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

Preliminary Investigation of Residual Limb Plantarflexion and Dorsiflexion Muscle Activity During Treadmill Walking for Trans-tibial Amputees

Background: Novel powered prosthetic ankles currently incorporate finite state control, using kinematic and kinetic sensors to differentiate stance and swing phases/sub-phases and control joint impedance and position or torque. For more intuitive control, myoelectric control of the ankle using the remnant residual limb dorsiflexors and plantarflexors, perhaps in concert with kinetic and kinematic sensors, may be possible. Objective: The specific research objective was to assess the feasibility of using myoelectric control of future active or powered prosthetic ankle joints for trans-tibial amputees. Study Design: The project involved human subject trials to determine whether current techniques of myoelectric control of upper extremity prostheses might be readily adapted for lower extremity prosthetic control. Methods: Gait analysis was conducted for three unilateral trans-tibial amputee subjects during ambulation on an instrumented split belt treadmill. Data included ankle plantarflexor and dorsiflexor activity for the residual limb, as well as lower limb kinematics and ground reaction forces and moments of both the sound and prosthetic limbs. Results: These data indicate that: 1) trans-tibial amputees retain some independent ankle plantarflexor and dorsiflexor muscle activity of their residual limb; 2) it is possible to position surface electromyographic electrodes within a trans-tibial socket that maintain contact during ambulation; 3) both the plantarflexors and dorsiflexors of the residual limb are active during gait; 4) plantarflexor and dorsiflexor activity is consistent during multiple gait cycles; and 5) with minimal training, trans-tibial amputees may be able to activate their plantarflexors during push-off. Conclusions: These observations demonstrate the potential for future myoelectric control of active prosthetic ankles. Clinical relevance This study demonstrated the feasibility of applying upper extremity prosthetic myoelectric signal acquisition, processing and control techniques to future myoelectric control of active prosthetic ankles for trans-tibial amputees

Within-socket Myoelectric Prediction of Continuous Ankle Kinematics for Control of a Powered Transtibial Prosthesis

Objective. Powered robotic prostheses create a need for natural-feeling user interfaces and robust control schemes. Here, we examined the ability of a nonlinear autoregressive model to continuously map the kinematics of a transtibial prosthesis and electromyographic (EMG) activity recorded within socket to the future estimates of the prosthetic ankle angle in three transtibial amputees. Approach. Model performance was examined across subjects during level treadmill ambulation as a function of the size of the EMG sampling window and the temporal \u27prediction\u27 interval between the EMG/kinematic input and the model\u27s estimate of future ankle angle to characterize the trade-off between model error, sampling window and prediction interval. Main results. Across subjects, deviations in the estimated ankle angle from the actual movement were robust to variations in the EMG sampling window and increased systematically with prediction interval. For prediction intervals up to 150 ms, the average error in the model estimate of ankle angle across the gait cycle was less than 6°. EMG contributions to the model prediction varied across subjects but were consistently localized to the transitions to/from single to double limb support and captured variations from the typical ankle kinematics during level walking. Significance. The use of an autoregressive modeling approach to continuously predict joint kinematics using natural residual muscle activity provides opportunities for direct (transparent) control of a prosthetic joint by the user. The model\u27s predictive capability could prove particularly useful for overcoming delays in signal processing and actuation of the prosthesis, providing a more biomimetic ankle response

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

Continuous Myoelectric Prediction of Future Ankle Angle and Moment Across Ambulation Conditions and Their Transitions

A hallmark of human locomotion is that it continuously adapts to changes in the environment and predictively adjusts to changes in the terrain, both of which are major challenges to lower limb amputees due to the limitations in prostheses and control algorithms. Here, the ability of a single-network nonlinear autoregressive model to continuously predict future ankle kinematics and kinetics simultaneously across ambulation conditions using lower limb surface electromyography (EMG) signals was examined. Ankle plantarflexor and dorsiflexor EMG from ten healthy young adults were mapped to normal ranges of ankle angle and ankle moment during level overground walking, stair ascent, and stair descent, including transitions between terrains (i.e., transitions to/from staircase). Prediction performance was characterized as a function of the time between current EMG/angle/moment inputs and future angle/moment model predictions (prediction interval), the number of past EMG/angle/moment input values over time (sampling window), and the number of units in the network hidden layer that minimized error between experimentally measured values (targets) and model predictions of ankle angle and moment. Ankle angle and moment predictions were robust across ambulation conditions with root mean squared errors less than 1° and 0.04 Nm/kg, respectively, and cross-correlations (R2) greater than 0.99 for prediction intervals of 58 ms. Model predictions at critical points of trip-related fall risk fell within the variability of the ankle angle and moment targets (Benjamini-Hochberg adjusted p \u3e 0.065). EMG contribution to ankle angle and moment predictions occurred consistently across ambulation conditions and model outputs. EMG signals had the greatest impact on noncyclic regions of gait such as double limb support, transitions between terrains, and around plantarflexion and moment peaks. The use of natural muscle activation patterns to continuously predict variations in normal gait and the model’s predictive capabilities to counteract electromechanical inherent delays suggest that this approach could provide robust and intuitive user-driven real-time control of a wide variety of lower limb robotic devices, including active powered ankle-foot prostheses

Comparison of Socket Suspension Systems During Stair Ascent in Individuals with Transtibial Amputees

Socket suspension systems have an important role in an amputee’s ability to perform activities of daily living. There are three common modes of suspension used to attach the prosthetic foot to the residual limb including lock and pin (PIN), suction, and vacuum suspension systems. A new vacuum suspension system has been developed, the PUCK, which has a vacuum system internal to the socket and maintains pressure throughout the residual limb. Previous literature has focused on the role of suspension during over-ground walking but few have examined the effects during a more difficult task such as stair ascent. The purpose of this thesis was to understand if differences exist between PIN and PUCK suspension systems during stair ascent. Five male unilateral transtibial amputees participated in this study. The task was analyzed in two phases: GROUND (stride from level ground to second step) and STAIR (stride from first to third step). The participants attended two sessions; one with each suspension system (PIN and PUCK). Motion and forces between foot and GROUND (STAIR) were measured. Data analysis resulted in numerous kinematic and kinetic measures during each stride. Differences between limbs and between suspension systems were examined. The only difference between suspension systems was knee range of motion (ROM) during steps on the GROUND. The PUCK knee ROM was reduced compared to the PIN knee ROM, and this could be related to the neoprene sleeve worn with the PUCK system. A hip-dominant strategy was utilized by the transtibial amputees (TTA) for both GROUND and STAIR. The utilization of the hip of the amputated limb is a compensation strategy used by TTA since there is a reduction of knee ROM and ankle power of the amputated limb. Inter-limb differences were still present during both steps on the GROUND and STAIR regardless of suspension system. This study contributes to the body of literature by the uniqueness of the tasks analyzed (GROUND and STAIR) and the comparison between suspension systems. Future directions should focus on TTA of similar qualities to better understand the influence of suspension systems during steps on the GROUND and STAIR

The design, control and testing of an integrated electrohydrostatic powered ankle prosthesis

This paper presents a prototype powered ankle prosthesis that can operate passively in most of the gait cycle and provide powered assistance for toe push-off and subsequent foot dorsiflexion. The use of an electrohydrostatic actuator (EHA) gives the ability to switch quickly and smoothly between passive and active modes. In this new powered ankle prosthesis, the motor-pump unit is integrated with the ankle joint and the battery and controller are held in a backpack. A 100 W brushless dc motor is used to drive a 0.45 cc/rev gear pump, controlling flow to an ankle cylinder through a bespoke manifold. The motor runs wet, pressurized to 6 MPa, avoiding the need for a pump shaft seal and a refeeding circuit for external leakage. A dynamic system model has been develop to help analyze the EHA performance. A motor control method is proposed based on heel strike recognition and a middle stance time delay. The prosthesis has been tested with a 70 kg transtibial amputee, and results are presented for walking on a treadmill at three different speeds (2.8, 3.8, and 4.8 km/h). The amputee has provided positive subjective feedback. We conclude that the hybrid passive-active approach has significant advantages for prosthesis design, and we outline future testing and development requirements.</p