Advancements in Enhancing Degrees of Freedom for Upper-Limb Prostheses: Mechanisms, Control, and Sensory Feedback

Abstract

Upper-limb amputation seriously affects a person's daily life. Traditional commercial myoelectric prostheses have only 2-6 degrees of freedom (DOFs) and are not yet capable of fine-motor manipulation. This paper reviews representative progress from 2014 to the first half of 2026 in three main directions: mechanism design and actuation, intelligent control and intention decoding, and sensory feedback and closed-loop interaction. The reviewed studies show that advanced mechanical configurations can add more active DOFs while reducing weight; deep learning decoding and shared semi-autonomous control can improve the accuracy and ease of control; and bidirectional neural interfaces, such as the e-OPRA system, have demonstrated the feasibility of closed-loop interaction. The analysis indicates that increasing the effective DOFs of prostheses requires the systematic integration of mechanisms, control and sensory feedback, rather than simply adding more joints.