Functional Electrical Stimulation (FES) ©
I. Electrical Stimulation (E-stim)
Application of electrical stimulus to a nerve or muscle is termed electrical stimulation. As electrical current passes through a muscle/nerve fiber, partial depolarization of the cell at the region of the cathode will occur and if the level of depolarization reaches a critical value, muscle fiber contraction will occur. This effect can be used for muscle reeducation and strengthening, retardation of atrophy, tissue healing, pain and tone control. Specifically, we use electrical stimulation in our SCI patients during their acute rehabilitation period in order to preserve muscle mass and prevent denervation atrophy in muscles in the upper extremities. In the case of chronic SCI, electrical stimulation is used to initiate the lower extremities ERGYS bicycle program in order to modulate tone and avoid traumatic fractures of the osteoporotic lower extremity bones. We also use e-stim to assess stimulable muscles in patients considered for implantation of an upper extremity functional electrical stimulation system (Freehand).
II. Functional Electrical Stimulation (FES)
Application of an electrical stimulus to the paralyzed nerve or muscle to restore or achieve the desired function is known as FES. Electrical stimulus can be applied either by surface stimulation (stimulus is delivered transcutaneously), or through an implanted stimulation system (percutaneous, epimyseal or even on the nerve). The best-known FES devices are cardiac pacemakers and defibrillators as well as cochlear implants. FES has a wide range of clinical applications in spinal cord injury as described in Table 1.
Table 1. Clinical Applications of Electrical Stimulation for SCI
Muscle Strengthening
Cardiovascular Conditioning, improvement of circulation
Cough and breathing assistance
(Avery Phrenic Pacing System)
Assistance with transfers and standing
Assistance with walking
Erection and Ejaculation
Bladder and bowel control
(Vocare SystemÓ - FDA approved 1998)
Hand grasp and release
(Freehand SystemÓ-FDA approved 1997)
Pain control
Spasticity control
Prevention and treatment of contractures
Treatment of pressure ulcers
III. FES for restoration of hand function
FES in tetraplegic patients has focused primarily on restoring grasp and pinch function. The best candidates are patients with C5/C6 level of injury who have preserved peripheral innervation to the muscles that are considered for electrical stimulation. These muscles should also demonstrate the ability to generate sufficient strength and be fatigue resistant.
To improve function of a paralyzed hand in a C6 tetraplegic patient, the most common approach of traditional rehabilitation has been to use an orthotic device to translate wrist extension motion into passive finger flexion motion to achieve grasp function (tenodesis splint). These orthoses are not always effective, are cumbersome to use, require assistance to apply, and only marginally improve hand function. For patients with injuries causing loss of function at C4 level, orthosis are not usually effective, and other treatment options to restore hand function are very limited.
Use of FES systems in persons with injuries at C5/C6 levels offers a unique treatment opportunity for restoring hand function. NeuroControl Freehand System (Figure 1) is an implantable FES system approved by U.S. Food and Drug Administration (FDA) in 1997 for people with tetraplegia to regain use of the paralyzed hand. Candidates eligible for the Freehand system should meet specific requirements (Table 2).
Table 2. FREEHAND System Selection Criteria
C5 or C6 ASIA motor level
Skeletal maturity
Good health
Intact vision
Adequate proximal muscles strength
Controlled spasticity
Adequate range of motion in upper extremity
Stable neurologic lesion (minimum 12 months after injury)
Good wheelchair balance
Independent with wheelchair mobility
Intact lower motor neuron lesion
Adequate social support
Motivated patient with realistic goals
As of now, there are no available adaptive devices or treatments to restore hand function in persons with injuries at C4 or above.
IV. FES system for lower extremities
FES systems for strength training and cardiovascular conditioning utilize computer controlled closed – loop systems which provide electrical activation to the lower extremities muscles in a sequential and alternating pattern. Electrical activation of muscles occurs through surface electrodes applied to hip extensors (gluteal groups), knee extensors (quadriceps) and knee flexors (hamstrings). The FES principle is built into a stationary bicycle ergometer allowing the patient to pedal the bicycle. Two commercial systems are currently available: ERGYS (Figure 2) (www.MusclePower.com) and StimMaster (www.electrologic.com). Both systems can be used at home and in hospital/clinic environment.
The systems provide cardiovascular conditioning when training is performed at 35-50 RPM for approximately 30 minutes/day 3-5 days/week. Other benefits may include improvements in muscle mass, blood flow, improvement of bladder and bowel function, decrease in urinary tract infection as well as reductions in the severity of spasticity and spasms and other secondary medical complication of SCI. Furthermore, common medical complications of SCI such as venous thrombosis, skin breakdown, osteoporosis and pathological bone fractures may be reduced. The stimulation is not well tolerated if the patient has either normal or partially preserved sensation in the lower extremities as the intensity of required electric current required is high (100-140A). More recent evidence from studies in animal models suggests that electrical stimulation of muscles below the level of the injury might facilitate neural regeneration and re-establish patterned activation of the injured CNS.
FES of lower extremities is also applied for restoration of standing and stepping function in paraplegic patients; however, patients need extensive bracing and assistive walking devices such as walker of crutches for balance. These activities require intensive and prolonged training and demand high metabolic energy consumption, which significantly limit true functional utilization of these systems.
V. Phrenic nerve pacing
Electrical stimulation of the phrenic nerve (Figure 3) in order to achieve effective diaphragmatic contraction has been available in clinical practice for the last 25 years, being employed in the care of patients who have damage to the respiratory control centers or their pathways in the brainstem or spinal cord above the origin of the phrenic nerve (generally C3 and above). It requires the presence of intact phrenic nerves although an intercostal to phrenic nerve anastomosis performed together with implantation of a pacing electrode has been used to reinnervate recently denervated diaphragm. Pacer implantation should be done only in complete injuries and after the one-year post-injury mark, as there is a risk of nerve damage.
Pre-implantation evaluation includes performance of electromyographic and fluoroscopic assessment of the diaphragm and nerve conduction studies of the phrenic nerves. Cuff electrodes are placed around the phrenic nerves in the upper thoracic area to ensure stimulation of all phrenic axons. Post-operative care requires 4-6 weeks of mostly inpatient training. Cost, surgical risk, components failure and need to retain a tracheostomy are limiting factors.
VI. Restoration of bladder and bowel function
Voluntary and conscientious control of bladder and bowel function is lost or significantly impaired after SCI depending on the severity and degree of incompleteness of injury. FES technology offers new solution in this arena as well. VOCARE Bladder System is an implantable FES device, which consists of External controller, External Transmitter, Implantable Receiver – Stimulator and implantable electrodes (Figure 4). The system is operated by the radio frequency signal, which activates electrodes placed on the sacral spinal nerve roots (S2 – S4) leading to bladder/large bowel and urethral/ anal sphincter contraction. Contractions alternate with relaxation in between bursts of stimuli – sphincters relax while bladder/bowel continue to contract allowing urination/defecation to occur.
The VOCARE System was approved by FDA in 1998 and is available for the appropriately selected patients exclusively through NeuroControl Corporation (www.neurocontrol.com). This system is not indicated for every patient with spinal cord injury and a clear understanding of the benefits, risks, and limitations is important for both physicians and patients in order to make proper recommendations and sound decisions. Primary indications for the VOCARE System include: suprasacral and clinically complete spinal cord lesion, intact peripheral (parasympathetic) innervation of the bladder in a skeletally mature and neurologically stable patient. Benefits of the VOCARE System include urination on demand, elimination of urethral catheters, decreased incidence of incontinence, improved bladder emptying, decreased incidence of urinary tract infections, and enhanced bowel evacuation. Most patients report significant reduction of time required for the bowel program.
To eliminate reflex bladder incontinence, improve bladder compliance, reduce detrusor – sphincter dyssenergia and reduce risk of hydronephrosis, implantation of the VOCARE system is combined with the dorsal (sensory) rhizotomy (S2 – S5) performed through laminectomy at 5 levels, L3 – S2. This procedure, however, causes loss of perineal sensation, loss of reflex erection and ejaculation. Loss of the latter two functions presents a significant concern to male SCI patients even though these functions are quite impaired after spinal cord injury. It is important to know that alternative options such as papaverine injections, external devices, and penile implants are available and about 1/3 of males can achieve penile erection while using VOCARE system. In general, the disadvantage of the system is the requirement for a major surgery and dorsal rhizotomy. For many patients, the concept of a major surgery is a problem and the idea of inducing additional damage (rhizotomy) is even a greater barrier.
NeuroControl is currently developing a new approach to electrically inactivate dorsal roots function. This will eliminate the need for the rhizotomy procedure and hopefully eliminate it from the VOCARE system requirements. Approximately 50 Vocare systems have been already implanted in the US and over 1500 similar systems have been implanted in Europe. Considerable outcome data is available from the European experience. The advantages offered by the system include improvement of the quality of life, social ease, reduction and prevention of urinary tract complications and long term cost savings. The VOCARE system pays for itself and begins to accrue net savings within 5 years after implantation.