rheumatoid hand, maintained an adequate safety factor (>2.5) under operational loading conditions, and enabled the development of a lightweight and ergonomic device. This technological solution positions additive manufacturing as an accessible, functional, and sustainable alternative for improving usability, reducing physical effort, and promoting the independence and quality of life of individuals with rheumatoid arthritis.