PROPORTIONAL MYOELECTRIC HAND CONTROL - AN EVALUATION

The authors review the principle of proportional myoelectric control, in which the motor voltage of a prosthetic hand varies in direct proportion to the EMG signal, giving the amputee control over speed and force of grip. This type of myoelectric control is contrasted with digital myoelectric control, in which the system is fully on or off, giving the amputee no control over speed of hand opening and closing, and the grip force is increased only by increasing the time of the sustained EMG signal. A survey was conducted of 33 patients wearing the proportional myoelectric hand. Patients rated quickness of opening and closing; control over speed and force; effort required to open and close; and comfort, convenience, and cosmesis of the hand; as well as giving it an overall rating in comparison with their previous terminal device. The ratings were made on a 5-level scale, so that they could be quantified. Patient responses were grouped according to previous experience with a terminal device type: group A: digital myoelectric hand; group B: body-powered terminal device; group C: no terminal device. Differences in group means were compared using Student's t test. Previous digital hand wearers gave significantly higher ratings to the proportionally controlled hand overall, especially for its quickness, control of speed and force, and the effort required to open and close the hand. Former body-powered terminal device wearers rated the proportionally controlled hand significantly better on control over speed and force and on cosmesis. Amputees with no previous terminal device had no basis for comparison but gave the proportionally controlled hand high ratings on control over speed and force, effort for opening and closing, and cosmesis. The former digital hand wearers rated the proportionally controlled hand significantly lower on convenience. This reflected early problems with battery life and reliability. Of the three groups of patients, the former digital hand wearers were most impressed with the proportionally controlled hand, and gave it the highest overall ratings.