Functional electrical stimulation and lower extremity bracing for ambulation exercise of the spinal cord individual: a medically prescribed system.

Functional Electrical Stimulation and Lower Extremity Bracing for Ambulation Exercise of the Spinal Cord Injured Individual: A Medically Prescribed System

The purpose of this study was to determine whether commercially available electrical muscle stimulators could provide functional ambulation exercise for the spinal cord injured individual. Commercially available electrical muscle stimulators were used for functional electrical stimulation and interfaced with reciprocating gait orthoses so that a new system has been developed. Advantages of the system include commercially available subsystems and subsystems for applications such as gait training. The system involves six electrical stimulation units worn on a belt; controlled by remote switches; and interfacing to electrodes placed over the quadriceps femoris, hamstring, and gluteal muscle groups of each leg. Four electrical stimulation units (for quadriceps femoris muscle stimulation) function primarily for stand-up and sit-down activities. Two other units (for stimulation of the hip extensor muscles) function primarily for ambulation. The system is described for use with a C7-level quadriplegic individual. The patient successfully performed over 20 repetitions of stand-up and sit-down exercises with the system. An average walking distance of about 0.8 km was routinely traversed at velocities ranging from 1.2 to 2.0 km per hour. It was concluded that muscle fatigue, rather than battery power, was the functionally limiting factor for the quadriplegic patient. A recommendation is that application of the system for walking exercise should be preceded by a physical conditioning program of functional electrical stimulation. Specific medical criteria should be satisfied prior to formally prescribing the system for an individual. Finally, the steps involved in the writing of the walking system prescription are outlined. [Phillips CA: Functional electrical stimulation and lower extremity bracing for ambulation exercise of the spinal cord injured individual: A medically prescribed system. Phys Ther 69:842-849, 1989]

Key Words: Ambulation aids; Electrotherapy, electrical stimulation; Gait; Spinal cord injuries.

Different investigators have used functional electrical stimulation for standing and walking via a variety of lower extremity neural prostheses.[1-6] In 1982, computer-controlled standing and walking with FES was introduced by researchers at Wright State University (Dayton, Ohio). The investigators used closed-loop control,[5],[7] and their approach has recently been reviewed.[8] Closed-loop control requires that data from sensors modify the output of a controller to help coordinate walking. Sensors are placed on the hips, knees, or ankles of the paralyzed subjects to provide positional data for the computer controller.[7],[9] Closed-loop control was developed using animal experiments,[10-12] although it was originally proposed for use on humans.[13,14]

More recently, a portable FES walking system has been developed and used in combination with a lower extremity orthosis.[15],[16] With such a combination system, selected patients have been able to regularly walk distances of up to 1 mile.(*)[17]

A major thrust of our laboratory during the past year has been to make this technology available to the medical community for use by the general spinal cord injured population. The limitations of our past approach have been[15,16]

1. A heavy and separate portable

power pack (consisting of four

Kodavision([single dagger]) 8-V batteries and eight

lead-acetate 2-V batteries). This

power pack weighs approximately

8 lb([double dagger]) and is carried on the back. 2. A heavier, bulkier FES electronic

package when the sit-down-stand-up

capability was combined with

the basic walking system. 3. A specialized and custom-built

electronic package and power

pack.

This article describes a new system that overcomes these limitations. By using commercially available electrical muscle stimulators in combination with reciprocating gait orthoses (RGOs), a new system has been developed. The advantages of the system are

1. The power pack is now reduced to

a single 9-V alkaline battery 

contained within each electrical

stimulator. 2. A total of six electrical stimulators

(each weighing less than 6 oz,([section])

with battery) provide complete

stand-up-sit-down and walking

functions. 3. Each component of the walking

system is commercially available

from various manufacturers,

recommended for applications such as

gait training, and available as a

prescription item from a physician.

The purpose of this study was to determine whether commercially available, physician-prescribed electrical stimulators, when appropriately interfaced and combined with orthotic bracing, will allow a quadriplegic patient to stand up, sit down, and functionally walk on level ground.

Method

Subject

A spinal cord injured individual participated in this study with informed consent. "GB" is a 28-year-old man with C7-level quadriplegia secondary to a spinal cord injury incurred six years previously. He sustained an incomplete injury with some sensation and slight (but functionally useless) movement below the level of injury. A somewhat modified system has been described for a paraplegic subject.[18]

Materials

Electrical muscle stimulator. The FES unit used in this study was the EMS-8100 muscle stimulator.(~~) The unit's technical specifications are given in Table 1. Six EMS-8100 muscle stimulators, designated as units A, A [prime], B, B [prime], C, and D, were used. Units A, A [prime], B, and B [prime] were worn in the front on a belt (Fig. 1), and units C and D were worn on the back of the belt.

The initial operating characteristics were adjusted for one set of values for units A, A [prime], B, and B [prime] and for another set of values for units C and D (Tab. 2). These operating characteristics were subsequently adjusted during the course of the study for optimal individual performance.

Switches. A commercially available remote control switch(~~) was part of the system. This device is a slide-type switch, normally "off," that will slide to and hold in the "on" state. Pressing down on the switch slide while in the "on" position activates a spring return to return the slide to the "off" position. The switch connects to a length of cable that is terminated by a subminiature phone plug. This plug inserts into the manual override jack on the side of the muscle stimulator. When the switch is "off," the contacts on the phone plug are open and no stimulation current is delivered from stimulator channels A and B to the electrodes. When the switch is "on," the contacts on the phone plug are shorted and stimulation current is delivered via both channels of the electrical stimulation unit to the electrodes.

The patient had some movement of the thumb and index and middle fingers of the left hand, but no thumb or finger movement of the right hand. One slide switch and two push-button switches, therefore, were mounted near the left handle of a conventional walker. The two push-button switches were mounted adjacent to each other on the medial side aspect near the walker handle. These switches were connected by ribbon cable to a subminiature cable connector (male) that was interconnected with a subminiature cable connector (female). The latter connector separated as two cables, each terminating with a subminiature phone plug that then connected to the manual override jacks of FES units C and D.

One remote slide switch was mounted near the left handle and oriented 45 degrees obliquely between the medial side aspect and the superior aspect (Fig. 2). The remote slide switch cable was then divided into four cables connected in parallel. Each cable was then terminated with a subminiature phone plug that was connected to the manual override jacks of FES units, A, A [prime], B, and B [prime].

In operation, the anterior and posterior push-button switches were actuated with the index and middle fingers and the slide switch was actuated with the thumb. The left palm and remaining fingers assisted with positioning and gripping of the walker handle.

Batteries. Nine-volt alkaline transistor batteries were used because each electrical stimulator was designed to operate with 9-V batteries. Rechargeable 7.2-V nickel-cadmium batteries were tried, but did not provide sufficient voltage amplitude to meet the particular current demands of the application.

Electrodes. This study used ten 2- x 4-in(#) Medtronic [R] Model 3793 carbon-rubber electrodes(**) and four 1.5- x 1.5-in Medtronic [R] Model 3795 carbon-rubber electrodes.(**) A Transcutaneous Transducer Garment (TTG)([single dagger][single dagger]) has also been successfully tested and used in our walking protocols, but has not been fully tested for stand-up- and sit-down-type activities.

As shown in Figure 3, four 2- x 4-in carbon-rubber electrodes were placed over each quadriceps femoris muscle group for a total of eight electrodes. Liqui-Cor [R] electrode gel([double dagger][double dagger]) was first applied, and then both adhesive patches and adhesive tape were used to secure the electrodes.

As shown in Figure 4, one 2- x 4-in carbon-rubber electrode and one 1.5- x 1.5-in carbon-rubber electrode were placed over each gluteal muscle group and each hamstring muscle group for a total of eight electrodes, four of each type. Electrode gel and adhesive were used as described previously. The FES units A and A [prime] were connected to the right quadriceps femoris muscle (Fig. 5), and units B and B [prime] were connected to the left quadriceps femoris muscle. The FES unit C was connected to the right hip extensor muscles, and unit D was connected to the left hip extensor muscles.

Lower extremity orthosis. The lower extremity orthoses used in this study were both right and left hip-knee-ankle-foot orthoses. Coupling occurs between the left and right orthoses in such a manner that hip extension in either one tends to force the other hip joint into flexion. This coupling provides coordinated motion between the legs and makes possible a "reciprocating" gait. A Bowden cable transmits the force from one orthosis to the other. Disconnects at each hip joint permit simultaneous flexion for sitting. A custom-molded plastic pelvic girdle was used.

The posterior thigh shells and the ankle-foot sections consisted of polypropylene molded over plaster models of the patient's lower extremity. Reinforcements of carbon-fiber inserts about the malleoli sections permitted the use of thin polypropylene. Aluminum offset knee joints were used. Each of the HKAFOs was provided with a drop lock and retention ball spring on the patient's lateral side.

System costs. Table 3 reports the initial cost (for a five-year period) for a FES-RGO program consisting of five walking sessions per week. Table 3 also reports the recurring costs on an annual basis for a FES-RGO walking program composed of five sessions per week. Table 4 reports the cost for each individual walking session using the FES-RGO system.

Overall, Tables 3 and 4 summarize the outpatient physical therapy costs associated with the prescription of the electrical stimulation system for ambulation of the spinal cord injured (quadriplegic) patient. Comparable data have been published for the outpatient physical therapy costs associated with the prescription of a similar system for paraplegic patients.[18]

Procedures

The walking system interacts with the patient to allow him or her to perform a variety of tasks including standing up, walking, turning, and sitting down.

Stand-up-sit-down procedure. This procedure is treated as two entirely different procedures. The stand-up procedure is performed as follows:

1. Subject sits with forelegs bent

slightly backward at the knees.

Subject leans forward at the hips (ie,

over knees). 2. Seat is elevated so that subject's

hip is flexed less than 90 degrees

(Fig. 6). 3. Activate FES units A, A [prime], B, and B [prime]

in the "constant-on" mode. 4. Subject rises as though in a

"forward-upward dive"

configuration (ie, on balls of feet). 5. When erect, subject inclines

backward (on heels of feet) to lock

knees. 6. Activate units C and D in

"continuous" mode for hip lock; hold only

until locked. 7. Deactivate units C and D. 8. Deactivate units A, A [prime], B, and B [prime];

allow time to "ramp down." 9. Proceed to "walk" mode. The sit-down procedure is performed as follows: 1. Subject stands upright about 4 to 6

in forward of the sitting platform

(Fig. 7). 2. Subject unlocks hip locks with

each hand separately (other hand

on walker). 3. Activate units C and D in

"continuous" or "intermittent" mode as

necessary to maintain upright balance. 4. Activate units A, A [prime], B, and B [prime] in

"continuous" mode; allow time to

"ramp up." 5. Release knee locks. 6. Deactivate units A, A [prime], B, and B [prime]. 7. Subject proceeds to sit down as

stimulation "ramps down."

Walking procedure. The walking procedure may be performed with either forward stepping or backward stepping. The forward-walking procedure is performed as follows:

1. With the right foot arbitrarily

positioned somewhat forward of the

left foot and weight equally

distributed on both feet, the subject takes

a left step forward. 2. Weight is shifted so that all weight

bearing is on the right foot. 3. Unit C is activated, resulting in

right hip extension. 4. The reciprocal connection of the

cross-connected hip cables ensures

contralateral (left hip) flexion. 5. Subject swings left leg forward; unit

C is deactivated simultaneously. 6. Weight is redistributed equally on

both feet with the left foot now

somewhat forward of the right

foot.

To continue forward walking, the procedure is repeated by shifting weight to the left foot and activating unit D, as appropriate. By alternating the shifting of weight and activation of the appropriate FES unit, the subject walks forward.

The backward-walking procedure is performed as follows:

1. With the right foot arbitrarily

positioned somewhat forward of the

left foot and the weight equally

distributed on both feet, the

subject takes a right step backward. 2. Weight is shifted so that all weight

bearing is on the left foot. 3. Unit C is activated, resulting in

right hip extension. 4. Subject swings right leg backward;

unit C is deactivated simultaneously. 5. Weight is redistributed equally on

both feet with the right foot now

somewhat behind the left foot. To continue backward walking, the procedure is repeated by shifting weight to the right foot and activating unit D, as appropriate. By alternating the shifting of weight and activation of the appropriate FES unit, the subject walks backward.

Turning procedure. The same turning procedure is used regardless of whether the person is making a 90-degree or a 180-degree turn. The turning procedure is performed as follows:

1. No FES is necessary. 2. Pattern follows a "military

maneuver" style. 3. Rightward turn is on heel of right

foot and ball of left foot. 4. Leftward turn is on heel of left foot

and ball of right foot. 5. Pattern proceeds as sections of an

arc, in between which the walker

is repositioned.

Results

The patient in this study performed over 20 acceptable repetitions of stand-up and sit-down exercises in the walking system. About five stand-up efforts were unsuccessful, primarily because of body position (eg, feet not behind knees, hip angle greater than 90 [degrees]). Inadequate quadriceps femoris muscle strength conditioning was a limiting factor for this quadriplegic patient. After two or three stand-up and sit-down efforts, the amplitude setting of FES units A, A', B, and B' had to be increased to the maximum of 9.0. At this point, all four units were providing maximal stimulation. Quadriceps femoris muscle fatigue then occurred after another two or three stand-up and sit-down efforts. The patient routinely averaged about 0.8 km of walking per experimental session at walking velocities ranging from 1.2 to 2.0 km per hour (Fig. 8). Muscle fatigue was usually the limiting factor (after 30 minutes to 1 hour) for this quadriplegic individual. The patient altered the initial electrical stimulation characteristic settings (before the end of the walking episode) such that the frequency (rate) setting was increased to the maximum of 100 Hz and the amplitude setting was increased to the maximum of 9.0.

In addition to the actual walking time, additional time was needed for the preparation of the patient. At the beginning of each walking session, 30 to 45 minutes was required to attach the electrodes, apply the orthosis, and attach the stimulation units. At the conclusion of each walking session, another 30 minutes was required for removal of the gait orthosis, electrodes, and stimulation units.

Discussion

A majority of previous FES walking systems have used only electrical stimulation.[1-6] Petrofsky and colleagues were the first investigators to combine electrical stimulation with reciprocating gait orthotic devices.[15,16] This study has demonstrated that commercially available electrical muscle stimulators can now be used as the FES component (in combination with the gait orthosis) to allow walking in the paralyzed individual.

This study has determined that commercially available, physician-prescribed electrical stimulators, when appropriately interfaced and combined with orthotic bracing, allow a quadriplegic patient to perform stand-up and sit-down tasks and functional (level-ground) walking. Specifically, the quadriplegic patient in this study successfully performed over 20 stand-up and sit-down repetitions with the system. Furthermore, the patient routinely averaged about 0.8 km of walking at each experimental session at velocities ranging from 1.2 to 2.0 km per hour.

Muscle fatigue, rather than battery power, was the limiting factor in all the experimental trials. As fatigue approached, stimulation characteristics were increased to their maximum settings.

In any one experimental session, the patient was able to perform only about four to six stand-up and sit-down repetitions. The patient traversed an average of about 0.8 km per experimental session. Phillips, however, has shown for a quadriplegic individual that the system is capable of about 40 stand-up and sit-down repetitions and a total distance of about 4 km covered before the 9-V alkaline batteries must be replaced.[19]

The advantages of this approach (compared with the use of conventional braces alone) are that 1) good upper extremity strength is not necessary to produce the reciprocating gait pattern, 2) stand-up and sit-down procedures can be performed in an easy and coordinated manner by the subject alone, and 3) improved cardiopulmonary conditioning is achieved as reflected by reduced energy expenditure.[18] The disadvantages of this approach (compared with the use of conventional braces alone) are that 1) more time and more effort are required to apply electrodes and connect the stimulation units, 2) the patient's walker must be modified to accommodate the remote-control switches connected to the stimulation units, and 3) additional funds are required to purchase the electronic equipment.

As with any treatment modality, the patient must medically qualify for the equipment being prescribed. Specific medical criteria must be satisfied for prescription of walking exercise with the FES-RGO system. The initial evaluation of the patient includes a medical history, a physical examination, laboratory tests (eg, electrocardiogram, pulmonary function testing, serum chemistry, urinalysis), a report summary, and a FES prescription (level of clearance), as previously described by Phillips.[20]

In the Wright State University program, the isokinetic leg exerciser is currently considered to be the entry-level FES exercise modality. Progression to the FES bicycle ergometer requires adequate flexion and mediallateral stability at the knee, in addition to minimal dorsiflexion at the ankle.[20] Progression to the walking system and walking exercise then requires muscular, cardiovascular, and respiratory system function sufficient for 30 minutes of continuous FES bicycling at minimal (0 km per minute) load. Other medical criteria for walking exercise with the walking system are summarized elsewhere.[20]

The writing of the walking system prescription proceeds after the fulfillment of two prerequisites: 1) completion of the preliminary conditioning phases of a walking program and 2) satisfaction of the medical criteria for walking exercise with the FES-RGO system. The prescription is composed of two parts. The first part is prescription of the RGO and preliminary gait training. A pictorial description and applications manual is available from the manufacturer.[21] The prescription is to be filled by a certified orthotist knowledgeable about and competent in the fitting of this type of orthosis. Finally, suitable arrangements must be made with a physical therapist for gait training using the orthosis.

The second part is prescription of the electrical muscle stimulators. Technical information on the electrical stimulators is available as a patient instruction booklet from the manufacturer.[22] Next, the physician prescribes the electrical stimulators, which is usually a "hands-on" demonstration because the manufacturer provides the FES units of the physician on a consignment basis. The information provided in this article should provide sufficient detail for the successful interfacing of FES units, electrodes (or TTG), and the gait orthosis. Finally, suitable arrangements should be made for gait training in the walking system.

Conclusion

Commercially available electrical muscle stimulators can be used for FES and (when combined with a gait orthosis) provide functional (level-ground) walking in a spinal cord injured individual. The patient in this study routinely averaged 0.8 km of walking per experimental session, which was accomplished at velocities ranging from 1.2 to 2.0 km per hour. Over 20 stand-up and sit-down repetitions were also performed successfully. Muscle fatigue, rather than battery power, was found to be the limiting factor for this quadriplegic individual. It is recommended that the writing of the walking system prescription be preceded by an appropriate physical conditioning program. [Tabular Data 1 to 4 Omitted] [Figures 2 to 5 Omitted]

(*)1 mile = 1.6 km. ([single dagger])Eastman Kodak Co, 343 State St, Rochester, NY 14650. ([double dagger])1 lb = 0.4536 kg. ([section])1 oz = 28 g. (~~)NTRON Electronics Inc, 3833 Redwood Hwy, PO Box 7000, San Rafael, CA 94912. (#)1 in = 2.54 cm. (**)Medtronic Inc, Neuro Division, 6951 Central Ave NE, PO Box 1250, Minneapolis, MN 55440. ([single dagger][single dagger )Bio-Stimu Trend Corp, 14851 NW 27th Ave, Opa Locka, FL 33054. (#)The Burdick Corporation, Milton, WI 53563.

PHOTO : Fig. 1. Four functional electrical stimulation units worn on front of belt of a

PHOTO : quadriplegic patient.

PHOTO : Fig. 6. Quadriplegic patient in sitting position just prior to standing.

PHOTO : Fig. 7. Quadriplegic patient standing erect and outfitted with walking system.

PHOTO : Fig. 8. Quadriplegic patient walking while using walking system.

References

[1]Brindley GS, Polkey GE, Rushton DN: Electrical splinting of the knee in paraplegia. Paraplegia 16:428-435, 1978 [2]Holle J, Gruber H, Frey M, et al: Functional electrical stimulation in paraplegics. Orthopedics 7:1145-1160, 1984 [3]Kralj A, Bajd T, Turk R: Electrical stimulation providing functional use of paraplegic patient muscles. Med Prog Technol 7:3-15, 1980 [4]Marsolais EB, Kobetic R: Functional walking in paralyzed patients by means of electrical stimulation. Clin Orthop 175:30-36, 1983 [5]Petrofsky JS, Phillips CA, Heaton HH: Feedback control system for walking in man. Comput Biol Med 14:135-149, 1984 [6]Vodovnik L, Bajd T, Kralj A, et al: Functional electrical stimulation for control of locomotor systems. CRC Critical Reviews in Biomedical Engineering 6:63-131, 1981 [7]Petrofsky JS, Phillips CA: Computer-controlled walking in the neurological paralyzed individual. Journal of Neurological and Orthopedic Medicine and Surgery 4:153-164, 1983 [8]Petrofsky JS, Phillips CA: Closed-loop control of movement of skeletal muscle. CRC Critical Reviews in Biomedical Engineering 6:35-94, 1985 [9]Petrofsky JS, Phillips CA: Electrically-controlled movement of muscle: A potential aid to muscle paralysis. In Ghista DN, Frankel HL (eds): Spinal Cord Injury Medical Engineering. Springfield, IL, Charles C Thomas, Publisher, 1986, pp 393-437 [10]Petrofsky JS, Phillips CA: Constant velocity contractions in skeletal muscle of the cat. Med Biol Eng Comput 17:583-592, 1979 [11]Phillips CA, Petrofsky JS: Velocity of contraction of skeletal muscle as a function of electrical activation and fiber composition. J Biomech 13:549-558, 1980 [12]Phillips CA, Petrofsky JS: The passive element force-velocity relationship: Influence on maximal contractile element velocity. J Biomech 14:399-403, 1981 [13]Stanic U, Trnkoczy A: Closed-loop positioning of hemiplegic patient's joint by means of functional electrical stimulation. IEEE Trans Biomed Eng 21:365-370, 1974 [14]Vodovnik L, Crochetiere WJ, Reswick JB: Control of a skeletal joint by electrical stimulation of antagonists. Med Biol Eng 5:97-109, 1967 [15]Petrofsky JS, Phillips CA, Douglas R, et al: A computer-controlled walking system: The combination of an orthosis with functional electrical stimulation. Journal of Clinical Engineering 11:121-133, 1986 [16]Petrofsky JS, Phillips CA, Larson P, et al: Computer-synthesized walking: An application of orthosis and functional electrical stimulation (FES). Journal of Neurological and Orthopedic Medicine and Surgery 6:219-230, 1985 [17]Hendershot DM, Moore ML, Phillips CA: Cardiopulmonary conditioning when walking with and without FES in the paralyzed. Abstract. Fed Proc 46:680, 1987 [18]Phillips CA: Electrical stimulation for ambulation of selected paraplegics and quadriplegics. Journal of Neurological and Orthopedic Medicine and Surgery 10:109-110, 1989 [19]Phillips CA: An interactive system of electronic stimulators and gait orthosis for walking in the spinal cord injured. Automedica (Lond) 11:247-261, 1989 [20]Phillips CA: The medical criteria for active physical therapy: Physician guidelines for patient participation in a program of functional electrical rehabilitation. Am J Phys Med 66:269-286, 1987 [21]LSU Reciprocating Gait Orthosis: A Pictorial Description and Applications Manual. Chattanooga, TN, Durr-Fillauer Medical, Inc, Orthopedic Div [22]NTRON Electronics EMS-8100: Patient Instruction Booklet. San Rafael, CA, NTRON Electronics Inc

C Phillips, MD, PE, is Professor, Department of Biomedical Engineering, College of Engineering and Computer Science, Wright State University, Dayton, OH 45435 (USA).