Design of a new biofeedback proprioceptive neuromuscular facilitation system for below-knee amputees

Proprioceptive neuromuscular facilitation and foot sensory compensation are critical to balance control and ambulatory performance in below-knee amputees. Sub-sensory stimulation has been shown to be effective in enhancing the sensitivity of the human somatosensory system. In addition, visual-auditory biofeedback to improve foot sensory compensation for amputees was suggested in recent articles. The purpose of this study is to develop a new biofeedback proprioceptive neuromuscular facilitation system for improving balance control and foot sensory compensation in below-knee amputees. The proposed system functioned with sub-threshold electrical stimulation and visual-auditory biofeedback was developed for clinical study. Two unilateral trans-tibial amputees who consecutively wore prosthetics over 10 years were participated in this study. Subjects performed multiple single leg quite standing trails with sub-sensory electrical stimulation applied at the quadriceps muscle during half of the trails. Four static balance performance indices (i.e. Holding Time Index, HTI; Sway Length Index, SLI; Max Sway Distance Index, MSDI; Average Sway Distance Index, ASDI) were characterized using Zebris motion analysis system. The improvement ratio of these static balance performance indices across subjects for single leg quiet standing tests were resulted in a 209.7% in HTI, 39.1% in SLI, 24.3% in MSDI, and 65.4% in ASDI respectively. In addition, multiple treadmill ambulatory trails with or without visual-auditory biofeedback were evaluated. Four dynamic gait performance indices (i.e. Double Support Time Index, DSTI; Constant Time Cadence Index, CTCI; Single Support Time Index, SSTI; Stance/Swing Phase Index, SSPI) were characterized with Zebris instrumented insole and associated FMS analysis software. With visual-auditory biofeedback, the improvement of all four dynamic gait performance indices in below-knee amputees was verified. The improvement ratio of four gait performance indices across subjects resulted in a 14.81% in DSTI (sound side), 14.29% in DSTI (affected side), 14% in CTCI, 13.00% in SSTI (sound side), 6.02% in SSTI (affected side), 45.17% in SSPI (sound side), and 27.49% in SSPI (affected side) respectively. These findings suggest that sub-threshold electrical stimulation and visual-auditory biofeedback proprioceptive neuromuscular facilitation strategies may be effective in compensating foot sensory loss and improving balance control for below-knee amputees.