There are many limitations associated with the current interface between the residual limb and the prosthesis for individuals with upper-limb deficiencies. The suspension of the device, which can be heavy, is often a product of awkward harnessing, localized pressures over bony elements in the residual arm, or sometimes unreliable suction environments. Prosthetic control is both limited and limiting. In body-powered devices, unrelated gross body motions create restricted movements of the prosthesis, while in externally powered systems, the activation of residual muscle bellies provides control of distal prosthetic joints that are often removed from their pre-amputation functions. At more proximal amputation levels, the problem is compounded by the need for single muscles to control multiple joints through a series of artificial myoelectric signals and patterns. Sensory feedback remains limited or absent. Body-powered designs offer some sense of the amount of prehensile force experienced at the terminal device, while externally powered designs fail to provide any sensory feedback. These limitations are exacerbated by their influences on one another. Compromises in suspension, for example, can alter the position of the electrodes relative to the target muscle bellies, further compromising control of the system.
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