Control Systems for High-Level Upper-Limb Amputees: Comparison of Myoelectric and Proportional Touch Control

WILLIAM NICHOL, CPO(C)*Winnipeg, Manitoba

Fitting upper-limb amputees with externally powered prostheses is becoming more commonplace in prosthetic clinics all over the world. With the currently available myoelectric systems, most upper-limb amputees can be readily fit with a myoelectrically controlled prosthesis. However, very-high-level upper-limb deficiencies such as shoulder disarticulation and forequarter amputation present more complex problems when being fit with a powered prosthesis controlled by myoelectric signals. Concerted efforts were carried out at this centre to achieve functional and reliable control of a powered terminal device through the use of a myoelectric control unit. Although patients demonstrated satisfactory control of the terminal device in the prosthetics laboratory and during training sessions in therapy, they became discouraged with the system during everyday activities, as the electrodes very often picked up involuntary EMG signals from trunk and respiratory muscles. Adequate function of hand, wrist and elbow was eventually achieved through the use of microswitches, but various problems were identified with the currently available types. Myoelectric systems have not proved to be consistently reliable for controlling prostheses constructed for very high-level upper-limb deficiencies. A definite need exists to develop a touch control which can be used as an alternative to myoelectric control for these protheses as well as other rehabilitative devices.

*Rehabilitation Centre for Children, 633 Wellington Crescent, Winnipeg, Manitoba, R3M 2A8, Canada

Vol. 20, No. 3, Autumn 1985