Implanted functional electrical stimulation system for mobility in paraplegia: a follow-up case report

An implantable neuroprosthesis for standing and walking in paraplegia: 5-year patient follow-up

We present the results of a 5-year patient follow-up after implantation of an original neuroprosthesis. The system is able to stimulate both epimysial and neural electrodes in such a way that the complete flexor-extensor chain of the lower limb can be activated without using the withdrawal reflex. We demonstrate that standing and assisted walking are possible, and the results have remained stable for 5 years. Nevertheless, some problems were noted, particularly regarding the muscle response on the epimysial channels. Analysis of the electrical behaviour and thresholds indicated that the surgical phase is crucial because of the sensitivity of the functional responses to electrode placement. Neural stimulation proved to be more efficient and more stable over time. This mode requires less energy and provides more selective stimulation. This FES system can be improved to enable balanced standing and less fatiguing gait, but this will require feedback on event detection to trigger transitions between stimulation sequences, as well as feedback to the patient about the state of his lower limbs.

Original electronic design to perform epimysial and neural stimulation in paraplegia

This paper presents an original electronic architecture to manage epimysial and neural stimulation using the same implantable device. All the muscles needed to achieve lower limb movements such as standing and walking can thus be activated. Mainly for surgical reasons, some muscles need to be stimulated through different inputs: epimysium or motor nerve. We developed an electronic solution, including the design of an application-specific integrated circuit, to meet the requirements of both types of stimulation. Five years after the successful implantation of the system, we were able to evaluate the system's performance. The patient is still using the system at home and no failure occurred during this 5-year period. We conclude that the electronic design not only provides a unique investigative tool for research, but that it can also be used to restore the motor function of the lower limb. This technology has an advantage over external stimulation because the patient can safely use the system at home. However, improvements such as lower power consumption, and thus greater autonomy, are needed. We further conclude that the modelling of the electrical behaviour of the electrodes is reliable and the estimated parameter values are homogeneous and consistent for the same type of electrode. Thus, the three parameters of the first-order model can be identified from an acute animal experiment and provide a means to optimize the design of the output stage of implanted stimulators.

Design and simulation of a pneumatic, stored-energy, hybrid orthosis for gait restoration

Loss of mobility due to lower limb paralysis is a common result of thoracic level spinal cord injury. Functional electrical stimulation (FES) can restore primitive gait in the vicinity of a wheelchair by using electrical stimulation to generate muscle contractions. A new concept for FES-assisted gait is presented that combines electrical stimulation with an orthosis that contains a fluid power system to store and transfer energy during the gait cycle. The energy storage orthosis (ESO) can be driven through a complete gait cycle using only stimulation of the quadriceps muscles. The conceptual design of the ESO was completed and implemented in a dynamic simulation model and in a benchtop prototype for engineering measurements. No studies were conducted with human subjects. The results demonstrate the potential of the ESO concept for a feasible gait-assist system and the validity of the simulation model as a means for designing the system.

A critical review of interfaces with the peripheral nervous system for the control of neuroprostheses and hybrid bionic systems

Considerable scientific and technological efforts have been devoted to develop neuroprostheses and hybrid bionic systems that link the human nervous system with electronic or robotic prostheses, with the main aim of restoring motor and sensory functions in disabled patients. A number of neuroprostheses use interfaces with peripheral nerves or muscles for neuromuscular stimulation and signal recording. Herein, we provide a critical overview of the peripheral interfaces available and trace their use from research to clinical application in controlling artificial and robotic prostheses. The first section reviews the different types of non-invasive and invasive electrodes, which include surface and muscular electrodes that can record EMG signals from and stimulate the underlying or implanted muscles. Extraneural electrodes, such as cuff and epineurial electrodes, provide simultaneous interface with many axons in the nerve, whereas intrafascicular, penetrating, and regenerative electrodes may contact small groups of axons within a nerve fascicle. Biological, technological, and material science issues are also reviewed relative to the problems of electrode design and tissue injury. The last section reviews different strategies for the use of information recorded from peripheral interfaces and the current state of control neuroprostheses and hybrid bionic systems.

Intraspinal Microstimulation using Cylindrical Multielectrodes

A cylindrical multielectrode system specifically designed for intraspinal microstimulation was mechanically and electrically evaluated in the ventral horn of the feline lumbo-sacral spinal cord. Electrode insertions proved to be straight as evaluated from radiographs. Impedances were measured in situ and force recruitment curves from quadriceps muscles were collected over a wide range of stimulus parameters. For a given charge, higher current amplitudes produced greater forces than proportionally longer pulse durations, indicating that charge is not the sole indicator of evoked force in applications utilizing electrical stimulation. Overlap measurements for calculating current-distance constants were collected at a variety of current amplitudes, electrode pair separations, and pair orientations in the spinal grey matter. Forces obtained in the majority of these trials demonstrated an order effect, presumably due to asymmetric neuronal connectivity within the spinal cord. In the cases showing no order effect, the dorso-ventral electrode pair orientation yielded a higher average current-distance constant (278 microA/mm2) than either the medio-lateral or rostro-caudal electrode pair orientations (197 microA/mm2). Specifications of an array of cylindrical multielectrodes for use in future intraspinal microstimulation prostheses were updated.

Ambulation after incomplete spinal cord injury with electromyogram-triggered functional electrical stimulation

Ambulation after spinal cord injury is possible with the aid of functional electrical stimulation (FES). Individuals with incomplete spinal cord injury (iSCI) retain partial volitional control of muscles below the level of injury, necessitating careful integration of FES with intact voluntary motor function for efficient walking. In this study, the surface electromyogram (sEMG) of the volitionally controlled Erector Spinae was used to detect the intent to step and trigger FES-assisted walking in a volunteer with iSCI via 8-channel implanted stimulation system. The inference system was able to trigger the FES-assisted swing-phase of gait with a false positive rate of 1% during over ground ambulation on a level surface. The performance of the sEMG inference system highlights its potential as a natural command interface to better coordinate stimulated and volitional muscle activities than conventional manual switches and facilitate FES-assisted community ambulation.

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.

Foot placement alters the mechanisms of postural control while standing and reaching

This study investigated the effects of altering foot placement on the strategies used by able-bodied subjects to perform reaching tasks while standing. The motivation for this study was to consider the results in the context of a person with a spinal cord injury using a functional neuromuscular stimulation (FNS) system to stand while reaching. Three foot placement conditions were compared as subjects reached to the left, right, and center. Centers of pressure (COP), joint angles, and joint moments were calculated as postural parameters using force platform and video marker data. Side-by-side and wide foot placements resulted in similar postural parameters. In contrast, the modified tandem stance (feet spaced at pelvic width with one foot shifted forward) resulted in anterior/posterior COP excursions that were larger in magnitude and more consistent across reach directions when compared to the other foot placement conditions. Furthermore, the movement patterns used during the tandem stance were more consistent and may be more readily achievable with FNS than the movement patterns utilized with the side-by-side and wide stances. These results suggest that the modified tandem stance may enhance the functionality of FNS standing systems and may also be useful in other standing rehabilitation programs.

A sensorized thumb for force closed-loop control of hand neuroprostheses

In this paper, we presented a sensorized thumb based on a matrix of piezoresistive force sensors, with an acquisition unit and a special wearing support. The sensor was calibrated and then the device was tested during different tasks simulating activities of daily living performed by seven able-bodied subjects. By means of these experiments, we verified that the device proposed can be used to extract force information during grasp. In fact, the device was able to provide useful force information in the 98% of the trials with a good repeatability during all the different conditions. Moreover, we evaluated the patterns obtained during the different grasping tasks. The palmar grasps were performed in a similar manner, whereas the lateral pinch and the spherical volar grip were more different. This device can provide force information with good performance and acceptability and it can be used for force closed-loop control of hand neuroprostheses.

Implanted functional electrical stimulation: an alternative for standing and walking in pediatric spinal cord injury

STUDY DESIGN

Post intervention, repeated measures design, comparing two interventions.

SETTING

Orthopedic pediatric hospital specializing in spinal cord injury.

METHODS

Nine subjects, ages 7-20 years, received an eight-channel implanted lower extremity functional electrical stimulation (FES) system for standing and walking. Electrodes were placed to stimulate hip and knee extension, and hip abduction and adduction. Standing and walking were achieved through constant stimulation to the implanted muscles, allowing a swing through gait pattern with an assistive device. After training with FES and long leg braces (LLB), subjects were tested in eight upright mobility activities, which were scored based upon completion time and level of independence.

RESULTS

Seven subjects completed data collection. These subjects completed four activities faster (P<0.02) and five activities more independently (P<0.025) with FES as compared to LLB. Transitions between sitting and standing, which were scored in isolation for two mobility activities, were achieved faster and with more independence with FES. In addition, subjects reported preferring FES for the majority of activities. No activity required more time or more assistance to complete with FES as compared to LLB.

CONCLUSION

The implanted FES system provided these subjects with enhanced functional abilities over traditional LLB and decreased the need for physical assistance by a caregiver, suggesting that it is a realistic alternative for upright mobility in a pediatric population with spinal cord injury.

Computer added locomotion by implanted electrical stimulation in paraplegic patients (SUAW)

Paraplegia means a live long sentence of sensory loss, paralysis and dependence with approximately 1000 new victims in every European country every year and 11.500 new traumatic SCI cases in the US. respectively. Sixty percent are injured before age 30. More than 90% of SCI victims may survive with nearly normal experience of live. Most patients will recover somewhat from SCI over time but no patient who remained plegic for one year regains voluntary motor function after that time period. Despite remarkable efforts and recent achievements in rehabilitation no treatment can be recommended so far to enhance functional recovery and restoring locomotion in paraplegic humans. FES as a technical compensation has become therefore a challenging treatment to restore muscle function and to prevent atrophy and to improve mobility and quality of life at the same time. In paraplegics FES could be the basis to restore locomotion. One of the advantages of an implanted FES version (neuroprosthesis) is that the FES system, electrodes, and cables remain permanently implanted within the body, so that the patient can stay without cables, the programmer attached to the crutches. The SUAW project, supported under BIOMED II Programme by the European Community was aimed to finalize and to put into practice the results of previous research and development. The novel implant with an ASCI-Chip has 16 channels, 8 on each side, 20 mA for monopolar and 2 mA for bipolar stimulation, only one electrode can be stimulated at a given time. Stimulation of 6 muscle groups of both legs are known to be sufficient for locomotion: M. ileopsoas (erector of the body, hip flexor), M. gluteus maximus (hip extensor), M. gluteus medius (lateral hip stabilisator, knee abductor), Mm. hamstrings (knee flexor) stimulated by epimysial electrodes, Mm. sartorius and rectus femoris (knee extensor) stimulated by neural, bipolar electrodes. Patient's selection criteria were: stable spinal cord lesion between T7 and T11, minimum 1 year after the accident without deformity of the spine, the muscle groups for locomotion responding to external FES with the EXOSTIM programmer with the same programme used later for the neuroprosthesis. Two paraplegic male patients, T8, 38 and 31 years old respectively, were operated on by an international group of surgeons according to the protocol in 09/1999, respectively 7/2000. The postop. course was uneventful. Because the threshold of the primary implant was too low regarding scare tissue around the electrodes, this implant was changed in 01/2000 and worked perfectly. Both patients are happy with the success of the novel treatment modalities.

The Vienna functional electrical stimulation system for restoration of walking functions in spastic paraplegia

An eight-channel stimulation system, currently intended for stimulation of lower extremities, was developed and is introduced. The major development goals were easy handling, modularity to make the system easily adaptable for other functional electrical stimulation (FES) applications, and a wide stimulation parameter range for application-specific parameter optimization. For paraplegic stepping, the system worn by the patient consists of 2 four-channel stimulation modules, a central unit holding the battery and circuitry for power management and communication control, a wireless remote control unit, and a palmtop computer as the main control and input device. A software package for Microsoft Windows supports the design and optimization of stimulation sequences in the rehabilitation center. First tests with patients familiar with FES showed smoother movements during stepping and acceptable good handling. In combination with the PC software, the required stimulation sequences could be created in a very short time.

Three-dimensional shoulder kinematics in individuals with C5-C6 spinal cord injury

The shoulder kinematics of five able-bodied subjects and those of five arms in three subjects with spinal cord injuries at C5 or C6 levels were measured as the subjects elevated their arms in three different planes: coronal, scapular and sagittal. The range of humeral elevation was significantly reduced in all spinal cord injury (SCI) subjects relative to able-bodied subjects. Over this restricted range of humeral motion, the scapula of SCI subjects tended to be medially rotated, relative to able-bodied subjects, and the protraction and spinal tilt angles of the scapula of the SCI subjects indicated scapular winging. These results are consistent with paralysis or at least with significant weakness of the serratus anterior muscle. If further study confirms this hypothesis, functional neuromuscular stimulation of the serratus anterior muscle via a nerve cuff electrode may be an effective intervention for improving shoulder function in C5-C6 SCI.

Functional and biological test of a 20 channel implantable stimulator in sheep in view of functional electrical stimulation walking for spinal cord injured persons

A newly developed implantable stimulator with 20 output channels, mainly intended for the stimulation of lower extremities in paraplegics, was implanted in 6 sheep over a time period of 26 weeks. Five epineural electrodes each were used to contact various nerves at different locations to elicit hip and knee extension and flexion and to make carrousel and selective stimulation possible. Different electrode application strategies in view of paraplegic standing and walking were investigated. Additional implanted electrodes allowed M-wave monitoring for selectivity investigations in 3 sheep. Stimulator, electrode leads, and electrodes proved to be reliable. Selective stimulation with electrodes placed on the trunk of the sciatic nerve could be demonstrated but with bad reproducibility. Histological investigation of the tissues surrounding electrodes and leads showed the expected stable foreign body response. Strong hip and knee extension could be gained in all cases while only weak flexion forces could be elicited in most cases. Muscle biopsies showed that daily stimulation for 8 h at threshold level caused an increase in muscle Type I fibers and a decrease in Type IIc fibers. Implants and electrodes fulfill the most important functional and biological criteria for their clinical application for paraplegic walking. The intention to provide selective flexion functions via epineural stimulation could not be demonstrated sufficiently in this animal model.

Selective stimulation of cat sciatic nerve using an array of varying-length microelectrodes

Restoration of motor function to individuals who have had spinal cord injuries or stroke has been hampered by the lack of an interface to the peripheral nervous system. A suitable interface should provide selective stimulation of a large number of individual muscle groups with graded recruitment of force. We have developed a new neural interface, the Utah Slanted Electrode Array (USEA), that was designed to be implanted into peripheral nerves. Its goal is to provide such an interface that could be useful in rehabilitation as well as neuroscience applications. In this study, the stimulation capabilities of the USEA were evaluated in acute experiments in cat sciatic nerve. The recruitment properties and the selectivity of stimulation were examined by determining the target muscles excited by stimulation via each of the 100 electrodes in the array and using force transducers to record the force produced in these muscles. It is shown in the results that groups of up to 15 electrodes were inserted into individual fascicles. Stimulation slightly above threshold was selective to one muscle group for most individual electrodes. At higher currents, co-activation of agonist but not antagonist muscles was observed in some instances. Recruitment curves for the electrode array were broader with twitch thresholds starting at much lower currents than for cuff electrodes. In these experiments, it is also shown that certain combinations of electrode pairs, inserted into an individual fascicle, excite fiber populations with substantial overlap, whereas other pairs appear to address independent populations. We conclude that the USEA permits more selective stimulation at much lower current intensities with more graded recruitment of individual muscles than is achieved by conventional cuff electrodes.

A new hybrid spring brake orthosis for controlling hip and knee flexion in the swing phase

In this study it is proposed that active contraction of muscles might be artificially replaced by a spring brake orthosis (SBO) to provide near-natural knee and hip swing phase trajectories for gait in spinal cord injured subjects. The SBO is a new gait restoration system in which stored spring elastic energy and potential energy of limb segments are utilized to aid gait. It is also shown that hip flexion can be produced without the need for withdrawal reflex, hip flexor stimulus or any mechanical actuator at the hip. A hip flexion angle of 21 degrees was achieved by a nonimpaired subject wearing a prototype orthosis.

Implanted stimulators for restoration of function in spinal cord injury

Neuroprostheses that electrically stimulate paralyzed muscles provide functional enhancements for individuals with spinal cord injury and stroke such as standing and stepping, reaching and grasping, and bladder and bowel function. For chronic applications, implanted neuroprostheses lead to reliable, low-maintenance and patient-acceptable systems. The advantages of such systems are discussed followed by a generic description of implantable stimulators. Features of current first and second generation neuroprostheses developed at our centre are discussed followed by our experience in the application of these devices in the rehabilitation of individuals with spinal cord injury.