Effects of stimulated hip extension moment and position on upper-limb support forces during FNS-induced standing--a technical note.

This study explores the effects of active hip extension moment produced by electrical stimulation on the support forces the arms must exert through an assistive device during quiet erect standing with functional neuromuscular stimulation (FNS) in individuals with spinal cord injuries (SCI). A static sagittal plane biomechanical model of human standing was developed to predict the effects of stimulated hip extension moment and sagittal plane hip angle on the arm support necessary to maintain an upright posture. Two individuals with complete thoracic SCI were then tested while they stood with continuous stimulation to the knee and trunk extensors. The steady-state active extension moment exerted at the hip was varied by activating different combinations of hip extensor muscles with continuous stimulation while steady-state support forces applied to the arms and feet during standing were measured. The steady-state support forces imposed on the arms during quiet standing decrease with increased stimulated hip extension moment and are highly dependent upon hip flexion angle, as predicted by the biomechanical simulations. Experimentally, the combination of gluteus maximus and semimembranosus stimulation produced three times more steady-state hip extension moment than did stimulation of the gluteus maximus and adductor magnus. This resulted in a ten-fold decrease in body weight supported on the arms. More vertical postures (smaller hip flexion angles) improve the effectiveness of the hip extensor muscles in reducing the support forces placed on the arms. A single Newton-meter of stimulated hip extension moment with the hips fixed at 5 degrees of flexion results in almost five times the reduction in arm support forces as with the hips at 20 degrees. To minimize the forces applied by the arms on an assistive device for support while standing with FNS, these preliminary results suggest that (1) efforts should be made to assume the most erect postures possible and (2) muscles and stimulation paradigms that maximize active hip extension moment should be chosen.

Implanted functional electrical stimulation system for mobility in paraplegia: a follow-up case report.

A 16-channel functional electrical stimulation (FES) system has been implanted in a person with T10 paraplegia for over a year. The system consists of two eight-channel radio frequency controlled receiver-stimulators delivering stimuli through a network of 14 epimysial and two intramuscular electrodes. Using this system and a walker for support, the subject was able to stand up for 8 min and walk regularly for 20 m. The standing duration was limited by arm fatigue since upper extremities supported an average of 25% of body weight. This was due to suboptimal hip extension and some undesired recruitment of rectus femoris and sartorius with stimulation of quadriceps electrodes. The left quadriceps exhibited rapid fatigue that limited walking distance and duration. The metabolic energy requirements were well within the aerobic limits of the sedentary paraplegic population. At one-year follow-up evaluation all electrodes are functional except one intramuscular electrode. The implant caused no adverse physiological effects and the individual reported health benefits such as increased energy and overall fitness as a result of the FES system use. With further improvements in muscle response through innovative surgical techniques, the 16-channel implanted FES system can be a viable addition to exercise and mobility function in persons with paraplegia.