Monitoring Contact Behavior During Assisted Walking With a Lower Limb Exoskeleton

Bilateral tibial fractures associated with powered exoskeleton use in complete spinal cord injury - a case report & literature review

INTRODUCTION

Powered robotic exoskeleton (PRE) physiotherapy programmes are a relatively novel frontier which allow patients with reduced mobility to engage in supported walking. Research is ongoing regarding their utility, risks, and benefits. This article describes the case of two fractures occurring in one patient using a PRE.

CASE

We report the case of a 54 year old man who sustained bilateral tibial fractures while using a PRE, on a background of T10 AIS A SCI. The initial session was discontinued due to acute severe bilateral knee swelling after approximately 15 min. The patient attended their local hospital the following day, where radiographs demonstrated bilateral proximal tibial fractures. The patient was treated with manipulation under anaesthetic and long-leg casting for five weeks, at which point he was stepped down to hinged knee braces which were weaned gradually while he remained non-weight bearing for 12 weeks. The patient was investigated with DEXA scan and was diagnosed with osteoporosis. He was liaised with rheumatology services and bone protection was initiated. Fracture healing was achieved and weight-bearing precautions were discontinued, however this period of immobilisation led to significant spasticity. The patient was discharged from orthopaedic services, with ongoing rehabilitation and physiotherapy follow-up.

CONCLUSION

PRE assisted physiotherapy programmes are a promising concept in terms of rehabilitation and independence, however they are not without risk and it is important that both providers and patients are aware of this. Furthermore, SCI patients are at increased risk for osteoporosis and should be monitored and considered for bone protection.

Design and analysis of a lower limb assistive exoskeleton robot

BACKGROUND

In recent years, exoskeleton robot technology has developed rapidly. Exoskeleton robots that can be worn on a human body and provide additional strength, speed or other abilities. Exoskeleton robots have a wide range of applications, such as medical rehabilitation, logistics and disaster relief and other fields.

OBJECTIVE

The study goal is to propose a lower limb assistive exoskeleton robot to provide extra power for wearers.

METHODS

The mechanical structure of the exoskeleton robot was designed by using bionics principle to imitate human body shape, so as to satisfy the coordination of man-machine movement and the comfort of wearing. Then a gait prediction method based on neural network was designed. In addition, a control strategy according to iterative learning control was designed.

RESULTS

The experiment results showed that the proposed exoskeleton robot can produce effective assistance and reduce the wearer's muscle force output.

CONCLUSION

A lower limb assistive exoskeleton robot was introduced in this paper. The kinematics model and dynamic model of the exoskeleton robot were established. Tracking effects of joint angle displacement and velocity were analyzed to verify feasibility of the control strategy. The learning error of joint angle can be improved with increase of the number of iterations. The error of trajectory tracking is acceptable.

Neuromechanical Adaptation to Walking With Electromechanical Ankle Exoskeletons Under Proportional Myoelectric Control

OBJECTIVE

To determine if robotic ankle exoskeleton users decrease triceps surae muscle activity when using proportional myoelectric control, we studied healthy young participants walking with commercially available electromechanical ankle exoskeletons (Dephy Exoboot) with a novel controller. The vast majority of robotic lower limb exoskeletons do not have direct neural input from the user which makes adaptation of exoskeleton dynamics based on user intent difficult. Proportional myoelectric control has proven to allow considerable adaptation in muscle activation and gait kinematics in pneumatic, tethered ankle exoskeletons. In this study we quantified the changes in muscle activity and joint biomechanics of twelve participants walking for 30 minutes on a treadmill.

RESULTS

The exoskeletons provided 29% of the peak total ankle power and 18% of the peak total ankle moment by the end of the practice session. There was a decrease of 12% in soleus, 17% in lateral gastrocnemius and 5% in medial gastrocnemius electromyography (EMG) root mean square (root mean squared) after walking with the exoskeleton for 30 minutes compared to not wearing the exoskeleton, but this difference was not statistically significant. There were no differences in joint biomechanics of the ankle, hip, or knee between the end of training compared to walking without the exoskeletons.

CONCLUSIONS

Contrary to expectations, triceps surae muscle activity showed only small non-significant decreases in 30 minutes of walking with portable, electromechanical ankle exoskeletons under proportional myoelectric control. The commercially available ankle exoskeletons were likely too weak to produce a statistically meaningful decline in triceps surae recruitment. Future research should include a wider variety of tasks, including measurements of metabolic energy expenditure, and provide a longer period of adaptation to evaluate the ankle exoskeletons.

Spatiotemporal Compliance Control for a Wearable Lower Limb Rehabilitation Robot

Compliance control is crucial for physical human-robot interaction, which can enhance the safety and comfort of robot-assisted rehabilitation. In this study, we designed a spatiotemporal compliance control strategy for a new self-designed wearable lower limb rehabilitation robot (WLLRR), allowing the users to regulate the spatiotemporal characteristics of their motion. The high-level trajectory planner consists of a trajectory generator, an interaction torque estimator, and a gait speed adaptive regulator, which can provide spatial and temporal compliance for the WLLRR. A radial basis function neural network adaptive controller is adopted as the low-level position controller. Over-ground walking experiments with passive control, spatial compliance control, and spatiotemporal compliance control strategies were conducted on five healthy participants, respectively. The results demonstrated that the spatiotemporal compliance control strategy allows participants to adjust reference trajectory through physical human-robot interaction, and can adaptively modify gait speed according to participants' motor performance. It was found that the spatiotemporal compliance control strategy could provide greater enhancement of motor variability and reduction of interaction torque than other tested control strategies. Therefore, the spatiotemporal compliance control strategy has great potential in robot-assisted rehabilitation training and other fields involving physical human-robot interaction.

A mechatronic leg replica to benchmark human-exoskeleton physical interactions

Evaluating human-exoskeleton interaction typically requires experiments with human subjects, which raises safety issues and entails time-consuming testing procedures. This paper presents a mechatronic replica of a human leg, which was designed to quantify physical interaction dynamics between exoskeletons and human limbs without the need for human testing. In the first part of this work, we present the mechanical, electronic, sensory system and software solutions integrated in our leg replica prototype. In the second part, we used the leg replica to test its interaction with two types of commercially available wearable devices, i.e. an active full leg exoskeleton and a passive knee orthosis. We ran basic test examples to demonstrate the functioning and benchmarking potential of the leg replica to assess the effects of joint misalignments on force transmission. The integrated force sensors embedded in the leg replica detected higher interaction forces in the misaligned scenario in comparison to the aligned one, in both active and passive modalities. The small standard deviation of force measurements across cycles demonstrates the potential of the leg replica as a standard test method for reproducible studies of human-exoskeleton physical interaction.

Ankle strategy assistance to improve gait stability using controllers based on in-shoe center of pressure in 2 degree-of-freedom powered ankle-foot orthoses: a clinical study

Background

Although the ankle strategy is important for achieving frontal plane stability during one-leg stance, previously developed powered ankle–foot orthoses (PAFOs) did not involve ankle strategies because of hardware limitations. Weakness of movement in frontal plane is a factor that deteriorates gait stability and increases fall risk so it should not be overlooked in rehabilitation. Therefore, we used PAFO with subtalar joint for frontal plane movement and tried to confirm that the existence of it is important in balancing through clinical experiments.

Methods

We developed a proportional CoP controller to assist ankle strategy or stabilizing moment and enhance eversion to compensate for the tilting moment with 2 dof PAFO. It was true experimental study, and we recruited seven healthy subjects (30 ± 4 years) who did not experience any gait abnormality participated in walking experiments for evaluating the immediate effect of subtalar joint of PAFO on their gait stability. They walked on the treadmill with several cases of controllers for data acquisitions. Indices of gait stability and electromyography for muscle activity were measured and Wilcoxon signed-rank tests were used to identify meaningful changes.

Results

We found that subjects were most stable during walking (in terms of largest Lyapunov exponents, p < 0.008) with the assistance of the PAFO when their electromyographic activity was the most reduced (p < 0.008), although postural sway increased when a proportional CoP controller was used to assist the ankle strategy (p < 0.008). Other indices of gait stability, kinematic variability, showed no difference between the powered and unpowered conditions (p > 0.008). The results of the correlation analysis indicate that the actuator of the PAFO enhanced eversion and preserved the location of the CoP in the medial direction so that gait stability was not negatively affected or improved.

Conclusions

We verified that the developed 2 dof PAFO assists the ankle strategy by compensating for the tilting moment with proportional CoP controller and that wearer can walk in a stable state when the orthosis provides power for reducing muscle activity. This result is meaningful because an ankle strategy should be considered in the development of PAFOs for enhancing or even rehabilitating proprioception.

Trial registration 7001988-202003-HR-833-03

Characterization and Evaluation of Human-Exoskeleton Interaction Dynamics: A Review

Exoskeletons and exosuits have witnessed unprecedented growth in recent years, especially in the medical and industrial sectors. In order to be successfully integrated into the current society, these devices must comply with several commercialization rules and safety standards. Due to their intrinsic coupling with human limbs, one of the main challenges is to test and prove the quality of physical interaction with humans. However, the study of physical human-exoskeleton interactions (pHEI) has been poorly addressed in the literature. Understanding and identifying the technological ways to assess pHEI is necessary for the future acceptance and large-scale use of these devices. The harmonization of these evaluation processes represents a key factor in building a still missing accepted framework to inform human-device contact safety. In this review, we identify, analyze, and discuss the metrics, testing procedures, and measurement devices used to assess pHEI in the last ten years. Furthermore, we discuss the role of pHEI in safety contact evaluation. We found a very heterogeneous panorama in terms of sensors and testing methods, which are still far from considering realistic conditions and use-cases. We identified the main gaps and drawbacks of current approaches, pointing towards a number of promising research directions. This review aspires to help the wearable robotics community find agreements on interaction quality and safety assessment testing procedures.

Human-device interface pressure measurement in prosthetic, orthotic and exoskeleton applications: A systematic review

This study aimed to investigate normal and shear load sensor technology that has been characterised and used at the human-device interface in prosthetic, orthotic and exoskeleton applications. In addition to taking a cross-disciplinary view, this study expands on previous reviews by considering recently published papers, clinical translation of sensors, and development of the sensor technology itself. A search of MEDLINE, INSPEC, SCOPUS and Web of Science was performed up to 26 January 2021. A total of 33 studies were assessed for quality and their data extracted. The review found variable quality of published papers, with normal load being most commonly measured, and resistive sensor technology most commonly used. The translation to clinical environments was indicated in most studies, though the study population was not always made up of the target users. Studies could benefit from more direct comparison with clinically relevant load thresholds and by ensuring clinical testing is performed in the most realistic and representative way possible. Additionally, more focus on developing sensors that measure shear loads would enable further insights into conditions at the human-device interface. Finally, all researchers would benefit from better and more widespread anonymous data sharing practices to facilitate further experimentation.