A comparison between control methods for implanted FES hand-grasp systems

A Virtual Reality-Based Protocol to Determine the Preferred Control Strategy for Hand Neuroprostheses in People With Paralysis

Hand neuroprostheses restore voluntary movement in people with paralysis through neuromodulation protocols. There are a variety of strategies to control hand neuroprostheses, which can be based on residual body movements or brain activity. There is no universally superior solution, rather the best approach may vary from patient to patient. Here, we propose a protocol based on an immersive virtual reality (VR) environment that simulates the use of a hand neuroprosthesis to allow patients to experience and familiarize themselves with various control schemes in clinically relevant tasks and choose the preferred one. We used our VR environment to compare two alternative control strategies over 5 days of training in four patients with C6 spinal cord injury: (a) control via the ipsilateral wrist, (b) control via the contralateral shoulder. We did not find a one-fits-all solution but rather a subject-specific preference that could not be predicted based only on a general clinical assessment. The main results were that the VR simulation allowed participants to experience the pros and cons of the proposed strategies and make an educated choice, and that there was a longitudinal improvement. This shows that our VR-based protocol is a useful tool for personalization and training of the control strategy of hand neuroprostheses, which could help to promote user comfort and thus acceptance.

Implanted Electrodes for Functional Electrical Stimulation to Restore Upper and Lower Extremity Function: History and Future Directions

Functional electrical stimulation (FES) to activate nerves and muscles in paralyzed extremities has considerable promise to improve outcome after neurological disease or injury, especially in individuals who have upper motor nerve dysfunction due to central nervous system pathology. Because technology has improved, a wide variety of methods for providing electrical stimulation to create functional movements have been developed, including muscle stimulating electrodes, nerve stimulating electrodes, and hybrid constructs. However, in spite of decades of success in experimental settings with clear functional improvements for individuals with paralysis, the technology has not yet reached widespread clinical translation. In this review, we outline the history of FES techniques and approaches and describe future directions in evolution of the technology.

Design and Testing of Stimulation and Myoelectric Recording Modules in an Implanted Distributed Neuroprosthetic System

Implantable motor neuroprostheses can restore functionality to individuals with neurological disabilities by electrically activating paralyzed muscles in coordinated patterns. The typical design of neuroprosthetic systems relies on a single multi-use device, but this limits the number of stimulus and sensor channels that can be practically implemented. To address this limitation, a modular neuroprosthesis, the "Networked Neuroprosthesis" (NNP), was developed. The NNP system is the first fully implanted modular neuroprosthesis that includes implantation of all power, signal processing, biopotential signal recording, and stimulating components. This paper describes the design of stimulation and recording modules, bench testing to verify stimulus outputs and appropriate filtering and recording, and validation that the components function properly while implemented in persons with spinal cord injury. The results of system testing demonstrated that the NNP was functional and capable of generating stimulus pulses and recording myoelectric, temperature, and accelerometer signals. Based on the successful design, manufacturing, and testing of the NNP System, multiple clinical applications are anticipated.

Control Modification of Grasp Force Covaries Agency and Performance on Rigid and Compliant Surfaces

This study investigated how modifications in the display of a computer trace under user control of grasp forces can co-modulate agency (perception of control) and performance of grasp on rigid and compliant surfaces. We observed positive correlation (p < 0.01) between implicit agency, measured from time-interval estimation for intentional binding, and grasp performance, measured by force-tracking error, across varying control modes for each surface type. The implications of this work are design directives for cognition-centered device interfaces for rehabilitation of grasp after neurotraumas such as spinal cord and brain injuries while considering if grasp interaction is rigid or compliant. These device interfaces should increase user integration to virtual reality training and powered assistive devices such as exoskeletons and prostheses. The modifications in control modes for this study included changes in force magnitude, addition of mild noise, and a measure of automation. Significant differences (p < 0.001) were observed for each surface type across control modes with metrics for implicit agency, performance, and grasp control efficiency. Explicit agency, measured from user survey responses, did not exhibit significant variations in this study, suggesting implicit measures of agency are needed for identifying co-modulation with grasp performance. Grasp on the compliant surface resulted in greater dependence of performance on agency and increases in agency and performance with the addition of mild noise. Noise in conjunction with perceived freedom at a flexible surface may have amplified visual feedback responses. Introducing automation in control decreased agency and performance for both surfaces, suggesting the value in continuous user control of grasp. In conclusion, agency and performance of grasp can be co-modulated across varying modes of control, especially for compliant grasp actions. Future studies should consider reliable measures of implicit agency, including physiological recordings, to automatically adapt rehabilitation interfaces for better cognitive engagement and to accelerate functional outcomes.

A Case Study With Symbihand: An sEMG-Controlled Electrohydraulic Hand Orthosis for Individuals With Duchenne Muscular Dystrophy

With recent improvements in healthcare, individuals with Duchenne muscular dystrophy (DMD) have prolonged life expectancy, and it is therefore vital to preserve their independence. Hand function plays a central role in maintaining independence in daily living. This requires sufficient grip force and the ability to modulate it with no substantially added effort. Individuals with DMD have low residual grip force and its modulation is challenging and fatiguing. To assist their hand function, we developed a novel dynamic hand orthosis called SymbiHand, where the user's hand motor intention is decoded by means of surface electromyography, enabling the control of an electrohydraulic pump for actuation. Mechanical work is transported using hydraulic transmission and flexible structures to redirect interaction forces, enhancing comfort by minimizing shear forces. This paper outlines SymbiHand's design and control, and a case study with an individual with DMD. Results show that SymbiHand increased the participant's maximum grasping force from 2.4 to 8 N. During a grasping force-tracking task, muscular activation was decreased by more than 40% without compromising task performance. These results suggest that SymbiHand has the potential to decrease muscular activation and increase grasping force for individuals with DMD, adding to the hand a total mass of no more than 241 g. Changes in mass distributions and an active thumb support are necessary for improved usability, in addition to larger-scale studies for generalizing its assistive potential.

A Rare Case of Cervical Charcot After Spinal Cord Injury: A Case Report

CASE

We present a rare case of cervical Charcot disease that was diagnosed in a paraplegic patient by loss of function caudal to the original level of spinal cord injury. Clinical imaging, diagnosis, differentials, and operative management are discussed.

CONCLUSIONS

Charcot disease of the cervical spine is rare and very difficult to diagnose in the paraplegic patient population. High clinical suspicion should be maintained in these patients who demonstrate any form of neurologic deterioration, mechanical instability, or change in spinal alignment. It is often necessary to rule out infection. Spinal decompression and surgical stabilization is the treatment of choice.

Myoelectric signal from below the level of spinal cord injury as a command source for an implanted upper extremity neuroprosthesis - a case report

Implanted motor neuroprostheses offer significant restoration of function for individuals with spinal cord injury. Providing adequate user control for these devices is a challenge but is crucial for successful performance. Electromyographic (EMG) signals can serve as effective control sources, but the number of above-injury muscles suitable to provide EMG-based control signals is very limited. Previous work has shown the presence of below-injury volitional myoelectric signals even in subjects diagnosed with motor complete spinal cord injury. In this case report, we present a demonstration of a hand grasp neuroprosthesis being controlled by a user with a C6 level, motor complete injury through EMG signals from their toe flexor. These signals were successfully translated into a functional grasp output, which performed similarly to the participant’s usual shoulder position control in a grasp-release functional test. This proof-of-concept demonstrates the potential for below-injury myoelectric activity to serve as a novel form of neuroprosthesis control.

Investigating Upper Limb Movement Classification on Users with Tetraplegia as a Possible Neuroprosthesis Interface

Spinal cord injury (SCI), stroke and other nervous system conditions can result in partial or total paralysis of individual's limbs. Numerous technologies have been proposed to assist neurorehabilitation or movement restoration, e.g. robotics or neuroprosthesis. However, individuals with tetraplegia often find difficult to pilot these devices. We developed a system based on a single inertial measurement unit located on the upper limb that is able to classify performed movements using principal component analysis. We analyzed three calibration algorithms: unsupervised learning, supervised learning and adaptive learning. Eight participants with tetraplegia (C4C7) piloted three different postures in a robotic hand. We achieved 89% accuracy using the supervised learning algorithm. Through offline simulation, we found accuracies of 76% on the unsupervised learning, and 88% on the adaptive one.

Evolution of Neuroprosthetic Approaches to Restoration of Upper Extremity Function in Spinal Cord Injury

Background: Spinal cord injury (SCI) occurring at the cervical levels can result in significantly impaired arm and hand function. People with cervical-level SCI desire improved use of their arms and hands, anticipating that regained function will result in improved independence and ultimately improved quality of life. Neuroprostheses provide the most promising method for significant gain in hand and arm function for persons with cervical-level SCI. Neuroprostheses utilize small electrical currents to activate peripheral motor nerves, resulting in controlled contraction of paralyzed muscles. Methods: A myoelectrically-controlled neuroprosthesis was evaluated in 15 arms in 13 individuals with cervical-level SCI. All individuals had motor level C5 or C6 tetraplegia. Results: This study demonstrates that an implanted neuroprosthesis utilizing myoelectric signal (MES)-controlled stimulation allows considerable flexibility in the control algorithms that can be utilized for a variety of arm and hand functions. Improved active range of motion, grip strength, and the ability to pick up and release objects were improved in all arms tested. Adverse events were few and were consistent with the experience with similar active implantable devices. Conclusion: For individuals with cervical SCI who are highly motivated, implanted neuroprostheses provide the opportunity to gain arm and hand function that cannot be gained through the use of orthotics or surgical intervention alone. Upper extremity neuroprostheses have been shown to provide increased function and independence for persons with cervical-level SCI.

A Knowledge Based System for the Selection of Muscles for Gait Phase Detection using EMGs

Purpose: This paper presents the development of a knowledge based system for the detection of gait phases based on EMGs from muscles of the lower limb. Methods: An empirical analysis of the EMG characteristics for the most representative muscle of every muscle group concerning their suitability for the gait phase detection is presented. The same approach is applied to every lower limb muscle where an EMG could be received. The entities and the decision-making mechanism of the knowledge based system is presented in a formal way. Results: A knowledge based system is built upon the knowledge acquired from this analysis. Finally, an example is presented where the developed knowledge based system is used to support the conceptual design of a drop foot correction system. Conclusions: The knowledge based system can be used in the conceptual design of any rehabilitation system for lower limb disabilities using EMG signals from the lower limbs.

A Novel EMG Interface for Individuals With Tetraplegia to Pilot Robot Hand Grasping

This paper introduces a new human-machine interface for individuals with tetraplegia. We investigated the feasibility of piloting an assistive device by processing supra-lesional muscle responses online. The ability to voluntarily contract a set of selected muscles was assessed in five spinal cord-injured subjects through electromyographic (EMG) analysis. Two subjects were also asked to use the EMG interface to control palmar and lateral grasping of a robot hand. The use of different muscles and control modalities was also assessed. These preliminary results open the way to new interface solutions for high-level spinal cord-injured patients.

Rebuilding motor function of the spinal cord based on functional electrical stimulation

Rebuilding the damaged motor function caused by spinal cord injury is one of the most serious challenges in clinical neuroscience. The function of the neural pathway under the damaged sites can be rebuilt using functional electrical stimulation technology. In this study, the locations of motor function sites in the lumbosacral spinal cord were determined with functional electrical stimulation technology. A three-dimensional map of the lumbosacral spinal cord comprising the relationship between the motor function sites and the corresponding muscle was drawn. Based on the individual experimental parameters and normalized coordinates of the motor function sites, the motor function sites that control a certain muscle were calculated. Phasing pulse sequences were delivered to the determined motor function sites in the spinal cord and hip extension, hip flexion, ankle plantarflexion, and ankle dorsiflexion movements were successfully achieved. The results show that the map of the spinal cord motor function sites was valid. This map can provide guidance for the selection of electrical stimulation sites during the rebuilding of motor function after spinal cord injury.

Neuromuscular Electrical Stimulation for Motor Restoration in Hemiparesis

This article assesses the clinical efficacy of established neuromuscular electrical stimulation (NMES) technologies for motor restoration in hemiparesis and provides an overview of evolving technologies. Transcutaneous NMES facilitates motor recovery. However, its impact on physical disability remains uncertain. Transcutaneous NMES also decreases shoulder subluxation, but its effect on shoulder pain remains uncertain. Clinically deployable upper extremity neuroprosthesis systems will not be available until sometime in the distant future. However, there is stronger evidence for the clinical utility of lower extremity neuroprosthesis systems. Evolving technology utilizes semi-implanted or fully implanted systems with more sophisticated control paradigms. Initial experiences with these systems are reviewed and directions for future research are discussed in this article.

Advances in functional electrical stimulation (FES)

This review discusses the advancements that are needed to enhance the effects of electrical stimulation for restoring or assisting movement in humans with an injury/disease of the central nervous system. A complex model of the effects of electrical stimulation of peripheral systems is presented. The model indicates that both the motor and sensory systems are activated by electrical stimulation. We propose that a hierarchical hybrid controller may be suitable for functional electrical stimulation (FES) because this type of controller acts as a structural mimetic of its biological counterpart. Specific attention is given to the neural systems at the periphery with respect to the required electrodes and stimulators. Furthermore, we note that FES with surface electrodes is preferred for the therapy, although there is a definite advantage associated with implantable technology for life-long use. The last section of the review discusses the potential need to combine FES and robotic systems to provide assistance in some cases.

Multimodal decoding and congruent sensory information enhance reaching performance in subjects with cervical spinal cord injury

Cervical spinal cord injury (SCI) paralyzes muscles of the hand and arm, making it difficult to perform activities of daily living. Restoring the ability to reach can dramatically improve quality of life for people with cervical SCI. Any reaching system requires a user interface to decode parameters of an intended reach, such as trajectory and target. A challenge in developing such decoders is that often few physiological signals related to the intended reach remain under voluntary control, especially in patients with high cervical injuries. Furthermore, the decoding problem changes when the user is controlling the motion of their limb, as opposed to an external device. The purpose of this study was to investigate the benefits of combining disparate signal sources to control reach in people with a range of impairments, and to consider the effect of two feedback approaches. Subjects with cervical SCI performed robot-assisted reaching, controlling trajectories with either shoulder electromyograms (EMGs) or EMGs combined with gaze. We then evaluated how reaching performance was influenced by task-related sensory feedback, testing the EMG-only decoder in two conditions. The first involved moving the arm with the robot, providing congruent sensory feedback through their remaining sense of proprioception. In the second, the subjects moved the robot without the arm attached, as in applications that control external devices. We found that the multimodal-decoding algorithm worked well for all subjects, enabling them to perform straight, accurate reaches. The inclusion of gaze information, used to estimate target location, was especially important for the most impaired subjects. In the absence of gaze information, congruent sensory feedback improved performance. These results highlight the importance of proprioceptive feedback, and suggest that multi-modal decoders are likely to be most beneficial for highly impaired subjects and in tasks where such feedback is unavailable.

Biomechanical evaluation of wrist-driven flexor hinge orthosis in persons with spinal cord injury

The wrist-driven flexor hinge orthosis (WDFHO) is a device used to restore hand function in persons with tetraplegic spinal cord injury by furnishing three-point prehension. We assessed the effectiveness and biomechanical properties of the WDFHO in 24 persons with cervical 6 or 7 tetraplegia who have severely impaired hand function. This study introduces a mechanical operating model to assess the efficiency of the WDFHO. Experimental results showed that pinch force increased significantly (p < 0.001) after using the WDFHO and was found to positively correlate with the strength of wrist extensor muscles (r = 0.41, p < 0.001). However, when the strength of the wrist extensors acting on the WDFHO was greater, the reciprocal wrist and finger motion that generates three-point prehension was less effective (r = 0.79, p < 0.001). Reliable and valid biomechanical evaluation of the WDFHO could improve our understanding of its biomechanics.

Command and control interfaces for advanced neuroprosthetic applications

Command and control interfaces permit the intention and situation of the user to influence the operation of the neural prosthesis. The wishes of the user are communicated via command interfaces to the neural prosthesis and the situation of the user by feedback control interfaces. Both these interfaces have been reviewed separately and are discussed in light of the current state of the art and projections for the future. It is apparent that as system functional complexity increases, the need for simpler command interfaces will increase. Such systems will demand more information to function effectively in order not to unreasonably increase user attention overhead. This will increase the need for bioelectric and biomechanical signals in a comprehensible form via elegant feedback control interfaces. Implementing such systems will also increase the computational demand on such neural prostheses.

Three-Dimensional Model to Predict Muscle Forces and Their Relation to Motor Variances in Reaching Arm Movements

A three-dimensional (3-D) arm movement model is presented to simulate kinematic properties and muscle forces in reaching arm movements. Healthy subjects performed reaching movements repetitively either with or without a load in the hand. Joint coordinates were measured. Muscle moment arms, 3-D angular acceleration, and moment of inertias of arm segments were calculated to determine 3-D joint torques. Variances of hand position, arm configuration, and muscle activities were calculated. Ratios of movement variances observed in the two conditions (load versus without load) showed no differences for hand position and arm configuration variances. Virtual muscle force variances for all muscles except deltoid posterior and EMG variances for four muscles increased significantly by moving with the load. The greatly increased variances in muscle activity did not imply equally high increments in kinematic variances. We conclude that enhanced muscle cooperation through synergies helps to stabilize movement at the kinematic level when a load is added.

Application of system identification methods for decoding imagined single-joint movements in an individual with high tetraplegia

This study investigated the decoding of imagined arm movements from M1 in an individual with high level tetraplegia. The participant was instructed to imagine herself performing a series of single-joint arm movements, aided by the visual cue of an animate character performing these movements. System identification was used offline to predict the trajectories of the imagined movements and compare these predictions to the trajectories of the actual movements. We report rates of 25 - 50% for predicting completely imagined arm movements in the absence of a priori movements to aid in decoder building.

Advances in the use of electrical stimulation for the recovery of motor function

This chapter sheds light on several issues that are being explored to optimize the application of electrical stimulation in a motor neural prosthesis (MNP) for the restoration of movement in humans with paralysis. Although several MNPs are commercially available, there are issues that limit their use in therapy and/or daily assistance: (1) the users' intention of what and how to move needs to be effectively transmitted to the MNP controller; (2) interface to the neural pathways that leads to physiological-like activation should be improved; (3) artificial control of the MNP should match the biological control of the preserved biological systems; and (4) sensors information should be fused and provided to both the controller of the MNP and the user. We suggest that with the improved use of cortical or other physiological signals, application of multipad electrodes with special protocols, rule-based control that mimics biological control, and with the incorporation of micro- and nanotechnologies, wireless communications, and microcontrollers, the MNP operation can be greatly enhanced. The chapter specifically addresses the control of MNP for the upper extremities and provides details on the new surface multipad electrodes that are of interest for neurorehabilitation of stroke patients.

Design and testing of an advanced implantable neuroprosthesis with myoelectric control

An implantable stimulator-telemeter (IST-12) was developed for applications in neuroprosthetic restoration of limb function in paralyzed individuals. The IST-12 provides 12 stimulation channels and two myoelectric signal (MES) channels. The MES circuitry includes a two-channel multiplexer, preamplifier, variable gain amplifier/bandpass filter, full-wave rectifier, and bin integrator. Power and control signals are transmitted from an external control unit to the IST-12 through an inductive link. Recorded MES signals are telemetered back to the external control unit through the same inductive link. Following bench testing, one device was implanted chronically in a dog for 15 months and evaluated. Conditions were identified in which MES could be recorded with minimal stimulus artifact. The ability to record MES in the presence of stimulation was verified, confirming the potential of the IST-12 to be used as a myoelectric controlled neuroprosthesis.

Toward the restoration of hand use to a paralyzed monkey: brain-controlled functional electrical stimulation of forearm muscles

Loss of hand use is considered by many spinal cord injury survivors to be the most devastating consequence of their injury. Functional electrical stimulation (FES) of forearm and hand muscles has been used to provide basic, voluntary hand grasp to hundreds of human patients. Current approaches typically grade pre-programmed patterns of muscle activation using simple control signals, such as those derived from residual movement or muscle activity. However, the use of such fixed stimulation patterns limits hand function to the few tasks programmed into the controller. In contrast, we are developing a system that uses neural signals recorded from a multi-electrode array implanted in the motor cortex; this system has the potential to provide independent control of multiple muscles over a broad range of functional tasks. Two monkeys were able to use this cortically controlled FES system to control the contraction of four forearm muscles despite temporary limb paralysis. The amount of wrist force the monkeys were able to produce in a one-dimensional force tracking task was significantly increased. Furthermore, the monkeys were able to control the magnitude and time course of the force with sufficient accuracy to track visually displayed force targets at speeds reduced by only one-third to one-half of normal. Although these results were achieved by controlling only four muscles, there is no fundamental reason why the same methods could not be scaled up to control a larger number of muscles. We believe these results provide an important proof of concept that brain-controlled FES prostheses could ultimately be of great benefit to paralyzed patients with injuries in the mid-cervical spinal cord.

Feasibility of EMG-based neural network controller for an upper extremity neuroprosthesis

The overarching goal of this project is to provide shoulder and elbow function to individuals with C5/C6 spinal cord injury (SCI) using functional electrical stimulation (FES), increasing the functional outcomes currently provided by a hand neuroprosthesis. The specific goal of this study was to design a controller based on an artificial neural network (ANN) that extracts information from the activity of muscles that remain under voluntary control sufficient to predict appropriate stimulation levels for several paralyzed muscles in the upper extremity. The ANN was trained with activation data obtained from simulations using a musculoskeletal model of the arm that was modified to reflect C5 SCI and FES capabilities. Several arm movements were recorded from able-bodied subjects and these kinematics served as the inputs to inverse dynamic simulations that predicted muscle activation patterns corresponding to the movements recorded. A system identification procedure was used to identify an optimal reduced set of voluntary input muscles from the larger set that are typically under voluntary control in C5 SCI. These voluntary activations were used as the inputs to the ANN and muscles that are typically paralyzed in C5 SCI were the outputs to be predicted. The neural network controller was able to predict the needed FES paralyzed muscle activations from "voluntary" activations with less than a 3.6% RMS prediction error.

The development of a new orthosis (neuro-orthosis) for patients with carpal tunnel syndrome: its effect on the function and strength of the hand

Static wrist orthoses (SWOs) are used in the treatment of carpal tunnel syndrome (CTS) with some drawbacks. As an alternate approach to SWOs, an active closed-loop wrist control strategy based on the principles of functional electrical stimulation was proposed to limit wrist movements. The purpose of the study was to determine whether the proposed 'neuro-orthosis' (NeO) system resulted in less restriction in the hand compared to clinically accepted custom-made SWOs while limiting the wrist movements. A case-control study was designed to determine the specific effects of the system on patients with CTS. A total of 24 right-handed female volunteers (12: CTS, 12: healthy) participated in the study. Function, dexterity, and strengths were measured under three different testing conditions: without orthosis, with SWO, and with the NeO system. Maximum angles in one subtest while the NeO system was on and off and general discomfort levels in SWO and NeO test conditions were recorded. The NeO system resulted in less restriction with respect to SWO and provided considerable angular limitation compared to placebo. It was concluded that the proposed prototype control system can be a good candidate to limit the wrist movements in place of SWOs with a better degree of freedom in patients with CTS.

An implanted upper-extremity neuroprosthesis using myoelectric control

PURPOSE

The purpose of this study was to evaluate the potential of a second-generation implantable neuroprosthesis that provides improved control of hand grasp and elbow extension for individuals with cervical level spinal cord injury. The key feature of this system is that users control their stimulated function through electromyographic (EMG) signals.

METHODS

The second-generation neuroprosthesis consists of 12 stimulating electrodes, 2 EMG signal recording electrodes, an implanted stimulator-telemeter device, an external control unit, and a transmit/receive coil. The system was implanted in a single surgical procedure. Functional outcomes for each subject were evaluated in the domains of body functions and structures, activity performance, and societal participation.

RESULTS

Three individuals with C5/C6 spinal cord injury received system implantation with subsequent prospective evaluation for a minimum of 2 years. All 3 subjects demonstrated that EMG signals can be recorded from voluntary muscles in the presence of electrical stimulation of nearby muscles. Significantly increased pinch force and grasp function was achieved for each subject. Functional evaluation demonstrated improvement in at least 5 activities of daily living using the Activities of Daily Living Abilities Test. Each subject was able to use the device at home. There were no system failures. Two of 6 EMG electrodes required surgical revision because of suboptimal location of the recording electrodes.

CONCLUSIONS

These results indicate that a neuroprosthesis with implanted myoelectric control is an effective method for restoring hand function in midcervical level spinal cord injury.

A control system for a powered prosthesis using positional and myoelectric inputs from the shoulder complex

The integration of multiple input sources within a control strategy for powered upper limb prostheses could provide smoother, more intuitive multi-joint reaching movements based on the user's intended motion. The work presented in this paper presents the results of using myoelectric signals (MES) of the shoulder area in combination with the position of the shoulder as input sources to multiple linear discriminant analysis classifiers. Such an approach may provide users with control signals capable of controlling three degrees of freedom (DOF). This work is another important step in the development of hybrid systems that will enable simultaneous control of multiple degrees of freedom used for reaching tasks in a prosthetic limb.

Neuromuscular electrical stimulation in neurorehabilitation

This review provides a comprehensive overview of the clinical uses of neuromuscular electrical stimulation (NMES) for functional and therapeutic applications in subjects with spinal cord injury or stroke. Functional applications refer to the use of NMES to activate paralyzed muscles in precise sequence and magnitude to directly accomplish functional tasks. In therapeutic applications, NMES may lead to a specific effect that enhances function, but does not directly provide function. The specific neuroprosthetic or "functional" applications reviewed in this article include upper- and lower-limb motor movement for self-care tasks and mobility, respectively, bladder function, and respiratory control. Specific therapeutic applications include motor relearning, reduction of hemiplegic shoulder pain, muscle strengthening, prevention of muscle atrophy, prophylaxis of deep venous thrombosis, improvement of tissue oxygenation and peripheral hemodynamic functioning, and cardiopulmonary conditioning. Perspectives on future developments and clinical applications of NMES are presented.

On the design of robotic hands for brain–machine interface

✓ Brain–machine interface (BMI) is the latest solution to a lack of control for paralyzed or prosthetic limbs. In this paper the authors focus on the design of anatomical robotic hands that use BMI as a critical intervention in restorative neurosurgery and they justify the requirement for lower-level neuromusculoskeletal details (relating to biomechanics, muscles, peripheral nerves, and some aspects of the spinal cord) in both mechanical and control systems. A person uses his or her hands for intimate contact and dexterous interactions with objects that require the user to control not only the finger endpoint locations but also the forces and the stiffness of the fingers. To recreate all of these human properties in a robotic hand, the most direct and perhaps the optimal approach is to duplicate the anatomical musculoskeletal structure. When a prosthetic hand is anatomically correct, the input to the device can come from the same neural signals that used to arrive at the muscles in the original hand. The more similar the mechanical structure of a prosthetic hand is to a human hand, the less learning time is required for the user to recreate dexterous behavior. In addition, removing some of the nonlinearity from the relationship between the cortical signals and the finger movements into the peripheral controls and hardware vastly simplifies the needed BMI algorithms. (Nonlinearity refers to a system of equations in which effects are not proportional to their causes. Such a system could be difficult or impossible to model.) Finally, if a prosthetic hand can be built so that it is anatomically correct, subcomponents could be integrated back into remaining portions of the user's hand at any transitional locations. In the near future, anatomically correct prosthetic hands could be used in restorative neurosurgery to satisfy the user's needs for both aesthetics and ease of control while also providing the highest possible degree of dexterity.

Application of a neuro-fuzzy network for gait event detection using electromyography in the child with cerebral palsy

An adaptive neuro-fuzzy inference system (ANFIS) with a supervisory control system (SCS) was used to predict the occurrence of gait events using the electromyographic (EMG) activity of lower extremity muscles in the child with cerebral palsy (CP). This is anticipated to form the basis of a control algorithm for the application of electrical stimulation (ES) to leg or ankle muscles in an attempt to improve walking ability. Either surface or percutaneous intramuscular electrodes were used to record the muscle activity from the quadriceps muscles, with concurrent recording of the gait cycle performed using a VICON motion analysis system for validation of the ANFIS with SCS. Using one EMG signal and its derivative from each leg as its inputs, the ANFIS with SCS was able to predict all gait events in seven out of the eight children, with an average absolute time differential between the VICON recording and the ANFIS prediction of less than 30 ms. Overall accuracy in predicting gait events ranged from 98.6% to 95.3% (root mean-squared error between 0.7 and 1.5). Application of the ANFIS with the SCS to the prediction of gait events using EMG data collected two months after the initial data demonstrated comparable results, with no significant differences between gait event detection times. The accuracy rate and robustness of the ANFIS with SCS with two EMG signals suggests its applicability to ES control.

Functional Electrical Stimulation for Neuromuscular Applications

Paralyzed or paretic muscles can be made to contract by applying electrical currents to the intact peripheral motor nerves innervating them. When electrically elicited muscle contractions are coordinated in a manner that provides function, the technique is termed functional electrical stimulation (FES). In more than 40 years of FES research, principles for safe stimulation of neuromuscular tissue have been established, and methods for modulating the strength of electrically induced muscle contractions have been discovered. FES systems have been developed for restoring function in the upper extremity, lower extremity, bladder and bowel, and respiratory system. Some of these neuroprostheses have become commercialized products, and others are available in clinical research settings. Technological developments are expected to produce new systems that have no external components, are expandable to multiple applications, are upgradable to new advances, and are controlled by a combination of signals, including biopotential signals from nerve, muscle, and the brain.

Transcutaneous functional electrical stimulation for grasping in subjects with cervical spinal cord injury

STUDY DESIGN

Case series.

OBJECTIVES

To evaluate the benefit, shortcomings and acceptance of a new transcutaneous functional electrical stimulation (FES) technology aimed at improving the grasp function in tetraplegic subjects in acute and postacute rehabilitation.

SETTING

Spinal cord injury (SCI) centre, university hospital.

METHODS

: Subjects (N=11) with complete or incomplete SCI at C4/5-C7 who started FES 1-67 months after their accident were included. Hand function tests, analysis of video recordings and of written documentation of FES sessions, status of muscle strength, and follow-up query were used as outcome measures.

RESULTS

Nine subjects used FES as a neuroprosthesis. Eight demonstrated improved grasp function and performance in activities of daily living. In one subject, no benefit from FES was observed. Two other subjects showed improvements in muscle strength and facilitation of active movement with FES. Four subjects successfully integrated FES as neuroprosthesis in everyday life within the rehabilitation centre. Three received the system for home use. The most relevant reasons for stopping the FES application were: (i) improvement of voluntary grasp function, (ii) physical and psychological problems, (iii) no available stimulator for home use, and (iv) insufficient assistance for electrode placement at home. Shortcomings related to the transcutaneous surface technology (eg pain or coactivation of neighbouring muscles) could usually be reduced, or did not limit the efficiency or acceptance of FES. Individually designed digital or analogue control devices were preferred.

CONCLUSION

Tetraplegic subjects in acute and postacute rehabilitation can profit from a new transcutaneous FES system with respect to functional use and independence. It can be implemented in the rehabilitation programme for muscle strengthening and facilitation of voluntary activity. For a successful application of FES, there is a need for individual electrode placement, stimulation programmes, and FES control devices.

Implementation of natural sensory feedback in a portable control system for a hand grasp neuroprosthesis

This paper presents the design and implementation of the first generation of a portable system for a hand grasp neuroprosthesis that is controlled by means of signals from natural sensors in the skin of the index finger. To reduce development time and costs, we based our design on readily available, standardised modules such as a 486DX100 compatible CPU, a data acquisition board, a flash disk storage unit, and a high-efficiency DC/DC switch-mode power supply. Additionally, we designed and built a telemeter to supply an implanted muscle stimulator with power and control data. The signal from the natural sensors was recorded with a cuff electrode implanted around the palmar digital nerve innervating the radial aspect of the index finger. For amplification of the recorded nerve signal, we added an external low-noise nerve signal amplifier. For pre-processing of the recorded nerve signal, an optimised band-pass filter was used. A data-recording unit allowed storage and off-line analysis of the stimulator command and the recorded nerve signal. The portable system was used by a tetraplegic volunteer to test the feasibility of including natural sensors in a hand grasp neuroprosthesis for activities of daily living. The flexibility of the presented system allows rapid prototyping of experimental FES hand grasp systems intended for portable use.

Improving elbow torque output of stroke patients with assistive torque controlled by EMG signals

This paper develops an assistive torque system which uses homogeneic surface electromyogram (EMG) signals to improve the elbow torque capability of stroke patients by applying an external time-varying assistive torque. In determining the magnitude of the torque to apply, the incorporated assistive torque algorithm considers the difference between the weighted biceps and triceps EMG signals such that the applied torque is proportional to the effort supplied voluntarily by the user. The overall stability of the assistive system is enhanced by the incorporation of a nonlinear damping element within the control algorithm which mimics the physiological damping of the elbow joint and the co-contraction between the biceps and triceps. Adaptive filtering of the control signal is employed to achieve a balance between the bandwidth and the system adaptability so as to ensure a smooth assistive torque output. The innovative control algorithm enables the provision of an assistive system whose operation is both natural to use and simple to learn. The effectiveness of the proposed assistive system in assisting elbow movement performance is investigated in a series of tests involving five stroke patients and five able-bodied individuals. The results confirm the ability of the system to assist all of the subjects in performing a number of reaching and tracking tasks with reduced effort and with no sacrifice in elbow movement performance.

Implanted neuroprostheses for restoration of hand function in tetraplegic patients

Restoration of hand function through functional electrical stimulation allows tetraplegic patients to use existing abilities to control paralyzed muscles. In patients with C5 or C6 spinal cord injuries, implanted upper extremity neuroprostheses use functional electrical stimulation technology to power hand and arm muscles. A variety of devices, often using contralateral shoulder motion, sends signals via a small external controller and transmitting coil to an implanted stimulator. The stimulator powers designated upper extremity muscles via implanted electrodes. The surgical procedure is minimally invasive and easily reversed. Palmar and lateral grasp, among other functions, can be reliably restored, leading to significant improvements in functional capacity. High user satisfaction, low complication rates, and recent advances in technology and control systems contribute to the success of this technology in the treatment of devastating spinal cord injuries.

Command control for functional electrical stimulation hand grasp systems using miniature accelerometers and gyroscopes

Recent commercially available miniature sensors have the potential to improve the functions of functional electrical stimulation (FES) systems in terms of control, reliability and robustness. A new control approach using a miniature gyroscope and an accelerometer was studied. These sensors were used to detect the linear acceleration and angular velocity of residual voluntary movements on upper limbs and were small and easy to put on. Five healthy subjects and three cervical spinal cord injured subjects were recruited to evaluate this controller. Sensors were placed on four locations: the shoulder, upper arm, wrist and hand. A quick forward-and-backward movement was employed to produce a distinctive waveform that was different from general movements. A detection algorithm was developed to generate a command signal by identifying this distinctive waveform through the detection of peaks and valleys in the sensor's signals. This command signal was used to control different FES hand grasp patterns. With a specificity of 0.9, the sensors had a success rate of 85-100% on healthy subjects and 82-97% on spinal cord injured subjects. In terms of sensor placement, the gyroscope was better as a control source than the accelerometer for wrist and hand positions, but the reverse was true for the shoulder.

Intramuscular hand neuroprosthesis for chronic stroke survivors

The purpose of this study was to assess the feasibility of a percutaneous hand neuroprosthesis system for stroke survivors. Case reports of 4 chronic stroke survivors who were implanted with percutaneous intramuscular electrodes in various muscles of the forearm for hand grasp and release are presented. A percutaneous hand neuroprosthesis was able to open a spastic hemiparetic hand as long as the upper limb was in a resting position, the wrist and proximal forearm were supported, participants did not try to assist the stimulation, and an individual other than the participant modulated the stimulation. However, when participants tried to assist the stimulation or complete a functional task, hand opening was significantly reduced due to increased finger flexor hypertonia, even with increased stimulation intensity. Similarly, electrically stimulated hand opening was significantly reduced following voluntary hand closure. Techniques that provide real-time modulation of hypertonia with closed loop control, control strategies that are independent of the contralateral limb, and methods to enhance proximal control must be developed to demonstrate the feasibility of a hand neuroprosthesis system for persons with hemiparesis.

Biopotentials as command and feedback signals in functional electrical stimulation systems

Today Functional Electrical Stimulation (FES) is available as a clinical tool in muscle activation used for picking up objects, for standing and walking, for controlling bladder emptying, and for breathing. Despite substantial progress in development and new knowledge, many challenges remain to be resolved to provide a more efficient functionality of FES systems. The most important task of these challenges is to improve control of the activated muscles through open loop or feedback systems. Command and feedback signals can be extracted from biopotentials recorded from muscles (Electromyogram, EMG), nerves (Electroneurogram, ENG), and the brain (Electroencephalogram (EEG) or individual cells). This paper reviews work in which EMG, ENG, and EEG signals in humans have been used as command and feedback signals in systems using electrical stimulation of motor nerves to restore movements after an injury to the Central Nervous System (CNS). It is concluded that the technology is ready to push for more substantial clinical FES investigations in applying muscle and nerve signals. Brain-computer interface systems hold great prospects, but require further development of faster and clinically more acceptable technologies.

Control of a hand grasp neuroprosthesis using an electroencephalogram-triggered switch: demonstration of improvements in performance using wavepacket analysis

Volitionally modulated electroencephalographic (EEG) waves were monitored for the purpose of controlling a hand neuroprosthesis in people with tetraplegia. The region of the EEG signal spectrum monitored was the occipital alpha wave (8-13 Hz), and volitional modulation was achieved with the opening and closing of the eyes. In a set of 13 trials evaluated, a subject with tetraplegia successfully completed ten trials undertaking stimulated grasp and release using the EEG-triggered switch. EEG signal data recorded during the 13 trials were also post-processed off-line using wavepacket analysis. Following this signal processing, the speed and reliability of the EEG-triggered switch, when operated by the subject with tetraplegia, was significantly improved (p < 0.002). Such improvements provide system performance that is likely to be acceptable to a neuroprosthesis user during activities of daily life.

Indications and future directions for upper limb neuroprostheses in tetraplegic patients: a review

The development of the upper extremity neuroprosthesis has been a challenging and rewarding contribution to the management of the SCI patient. The authors' experience and that of their clinical trial teams has verified that this technology is a strong alternative to conventional reconstruction and conservative management. In the future, even more powerful tools will emerge from the laboratory as these devices and collaborative surgical procedures evolve.

Neuroprostheses for grasping

In recent years a number of neuroprostheses have been developed and used to assist stroke and spinal cord injured subjects to restore or improve grasping function. These neuroprostheses clearly demonstrated that the targeted group of subjects can significantly benefit from this technology and that functional electrical stimulation (FES) is a viable method for restoring or improving grasping function. In this article the FES technology is briefly explained and some of the better known neuroprostheses for grasping are discussed. Furthermore, a typical population of subjects that can benefit from this technology is indicated as well as the methodology to select and train these subjects to apply the neuroprosthesis in daily living activities. This article also provides a brief summary of the achieved results with the existing neuroprostheses for grasping and discusses some of the challenges this technology is currently facing.

Evaluation of command algorithms for control of upper-extremity neural prostheses

Five new command control algorithms were created to enable increased control over grasp force in upper-extremity neural prostheses. Most of these algorithms took advantage of the ability to lock or assign a steady command value to the hand neural prosthesis. Five able-bodied subjects tested the algorithms by using a shoulder controller that controlled a video-simulated hand to repeatedly complete a consistent evaluation task. A generalized estimating equations-based linear model was used to analyze the data. The algorithms were ranked via contrast analyses between the coefficient values from the linear model of the proportional control with lock algorithm, which is the algorithm presently used in neural prostheses, and each of the other algorithms. The algorithms that allowed adjustment of the command value after the hand was locked as well as algorithms that allowed a decrease in controller gain after the hand was locked performed better than the proportional control with lock algorithm. Algorithms that changed command as a function of time performed worse than the proportional control with lock algorithm. Further, the computer-based video simulator proved to be useful as a first-pass evaluation tool for neural prosthesis control.

An advanced neuroprosthesis for restoration of hand and upper arm control using an implantable controller

An advanced neuroprosthesis that provides control of grasp-release, forearm pronation, and elbow extension to persons with cervical level spinal cord injury is described. The neuroprosthesis includes implanted and external components. The implanted components are a 10-channel stimulator-telemeter, leads and electrodes, and a joint angle transducer; the external components are a control unit and transmitter-receiver coil. The system has completed preclinical testing and has been implanted fully in 3 persons and partially in 1 person, all with tetraplegia caused by spinal cord injury at C5 and C6. The minimum follow-up time for any system component is 16 months. All subjects had improvements in grasp strength, range of motion, and ability to grasp objects and increased independence in activities of daily living. Each subject became a regular user of the neuroprosthesis and is satisfied with it. The implanted components have not caused any medical complications. The operation of the electrodes and sensors has been stable. The data show that this advanced neuroprosthetic system is safe and can provide grasping and reaching ability to individuals with cervical level spinal cord injury.

Neuroprostheses for the upper extremity

Functional electrical stimulation (FES) neuroprostheses can be used to replace lost motor and sensory function in persons with neurological disorders. FES technology has subsequently been shown effective and safe in restoring hand function in adults with spinal cord injury. The freehand system consists of an implanted receiver-stimulator, an external shoulder position sensor, and an external control unit. Commands are originated by voluntary movement of the contralateral shoulder and are measured by the sensor. There are several types of electrodes: epimysial, intramuscular, nerve cuff, and intraneural. Neuroprostheses are recommended within the context of all available reconstructive options for the upper limbs. Voluntary tendon transfers are the first choice. The clinical outcomes as measured by improvement on scales of impairment, activities of daily living, and satisfaction are rewarding. The next step in improvement of the motor function of person with spinal cord injury will be the addition of a controllable second upper extremity and the elimination of additional external hardware.

Reciprocal EMG control of elbow extension by FES

Elbow extension is critical in performing activities of daily living. Individuals with a C5-C6 spinal cord injury have paralyzed elbow extensors, yet retain weak to strong voluntary control of elbow flexion. Previous studies have shown that functional electrical stimulation (FES) of the triceps provides sufficient elbow extension strength and control to greatly improve function. With triceps stimulation applied at a constant level, elbow angle is controlled naturally by voluntary flexion opposing the stimulated extension-referred to as voluntary antagonist control. We have investigated an alternative reciprocal control scheme employing biceps electromyogram (EMG) to modulate triceps stimulation. With reciprocal control, increasing biceps EMG proportionally reduces triceps stimulation. A personal computer (PC)-based lab system was designed to test the feasibility of reciprocal control. Reciprocal control increased the range of elbow moments, was stable during maintained elbow angle or isometric moment, and used less stimulation. Reciprocal control of triceps stimulation using biceps EMG is an effective method for restoring elbow extension to C5-C6 spinal cord injury patients, and could be extended to other situations where a voluntarily controlled muscle can be opposed by stimulating an antagonist.