Robotic Functional Gait Rehabilitation with Tethered Pelvic Assist Device

The primary goal of human locomotion is to stably translate the center of mass (CoM) over the ground with minimum expenditure of energy. Pelvic movement is crucial for walking because the human CoM is located close to the pelvic center. Because of this anatomical feature, pelvic motion directly contributes to the metabolic expenditure, as well as in the balance to keep the center of mass between the legs. An abnormal pelvic motion during the gait not only causes overexertion, but also adversely affects the motion of the trunk and lower limbs. In order to study different interventions, recently a cable-actuated robotic system called Tethered Pelvic Assist Device (TPAD) was developed at ROAR laboratory at Columbia University. The cable-actuated system has a distinct advantage of applying three dimensional forces on the pelvis at discrete points in the gait cycle in contrast to rigid exoskeletons that restrict natural pelvic motion and add extra inertia from the rigid linkages. However, in order to effectively use TPAD for rehabilitation purposes, we still need to have a better understanding of how human gait is affected by different forces applied by TPAD on the pelvis. In the present dissertation, three different control methodologies for TPAD are discussed by performing human experiments with healthy subjects and patients with gait deficits. Moreover, the corresponding changes in the biomechanics during TPAD training are studied to understand how TPAD mechanistically influences the quality of the human gait. In Chapter 2, an ‘assist-as-needed’ controller is implemented to guide and correct the pelvic motion in three dimensions. Here, TPAD applies the correction force based on the deviation of the current position of the pelvic center from a pre-defined target trajectory. This force acts on the pelvic center to guide it towards the target trajectory. A subject in the device experiences a force field, where the magnitude becomes larger when the subject deviates further away from the target trajectory. This control strategy is tested by performing the experiments on healthy subjects with different target pelvic trajectories. Chapter 3 describes a robotic resistive training study using a continuous force on the pelvis to strengthen the weak limbs so that subjects can improve their walking. This study is designed to improve the abnormal gait of children with Cerebral Palsy (CP) who have a crouch gait. Crouch gait is caused by a combination of weak extensor muscles that do not produce adequate muscle forces to keep the posture upright, coupled with contraction of muscles that limit the joint range of motion. Among the extensor muscles, the soleus muscle acts as the major weight-bearing muscle to prevent the knees from collapsing forward during the middle of the stance phase when the foot is on the ground. Electromyography, kinematics, and clinical measurements of the patients with crouch gait show significant improvements in the gait quality after the resistive TPAD training performed over five weeks. Both Chapters 2 & 3 present interventions that are bilaterally applied on both legs. Chapter 4 introduces a training strategy that can be used for patients who have impairments in only one leg which results in manifests as asymmetric weight-bearing while walking. This training method is designed to improve the asymmetric weight bearing of the hemiparetic patients who overly rely on the stronger leg. The feasibility of this training method is tested by experiments with healthy subjects, where the controller creates an asymmetric force field to bring asymmetry in weight bearing during walking. In summary, the present dissertation is devoted to developing new training methods that utilize TPAD for rehabilitation purposes and characterize the responses of different force interventions by investigating the resulting biomechanics. We believe that these methodologies with TPAD can be used to improve abnormal gait patterns that are often observed in cerebral palsy or stroke patients

Functional Resistance Training During Walking: Design, Testing, and Evaluation of Passive and Semi-Passive Wearable Devices for Providing Targeted Resistance to the Leg During Gait

Injuries to the neuromusculoskeletal systems often result in muscle weakness, abnormal coordination strategies, and gait impairments. Functional resistance training during walking—where a patient walks while a device increases loading on the leg—is an emerging approach to combat these symptoms. While simple passive devices (i.e., ankle weights and resistance bands) can be applied for this training, rehabilitation robots have more potential upside because they can be controlled to treat multiple gait abnormalities and can be monitored by clinicians. However, the cost of conventional robotic devices limits their use in the clinical or home setting. Hence, in this dissertation, we designed, developed, and tested passive and semi-passive wearable exoskeleton devices as low-cost solutions for providing controllable/configurable functional resistance training during walking. We developed and tested two passive exoskeleton devices for providing resistance to walking and tested their effects on able-bodied participants and stroke survivors. First, we created a patented device that used a passive magnetic brake to provide a viscous (i.e., velocity-dependent) resistance to the knee. The resistive properties of the device could be placed under computer control (i.e., made semi-passive) to control resistance in real-time. Next, we created a passive exoskeleton that provided an elastic (i.e., position-dependent) resistance. While not controllable, this device was highly configurable. Meaning it could be used to provide resistance to joint flexion, extension, or to both (i.e., bidirectionally). Human subjects testing with these devices indicated they increased lower-extremity joint moments, powers, and muscle activation during training. Training also resulted in significant aftereffects—a potential indicator of therapeutic effectiveness—once the resistance was removed. A separate experiment indicated that individuals often kinematically slack (i.e., reduce joint excursions to minimize effort) when resistance is added to the limb. We also found that providing visual feedback of joint angles during training significantly increased muscle activation and kinematic aftereffects (i.e., reduced slacking). With passive devices, the type of passive element used largely dictates the muscle groups, types of muscle contraction, joint actions, and the phases of gait when a device is able to apply resistance. To examine this issue, we compared the training effects of viscous and elastic devices that provided bidirectional resistance to the knee during gait. Additionally, we compared training with viscous resistances at the hip and knee joints. While the resistance type and targeted joint altered moments, powers, and muscle activation patterns, these methods did not differ in their ability to produce aftereffects, alter neural excitability, or induce fatigue in the leg muscles. While this may indicate that the resistance type does not have a large effect on functional resistance training during walking, it is possible that an extended training with these devices could produce a different result. Lastly, we used musculoskeletal modeling in OpenSim to directly compare several strategies that have been used to provide functional resistance training to gait in the clinic or laboratory setting. We found that devices differed in their ability to alter gait parameters during walking. Hence, these findings could help clinicians when selecting a resistive strategy for their patients, or engineers when designing new devices or control schemes. Collectively, this dissertation introduces a new class of wearable devices for functional resistance training during walking and establishes the biomechanical and neurophysiological effects and the clinical potential of these devices in able-bodied and stroke survivors.PHDBiomedical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/169867/1/epwiv_1.pd

Abnormal joint torque patterns exhibited by chronic stroke subjects while walking with a prescribed physiological gait pattern

<p>Abstract</p> <p>Background</p> <p>It is well documented that individuals with chronic stroke often exhibit considerable gait impairments that significantly impact their quality of life. While stroke subjects often walk asymmetrically, we sought to investigate whether prescribing near normal physiological gait patterns with the use of the Lokomat robotic gait-orthosis could help ameliorate asymmetries in gait, specifically, promote similar ankle, knee, and hip joint torques in both lower extremities. We hypothesized that hemiparetic stroke subjects would demonstrate significant differences in total joint torques in both the frontal and sagittal planes compared to non-disabled subjects despite walking under normal gait kinematic trajectories.</p> <p>Methods</p> <p>A motion analysis system was used to track the kinematic patterns of the pelvis and legs of 10 chronic hemiparetic stroke subjects and 5 age matched controls as they walked in the Lokomat. The subject's legs were attached to the Lokomat using instrumented shank and thigh cuffs while instrumented footlifters were applied to the impaired foot of stroke subjects to aid with foot clearance during swing. With minimal body-weight support, subjects walked at 2.5 km/hr on an instrumented treadmill capable of measuring ground reaction forces. Through a custom inverse dynamics model, the ankle, knee, and hip joint torques were calculated in both the frontal and sagittal planes. A single factor ANOVA was used to investigate differences in joint torques between control, unimpaired, and impaired legs at various points in the gait cycle.</p> <p>Results</p> <p>While the kinematic patterns of the stroke subjects were quite similar to those of the control subjects, the kinetic patterns were very different. During stance phase, the unimpaired limb of stroke subjects produced greater hip extension and knee flexion torques than the control group. At pre-swing, stroke subjects inappropriately extended their impaired knee, while during swing they tended to abduct their impaired leg, both being typical abnormal torque synergy patterns common to stroke gait.</p> <p>Conclusion</p> <p>Despite the Lokomat guiding stroke subjects through physiologically symmetric kinematic gait patterns, abnormal asymmetric joint torque patterns are still generated. These differences from the control group are characteristic of the hip hike and circumduction strategy employed by stroke subjects.</p

A Novel Design of a Cable-driven Active Leg Exoskeleton (C-ALEX) and Gait Training with Human Subjects

Exoskeletons for gait training commonly use a rigid-linked "skeleton" which makes them heavy and bulky. Cable-driven exoskeletons eliminate the rigid-linked skeleton structure, therefore creating a lighter and more transparent design. Current cable-driven leg exoskeletons are limited to gait assistance use. This thesis presented the Cable-driven Active Leg Exoskeleton (C-ALEX) designed for gait retraining and rehabilitation. Benefited from the cable-driven design, C-ALEX has minimal weight and inertia (4.7 kg) and allows all the degrees-of-freedom (DoF) of the leg of the user. C-ALEX uses an assist-as-needed (AAN) controller to train the user to walk in a new gait pattern. A preliminary design of C-ALEX was first presented, and an experiment was done with this preliminary design to study the effectiveness of the AAN controller. The result on six healthy subjects showed that the subjects were able to follow a new gait pattern significantly more accurately with the help of the AAN controller. After this experiment, C-ALEX was redesigned to improve its functionality. The improved design of C-ALEX is lighter, has more DoFs and larger range-of-motion. The controller of the improved design improved the continuity of the generated cable tensions and added the function to estimate the phase of the gait of the user in real-time. With the improved design of C-ALEX, an experiment was performed to study the effect of the weight and inertia of an exoskeleton on the gait of the user. C-ALEX was used to simulate exoskeletons with different levels of weight and inertia by adding extra mass and change the weight compensation level. The result on ten subjects showed that adding extra mass increased step length and reduced knee flexion. Compensating the weight of the mass partially restored the knee flexion but not the step length, implying that the inertia of the mass is responsible for the change. This study showed the distinctive effect of weight and inertia on gait and demonstrated the benefit of a lightweight exoskeleton. C-ALEX was designed for gait training and rehabilitation, and its training effectiveness was studied in nine healthy subjects and a stroke patient. The healthy subjects trained with C-ALEX to walk in a new gait pattern with 30% increase in step height for 40 min. After the training, the subjects were able to closely repeat the trained gait pattern without C-ALEX, and the step height of the subjects increased significantly. A stroke patient also tested C-ALEX for 40 minutes and showed short-term improvements in step length, step height, and knee flexion after training. The result showed the effectiveness of C-ALEX in gait training and its potential to be used in stroke rehabilitation

Building Better Exoskeletons: Understanding How Design Affects Robot Assisted Gait Training

Physical therapy is a field with ever increasing demands as the population ages, resulting in a larger number of individuals living with impairments. Therapy is both physically intensive and time intensive for physical therapists, and can require more than one therapist per patient. The use of technology can reduce both these physical and time demands if appropriately applied, while improving repeatability and providing quantitative evaluation of performance. Through these abilities, it may also improve the quality of life for patients. The work presented here explores how the mechanical and controller design of exoskeletons can be used to improve adaptations to new gait patterns in healthy individuals. Armed with this knowledge, new treatment methods can be adapted, applied, and validated for impaired populations with the intention of recovering a more natural gait pattern. First, the ALEX II device is presented. It is a unilateral device, designed to aid in gait training for stroke survivors. The previous version, ALEX I, had several limitations in terms of pelvic freedom, leg range of motion, and the support of the gravitational load. ALEX II was designed to address these issues. Next, a study is presented, using healthy young adults (N=30), in which ALEX II was used to explore how the amount of freedom allowed at the pelvis during gait training affects the level of adaptation subjects are able to achieve. This was evaluated for five separate configurations which resemble existing exoskeletons. It was found that intermediate levels of pelvic freedom degrade the amount of adaptation and that pelvic translation contributes more to this effect than hip abduction/adduction. The next work concerns the design of ALEX III, a bilateral device with twelve active degrees-of-freedom. ALEX III was created to increase the ability to explore the functionality required for gait training, which is why it is capable of controlling 4 degrees-of-freedom at each leg, and 4 degrees-of-freedom at the pelvis. This is followed by the the design of a new type of haptic feedback which utilizes a variable, viscous damping field, which increases the damping coeffiecent as the subject moves away from a specified path. This feedback type was tested in a set of experiments in healthy young adults. The first study (N=32) compared four different settings for the new feedback, finding that while all groups demonstrated adaptations in gait, the lowest rate of change of the damping field exhibited less adaptation. The final study (N=36) compared this haptic feedback to two previously used haptic feedback types. The previously used feedback strategies used a force that pushed the leg either towards or away from the desired path. All three of these strategies were found to produce similar levels of adaptation, however the damping field used much less external force. These findings may change the way exoskeletons for gait training are designed and increase their accessibility. While all the findings need to be validated in impaired populations they can still inform the design of future exoskeletons. The first finding, that providing an intermediate amount of freedom to the pelvis can interfere with gait training, suggests that future devices should have very high amounts of freedom or very restricted pelvic motions. The final finding, that damping fields can be used to induce gait adaptations using a much lower force, can drastically change exoskeleton design and how robotic therapy is provided. Exoskeletons can be made lighter as a result of the force being highly reduced so that lighter weight components can be used, and the dissipative nature of the force reduces dependence on heavy power sources because regenerative breaking can be used to power the device. These factors also make it possible to for devices to be used overground, which may make training more transferable to the real world