An EMG-controlled grasping system for tetraplegics.

A two-channel, portable, battery operated, functional electrical stimulation (FES) system with surface electrodes to enhance grasping in tetraplegics was developed and tested. This system is meant for tetraplegics capable of grasping by tenodesis. Candidates for this system must retain some wrist extension, and have paralyzed but innervated finger flexors, and nearly normal shoulder and elbow coordination within the working space. The control signal that turns the stimulation of forearm finger and thumb flexors on and off is based on the detection of the threshold of the amplified, rectified, and integrated electromyographic recordings using surface electrodes positioned over the wrist extensors. The voluntary contraction of wrist extensors is suitable for triggering the stimulation, and it is reproducible enough for daily home use. The new device was tested on subjects with tetraplegia, and the general conclusions are: 1) the system increases the strength of the grasp: 2) no side effects or related problems were noticed: 3) the training period is short: 4) the reliability of the operation is good; and, 5) the design of the analog part of the system allows its easy integration into a computerized device. Functional tests of the system showed that some of the study subjects did not benefit from this approach due to disuse and denervation types of muscle atrophy of their finger flexors, lack of controllable wrist extension, curled resting position of distal and proximal interphalangeal (IP) joints, and/or inability to bring the thumb in the opposition of fingers.