This article presents a comprehensive approach to the design and fabrication of an upper-limb prosthesis developed using a modular concept and generated through the AutoMedPrint system on the basis of high-resolution 3D scans of the patient’s residual limb. Biomedical engineering, which integrates core engineering disciplines such as mechanics, electronics, chemistry, and optics, provides the methodological framework for creating advanced prosthetic devices aimed at restoring lost functionality by replacing absent or damaged biological structures. The clinical demand for functional upper-limb prostheses is particularly noticeable among young users, who often exhibit increased expectations regarding device speed, strength, ergonomics, and aesthetics. At the same time, the high rejection rates reported in paediatric and adolescent populations underline the importance of personalized and adaptable prosthetic solutions. In the presented article, the digital prosthetic model was integrated with an electronic control system enabling functional actuation of the device. The structural components were produced using additive manufacturing technologies, ensuring high geometric accuracy, reduced production costs, and the possibility of rapid iteration during the design process. A detailed geometric analysis was carried out in a virtual environment, allowing verification of fit, structural correctness, and component interactions before physical fabrication. The objective of the study was to develop a cost-effective, patient-specific mechatronic prosthesis that meets the functional requirements of an adolescent user while addressing the broader challenges associated with long-term prosthesis acceptance.