1) Introduction

2)Therapeutic Exercise

3) Standing/Ambulation

4) Manual Grasping Control

5) Bladder/Bowel Management

6) Respiratory Support

1) Introduction: Functional Electrical Stimulation (FES) uses low levels of electrical current to stimulate physical or bodily functions lost through nervous system impairment. FES is also referred to as Functional Neuromuscular Stimulation (FNS) or Neuromuscular Electrical Stimulation (NMES). FES is applied to peripheral nerves that control specific muscles or muscle groups.

Because FES is an involved area with extensive history, the summaries below can only provide a relatively superficial overview of the technology. Various FES applications have moved to the forefront as they evolved and then receded in priority. This ebb and flow will undoubtedly continue in the future. As such, readers interested in learning more about the subject are encouraged to consult the linked references.

FES is not a cure for SCI. It is a tool used to regain specific functions. In some cases FES can have therapeutic effects. But it does not repair or regenerate the damaged spinal cord.

Physical therapists use therapeutic electrical stimulation (ES), a temporary therapy used to increase muscle strength, range of motion, inhibit spasticity, and reeducate voluntary muscles. ES does not directly facilitate specific functions in daily life, which is the goal of FES.

FES is ineffective if target muscles become denervated. Muscle denervation occurs if corresponding spinal cord motor roots or anterior horn cells are damaged. Denervation can be slight or extensive, depending on location, extent, and type of injury. In some cases, when denervation is too extensive, it may be possible to surgically transfer innervated muscles (or tendons) in place of one or two denervated muscles needed for desired functions.

The use of external FES in patients with cardiac pacemakers, or automatic implanted defibrillators should be approached with caution. Contraindications for internal FES (implanted electrodes) include uncontrolled spasticity, active or recurrent sepsis, and the use of cardiac pacemakers.

Relative contraindications include severe muscular contractures (in the hands, feet, or legs), pregnancy, electrode sensitivity, congestive heart failure, cardiac arrhythmias, and active wounds that electrical stimulation would stress.

A qualified physician should determine the applicability of FES regarding the patient's needs and medical condition.

FES applications include standing, limited ambulation, cycling, manual grasping, bowel and bladder control, male sexual and reproductive assistance, breath control, and airway clearance. Physical benefits that FES may offer include improved venous return from lower limbs, osteoporosis avoidance and reversal, reduced incidence of urinary and bladder infections, muscle mass retention, and cardiovascular health. Psychological benefits can result from improved functionality and greater independence.

Components commonly found in FES systems include an electronic stimulator, a feedback or control unit, leads, and electrodes.

Electrical stimulators can have one or multiple channels (outputs), which are activated in unison or in sequence to produce desired movements. Batteries are primarily used to provide FES electrical stimulation, although alternate power sources are used if indicated for safety or specific needs.

Therapist-operated FES systems use switches or dials to control FES activation. Control mechanisms for subject-controlled FES include joysticks, buttons, switches, joint positions sensors, heel switches, sip-and-puff devices, EMG electrodes, and voice activation.

Subject-controlled FES can be open- or closed-loop. In open-loop controlled FES the electrical stimulator controls the output. Closed-loop FES employs joint or muscle position sensors to facilitate greater responsiveness to muscle fatigue, or to irregularities in the environment.

Electrodes act as interfaces between the electrical stimulator and the nervous system. Surface electrodes are used exclusively for routine physical therapy. FES electrodes can be external (surface) or surgically implanted depending on the application, device, and the patient's needs.

General Information:

2) Therapeutic Exercise: Individuals with SCI can suffer further health impairment through chronic lack of physically balanced exercise. Long-term wheelchair use can lead to overuse syndrome and upper extremity pain. Individuals with SCI are much more likely to develop Type-II diabetes that the general population. Due to elevated cholesterol levels they develop coronary heart disease three to four times more often than the able-bodied. Also, poor circulation in extremities contributes to risks of pressure sores and impaired wound healing.

FES-assisted therapeutic exercise (TE) may offer varying degrees of physical benefits that address these concerns. Primary limiting factors are level of injury, availability, and exercise regimen consistency.

SCI above C5 impairs the body's ability to match cardiac performance with physical exertion. The heart cannot adequately respond to exercise and its ability to benefit from exercise over time is impaired. Therefore, tetraplegic subjects with injuries above C5 may not fully benefit from FES-assisted upper extremity cycling.

However, Christopher Reeve, whose injury was clinically classified a C2 complete, reportedly benefited from the use of an FES lower extremity cycle (see discussion under Dr. John McDonald in the Aggressive Rehabilitation section).

FES-assisted ergometers that exercise lower extremities are more readily available for home use than upper extremity FES TE devices. Individuals interested in upper extremity FES-assisted TE should discuss this modality with their rehab physician.

FES TE primarily uses ergometers (stationary cycles or hand cranks) to exercise upper or lower extremities. FES-assisted rowing is being developed in Canada and the United Kingdom. Physical benefits resulting from FES TE include improved cardiac output, peripheral venous (blood) return, and muscle oxidative capacity. Persistent FES TE can decrease spasticity, while increasing plasma endorphins, muscle bulk, range of motion, and bone mineral density. FES TE can improve glucose tolerance and insulin sensitivity, cortisol levels, wound healing, and self image.

FES ergometers use surface electrodes to activate muscles in a programmed sequence, facilitating smooth crankshaft rotation. Two machines, the ERGYS 2 system (photo) by Therapeutic Technologies Inc., and the Functional Electrical Stimulation Motorized Ergometer (Model RT300-S) by Restorative Therapies, Inc., are currently approved for use in the U.S. Additional machines may be available in Europe and Asia. The user sits on the ERGYS 2 machine, whereas the RT300-S is designed for use from the wheelchair.

Links to Device resources:

Lower-extremity FES-assisted devices:

Research and Development:

3) Standing/Ambulation: In addition to the physical effects of exercise, FES for standing, transfer, and ambulation applications can offer functional and psychological benefits. Physiological effects can include improved digestion, bowel and bladder functions, retardation of bone-density loss, decreased spasticity, reduced risks of pressure sores, improved cardiovascular health, improved skin and muscle tone. Functionally, FES-assisted ambulation can allow the user greater access to locations inaccessible to wheelchairs, assist transfers, and facilitate face-to-face interaction with others.

FES systems for standing and ambulation can be strictly FES, or combine FES with various types of braces (hybrid systems), including foot and ankle, knee, and long leg braces. All FES standing or ambulation systems use walkers, parallel bars, or elbow (Canadian) canes for balance and support. Depending on the system being used, and its application, physical requirements and contraindications for FES-assisted walking can vary. General guidelines are as follows:

Requirements:

Contraindications:

The physical effort of FES-assisted ambulation is six to eight times that of able-bodied walking. For this reason, less than five percent of those who ambulate with FES walk more than 1,500 meters without rest. FES ambulation is therefore not considered to be a practical replacement for wheelchairs. Nevertheless, for those who are able and motivated to ambulate using FES, the quality of life and physical benefits this modality offers may be significant.

The Parastep^® is a widely used, commercially available FES standing/ambulation system by Sigmedics, Inc (photo from company website). This system uses six output channels to stimulate the right and the left quadriceps muscles for leg extension, the right and left common peroneal nerve for hip flexion, and the right and the left paraspinal muscles (or the gluteus maximus) for trunk stability. Its 7.6-ounce stimulator (attached to a belt) connects via wire leads to twelve self-adhesive electrodes. The surface electrodes, which require no gel, are reusable for 14 days. They are attached in the morning and removed each evening, or as desired. The stimulator’s battery pack is rechargeable. Manual controls for the Parastepâ system are located on the walker’s hand grips for convenient access.

Several training programs are recommended for new Parastepâ users, which reveal the degree of commitment and work needed to safely and effectively walk with FES. Programs vary, but all involve considerable time and effort:

All Parastepâ training programs recommend that the patient supplement the supervised training with fifteen minutes or more of after hours work daily.

In addition to the commercially available Parastepâ, clinical trials in several countries offer a means for motivated individuals who meet requirements to experience FES standing and ambulation benefits. FES systems being studied include systems with implanted or surface electrodes, open- or closed-loop control, and hybrid FES/orthotics systems.

Clinical Trials:

Comparative Studies:

Miscellaneous:

4) Manual Grasping Control: FES can offer quality of life benefits for those with upper extremity impairment. However, rapid changes have affected its use for manual grasping in recent years. The primary implanted FES grasping device, The Freehand™ system, is no longer available. Currently, the only commercially available FES grasping device is the external Ness H200.

Wireless electrode technology for all FES, including upper extremity grasping, is being developed to avoid the risks of infection (due to external wire leads) and provide lead-free ease of movement. Also, thought-controlled FES may be a future option for those with high-level SCI. This overview is provided in anticipation of emerging FES options for those with upper extremity SCI.

Individuals with complete tetraplegia who use FES to facilitate manual grasping report greater independence from adaptive equipment, a reduced need for personal assistance, and improved self-image. FES grasping assistance can increase the number of activities an individual can perform or improve existing abilities.

FES manual grasping can also be a rehabilitation tool. FES grasping reportedly improves voluntary manual control  in some with complete or incomplete tetraplegia when used between 1-67 months post injury. Whether used for rehabilitation or daily functional use, FES can facilitate three grasping techniques.

A surface FES conditioning program may be needed to retrain disused muscles before implanted systems are applied. Reconditioning can take from one to three months, requiring several hours of work each day. Multiple visits are usually needed to properly fit electrodes, to train personal assistants in their placement, and to monitor progress. For these reasons the best results using upper extremity FES are often found in individuals strongly motivated to use FES who have good social support.

Physical requirements for upper extremity FES include:

Individuals considering upper extremity FES for manual grasping should be professionally evaluated to determine if they meet the physical requirements. Standard ‘ASIA’ functional tests fail to distinguish functionality in specific muscles of the forearm and hand. The International Classification of Hand Function in Tetraplegia was established to meet this need. In addition, the strength and control of proximal musculature must be assessed.

Contraindications can limit the safe use of upper extremity FES. In some cases, such as diabetes, a condition may not present an absolute barrier, but a doctor should determine this point. Upper extremity FES contraindications include:

According to the makers of the Ness H200, “The only way to determine if the NESS H200 is the right rehabilitation therapy for you is to contact your physician or rehabilitation medical specialist.” This prudent advice is applicable for all FES systems, for any FES application.

FES Manual Grasping Clinical Trials:

5) Bladder/Bowel Management: FES may offer a means of bladder control for qualifying individuals with SCI. In Europe, Asia, and the U.S., two devices provide this service, the Brindley/Vocare^TM by FineTech Ltd. and the InterStim^TM system by Medtronic, Inc. Both products are surgically implanted. Both stimulate sacral nerves to achieve desired effects. However differences in design affect their relative ability to address SCI-related bladder or bowel incontinence.

The Interstim was not specifically designed for SCI use. Unlike the Brindley/Vocare device, implantation of the InterStim does not involve the cutting of nerves. Therefore the InterStim can be used to treat urinary incontinence in individuals with complete and incomplete SCI. Clinical results using Interstim – not specifically for those with SCI – indicate that reliable continence is achieved in two out of five cases.  An additional 34% of InterStim users report that urinary incontinence is reduced by 50% or greater.

Continence is achieved using the Brindley/Vocare system in 85% of its users with SCI. Secondary to bladder control, 50% of Brindley/Vocare users report that it assists in bowel management. Sixty percent of its male users can produce erections with the device.

The ideal candidate for the Brindley/Vocare bladder-control system is an individual with complete SCI who suffers periodic bladder incontinence and frequent urinary tract infections. The user should be able to transfer to the toilet or wear a condom catheter. The Brindley/Vocare system drains the bladder’s volume to less than 50 cc, which eliminates the need for internal catheterization and greatly reduces risks of infection.

The use of the Brindley/Vocare is restricted to those with complete SCI because it often requires the cutting of sacral sensory nerves and bladder nerve roots. The former provides a means for stimulating bladder contractions. The latter eliminates reflex incontinence due to bladder spasms. However, cutting sacral sensory nerves permanently block the sensations needed for reflex erections. Cutting bladder nerve roots preclude spontaneous improvements in voluntary bladder control.

Studies are underway to determine if combined anterior and sacral stimulation can provide adequate bladder control without cutting sacral sensory nerves.

Surgically implanted components of the Brindley/Vocare system include an electrical stimulator, wire leads, and cuff electrodes. The stimulator is implanted in the abdomen under the skin, usually beneath the ribs. Silicon-coated electrodes are implanted around surgically exposed spinal sacral roots. Implanted wire leads connect the components. The surgery needed to implant the Brindley/Vocare device lasts from five to eight hours, requiring an average hospitalization of four to five days. Pre-operative testing can take two to three days, usually on an outpatient basis

Using separate frequencies and pulse durations, an external radio frequency control device directs the Brindley/Vocare system to stimulate lower bowel contractions or reflex erections. To achieve an erection the transmitter must be held over the implanted receiver/stimulator while in use.

As is true of all FES, peripheral nerves must be intact to target organs in order for FES to effectively address urinary incontinence. An urodynamic study can determine if an individual is a good candidate for Brindley/Vocare bladder control. Medtronic Inc., the makers of the InterStim device, offer a temporary external system (through participating physicians) that tests whether the InterStim is likely to be effective for prospective users.

Basic physical requirements for the Brindley/Vocare bladder control include the following:

Clinical Trials and Resources:

6) Respiratory Support: Note: Recent advances in FES-respiratory support may be available only through clinical trials or medical research centers. Those interested in this technology are urged to discuss its potential with their doctor and investigate the indicated links.

FES-Assisted Breathing: Since the 1960s, FES has provided respiratory assistance for individuals with SCI, especially those with C5 or above respiration-compromising injuries. Although mechanical ventilation provides respiratory support, it distorts the voice, limits mobility, and increase infection risks. Using FES to stimulate diaphragmatic contractions, called phrenic-nerve pacing, allows users to minimize ventilator use. This can improve the subject’s mobility and speech, while reducing respiratory secretions, respiratory-infection incidence, and personal care needs. Unfortunately, phrenic-nerve pacing is not an option for all who require respiratory support.

SCI between C3-5 can damage the cord’s anterior horn cells, which can denervate two diaphragm-controlling phrenic nerves that FES stimulates. Therefore, bilateral phrenic nerve functionality must be confirmed before phrenic-nerve pacing is considered. This functionality is verified by testing phrenic-nerve conduction velocities or observing diaphragm movements by fluoroscopy imaging.

Individuals interested in phrenic-nerve pacing, who have denervated phrenic nerves, may be able to overcome this obstacle through the surgical transfer of intercostal nerves (Kreiger LM & Kreiger AJ, Plast Reconst Surg 105(4), 2005). Eight of 10 subjects who had this surgery achieved successful diaphragmatic pacing. An average of nine months was required for transferred nerves to innervate the diaphragms of these eight and respond to stimulation.

For individuals with one functioning phrenic nerve, it may be possible to achieve full or partial ventilator independence by combining intercostal muscle stimulation with unilateral phrenic-nerve pacing.

A surgical improvement over conventional phrenic-nerve pacing is intramuscular-diaphragm pacing. This relatively new technique also stimulates phrenic nerves, but unlike phrenic pacing, intramuscular-diaphragm pacing does not require the cutting of phrenic nerves. Moreover, the surgery required for intramuscular-diaphragm pacing can be done on an outpatient basis or overnight hospitalization, whereas traditional phrenic-nerve pacing requires five to ten days of hospitalization.

Provided the phrenic nerves are intact or the diaphragm can be innervated through intercostal nerve transfer, FES-respiratory assistance is a treatment option for those on ventilation regardless of time post injury. However, respiratory muscles atrophy from chronic disuse, which occurs with mechanical ventilation. Therefore FES respiratory support requires an initial training period. During this time, the diaphragm is stimulated in gradually increasing intervals, which rebuilds and strengthens atrophied muscles.    

Additional information on intramuscular diaphragm pacing:

FES-Assisted Cough: Abdominal muscle impairment due to SCI (T7 and above) can affect coughing ability needed to clear airways of secretions and irritants. In addition to clogging breathing airways, coughing inability increases risks of respiratory infections and can lead to atelectasis (a collapsed or airless state of the lungs). Several techniques provide cough assistance: manual cough through caregiver assistance, the use of cough-assistance devices, functional magnetic stimulation of expiratory muscles, or FES-assisted cough.

FES-assisted cough involves taking a deep breath and then coordinating FES-stimulated abdominal contractions with forced expiration. In addition, abdominal FES stimulation can also be used to regulate blood pressure. An external FES system for cough assistance, called Quik Coff™, was reportedly effective but is no longer commercially available.  Those interested in FES for cough assistance should discuss its potential with their physician, or contact an appropriate FES clinical facility.

Additional FES-for-cough-assistance information:

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