Electrically stimulated elbow extension in persons with C5/C6 tetraplegia: a functional and physiological evaluation

Use and evaluation of assistive technologies for upper limb function in tetraplegia

CONTEXT

More than half of all spinal cord injuries (SCI) occur at the cervical level leading to loss of upper limb function, restricted activity and reduced independence. Several technologies have been developed to assist with upper limb functions in the SCI population.

OBJECTIVE

There is no clear clinical consensus on the effectiveness of the current assistive technologies for the cervical SCI population, hence this study reviews the literature in the years between 1999 and 2019.

METHODS

A systematic review was performed on the state-of-the-art assistive technology that supports and improves the function of impaired upper limbs in cervical SCI populations. Combinations of terms, covering assistive technology, SCI, and upper limb, were used in the search, which resulted in a total of 1770 articles. Data extractions were performed on the selected studies which involved summarizing details on the assistive technologies, characteristics of study participants, outcome measures, and improved upper limb functions when using the device.

RESULTS

A total of 24 articles were found and grouped into five categories, including neuroprostheses (invasive and non-invasive), orthotic devices, hybrid systems, robots, and arm supports. Only a few selected studies comprehensively reported characteristics of the participants. There was a wide range of outcome measures and all studies reported improvements in upper limb function with the devices.

CONCLUSIONS

This study highlighted that assistive technologies can improve functions of the upper limbs in SCI patients. It was challenging to draw generalizable conclusions because of factors, such as heterogeneity of recruited participants, a wide range of outcome measures, and the different technologies employed.

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.

Effects and effectiveness of dynamic arm supports: a technical review

Numerous dynamic arm supports have been developed in recent decades to increase independence in the performance of activities of daily living. Much effort and money have been spent on their development and prescription, yet insight into their effects and effectiveness is lacking. This article is a systematic review of evaluations of dynamic arm supports. The 8 technical evaluations, 12 usability evaluations, and 27 outcome studies together make 47 evaluations. Technical evaluations were often used as input for new developments and directed at balancing quality, forces and torques, and range of motion of prototypes. Usability studies were mostly single-measure designs that had varying results as to whether devices were usable for potential users. An increased ability to perform activities of daily living and user satisfaction were reported in outcome studies. However, the use of dynamic arm supports in the home situation was reported to be low. Gaining insight into why devices are not used when their developers believe them to be effective seems crucial for every new dynamic arm support developed. The methodological quality of the outcome studies was often low, so it is important that this is improved in the future.

Feedback control of arm movements using Neuro-Muscular Electrical Stimulation (NMES) combined with a lockable, passive exoskeleton for gravity compensation

Within the European project MUNDUS, an assistive framework was developed for the support of arm and hand functions during daily life activities in severely impaired people. This contribution aims at designing a feedback control system for Neuro-Muscular Electrical Stimulation (NMES) to enable reaching functions in people with no residual voluntary control of the arm and shoulder due to high level spinal cord injury. NMES is applied to the deltoids and the biceps muscles and integrated with a three degrees of freedom (DoFs) passive exoskeleton, which partially compensates gravitational forces and allows to lock each DOF. The user is able to choose the target hand position and to trigger actions using an eyetracker system. The target position is selected by using the eyetracker and determined by a marker-based tracking system using Microsoft Kinect. A central controller, i.e., a finite state machine, issues a sequence of basic movement commands to the real-time arm controller. The NMES control algorithm sequentially controls each joint angle while locking the other DoFs. Daily activities, such as drinking, brushing hair, pushing an alarm button, etc., can be supported by the system. The robust and easily tunable control approach was evaluated with five healthy subjects during a drinking task. Subjects were asked to remain passive and to allow NMES to induce the movements. In all of them, the controller was able to perform the task, and a mean hand positioning error of less than five centimeters was achieved. The average total time duration for moving the hand from a rest position to a drinking cup, for moving the cup to the mouth and back, and for finally returning the arm to the rest position was 71 s.

Functional reorganization of upper-body movement after spinal cord injury

Survivors of spinal cord injury need to reorganize their residual body movements for interacting with assistive devices and performing activities that used to be easy and natural. To investigate movement reorganization, we asked subjects with high-level spinal cord injury (SCI) and unimpaired subjects to control a cursor on a screen by performing upper-body motions. While this task would be normally accomplished by operating a computer mouse, here shoulder motions were mapped into the cursor position. Both the control and the SCI subjects were rapidly able to reorganize their movements and to successfully control the cursor. The majority of the subjects in both groups were successful in reducing the movements that were not effective at producing cursor motions. This is inconsistent with the hypothesis that the control system is merely concerned with the accurate acquisition of the targets and is unconcerned with motions that are not relevant to this goal. In contrast, our findings suggest that subjects can learn to reorganize coordination so as to increase the correspondence between the subspace of their upper-body motions with the plane in which the controlled cursor moves. This is effectively equivalent to constructing an inverse internal model of the map from body motions to cursor motions, established by the experiment. These results are relevant to the development of interfaces for assistive devices that optimize the use of residual voluntary control and enhance the learning process in disabled users, searching for an easily learnable map between their body motor space and control space of the device.

A real-time, 3-D musculoskeletal model for dynamic simulation of arm movements

Neuroprostheses can be used to restore movement of the upper limb in individuals with high-level spinal cord injury. Development and evaluation of command and control schemes for such devices typically require real-time, "patient-in-the-loop" experimentation. A real-time, 3-D, musculoskeletal model of the upper limb has been developed for use in a simulation environment to allow such testing to be carried out noninvasively. The model provides real-time feedback of human arm dynamics that can be displayed to the user in a virtual reality environment. The model has a 3-DOF glenohumeral joint as well as elbow flexion/extension and pronation/supination and contains 22 muscles of the shoulder and elbow divided into multiple elements. The model is able to run in real time on modest desktop hardware and demonstrates that a large-scale, 3-D model can be made to run in real time. This is a prerequisite for a real-time, whole-arm model that will form part of a dynamic arm simulator for use in the development, testing, and user training of neural prosthesis systems.

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.

Exercise as a Health-Promoting Activity Following Spinal Cord Injury

Spinal cord injury is a catastrophic event that immeasurably alters activity and health. Depending on the level and severity of injury, functional and homeostatic decline of many body systems can be anticipated in a large segment of the paralyzed population. The level of physical inactivity and deconditioning imposed by SCI profoundly contrasts the preinjury state in which most individuals are relatively young and physically active. Involvement in sports, recreation, and therapeutic exercise is commonly restricted after SCI by loss of voluntary motor control, as well as autonomic dysfunction, altered fuel homeostasis, inefficient temperature regulation, and early-onset muscle fatigue. Participation in exercise activities also may require special adaptive equipment and, in some instances, the use of electrical current either with or without computerized control. Notwithstanding these limitations, considerable evidence supports the belief that recreational and therapeutic exercise improves the physical and emotional well-being of participants with SCI. This article will examine multisystem decline and the need for exercise after SCI. It will further examine how exercise might be used as a tool to enhance health by slowing multisystem medical complications unique to those with SCI. As imprudent exercise recommendations may pose avoidable risks of incipient disability, orthopedic deterioration, or pain, the special risks of exercise misuse in those with SCI will be discussed.

EEG-based neuroprosthesis control: a step towards clinical practice

This case study demonstrates the coupling of an electroencephalogram (EEG)-based Brain-Computer Interface (BCI) with an implanted neuroprosthesis (Freehand system). Because the patient was available for only 3 days, the goal was to demonstrate the possibility of a patient gaining control over the motor imagery-based Graz BCI system within a very short training period. By applying himself to an organized and coordinated training procedure, the patient was able to generate distinctive EEG-patterns by the imagination of movements of his paralyzed left hand. These patterns consisted of power decreases in specific frequency bands that could be classified by the BCI. The output signal of the BCI emulated the shoulder joystick usually used, and by consecutive imaginations the patient was able to switch between different grasp phases of the lateral grasp that the Freehand system provided. By performing a part of the grasp-release test, the patient was able to move a simple object from one place to another. The results presented in this work give evidence that Brain-Computer Interfaces are an option for the control of neuroprostheses in patients with high spinal cord lesions. The fact that the user learned to control the BCI in a comparatively short time indicates that this method may also be an alternative approach for clinical purposes.

Targeting recovery: priorities of the spinal cord-injured population

In the United States alone, there are more than 200,000 individuals living with a chronic spinal cord injury (SCI). Healthcare for these individuals creates a significant economic burden for the country, not to mention the physiological, psychological, and social suffering these people endure everyday. Regaining partial function can lead to greater independence, thereby improving quality of life. To ascertain what functions are most important to the SCI population, in regard to enhancing quality of life, a novel survey was performed in which subjects were asked to rank seven functions in order of importance to their quality of life. The survey was distributed via email, postal mail, the internet, interview, and word of mouth to the SCI community at large. A total of 681 responses were completed. Regaining arm and hand function was most important to quadriplegics, while regaining sexual function was the highest priority for paraplegics. Improving bladder and bowel function was of shared importance to both injury groups. A longitudinal analysis revealed only slight differences between individuals injured <3 years compared to those injured >3 years. The majority of participants indicated that exercise was important to functional recovery, yet more than half either did not have access to exercise or did not have access to a trained therapist to oversee that exercise. In order to improve the relevance of research in this area, the concerns of the SCI population must be better known and taken into account. This approach is consistent with and emphasized by the new NIH roadmap to discovery.

Triceps denervation as a predictor of elbow flexion contractures in C5 and C6 tetraplegia

OBJECTIVE

To determine whether the existence of elbow flexion contractures in persons with C5 or C6 tetraplegia is related to a lack of residual voluntary triceps function and triceps denervation (ie, lower motoneuron damage).

DESIGN

A retrospective study of impairment data from 74 arms to identify the incidence of elbow flexion contractures and the contributing factors toward this deformity.

SETTING

Five spinal cord injury (SCI) rehabilitation centers in the United States, 1 in England, and 1 in Australia.

PARTICIPANTS

Forty-three subjects with motor complete C5 or C6 traumatic SCI.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Active and passive elbow extension, triceps voluntary muscle strength, and triceps response to electric stimulation.

RESULTS

Subjects with weak voluntary triceps had significantly fewer and less severe elbow flexion contractures than those with paralyzed triceps ( P =.024). Subjects with completely denervated triceps (ie, no response to electric stimulation) had significantly more elbow flexion contractures than subjects with even a weak response to electric stimulation ( P =.003). Overall, 51% of the arms could not be passively extended to zero. Forty-six percent of the arms classified as C5 lacked full passive elbow extension, compared with 63% of the arms classified as C6 ( P =.302).

CONCLUSIONS

A relationship has been found between elbow flexion contractures and lack of residual voluntary triceps and triceps denervation in subjects with C5 or C6 tetraplegia. There should be a greater awareness of the elbow flexion contractures that may develop as a result of this relationship. A better understanding of this deformity and its characteristics can lead to more effective clinical treatment and prevention strategies.

Exercise Recommendations for Individuals with Spinal Cord Injury

Persons with spinal cord injury (SCI) exhibit deficits in volitional motor control and sensation that limit not only the performance of daily tasks but also the overall activity level of these persons. This population has been characterised as extremely sedentary with an increased incidence of secondary complications including diabetes mellitus, hypertension and atherogenic lipid profiles. As the daily lifestyle of the average person with SCI is without adequate stress for conditioning purposes, structured exercise activities must be added to the regular schedule if the individual is to reduce the likelihood of secondary complications and/or to enhance their physical capacity. The acute exercise responses and the capacity for exercise conditioning are directly related to the level and completeness of the spinal lesion. Appropriate exercise testing and training of persons with SCI should be based on the individual's exercise capacity as determined by accurate assessment of the spinal lesion. The standard means of classification of SCI is by application of the International Standards for Classification of Spinal Cord Injury, written by the Neurological Standards Committee of the American Spinal Injury Association. Individuals with complete spinal injuries at or above the fourth thoracic level generally exhibit dramatically diminished cardiac acceleration with maximal heart rates less than 130 beats/min. The work capacity of these persons will be limited by reductions in cardiac output and circulation to the exercising musculature. Persons with complete spinal lesions below the T(10) level will generally display injuries to the lower motor neurons within the lower extremities and, therefore, will not retain the capacity for neuromuscular activation by means of electrical stimulation. Persons with paraplegia also exhibit reduced exercise capacity and increased heart rate responses (compared with the non-disabled), which have been associated with circulatory limitations within the paralysed tissues. The recommendations for endurance and strength training in persons with SCI do not vary dramatically from the advice offered to the general population. Systems of functional electrical stimulation activate muscular contractions within the paralysed muscles of some persons with SCI. Coordinated patterns of stimulation allows purposeful exercise movements including recumbent cycling, rowing and upright ambulation. Exercise activity in persons with SCI is not without risks, with increased risks related to systemic dysfunction following the spinal injury. These individuals may exhibit an autonomic dysreflexia, significantly reduced bone density below the spinal lesion, joint contractures and/or thermal dysregulation. Persons with SCI can benefit greatly by participation in exercise activities, but those benefits can be enhanced and the relative risks may be reduced with accurate classification of the spinal injury.

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.

Management of the paralyzed elbow in tetraplegia

The management of the paralytic conditions in tetraplegia requires understanding neural pathophysiology. A comprehensive rehabilitative and surgical plan requires a multidisciplinary approach. Prior to redistributing the muscle forces across the elbow, a supple osseo-articular platform must be created. The authors recommend PDT and BTT transfers and a FES neuroprosthesis. Future work in this field will advance the application of neuromodulation and its deployment in different neurophysiologic states.

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.

Postural arm control following cervical spinal cord injury

This study used estimates of dynamic endpoint stiffness to quantify postural arm stability following cervical spinal cord injury (SCI) and to investigate how this stability was affected by functional neuromuscular stimulation (FNS). Measurements were made in the horizontal plane passing through the glenohumeral joint on three SCI-impaired arms, which ranged in functional level from a weak C5 to a strong C6. Endpoint stiffness, which characterizes the relationship between externally imposed hand displacements and the resultant forces, was estimated during the application of planar, stochastic perturbations to each arm. These estimates were used in conjunction with voluntary endpoint force measurements to quantify stability and strength during voluntary contractions and during voluntary contractions in the presence of triceps FNS. The primary findings were: 1) the differences in the force generating capabilities of these arms were due primarily to differences in shoulder strength; 2) measurements of strength alone could not be used to predict arm stability; and 3) triceps FNS improved postural arm stability for all tested conditions. These results suggest strategies for improved control of FNS systems designed to restore arm function following cervical SCI and underscore the importance of examining the effects of FNS on both strength and stability.