Mitigating Crouch Gait With an Autonomous Pediatric Knee Exoskeleton in the Neurologically Impaired.

Crouch gait is one of the most common compensatory walking patterns found in individuals with neurological disorders, often accompanied by their limited physical capacity. Notable kinematic characteristics of crouch gait are excessive knee flexion during stance and reduced range of motion during swing. Knee exoskeletons have the potential to improve crouch gait by providing precisely controlled torque assistance directly to the knee joint. In this study, we implemented a finite-state machine-based impedance controller for a powered knee exoskeleton to provide assistance during both stance and swing phases for five children and young adults who exhibit chronic crouch gait. The assistance provided a strong orthotic effect, increasing stance phase knee extension by an average of 12 deg. Additionally, the knee range of motion during swing was increased by an average of 15 deg. Changes to spatiotemporal outcomes, such as preferred walking speed and percent stance phase, were inconsistent across subjects and indicative of the underlying intricacies of user response to assistance. This study demonstrates the potential of knee exoskeletons operating in impedance control to mitigate the negative kinematic characteristics of crouch gait during both stance and swing phases of gait.

Biomechanical Evaluation of Stair Ambulation Using Impedance Control on an Active Prosthesis.

Active prostheses can provide net positive work to individuals with amputation, offering more versatility across locomotion tasks than passive prostheses. However, the effect of powered joints on bilateral biomechanics has not been widely explored for ambulation modes different than level ground and treadmill walking. In this study, we present the bilateral biomechanics of stair ascent and descent with a powered knee-ankle prosthesis compared to the biomechanical profiles of able-bodied subjects at different configurations of stair height between 102 mm and 178 mm. In addition, we include reference profiles from users with passive prostheses for the nominal stair height of 152 mm to place our findings in relation to the typical solution for individuals with transfemoral amputation (TFA). We report the biomechanical profiles of kinematics, kinetics, and power, together with temporal and waveform symmetry and distribution of mechanical energy across the joints. We found that an active prosthesis provides a substantial contribution to mechanical power during stair ascent and power absorption during stair descent and gait patterns like able-bodied subjects. The active prosthesis enables step-over-step gait in stair ascent. This translates into a lower mechanical energy requirement on the intact side, with a 57% reduction of energy at the knee and 26% at the hip with respect to the passive prosthesis. For stair descent, we found a 28% reduction in the negative work done by the intact ankle. These results reflect the benefit of active prostheses, allowing the users to complete tasks more efficiently than passive legs. However, in comparison to able-bodied biomechanics, the results still differ from the ideal patterns. We discuss the limitations that explain this difference and suggest future directions for the design of impedance controllers by taking inspiration from the biological modulation of the knee moment as a function of the stair height.

Comparing the lower limb joint biomechanics of the Power Knee, C-Leg and Rheo Knee during ramp and stair ambulation.

One of the most significant developments in prosthetic knee technology has been the introduction of the Microprocessor-Controlled Prosthetic Knee (MPK). However, there is a lack of consensus over how different types of MPKs affect performance in different ambulation modes. In this study, we investigated the biomechanical differences in ramp and stair maneuvers when an individual with transfemoral amputation wears three commercial MPKs: the Össur Power Knee, the Össur Rheo Knee and the Ottobock C-Leg 4. The primary outcome variable for this study was the lower limb biological joint work, inclusive of the intact leg and prosthetic side hip. We hypothesized that (1) the Power Knee would result in lower biological work during ascent activities than the C-Leg and Rheo, both passive MPKs, and (2) the C-Leg and Rheo would result in lower biological work during descent activities than the Power Knee. During ramp ascent, the C-Leg was associated with lower biological joint work (p < 0.05) than the Power Knee. However, this relationship did not hold during stair ascent, where the Power Knee showed advantages for stair ascent with net reductions in biological joint work of 14.1% and 23.3% compared to the Rheo and C-leg, respectively. There were no significant differences in biological joint work between the knees during ramp and stair descent, indicating that choice of MPK may not be as important for descent activities. Our results demonstrate that differences are present between different types of MPKs during ascent activities which could prove useful in the prescription of these devices.

Gait quality in prosthesis users is reflected by force-based metrics when learning to walk on a new research-grade powered prosthesis.

Introduction: Powered prosthetic feet require customized tuning to ensure comfort and long-term success for the user, but tuning in both clinical and research settings is subjective, time intensive, and the standard for tuning can vary depending on the patient's and the prosthetist's experience levels. Methods: Therefore, we studied eight different metrics of gait quality associated with use of a research-grade powered prosthetic foot in seven individuals with transtibial amputation during treadmill walking. We compared clinically tuned and untuned conditions with the goal of identifying performance-based metrics capable of distinguishing between good (as determined by a clinician) from poor gait quality. Results: Differences between the tuned and untuned conditions were reflected in ankle power, both the vertical and anterior-posterior impulse symmetry indices, limb-force alignment, and positive ankle work, with improvements seen in all metrics during use of the tuned prosthesis. Discussion: Notably, all of these metrics relate to the timing of force generation during walking which is information not directly accessible to a prosthetist during a typical tuning process. This work indicates that relevant, real-time biomechanical data provided to the prosthetist through the future provision of wearable sensors may enhance and improve future clinical tuning procedures associated with powered prostheses as well as their long-term outcomes.

Towards meaningful community ambulation in individuals post stroke through use of a smart hip exoskeleton: a preliminary investigation.

Stroke is the leading cause of long-term disability in the United States, leaving survivors with profound mobility challenges that impact independent community ambulation. Evidence shows assistance at the hip during walking may be beneficial for stroke survivors. In this cross-over design study, we examine the impact of a novel hip exoskeleton on both functional and patient reported outcomes measuring speed, fall risk, gait symmetry, energy expenditure and perceived walking ability during both indoors and outdoors in single and serial counting dual task paradigms. Nine ambulatory stroke survivors with hemiplegia were included. No differences were seen between the exoskeleton and baseline conditions for any outcomes. Only the patient reported outcome in which subjects were asked to rate their ability to walk outdoors approached statistical significance (p = 0.051) with greater improvement reported for the exoskeleton condition. When asked to rate several key factors about the exoskeleton, weight and assistance emerged as primary perceived negative factors of the exoskeleton underscoring the need for improvements to the technology in this area. Despite lack of differences across groups, some individuals responded positively to the exoskeleton for several functional outcomes measured, highlighting the need for additional exploration into the use of personalized hip exoskeletons for post-stroke rehabilitation.

Towards comprehensive evaluation of the FLEXotendon glove-III: a case series evaluation in pediatric clinical cases and able-bodied adults.

Injuries involving the nervous system, such as a brachial plexus palsy or traumatic brain injury, can lead to impairment in the functionality of the hand. Assistive robotics have been proposed as a possible method to improve patient outcomes in rehabilitation. The work presented here evaluates the FLEXotendon Glove-III, a 5 degree-of-freedom, voice-controlled, tendon-driven soft robotic hand exoskeleton, with two human subjects with hand impairments and four able-bodied subjects. The FLEXotendon Glove-III was evaluated on four unimpaired subjects, in conjunction with EMG sensor data, to determine the quantitative performance of the glove in applied pinch force, perturbation resistance, and exertion reduction. The exoskeleton system was also evaluated on two subjects with hand impairments, using two standardized hand function tests, the Jebsen-Taylor Hand Function Test and the Toronto Rehabilitation Institute Hand Function Test. The subjects were also presented with three qualitative questionnaires, the Capabilities of Upper Extremities Questionnaire, the Quebec User Evaluation of Satisfaction with Assistive Technology, and the Orthotics Prosthetics User Survey-Satisfaction module. From the previous design, minor design changes were made to the exoskeleton. The quick connect system was redesigned for improved performance, the number of motors was reduced to decrease overall footprint, and the entire system was placed into a compact acrylic case that can be placed into a backpack for increased portability.

Evaluation of the FLEXotendon glove-III through a human subject case study.

Cervical spinal cord injury (SCI) can significantly impair an individual's hand functionality due to the disruption of nerve signals from the brain to the upper extremity. Robotic assistive hand exoskeletons have been proposed as a potential technology to facilitate improved patient rehabilitation outcomes, but few exoskeleton studies utilize standardized hand function tests and questionnaires to produce quantitative data regarding exoskeleton performance. This work presents the human subject case study evaluation of the FLEXotendon Glove-III, a 5 degree-of-freedom voice-controlled, tendon-driven soft robotic assistive hand exoskeleton for individuals with SCI. The exoskeleton system was evaluated in a case study with two individuals with SCI through two standardized hand function tests namely, the Jebsen-Taylor Hand Function Test and the Toronto Rehabilitation Institute Hand Function Test and three questionnaires (Capabilities of Upper Extremities Questionnaire, Orthotics Prosthetics Users Survey, Quebec User Evaluation of Satisfaction with Assistive Technology). Minor design changes were made to the exoskeleton: integrated fingertip force sensors to sense excessive grasp force, a quick connect system to expedite the exoskeleton glove swapping process between users, compact tendon tension sensors to measure tendon force for admittance control, and a redesigned smartphone app to encompass all aspects of exoskeleton use.

Effects of Bilateral Assistance for Hemiparetic Gait Post-Stroke Using a Powered Hip Exoskeleton.

Hemiparetic gait due to stroke is characterized by an asymmetric gait due to weakness in the paretic lower limb. These inter-limb asymmetries increase the biomechanical demand and reduce walking speed, leading to reduced community mobility and quality of life. With recent progress in the field of wearable technologies, powered exoskeletons have shown great promise as a potential solution for improving gait post-stroke. While previous studies have adopted different exoskeleton control methodologies for restoring gait post-stroke, the results are highly variable due to limited understanding of the biomechanical effect of exoskeletons on hemiparetic gait. In this study, we investigated the effect of different hip exoskeleton assistance strategies on gait function and gait biomechanics of individuals post-stroke. We found that, compared to walking without a device, powered assistance from hip exoskeletons improved stroke participants' self-selected overground walking speed by 17.6 ± 2.5% and 11.1 ± 2.7% with a bilateral and unilateral assistance strategy, respectively (p < 0.05). Furthermore, both bilateral and unilateral assistance strategies significantly increased the paretic and non-paretic step length (p < 0.05). Our findings suggest that powered assistance from hip exoskeletons is an effective means to increase walking speed post-stroke and tuning the balance of assistance between non-paretic and paretic limbs (i.e., a bilateral strategy) may be most effective to maximize performance gains.

Reducing Knee Hyperextension With an Exoskeleton in Children and Adolescents With Genu Recurvatum: A Feasibility Study.

Genu recurvatum, or knee hyperextension, is a complex gait pattern with a variety of etiologies, and is often connected with knee weakness, lack of motor control, and spasticity. Because of the atypical forces placed on the soft tissues, early treatment or prevention of knee hyperextension may help prevent further degradation of the knee joint. In this study, we assessed the feasibility of a knee exoskeleton to mitigate hyperextension and increase swing range of motion in five children/adolescents who presented with unilateral genu recurvatum. Over the course of three visits, each participant practiced walking with the exoskeleton, which provided torque assistance during both stance and swing based on an impedance control law. In final validation trials, the exoskeleton was effective in reducing knee hyperextension (0.2 ± 4.7° average peak knee extension without exo to 9.9 ± 10.3° with exo) and improving swing range of motion by 14.0 ± 4.5° increase on average. However, while the exoskeleton was effective in normalizing the kinematics, it did not lead to improved spatio-temporal asymmetry measures. This work showcases a promising potential application of a robotic knee exoskeleton for improving the kinematic characteristics of genu recurvatum gait.

Electrical Stimulation of Distal Tibial Nerve During Stance Phase of Walking May Reverse Effects of Unilateral Paw Pad Anesthesia in the Cat.

Cutaneous feedback from feet is involved in regulation of muscle activity during locomotion, and the lack of this feedback results in motor deficits. We tested the hypothesis that locomotor changes caused by local unilateral anesthesia of paw pads in the cat could be reduced/reversed by electrical stimulation of cutaneous and proprioceptive afferents in the distal tibial nerve during stance. Several split-belt conditions were investigated in four adult female cats. In addition, we investigated the effects of similar distal tibial nerve stimulation on overground walking of one male cat that had a transtibial, bone-anchored prosthesis for 29 months and, thus, had no cutaneous/proprioceptive feedback from the foot. In all treadmill conditions, cats walked with intact cutaneous feedback (control), with right fore- and hindpaw pads anesthetized by lidocaine injections, and with a combination of anesthesia and electrical stimulation of the ipsilateral distal tibial nerve during the stance phase at 1.2× threshold of afferent activation. Electrical stimulation of the distal tibial nerve during the stance phase of walking with anesthetized ipsilateral paw pads reversed or significantly reduced the effects of paw pad anesthesia on several kinematic variables, including lateral center of mass shift, cycle and swing durations, and duty factor. We also found that stimulation of the residual distal tibial nerve in the prosthetic hindlimb often had different effects on kinematics compared with stimulation of the intact hindlimb with paw anesthetized. We suggest that stimulation of cutaneous and proprioceptive afferents in the distal tibial nerve provides functionally meaningful motion-dependent sensory feedback, and stimulation responses depend on limb conditions.

Quantifying Asymmetry Between Medial and Lateral Compartment Knee Loading Forces Using Acoustic Emissions.

OBJECTIVE: Osteoarthritis is the most common type of knee arthritis that can be affected by excessive and compressive loads and can affect one or more compartments of the knee: medial, lateral, and patellofemoral. The medial compartment tends to be the most vulnerable to injuries and research suggests that a better understanding of the medial to lateral load distribution conditions could provide insights to the quantitative usage of knee compartments in activities of daily life. METHODS: Prior to study in an osteoarthritic clinical population which may present with various complicating anatomical and physiological changes, we investigate knee acoustical emissions of able-bodied individuals during a varying width squat exercise which simulates loading asymmetries that would typically be seen in this clinical population. To that end, we present a novel method to quantify the directional bias of asymmetry between the medial and lateral compartment knee joint load in healthy individuals by recording knee acoustical emissions and analyzing them using a deep neural network in a subject independent model. We placed four miniature contact microphones on the medial and lateral sides of the patella on both the left and right leg. We compared the handcrafted audio features with the automated features extracted from the convolutional autoencoder which is an unsupervised model that learns the comprehensive representation of the input to determine whether these automated features can better represent the signal's characteristic in regard to the structural asymmetry of the knee joint. The input to the convolutional auto encoder (CAE) is a time-frequency representation and different types of these images such as spectrogram and scalogram are compared. We alsocompared the multi-sensor fusion approach with the performance of a single sensor to determine the robustness of using multiple sensors. RESULTS: Using a representation learning based approach, we developed a subject independent classification model capable of classifying the asymmetry of the medial and lateral joint load across subjects (accuracy = 83%). CONCLUSION: The result indicates that wavelet coherence which is the time-frequency correlation of two signals using a wavelet transform yields the best accuracy. SIGNIFICANCE: These findings suggest that acoustic signals could potentially quantify the direction of medial to lateral load distribution which would broaden the implications for wearable sensing technology for monitoring cartilage health and factors responsible for cartilage breakdown and assessing appropriate rehabilitation exercises without overloading on one side.

A comparison of orthoses in the treatment of idiopathic toe walking: A randomized controlled trial.

BACKGROUND: Orthotic treatment of idiopathic toe walking is complicated by the lack of a known etiology. This study compared control of toe walking using an articulated ankle-foot orthosis versus a rigid carbon fiber footplate attached to a foot orthosis. OBJECTIVES: Ascertain differences between two orthoses in the control of idiopathic toe walking. STUDY DESIGN: Randomized controlled trial. METHODS: A total of 18 children with idiopathic toe walking were randomized to either the ankle-foot orthosis or foot orthosis treatment group in a Parallel Randomized Controlled Trial with no blinding. Prior to and after 6 weeks of treatment, participants completed three-dimensional gait assessment and the L-test of Functional Mobility. Parents completed a satisfaction survey and a subset of the Orthotic and Prosthetic User Survey after treatment. RESULTS: Nine participants were analyzed in each group. Both groups showed significant improvement in kinematics versus baseline with orthoses; however, when the orthoses were removed, the ankle-foot orthosis group did not immediately sustain this improvement, while the foot orthosis group did. Parents preferred the foot orthosis for donning and appearance. CONCLUSION: The ankle-foot orthosis controls idiopathic toe walking, but subjects may revert to earlier patterns following treatment. The foot orthosis does not control idiopathic toe walking as well but is less restrictive and more accepted by children and their parents, with similar out-of-brace effects. CLINICAL RELEVANCE: This study suggests that sequential orthotic treatment for children with idiopathic toe walking (ITW) may be beneficial. Initial treatment could include a less restrictive orthosis like a foot orthosis (FO); if this is unsuccessful within a set time frame, then the patient may require a more restrictive form of treatment such as an ankle-foot orthosis (AFO).