A Novel Electromechanical Shoulder Articulation for Upper-Limb Prostheses: from the Design to the First Clinical Application

This article reports the design, development, and the first clinical test of a new electromechanical shoulder articulation for interscapulothoracic and first-proximal transhumeral amputees. The new prosthetic component was conceived to overcome the limitations imposed to amputees by passive shoulder mechanisms and was developed to be compatible with commercial battery-powered prosthetic joints. The development of the mechanism is the result of a rigorous approach, which made it possible to optimize the functionality and the wearability of the prosthetic device. The articulation consists of two connected electrically powered joints that actuate the spherical motion of the upper arm, i.e., they allow the elevation of the upper arm in any vertical plane passing through the shoulder centre of rotation. A passive frictional revolute joint is also present to realize the humeral internal-external rotation. The prototype underwent laboratory tests needed to evaluate the mechanism's performance (e.g., the actual maximum payload) and the electrical requirements (e.g., the current draining). Based also on the results retrieved from these tests, an on-board control-unit was implemented for the control of an entire upper-limb prosthesis. The control unit can drive up to five motors and can manage different control strategies according to the amputees' preferences. A prosthetic arm equipped with the new shoulder prototype and the on-board control-unit-along with a myoelectric elbow, prosupination unit, and hand-was tested by a patient with a first-proximal transhumeral amputation. Results showed that some improvements are needed concerning the control strategy, the noise, and the socket. However, they also showed that the new shoulder is really applicable in the clinical practice.