Affiliations: [a] Swiss Paraplegic Center, University Hospital Balgrist, Forchstrasse 340, CH-8008 Zurich, Switzerland | [b] Automatic Control Laboratory, Swiss Federal institute of Technology, Zurich, Switzerland
Abstract: A four channel functional electrical stimulation system with surface electrodes was developed and tested to give individuals with complete C4 and C5 tetraplegia a possibility to perform a grasping function. The proposed neuroprosthesis is EMG controlled, and it is voluntarily activated using the deltoid muscle of the contralateral arm. The duration of the processed above the threshold EMG signal was used to control the duration of the grasp, and the amplitude of the EMG signal was used to control the grasp strength. The following are the benefits of the proposed system: (1) restoration of the lost grasping function; (2) natural and easy to train control of hand opening and closing; (3) smooth adjustment of the grasping force; (4) a subject can use natural control strategies to control the prosthesis; and (5) the control algorithm is easy to integrate into a micro-controller device. Functional tests with a subject with C4 to C5 complete tetraplegia showed that the system significantly increased the subject’s independence in performing everyday tasks. The limiting factor for using the proposed neuroprosthesis was the fatigue of the proximal arm muscles. Surprisingly, the fatigue of the finger flexors, finger extensors and the contralateral arm deltoid muscles were not the limiting factor. Note that the deltoid muscle of the contalateral arm was used to control the prosthesis.
