Powered ankle-foot prosthesis for the improvement of amputee walking economy

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.Includes bibliographical references (p. 103-108).The human ankle provides a significant amount of net positive work during the stance period of walking, especially at moderate to fast walking speeds. On the contrary, conventional ankle-foot prostheses are completely passive during stance, and consequently, cannot provide net positive work. Clinical studies indicate that transtibial amputees using conventional prostheses exhibit higher gait metabolic rates as compared to intact individuals. Researchers believe the main cause for the observed increase in metabolism is due to the inability of conventional prostheses to provide net positive work at terminal stance in walking. This objective of this thesis is to evaluate the hypothesis that a powered ankle-foot prosthesis, capable of providing active mechanical power at terminal stance, can improve amputee metabolic walking economy compared to a conventional passive-elastic prosthesis. To test the hypothesis, a powered prosthesis is designed and built that comprises a unidirectional spring, configured in parallel with a force-controllable actuator with series elasticity. The prosthesis is controlled to mimic human ankle walking behavior, in particular, the power generation characteristics observed in normal human walking. The rate of oxygen consumption is measured as a determinant of metabolic rate on three unilateral transtibial amputees walking at self-selected speeds. The initial clinical evaluation shows that the powered prosthesis improves amputee metabolic economy from 7% to 20% compared to the conventional passive-elastic prostheses (Flex-Foot Ceterus and Freedom Innovations Sierra), even though the powered system is twofold heavier than the conventional devices. These results support the proposed hypothesis and also suggest a promising direction for further advancement of ankle-foot prosthesis.by Samuel Kwok-Wai Au.Ph.D

Proportional EMG Control of Ankle Plantar Flexion in a Powered Transtibial Prosthesis

The human calf muscle generates 80% of the mechanical work to walk throughout stance-phase, powered plantar flexion. Powered plantar flexion is not only important for walking energetics, but also to minimize the impact on the leading leg at heel-strike. For unilateral transtibial amputees, it has recently been shown that knee load on the leading, intact limb decreases as powered plantar flexion in the trailing prosthetic ankle increases. Not surprisingly, excessive loads on the leading, intact knee are believed to be causative of knee osteoarthritis, a leading secondary impairment in lowerextremity amputees. In this study, we hypothesize that a transtibial amputee can learn how to control a powered anklefoot prosthesis using a volitional electromyographic (EMG) control to directly modulate ankle powered plantar flexion. We here present preliminary data, and find that an amputee participant is able to modulate toe-off angle, net ankle work and peak power across a broad range of walking speeds by volitionally modulating calf EMG activity. The modulation of these key gait parameters is shown to be comparable to the dynamical response of the same powered prosthesis controlled intrinsically (No EMG), suggesting that transtibial amputees can achieve an adequate level of powered plantar flexion controllability using direct volitional EMG control.United States. Dept. of Defense (award number 6920559)United States. Dept. of Defense (award number 6920877)Swiss National Science Foundation (grant PBELP3_140656

Simulación del modelo de actuador serial elástico para prótesis Tobillo-Pie en Matlab

The ankle - foot set plays a very important role for human displacement, such as walking or running, giving vertical support and propulsion to the human walking progression by using the muscle extension and contraction. Many designs have been developed to replicate the function of normal gait, lost by injuries or diseases affecting the limb below the knee [1]. Motor rehabilitation has become a field of growing interest, due to the large number of cases of people with injuries or mutilation in its members or in other cases by cerebrovascular accidents and spinal cord damage that cause paralysis or any kind of disability. [2], [3]. This paper shows the process to get the model of SEA mechanism in Matlab, linking VR-World of Simulink from 3D Solidworks Model to test the model and finally checking the characteristic curves of normal gait to 1.5 m/s with this SEA prosthesis.El conjunto tobillo-pie desempeña un papel muy importante para el movimiento humano, como caminar o correr, ya que proporciona apoyo vertical y propulsión de la progresión de la marcha humana mediante la extensión y contracción muscular. Se han desarrollado muchos diseños para replicar la función de la marcha normal, perdida por lesiones o enfermedades que afectan la extremidad debajo de la rodilla [1]. La rehabilitación motora se ha convertido en un campo de amplio interés, ya que en Colombia hay gran cantidad de casos de personas con lesiones o mutilaciones en sus miembros o en otros casos por accidentes cerebrovasculares y daño medular que provocan parálisis o cualquier tipo de discapacidad. [2], [3]. Este artículo muestra el proceso para obtener el modelo del mecanismo SEA en Matlab, vinculando el VR-World de Simulink con un modelo 3D en Solidworks de la prótesis para validarlo y finalmente verificar las curvas características de la marcha normal a 1,5 m / s con esta prótesis SEA

Biologically inspired design and development of a variable stiffness powered ankle-foot prosthesis

Recent advancements in powered lower limb prostheses have appeased several difficulties faced by lower limb amputees by using a Series-Elastic Actuator (SEA) to provide powered sagittal plane flexion. Unfortunately, these devices are currently unable to provide both powered sagittal plane flexion and 2-DOF at the ankle, removing the ankle’s capacity to invert/evert, thus severely limiting terrain adaption capabilities and user comfort. The developed 2-DOF ankle system in this paper allows both powered flexion in the sagittal plane and passive rotation in the frontal plane; a SEA emulates the biomechanics of the gastrocnemius and Achilles tendon for flexion, while a novel universal-joint system provides the 2-DOF. Several studies were undertaken to thoroughly characterize the capabilities of the device. Under both level and sloped-ground conditions, ankle torque and kinematic data was obtained by using force-plates and a motion capture system. The device was found to be fully capable of providing powered sagittal plane motion and torque very close to that of a biological ankle, while simultaneously being able to adapt to sloped terrain by undergoing frontal plane motion, thus providing 2-DOF at the ankle. These findings demonstrate that the device presented in this paper poses radical improvements to powered PAFD design

Foot/Ankle Prostheses Design Approach Based on Scientometric and Patentometric Analyses

There are different alternatives when selecting removable prostheses for below the knee amputated patients. The designs of these prostheses vary according to their different functions. These prostheses designs can be classified into Energy Storing and Return (ESAR), Controlled Energy Storing and Return (CESR), active, and hybrid. This paper aims to identify the state of the art related to the design of these prostheses of which ESAR prostheses are grouped into five types, and active and CESR are categorized into four groups. Regarding patent analysis, 324 were analyzed over the last six years. For scientific communications, a bibliometric analysis was performed using 104 scientific reports from the Web of Science in the same period. The results show a tendency of ESAR prostheses designs for patents (68%) and active prostheses designs for scientific documentation (40%).Beca Conacyt Doctorad

Volitional control of ankle plantar flexion in a powered transtibial prosthesis during stair-ambulation.

Although great advances have been made in the design and control of lower extremity prostheses, walking on different terrains, such as ramps or stairs, and transitioning between these terrains remains a major challenge for the field. In order to generalize biomimetic behaviour of active lower-limb prostheses top-down volitional control is required but has until recently been deemed unfeasible due to the difficulties involved in acquiring an adequate electromyographic (EMG) signal. In this study, we hypothesize that a transtibial amputee can extend the functionality of a hybrid controller, designed for level ground walking, to stair ascent and descent by volitionally modulating powered plantar-flexion of the prosthesis. We here present data illustrating that the participant is able to reproduce ankle push-off behaviour of the intrinsic controller during stair ascent as well as prevent inadvertent push-off during stair descent. Our findings suggest that EMG signal from the residual limb muscles can be used to transition between level-ground walking and stair ascent/descent within a single step and significantly improve prosthesis performance during stair-ambulation

Split-belt adaptation and gait symmetry in transtibial amputees walking with a hybrid EMG controlled ankle-foot prosthesis

Our ability to automatically adapt our walking pattern to the demands of our environment is central to maintaining a steady gait. Accordingly, a large effort is being made to extend and integrate this adaptability to lower-limb prostheses. To date, the main focus of this research has been on short term adaptation, such as in response to a terrain transition or a sudden change in the environment. However, long term adaptation and underlying sensorimotor learning processes are critical to optimizing walking patterns and predictively changing our gait when faced with continued perturbations. Furthermore, investigating these processes in lower-limb amputees may provide a unique window into the interplay between sensory driven adaptation and top-down cerebellar modulation of locomotor reflexes and may potentially help alleviate gait asymmetries. In the current exploratory study, we therefore investigated adaptation, sensorimotor learning, and gait symmetry in a group of transtibial amputees walking with a hybrid-EMG controlled powered prosthesis and matched controls (both groups N=3). Participants were asked to perform a split-belt walking trial during which the belt on the affected side ran at twice the speed of the contralateral belt (1.0m/s and 0.5m/s respectively). Adaptation, sensorimotor learning, and symmetry are compared to two baseline conditions. Initial results illustrate that the amputees were readily able to use the hybrid controller, modulated their EMG depending on treadmill speed, and successfully adapted their gait during split-belt walking. However, the temporal gait parameters suggest that amputees used a different adaptation technique and showed reduced sensorimotor learning, while gait symmetry was improved, in the short term, post-adaptation

Optimally-calibrated non-invasive feedback improves amputees' metabolic consumption, balance and walking confidence

Objective.Lower-limb amputees suffer from a variety of health problems, including higher metabolic consumption and low mobility. These conditions are linked to the lack of a natural sensory feedback (SF) from their prosthetic device, which forces them to adopt compensatory walking strategies that increase fatigue. Recently, both invasive (i.e. requiring a surgery) and non-invasive approaches have been able to provide artificial sensations via neurostimulation, inducing multiple functional and cognitive benefits. Implants helped to improve patient mobility and significantly reduce their metabolic consumption. A wearable, non-invasive alterative that provides similar useful health benefits, would eliminate the surgery related risks and costs thereby increasing the accessibility and the spreading of such neurotechnologies.Approach.Here, we present a non-invasive SF system exploiting an optimally-calibrated (just noticeable difference-based) electro-cutaneous stimulation to encode intensity-modulated foot-ground and knee angle information personalized to the user's just noticeable perceptual threshold. This device was holistically evaluated in three transfemoral amputees by examination of metabolic consumption while walking outdoors, walking over different inclinations on a treadmill indoors, and balance maintenance in reaction to unexpected perturbation on a treadmill indoors. We then collected spatio-temporal parameters (i.e. gait dynamic and kinematics), and self-reported prosthesis confidence while the patients were walking with and without the SF.Main results.This non-invasive SF system, encoding different distinctly perceived levels of tactile and knee flexion information, successfully enabled subjects to decrease metabolic consumption while walking and increase prosthesis confidence. Remarkably, more physiological walking strategies and increased stability in response to external perturbations were observed while walking with the SF.Significance.The health benefits observed with the use of this non-invasive device, previously only observed exploiting invasive technologies, takes an important step towards the development of a practical, non-invasive alternative to restoring SF in leg amputees

A Generalized Method for Predictive Simulation-Based Lower Limb Prosthesis Design

Lower limb prostheses are designed to replace the functions and form of the missing biological anatomy. These functions are hypothesized to improve user outcome measures which are negatively affected by receiving an amputation – such as metabolic cost of transport, preferred walking speed, and perceived discomfort during walking. However, the effect of these design functions on the targeted outcome measures is highly variable, suggesting that these relationships are not fully understood. Biomechanics simulation and modeling tools are increasingly capable of analyzing the effects of a design on the resulting user gait. In this work, prothesis-aided gait is optimized in simulation to reduce both muscle effort and peak loads on the residual limb using a generalized prosthesis model. Compared to a traditional revolute powered ankle joint model, a two degree-of freedom generalized model reduced muscle activations by 50% and peak loads by 15%. Simulated prosthesis behaviors corresponding to the optimal gait patterns were translated into a two degree-of-freedom ankle-foot prosthesis design with powered bidirectional linear translation and plantarflexion. The prototype is capable of delivering up to 171 N-m of plantarflexion torque and 499 N of translation force, with 15° dorsi-/35° plantarflexion and 10 cm translation range of motion. The mass and height of the ankle-foot are 2.29 kg and 19.5 cm, respectively. The mass of the entire system including the wearable offboard system is 8.58 kg. This platform is designed to emulate the behavior of the simulated prosthesis, as well as be configurable to emulate alternate behaviors obtained from simulations with different optimization objectives. The prototype is controlled to replicate simulated walking patterns using a high level finite state controller, mid-level stiffness controller, and low level load controller. Closed loop load control has bandwidth of 15 Hz in translation and 7.2 Hz in flexion. Load tracking during walking with a single able-bodied human subject ranges from 93 to 159 N in translation and 4.6 to 21.3 N-m in flexion. The contribution of this work is to provide a framework for predictive simulation-based prosthesis design, evidence of its practical implementation, and the experimental tools to validate future predictive simulation studies