A myoelectrically controlled powered elbow.

2 Research Physiologist, Rancho Los Amigos Hospital, 7601 East Imperial Highway, Downey, Calif. 90242. 3 Research Electronics Engineer. 4 Principal Investigator. Present address: School of Medicine, University of California, Davis, Calif. 5 Medical Director. Since the appearance of the "Russian hand" about ten years ago (3), an increasing number of externally powered prostheses controlled by electrical signals from muscles have been developed. Most of these are built as entire systems, including electrodes, circuitry, motor, and battery. A basic requirement of such systems has been that the user must have two essentially normal muscles in order to operate the motor bidirectionally and so control prehension and release, or elbow flexion and extension. Because of our concern in fitting patients having greatly reduced muscular function, we have developed circuitry using as control signals the minute electrical activity generated in severely paralyzed muscles. In addition, because of the disabilities of our patients, we have not only circuitry for control from two muscles, but also circuitry which permits bidirectional control from a single muscle site, as does that of Dorcas and Scott (2). In the latter case, when the muscle is relaxed, the motor controlling the orthotic device holds its position. With a small effort, the motor is turned on and the device moves in one direction; a moderate effort operates the motor in the reverse direction. Until recently, all our fittings had been for patients with orthotic devices. The present report describes our first fitting using a prosthesis. Mrs. S. S. had a traumatic complete avulsion of her right forearm from the elbow. We first saw her nine months post injury, when she was using a prosthesis with two cables, for control of the elbow and the terminal device. The prosthesis was not entirely comfortable, and it required enough force in operation to be rather fatiguing. We decided to fit her with power at one joint; the elbow was selected because it was believed that the sensory feedback of cable control would be more valuable in operating the terminal device than the elbow. Because there was some remaining musculature in the upper arm, it was hoped that electrical signals from the biceps and triceps muscles could be used to control the powered elbow.