There have been over 24 centers worldwide that have participated over the years in investigation of the use of FES for lower extremity standing and walking in paraplegia (Peckham, 1987; Peckham and Creasey, 1992). Standing alone is a goal of some systems. The potential physiologic benefits of standing include a beneficial effect on digestion, bowel and bladder function. There are also functional standing goals of reaching for high objects and face-to-face interaction with other people, and improved transfer between surfaces. The muscles usually stimulated to provide for standing function are the quadriceps and hip extensors, which provide for knee and hip extension and joint stability in a locked position in a similar biomechanical way as do knee-ankle-foot orthoses. Implanted systems, which provide activation of eight separate muscle groups, also employ trunk extension for greater postural stability (Triolo et al., 1996).
Several different approaches have been used in helping paraplegics walk. Hybrid approaches, such as the reciprocating gait orthosis (RGO) originally developed at Louisiana State University, and modified at Wright State University, use both mechanical bracing and surface FES. Specifically, FES hip extension on one side provides contralateral leg swing through the RGO mechanism (Solomonow et al., 1997). In general, patients with injuries between T4 and T12 with upper body strength and stability as well as intact lower motor neurons are appropriate candidates for consideration, although higher-level patients have been involved in some protocols.
There is one FDA approved class III surface FES walking system available for use in the USA. Made by Sigmetics Inc., the Parastep system is a four- or six-channel surface stimulation device for ambula-tion with the aide of a walker. The Parastep system uses the triple-flexion response elicited by peroneal nerve stimulation as well as knee and hip extensor surface stimulation to construct the gait cycle. The patient controls the gait with switches integrated into a rolling walker. The electronic controller is housed in a cassette-sized box mounted on the patient's belt. The Parastep System and other similar systems have been used by paraplegics not only for functional standing and walking but also for aerobic exercise (Graupe and Kohn, 1998). In April, 2003, the Centers for Medicare and Medicaid Services (CMS)
started to provide insurance coverage for the purchase of and training with the Parastep.
Implantable lower extremity FES has also been developed. The percutaneous system developed in Cleveland used up to 48 different electrodes to provide reciprocal gait. The considerable effort required for maintenance of percutaneous electrodes has made that type of system impractical for widespread use, however. Implantable eight-channel systems with the more limited goals of standing and transfer are also under investigation.
All of the above mentioned pure FES systems require use of a walker for stability and safety. The energy expenditures required for continuous FES walking using any system is at least twice (if not more) than that for normal upright ambulation. Future directions for lower extremity FES for paraplegia would be to achieve more modest goals than originally envisioned, such as standing, transfer assistance, and possibly short distance (e.g., home) mobility. It is not anticipated that FES for walking in paraplegia will replace the wheelchair as the primary mobility aide.
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