Abstract
This chapter reviews the therapeutic and neuroprosthetic applications of functional electrical stimulation (FES) among stroke survivors. There is growing evidence that therapeutic applications of surface and intramuscular FES are efficacious in facilitating upper- and lower-limb motor relearning and reducing poststroke shoulder pain. Neuroprosthetic applications such as surface and implanted peroneal nerve stimulation are efficacious in enhancing the gait speed of stroke survivors with foot drop. The clinical viability of upper-limb neuroprostheses must await the availability of additional fundamental and technical advances. The efficacy, limitations, and future development of FES for motor restoration in hemiplegia are discussed.
Keywords
Hemiparesis, Hemiplegic shoulder pain, Neuromuscular electrical stimulation, Rehabilitation, Therapy
Acknowledgments
The preparation of this chapter was supported in part by grants R01HD068588 and R01HD075542 from the National Institute of Child Health and Human Development, and KL2TR000440 from the National Center for Advancing Translational Sciences.
Acknowledgments
The preparation of this chapter was supported in part by grants R01HD068588 and R01HD075542 from the National Institute of Child Health and Human Development, and KL2TR000440 from the National Center for Advancing Translational Sciences.
Introduction
Stroke is the leading cause of disability or activity limitation among older adults in the United States. Approximately 800,000 strokes occur each year, with a prevalence of approximately 6.6 million ( ). Hemiparesis, or motor impairment of one side of the body, is a major consequence of stroke and is associated with significant activity limitation and reduction of quality of life. This chapter reviews the clinical uses of functional electrical stimulation (FES) to mitigate the effects of motor impairment following stroke. Although FES is a term that applies to a broad range of neurostimulation and neuromodulation application, in this chapter the scope of FES is narrowed to applications in which electrical stimulation is applied to an intact lower motor neuron to produce functional contractions of paralyzed or paretic muscles. The purpose of FES in stroke rehabilitation is to produce either therapeutic or neuroprosthetic effects.
Therapeutic FES is referred to as neuromuscular electrical stimulation (NMES) in this chapter. NMES applications are temporary and intended to produce specific effects over time to enhance recovery. A therapeutic effect is a change in voluntary movement or function as a result of a period of treatment with NMES (i.e., a before/after effect). Therapeutic applications include various means of NMES-mediated repetitive movement training to improve the recovery of volitional movement and function of the upper and lower limbs. Emerging basic and clinical data suggests that repetitive movements which are novel, goal oriented, and functionally relevant facilitate motor relearning following stroke or brain injury ( ). Motor relearning is defined as “the recovery of previously learned motor skills that have been lost following localized damage to the central nervous system” ( ). The use of NMES for motor relearning is based on the premise that if novel goal-oriented repetitive movement therapy facilitates motor relearning, then NMES-mediated goal-oriented repetitive movement therapy may also facilitate motor relearning. The use of NMES for the treatment of poststroke shoulder pain is another therapeutic application of NMES.
Neuroprosthetic FES refers to the long-term use of assistive electrical stimulation devices to activate paralyzed muscles in precise sequence and intensity so as to accomplish functional tasks directly. Such devices are called neuroprostheses because they replace lost neuromuscular function with FES. A neuroprosthetic effect is the change in movement or function produced when the neuroprosthesis is being used (i.e., an on/off effect). Large segments of the chronic stroke population exhibit minimal to no residual motor function and therefore may not be candidates for motor relearning strategies. For this population, a neuroprosthesis may be the only viable option for accomplishing upper- or lower-limb functions. A neuroprosthesis electrically stimulates the paretic muscles of the upper or lower limbs and produces movements that make it possible to perform specific activities of daily living and mobility tasks.
This chapter is organized into the three most common areas of FES application in stroke rehabilitation: upper-limb motor restoration, lower-limb motor restoration, and mitigation of shoulder pain. The development and effectiveness of therapeutic and neuroprosthetic FES are reviewed for each area.
Lower-Limb Applications
Approximately 70% of strokes result in the acute loss of independent household ambulation ( ). Of those who are nonambulatory early after stroke, up to 25% do not recover independent walking ( ). Weakness frequently persists in the ankle dorsiflexors, which have been the focus of much research and development. Unfortunately, all major muscle groups in the lower limb are affected after stroke ( ), but solutions for weakness of muscles at the hip and knee are not available. Thus there is a need for more effective lower-extremity rehabilitation approaches.
NMES Applications
A major contributor to impaired ambulation is the inability to dorsiflex the ankle during the swing phase of gait, which causes the foot to drag and results in inefficient and unsafe ambulation or nonambulation. NMES therapies for poststroke gait focus on improving toe clearance to prevent falls, improving coordination, and increasing walking speed. Research in the 1960s first demonstrated that surface peroneal nerve stimulation (PNS) could be used to prevent poststroke foot drop during gait ( ). This work also provided preliminary evidence that PNS had a therapeutic effect in some cases, with patients regaining the ability to dorsiflex the ankle volitionally.
PNS activates the common peroneal nerve to produce ankle dorsiflexion, and may be triggered either by a heel switch in the shoe or by a tilt sensor and accelerometer measuring shank angle ( ). Recently there have been four large RCTs that evaluated the therapeutic and neuroprosthetic effects of surface PNS devices approved by the United States Food and Drug Administration (FDA) in comparison to an ankle–foot orthosis (AFO), which is usual care ( Table 94.1 ). compared the therapeutic effects of 12 weeks of PNS to an AFO and found that both improved functional ambulation, but there were no between-group differences. compared the combined therapeutic and neuroprosthetic effect of 24 weeks of PNS to that of an AFO and found both groups improved equivalently on the 10 m walk test, but there were no between-group differences. used a 30-week treatment duration and found positive neuroprosthetic effects of both PNS and AFO on walking speed, but no between-group differences. evaluated the therapeutic and neuroprosthetic effects of 6 weeks of treatment and found that the PNS and AFO groups improved equivalently in walking speed, but there were no between-group differences. When participants were asked about device preference, the majority said they preferred PNS to an AFO because they felt more confident, safer, and more comfortable, and found PNS easier to don and doff and use long term ( ). In summary, using surface PNS for 6–30 weeks can have significant therapeutic effects on functional mobility and walking speed. Wearing a PNS device (neuroprosthetic effect) can further improve walking speed and walking endurance beyond the therapeutic effect. But PNS devices are neither superior nor inferior to AFOs with respect to these outcomes, although some patients may prefer PNS to an AFO ( ).
| Reference | Participants Chronicity | Duration of Treatment (Weeks) | FDA-Approved PNS Device |
|---|---|---|---|
| N = 110, >3 mo (mean: 3.8 years) | 12 | Odstock Footdrop Stimulator a | |
| N = 197, >3 mo (mean: 4.5 years) | 30 | Bioness L300 b | |
| N = 495, >6 mo (mean: 6.9 years) | 24 | WalkAide c | |
| N = 93, <12 mo (mean: 6.4 mo) | 6 | WalkAide c |
a Odstock Footdrop Stimulator is available through Boston Brace, Avon, MA.
b Bioness L300 is available through Bioness Inc., Valencia, CA.
c WalkAide is available through Innovative Neurotronics Inc., Austin, TX.
Some patients find surface stimulation painful or may have difficulty consistently positioning electrodes. Thus implanted PNS systems have also been developed since the 1960s to mitigate these issues. Implanted systems currently available in Europe have implanted pulse generators with cuff electrodes that wrap around the peroneal nerve. Initial studies of these systems have had variable results. In a study of 29 chronic (>6 months) stroke survivors the STIMuSTEP system (FineTech Medical Ltd), with its two bipolar cuff electrodes implanted around the deep and superficial branches of the common peroneal nerve, was compared to a control group using a conventional device (AFO, orthopedic shoes, or no device) ( ). Physical therapy was not provided as part of the study, but participants could continue their usual physical therapy. No therapeutic effect was found in either group. A significant difference between groups in the combined therapeutic and neuroprosthetic effect was found in favor of PNS after 26 weeks of using the device, but not after 12 weeks. Another study evaluated 27 chronic participants with the Actigait system (OttoBock), which uses a single nerve cuff with four channels of tripolar electrodes ( ). After 4 weeks of training they found a substantial combined therapeutic and neuroprosthetic effect in walking speed (∼0.4 m/s). Participants perceived substantial improvements in their quality of life, with most reporting a complete return to normal. Adverse events related to implanted components in both studies included a single nerve injury resulting from a cuff pulling on the nerve and an infection resulting from neurodermatitis and subsequent device removal. The participant recovered completely from the nerve injury, which was corrected by a surgery. Another participant was treated for a wound-healing disorder. One device failed, requiring removal. Overall, improvements from implanted PNS systems are similar to surface PNS systems, but they may be easier to use in daily life and provide improved selectivity.
Although foot-drop stimulation can provide therapeutic and neuroprosthetic benefits, many patients have additional gait deficits at the hip, knee, and ankle, thus multichannel NMES systems are being investigated. FastFES therapy combines fast treadmill walking with stimulated dorsiflexion for toe clearance during swing and stimulated plantarflexion for propulsion at push off. The approach encourages participants to walk faster than their comfortable walking speed. A three-arm RCT compared the therapeutic effects of 12 weeks of FastFES, fast walking, and comfortable speed walking in 50 participants ( ). Gait speed improved (therapeutic effect) for each group, but there was no difference between groups over time. However, FastFES training resulted in decreased energy cost of walking compared to other groups.
The NESS L-300Plus (Bioness Inc., Valencia, CA) adds to PNS a cuff that can be positioned to stimulate either knee flexors or extensors, depending on the patient’s needs. A case series study evaluated neuroprosthetic and therapeutic effects in 45 participants in the acute and chronic phases after stroke ( ). Neuroprosthetic effects were evaluated by comparing walking speed during no stimulation, PNS only, and PNS plus knee stimulation. Participants experienced therapeutic and neuroprosthetic improvements similar to previously described PNS studies. Adding stimulation of knee flexors or extensors to PNS had a statistically significant, but not clinically relevant, additive neuroprosthetic effect.
Some muscle functions, like hip flexion, can be difficult to stimulate selectively with surface electrodes, and placement of several external electrodes each day is not practical for users with limited manual dexterity. Implanted electrodes provide a way to stimulate muscles selectively and simplify set-up for patients. An RCT compared the therapeutic effects of a gait-training protocol with and without multijoint percutaneous stimulation ( ). All participants received a combination of strengthening and coordination exercises, bodyweight-supported treadmill training, and over-ground gait training. Participants in the FES group had up to eight percutaneous wire electrodes implanted in hip, knee, and ankle muscles. Stimulation patterns were delivered during the different activities to assist movements during 12 weeks of gait training. Both groups had therapeutic improvements, but the group who received multijoint NMES also had greater improvements in gait speed. The NMES group maintained improvements at 6 months follow-up, while benefits for the group without NMES did not persist as well.
FES Applications
Although participants have benefited from these approaches, significant gait deficits remain for many patients. The ability to regain independent walking after stroke is of great importance to patients who fear losing independence, and also for their carers. For those who do not gain significant therapeutic benefit from NMES approaches, a fully implanted multijoint FES system may provide continuous ambulation assistance with relative ease of use, thus addressing a critical unmet need. A case study demonstrated initial feasibility of a fully implanted neuroprosthesis to improve poststroke gait ( ). An eight-channel stimulator with intramuscular electrodes in hip, knee, and ankle flexor/extensor muscles was surgically implanted ( Fig. 94.2 ). The participant underwent gait training and stimulation pattern development to coordinate stimulation with volitional walking. Therapeutic improvements in gait speed and spatio–temporal characteristics were statistically significant, but modest. However, walking with stimulation assistance (i.e., the neuroprosthetic effect) had a clinically relevant effect on gait speed (>0.2 m/s) with associated improvements in spatio–temporal characteristics.
In summary, FES has potential to improve poststroke walking through therapeutic and neuroprosthetic effects. PNS has shown equivalence to an AFO in the subacute and chronic phases after stroke ( ). A metaanalysis including eight RCTs of single-joint or multijoint lower-limb surface FES added to gait training concluded that the addition of FES improved walking speed (therapeutic effect) by an additional 0.08 m/s compared to gait training alone ( ). Patients who retain deficits after therapy may benefit from a neuroprosthesis providing assistance for everyday use. Poststroke impairments are heterogeneous, and interventions will be tailored to individuals’ needs. Multichannel implanted neuroprostheses may be useful for patients with greater walking impairments, but these devices are still in development.
Lower-Limb Applications
Approximately 70% of strokes result in the acute loss of independent household ambulation ( ). Of those who are nonambulatory early after stroke, up to 25% do not recover independent walking ( ). Weakness frequently persists in the ankle dorsiflexors, which have been the focus of much research and development. Unfortunately, all major muscle groups in the lower limb are affected after stroke ( ), but solutions for weakness of muscles at the hip and knee are not available. Thus there is a need for more effective lower-extremity rehabilitation approaches.
NMES Applications
A major contributor to impaired ambulation is the inability to dorsiflex the ankle during the swing phase of gait, which causes the foot to drag and results in inefficient and unsafe ambulation or nonambulation. NMES therapies for poststroke gait focus on improving toe clearance to prevent falls, improving coordination, and increasing walking speed. Research in the 1960s first demonstrated that surface peroneal nerve stimulation (PNS) could be used to prevent poststroke foot drop during gait ( ). This work also provided preliminary evidence that PNS had a therapeutic effect in some cases, with patients regaining the ability to dorsiflex the ankle volitionally.
PNS activates the common peroneal nerve to produce ankle dorsiflexion, and may be triggered either by a heel switch in the shoe or by a tilt sensor and accelerometer measuring shank angle ( ). Recently there have been four large RCTs that evaluated the therapeutic and neuroprosthetic effects of surface PNS devices approved by the United States Food and Drug Administration (FDA) in comparison to an ankle–foot orthosis (AFO), which is usual care ( Table 94.1 ). compared the therapeutic effects of 12 weeks of PNS to an AFO and found that both improved functional ambulation, but there were no between-group differences. compared the combined therapeutic and neuroprosthetic effect of 24 weeks of PNS to that of an AFO and found both groups improved equivalently on the 10 m walk test, but there were no between-group differences. used a 30-week treatment duration and found positive neuroprosthetic effects of both PNS and AFO on walking speed, but no between-group differences. evaluated the therapeutic and neuroprosthetic effects of 6 weeks of treatment and found that the PNS and AFO groups improved equivalently in walking speed, but there were no between-group differences. When participants were asked about device preference, the majority said they preferred PNS to an AFO because they felt more confident, safer, and more comfortable, and found PNS easier to don and doff and use long term ( ). In summary, using surface PNS for 6–30 weeks can have significant therapeutic effects on functional mobility and walking speed. Wearing a PNS device (neuroprosthetic effect) can further improve walking speed and walking endurance beyond the therapeutic effect. But PNS devices are neither superior nor inferior to AFOs with respect to these outcomes, although some patients may prefer PNS to an AFO ( ).
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