Ta. Perkins et al., IMPLANT PROVISION OF KEY, PINCH AND POWER GRIPS IN A C6 TETRAPLEGIC, Medical & biological engineering & computing, 32(4), 1994, pp. 367-372
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 o
ld 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 h
er stimulated hand with a joystick under her contralateral hand which
she moves from the shoulder and elbow. Since 1986, we have tried a var
iety of joystick control schemes involving power and key grips. Curren
tly, for grip adjustment, forward and backward joystick movements corr
espond to thumb extension and abduction, respectively giving in additi
on both finger and wrist extension, whereas right and left joystick mo
vements yield fist closure and thumb opposition/adduction and flexion,
respectively. Useful grasps are available by moving the joystick forw
ard 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 desi
rable to augment the patient's limited voluntary wrist positioning and
provide wrist stability while adjusting finger grip.