A New Externally Powered, Myoelectrically Controlled Prosthesis for Persons with Partial-Hand Amputations at the Metacarpals

A new externally powered, myoelectrically controlled partial-hand prosthesis mechanism and prosthetic interface are described. There is a need for such a device in the fitting of amputees with a loss of all digits at or more proximal to the level of the metacarpals. In addition, preservation of the wrist motion for positioning of the hand mechanism is very important if maximum function and cosmesis are to be achieved. In an aesthetically pleasing, self-contained partial-hand prosthesis, the only volume for the mechanism and for electronics is in the digits. To fit all the requisite mechanisms and electronics in this highly confined volume and still have reasonable performance is a very challenging design problem. An initial prototype transmetacarpal hand mechanism and its associated electronics and a prosthetic interface have been developed. The hand has a width of opening of about 10 cm (or approximately 4 inches) and a speed of opening of approximately 2 radians/second (approximately 105°/second), with a pinch force of approximately 53 N (or about 12 poundsf). The weight of the mechanism alone is 145 g (0.32 pounds), and its length in the closed position, from back plate to finger tip, is 85 mm (or 3.5 inches). The weight of the mechanism with battery and electronics is 210 g (0.46 pounds), and the total weight of the mechanism and current silicone interface is 425 g (0.937 pounds, ie, less than 0.5 kg).