Abstract:
Percutaneous functional electrical stimulation system for exercise, standing, and walking in individuals with paraplegia was developed during 1982-92. The components include 1. a portable microprocessor-controlled stimulator; 2. a finger controlled switch to activate stimulation, and 3. intramuscular electrode. The most common problems were daily care of electrodes at exit sites, frequent irritation of the skin around electrodes, and replacement of failed electrodes. While the intent of this system was a temporary use, it has been found effective and relatively safe for up to sixteen years. Two current long time users of the system had no adverse effects to their skeletal system. This system has proven effective for defining the critical muscles for implantable walking system and gait training in incomplete paraplegia before considering implant. The percutaneous system has potential for short-term rehabilitation of incomplete paraplegia and stroke population.
Introduction:
Functional electrical stimulation (
Materials and Methods:
Subjects: Eleven male volunteers with
complete paraplegia following spinal cord injury at the level ranging from the
fourth to the eleventh thoracic vertebra were implanted with percutaneous
intramuscular electrodes between 1982 and 1985. One was unable to gain enough force in the
right quadriceps to extend the knee to stand up and another found the regimen
of the exercise and testing to be too time-consuming and discontinued the
participation after three months. Three subjects were able to stand and walk in
parallel bars but all of them left the program within two years due to various
reasons. [2] The remaining six subjects (Table I) that continued participation
for an average of nine years (Range, 4 years and 5 months to 16 years and 9
months) were included in the follow-up study.
Two subjects (Subject 5, 6) were still using the system daily for more
than 15 years. Electrodes: During initial years subjects received coil
wire electrode. This electrode was associated with poor tissue fixation and
mechanical weakness leading to frequent displacement and breakage of electrode.
[2] Therefore a double helix electrode [4] was designed and used during later
part of follow-up. It was multi-stranded
stainless steel wire insulated with extruded biocompatible polymer
coating. A 5-0 polypropylene suture
material was used for the lead core and arbor for a helical wind. Implantation
Procedure: The muscles to be implanted were categorized into five groups:
trunk (erector spinae and iliopsoas), anterior thigh (quadriceps and
sartorius), glutei (gluteus maximus and gluteus medius), posterior thigh
(hamstrings and posterior adductor magnus), and shank (tibialis anterior and
paronei). [2] Probing with a 26-gage needle was done first to locate the point
of maximum isolated muscle contraction (i.e., motor point) without unwanted
motor or sensory response. After locating motor point electrodes were implanted
with the help of specially designed needles, sheaths, and cannulae. [2] Next,
the electrode lead was passed subcutaneously to the common exit site, typically
at the anteromedial aspect of the thigh. Postimplantation Management:
After implantation the electrodes were attached to a microprocessor controlled
stimulator. Implanted muscles were electrically exercised three times per week
for 30 minutes to increase their endurance and strength and were included in
the stimulation patterns for standing, walking and stair climbing. After
several weeks of electrical exercise of quadriceps, the subjects stood between
parallel bars, and progressed to rolling walker. The subjects were instructed to exercise for
one hour a day while lying in the bed, with the walking patterns set to recycle
automatically. Subjects were followed for gait evaluation, electrode
assessment, and any clinical complication.
Implanted electrodes were monitored and assessed by visual inspection of
the electrodes and the surrounding skin at the exit site. In addition, stimulus
threshold, electrical impedance, and force recruitment properties were assessed
at outpatient visits. The electrodes
were removed either because of 1. nonfunctional electrodes, 2. patient left the
program, or 3. adverse reaction related to the electrodes. No attempt was made
to remove the retained fragment. System Development: Initially 48-channel
system using coil wire percutaneous electrodes was implanted with subjects
achieving a satisfactory functional level. But these coil wire electrodes were
associated with high failure rate and required frequent replacement. This was
one of the reasons that some subjects lost interest and stopped using the
system even though it was functional.
Later with modification of electrode design, implantation of double
helix electrode was started in 1987 that increased the acceptability of system
among the subjects with reduced failure rates. A walking system with 16 and 26 channels with
reasonable repeatability in standing and walking function was developed. These percutaneous systems were maintained
(1992-2001) with an average of 20-30 functioning electrodes that required
smaller number of implantation session.
Results:
Clinical Performance: All subjects were able to use the system
for electrical muscle exercises daily at home and for therapist assisted
walking with AFO and rolling walker for up to five times/week in the lab (Table
I). One subject (Case 5) later on
started using electrical stimulation for walking with modified isocentric
reciprocal gait orthosis (RGO). [5] Cases 5 and 6 were still
actively using the system on regular basis for 16.5 and 15 years,
respectively. Both were highly motivated
individuals. In spite of the fact that
system was temporary, both subjects were happy with their achievements and
decided to continue until a reliable, totally implantable FES system [1] was
available. Case 5 used the system at home for quadriceps exercise six days a
week for one hour daily mainly to relief spasticity. He walked 200 m/session with a rolling walker
at the lab for exercise five days a week. He had also achieved stair climbing
and descent, side and back stepping in the lab.
His FES goal was stair climbing out of the lab. Case 6 used his system
daily at home without supervision and visited the lab once a month. He did quadriceps exercise with the system
three times a week for an average of forty-five minutes per week. He stood
TABLE I: Subject Characteristics
|
# |
Time Since Injury* (Mos.) |
Level of Injury |
Time in Study |
Walking |
|
|
Speed (m/sec) |
Distance (m) |
||||
|
1 |
5 |
T8 |
8yr, 6mo. |
0.8 |
330 |
|
2 |
30 |
T5 |
5yr, 1mo. |
0.2 |
55 |
|
3 |
54 |
T4 |
4yr, 5mo. |
0.7 |
250 |
|
4 |
42 |
T11 |
5yr, 3mo. |
0.7 |
90 |
|
5 |
54 |
T9 |
16yr,3mo |
0.6 |
200 |
|
6 |
6 |
T7 |
15yr,8mo |
0.4 |
150 |
*At
the entrance into the study.
and walked at home for exercise
and minor household activities.
He walked three times a week at home for about twenty
minutes a week. He felt that regular use
of system was an excellent work out and that helped him to stand and walk
better and made his legs looks better. Clinical Complications: There
were fourteen (0.8%) incidents of superficial infection with discharge. Out of fourteen culture sensitivity reports
for superficial infection, ten were positive for staphylococcus aureas
organism. Nine electrodes (0.5%) were
removed and all responded positively to antibiotics after removal. Remaining five electrodes were treated
successfully with antibiotics and were left in place. One subject (Case 5) was
burned twice, once as a result of a transistor failure in the stimulator and
another time from allowing an unconnected channel connector pin to remain in
contact with his perspiring skin during electrical exercise. There were fourteen
incidents (0.86 %) of tissue reaction due to presence of left over electrode
fragments after removal of electrodes.
These were treated with probing with forceps as an outpatient and
electrode fragments were removed on twelve occasion. Electrode performance:
A total of 1713 intramuscular electrodes were implanted in the six subjects. Three subjects had only coil wire electrode and remaining had both types of electrode. Five-year survival probability for double helix electrode was 48%. Two subjects (Case 5 & 6) with the longest duration of use were implanted with 427 and 298 electrodes respectively. During system development period (1984-92) with coil wire electrode, these subjects required average 10 implantation sessions to replace the failed electrodes and average 3 electrodes were replaced per such session. This was improved with the use of double helix electrode. Modification in electrode design improved the one-year survival from 35% at the beginning of the study to 80% at the follow-up evaluation. This was further confirmed by the fact that cases 5 and 6 required replacement of an average 2 electrode every 6 months in last 8 years. The most common problem was failure of electrodes due to movement of electrode from implantation site and breakage of the electrode, mostly occurring during first year of implantation. Breakage of the electrode was more frequent with fine wire electrode (41%) than double helix electrodes (18%). Movement of electrode leading to unwanted muscle response was also more frequent with fine wire electrode (35%) than double helix electrode (12%).
Discussion:
A temporary percutaneous functional electrical stimulation system was devised as a temporary means of achieving selective functional muscle activation for gait restoration in paraplegia until a permanent means could be developed. The implantation procedure was minimally invasive without the use of anesthesia, and useful muscle contractions were achieved in a high percentage of implantations with relative ease. There was no loss of function or deaths from these interventions. Two individuals found the system effective and relatively safe and were satisfied to the extent that they elected to continue using “temporary” system for over fifteen years.
The most common clinical problem was tissue inflammation with redness and swelling at the electrode lead exit site but that was easily treated with topical antibiotics. The exit sites needed regular care of electrodes and surrounding skin. Nine (0.5%) electrodes with infection required removal. Similar rate of infection (0.4%) was reported for percutaneous electrode usage in the upper extremities. [6] The fragments remaining in the body after electrode removal were well tolerated. On occasions these have caused localized skin inflammation and have been removed by probing with hemostats. Current system stimulates muscles excessively in order to provide the needed margin of safety to deal with muscle fatigue. But there were no adverse effects to bone mass or cartilage in long term users of the system. Their feet, ankle, knee and hip joints appeared normal in the radiographs and CT scans. Modifications to the electrode design and manufacture improved the one-year survival rate to 80%, which was consistent with results in upper extremity FES system. [6]
The major drawbacks of this system were the regular cleaning the exit site, replacement of the broken electrode, and cosmetically undesirable external cables. These can be eliminated by implanting a reliable implantable system. Short distance walking with this system had a negligible impact on performance of functions of daily living, but has a major impact on the patient’s psychological and medical condition. Standing up and walking a few minutes every day greatly improved the outlook of the patients and also relieved the pressure, heat, and poor circulation in the lower body. [1] It also allowed sufficient stretching to reduce the spasticity and contractures.
Considering the effectiveness of the system, improved electrode survival rate, easy implantation technique and no major complications two subjects decided to use the system regularly for more than 15 years until more reliable implantable system is available. This system was beneficial for maintaining the body shape, reducing the troublesome spasms, standing, pivot transfer and limited walking. They were highly satisfied with their current achievements. This proved the system as a good alternative to regular exercise in paraplegic individuals until permanent solution is available.
The percutaneous system has proven ideal for defining the critical muscles for a 16-channel implantable FES walking system and for gait training in partial paraplegia individuals before an implanted system is considered. [1] This system is also being used for experimental short-term rehabilitation of stroke patients. [3] While the goal for a long term use of FES for exercise, standing and for walking in paraplegia is the use of implantable systems, the convenience and ease of percutaneous implementation remains a good interim solution until the implanted system is more fully developed and tested.
References:
[1] Triolo, R. J.: Lower extremity applications of functional neuromuscular stimulation after spinal cord injury. Topics in SCI Rehabilitation.5 (1): 44-65, 1999.
[2] Marsolais, E.B.: Development of a practical electrical stimulation system for restoring gait in the paralyzed patient. Clin Orthop. 233: 64-74, 1988.
[3] Daly, J. J.: Electrically induced gait changes post
stroke, using an FNS system with intramuscular electrodes and multiple channels. J Neuro Rehabil. 7: 17-25, 1993
[4] Scheiner, A.: Design and clinical application of
a double helix electrode for functional electrical stimulation. IEEE Trans. Biomed. Eng., 41 (5): 425-431, 1994
[5] Motloch, W.: Principles of orthotic management
for child and adult paraplegia and clinical experience with isocentric RGO. (Abstract) Proc 7th World congress ISPO, Chicago, IL, June 28 – July 3, 1992
[6] Memberg, W. D.: An analysis of the reliability of purcutaneous intramuscular electrodes in upper extremity FNS application. IEEE Trans. Biomed. Eng., 1(2): 126-132, 1993.
Acknowledgement:
This study was funded by the Rehabilitation Research and Development Service of the Department of Veterans Affairs and National Institute of Health.