Walking was tested in 4 people with thoracic-level paraplegia using stimulation of quadriceps muscles, the flexor reflex and unlocking knee-ankle-foot orthoses (KAFO). Heart rate, speed, distance, kinematics and ground reaction forces were measured while subjects walked using a walker. None of the subjects could walk without the system; all could walk continuously for at least 4 minutes with it. Joint angles and some other kinematic features resembled normal walking, but the walking was too slow (average speed: 3.8 m/min.) and too demanding (heart rate: 128 b/min; physiological cost index: 15 b/m) to be practical. Subjects supported about 1/3 of their weight with their arms during stance and about 2/3 during swing. Our results suggest that the braces reduced the effort needed and that the low speeds were due to both a lack of power at push-off and the time needed to stabilize the hip and trunk. The high heart rates arose from excessive contraction of the arm and trunk muscles for balance and propulsion.

Functional electrical stimulation (FES) can improve walking in individuals with mobility impairments. We evaluated accelerometers, force sensitive resistors, segment angles, and segment angular velocities to identify which sensor best determines the activation and deactivation times of the main muscles used during walking. This sensor(s) can be used in the future in conjunction with FES systems to improve walking. Able-bodied subjects walked at various speeds. Threshold levels were set for each sensor that minimized the difference between the times of activating and deactivating the electromyogram (EMG) of six muscles and the times of sensor threshold crossings as a percent of the step cycle. Mobility-impaired subjects walked at their preferred speed with and without FES to correct foot drop. Thresholds were set for these subjects so that sensor signals would cross at times that matched those of able-bodied subjects. Segment angles were generally the most effective sensor signals. Using segment angles of the thigh, shank, and foot, activation and deactivation times of the six muscles could be determined to within 6% of the step cycle. The shank segment angle produced the lowest overall error and was among the top three sensors for 10 of the 12 events (activation and deactivation of six muscle groups). A segment angle sensor was implemented using a complementary filter (accelerometer/gyroscope combination). Using this sensor improved rule-based timing of FES in subjects with foot drop as compared to accelerometers alone.

Use of electrical stimulation to correct foot drop in hemiplegia was proposed over 40 years ago. Recently, improved control strategies have been developed and implemented in commercially available devices. In this article we review the control methods that have been used and present some results from a multi-center clinical trial. A foot-drop stimulator improves the gait pattern and results in an immediate increase in walking speed. In this sense it acts like an ankle-foot orthosis and this immediate increase will be referred to as an orthotic effect. Prolonged use of a foot drop stimulator over a period of months results in further, large increases in walking speed both with the stimulator on and off. Evidence indicates that a part of this increase results from daily use that strengthens residual cortico-spinal connections. Therefore the improvement over time will be referred to as a therapeutic effect. We found that people with non-progressive and progressive conditions of the central nervous system have an orthotic benefit, as well as a therapeutic up to 3 months of use. In generally non-progressive conditions such as stroke, further therapeutic increases are seen up to at least 11 months of use. In disorders such as multiple sclerosis, the progression of the disease eventually overcomes the early therapeutic effects. In conclusion, many individuals can benefit from commercially available foot-drop stimulators with improved control strategies and cosmetic design.

Objectives. To test the efficacy and acceptance of a footdrop stimulator controlled by a tilt sensor. Methods. A nonrandomized, test-retest study of 26 subjects with footdrop of more than 1 year’s duration, resulting from various central nervous system disorders, was performed in 4 centers for at least 3 months. Speed of walking in a straight line, speed around a figure of 8, and physiological cost index (PCI) were measured with and without the device. Hours/day and steps/day using the device were recorded. Results.All but 2 subjects used the tilt sensor at home, rather than a foot switch. Walking speed increased by 15% after 3 months ( n = 26; P < 0.01), 32% after 6 months ( n = 16; P < 0.01), and 47% after 12 months ( n = 8; P < 0.05), while PCI decreased. The number of steps taken per day of use increased significantly over time, and increased speed was directly correlated with usage. Walking speed also increased with the stimulator off, but to a lesser extent, indicating a training effect. Subject feedback from a questionnaire indicated satisfaction with the stimulator. Conclusions. Both efficacy and acceptance of the stimulator were good in a population of subjects with chronic footdrop.