Functional electrical stimulation systems: what have we accomplished, where are we going?

Few fields of rehabilitation research have generated as much excitement and public interest as functional electrical stimulation (FES) by computer control . Early publicity gave the potential users of FES systems hopes that this modern technology could almost normalize their impaired functions. Unfortunately, the great expectations of persons with physical disability (limb paralysis) have been deflated by the lengthy development process of FES systems and their high cost, and ultimately, by their limited clinical applicability and functional significance . No user of any FES system for limb control has performed at a skill level anywhere close to normal or that of the fictional "bionic" characters of movies and television that are so well known to the public . However, when expectations are realistic and match the achievable performance, FES systems have had a positive impact on the lives of many individuals with disability. Successful clinical application of FES systems depends on several factors : a) simplicity of the desired task, b) total implantation of the device which usually results in improved cosmesis and eases donning and doffing, c) low rate of mechanical failure and medical complications, d) functional improvement greater than can be achieved by other means, and e) relatively low cost . Expanding briefly on these five criteria, it is generally accepted that, given the current state of the art, stimulation of a single muscle or muscle group without need for sensory feedback in order to complete a relatively simple motor task is more likely to result in acceptable function than synchronized stimulation of multiple muscles for prolonged performance of a complex task that requires continuous sensory feedback to obtain coordination and balance . In contrast to external devices, totally implanted systems, safe and free of mechanical failures, appeal more to the user in chronic applications of FES as they are cosmetic, require no or little donning and doffing time, and are not likely to affect the health and well being of the person . External FES devices will remain the preferred choice for temporary applications for both functional and therapeutic purposes. Cost is a relative term and includes user evaluation, the device, implantation, training, indirect costs, and maintenance . Ultimately, the cost must be Kristjan T. Ragnarsson, M .D. Lucy G. Moses Professor and Chairman, Department of Rehabilitation Medicine, Mount Sinai Medical Center, New York, NY.