An 11-channel multiplexed stimulator of nerves and muscles in the left forearm was implanted for hand control in January 1986
in a 21 year old woman who, after sustaining a C6 spinal lesion 7 years earlier, had voluntary shoulder and elbow movement
but paralysed hands, trunk and legs. The patient controls the stimulation via a microcomputer control box and an RF transdermal
link. We have investigated the control of her stimulated hand with a joystick under her contralateral hand which she moves
from the shoulder and elbow. Since 1986, we have tried a variety of joystick control schemes involving power and key grips.
Currently, for grip adjustment, forward and backward joystick movements correspond to thumb extension and abduction, respectively
giving in addition both finger and wrist extension, whereas right and left joystick movements yield first closure and thumb
opposition/adduction and flexion, respectively. Useful grasps are available by moving the joystick forward and then left (key
grip), by moving the joystick backward and left (pinch grip), or by moving the joystick back and right (power grip). Thus,
three distinct grips may be selected using these three quadrants of joystick movement. An additional control mode was found
to be desirable to augment the patient's limited voluntary wrist positioning and provide wrist stability while adjusting finger
grip.
Keywords FES - finite state control - grip selection - hand function restoration - implant - joystick - portable microcomputer - tetraplegia