abstract: Locomotion is of prime importance in enabling human beings to effectively respond in space and time to meet different needs. Approximately 2 million Americans live with an amputation with most of those amputations being of the lower limbs. To advance current state-of-the-art lower limb prosthetic devices, it is necessary to adapt performance at a level of intelligence seen in human walking. As such, this thesis focuses on the mechanisms involved during human walking, while transitioning from rigid to compliant surfaces such as from pavement to sand, grass or granular media. Utilizing a unique tool, the Variable Stiffness Treadmill (VST), as the platform for human walking, rigid to compliant surface transitions are simulated. The analysis of muscular activation during the transition from rigid to different compliant surfaces reveals specific anticipatory muscle activation that precedes stepping on a compliant surface. There is also an indication of varying responses for different surface stiffness levels. This response is observed across subjects. Results obtained are novel and useful in establishing a framework for implementing control algorithm parameters to improve powered ankle prosthesis. With this, it is possible for the prosthesis to adapt to a new surface and therefore resulting in a more robust smart powered lower limb prosthesis. / Dissertation/Thesis / Masters Thesis Biomedical Engineering 2019

Currently there are nearly 2 million people living with limb loss in the United States [1]. Many of these individuals are either transtibial (below knee) or transfemoral (above knee) amputees and require an ankle-foot prosthesis for basic mobility. While there are an abundance of options available for individuals who require an ankle-foot prosthesis, these options fail to mimic an intact ankle when it comes to key evaluation criteria such as range of motion, push-off force, and roll over shape. The roll over shape is created by plotting the center of pressure during a step in a shank-based coordinate system. To address the need for a prosthesis that effectively replaces the ankle's contribution to an able-bodied gait, a biomimetic approach is taken in the design the Compliant & Articulating Prosthetic Ankle (CAPA) foot. The passive CAPA foot consists of four components connected by torsion springs representing the Phalanges, Metatarsal bones, Talus, and Calcaneus. Biomimetic functionality is exhibited by CAPA foot with regards to the roll over shape and a linear relationship between moment exerted and ankle angle, distinguishing the CAPA foot from other ankle-foot prostheses. A mathematical model of the CAPA foot is created to determine the roll over shape a specific CAPA foot geometry would produce and support eventual customization of the 3D printed components. The mathematical model is used to optimize the design to two distinctly different roll over shapes, one with a rocker radius closer to that of the Talus bone and the other closer to the energetically advantageous value of 0.3 times leg length [2, 3]. Compliant and stiff versions of the two CAPA feet were compared to a conventional Solid Articulating Cushioned Heel (SACH) foot and a passive dynamic response foot (Renegade® AT produced by Freedom Innovations). Ten able bodied subjects walked on the Computer Assisted Rehabilitation Environment normally, and then with a transfemoral prosthetic simulator. The study was separated into two experiments. For the second experiment (subjects 6-10), the versions of the CAPA foot had pretension in the dorsiflexion springs. Overall the ankle angles and sagittal plane ground reaction forces of the CAPA foot better mimicked an intact ankle-foot than the existing passive ankle-foot prostheses. Added pretension increased the sagittal plane ground reaction forces and roll over shape radius of curvature and arc length. Nine out of ten participants preferred the CAPA foot and there was a statistical significant difference (F=14.2, p<0.01) between the difficulty level rating given for trials with the CAPA foot versus the existing ankle-foot prostheses. The mathematical model is found to be capable of accurately predicting experimental roll over shape trends and the concept of roll over shape based design is demonstrated. Successful aspects of the CAPA foot can be applied to other ankle-foot prosthesis. The CAPA foot could provide a passive, cheap, and personalizable ankle-foot prosthesis that improves mobility the quality of life for individual’s lacking an intact ankle.

Individuals with various lower-limb neuromuscular and musculoskeletal impairments are often prescribed passive-dynamic ankle-foot orthoses (PD-AFOs) to compensate for impaired ankle muscle weakness. Several studies have demonstrated the beneficial effects of PD-AFOs on pathological gait, but few studies have examined the influence of the AFO stiffness characteristics on gait performance. One challenge to performing such studies is the difficulty of manufacturing custom AFOs with a wide range of controlled stiffness levels. However, selective laser sintering (SLS) is a well-suited additive manufacturing technique for generating subject-specific PD-AFOs of varied stiffness. Therefore, the overall goal of this study was to use SLS manufactured PD-AFOs to identify the relationships between AFO stiffness and gait performance in patients with various lower-limb neuromuscular and musculoskeletal impairments. Six subjects with unilateral impairments were enrolled in this study. For each subject, one subject-specific PD-AFO equivalent to the subject’s clinically prescribed carbon fiber PD-AFO (nominal), one 20% more compliant and one 20% more stiff were manufactured using SLS. Three-dimensional kinematic and kinetic data were collected from each subject while ambulating with each PD-AFO at two different speeds to allow a comprehensive biomechanical analysis to assess the influence of PD-AFO stiffness on gait performance. The results showed that in the compliant AFO condition, the AFO limb vertical ground reaction force (GRF) impulse during loading and the non-AFO limb medial GRF impulse during push-off decreased. In addition, the AFO limb braking GRF impulse during loading and the non-AFO limb braking GRF impulse in early single-limb stance decreased. Furthermore, in the compliant AFO condition, negative knee work during early single-limb stance increased while positive hip work in early swing decreased in the AFO limb. Overall, as AFO stiffness decreased, the AFO limb contributed less to body support and braking. In addition, a decreased medial GRF impulse coupled with an increased vertical GRF impulse during non-AFO single-limb stance suggests that walking stability may be compromised as AFO stiffness decreases. Thus, a tradeoff may exist between preserving stability and increasing net propulsion, which should be considered when assessing the mobility needs of individuals prescribed PD-AFOs as a result of various neuromuscular and musculoskeletal impairments. / text

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The Ottawalk-Speed (OWS) orthosis prevents knee collapse in stumble situations. The purpose of this study was to develop a virtual stumble perturbation to measure OWS response to a knee collapse when walking. A new split speed perturbation was developed for the CAREN virtual reality system. This perturbation induced a stumble with increased knee flexion for five able-bodied participants, with either a hopping or stopping recovery strategy. Three knee-ankle-foot orthosis users were subjected to five stumble trials while wearing the OWS. OWS participants used a straight-legged recovery strategy, and extended the knee through recovery weight acceptance. Therefore, the split speed perturbation was not appropriate to measure OWS response to a stumble since knee collapse did not occur. The OWS allowed free knee motion during gait. Further study is required to measure OWS response during a stumble with a knee collapse event.

Individuals with stroke often demonstrate impaired ankle-foot function, commonly termed dropped foot that affects their ability to walk safely at home and within their community. While interventions are available to improve gait function, they have inconsistency demonstrated positive effects due to the lack of evidence-based practice guidelines and a limited understanding of the mechanisms leading to dropped foot. The aim of this dissertation was to 1) determine the relationship between dropped foot gait deviations and impaired sensorimotor control, 2) compare gait biomechanics between stroke survivors with and without dropped foot impairment, and 3) evaluate the immediate effects of an ankle-foot orthotic (AFO) and functional electrical stimulation (FES) device among stroke survivors with dropped foot impairment. Our evaluation combined standardized clinical measures of ankle-foot function (i.e. sensorimotor control, strength, spasticity and range of motion) and gait analysis using advanced laboratory techniques (i.e. electromyography and electrical goniometers) to quantify mechanisms of dropped foot impairment. Fifty-five stroke survivors completed the assessment prior to discharge from inpatient rehabilitation. Individuals with poor generation of isometric dorsiflexor force and reduced passive ankle range of motion were likely to demonstrate greater plantarflexion in swing and limited stance phase ankle joint excursion, respectively. Results from the gait analysis revealed a delayed onset and reduced activation time of the ankle dorsiflexors, and decreased co-activation time in the stance phase as possible mechanisms leading to dropped foot. A detailed case series was performed with four stroke survivors with dropped foot currently using an AFO. Application of an AFO immediately improved peak dorsiflexion in the swing phase and limited ankle range of motion during stance. When walking with the FES device, individuals with moderate dorsiflexor muscle weakness improved their ankle position at initial contact and increased peak dorsiflexion during stance, while no significant changes were observed among individuals with greater impairment. Overall, the results highlighted individual differences in response to interventions aimed at improving dropped foot gait deviations. These findings contribute to a greater understanding of gait dysfunction post stroke, and may lead to the development of a more effective clinical assessment and intervention strategies to improve dropped foot impairment.

After a stroke, gait and balance are often affected and an orthosis is typically required to facilitate postural control. This study has been conducted to examine how the Range of Motion in an Ankle-Foot-Orthosis (AFO) impacts on stroke patients’ dynamic balance. It was hypothesized that better dynamic balance would be recorded when individuals were wearing a flexible AFO. The tests that was used in this study were the Timed Up and Go test (TUG), and the Center of Pressure (CoP)/Center of Mass (CoM) inclination angle, both in Anterior-Posterior (AP) and Medio-Lateral (ML) planes. The three patients participating in this study were all users, or had been users of AFO’s, and during the study they were asked to wear a customized AFO with the possibility to change the settings to open, flexible and rigid ankle joints. The order was randomized within each patient. No clear pattern was observed across all patients, either in the TUG test or CoP/CoM inclination angles. Further studies are required to explore the impact that AFO flexibility has on dynamic balance in individuals who have had a stroke.

The Ottawalk-Speed (OWS) orthosis prevents knee collapse in stumble situations. The purpose of this study was to develop a virtual stumble perturbation to measure OWS response to a knee collapse when walking. A new split speed perturbation was developed for the CAREN virtual reality system. This perturbation induced a stumble with increased knee flexion for five able-bodied participants, with either a hopping or stopping recovery strategy. Three knee-ankle-foot orthosis users were subjected to five stumble trials while wearing the OWS. OWS participants used a straight-legged recovery strategy, and extended the knee through recovery weight acceptance. Therefore, the split speed perturbation was not appropriate to measure OWS response to a stumble since knee collapse did not occur. The OWS allowed free knee motion during gait. Further study is required to measure OWS response during a stumble with a knee collapse event.

abstract: The human ankle is a critical joint required for mobility and stability of the body during static and dynamic activity. The absence of necessary torque output by the ankle due to neurological disorder or near-fatal injury can severely restrict locomotion and cause an inability to perform daily tasks. Physical Human-Robot Interaction (pHRI) has explored the potential of controlled actuators to positively impact human joints and partly restoring the required torque and stability at the joint to perform a task. However, a trade-off between agility and stability of the control technique of these devices can reduce the complete utilization of the performance to create a desirable impact on human joints. This research focuses on two control techniques of an Active Ankle Foot Orthosis (AFO) namely, Variable Stiffness (VS) and Variable Damping (VD) controllers to modulate ankle during walking. The VS controller is active during the stance phase and is used to restore the ankle trajectory of healthy participants that has been altered by adding a dead-weight of 2 Kgs. The VD controller is active during the terminal stance and early-swing phase and provides augmentative force during push-off that results in increased propulsion and stabilizes the ankle based on user-intuitions. Both controllers have a positive impact on Medial Gastrocnemius (GAS) muscle and Soleus (SOL) muscle which are powerful plantar - flexors critical to propulsion and kinematic properties during walking. The VS controller has recorded an 8.18% decrease in GAS and an 9.63 % decrease in SOL muscle activity during the stance phase amongst participants while decreasing mean ankle position error by 22.28 % and peak ankle position error by 17.43%. The VD controller demonstrated a 7.59 % decrease in GAS muscle and a 10.15 % decrease in SOL muscle activity during push-off amongst the participants while increasing the range-of-motion (ROM) by 7.84 %. Comprehensively, the study has shown a positive impact on ankle trajectory and the corresponding muscle effort at respective stages of the controller activity. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2020

No description available.