Crossed four-bar mechanism for improved prosthetic grasp.

Passive linkages were developed to improve grasp functionality and minimize a prosthetic terminal device's number of user-controlled inputs. The linkages act to stabilize grasped objects and substitute for the palp of normal anatomical fingers. The Southampton Hand Assessment Procedure was used to compare the normal anatomical hand, this prototype, and a commercially available (Hosmer) hook. In testing, prosthetic terminal devices took three times as long as the normal anatomical hand to perform tasks. Nevertheless, heavyweight power and spherical grasps were improved with the use of the new mechanism compared with the commercial hook. Conversely, precision grasps were worsened because of the lack of a high-friction surface on the distal end of the prototype.