A functional electrical stimulation system for human walking inspired by reflexive control principles

This study presents an innovative multichannel functional electrical stimulation gait-assist system which employs a well-established purely reflexive control algorithm, previously tested in a series of bipedal walking robots. In these robots, ground contact information was used to activate motors in the legs, generating a gait cycle similar to that of humans. Rather than developing a sophisticated closed-loop functional electrical stimulation control strategy for stepping, we have instead utilised our simple reflexive model where muscle activation is induced through transfer functions which translate sensory signals, predominantly ground contact information, into motor actions. The functionality of the functional electrical stimulation system was tested by analysis of the gait function of seven healthy volunteers during functional electrical stimulation–assisted treadmill walking compared to unassisted walking. The results demonstrated that the system was successful in synchronising muscle activation throughout the gait cycle and was able to promote functional hip and ankle movements. Overall, the study demonstrates the potential of human-inspired robotic systems in the design of assistive devices for bipedal walking

Automatic identification of gait events using an instrumented sock

Background: textile-based transducers are an emerging technology in which piezo-resistive properties of materials are used to measure an applied strain. By incorporating these sensors into a sock, this technology offers the potential to detect critical events during the stance phase of the gait cycle. This could prove useful in several applications, such as functional electrical stimulation (FES) systems to assist gait. Methods: we investigated the output of a knitted resistive strain sensor during walking and sought to determine the degree of similarity between the sensor output and the ankle angle in the sagittal plane. In addition, we investigated whether it would be possible to predict three key gait events, heel strike, heel lift and toe off, with a relatively straight-forward algorithm. This worked by predicting gait events to occur at fixed time offsets from specific peaks in the sensor signal. Results: our results showed that, for all subjects, the sensor output exhibited the same general characteristics as the ankle joint angle. However, there were large between-subjects differences in the degree of similarity between the two curves. Despite this variability, it was possible to accurately predict gait events using a simple algorithm. This algorithm displayed high levels of trial-to-trial repeatability. Conclusions: this study demonstrates the potential of using textile-based transducers in future devices that provide active gait assistance

The clinical- and cost-effectiveness of functional electrical stimulation and ankle-foot orthoses for foot drop in Multiple Sclerosis: a multicentre randomized trial

Objective: To compare the clinical- and cost-effectiveness of ankle-foot orthoses (AFOs) and functional electrical stimulation (FES) over 12 months in people with Multiple Sclerosis with foot drop. Design: Multicentre, powered, non-blinded, randomized trial. Setting: Seven Multiple Sclerosis outpatient centres across Scotland. Subjects: Eighty-five treatment-naïve people with Multiple Sclerosis with persistent (>three months) foot drop. Interventions: Participants randomized to receive a custom-made, AFO (n = 43) or FES device (n = 42). Outcome measures: Assessed at 0, 3, 6 and 12 months; 5-minute self-selected walk test (primary), Timed 25 Foot Walk, oxygen cost of walking, Multiple Sclerosis Impact Scale-29, Multiple Sclerosis Walking Scale-12, Modified Fatigue Impact Scale, Euroqol five-dimension five-level questionnaire, Activities-specific Balance and Confidence Scale, Psychological Impact of Assistive Devices Score, and equipment and National Health Service staff time costs of interventions. Results: Groups were similar for age (AFO, 51.4 (11.2); FES, 50.4(10.4) years) and baseline walking speed (AFO, 0.62 (0.21); FES 0.73 (0.27) m/s). In all, 38% dropped out by 12 months (AFO, n = 21; FES, n = 11). Both groups walked faster at 12 months with device (P < 0.001; AFO, 0.73 (0.24); FES, 0.79 (0.24) m/s) but no difference between groups. Significantly higher Psychological Impact of Assistive Devices Scores were found for FES for Competence (P = 0.016; AFO, 0.85(1.05); FES, 1.53(1.05)), Adaptability (P = 0.001; AFO, 0.38(0.97); FES 1.53 (0.98)) and Self-Esteem (P = 0.006; AFO, 0.45 (0.67); FES 1 (0.68)). Effects were comparable for other measures. FES may offer value for money alternative to usual care. Conclusion: AFOs and FES have comparable effects on walking performance and patient-reported outcomes; however, high drop-outs introduces uncertainty

Design, control and evaluation of a low-cost active orthosis for the gait of spinal cord injured subjects

Robotic gait training after spinal cord injury is of high priority to maximize independence and improve the living conditions of the patients. Current rehabilitation robots are expensive and heavy, and are generally found only in the clinical environment. To overcome these issues, we present the design of a low-cost, low-weight and personalized robotic orthosis for incomplete spinal cord injured subjects. The paper also presents a preliminary experimental evaluation of the assistive device on one subject with spinal cord injury that can control hip flexion to a certain extent, but lacks control of knee and ankle muscles. Results show that gait velocity, stride length and cadence of walking increased (24,11%, 7,41% and 15,56%, respectively) when wearing active orthoses compared to the case when the subject used the usual passive orthoses.Postprint (published version

FOOT DROP AND FATIGABILITY IN PEOPLE WITH MULTIPLE SCLEROSIS

People with Multiple Sclerosis (pwMS) often experience walking impairments such as foot drop which can lead to trip and falls. Foot drop can be either transient and is often induced by exercise (fatigability) in pwMS whose walking ability is not affected and can become more fixed with disease progression. The overall aim of this PhD was to explore foot drop, its presence in pwMS with different disability levels and the psychometric properties of outcomes used to evaluate walking impairments. The first study in this thesis was a systematic review into the level of evidence for the psychometric properties of walking measures that have been used to evaluate the effect of assistive technology such as FES for foot drop in MS. Moderate to strong psychometric evidence was found for the Multiple Sclerosis Walking Scale, Timed 25 Foot Walk, 6 minute and 10 meter walk tests. There were no psychometric studies for three-dimensional (3D) gait kinematics in pwMS even though it was one of the most frequently used outcome measures. The second study assessed the test-retest reliability of 3D ankle kinematics and spatiotemporal parameters in pwMS, with low Expanded Disability Status Scale (EDSS < 3.5) and in those with moderate to high EDSS (EDSS: 4-6). Reliability was excellent for ankle kinematics and spatiotemporal parameters in both groups, with lower minimal detectable change (MDC95%) values in the low EDSS group compared to the higher EDSS group. The third study investigated transient exercise induced foot drop in highly physically active pwMS (EDSS < 3.5) and health controls using 3D kinematics. It was found that 6 out of 15 pwMS and none of the healthy controls presented this phenomenon. The fourth study examined the direct orthotic effect of FES during dual-tasking (i.e. walking combined with a cognitive task) and after inducing fatigability. Low to moderate effect sizes indicated that the direct orthotic effect was higher under dual-task and fatiguing conditions but this needs to be confirmed in appropriately powered studies. In conclusion, the studies in this thesis have contributed to the psychometric evidence of gait kinematics in pwMS, have objectively documented the presence of transient foot drop in highly physically active pwMS and orthotic effect of FES under a variety of conditions simulating the perceived benefits in ‘real life’ reported by FES users. Key words: multiple sclerosis, foot drop, fatigability, FES, psychometric properties, 3D gait kinematic

Quantification of gait kinematics and walking ability of people with multiple sclerosis who are new users of functional electrical stimulation

Objective: To assess whether the application of Functional Electrical Stimulation improves gait kinematics and walking ability in people with multiple sclerosis who experience foot drop. Design: Acute open labelled comparative observation trial. Participants: Twelve people (3 females, 9 males, EDSS 2-4) with relapsing remitting multiple sclerosis (47.8 years (standard deviation 6.6)) who were new users of functional electrical stimulation. Methods: Gait kinematics were recorded using 3D gait analysis. Walking ability was assessed through the 10-m walk test and the 6-min walk test. All assessments were performed with and without the assistance of functional electrical stimulation. The effect of functional electrical stimulation was analysed using paired t-tests. Results: Ankle dorsiflexion at initial contact (p-=-0.026), knee flexion at initial contact (p-=-0.044) and peak knee flexion during swing (p-=-0.011) were significantly greater whilst walking with Functional Electrical Stimulation. The increased peak dorsiflexion in swing of nearly 4 degrees during functional electrical stimulation assisted walking approached significance (p-=-0.069). The 10-m walk time was significantly improved by functional electrical stimulation (p-=-0.004) but the 6 min walk test was not. Conclusion: The acute application of functional electrical stimulation resulted in an orthotic effect through a change in ankle and knee kinematics and increased walking speed over a short distance in people with multiple sclerosis who experience foot dropsch_phy45pub3130pub

Evaluating the Effects of Ankle-Foot-Orthoses, Functional Electrical Stimulators, and Trip-specific Training on Fall Outcomes in Individuals with Stroke

abstract: This dissertation aimed to evaluate the effectiveness and drawbacks of promising fall prevention strategies in individuals with stroke by rigorously analyzing the biomechanics of laboratory falls and compensatory movements required to prevent a fall. Ankle-foot-orthoses (AFOs) and functional electrical stimulators (FESs) are commonly prescribed to treat foot drop. Despite well-established positive impacts of AFOs and FES devices on balance and gait, AFO and FES users fall at a high rate. In chapter 2 (as a preliminary study), solely mechanical impacts of a semi-rigid AFO on the compensatory stepping response of young healthy individuals following trip-like treadmill perturbations were evaluated. It was found that a semi-rigid AFO on the stepping leg diminished the propulsive impulse of the compensatory step which led to decreased trunk movement control, shorter step length, and reduced center of mass (COM) stability. These results highlight the critical role of plantarflexors in generating an effective compensatory stepping response. In chapter 3, the underlying biomechanical mechanisms leading to high fall risk in long-term AFO and FES users with chronic stroke were studied. It was found that AFO and FES users fall more than Non-users because they have a more impaired lower limb that is not fully addressed by AFO/FES, therefore leading to a more impaired compensatory stepping response characterized by increased inability to generate a compensatory step with paretic leg and decreased trunk movement control. An ideal future AFO that provides dorsiflexion assistance during the swing phase and plantarflexion assistance during the push-off phase of gait is suggested to enhance the compensatory stepping response and reduce more falls. In chapter 4, the effects of a single-session trip-specific training on the compensatory stepping response of individuals with stroke were evaluated. Trunk movement control was improved after a single session of training suggesting that this type of training is a viable option to enhance compensatory stepping response and reduce falls in individuals with stroke. Finally, a future powered AFO with plantarflexion assistance complemented by a trip-specific training program is suggested to enhance the compensatory stepping response and decrease falls in individuals with stroke.Dissertation/ThesisDoctoral Dissertation Mechanical Engineering 201

Smart Protocols for Physical Therapy of Foot Drop Based on Functional Electrical Stimulation: A Case Study

Functional electrical stimulation (FES) is used for treating foot drop by delivering electrical pulses to the anterior tibialis muscle during the swing phase of gait. This treatment requires that a patient can walk, which is mostly possible in the later phases of rehabilitation. In the early phase of recovery, the therapy conventionally consists of stretching exercises, and less commonly of FES delivered cyclically. Nevertheless, both approaches minimize patient engagement, which is inconsistent with recent findings that the full rehabilitation potential could be achieved by an active psycho-physical engagement of the patient during physical therapy. Following this notion, we proposed smart protocols whereby the patient sits and ankle movements are FES-induced by self-control. In six smart protocols, movements of the paretic ankle were governed by the non-paretic ankle with different control strategies, while in the seventh voluntary movements of the paretic ankle were used for stimulation triggering. One stroke survivor in the acute phase of recovery participated in the study. During the therapy, the patient’s voluntary ankle range of motion increased and reached the value of normal gait after 15 sessions. Statistical analysis did not reveal the differences between the protocols in FES-induced movements.The APC was funded by Lund University Librar